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Characterisation of microstructure and mechanical properties of cermets at micro-and nanoscales
Abstract
High resolution measurements of mechanical properties of the constituent phases of multi-phase materials are of immerse importance in design of new composites. In this study, the nanoindentation, X-ray analysis and microstructural SEM investigations have been used to reveal the properties and structural features of ceramic – metal composites involving chromium carbide based cermets with different additives (Mo and Cu) in nickel binder. The additives influence microstructural parameters such as grain size and residual stresses; however, nanohardness and Young's moduli of constituent phases remain less affected. Phase – specific mechanical properties are measured and correlated with bulk behaviour. Furthermore, hardness of the binder metal is found to be higher in cermet as compared to the bulk hardness of metal.
... CrNi 3 peaks are observed in both conditions; the coating pattern shows secondary Cr 3 C 2 peaks with less intensity, and some disappear (not detected) compared with the powder pattern. This phenomenon is due to the decarburization of Cr 3 C 2 and the Cr oxidation processes that the material experiences during the spraying process (formation of Cr 7 C 3 and Cr 2 O 3 , respectively) [31][32][33][34][35][36][37]. Due to the high content of Cr 3 C 2 -NiCr (70 wt.%) the C2 material contains, the diffraction patterns of both powders and coating ( Figure 4b) are similar to those observed for the C1 material, only showing additional peaks corresponding to SiC phases and Ni 5 Y related to NiCrAlY [38]. ...
... CrNi3 peaks are observed in both conditions; the coating pattern shows secondary Cr3C2 peaks with less intensity, and some disappear (not detected) compared with the powder pattern. This phenomenon is due to the decarburization of Cr3C2 and the Cr oxidation processes that the material experiences during the spraying process (formation of Cr7C3 and Cr2O3, respectively) [31][32][33][34][35][36][37]. Due to the high content of Cr3C2-NiCr (70 wt.%) the C2 material contains, the diffraction patterns of both powders and coating (Figure 4b) are similar to those observed for the C1 material, only showing additional peaks corresponding to SiC phases and Ni5Y related to NiCrAlY [38]. ...
... The cross-section of C1 ( Figure 5) shows the typical microstructure generated with the HVOF process consisting of a dense Cr3C2-NiCr splat-like structure (chromium carbides distribution in the nickel-chromium (CrNi3) matrix). The porosity percentage was less than 1%, as is expected for this type of coating [33,35,36]. The cross-section of C1 ( Figure 5) shows the typical microstructure generated with the HVOF process consisting of a dense Cr 3 C 2 -NiCr splat-like structure (chromium carbides distribution in the nickel-chromium (CrNi 3 ) matrix). ...
High-temperature erosion is a detrimental phenomenon in industries where particle flow exists, in which the search for new materials and mixes to increase the lifespan of mechanical components exposed to erosion is crucial. The present work studied the erosion resistance of two coatings at 25 °C (RT) and 900 °C in a sandblast-type rig. The coatings were fabricated with cermet-type powders: (C1) commercial Cr3C2-NiCr and (C2) commercial Cr3C2-NiCr mixed with a laboratory-conditioned powder consisting of NiCrAlY (linking matrix) and SiC (ceramic phase). Both coatings were applied on an Incoloy 330 substrate using an HVOF thermal spray process. The C2 coating was 11% harder than C1 but had a 62.2% decrement in its KIC value. The erosion test results at RT and 900 °C showed better erosion resistance on C1 than C2 at both testing temperatures and the three impact angles (30°, 60°, and 90°); this was attributed to the minor KIC induced by SiC hard particles and the bigger propagation of inter-splat and trans-splat cracks in C2. The erosion mechanisms at RT and 900 °C were similar, but at high temperature, the apparent size of plastic deformation (micro-cutting, grooves, and craters) increased due to an increase in the matrix ductility. Maximum penetration depth always occurred at a 60° impact angle.
... In general, the particle exposed to abrasive effect is harder, but there are exceptional cases. Abrasive wear is a phenomenon that occurs especially in metal cutting processes and is closely related to the hardness of materials [33][34][35]. ...
Today a wide variety of studies are carried out to discover new materials and develop production methods, and solutions to various technological needs are sought. Thanks to scientific and technological advances, we have reached a point where materials can be designed according to the needs of the product to be manufactured. In this regard, composite materials, in which a new material with better properties is obtained by combining the properties of its components, offer many technological innovations and developments and are the subject of scientific examination and research. It is possible to achieve the desired properties by manufacturing composites with various production techniques using the powder metallurgy technique. Therefore, it is important to reduce foreign dependency in this field and ensure academic accumulation by developing such materials. Considering the above-mentioned situations, this study aims to develop cermet materials with high specific strength and density by mechanical alloying, one of the production techniques of powder metallurgy.
