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Influence of the structure of the composite: 'Nitrided layer/PVD coating' on the durability of forging dies made of steel DIN-1.2367
Abstract
The paper presents research results of the influence of the ‘nitrided layer/PVD coating’ composite structure on the durability of forging dies made of steel DIN-1.2367. Five structures of the composite with different PVD coating materials were investigated. The following types of PVD coatings were applied: TiN/Ti(C,N)gradient, (Ti,Cr)N, (CrN/TiN)×3, (Cr/CrN)×3, CrN. The investigated composites were created by means of the surface ‘duplex’ treatment method in a two-stage separable cycle. The nitriding process was executed with the use of the regulated gas nitriding method, whereas the PVD coatings were created by means of the arc-vacuum method. The paper presents results of materials investigations (metallographic analysis, X-ray diffraction phase analysis, adhesion scratch tests and thermal fatigue tests) as well as the results of laboratory forging tests executed in different conditions (two different temperatures of the forged material and two different temperatures of the die) for dies covered with each of the investigated composites. The wear intensity of the investigated dies was assessed by means of precise three-dimensional measurements while the wear mechanisms were investigated by optical microscopy. On the basis of the received results authors determined the influence of the composite structure and its material properties on the mechanisms and intensity of forging dies destruction.
... Due to their high temperature stability, high hardness, superior toughness, good wear resistance, and lower friction coefficient than TiN, chromium nitride has received much attention in a variety of applications [14]. Additionally, CrN coatings provide a low thermal conductivity coefficient [15], which is crucial for reducing plastic deformation of coatings applied for protection on forging dies [16]. The hardness of the CrAlN coating system is considerably increased by adding Al to the cubic CrN structure [17]. ...
... Combining nitriding pretreatment with coating deposition increases adhesion and wear resistance of CrAlN coating. Some groups have already made improvements to X38CrMoV5-3 (DIN 1.2367) steel used to produce forging tools [16,24]. Pashke et al. [24] discovered that by choosing the right parameters of plasma nitriding, crack behavior of hot-forming tool steel can be effectively modified. ...
In this study, heat-treated and multisurface engineered DIN 1.2367 tool steel was subjected to room and elevated temperature wear tests, and the effect of nitriding on its tribological behavior was investigated. CrN, AlTiN, and CrN/AlTiN coatings with a total thickness of 2 µm were obtained by arc cathodic physical vapor deposition on conventional heat-treated and gas-nitrided steels. The white layer formed during nitriding was removed, and a diffusion layer (100 µm) was achieved in the cross section of the steel having a tempered martensitic matrix. The highest surface hardness was attained with an integral coating (CrN/AlTiN), and surface hardness increased even more after nitriding due to the formation of a multicomponent ceramic layer on top of the diffusion layer. The room temperature wear tests performed against an alumina counterpart revealed that (i) CrN/AlTiN-coated steel had the highest friction coefficient of 0.26, which further increased to 0.33 by nitriding due to the increase in shear strength, and that (ii) with increasing surface hardness, the specific wear rates (W) of the heat-treated and coated steels could be ranked as follows: WCrN/AlTiN < WAlTiN < WCrN. The wear rates decreased when nitriding was carried out prior to coating. In order to simulate the aluminum extrusion conditions, hot wear behavior of the surfaces against AA6080 alloy at 450 °C was investigated. The hot wear tests revealed that (i) high friction coefficients were reached due to the adhesive characteristic of aluminum to the surfaces, (ii) the nitrided and CrN/AlTiN-coated sample exhibited the lowest wear rate among all studied surfaces, and (iii) the film damage on the worn surfaces mostly occurred in the form of droplet delamination.
... The best known hybrid layer made with the use of hybrid technologies consists of a nitrided layer-NL and coating obtained by physical vapor deposition method-PVD (NL + PVD) [52][53][54][55]. Due to interaction of two elements of this structure, i.e., the nitrided layer and the PVD coating, the hybrid layer is characterized by properties that would be unattainable if these elements were obtained separately. ...
... Results presented in Figure 6 showed that dies covered with the hybrid layer NL + CrN are characterized by the best durability, compared to three other PVD coatings tested. The destruction mechanism of the forging dies covered with the hybrid layer NL + CrN [54,67,68], where the thickness of CrN coating was 4 microns, are presented schematically in Figure 7. A specially designed research die was used for this purpose, as shown in Figure 7a. ...
The article presents a summary of many years of activities in the area of increasing the durability of forging dies. The results of comprehensive research work on the analysis of the destructive mechanisms of forging dies and the possibility of increasing their durability with the use of modern surface engineering methods are presented. Great possibilities in terms of shaping operational properties of forging dies by producing hybrid layers of the “Nitrided Layer + PVD Coating” (NL + PVD coating) type were confirmed. An analysis of changes in forging dies durability under various operating conditions was performed, i.e., forging—die—forging press—pressures. It has been shown that the variety of parameters of the forging process, including forgings’ geometry and weight, materials, precision, pressures applied, and, what is very important, quality of machines, makes it very difficult to compare the effectiveness of various PVD coating solutions in the process of increasing the durability of forging dies. Hybrid layers of the “NL + PVD coating” type create great possibilities in shaping the operational properties of tools and machine elements. However, in each application a precise diagnosis of the wear mechanism and the design of an individual PVD coating material solution is required.
... According to the strength versus load concept the strength of the tool can either be increased or the occurring stresses reduced in order to counteract fatigue failure [2]. Measures to increase the strength include the use of different tool materials [6], coatings [16], tool production methods [17], or heat treatments [18]. Despite the various approaches, strength can only be increased up to a certain point. ...
... The tangential prestresses show, that for all interferences the values with stress pins are lower than without them. With increasing interferences, the prestresses decrease in a linear manner 16 Effect of stress pin interference on tangential stress distribution at maximum load from − 1082 MPa for 1‰ to − 1385 MPa for 9‰, because the inner pressure acting on the bore increases. The stresses at maximum load decrease continuously up to 7‰, before increasing again at 9‰. ...
The trend towards lightweight design leads to an increasing demand for sophisticated part geometries with high functional integration. In order to use the advantages of cold forging regarding the time- and resource-efficient production of high-quality parts, high local stresses causing fatigue failure in geometrically complex tools have to be controlled. The objective of this manuscript is to analyse the use of stress pins for a local influence on the stress state within forging, especially in non-circular symmetrical cold forging dies. For this purpose, a closed-die forging process for elliptical parts is designed and analysed regarding the die stresses. Distinct areas with local compressive and tensile stresses occur in the process. To counteract the tensile stresses critical for fatigue failure, the effect of stress pins pressed into the die creating a local prestress is analysed. Around the pins, compressive radial and tensile tangential stresses occur. While large pin diameters, interferences and close positioning to the tensile area lead to an increasing prestressing effect, too high values of these parameters cause a detrimental superposition of tensile process and pin stresses. If used correctly, there is high potential to improve the stress state and tool life especially for locally stressed complex tools.
... This finding is compatible with some studies encountered in the open literature. 48,49 Smolik et al. 49 have demonstrated that coating thickness increased with low chamber pressure in various coating films they produce using various pressures. The average free path of ions in the plasma decreases with increasing working pressure. ...
... This finding is compatible with some studies encountered in the open literature. 48,49 Smolik et al. 49 have demonstrated that coating thickness increased with low chamber pressure in various coating films they produce using various pressures. The average free path of ions in the plasma decreases with increasing working pressure. ...
In this study, TiAlZrN films were coated on the hardened 1.2344 (X 40 CrMoV 5 1) steels using DC power supplied closed field unbalanced magnetron sputtering (CFUBMS) technique. Structural investigations of coatings were carried out using scanning electron microscope and X-ray diffraction. The thickness of coatings was measured from the cross-sectional scanning electron microscope images, and the grain size value and residual stress were calculated by using X-ray diffraction data in the Scherrer formula. Nano indentation method was used to investigate the surface hardness for reducing the substrate effect due to very thin coating thickness (∼2–3 µm). Scratch test was performed for determining the adhesion strength of the coatings. As a tribo-test, a ball-on-disk system was used. From the results, it was understood why TiAlZrN coatings were attractive. The highest hardness was observed as 50.67 GPa, and the highest scratch resistance was reached to 56 N. Also, it was determined that the coating having the highest tribological properties (5.46 × 10−5 mm3/Nm) increased the wear resistance of the substrate six times (3.06 × 10−4 mm3/Nm).
... ternäre Nitride wie TiCN oder TiAlN werden kommerziell seit Jahrzehnten als typisches Material für den Verschleißschutz verwendet [14,15]. Ein effektiver Verschleißschutz von Schmiedegesenken kann durch eine Duplex-Behandlung, bestehend aus einer Nitrierung und anschließend aufgebrachten Beschichtung, erzielt werden [16,17]. Dabei zeigen insbesondere Multilagenbeschichtungen höheren Widerstand gegen Abrasion. ...
... Der Einsatz verschiedener Wechsellagerungen aus Titannitrid mit Chromnitrid, die auf eine zuvor nitrierte Randschicht appliziert werden verringern Abrasion und plastische Verformung des Gesenks. Hier spielt die Schichtdicke und insbesondere die Härte eine wichtige Rolle [16]. ...
Zusammenfassung
Die Steigerung der Standmenge von Schmiedegesenken stellt eine vielversprechende Möglichkeit zur Verbesserung der Wirtschaftlichkeit von Schmiedeprozessen dar. Hartstoffschichten auf Titanbasis eignen sich für die Steigerung der Verschleißbeständigkeit belasteter Oberflächen. Im Vergleich zur bestehenden Aufbringung von titanbasierten Beschichtungen mittels CVD-Verfahren, bietet das PVD-Verfahren die Möglichkeit zur Herstellung von Mehrlagenbeschichtungen mit zahlreichen dünnen Einzellagen. In Untersuchungen zum Einsatzverhalten unter industrienahen Bedingungen wurden unterschiedliche Schichtsysteme bewertet. Dazu wurde in verschiedenen Analysen zunächst die Schichtqualität untersucht. In darauf aufbauenden Serienschmiedeversuchen mit prozessbegleitender Verschleißanalytik wurde der Einfluss verschiedener titanbasierter Schichtsysteme in Kombination mit unterschiedlichen Nitrierungen auf das Verschleißverhalten analysiert. Es wurde festgestellt, dass geometriespezifische Beanspruchungen lokal angepasste optimale verschleißmindernde Behandlungsparameter erfordern. Sowohl die Variation der Nitrierung als auch des Schichtsystems zeigen einen deutlichen Einfluss auf das Verschleißverhalten an unterschiedlichen Bereichen der betrachteten Gesenkgeometrie.
