Article

Surface Modification using High-Power Lasers

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Abstract

Laser beams provide a highly concentrated energy source that can easily be transmitted and manipulated using fibre optics and other optical cOlnponents such as mirrors. Advantages of laser treatment of componentsinclude: lowdistortion of treated parts; the ability to treat specific areas accurately; flexibility compared with, for example, electron beams; and the ability to conduct treatlnent in air or in inert or reactive gases. Apart fr01n cutting and welding, the first application in the Inaterials field was for heat treatment and involved laser surface hardening in the solid state, based on the heating of a thin sUlface layer that was self quenched by the bulk of the cOlnponent. Numerous further treatments have since been developed that involve melting of the surface layer, with or without addition of material, and more recently purely mechanical processes based on the laser shock phenomenon have emerged. The main laser processes that have already been commercialised or are expected shortlyto be so are reviewed. In each case, the principle and some fundamentals, and the characteristics of the treated surface and their influence on mechanical properties are discussed. Specific applications, particularly in the aerospace industry, are then examined. The influence of sUlface dalnage caused during treatment and the ability of laser processing to repair this damage are also discussed.

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... The distribution of residual stresses in the target surface plane was investigated experimentally in [5,69], (see also Fig. 9d and the reviews [73,102]). A central hole in the surface residual stress distribution appears in the case of a circular laser impact and is caused by the focusing of Rayleigh waves [102]. ...
... The distribution of residual stresses in the target surface plane was investigated experimentally in [5,69], (see also Fig. 9d and the reviews [73,102]). A central hole in the surface residual stress distribution appears in the case of a circular laser impact and is caused by the focusing of Rayleigh waves [102]. A qualitative interpretation of the central hole formation is given in [76] (see also Fig. 9c). ...
... Forget et al. [5] give an analytical model for predicting qualitatively both the radial and the orthoradial stress distribution. The hole in stress distribution may be suppressed by overlapping impacts [5] or using an elliptical [73,102] or quadratic [5] laser beam profile. For stress distribution in a case of overlapping impacts, see also [80]. ...
Article
Water is always present in laser processing in air: as vapor, condensate or adsorbate. Water is the working environment in underwater processing—but it can also be added on purpose to gain better results: to avoid redeposition of debris, to cool the material, to increase plasma pressure or to conduct light. Water can also act as a chemical reagent. The first part of the article will review the advantages and disadvantages of laser processing in the presence of water, light transmission by water, and the two most mature methods of water-assisted laser processing: steam cleaning and shock processing.
... As the Rayleigh wave approaches the centre of the impact, it induces a V-shaped plastic deformation of the surface near the centre of the impact zone. After the passage of the Rayleigh wave, the bulk of the substrate tends to react against the deformation created in the surface layer, flattening the V shape [48]. As consequence of the material reaction, the stress drops at the centre of the impact. ...
... The red triangles and the blue circles indicate respectively the HD and the FE results. The numerical results for one peen and the analytical results from the well-known Ballard model [3, 48, 50] are also illustrated with black points. Even though the numerical prediction underestimate the experimental values, it is possible to identify the same trend: LSP treatment of a material with low HEL, and therefore low yield strength, can produce higher values of the zerodepth than a material with higher HEL for the same peening conditions . ...
Article
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Laser Shock Peening is a fatigue enhancement treatment using laser energy to induce compressive Residual Stresses (RS) in the outer layers of metallic components. This work describes the variations of introduced RS-field with peen size and coverage for thin metal samples treated with under-water-LSP. The specimens under investigation were of aluminium alloy AA2024-T351, AA2139-T3, AA7050-T76 and AA7075-T6, with thickness 1.9 mm. The RS were measured by using Hole Drilling with Electronic Speckle Pattern Interferometry and X-ray Diffraction. Of particular interest are the effects of the above mentioned parameters on the zero-depth value, which gives indication of the amount of RS through the thickness, and on the value of the surface compressive stresses, which indicates the magnitude of induced stresses. A 2D-axisymmetrical Finite Element model was created for a preliminary estimation of the stress field trend. From experimental results, correlated with numerical and analytical analysis, the following conclusions can be drawn: increasing the spot size the zero-depth value increases with no significant change of the maximum compressive stress; the increase of coverage leads to significant increase of the compressive stress; thin samples of Al-alloy with low Hugoniot Elastic Limit (HEL) reveal deeper compression field than alloy with higher HEL value.