... One of the metal assessment methods used for products while in work and operation is their hardness testing [5][6]. For the last two decades, metal assessment methods have been intensively developed as well as instruments and scopes of their application [7][8][9]. The traditional use of durometers implies measurement of product at its several points, and the average value of obtained results should be used to assess the metal hardness. ...
The paper presents a combination of theoretical suggestions, results, and observations allowing to improve the informativeness of hardness testing process in solving problems of metal product assessment while in operation. The hardness value of metal surface obtained by a single measurement is considered to be random. Various measures of location and scattering of the random variable were experimentally estimated for a number of test samples using the correlation analysis, and their close interaction was studied. It was stated that in metal assessment, the main informative characteristics of hardness testing process are its average value and mean-square deviation for measures of location and scattering, respectively.
... Their structures are optimized for different applications by varying the binder content as well as the composition and grain size of the hard phases [1, 2]. It is a well-known fact that the homogeneous distribution of phases in composites is a half the battle for designed mechanical, tribological and other properties of multi-phase materials1234. To obtain the materials of desired microstructure and provide properties required for the different applications a precise technological plan should be considered. ...
Technological routines for fabrication of WC-8wt.%Ni-6wt.%ZrO2 composites with a uniformly distributed microstructure are described. The structure optimization was held on the different milling and sintering devices. Ball mill, attritor mill and special mixer device in combination with HIP, sinter/HIP and half commercial vacuum sintering technologies were used to find the best parameters for satisfactory microstructure. It was revealed that there is significant influence of milling or sintering technique used on the formation of the microstructure. Compact hard metals composed of fine and homogeneously distributed WC and ZrO2 grains with little flaws can be achieved after adding 0.2 wt.% of graphite in a combination with 0.4 wt.% of chromium carbide. This grade has also demonstrated the high hardness of 1600 HV in a combination with impressive fracture toughness of 13.2 MPa·m 1/2.
Sintering behavior of ZrC-ZrO2 ceramic composites processed by vacuum and spark plasma sintering routines as well as mechanical properties of the obtained materials were studied in the present paper. It has been shown that both methods of the composites fabrication are suitable for producing ZrC-ZrO2 composites; however, composition sintered with spark plasma sintering (SPS) technique gives somewhat higher hardness of the bulk.
A comparison between the indentation grid (IG) analysis of nanoindentation bulk and in situ properties of ceramic phases is discussed. Single microstructural elements, by nanoindentation, can be tested as grains in polycrystals or single phases in composites, while in situ properties are evaluated by imaging the indentation marks making use of a scanning electron microscope (SEM) for detecting which phase was indented. IG will be applied to particle-reinforced ceramic composites, some of which are based on well-known phases, including MoSi2 and TiN, and others based on ultra high temperature ceramics (UHTC), including HfC and ZrB2. IG is also considered to extract properties from relatively dense UHTC phases that are not possible to be tested in bulk form. Indentation grids also is basically comprised of indentations matrices having a space of 5 μm between each indentation.
Nanoindentation technique has been widely used for measuring mechanical properties from a very small volume of material. The hardness measured using the depth sensing nanoindentation technique often decreases with increasing indentation size, the so called indentation size effect (ISE)[1, 2]. It has been generally acknowledged that the ISE in crystalline materials originates from the density change of geometrically necessary dislocations (GND) needed to accommodate a permanent indentation imprint. Conventionally, to characterize an ISE often requires a series measurement of hardness values at different indentation size. Based on the celebrated Oliver-Pharr scheme[3]. We propose a method to derive the ISE from the loading curve of one single indentation test. The application and limitation of the proposed method will be discussed.
Ceramic–metal composites are a success story from the viewpoint of their many applications. However, the lack of design criteria and predictive models for durable applications of cermets poses a significant barrier to their wider application. The main objective of this paper is to review the cermets behaviour in tribological environment for better understanding material performance and durability in erosive media. For this reasons, microstructure of multiphase materials, features of structure development during sintering, fracture mechanisms, interface phenomenon, ability of energy dissipation and thermo-mechanical parameters were analysed with reference to WC-, TiC-, and Cr 3 C 2 -based cermets.
