Laser Surface Modification Technique Research Articles

Microstructure Characterization of Al-alloy AW 5454 Intended for Ecological Laser Hybrid Welding

The article deals with the presentation of the microstructure characterization of Al-alloy AW 5454, which is intended for laser hybrid welding. In the first part, the procedure of laser hybrid welding and comparison to other laser surface modification techniques is presented. In the following, the key methods of metallographic characterization and hardness measurements at selected locations of Al-alloy AW 5454 are presented, which made it possible to carry out a scientific evaluation of the obtained results. The goal of the research was to gain insight into the microstructure of Al-alloy AW 5454, which in the future will make it possible to determine those technological parameters of laser hybrid welding that have the greatest influence on the resulting final microstructure and thus on the properties of the weld.

The Interplay of Thermal Gradient and Laser Process Parameters on the Mechanical Properties, Geometrical and Microstructural Characteristics of Laser-Cladded Titanium (Ti6Al4V) Alloy Composite Coatings

With the development of laser surface modification techniques like direct laser metal deposition (DLMD), titanium alloy (TI6Al4V) may now have its entire base metal microstructure preserved while having its surface modified to have better characteristics. Numerous surface issues in the aerospace industry can be resolved using this method without changing the titanium alloy’s primary microstructure. As a result, titanium alloy is now more widely used in sectors outside of aerospace and automotive. This is made possible by fabricating metal composite coatings on titanium alloys using the same DLMD method. Any component can be repaired using this method, thereby extending the component’s life. The experimental process was carried out utilizing a 3000 W Ytterbium Laser System at the National Laser Centre of the CSIR in South Africa. Through the use of a laser system, AlCuTi/Ti6Al4V was created. The characterization of the materials for grinding and polishing was performed according to standard methods. There is a substantial correlation between the reinforcement feed rate, scan speed, and laser power components. Due to the significant role that aluminum reinforcement played and the presence of aluminum in the base metal structure, Ti-Al structures were also created. The reaction and solidification of the copper and aluminum reinforcements in the melt pool produced the dendritic phases visible in the microstructures. Compared to the base alloy, the microhardness’s highest value of 1117.2 HV1.0 is equivalent to a 69.1% enhancement in the hardness of the composite coatings. The enhanced hardness property is linked to the dendritic phases formed in the microstructures as a result of optimized process parameters. Tensile strengths of laser-clad ternary coatings also improved by 23%, 46.2%, 13.1%, 70%, 34.3%, and 51.7% when compared to titanium alloy substrates. The yield strengths of laser-clad ternary coatings improved by 19%, 46.7%, 12.9%, 69.3%, 34.7%, and 52.1% when compared to the titanium alloy substrate.

Recent advances of high entropy alloys for aerospace applications: a review

PurposeThis study aims to review the recent advancements in high entropy alloys (HEAs) called high entropy materials, including high entropy superalloys which are current potential alternatives to nickel superalloys for gas turbine applications. Understandings of the laser surface modification techniques of the HEA are discussed whilst future recommendations and remedies to manufacturing challenges via laser are outlined.Design/methodology/approachMaterials used for high-pressure gas turbine engine applications must be able to withstand severe environmentally induced degradation, mechanical, thermal loads and general extreme conditions caused by hot corrosive gases, high-temperature oxidation and stress. Over the years, Nickel-based superalloys with elevated temperature rupture and creep resistance, excellent lifetime expectancy and solution strengthening L12 and γ´ precipitate used for turbine engine applications. However, the superalloy’s density, low creep strength, poor thermal conductivity, difficulty in machining and low fatigue resistance demands the innovation of new advanced materials.FindingsHEAs is one of the most frequently investigated advanced materials, attributed to their configurational complexity and properties reported to exceed conventional materials. Thus, owing to their characteristic feature of the high entropy effect, several other materials have emerged to become potential solutions for several functional and structural applications in the aerospace industry. In a previous study, research contributions show that defects are associated with conventional manufacturing processes of HEAs; therefore, this study investigates new advances in the laser-based manufacturing and surface modification techniques of HEA.Research limitations/implicationsThe AlxCoCrCuFeNi HEA system, particularly the Al0.5CoCrCuFeNi HEA has been extensively studied, attributed to its mechanical and physical properties exceeding that of pure metals for aerospace turbine engine applications and the advances in the fabrication and surface modification processes of the alloy was outlined to show the latest developments focusing only on laser-based manufacturing processing due to its many advantages.Originality/valueIt is evident that high entropy materials are a potential innovative alternative to conventional superalloys for turbine engine applications via laser additive manufacturing.