... Pariona et al. [2] also observed these structures in Al-1.5 wt.% Fe and Li et al. [11], these last authors stated that Al-Co-Ce alloys contain Al-rich eutectic regions whose structure and was similar to Al-2.0 wt.% Fe alloy. Peculiar characteristics of the microstructure shown in Figure 2(d), so it presented highly improved properties, such as: hardness, corrosion and wear resistance, which is resulted of precipitates dissolution and formation of metastable phases, to respect, several authors have reported similar results, among them, Damborenea [12], Pinto [13], Yue et al. [14], Majumdar et al. [15], Bertelli et al. [16], and Pariona et al. [2]. ...
... Laser pulse from a Q-switched laser with high-power density strikes a metal surface inducing shock waves in surface and subsurface layers of the metal. 210,211 The shock waves diffuse in an exponential manner creating a plastic deformation in the subjected volume. 212 Before LSP, the surface of the metals or alloys is commonly coated with a black tape or paint and inertial tamping stream (water) is flown on coating as shown in Figure 17. ...
Article
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Many efforts have been made to understand the effects of hydrogen on titanium alloys, resulting in an abundance of theoretical models and papers. Titanium alloys are crucial advanced materials that provide an excellent combination of a high strength-to-weight ratio and good corrosion behaviour even though they are reasonable to corrosion attack. Titanium alloys are susceptible to hydrogen embrittlement when comes into contact with hydrogen, and galvanic pair with an active metal current, or the pH is greater than 12 or less than 3 or an impressed current. In view of the fact that hydrogen behaves differently with α and β phases, hydrogen degradation may vary markedly in titanium alloys. Hydrogen diminishes the corrosion and erosion resistance and fatigue life of in-service titanium components. A laser peening or laser shock peening is a novel technique for making the metal surfaces and sub-layers densify. It evokes that laser shock peening adoption results in yielding and plastic deformation, thereby creating high compressive residual stresses extending below the surface of the material which is desirable for hydrogen embrittlement resistance and reduction of crack initiation and growth of the component. This article is a review of information relating hydrogen embrittlement of titanium alloys and surface modification technique which influence the strength potential of titanium alloys.
... Peculiar characteristics of the microstructure shown in Figure 2 (d), so it presented highly improved properties, such as: hardness, corrosion and wear resistance, which is resulted of precipitates dissolution and formation of metastable phases, to respect, several authors have reported similar results ( Figure 2). 2,[12][13][14][15][16] In 2 analyzed hypoeutectic Al-1.5 wt. % Fe alloy LSR-treated and observed presence of microcracks between the weld fillets. ...
... Alloying elements can be coated by electrolysis [3], pre-placing alloys with chemical binders [4][5][6], injecting powders of alloying elements co-axially from the side of laser beam [7][8][9]and direct wire feeding into the melt pool [10][11]. In laser surface alloying high cooling ratesand homogeneous fine solidification microstructures can be achieved [12]. Aluminium laser surface alloying with ceramics such as SiC, B 4 C, and TiC improves hardness and thermal stability. ...
... The most widespread methods of modifying the properties of the surface layers of materials based on of concentrated energy flux (ion and electron beams, plasma flows, laser radiation) influence [1][2][3]. From the point of view of alloying of materials with other elements, these methods are effectively combined with the preliminary application of thin film coatings which allows to carry out the impact of the concentrated energy flux to produce an alloy based on the metal from the matrix and cover one [4]. This way of alloys synthesis provides the control of elemental composition of the forming alloy due to varying of both the parameters of the concentrated energy flux and the coating thickness. ...
Article
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In the present the results of research of structure, phase composition and microhardness measurement of the surface layers of the Cr/Ti system treated by short-pulsed high intensity ion beams (HPIB) are presented. It was shown that the HPIB impact on a “coating/substrate” system can serve as an affective way to produce near-surface alloys in the metals. In particular, in the Cr/Ti system the formation of solid solution β-Ti (Cr) as well as titanium carbide TiCx was revealed. The found changes in structure and phase composition of titanium caused by the HPIB impact allow to increase its microhardness in 2 times.