... Los recubrimientos cerámicos binarios, como el nitruro de titanio (TiN), nitruro de cromo (CrN), carburo de titanio (TiC), entre otros, son ampliamente utilizados en piezas con diversas aplicaciones, como herramientas de corte y conformado (Smolik et al., 2004), partes de sistemas en movimiento en ambientes agresivos (Kowalksi y Stachowiak, 2021) y piezas utilizadas en la industria automotriz y aeronáutica (Szparaga et al., 2019;Bayón et al., 2011) debido a su alta dureza, bajo coeficiente de rozamiento y alta resistencia al desgaste y a la corrosión. En particular, el nitruro de cromo presenta un coeficiente de rozamiento menor que el nitruro de titanio (Tang et al., 2019). ...
Los recubrimientos cerámicos permiten mejorar la resistencia al desgaste de piezas mecánicas. Sin embargo, la adhesión de los recubrimientos duros a aceros blandos y dúctiles suele ser pobre debido a que el recubrimiento y el sustrato no se deforman de manera similar. En este trabajo se estudiaron recubrimientos constituidos por una capa de Cr y una de CrN depositados por PVD con una descarga tipo arco catódico sobre acero AISI 4140 nitrurado por plasma y sin nitrurar. La microestructura se estudió mediante difracción de rayos X. La adhesión se analizó con indentación Rockwell C y ensayo de “Scratch Test” y la resistencia al desgaste mediante el ensayo de pin-on-disk. Los resultados obtenidos permiten concluir que los recubrimientos depositados sobre el acero nitrurado presentan mejor adhesión. La resistencia al desgaste de este sistema resultó ser mejor que el acero sin nitrurar sólo recubierto y que el acero nitrurado.
... Novel formulations of laminated material with varying elastic properties have been shown to reduce damage while retaining crucial wear characteristics of the protective coating [19,20]. Such coatings are already an industry standard for specialty cutting and forming applications, such as for hard milling or hobbing of steels, machining of superalloys and other demanding applications [21]. ...
Optimally, hard protective coatings should effectively absorb impact energy to reduce the likelihood of failure events. In this work, an arc-PVD approach was utilised for the deposition of thick ceramic multilayer AlCrTiN/CrN-based coatings containing a distribution of metallic nickel inclusions throughout sequential CrN-based interlayers. The aim of such coatings is to provide resistance to impact loading in intensive application environments, such as drop forging of steel and turbine blades exposed to abrasive particles. The structure and micro-structural development of the ceramic was first investigated using transmission electron microscopy, where discrete Ni inclusions were observed as both larger discs (d ~ 600–800 nm, h ~ 200 nm) and smaller (d ~ 50 nm) nanoclusters. Confirmation of the distribution and nanocluster chemistry was achieved using atom probe tomography. For mono-block coatings, XRD data showed drastically reduced internal stresses as a result of the Ni inclusions, enabling the creation of thicker protective coatings which minimise substrate stress concentration upon loading. Nickel inclusion additionally provides a softening of the containing hard ceramic layer, allowing for tuning of mechanical properties. Supporting this idea, in situ micropillar compression measurements of the multi-layered coating systems showed that Ni clusters hindered crack propagation through the coating during failure, while the fracture strength could be increased by incorporating both Ti and Ni in the softer CrN-based layer. High-load impact testing highlighted the influence of Ni ‘shock absorbers’ in reducing circumferential cracking, which was further confirmed by an industrial die forging test that demonstrated a 15–22% life-time increase compared to a much thicker hard-chrome plated reference. The results of this study demonstrate an exciting way to produce Ni nanocluster integrated hard ceramic multi-layers using arc-PVD in a single processing step. Such tuneable thin-film composite systems show great promise in minimising damage from impact loading, even under severe working conditions such as in hot forging.
... From the development of single-layer coating systems, the design of two or more nano-structured layers forming a composite or hybrid coating have evolved, a so-called multilayer coating, combining the physical characteristics of two or more materials. Multilayer coatings offering, for example, both hard and lubricious properties are reported [7,8] and have now become the standard adopted by the industry [9][10][11]. ...
The lifetimes and the premature wear of machining tools impact on manufacturing efficiencies and productivities. A significant proportion of machining tool damage can be attributed to component wear. Here, titanium aluminium nitride (TiAlN) multi-layered with titanium diboride (TiB2) prepared by PVD (Physical Vapour Deposition) sputtering onto H-13 substrates are studied as potential wear-resistant coatings for forging die applications. The TiB2 content has been altered and two-sets of coating systems with a bilayer thickness either less than or greater than 1 μm are investigated by tribological and microstructural analysis. XRD analysis of the multilayers reveals the coatings to be predominately dominated by the TiAlN (200) peak, with additional peaks of TiN (200) and Ti (101) at a TiB2 content of 9%. Progressive loads increasing to 100 N enabled the friction coefficients and the coating failure at a critical load to be determined. Friction coefficients of around 0.2 have been measured in a coating containing 9% TiB2 at critical loads of approximately 70 N. Bi-directional wear tests reveal that bilayers with thicknesses greater than 1 μm have frictional coefficients that are approximately 50% lower than those where the bilayer is less than 1 μm. This is due to the greater ability of thicker bilayers to uniformly distribute the stress within the layers. There are two observed frictional coefficient regimes corresponding to a lower and higher rate of material loss. At the lower regime, with TiB2 contents below 20%, material loss occurs mainly via delamination between the layers, whilst at compositions above this, material loss occurs via a break-up of material into finer particles that in combination with the higher loads results in greater material loss. The measured wear scar volumes for the TiAlN/TiB2 multilayer coatings are approximately three times lower than those measured on the substrate, thus validating the increased wear resistance offered by these composite coatings.
... Cr-Mo-V steels are members of hot work tool steel grades and are heat and surface treatable; thus, they can be used as die materials in metal forming processes, i.e., Al extrusion [1]. Among these grades, DIN 1.2343, 1.2344, and 1.2367 have been most extensively studied [1][2][3][4][5][6][7]. Heat-treatment processes consist of austenization, quenching, and multi-tempering to obtain a tempered martensitic structure; however, this structure suffers from thermal, mechanical, and tribological stresses because it lacks adequate oxidation, corrosion, and wear resistance under real processing conditions [8−9]. ...
DIN 1.2343 and 1.2367 steels are commonly used as die materials in aluminum extrusion, and single/duplex/multi-coatings enhance their surface properties. The design of an appropriate substrate/coating system is important for improving the tribological performance of these steels under service conditions because the load-carrying capacity of the system can be increased by decreasing the plastic deformation of the substrate. In this study, the tribological behavior of CrN-coated Cr–Mo–V steels (DIN 1.2343, 1.2367, and 1.2999 grades) was investigated using different setups and tribological pairs at room and elevated temperatures. The aim of this study was to reveal the wear resistance of a suggested system (1.2999/CrN) not yet studied and to understand both the wear and the failure characteristics of coated systems. The results showed that (i) among the steels studied, the DIN 1.2999 grade steel exhibited the lowest friction coefficient because it had the highest load-carrying capacity as a result of secondary hardening at elevated temperatures; (ii) at room temperature, both abrasive tracks and adhesive layers were observed on the worn surfaces; and (iii) a combination of chemical reactions and progressive oxidation caused aluminum adhesion on the worn surface, and the detachment of droplets and microcracking were the characteristic damage mechanisms at high temperatures.
... With regard to the research directly on the protective coatings used on the forging tools conducted by the other scientists which tested of hybrid layers and coatings containing Al, Ti, and Cr [34,40,50], they are similar especially in their resistance to thermo-mechanical fatigue [51]. Are carried out also studies with using of alternative multi-layered coatings PACVD, on the basis of B and Ti, as well only nitrided tool surface [36,40,[52][53][54][55] for which operational results are similar to obtained in this work. ...
The article presents a detailed analysis of the degradation phenomena and mechanisms of selected forging punches made of UNIMAX tool steel. Analyzed punches are used in the manufacture of a constant velocity joint boot forging (CVJB) applied in motorcars with front axle drive. The thorough analysis concerned the punches used in the fourth forging operation after a multi-operational process of forging at elevated temperatures, due to the lowest durability equaling only 4000 forgings. A comparison was made of 5 variants of surface thermo-chemical treatment including 2 types of nitriding (with a low and high potential) and 2 different coatings: CrN and AlCrTiN as well as a punch with and without additional thermo-chemical treatment. The performed complex analysis included a macroscopic analysis combined with scanning of the working surfaces, numerical modeling, microstructural tests, SEM microscopic tests, and microhardness measurements. The obtained results make it possible to select of the optimal variant of thermo-chemical surface treatment which improves the durability of these tools. In particular, the analysis included the manner and areas of wear of the punches as well as their resistance to the particular degradation mechanisms.
... Are carried out also studies with using of alternative multi-layered coatings PACVD, on the basis of B and Ti, for which operational results are similar [27,29,41]. In addition, there are very few studies concerning research in industrial processes (forging) conducted by other independent research teams, therefore you can only refer to other publications, of this manuscript author's [30][31][32][33]. ...
The performed research involved a thorough analysis of the phenomena occurring at an early stage of performance of selected forging tools – stamps (up to 4000 manufactured forgings), used in the second hot forging operation of a lid-type forging, which made it possible to point to the hybrid layer with the highest wear resistance, in order to increase tool life. Three different coatings were applied: AlCrTiSiN, Cr/CrN and AlCrTiN. The coatings were tested on 19 tools, and 3 representatives for each coating were selected, followed by their through research analysis. In particular, the analysis concerned the manner of wear of the hybrid layers and their resistance to specific degradation mechanisms. Based on the performed studies, it was possible to select the most optimal hybrid layer, which allows one to improve tool life.