Effect of nickel-based laser coatings on phase composition and corrosion behaviour of titanium alloy for offshore application

Recent advances in titanium alloy applications in the offshore industry have been realized through the development of laser surface modification technique. The distinctive outcome of this technique has provided increase in the utilization of titanium in offshore drilling risers for special drilling operations and various subsea and tubing applications. In this work, surface mitigation and corrosion degradation of titanium alloy in aggressive sulfuric acid were investigated using electrochemical technique (linear potentiodynamic polarization) while the surface characterization (morphology) and phases of the resultant coatings were analyzed using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Prior to that, laser surface technique was used to fabricate Nickel-based powder on the substrate (Ti-6Al-4V). Results revealed that laser clad sample with high scan speed was more effective in improving the corrosion resistance compared to low scan speed. The enhanced corrosion resistance with high laser scan speed has been attributed to the presence of hard intermetallic compounds in the metallic coating.

A Hybrid Approach for Modelling and Optimization of Laser Cladding Process

To develop the hard surfaces of superalloys usually, laser surface modification is employed. Out of several laser surface modification techniques, the laser cladding process allows obtaining sound surface clads. Laser Cladding being a complex process depends on many input parameters. Knowledge of these input parameters during laser cladding is essential for the development of good clad. Artificial intelligence has proven to be a better tool for modeling processes having complex and non-linear behavior. A hybrid approach of any two individual methodologies may even perform better. In this paper, a coupled methodology of Artificial Neural Network (ANN) and Particle Swarm Optimization (PSO) for modeling and optimization of process parameters (laser power, scan velocity, and powder feed rate) for quality characteristics (aspect ratio) in laser claddingInconel-738 is proposed. First, an ANN model is trained, tested, and developed for aspect ratio. Then, the PSO technique is used for optimization utilizing a trained ANN model. The developed hybrid model shows the minor error of 5.13% of mean square error and 8.68% error in predicting aspect ratio

Investigating the Microstructural Evolution and Characterization of Additive Manufactured Zn-Sn-Ti/Ti-6Al-4V Composite.

The investigation focused on studying how the reinforcement powders and titanium alloy substrate were influenced by the volumetric energy which was absorbed. The only processing parameters which were varied was the laser intensity and the scanning speed, which were employed to design the direct laser metal deposition (DLMD) single- and multi-tracks. Laser surface modification techniques has unique benefits and properties compared to other conventional techniques. These techniques have process factors that affect directly the microstructure of materials which in turn influence the materials properties. The results revealed dense microstructure in the fabricated coatings in terms of the microstructural evolution, the sizes of the different grains, the structure of the phases formed and the orientation. The modified surface layer of the additively manufactured coating had improved and had a fine microstructure. Optimizing the DLMD processing conditions resulted in a crack-free surface layer but still promoted a few population of gas defects. The micro-hardness measured in the 5Zn-10Sn-Ti coating at 900 W and scan speed of 1.0 m/min was approximated to be 637 HV at all processing conditions employed, and with respect to the hardness of the substrate, there was a 51.33% increase from 310 HV. But increase of 57.2% was noted at 900 W, 1.0 m/min for 5Zn-10Sn-Ti coating. There was enhancement in the results of the micro-hardness tests conducted and this was due to the resulting microstructural evolution. Homogeneous and dense microstructures was accountable for the micro-hardness performance measured.

Effects of Mo2C, Ni binder and laser surface modification on WC inserts for turning Ti-6Al-4V