... The intimate contact between the melt and the solid substrate causes very fast heat extraction during solidification resulting in very high cooling rates of the order of 10 5 -10 8 K/s (Kurz and Fisher, 1992). The high cooling rates at which this surface layer is submitted results in the formation of different microstructures from the bulk metal, leading to improved properties such as better resistance to wear and corrosion (Damborenea, 1998;Watkins et al., 1997;Cheung et al., 2000;Conde et al., 2000;Tomida et al., 2003;Colaço and Vilar, 2005;Grum and Sturm, 2005;Tian et al., 2005). The microstructures of materials via rapid solidification tend to show advantages of refined microstructure, reduced microsegregation, extensive solid solubility and formation of metastable phases (Munitz, 1985;Zimmermann et al., 1989). ...
Article
The aim of this work was to develop a heat transfer mathematical model based on the finite difference method in order to simulate temperature fields in the laser surface remelting process. Convective heat transfer in the remelted pool was taken into account by using the effective thermal conductivity approach. Theoretical predictions furnished by previous models from the literature were used for validation of numerical simulations performed with the proposed model. Experiments of laser surface remelting of Al-5 wt pct Ni samples were carried out in the present investigation, and numerical simulations were applied for the laser machine operating parameters. The work also encompasses an analysis of microstructural and microhardness variations throughout the resulting treated and untreated zones.
... Thus, laser surface treatments gain an increasing significance in the automotive industry. A wide range of automotive parts, from brake drums to engine parts [6][7][8][9][10], are laser treated to alter the surface and near surface properties of the materials. To improve the mechanical and tribological properties of different cylinder bores it is possible to use special mechanical treatment [11] or chemical coatings [12][13][14] and laser structuring treatments [15] or -which is used by a large European automotive manufacturer -a special laser surface treatment on the cast iron V-block engines to alter the properties of the cylinder bores. ...
Article
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http://www.pp.bme.hu/me/article/view/1274/678 The environmental and pollution materials emission standards in Europe are going to be more strict. In order to meet the standards, a European automotive manufacturer performs a finishing laser treatment on the honed cast iron cylinder bores of their V-engine blocks. Samples of laser treated cast iron cylinder bores with lamellar graphite were investigated. Due to the growing popularity and high efficiency of fiber lasers, samples treated with Yb-fiber lasers were investigated. In order to evaluate the microstructure and grain size of the laser treated layer, scanning electron microscopic images were taken on cross sectioned samples with a scanning electron microscope/focused ion beam dual beam electron microscope. The samples were found to be ultra fine grained. Nanoindentation hardness measurements of the surface layer showed a clear linear trend between the laser power density in the applied range and the measured hardness. Additional micro hardness measurements suggest an annealed region beneath the surface.
... mm when they usually transformed into compressive stresses. The surface modification of metals by high power lasers was studied by Damborenea [3]. He demonstrated that high power laser could be used as powerful tools for surface modification, in addition to established applications in welding, cutting, and drilling. ...
Article
Inconel 617 alloy has superior high temperature properties and finds application in thermal systems. The alloying elements of chromium and molybdenum make the alloy resistant to corrosion. In the present study, the corrosion properties of Inconel 617 alloy, after 37,000 h of operation as a transition piece in the gas turbine engine, are examined. The workpiece surfaces are treated using an Nd : YAG pulsed laser. The electrochemical tests are carried out in 0.1 N H2SO4+0.05 N NaCl deairated aqueous solution at room temperature. It is found that the laser treated workpieces result in improved corrosion rates. The locally scattered shallow pits are observed at the workpiece surface after the electrochemical tests.
... Currently in the laser process community, many works are published on the solidification behaviors and the microstructural evolution through interaction between the laser beam and a material [1,2], on the extended solid solution and nonequilibrium phase diagram for Al-Ni alloy formed during the laser cladding [3], on a two-dimensional transient model for convection in the laser molten pool [4], on the surface modification of metals by high power lasers [5], on the calculation of process parameters for laser alloying and cladding [6], and on the modeling of laser materials processing-melting, alloying, cladding [7][8][9][10][11]. Only small amount of works, however, are along with con-sideration of heat transfer in the laser cladding process. ...