The preliminary results showed that the best effects for the whole tool working surface were obtained for the Cr/CrN layer, characterizing in high adhesion as well as the lowest Young's modulus E and hardness. In the case of high tool forces and the related friction, the best results were obtained for the AlCrTiN coating, which, beside its good adhesion properties, also characterizes in the highest abrasive wear resistance.
... Through nitrogen implantation to CoCrMo alloy by means of the techniques mentioned above, it was found an increase of the surface hardness and a reduction in the wear rate. Nevertheless, duplex treatments, which consist of nitriding of the substrate following by PVD coating, have proved to be successful to improve the wear, fatigue resistance, and the load carrying capability of steel substrates [8][9][10][11]. Increasing the hardness of the substrates by means of the nitriding process, a proper load support for PVD coatings is provided, so that superior mechanical and tribological performance can be achieved. ...
Wear of metal-on-metal hip joints is a concern due to the toxicity and biological reaction of wear debris. Retrieved CoCrMo hip implants have shown that abrasive wear is the predominant failure mechanism in such joints. There have been some efforts to improve the wear resistance of joint implants through the application of hard biocompatible ceramic coatings. However, the adhesion of the coatings has been a concern. The aim of the present work was to study the wear resistance of surface engineered CoCrMo alloy intended for biotribological applications by means of an abrasive wear test, based on the ball-crater technique. Different surface conditions were obtained on surgical grade wrought CoCrMo alloy: plasma nitrided, physical vapor deposition (PVD) coated (monolayer CrN and multilayer (TiN/CrN)×3) and modified using duplex surface engineering technology (a combination of the two previous approaches: plasma nitriding followed by plasma assisted PVD). The engineered surfaces were characterized by scanning electron microscopy, nanoindentation and, atomic force microscopy (AFM). Scratch test was used to determine the influence of the duplex technology on the adhesion of the coatings to substrate. The wear resistance of the different surface conditions was determined using a slurry abrasive micro-abrasion testing device. It was found that the duplex engineering technology enables a significant rise in the resistance of surfaces against concentrated loading modes, improving the adhesion of the coatings to the substrate; however, it has no significant influence improving the wear resistance of the samples during the abrasive wear tests.
... A significant growth in the wear resistance of hot forging dies has already been achieved by the combination of thermo-chemical surface treatment and coating process (duplex-treatment). Wear resistance was greatly improved by ceramic-based multilayer composites of chromium nitride CrN and titanium nitride TiN [6], mono-or multilayer hard coatings of titanium nitride TiN, titanium carbon nitride TiCN and titanium carbide TiC [7] and boron-containing graded layer systems [8]. ...
In order to enhance the tool life of hot forging dies, increasing the wear resistance of the forming tool surface is of great importance. In addition to thermal and thermo-chemical surface treatments, methods applying thin wear-resistant coatings gain more importance. Therefore, ceramic-based mono- or multilayer hard coatings are used in combination with a supporting nitride layer. Due to their low material-specific thermal conductivity, ceramic coatings have an increased sensitivity to abrupt temperature changes. To avoid such thermal shocks, an adjustment of the cooling behaviour is required. This paper presents the results of laboratory forging tests conducted under different cooling and lubrication conditions on nitrided dies with ceramic coatings. By means of a selective cooling of the forming tool surface and using boron nitride as lubricant the wear behaviour of the forging dies could be improved.
... To reduce the required forming forces and to obtain higher formability of the metals, most of the bulk-metal forming (i.e., forging, extrusion) is performed at elevated temperatures [1,2]. At these elevated working temperatures the bearing surface of the forming die is exposed to increased mechanical and thermal stresses, high tribological loads and, in some cases, chemical attacks that lead to various types of damage, premature tool failure and poor work-piece quality [3][4][5][6][7][8]. ...
During the processes of forming aluminium alloys, adhesion, and in particular the formation of the aluminium-alloy transfer on the bearing surface of the die, is one of the main reasons for the failure of tools and the poor surface quality of products. The present work was focused on the transfer initiation of an aluminium alloy (EN AW-6060) and its evolution on a coated (CrN) and an uncoated, nitrided hot-work tool steel (AISI H13) at temperatures from room temperature to 500 °C. The contact was investigated in terms of the transferred aluminium alloy surface area size on the uncoated and coated tool-steel surfaces, the topography of the wear trace and the corresponding change in the coefficient of friction.
... Depending on their microstructure growth, they can be classified as nanocomposite, nanoscale multilayer, superlattice and nanocrystalline gradient coatings [3][4][5][6][7][8]. Especially in the case of the TiAlN systems, recent studies argued on their enhanced mechanical properties [9,10] and their superior performance under in-service severe surface loading [11][12][13][14][15]. The addition of Si in the ternary TiAlN system has been reported to contribute significantly on the mechanical properties, due to the formation of an amorphous SiN x matrix, which impedes cracks propagation during loading [16][17][18]. ...
The present study addresses the influence of the gradient microstructure of nanocrystalline TiAlSiN coatings on their tribological behaviour. Cathodic arc deposition was applied to elaborate such coatings, with a total thickness of 3.5 μm, onto stainless steel substrates. Their microstructure has been characterised via Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) and has been reported in detail previously. Since the main application of TiN-based coatings is the enhancement of the anti-wear resistance of metallic substrates, this work is focused on the tribological performance of gradient TiAlSiN coatings under dry sliding conditions. For this purpose, tests were carried out in a ball-on-disc apparatus, using an alumina ball as counterbody. The influence of the sliding velocity on the evolution of the friction coefficient and the wear lifetime of the gradient coatings has been evaluated in comparison to those of TiN coatings of the same thickness, tested under the same experimental conditions. It was found that the gradient microstructure results in an increase of the coatings’ mean lifetime by an average factor of three.
... The thermal fatigue is also a relevant property in hot forming , for which different test rigs are developed. Smolik et al. [72] applied the so called Coffin's test to characterize the thermal fatigue behaviour of various PVD duplex coating architectures on hot work steel DIN1.2367, and compared [74], and right fromFigure 1a of [80]). the results with hot forging operations. ...
This paper reports recent developments of vacuum coatings technologies for hot-forming tooling applications. Whilst well implanted in the machining and cutting industry, vacuum coatings face important challenges for the fabrication of forming tools, and more specifically in hot forming, due to the extreme operation conditions to be met, such as high loading forces, impact/thermal cycling, working material adhesion, etc. Present and future coatings adapted to hot work tooling are discussed in this paper: transition metal nitrides, carbon nitrides, borides and mixed oxides are among the currently postulated coating formulations for high temperature forming. The study is complemented with current strategies of characterizing the properties of the coatings in the adequate environment of high temperatures and contact loadings. To this aspect, a number of examples, from using standard laboratory equipment to the use of in-house developed tribological set-ups, are given, together with recent findings obtained from the authors’ research groups. The data available is, however, quite limited from the scientific literatures on the field trials with reliable, statistical relevance, which is, probably, attributed to the high costs normally incurred for carrying out experiments in real industrial environment. Nevertheless, we could still draw a conclusion of that vacuum coating for tooling applications is at a front edge of knowledge generation and technology transfer to industry, and while being already mature, there is still a needed effort for significant industrial up-take from the novel coatings developed or being under the development.
... A nitrided layer improves the anti-wear properties mainly by reducing a friction coefficient. The layers nitrided in the conditions making it impossible to create a continuous zone of nitrides at the steel surface may also represent a substrate for multizonal hybrid layers [32,33,45,56,57] with the better functional properties than those achieved after thermochemical treatment with the methods used to date. Nitriding is one of thermochemical treatment methods enhancing the wear-resistant of many tools, including those exposed to cyclical temperature variations. ...
The purpose of this article is to evaluate the development efficiency of classical steel thermochemical treatment. The criterion assumed for dividing the technologies into groups was the thermochemical treatment kind. Three technology groups were selected to realised researches, as follows: nitriding, carburising and diffusion boriding. In the framework of foresight-materials science researches: a group of matrices characterising technology strategic position was created, materials science experiments using: light microscope, transmission and scanning electron microscopes, X-ray diffractometer, microhardness tester, work-stands for testing of thermal fatigue resistance and mechanical fatigue strength, abrasion and corrosion resistance were conducted and technology roadmaps were prepared. The outcarried researches pointed out the great industrial importance of nitriding and carburising and good perspectives for these technology groups. However, diffusion boriding is obsolete and will slowly leave the market.
... The effect of the hybrid technology with such a configuration is a composite layer consisting of a nitrided layer and a PVD coating deposited directly on it. The effectiveness of the "behaviour" of composite layers ("nitrided layer / PVD coating") in the process of increasing the durability of dies has been widely discussed in the literature [5][6]. ...
Purpose: Hot working dies are influenced by three main factors causing their destruction: the cyclically changeable mechanical loads, intensive thermal shocks, as well as intensive friction, and erosion. The great variety of the shapes of forgings, the material they are made of (carbon steel, alloy steel, brass) and the precision of their production – whether they are supposed to undergo further treatment or are considered to be the final products – result in a variety of problems encountered in the production process. In this paper the wear mechanisms of different types of forging dies, covered by the composite layer "nitride layer / PVD coating" were analysed. Design/methodology/approach: In order to estimate the influence of the different shapes of forgings for their wear mechanism, it was decided to that maintenance tests on two series of tools with different shapes made of DIN 1.2344 steel, coated with composite layer "nitrided layer/CrN coating" needed to be taken. The first one was designed for production of gears pre-forging and the second one was designed for the production of steel synchronizer rings. Findings: The abrasive wear together with thermal-mechanical fatigue and plastic strain is a crucial factor of the process of wearing of forging dies for the production of forgings with high dimensional accuracy and not subject to further mechanical treatment. The variety of the shapes of the forging and the precision with which it is made have strong influence on the intensity of the abrasive wear of forging dies. Research limitations/implications: To ensure higher effectiveness of the application of hybrid technologies of surface treatment for the increase of the durability of forging dies, the complex analysis of the influence of such various aspects of the forging process as: surface treatment, the shape of the die and the cooling and lubricating system are necessary on the development of a new generation of dies with increased operational durability. Practical implications: The obtained results of the tests have been practically applied in the FA "Swarzędz" enterprise to increase the durability of the forging dies for steel synchronizer rings. Originality/value: In order to ensure a required level of effectiveness of the use of layered composites of the "nitrided layer/ PVD coating" type for the increase in the durability of forging dies, it is necessary to properly select the composites on the basis of the analysis of the intensity of forging dies wear mechanisms. Reference to this paper should be given in the following way: A. Mazurkiewicz, J. Smolik, Comparative analysis of wear mechanism of different types of forging dies, Archives of Materials Science and Engineering 49/1 (2011) 40-45.