The effects of rapid pulse electric current sintering (PECS), Ni as a Co binder substitute, Mo2C additions and laser surface modification (LSM) on the microstructure, mechanical properties and machining performance during roughing and finishing turning of Ti-6Al-4 V were investigated. Additions of Mo2C reduced the carbide grain size from 0.65 ± 0.01 μm to 0.5 ± 0.01 μm in liquid phase sintered (LPS) WC-Co/Ni cermets, with the PECS manufactured WC-0.5Cr3C2–3.5Mo2C-10Co (wt%) having the highest hardness. The LSM technique produced a ~2.5 μm self-carbide coating, increasing the surface hardness of all the samples. LSM was done to improve abrasion, attrition and thermal wear resistance. Turning was done at cuttings speeds (vc) of 45–120 m/min, depths of cut (ap) of 0.25–2.0 mm and feeds of 0.15–0.2 mm/revolution, under lubricated conditions. The developed inserts were compared to TH10 (an industrial reference), and performance was assessed by cutting forces, tool wear and tool life. The liquid phase sintered WC-0.5Cr3C2-10Co (wt%) and WC-0.5Cr3C2–3.5Mo2C-10Co (wt%) inserts had longer tool lives than TH10 during roughing at a cutting speed (vc) of 45 m/min, depth of cut (ap) of 2 mm and feed of 0.2 mm/revolution, although TH10 had the best tool life during finishing (vc = 120 m/min, ap = 0.25 mm and feed =0.15 mm/revolution). Generally, LSM had a negligible effect on tool life, WC-Ni based inserts had the shortest tool lives and LPS inserts performed better than PECS inserts.

Roughing, semi-finishing and finishing of laser surface modified nickel bonded NbC and WC inserts for grey cast iron (GCI) face-milling

An attempt to improve the machining performance of NbC-Ni cutting inserts by rapid pulse electric current sintering (PECS), TiC and Mo2C additions and laser surface modification (LSM) was done. Use of a nickel binder and additions TiC and Mo2C to liquid phase sintered (LPS) NbC based samples led to comparable hardness (>13 GPa) and KIC (~10 MPa.m1/2) to LPS WC-Co/Ni samples. The laser surface modification (LSM) technique produced a ~2.5 μm thick self-carbide coating, increasing the surface hardness of all the samples. Laser surface modification was done to improve abrasion and attrition wear resistance. Face-milling of grade 17 grey cast iron (BS 1452/GG35) was conducted at 100–500 m/min cutting speeds (vc) and 0.25–1.5 mm depths of cut (ap). The insert wear was measured after every pass, and analyzed by annular dark field scanning transmission electron microscopy (ADF-STEM). During roughing, WC-Co based inserts had the lowest flank wear rate (FWR) values, with the WC-10Co (LPS) insert having a FWR of 10.15 μm/min after 20 min cutting time. However, during semi-finishing and finishing, NbC-4TiC-12Ni (PECS) and NbC-4Mo2C-4TiC-12Ni (PECS) inserts had the lowest FWR values, showing up to six times longer tool life than the WC-Co (LPS) inserts based inserts and 12 times longer life than the WC-Ni based inserts. Generally, LSM improved the NbC inserts' tool life, reducing the FWR values in all NbC based inserts in all cutting tests.

Physical characterization and wear behavior of laser processed and PVD coated WC/Co in dry sliding and dry turning processes

The present study is an attempt to integrate the laser surface modification techniques with PVD-coatings. AlTiN and AlCrN coatings were deposited on different laser shock peened (LSP) and laser surface textured (LST) WC/Co surfaces. The developed surfaces and PVD coatings were characterized for surface morphology, elemental composition, surface topography, substrate/coating phases, and adhesion behavior. Tribological tests were performed to understand the friction and wear performance of developed surfaces against Ti6Al4V counter pair at varying sliding speeds. Tribo test results revealed that the coatings deposited on laser processed surfaces are helpful in reducing the coefficient of friction (COF) and wear loss. The associated wear mechanisms are discussed with the help of proposed wear models. For laser textured surfaces, the experimental evidence of texture induced micro cutting mechanism has been reported. The generation of weaker carbides for LSP surfaces reduced the coating adhesion and resulted in poor tribological performance. For machining of Ti6Al4V, improved performance of coated LST surfaces was achieved. Apparent friction coefficient and flank wear were reduced by 64% and 65% respectively.