Article
Laser cladding process accompanies phase transformations through melting (on heating) and solidifying (on cooling), which is an irreversible thermodynamic process. Most of analyses on material processing by laser as a heat source have been conducted on models of neglecting the latent heat in the process just for the reason of simplification. In this study the previous important works are summarized. And to further investigate the effects of latent heat on laser cladding process, this study develops a program accommodating an algorithm for enforcing the latent heat to run with ABAQUS™. The simulation technique of this study is verified by direct comparison of the present prediction with experimental publications elsewhere; the numerical results agreed accurately with the experiments. As a result, it is found that more accurate conclusions come out when considering the latent heat in process analyses.
Article
Surface modification processes of any metallic structure with the help of laser irradiation are a universal practice. The profoundly focused laser beam is to irradiate on the substrate surface to modify the surface condition for the improvement of the tribological properties in heavy and rouged engineering applications. There is a wide application of pure or raw Ti in the field of the biomedical sector specifically in implants and artificial joint prosthesis. In the viewpoint of the above, the present work determines the thermal characteristic aspect in a pure Ti physical domain by developing a two-dimensional heat transfer approach with the dual-phase-lag (DPL) model under the influence of the ultrashort pulsed laser heating. The physical domain has a Ti nanofilm of the 4 nm length, 2 nm width, and 0.02 nm thickness. A DPL model is developed for analyzing the ultrafast heating, as it is the most potential heat transfer model. The present study has modelled a hybrid analytical analysis comprising of the Duhamel’s theorem and the finite integral transform method. This work highlights the essentiality of applications of the DPL heat conduction model over the conventional Fourier’s model based on the qualitative assessment. The selection of thermal relaxation time lags was carefully chosen from the existing experimental evidence due to the requirement to reach the melting point temperature of pure Ti. The peak temperature of laser irradiation declines with the increase in the optical penetration depth and laser pulse time. Finally, the competence of the present analysis is validated with the published numerical and experimental works from the engineering accuracy standpoint.
Article
Nanosecond laser shock peening (NLSP) has been proved to be an effective way to enhance the mechanical properties of metallic components through modifying the surface microstructures. However, the micromechanism of structure and property fluctuations induced by shock wave propagation is still limited due to the intrinsic defects in crystalline materials. Here, NLSP treatment has been performed into the Ti-metallic glasses. Owing to the absence of dislocations, grain boundary and phase segregation, the structural signals caused by the shock wave could come into sight. According to grid nanoindentation results, the shock-affected region can be divided into three sections: (I) the rapid softening region, (II) the recovery region and (III) the matrix region. The fronted first pop-in event and the reduced hardness found in the subsurface region provide clear evidence of the release wave-induced structural rearrangement. The abnormal change of the average volume of the shear transformation zone (STZ) could be explained by a two-step transformation mechanism, due to the fluctuations of the “weak spot” induced by the release stress wave. By means of these results, this work provides an opportunity to shed light on the common laser-solid interaction.
Book
Laser processing of solid materials has been commonly performed in gas ambient. Having the workpiece immersed into liquid, having a liquid film on it, or soaking the material with liquid gives several advantages such as removal of the debris, lowering the heat load on the workpiece, and confining the vapour and plasma, resulting in higher shock pressure on the surface. Introduced in the 1980s, neutral liquids assisted laser processing (LALP) has proved to be advantageous in the cutting of heat-sensitive materials, shock peening of machine parts, cleaning of surfaces, fabrication of micro-optical components, and for generation of nanoparticles in liquids. The liquids used range from water through organic solvents to cryoliquids. The primary aim of the book is to present the essentials of previous research (tabulated data of experimental conditions and results), and help researchers develop new processing and diagnostics techniques (presenting data of liquids and a review of physical phenomena associated with LALP). Engineers can use the research results and technological innovation information to plan their materials processing tasks. Laser processing in liquids has been applied to a number of different tasks in various fields such as mechanical engineering, microengineering, chemistry, optics, and bioscience. A comprehensive glossary with definitions of the terms and explanations has been added. The book covers the use of chemically inert liquids under normal conditions. Laser chemical processing examples are presented for comparison only. - First book in this rapidly growing field impacting mechanical and micro/nano-engineering - Covers different kinds of liquid-assisted laser processing of a large variety of materials - Covers lasers emitting from UV to IR with pulse lengths down to femtoseconds - Reviews over 500 scientific articles and 300 inventions and tabulates their main features - Gives a qualitative and quantitative description of the physical phenomena associated with LALP - Tabulates 61 parameters for 100 liquids - Glossary of over 200 terms and abbreviations.