... Graded tool materials, characterised by their chemical composition, phase composition and the structure or arrangement of atoms varying according to the location, can be produced in laser treatment (remelting and alloying) [8][9][10][11], Physical Vapour Deposition (PVD) [12][13][14][15][16][17][18], hybrid (PVD and thermochemical treatment) [19][20][21][22] and sintering processes with the conventional powder metallurgy methods [23][24][25][26][27]. This chapter discusses the last of the mentioned groups of manufacturing the graded tool materials. ...
Purpose: The goal of this chapter is to evaluate the development efficiency of conventional technologies of powder metallurgy used for graded tool materials manufacturing. The tech-nologies were divided into three groups according to the matrix type and the percent fraction volume of components in the powders layers. Design/methodology/approach: In the framework of foresight-materials science research a foresight matrices set was created, materials science experiments using light, transmission and scanning electron microscopes, X-ray diffractometer, microhardness tester, work-stands for testing of fatigue resistance, mechanical fatigue strength, fracture toughness were conducted and technology roadmaps were prepared. Findings: Quite high potential and attractiveness of the analysed technologies against the environment, as well as good development perspectives in industry were shown. Research limitations/implications: Research concerning graded tool materials constitute a part of a larger research project aimed at identifying, researching, and characterising the priority innovative technologies in the field of materials surface engineering. Practical implications: The presented materials science results prove a manufacturing possibility of elements with ductile cores and hard coatings using conventional technologies of powder metallurgy. These technologies are recommended for practical implementation in industry, especially for cutting tools. Originality/value: The originality of this chapter the value evaluation of manufacturing technologies of graded tool materials against background environment including the influence of the chemical composition and sintering conditions on the surface layers hardness.
... When forming at elevated temperatures, the bearing surface of the forming die has to withstand mechanical and thermal stresses, tribological loads and in some cases chemical attack [3][4][5][6]. These severe conditions result in various types of damage to the forming tool's surface, which leads to premature tool failure and inadequate workpiece quality [7,8]. ...
During the forming of aluminium alloys there are several difficulties associated with controlling the process parameters and the product quality due to the severity of the contact. Adhesion and, in particular, the formation of transfer films of aluminium alloys on the surfaces of hot-work tool steels are very negative phenomena in this process and require a better understanding. The present work is focused on the initiation and evolution of the transfer of the aluminium alloy EN AW-6060 to the nitrided hot-work tool steel AISI H13 in the temperature range from 20 °C to 500 °C. All the tests were performed under cross cylinder single-pass, dry-sliding-contact conditions over different sliding distances. The contact was investigated in terms of the surface area and the volume of the transferred aluminium alloy to the surface of the tool steel, the topography of the wear trace and the corresponding coefficient of friction. The results show the strong dependence of the tribological properties in the contacts of the nitrided hot-work tool steel and the aluminium alloy on the temperature. However, it was found that the whole tribological behaviour is largely already defined during the very early stages of sliding, i.e., at the initiation of sliding, after which it becomes even more pronounced as the temperature increases. At low temperatures (20–200 °C) the surface roughness of the tool steel was found to be the key initial cause of the aluminium alloy׳s transfer, while at higher temperatures (300–500 °C) this transfer occurred predominantly due to strong adhesion.
... The shapes of the extruded profiles are usually very complex and it is generally assumed that on various, usually gas-nitrided, bearing surfaces of the dies, various contact pressures and temperatures prevail. The quality of the nitrided surface, i.e. of the compound as well as of the diffusion layer, depends on quality of used tool steel, the nitriding parameters as well as on the previous surface preparation [6][7][8][9][10][11][12][13][14][15][16][17][18]. The different contact pressures and temperatures on the die-bearing surfaces can be attributed to the intricate flow of Al in the die, to the different heat generation and to the heat transfer on the various bearing surfaces and in their vicinity, etc. ...
The progress of wear associated with the compound and diffusion layers of nitrided samples was studied by employing laboratory tests at low, medium and high contact pressures, simulating the conditions occurring during the hot extrusion of aluminium. It was found that with increasing of contact pressure also wear rates increase that indicates on predominately frictional removal of compound layer which was confirmed by scanning electron microscopy and back-scattered electron micrographs as well as energy-dispersive spectroscopy analysis of tested surfaces. Testing at medium contact pressures reveals some common features observed at testing at lower as well as at higher contact pressures. The essential difference between the testing at medium and low contact pressures is in the density of the obtained micro-craters and appearance of their extension in sliding direction at medium contact pressures. At higher contact pressure, removal of compound layer is already preferentially oriented in sliding direction in the first stage, while at medium contact pressure, this is observed only in later stages of degradation progress.
... The ability to carry out some of these operations in the same apparatus would make manufacturing much easier and cheaper. There have been several reports about attempts to combine ion nitriding and PVD plating in the same vacuum chamber [23,24]. Contemporary multipurpose vacuum furnaces can integrate precise austenizing, high pressure gas quenching, single or multiple tempering, and also low-pressure nitriding [7,25,26]. ...
The objective of this work was to select the optimum technological surface layer for casting cores and ejector pins used in pressure dies in the process of casting aluminum alloys. The controlled measurements of: microhardness, wear and friction coefficients, internal tress distribution, as well as superposition of internal and real tress, resulting from computer simulation of casting process, were performed for each sample. In order to experimentally determine the influence of the selected treatment methods on the state of stress of the material, the selected material and technological solutions were tested under service conditions. The optimal surface treatment, both from the point of view of durability and cost-effectiveness, was obtained in the case of multiplex technologies including sulfonitriding treatment followed by the deposition of a novel low-friction MoS2(Ti,W) coating or economical FineLPN vacuum nitriding followed by TiN coating deposition.
... Through nitrogen implantation to CoCrMo alloy by means of the techniques mentioned above, it was found an increase of the surface hardness and a reduction in the wear rate. Nevertheless, duplex treatments, which consist of nitriding of the substrate following by PVD coating, have proved to be successful to improve the wear, fatigue and corrosion resistance, and the load carrying capability of steel substrates [8][9][10][11]. Increasing the hardness of the substrates by means of the nitriding process, a proper load support for PVD coatings is provided, so that superior mechanical and tribological performance can be achieved. ...
... They stated that no damage was observed with duplex treated dies, except the rounding of the dies. The reason for the low increase in the service life of the die compared to AlTiN coated dies could be due to the structure of the coating, as stated by Smolik et al. (2004). ...
In this work, the effect of various surface treatment methods used to improve the hot forging die life were investigated in the forging department of a plant located in Turkey. For this aim, the surface treatments such as one layer of aluminum titanium nitride (AlTiN) surface coating, a special multilayer coating called TOKTEK (trademarks of the Teknoplasma, Industry and Trade Corporation), nitriding, and the weld overlay coating of the contact surface of the hot forging dies were studied under the same conditions. Then, the results were compared with the as received (uncoated) die.Performance tests, made on a real production line under continuous standard working parameters, showed that all of these methods improved die life in various amounts but the best results were obtained by weld overlay of the die contact surfaces with cobalt base welding electrodes.
... The removal of these asperities occurs according to various mechanisms such as abrasion, adhesion or fatigue contact, and depends on numerous parameters such as hardness of the surface, roughness, temperatures and lubrication [3]. Recent observations carried out on different tools either in cold or in hot forging, showed that all these wear mechanisms could be present at the same time on a single surface [4,5]. Moreover, classical tribotests, such as pin on disk or the four ball test, only represent a part of the observed damage on forging tools and does not represent the real contact conditions of the studied process. ...
This paper proposes a new approach to the degradation of cold forging tooling. First, a mechanical analysis of a given forming process is performed. Contact pressure, plastic strain, sliding velocity and temperatures are computed at tool–workpiece interface. These contact conditions are then simulated on a specific friction test. The friction test involved in this work is dedicated to the simulation of hot and cold metal forming tribology. It involves a contactor, which creates a given plastic strain along the sample surface under given contact pressure, sliding velocity and temperature. The main results of that friction test are the Coulomb's coefficient of friction, contactor and sample surface roughness, chemical composition of the third body. In order to study the industrial degradation of the tooling in laboratory conditions, samples come from actual workpiece and contactors come from actual tools at various stages of their lifetime.This new approach is applied to quantify wear of PVD and CVD TiN coated AISI M2 tools used to form a screw head. Friction tests highlight the drift of the friction conditions at the contact interface due to tool surface deterioration. The results show that the CVD coating has to be used to improve the production of the screw head forging sequence.