This work presents nanoindentation experiments with Berkovich tips, carried out on an Al–Li 8090 alloy reinforced with 15vol.% SiC particles to determine hardness and Young's modulus of the metal matrix and the ceramic reinforcements. The influence of pile-up effect has been estimated performing a finite element model of the nanoindentation tests to provide values representative of the materials’ behaviour. Results indicate a clear increase in matrix hardness in comparison with the unreinforced alloy and a slow decrease with the distance to the reinforcement particles. Piling up of the material tested overestimates the results obtained through nanoindentation. This effect could be corrected by means of the simulated test analysis.
Previous models for the deformation of two-phase materials with heterogeneous second phase distributions have been extended to account for damage coalescence. As in the previous work, the model is based on a self-consistent analysis and uses an incremental, tangent modulus approach. Damage coalescence is treated through a micro-crack linkage model that is sensitive to both the local volume fraction of damaged second phase particles and the local stress acting between damaged particles. This work suggests that micro-crack linkage rapidly leads to a loss of global stability and is critical in limiting the ductility exhibited by materials, at least for those exhibiting damage by particle cracking. Thus experimental data for metal-matrix composites agree well with the predictions of the micro-crack linkage model. Ductility predictions resulting from the model are sensitive to both the volume fraction and matrix work hardening exponent. By varying the latter over a range typical of aluminum alloys the model captures the experimentally observed range of ductility for a wide range of Al-based MMCs.
Reactive carburizing sintering is a novel process where synthesis reaction of the carbide phase is combined with liquid phase sintering of the Cr3C2–Ni cermet. This recently developed method is compared with traditional cermet industry routine. Powder of chromium, nickel, and carbon black were milled in a high-energy ball mill (attritor) to nanocrystalline size and pressed to compacts. During the next step—thermal treatment—the chromium carbide is formed and the cermet is sintered in one cycle. It is shown that mechanical properties, erosion, and wear resistance depend on the carbide-to-binder ratio, sintering parameters, and manufacturing technique. Reactive sintering allows for the acquisition of a uniform fine-grained cermet with high mechanical and tribological properties and to decrease the production costs of alloys.
The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
Methods for analyzing nanoindentation load-displacement data to determine hardness and elastic modulus are based on analytical solutions for the indentation of an elastic half-space by rigid axisymmetric indenters. Careful examination of Sneddon's solution for indentation by a rigid cone reveals several largely ignored features that have important implications for nanoindentation property measurement. Finite element and analytical results are presented that show corrections to Sneddon's equations are needed if accurate results are to be obtained. Without the corrections, the equations underestimate the load and contact stiffness in a manner that leads to errors in the measured hardness and modulus, with the magnitudes of the errors depending on the angle of the indenter and Poisson's ratio of the half-space. First order corrections are derived, and general implications for the interpretation of nanoindentation data are discussed.
Chromium carbide/nickel based composites are applicable in many environments involving tribo-corrosion due to their combined ability to resist wear and corrosion. Hence, they are candidate materials for use either in bulk as surface coatings in crude oil (offshore) or in power and marine industries. The aim of this work was to study the effect of material parameters such as composition and surface roughness, together with test conditions such as abrasive particle concentration, applied potential, temperature and time of experiment on the performance of chromium carbide based cermets. Potentiodynamic and potentiostatic tests were carried out as part of this work. SEM studies were also conducted to establish the mechanisms of the material degradation processes. Finally, erosion–corrosion maps were constructed based on the results. Material wastage, synergy and regime maps were developed for these materials and demonstrated that the performance of the cermet depends on the interplay of material and process variables.
Nanoindentation tests were carried out to investigate certain elastic properties of Al 2 O 3 /SiC p composites at microscopic scales (nm up to lm) and under ultra-low loads from 3 mN to 250 mN, with special attention paid to effects caused by SiC particles and pores. The measured Young's modulus depends on the volume fraction of SiC particles and on the composite porosity and it can compare with that of alumina. The Young's modulus exhibits large scatters at small penetrations, but it tends to be constant with lesser dispersion as the indentation depth increases. Further analysis indicated that the scatter results from specific microstructural heterogeneities. The mea-sured Young's moduli are in agreement with predictions, provided the actual role of the microstructure is taken into account.