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Chapter
This document is part of Subvolume B 'Laser Systems', Part 1 of Volume 1 'Laser Physics and Applications' of Landolt-Börnstein Group VIII 'Advanced Materials and Technologies'. It contains: 3.3.1 Introduction 3.3.1.1 Advantages and difficulties associated with short-wavelength lasers 3.3.1.2 General features of dual-wavelength laser systems 3.3.1.3 Comparison of high-power solid-state and excimer lasers 3.3.1.4 Seed pulse generation 3.3.1.4.1 General features of hybrid dye/excimer lasers 3.3.1.4.2 Hybrid solid-state/excimer lasers 3.3.2 Short-pulse amplification properties of excimers 3.3.3 Critical issues for a high-power excimer amplifier 3.3.3.1 Nonlinear effects, attainment of minimum pulse duration (spatially evolving chirped-pulse amplification) 3.3.3.2 Amplification in media having nonsaturable absorption 3.3.3.2.1 ASE content, nonsaturable absorption, limitations on the cross-section 3.3.3.2.2 Off-axis amplification 3.3.3.2.3 Multiple-pass off-axis amplification schemes 3.3.3.2.4 Requirements for the discharge geometries of off-axis amplifiers 3.3.3.3 Limited energy storage time (interferometric multiplexing) 3.3.3.3.1 Limitations on multiple-pass amplification 3.3.3.3.2 Optical multiplexing 3.3.3.3.3 Interferometric multiplexing 3.3.3.4 Focusability of short-wavelength high-intensity lasers 3.3.3.4.1 Pulse front distortion, spatially dependent temporal broadening 3.3.3.4.2 Origin of phase-front distortions in dual-wavelength laser systems 3.3.3.4.3 Active spatial filtering 3.3.3.4.4 Spectral filtering 3.3.3.4.5 Optimization of off-axis amplifiers for minimum phase-front distortion 3.3.3.4.6 Beam homogenization method for short-pulse excimers 3.3.3.4.7 Focusability measurements 3.3.4 Application of short laser pulses 3.3.4.1 Application of short laser pulses for plasma generation 3.3.4.2 Micromachining of materials with subpicosecond UV pulses References for 3.3
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Laser shock surface treatment could be envisaged to harden and induce compressive stresses within materials thus improving their fatigue and fretting-fatigue resistance. Both laser beam optical phenomena and deformation mechanisms are studied for applications of laser shock treatment to Ni-based mono- and polycrystalline superalloys. Deformation microstructure is studied using TEM applied to the monocrystalline superalloys. Macroscopic mechanical phenomena are determined by superficial or in-depth residual stress measurements using X-ray diffraction technique or the incremental hole drilling method. A fairly elementary analytical model involving surface release wave mechanisms is developed to describe the formation of residual stresses. Understanding of these phenomena leads to improving the laser treatment for application to processing of fatigue test specimens by overlapping of impacts.
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The so-called “laser peening” treatment based on laser shock processing has been developed to improve mechanical properties due to work-hardening and formation of residual stresses. When applied to aeronautical Ni-based superalloys, an increase of fatigue resistance is expected. This article deals with deformation resulting from laser shock. The study is centered on the observation of superficial micro-roughness in the impacted zone. Micro-roughness is discussed as resulting from crystallographic changes due to shock process. Various slip phenomena were in particular determined. More generally, superficial heterogeneities in the different parts of the shocked area are discussed in the light of results on release wave propagation and formation of residual stresses. Two Ni-based superalloys, i.e. AM1 single crystal and polycrystalline Inconel 718, were used. Le traitement de “grenaillage photonique” par choc laser vise à écrouir un matériau et à y introduire des contraintes résiduelles de compression en vue d'améliorer ses propriétés mécaniques. Dans le cas de superalliages aéronautiques à base de nickel, on attend une augmentation de la tenue en fatigue. On traite ici de la déformation induite par le choc grâce à une étude microstructurale fondée sur l'observation des microreliefs de surface dans la zone traitée. Ceux-ci sont interprétés comme le résultat de l'évolution cristallographique du matériau soumis au choc. Les phénomènes de glissement, sont, en particulier, précisément identifiés. Plus généralement, les hétérogénéités de surface dans les différentes parties de l'impact sont expliquées à la lumière de résultats sur la propagation des ondes de détente de surface et sur la création de contraintes résiduelles. Deux superalliages à base de nickel, l'AM1 monocristallin et l'Inconel 718 polycristallin, ont été étudiés.