In this research, the high temperature oxidation and corrosion resistance of TiN-TiAlN double coating and TiN-TiAlN-CrAlN triple coating applied by duplex process of plasma nitriding and cathodic arc physical vapor deposition (Arc-PVD) on the H13 hot-work tool steel substrate were studied in the absence and presence of molten aluminum at 850 °C for 18 h. Nanohardness indentation was performed to obtain the hardness and elastic modulus of the coatings. Scanning electron microscope (SEM) equipped with an energy-dispersive x-ray spectroscopy (EDS) was employed to observe the morphology and analyze the elemental composition of the samples before and after high temperature oxidation and corrosion experiments. Phase composition analysis was investigated using x-ray diffraction (XRD) patterns. The results indicated that the weight loss of the TiN-TiAlN and TiN-TiAlN-CrAlN coatings were ~ 42 and 45% lower than that of the uncoated H13 steel in the oxidative environment at 850 °C, respectively. Also, the thickness loss of the TiN-TiAlN and TiN-TiAlN-CrAlN coatings were obtained to be ~ 61 and 47% lower than that of the uncoated H13 steel in the molten aluminum at 850 °C, respectively. Overall, the results declared the greater stability of TiN-TiAlN-CrAlN triple coating in high temperature oxidation and corrosion in molten aluminum compared to the TiN-TiAlN double coating.
It is essential to explore temperature's crucial role while unveiling the intricacies of tribological interplay in CrN-coated steel-alloy systems. In the present study, tribological potential of CrN-coated hot-work tool steel was investigated under unidirectional single-pass sliding wear conditions. The sliding wear tests were performed at different temperatures (i.e., 20 °C, 100 °C, 200 °C, 300 °C, 400 °C and 500 °C) for the different sliding distances between 2 mm and 68 mm to explore the effect of temperature on the initiation and evolution of the transfer of an aluminium alloy (EN AW-6060). The effect was studied in terms of the contact area of the aluminium alloy and the volume transferred to the surface of the CrN. In addition, the structure of the wear trace and the equivalent friction coefficient were monitored with respect to the sliding distance and the temperature. The results show the strong dependency of the tribological potential of the CrN coating and the aluminium alloy on the temperature but show insignificant dependency on the sliding distance. When sliding up to 200 °C, the transfer was found to be dependent on the surface roughness of the coating, while strong adhesion led to the aluminium alloy's transfer during sliding at higher temperatures, that is, above 300 °C. At 500 °C, the CrN coating formed a self-protective Cr 2 O 3 oxide that reduced the adhesive transfer of the alloy to the CrN compared to that at 200 °C–300 °C.
The paper discusses the durability of forging punches used in the industrial precision forging process of prducing valve forgings for truck engines. The tools are made of 1.2365 steel, and the forging material is high chromium-nickel steel -NCF3015. Due to the hard operational conditions in the forging process (cyclic thermal loads and high mechanical stresses, intensive abrasive wear), the tool life, in the case of forming these steels, is much shorter than in the case of producing forgings from typical carbon steel. In order to increase the durability of the punches, a surface engineering hybrid layer type: GI (ion nitride surface) and four PVD coatings (CrN, TiAlN, AlTiCrN and AlTiCrSiN) were used on a punch, whose working surface was divided into 4 quarters (one coating by one quarter). The tool wear was analysed and represented by the material destruction on the working surface of the punches, based on the 3D scanning and the change of the material volume of the periodically collected forgings (Indirect 3D scanning method). The punches were also subjected to a surface analysis with the use of SEM as well as a microstructure analysis (Light microscope) and hardness measurements. Based on the preliminary analysis, it was established that a few various destructive mechanisms are dominant (coating chipping and adhesive wear). The best results were obtained for the TiAlN coating and the worst for AlTiCrN. In order to confirm the final results, it is necessary to carry out further tests (one coating for one working surface of the punch) under industrial conditions.
Nach [DIN8582] ist Umformen ein Fertigen durch bildsames, plastisches Ändern der Form eines festen Körpers, wobei sowohl die Masse als auch der Zusammenhalt beibehalten werden. Nach der Hauptbeanspruchung in den Umformzonen lassen sich die Umformverfahren in folgende Gruppen einteilen (vgl. Kap. 1.2).
The paper presents the results of laboratory studies performed on produced anti-wear coatings as well as the results of performance tests conducted on tools with these coatings in industrial conditions, in the process of hot die forging. Three different coatings were selected: AlCrTiSiN, Cr/CrN and AlCrTiN, deposited by means of the vacuum-arc method on test samples as well as forging tools used in the hot forging process of a lid. The first part of the paper discusses the results of the studies performed in laboratory conditions, which included: surface morphology by means of SEM, hardness and Young modulus measurements, determination of the chemical composition by means of the EDS method, adhesion tests by means of the scratch method and tribological tests by means of the ball-on-disk method. The obtained results were correlated and applied in the analysis of the performance tests on forging punches with these coatings at an early stage of their performance (up to 4000 produced forgings), which were tested on 19 tools, of which 3 representatives were selected for each coating. A thorough analysis was performed of the wear phenomena and mechanisms and the manner of wear of hybrid layers as well as their resistance to the particular destructive mechanisms. Based on the performed laboratory and performance studies as well as their analysis, it was possible to select the optimal hybrid layer, which enables an increase in the durability of forging tools used in industrial hot die forging processes. The preliminary results showed that the best results for the whole working surface of the tool were obtained for the Cr/CrN layer, which characterizes in high adhesion as well as a lower Young modulus and hardness. In the case of high pressures and the correlated friction, better results were obtained for the AlCrTiN coating, which, besides its good adhesion properties, also exhibited the highest frictional resistance.
Among the different treatments that can be carried out to locally improve the mechanical behaviour of gears a combination of case hardening followed by PVD coatings (duplex treatment) seems to give promising results in terms of surface hardness, residual stress profile and fatigue resistance. In particular considering the carburizing and the nitriding treatments they can be both aimed, in the same way than the surface coatings, to introduce a different mechanical behaviour between surface and core in order to improve life, reliability and load capacity of the treated component. This is fundamental for gears whose damage is mainly related to contact fatigue, fatigue at the tooth root and pitting on the tooth flank [1-3]. The need of optimising the surface material in order to delay the progressive deterioration of the components due to wear, fatigue or contact fatigue mechanisms, often worsened by the presence of hostile environments, explains the increasing attention on different coating technologies [5-7], In particular, considering the PVD coatings, chemical composition of the surface deposited film, coating thickness, hardness, adhesion with the substrate material and plastic deformation of the substrate material have an important influence on the damage mechanism affecting the coated component. Although hard PVD coatings are well known for improving friction and resistance to wear and corrosion, their tribological performance is often limited by elastic and plastic deformation of the substrate, which can allow to coating failures [12]. The emergence of the duplex treatments, consisting in the sequential application of two o more established surface technologies, has represented a novel approach to the achievement of enhancing coating properties. Duplex treatments, comprising a nitriding treatment followed by the deposition of a hard PVD coating, have been proven to be successful in increasing wear, thermal fatigue and corrosion resistance and the load carrying capability of different steel substrates [13-16]. By increasing the hardness of the substrate, for instance using a nitriding case, often provides a suitable load support for PVD coatings so that superior wear resistance can be achieved. The high values of hardness related to the thermochemical treatment, further enhanced by the introduction of the ceramic coating characterized by a strong difference in coefficient of thermal expansion with respect to the substrate material, affects the surface level of compression residual stress data [21-23], Therefore the residual stress gradient must be evaluated when a prediction of the gear life is requested: in fact the residual stress distribution affecting the nucleation of the fatigue cracks is a factor able to control the gear performance. Starting from such considerations, this work is focused on the microstructural (fig.2, fig. 4) and mechanical characterization (nanohardness and fatigue behaviour) of a CrN coating, about 5 μm thick, deposed by PVD technique on two different steels: a carburizing 16MnCrS5 steel grade and a nitriding 42CrMo4 steel grade (Table I). CrN films were deposited by means of the standard cathodic. arc using an industrial devices. Before coating the fatigue specimens (Fig. 1) were polished with a 3 μm diamond suspension and then ultrasonically cleaned. On the basis of published works [11] it is known that, in the case of nitrided substrates, the adhesion with the PVD coating is enhanced by the presence of Feα(N) structure while ε-Fe2-3N or γprime;-Fe 4N ones are detrimental. For such a reason a NITREG treatment was executed on the 42NiCrMo4 steel grade with the purpose of producing a low white layer, further reduced, before the coating deposition step, by means of a mechanical samples polishing targeted to remove the superficial brittle and porous layers. A short ion cleaning executed with Ar was carried out before the beginning of the coating deposition phase. The steel temperature was kept constant at 180°C with an initial peak of 210°C acting for about 2 minutes, independently from the type of substrate considered. Microhardness profiles were measured both on uncoated and on coated samples in order to determine both the thickness of the carburized and nitrided layers and the effect of the thin film deposition process (fig. 3). The coating nanohardness data were also measured by the depth sensing technique using a Fisherscope H100 nanoindenter operating by a computer controlled stress limited device and equipped with a Vickers indenter. X-ray diffractometry (XRD) was used to identify the chemical coating composition (fig. 2) and to measure the residual stresses induced from the sample's process route including the coating step. XRD with Bragg Brentano geometry were performed with a Philips PW 1830 instrument with a goniometer PW 3020 and a control unit Philips PW 3710 (Cu K α radiation, scan rate 1° /min). Surface residual stresses were detected using Cu Kα radiation by means of a Italstructure Stress X3000 diffractometer. The stresses (-120±25 MPa after carburizing; -580±40 MPa after nitriding; -1870±87 MPa after carburizing + PVD and -2350±114 MPa after nitriding + PVD) were calculated using the sinj2 method and adapting the elastic modulus value obtained by nanoindentation measurements and assuming a Poisson ratio of 0.2, value usually taken as a reference when ceramic CrN or Cr(C,N) thin films are considered. Using a rotating bending machine fatigue tests were carried out both on case hardened samples and nitrided plus PVD coated specimens (fig. 1). Experiments were executed at room temperature, in air, at a test frequency of 33 Hz using a sinusoidal load wave form and a load ratio (minimum to maximum load) of R=0. The stress level at which specimens can run without occurrence of failure after 3 · 106 stress cycles was chosen as the fatigue limit. Results of the fatigue tests were analysed according to the stair-case up and down method (Table II). The presence of the PVD film is responsible for a light increase in the fatigue resistance both for the carburized samples and for the nitrided ones. Fatigue nucleation sites resulted affected from the presence of PVD coating only in the case of carburized substrate: the high residual stress level characterizing the ceramic coating excludes the surface as nucleation zone and moves it at the interface with the steel material (fig. 5). No change in the nucleation areas were observed in the nitrided specimens or in the nitrided and coated samples (fig. 6) where the weak points resulted the non metallic inclusions inside the substrate material.