High-resolution measurements of mechanical properties are of immense importance in metallurgy. Measuring the intrinsic properties
of each phase separately in multiphase materials gives information that is valuable for the development of new materials and
for modelling. In this work, nanoindentation has been used to reveal mechanical properties of different phases in WC–Co with
very high resolution. The resolution limits of the equipment and this material as well as various techniques to accomplish
the measurements were evaluated. By making indents only 0.1 µm apart and using very low loads (1 mN) it was possible to distinguish
between the two different phases, WC and Co. Maps created from the measured properties, hardness and Young’s modulus, were
in excellent agreement with SEM images of the same area. Furthermore, it was also possible to detect an increased hardness
of the Co binder phase by a factor of four as compared to the bulk hardness of Co. This work verifies experimentally what
several authors have proposed earlier based on modelling.
The mechanical properties of two-phase composites are predicted using a rigorous continuum mechanics analysis and an equivalent microstructural transformation approach. This leads to a generalized law of mixtures which is contrasted with the classical linear law of mixtures which requires some explicit assumptions. The generalized law of mixtures enables prediction of a variety of mechanical properties of a two-phase composite with any volume fraction, grain shape and phase distribution. It is shown that the classical linear law of mixtures is a specific case of the generalized law of mixtures. Examples are given from continuous Cu-W composites, the particulate Co-WC system, Al/SiCp composites, - Ti-Mn alloys and - Cu-Zn alloys for the predictions of properties such as Young's modulus, yield strengths, flow stresses, the overall friction stresses and the overall Hall-Petch coefficients. It is shown that the theoretical predictions by the generalized law of mixtures are in very good agreement with the corresponding experimental results drawn from the literature, for both continuous fibre composites and particulate reinforced systems.
This paper is on comparison of the abrasive and erosive wear resistance of chromium carbide based and nickel bonded cermets prepared by two different methods: conventional powder metallurgy sintering and the new developed one—reactive carburizing sintering. The nickel content was varied at the weight percents of 10, 20 and 30%. Results indicate that sintering process and microstructural parameters influence materials resistance to erosion and abrasion. It is shown, that cermets produced by reactive carburizing sintering have some advantage in erosion and abrasion resistance over conventionally produced ones.
Several composites comprise material phases that cannot be recapitulated ex situ, including calcium silicate hydrates in cementitous materials, hydroxyapatite in bone, and clay agglomerates in geomaterials. This requirement for in situ synthesis and characterization of chemically complex phases obviates conventional mechanical testing of large specimens representative of these material components. Current advances in experimental micro and nanomechanics have afforded new opportunities to explore and understand the effect of thermochemical environments on the microstructural and mechanical characteristics of naturally occurring material composites. Here, we propose a straightforward application of instrumented indentation to extract the in situ elastic properties of individual components and to image the connectivity among these phases in composites. This approach relies on a large array of nano to microscale contact experiments and the statistical analysis of the resulting data. Provided that the maximum indentation depth is chosen carefully, this method has the potential of extracting elastic properties of the indented phase which are minimally affected by the surrounding medium. An estimate of the limiting indentation depth is provided by asssuming a layered, thin film geometry. The proposed methodology is tested on a “model” composite material, a titanium-titanium monoboride (Ti–TiB) of various volumetric proportions. The elastic properties, volume fractions, and morphological arrangement of the two phases are recovered. These results demonstrate the information required for any micromechanical model that would predict composition-based mechanical performance of a given composite material.
This study applies nanoindentation and other analysis techniques to investigate the influence of wire electrical discharge machining (EDM) process on the structure and properties of machined surface layers of WC–Co composites. Multiple indents were conducted on the cross-section of the surface recast layer, sub-surface heat-affected zone, and bulk material. The energy disperse X-ray spectrometry and X-ray diffraction were used to analyze the material compositions in the heat-affected zone and recast layer and to study the electrical spark eroded surface. The indents were inspected by scanning electron microscopy to distinguish between regular and irregular indents in these three regions. Irregular indents were caused by the porosity, soft matrix material, separation of grain boundaries, and thermal cracks caused by EDM process. The hardness and modulus of elasticity obtained from regular indents in bulk material and heat-affected zone were comparable to those of WC. It was found that the recast layer had lower hardness and modulus of elasticity than the bulk material and heat-affected zone.
The surface residual stresses in SiC particle-reinforced Al matrix composites are measured using a recently developed nanoindentation technique. The tensile biaxial residual stress in Al is found to increase with the particle concentration. The stress magnitudes are in reasonable agreement with those from numerical modeling.
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Reactive carburizing sintering-a novel production method for high quality chromium carbide-nickel cermets'
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Metals & Hard Metals, Vol. 24, pp.263-270.