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In-situ Ni-Cr-Al-Hf alloy was developed by laser surface cladding with a mixed-powder feed for improved high-temperature oxidation resistance. Oxidation-resistant materials for operation at elevated temperatures must satisfy two requirements: diffusion through the oxide scale must occur at the lowest possible rate, and the oxide scale must resist spallation. Formation of an Al/sub 2/O/sub 3/ protective scale fulfills the former requirement but its adherence is poor. A reactive metal such as Hf is added to improve adhesion. A 10-kW CO/sub 2/ laser was used for laser cladding. Optical, SEM and STEM microanalysis techniques were employed to characterize the different phases produced during the cladding process. Microstructural studies showed a high degree of grain refinement, increased solid solubility of Hf in the matrix and the formation of Hf-rich precipitates. A thermogravimetric analysis was carried out to determine the oxidation properties of these clad alloys with an extended solid solution of Hf. Considerable improvement over the base metal was observed. This paper discusses microstructural development in this laser-clad alloy and its effect on oxidation.
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Laser cladding techniques have recently enjoyed attention in preparing in-situ novel surface clad alloys with extended solid solution. Mass transport involved in this process is rather intriguing since it plays the major role in producing new materials without being restricted by equilibrium phase diagram. Although earlier work has identified convection as the dominant factor for homogeneous liquid metal composition, very little is understood about the solute redistribution at the solid-liquid interface under such non-equilibrium conditions. In this paper, a mathematical model is presented for determining the composition of extended solid solution formed due to rapid cooling in laser cladding. This model considers a diffusion mechanism for mass transport in a one-dimensional semi-infinite molten pool of the cladding material from which heat is removed by conduction through a one-dimensional semi-infinite solid substrate. The rate of solidification was obtained by modeling the cooling process as a composite medium heat transfer problem, and the discontinuity of the concentration field was simulated using a nonequilibrium partition coefficient. A non-similar exact solution for the mass transport equation was obtained using a set of similarity variables derived using Lie group theory.
Article
Tribological properties are considered as system properties and not as intrinsic properties of materials. The great number of parameters which can influence the wear resistance does not permit one to simply characterize a material as good'' or bad'' for low-wear applications. However, the wear behavior of materials is strongly dependent on microstructural parameters: type and mechanical properties of the matrix, second phase distribution, presence of hard particles, solid lubricants or pores. High speed steels are conventional cutting tool materials with a high wear resistance. The purpose of the present work is the investigation of the microstructure of a powder metallurgical M3 class 2 high speed steel before and after tempering at 600[degree]C, by means of the development of Quantitative Image Analysis (QIA) techniques for analyzing complex microstructures such as those exhibited by high speed steels. In particular, the effect of tempering on the mean size and distribution of the primary M[sub 6]C and MC carbides, as well as on the porosity, is studied. These microstructural features influence to a significant degree the general wear behavior of high speed steels. Therefore, the results of Quantitative Image Analysis are discussed in association with the role of primary carbides and porosity on the tribological properties of the studied material.
Article
The use of pulsed excimer lasers, operating at UV wavelengths, for surface modification has many potential applications in the tribology of metals and ceramics. Alterations of surface chemistry and microstructure are possible on standard engineering materials. We have demonstrated improved tribological performance in stainless steel by the formation of a unique oxide and by Ti mixing and in SiC by Ti mixing. Specifically, we have observed reduced friction in dry sliding conditions and a change in the wear process resulting in greatly reduced surface damage. We have also demonstrated the effectiveness of excimer laser mixing in other systems with potential tribological applications.
Article
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Article
Surfaces can be changed to suit a particular purpose by means of laser coatings. The method features advantages compared with other surface treatment processes, e.g. it requires scarcely any finishing off and provides high reproducibility, ease of automation, and minimum consumption of expensive alloying elements. Applications for laser coating are to be found principally in the automobile industry, in the aerospace sector, and in general mechanical engineering. Coatings giving protection against wear are deposited. A further application is the repair of damaged or worn component locations/contours. The examples given below demonstrate how laser coatings can be applied to advantage.