The continuing increase in the use of coated components is due to their improved performances also in presence of a high variety of substrates on which the coating can be deposed. In fact the durability of coated components is usually higher than uncoated ones especially when wear and corrosion resistance must be improved [14-16]. Among the coating technologies a well known position is assured from the PVD process used not only on several substrates (both ferrous and non ferrous alloys can be coated with PVD layers) but also in different chemical compositions (from the traditional TiN coatings to the more complex ceramic multilayer tailored for peculiar applications). Metallurgical studies on PVD coatings have been focused on the increasing of the mechanical properties such as fatigue, thermal fatigue, contact fatigue and toughness by controlling chemical composition, hardness and internal stress distribution ceramic layers. Nowadays the mechanical behaviour of newly developed PVD-coated components can be achieved by means of the so called "duplex treatment" [1-5] consisting in a thin PVD film deposed on a nitrided steel substrate. The nitrided case minimises the substrate deformation under the service applied loads while the high hardness and low friction coefficient characterizing the PVD coating increase the wear performance of the substrate treated parts. In the present research work a 42CrMo4 steel was considered in the following conditions: A) quenched and tempered, B) quenched and tempered + CrN PVD coating, C) nitrided D) nitrided + CrN PVD coating (duplex treatment). The functional coating was obtained by means of an arc device settled to obtain a 5 um total thickness. In order to verify the coating properties under dynamic loading and to simulate a wide range of tribological damage conditions, an "Impact Test" apparatus was appositely arranged at the Politecnico of Milan (Fig. 1). During the Impact test each specimen was cyclically loaded up to 5×104 cycles by a spherical indenter (diameter 6 mm) [18-22]. At the end of each test samples were observed by means of a scanning electron microscope (SEM) in order to investigate the mechanism of coating failure that resulted adhesive or cohesive. The mechanical characterization included also hardness and microhardness investigations carried out in order to measure the hardness profiles and the Young's modulus of all considered samples. Using a rotating bending machine, fatigue tests were also carried out in the different conditions induced by thermochemical treatments and /or coatings. Experiments were executed at room temperature, in air, at a test frequency of 33 Hz using a sinusoidal load waveform and a load ratio R=0. The endurance limit was set after 3×106 stress cycles. Results of the fatigue tests were analyzed according to the stair-case up and down method. The fracture surfaces of the cycled samples were also examined by SEM in order to identify the microstructural parameters governing the fatigue crack nucleation A good adhesion of the CrN layer was detected (Fig. 3) for all the examined substrate conditions; in addition no significant modification of the substrate mechanical properties can be reported (microhardness data on Fig. 2). The impact test shows a better resistance for the duplex treated specimens with respect both nitrided samples and quenched and tempered + PVD coated ones. Impact craters obtained at low loading applied stress (500 N and 5×104 cycles) do not show any cracks (Fig. 6-7); on the contrary when the maximum load is applied (1000N), several cracks affect the duplex treated surface. The stress gradient value calculated from the difference between the coating Young's modulus and the substrate Young's modulus can be used to interpret the experimental results: the condition minimizing this difference minimizes the impact damage too (Table 3). In all the considered conditions the rotating bending fatigue test (Table 2) allows the PVD tested to increase the fatigue limit even if in different percentages with respect to uncoated specimens. In particular, considering the nitrided 42CrMo4 steel grade, good fatigue behaviour was detected without any additional coating step. On the contrary a beneficial effect of PVD coating is evident in the quenched and tempered condition where the surface residual stress gradient due to the heat treatment is not able to produce a high level of compression stress and therefore to increase the fatigue behaviour. In conclusion the introduction of a duplex treatment instead of a less expensive nitrided treatment has to be certainly considered for its positive effect in terms of improved wear resistance and load capability while can not be proposed only on the basis of a significant increases in the fatigue behaviour.
The new hybrid technology is a combination of electron beam evaporation and arc-evaporation processes, enabling the creation of the anti-erosion multilayer composite coating Ni/Cr-Cr3C2 with different volume of Cr3C2 filling in soft Ni/Cr matrix. The soft matrix made of Ni/Cr alloy and hard filling of Cr3C2 are created at the same time and directly during the electron beam and arcevaporation process. Changes of the parameters of the hybrid process, i.e. pressure, current of arc discharge and substrate bias voltage Ubias, make it possible to control the volume of Cr3C2 and are a factor in filling the soft Cr/Ni matrix with carbides Cr3C2. With the use of the developed surface treatment hybrid technology, the multilayer composite coating Ni/Cr-Cr3C2 were obtained. For all composite layers created, the material properties, such as morphology, phase and chemical compositions, hardness, and Young modulus were investigated. The paper presents the original technological equipment, methodology, and technological parameters for the creation of the composite coating Ni/Cr-Cr3C2. Copyright © (2010) by Associação Brasileira de Metalurgia Materiais e Mineração (ABM).
The TiAlN coatings were deposited by closed field unbalanced magnetron sputterin g on substrate of plasma-nitrided H13 steel. The impacts of the coating condition s, the surface compactness of substrate in particular, on the microstructures and mechanical properties of the coatings were evaluated with scanning electron microscopy, metallurgical microscope, and conventional mechanical probes. The resu lts show that removal of the top layers of the nitrided H13 steel substrate by a n abrasive polishing significantly improves the surface compactness, interfacial adhesion, and mechanical properties of the TiAlN coatings, possibly because of the high densities of defects and pores on the rough loose nitrided surfaces and be cause of formation of soft nitrides in nitriding. The TiAlN coatings, deposited on well-polished H13 steel substrate displayed much improved surface hardness, inc reased wear-resistance, and enhanced interfacial adhesion.
Three coating systems, including single-layer AlCrSiN coatings, two-layer CrSiBN/CrN coatings, and single-layer TiAlN coatings were deposited using an arc evaporation system. The effects of various pre-, intermediate, and post-treatments on the properties and performance of the coatings were studied. The tribological properties of the AlCrSiN and TiAlN coatings were evaluated using ball-on-disc tests. The wear behavior of the AlCrSiN coatings was affected by coating morphology. The wear volume of the counter surface increased with the surface roughness of the coating. Furthermore, material transfer and build up to the coating surface were higher for the surfaces treated by grinding and shot blasting than those treated by other methods. The erosion and corrosion properties of the CrSiBN/CrN coatings were evaluated in molten aluminum and sulfuric acid, respectively. Intermediate treatment of the CrSiBN/CrN coatings improved their erosion and corrosion resistance by preventing formation of localized erosion and corrosion. Post-treatment of the TiAlN coatings decreased the amount of material transfer and wear volume of the counter surface. Meanwhile, drilling tests of the TiAlN coatings showed that post-treatment of the coatings improved the drilling regularity and stabilized the spindle torque, which helped to improve tool wear and cutting performance. Based on these results, mechanical surface pre-treatment by processes like micro-blasting, polishing, and buffing, along with plasma nitriding can improve the tribological properties and adhesion of coating systems. Likewise, intermediate and post-treatment of coating surfaces improve erosion and corrosion resistance and cutting performance. In conclusion, the studied treatment processes gave coatings with good performance that are possible candidates for forming and cutting tools.
Hot working dies are influenced by three main factors causing their destruction: the cyclically changeable mechanical loads, intensive thermal shocks, as well as intensive friction, and erosion. Modification of surface properties with the use of hybrid plasma methods seems to be an effective way of improving its durability. The best known and widely used surface treatment hybrid technology is a combination of the nitriding process with the deposition of hard antiwear coatings by means of PVD methods. The designed composite layer "nitrided layer / Cr-CrN" was obtained with the use of the hybrid technology, which consist of ion nitriding followed by arc-evaporation coating deposition. The maintenance testing was performed on the forging dies employed for production of various parts in the automotive industry. The best durability was obtained for the dies used for the forging of rolling bearing tracks. In comparison with the durability of the dies subjected solely to the gas nitriding, nearly an increase of 600% in the durability was noticed.
The new hybrid technology is a combination of electron beam evaporation and arcevaporation processes, enabling the creation of the anti-erosion multilayer composite coating Ni/Cr- Cr3C2 with different volume of Cr3C2 filling in soft Ni/Cr matrix. The soft matrix made of Ni/Cr alloy and hard filling of Cr3C2 are created at the same time and directly during the electron beam and arc-evaporation process. Changes of the parameters of the hybrid process, i.e. pressure, current of arc discharge and substrate bias voltage Ubias, make it possible to control the volume of Cr3C2 and are a factor in filling the soft Cr/Ni matrix with carbides Cr3C2. With the use of the developed surface treatment hybrid technology, the multilayer composite coating Ni/Cr-Cr3C2 were obtained. For all composite layers created, the material properties, such as morphology, phase and chemical compositions, hardness, and Young modulus were investigated. The paper presents the original technological equipment, methodology, and technological parameters for the creation of the composite coating Ni/Cr-Cr3C2.
Thermal fatigue performance of plasma nitrided hot work tool steel was investigated under conditions encountered by thixoforging dies in semi-solid processing of steels. Plasma nitriding does not offer any improvement in the thermal fatigue performance of hot work tool steels at elevated temperatures, due essentially to poor resistance to oxidation and to temper softening. Fe3O4 and Fe2O3 scales produced on the nitrided surface fail to sustain the thermal stresses produced by thermal cycling. They spall off, generating fresh surfaces for further oxidation. This sequence leads to substantial material loss and impairs the integrity of the surface beyond a quality level that would be tolerated in steel thixoforming. The surface hardening provided by plasma nitriding is also completely erased. The tempered martensitic structure is replaced by fine, equiaxed ferritic grains implying a dynamic recrystallization process during thermal cycling.
Nach /DIN8582/ ist Umformen ein Fertigen durch bildsames, plastisches Êndern der Form eines festen Körpers, wobei sowohl die
Masse als auch der Zusammenhalt beibehalten werden.
The paper presents results of the research carried out on two important aspects of continuous duplex treatment technology. The first one concerns the influence of the ion etching intensity on destruction of the compound zone in the nitrided layer. The second investigated problem is the influence of the compound zone occurrence on the adhesion of the CrN coating to the nitrided substrate, i.e. on the cohesion of the composite "nitrided layer/CrN coating". Two different nitrided layers: with mono-phase structure α-Fe(N), and with two-phase structure α-Fe(N)+(ε+γ') were created by the plasma nitriding process. Both types of nitrided layers underwent ion etching processes with different intensities and next the CrN coating was deposited with the use of the arc-vacuum method. Phase composition and cohesion of created in this way composites "nitrided layer/CrN coating" with different mono-phase and multi-phase structures of the nitrided layer were investigated with the use of the X-ray diffraction and the scratch-test methods. Besides, the wear mechanisms of the composites were identified on the basis of the scratch traces analysis carried out with the use of the metallographic and scanning electron microscopy.
A computer controlled equipment for testing and studying the wear of coated tools (dies) in hot forging processes has been designed. Physical simulation of the hot forging process was carried out on a Gleeble 1500 testing machine which was additionally equipped with a heating system and a system for feeding workpieces. The abilities of the testing equipment were well demonstrated by the results of wear testing on four tools with differently treated surfaces: two different heat treated tools, a plasma nitrided tool and a duplex treated tool (plasma nitrided+PVD multilayer coating (Futura)). Besides microhardness, indentation modulus for all those tools was measured. Plasma nitriding improved hardness of the surface layer significantly, while indentation modulus of the diffusion layer is the same as that of bulk H11 tool steel. Microhardness of the Futura coating was ca. 3000 HV while the indentation modulus was ca. 425 GPa. After a certain numbers of strokes, we made optical micrographs or SEM images of the tested tool surfaces and on their cross-sections, and additional measurements of roughness on the tool surface and of microhardness in the tool surface layer were carried out. The duplex treated tool improved the load-bearing capacity, the fracture resistance, the oxidation resistance and the wear resistance of hot forging tools since on few tool surface parts removal of coating occurred. On plasma nitrided and heat treated internally cooled tools considerably higher surface roughness were found in comparison to duplex treated tool. Non-cooled heat treated tool showed very high wear amounts.
The overriding philosophy proposed in this paper is that of specifically designing an optimized die coating system, or range of systems, to meet each material forming application, rather than trying to make one coating or an available range of coatings fit a specific application.Many different die coatings are being used in material forming processes such as aluminum pressure die casting, metal stamping, plastic molding, and glass forming, with different levels of success. This paper presents an optimized design methodology that is based on a multi-layered and graded coating system that first identifies the most appropriate working layer that has minimal chemical interaction with the material being formed, an intermediate layer that accommodates the residual thermal stresses induced by the forming cycle, and an engineered adhesion layer that provides strong adhesion of the coating system to the substrate. In addition the substrate can also be subjected to a surface modification treatment that will provide an improvement in the mechanical properties of the substrate surface to better support the coating system.This methodology is achieved using laboratory testing, simulated and in-plant die casting trials, and modeling in an effort to generate a fundamental understanding of how such optimized die coating systems may be designed. In order to achieve this objective, a fundamental understanding of how such die coatings degrade and fail is also of importance. This methodology has been specifically applied to design optimized coating systems for aluminum pressure die-casting dies.
Forging tools are often showing short lifetimes compared to cold forming tools e.g. for sheet metal forming. This is based on the process conditions where high local surface temperatures are alternating with chilling conditions due to the spray cooling with water based cooling lubricants. The resulting thermal shock is provoking fatigue of the tool material in the near surface regions. Crack initiation and crack growth due to thermal shock exposure then causes chipping of the tool steel material in the surface regions. These are starting points for extensive wear. Hardness and wear resistance of tool surfaces at elevated temperatures can be dramatically enhanced with nitriding pretreatments. This has become state-of-the-art for hot forming tool steels in many forging applications. With inappropriate adjustments of the nitriding parameters a decrease of the ductility can occur and will reduce the crack resistance of the tool surface especially under thermal shock conditions. The hot working steel DIN-1.2367 (X38CrMoV5) is currently one of the most often used chromium-molybdenum tool steels in the field of forging. Exemplary for this material is the influence of the nitriding parameters like temperature, nitrogen supply and plasma parameters on the nitriding depth, the maximum hardness and the crack sensitivity will be discussed. Nitrided samples will be investigated with methods developed for the adhesion measurement of hard coatings. It could be shown that this is also appropriate for a qualification of the crack sensitivity of tools. Comparative application tests in the production of automotive components show the influence on the wear behavior and lifetime of forging tools in an industrial environment.
Plasma nitriding treatments are approved to reduce wear occurring in the field of hot forging applications. But there are demands for a further optimization of the processes in order to achieve adapted properties for differently loaded forging tools. This work presents the influence of main process parameters on the wear behavior of dies. The focused steel material of this work is DIN-X38CrMoV5-1 (1.2343), a standard hot forming tool steel. The influence of nitriding parameters like temperature, nitrogen flow and time on the nitriding depth, hardness and crack sensitivity has been investigated. Comparative application tests show the influence of different surface treatments on the wear behavior and lifetime of forging tools in an industrial environment.
The effect of a Cr(C,N) PVD coating on the fatigue behavior of 42CrMo4 steel grade was investigated both in a quenched and tempered condition and after nitriding treatment. The latter, so-called “duplex process”, combines a nitriding pre-treatment in order to obtain a hard and stiff substrate and a PVD coating in order to reduce the friction coefficient and improve the wear resistance of tools and mechanical components.Prior to fatigue testing, the surface modifications were characterized by means of X-ray diffraction (XRD), residual stress distribution, Vickers nano-hardness measurements and scanning electron microscopy (SEM) analysis.For the quenched and tempered steels, the PVD coating acts as a high compressive residual stressed zone able to increase the fatigue resistance of the coated component. On the contrary, for the duplex-treated samples, a limited increase in the fatigue limit was detected with respect to uncoated nitrided samples. This result was interpreted by means of the residual stress gradient which does not show high differences for nitrided coated and uncoated samples.
Applications of hard protective nanocomposite coatings are frequently limited by in(s)ufficient adhesion related to high stress. In the present work, we study the of an intermediate Cr layer on top of the stainless steel 410 (SS410) substrate on the performance of the nanocomposite (nc) TiN-based coatings prepared by plasma enhanced chemical vapor deposition. The Cr layer was found to enhance the corrosion resistance of the SS410 substrate by a factor of 280 in terms of corrosion current, and to increase adhesion of the TiN coating by a factor of 4. We show that for the nc-TiN/a-SiN(x) and nc-TiCN/a-SiCN coatings, the substantial improvement of the corrosion resistance can be attributed to the combination of the inertness of the Cr layer, and of the densely packed homogeneous nc structure of the nc coatings containing Si and/or C in comparison to columnar crystalline TiN coatings. (C) 2010 Elsevier B.V. All rights reserved.
A duplex surface engineering technique has been developed in an attempt to successfully apply thin hard ceramic coatings on commonly used low alloy steels. The low alloy steel (En40B) was first plasma nitrided so as to produce a relatively thick and strong subsurface layer, and then deposited with such ceramic coatings as TiN, CrN and (TiAl) by plasma assisted PVD. A series experiments have been carried out to investigate the structures and properties of the duplex treated steel. It is shown that such combined plasma nitriding and PVD treatments can produce a variety of coating/substrate interface structures and tribological properties. By proper process control, the resultant ceramic coating/nitrided steel composite possesses superior tribological performance over the individually plasma nitrided or PVD coated steel.
Duplex treatment was applied to impove wear resistance of hot forging tools. Performance tests of these tools were carried out under laboratory conditions. Plates of construction steel, which were preheated at the temperature of approximately 1050 °C, were used as workpieces. A scanning electron microscope (SEM) was used to determine the coating damage on the cross-section of a worn tool. Microhardness depth profile on the polished cross-section, roughness of the tool working surface and roughness of the workpiece were measured after each 100 forgings. No visible wear of duplex treated tool was observed after 300 forgings. After 1100 forgings the TiN/TiAlN (Balzers, Futura) multilayer coating remained practically undamaged on the front side, while it was partially worn at the roundings of the tool, in the area of the largest sliding lengths.
The properties of polycrystalline (Ti, Al)N coatings deposited on non-nitrided, classically plasma-nitrided and low pressure plasma-nitrided AISI H11 steel samples were investigated. The plasma and deposition and low pressure plasma nitriding were performed in a Z700-LH magnetron sputter ion plating unit, while a separate unit was used for plasma nitriding of specimens at a pressure of several millibars. The (Ti, Al)N coating was deposited onto all the samples using the same equipment as for the plasma deposition and low pressure plasma nitriding. For the characterization of the composite structures, the following methods were used: scratch test, X-ray diffraction analysis, scanning electron microscopy, scanning tunnelling microscopy and microhardness testing. It was found that plasma nitriding prior to coating deposition strongly affects the growth and properties of hard coatings, such as the microhardness, adhesion, preferred orientation, structure and morphology. Plasma nitriding at low pressures has a greater effect than does conventional plasma nitriding: the adhesion is even more enhanced, the microhardness is increased, the preferred orientation is more pronounced and the structure is still columnar but more compact.
The paper presents research results of the influence of the ‘nitrided layer/PVD coating’ composite on the durability of tools for hot plastic working. Four structures of the composite differing in the PVD coating material were investigated. They were: TiN, CrN, (Ti,Cr)N and Ti(C,N). The composites investigated were created by means of the surface ‘duplex’ treatment method in a two stage separable cycle (the nitriding process and the PVD coating deposition were carried out with different devices). The nitriding process was executed with the use of the regulated gas nitriding method, whereas the PVD coating was executed by means of the arc-vacuum method. The tools tested were forge dies made of ISO steel 35CrMoV5 (0.4%C, 0.4%Mn, 1.0%Si, 5.0%Cr, 1.3%Mo, 0.3%V) designed for the plastic working of automotive half-shafts.The paper presents the results of maintenance investigations, executed under manufacturing conditions, obtained for tools used for hot forging which were covered with different composites. The investigations proved that the best durability was achieved for tools covered with the composite ‘nitrided layer/CrN coating’, for which the increase in durability was almost 90%. The smallest durability was noted for tools covered with the composite ‘nitrided layer/TiN coating’. The results obtained proved that a proper choice of the composite ‘nitrided layer/PVD coating’ structure may increase the durability of tools considerably for hot plastic working.