Article
This paper reviews the principles of laser melting and some of the processing techniques involved. The main aspects of the laser surface melting of cast irons, including the various microstructures and resultant properties, are discussed in detail and possible applications of laser melted components are also considered.
Article
Results on the deposition of titanium nitride on AISI M2 tool steel-type substrates by pyrolytic laser chemical vapour deposition are reported. Spots of TiN were deposited from a gas mixture of TiCI4, nitrogen and hydrogen using a continuous wave quasi-TEMoo C02 laser beam. The morphology and the structure of the deposited material were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. The chemical composition was studied with a scanning electron microscope with an energy dispersive spectrometer, and with an electron probe microanalyser. The topography of the coating was analysed with a stylus profilometer and different thickness profiles were measured depending on the laserpower densities and irradiation times. The morphology of the films showed a strong dependence on the laser-power density, interaction time and partial pressure of TiCI4.
Article
Nodular iron of martensitic structure was treated by means of a XeCl laser prototype. The energy density varied from 0.3 to 5 J/cm2 and the number of shots from 4 to 40. Conversion electron Mssbauer spectroscopy, conversion X-ray Mssbauer spectroscopy and grazing incidence X-ray diffraction were used to characterize the irradiated surface. Some Rutherford backscattering spectrometry measurements were performed to control surface oxidation and carbon distribution. It is shown that after irradiation austenite formed in a rather deep heat affected zone (10–20 m) compared to the thickness of the melted zone ( 1 m). The austenite amount as well as its carbon content increase with energy density and number of shots up to a threshold of carbide formation. Beyond the threshold Fe2C, Fe3C and Fe5C2 formed only in the melted zone. The carbon content as a function of depth is constant in the melted layer, then decreases quickly from the melted layer-heat affected zone interface down its initial value. The carbon content is shown to govern the evolution of phases content in the melted layer depending on the laser treatment conditions.
Article
Porosity is the distinguishing feature of sintered materials and has a negative effect on their mechanical properties. The influence of porosity on the wear behaviour of materials depends on the wear conditions and is not clearly identified. In the present investigation, the evolution of the dry sliding wear resistance of a sintered Distaloy AE with increasing total vol.% porosity (in the range 9–22 vol.%) was studied. Under certain conditions and depending on the pore size, porosity was observed to be beneficial for wear resistance by entrapping the wear debris and preventing the formation of large abrasive agglomerates. Pore filling superficially reinforced the material and resulted in diminishing plastic deformation and particle detachment around the pores.
Article
Today surface treatments are very important in the mechanical industry to increase the fatigue life of metal components. In addition to classical treatments such as shot peening, a new process is being developed. The laser shock surface treatment permits the creation of plastic strains and induction of compressive residual stresses in metals. It consists in irradiating a metallic sample with a short but intense laser pulse. As a consequence a high temperature high pressure plasma is created at the sample surface. An elastic-plastic wave propagates in the sample, creating plastic strains. The present study deals with the effects of laser-induced stress waves on residual stresses, microhardness and surface quality of a standard steel (0.55% C). The residual stresses generated are compressive for a depth of up to 1 mm. With optimum conditions, we can produce homogeneous cover strips without surface deterioration.
Article
The performance of laser-glazed zirconia (containing 8 wt.% Y2O3) thermal barrier coatings was evaluated in cyclic oxidation and cyclic corrosion tests. Plasma-sprayed zirconia coatings of two thickness (0.02 and 0.04 cm) were partially melted with a CO2 laser. The power density of the focused lasser beam was varied from 35 to 75W mm-2, while the scanning speed was about 80 cm min-1. In cyclic oxidation tests, the specimens were heated in a burner rig for 6 min and cooled for 3 min. The results obtained indicated that the laser-treated samples had the same life as the untreated samples. However, in corrosion tests, in which the burner rig flame contained 100 ppm Na fuel equivalent, the laser-treated samples exhibited a nearly fourfold life improvement over that of the reference samples. In both tests, the lives of the samples varied inversely with the thickness of the laser-melted layer of zirconia.
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