The duplex treatment of alloy steel (nitriding + hard coating) has been studied for a few years now. It is an interesting method not only for increasing fatigue strength and tempering resistance but also for improving corrosion and wear behaviours, particularly under high loads. Such treatments are used for dieing or hot-working applications and are often performed with a discontinuous combination of nitriding and hard coating. This solution has some disadvantages with regards to intermediate external steps prior to coating/polishing and grinding. The aim of this work is to investigate the possibilities and interests of performing duplex treatment during a single cycle within an industrial cathodic arc evaporation PVD device. Two types of plasma nitriding were tested: ‘conventional’ plasma nitriding in N2 + H2 mixtures and low-pressure enhanced plasma nitriding assisted by an electron beam produced by a new arc evaporation source. Hard coatings (TiN or CrN) with good adhesion can be deposited on nitrided high-alloy steels if nitriding, ion cleaning and coating parameters are adjusted. A smooth surface on the bright nitrided substrate (without compound layer) prior to the coating stage must be achieved in order to reach the best mechanical properties of the composite. This technology, which does not require additional polishing steps before completion, can result not only in lower production costs but in high continuity between the two stages of duplex treatment.
The subject of this paper is the technology of the production of composite-nitrided case/TiN coatings. This technology is used for improving the lifetime of tools operating at heavy thermal and mechanical loads and at conditions of intensive abrasive wear. In the case of such tools, the standard methods of improving the surface properties by thermal treatment, thermo-chemical treatment or by deposition of anti-wear monolayers [e.g. TiN, Ti(C, N)] do not lead to the desired increase in tool life. This goal can be achieved only by the application of a duplex surface treatment which involves beside the deposition of mono and multilayers, a thermo-chemical treatment (for example, nitriding), and determining the structure and properties of the tool's surface layer. As a result of a duplex treatment, a multi-layer composite is obtained, which in terms of anti-wear properties outdoes both diffusion layers obtained by thermo-chemical treatment and multilayers deposited by PAPVD methods. The chemical composition and internal structure of the composite must be selected with regard to its final application. The technology of duplex surface treatment was used to improve the durability of moulds for aluminium injection moulding.
In this paper, we present a comparison of tribological behaviour between conventional gas nitrided and PVD CrN coated extrusion dies used in industrial production. We found that PVD CrN coated dies proved to be superior to nitrided ones.
The paper concerns the process of the composite: ‘nitrided layer-PAPVD coating’ creation on substrates made of hot working steel. The composite properties are determined by the appropriate selection of coating parameters and nitrided case structure. The results of research concerning the influence of a method of substrate nitriding and the created nitrided case structure on the adhesion and plastic properties of the PAPVD coatings are presented in the paper. Substrates made of hot working steel EN X35CrMoV5 (0.4% C, 0.4% Mn, 1.0% Si, 5.0% Cr, 1.3% Mo, 0.3% V) underwent different processes of thermo-chemical and finishing surface treatment in order to obtain a nitrided layer of a different structure: Feα(N), Feα(N)+‘white layer’-ϵ,γ′. Research was carried out for nitrided layers created in a controlled gas nitriding process. Four different coatings of nitrides, TiN, Ti(C,N), CrN, (Ti,Cr)N, were deposited on substrates with nitrided layers using the arc-vacuum method and the MZ-383 equipment manufactured by Metaplas Ionon. For composite nitrided layer/PAPVD coating’ prepared in this way, the authors carried out a metallographic analysis, using the optical microscope Neophot32, and measurements of surface roughness of the deposited nitrides. The X-ray phase analysis carried out on the Philips PW1830 diffractometer enabled the phase composition of nitrided layers and the phase composition and the lattice parameter of the deposited PAPVD coatings to be determined. Then, the authors carried out measurements of the coating adhesion for all investigated composites using the scratch-test method by means of Revetest-CSEM. The authors demonstrated the significant influence of the presence of titanium ions (Ti+), in the vacuum arc deposition process, on the properties of the composite nitrided layer/PVD coating. The presence of titanium ions in the technological process deteriorates adhesion of the PVD coating to the nitrided substrate, when the nitrided layer includes the compound zone. This effect was not observed for a CrN coating deposited without the participation of titanium ions.
The structure, hardness and adhesive strength of CrN/plasma nitrided, gas nitrided and nitrocarburized and single CrN coated SKD 61 tool steel were studied. The CrN film was deposited by the cathodic arc ion plating (AIP) deposition process at low temperature (200°C). By Rockwell N-impact indentation testing and scratch testing, the surface failure mode between the CrN film and (un)pretreated substrate was used to determine the adhesion property. The CrN coated plasma and gas nitrided specimens showed better adhesion than that of the nitrocarburized specimens. The compound layer in nitrided layers was monophase ɛ-Fe2–3N which causes substrate hardening and provides excellent hardness, and adhesive strength for composite coated steels.
Recent results point out that it is possible to optimize the adhesion of a TiN coating on some pre-nitrided tool steel surfaces. This combination of plasma nitriding and physical vapour deposition (PVD) TiN coating has been investigated in various research groups as part of a broader objective to obtain an enhanced wear resistance of tools. The implementation of these results in industry, however, usually faces upscaling problems which hinder an efficient evaluation of the industrial performance. Two industrial applications were chosen to demonstrate the possibilities of tools treated by the duplex process. A steel milling tool consisting of 14 high speed steel teeth and knives made out of M2 tool steel for tube cutting were plasma nitrided and subsequently PVD coated. By application of various intermediate steps between nitriding and coating, a good coating adhesion could be obtained. The adhesion behaviour of both coating systems was evaluated by scratch tests. This laboratory performance of the duplex treatment was compared with a tool wear and lifetime evaluation in industry after producing a certain number of workpieces. First results point out that the duplex treatment gives a much better wear resistance for both applications. Extrapolation of laboratory performance to industrial conditions seems to be possible only when based on a close collaboration between industry and research groups.
Multifunctional coatings combining a nitriding treatment and physical vapour deposition allow the performance of cutting and forging tools to be boosted, since the improved mechanical support of the coating makes them withstand higher loads. This treatment can also be used for wear parts made from construction steels to increase their fatigue and wear resistance. Hard coatings applied on nitrided layers can replace or enhance the ε or γ′ layers currently used. These treatments can be made in a discontinuous mode using a dedicated equipment for the nitriding and coating treatment or in a continuous mode, i.e. directly in the coating reactor. These treatments were applied and optimized for a construction steel 35NCD16 and a hot working steel Z38CDV5-1. Coating conditions have a decisive impact on the thermal stability of the iron nitride layers. This aspect was studied in detail and several technical solutions have been identified. Finally, it will be shown that in contradiction to previous findings the coatings have only a negligible influence on the stress intensity in the nitrided zone.
Optimisation of manufacturing processes in mechanical engineering which involve working temperatures higher than 600°C and high surface loads, e.g. pressure die-casting, hot extrusion and hot forging, is today under intensive investigation worldwide. Traditional production procedures and the enormous quantities of products in these industries are serious limitations to the introduction of any kind of improvement to moulds, tools and dies with PVD coatings and duplex treatment. Thus, the simulation of selected tribo-systems is practically impossible and any performance testing of new technologies must therefore be carried out in real industrial manufacturing. In this paper we discuss the properties of surface improvements relevant to these topics. These comprise PVD CrN, TiAlN and FUTURA TiN/TiAlN multilayer coatings, and duplex treatments, including plasma nitriding (PN) and all three PVD coatings. We studied the applications of CrN, PN+CrN and PN+TiAlN in aluminium pressure die-casting, CrN in hot extrusion of Al and FUTURA and PN+FUTURA coating in hot forging of steel parts. Performance tests were carried out in various industrial plants in Slovenia. The results show that an improvement in tool or die life (cost saving) of up to several 100% is not the decisive factor. More important for these traditional industries are better reproducibility of the surface quality of the products, an increase in the manufacturing reliability in heavy machining, a decrease in manufacturing interruption (down-time) and finally, the protection of the environment.
The potential of the newer coating methods, such as plasma assisted physical vapour deposition (PAPVD) will not be realized across a wide applications range until certain intrinsic deficiencies are overcome. These relate, for example, to processing economics and the ability to coat low cost substrates. Within the solution of the latter requirement comes the need to provide load support for the coating. Also for many applications, especially those in which abrasion and corrosion may occur, thicker films are needed. In this paper we highlight four hybrid processes which, in different ways, seek to remove these constraints of the PAPVD process and thereby considerably widen its applicability.
Hardened and tempered low-alloy steel 31CrMoV9 and the high-alloy tool steels S 6-5-2 and X155CrMoV121 were nitrided to form a varied structure of the substrate for the subsequent hardcoating. The tool steels were nitrided and hardcoated in a continuous process in a modified commercial PVD plant. The duplex treatment of the low-alloy steel was realized by separate nitriding and hardcoating in different plants. The TiN and CrN were deposited with a thickness of approx. 3 μm by hollow cathode discharge evaporation.The composition and structure of the nitrided case, the interstage treatment before deposition, as well as the deposition parameters influence the properties of the composite. The adhesion can be improved essentially by prenitriding and deposition of a gradient interlayer system. The resistance of the tool steels to metal cutting and forming increases due to the production of an application-specific duplex layer. The resistance to sliding wear and contact fatigue was investigated on various duplex-treated low-alloy steel by nitriding the substrate. Whereas the nitrided case has a very high influence on the contact fatigue limit, the hardcoating reduces the wear by sliding and abrasion, which is of special interest for machine components with higher slip.