Effects of Laser Processing Parameters on Texturized Layer Development and Surface Features of Ti6Al4V Alloy Samples

Surface engineering is widely used in different areas, such as the aerospace industry or the biomechanical and medical fields. Specifically, laser surface modification techniques may obtain specific surface finishes for special applications. In texturing laser procedures, the control of processing parameters has a great influence on the geometry and characteristics of the treated area. When these processes are carried out on titanium alloys, thin oxide layers are usually developed on the irradiated surface, formed through the thermochemical combination of vaporized material with atmospheric oxygen in the air. In thermal oxidation treatments of Ti6Al4V, the highest concentration of oxides is mainly composed by rutile (TiO2), producing surface property modifications such as hardness, among others. In this research, a thermochemical oxidation of Ti6Al4V alloy has been performed through laser texturing, using laser scanning speed (Vs) and pulse rate (f) as process control variables, and its influence on the beam absorption capacity of the modified layer have been analyzed. Combined evaluations of microgeometrical features and mechanical properties, such as hardness, verified that, by means of laser texturing treatments, the ability to generate specific topographies and increase the initial hardness of the alloy is obtained. The most advantageous results for the increase of hardness by thermochemical oxidation have been detected in low scan speeds of laser beam treatments, resulting in an increase of approximately 270% using a scanning speed of 10 mm/s. On the other hand, a dependence between roughness values, in terms of Ra and Rz, and the energy density of pulse (Ed) has been observed, showing higher values of roughness for a 17.68 J/cm2 energy density of pulse.

Developments in laser-based surface engineering processes: with particular reference to protection against cavitation erosion

With the increasing demands of economical, reliable and durable hydraulic and pneumatic systems, it is necessary to minimize the material damage from cavitation erosion (CE) when systems are handling cavitating and corrosive fluids. Cavitation erosion is a nausea for many engineering components, such as ship propellers & rudders, turbine, diesel engine, cylinder liner, pump impeller vanes, control valves, hydraulic turbines, bearings, pipes, ultrasonic cleaners and mechanical heart valves, which are exposed to the high-speed flowing or vibratory fluids. This paper reviews the rationale behind the application of laser surface modification for achieving CE resistant surfaces of fluid handling components. The problem of CE may be tackled by enhancing the surface properties of the base materials (ferrous and non-ferrous alloys) with various laser surface modification techniques including laser transformation hardening (LTH), laser surface melting (LSM), laser surface alloying (LSA), laser cladding (LC), laser dispersion (LD) and laser plasma hybrid spraying (LPHS). The CE performance of a variety of laser-surface modified layers/coatings is discussed in this review. In particular, coatings of hard-facing alloys, shape memory alloys, surface metal or intermetallic matrix composites and cermets on ferrous and non-ferrous alloys are included. The mechanisms of the enhancement in cavitation erosion resistance (Re) are discussed.

Laser surface modification of AZ31B Mg alloy for bio-wettability.

Magnesium alloys are the potential degradable materials for load-bearing implant application due to their comparable mechanical properties to human bone, excellent bioactivity, and invivo non-toxicity. However, for a successful load-bearing implant, the surface of bio-implant must allow protein absorption and layer formation under physiological environment that can assist the cell/osteoblast growth. In this regard, surface wettability of bio-implant plays a key role to dictate the quantity of protein absorption. In light of this, the main objective of the present study was to produce favorable bio-wettability condition of AZ31B Mg alloy bio-implant surface via laser surface modification technique under various laser processing conditions. In the present efforts, the influence of laser surface modification on AZ31B Mg alloy surface on resultant bio-wettability was investigated via contact-angle measurements and the co-relationships among microstructure (grain size), surface roughness, surface energy, and surface chemical composition were established. In addition, the laser surface modification technique was simulated by computational (thermal) model to facilitate the prediction of temperature and its resultant cooling/solidification rates under various laser processing conditions for correlating with their corresponding composition and phase evolution. These predicted thermal properties were later used to correlate with the corresponding microstructure, chemical composition, and phase evolution via experimental analyses (X-ray diffractometer, scanning electron microscope, energy-dispersive spectroscopy).

Multiperformance optimization of tensile strength and heat input of laser transformation hardening of commercially pure titanium using Taguchi methodology and utility concept

Purpose of this paper: The main objective of this research paper is to investigate and evaluate the optimal values of laser process parameters: laser power, scanning speed, and focused position for the simultaneous minimization and maximization of heat input and tensile strength respectively by Taguchi method and utility concept approach in laser transformation hardening of commercially pure titanium sheet of 1.6mm thickness using continuous wave (CW) Nd:YAG laser beam. Design/methodology/approach: The effect of laser process parameters on the heat input and tensile strength properties of commercially pure titanium and subsequent optimal settings of the parameters have been obtained using Taguchi’s parametric design approach and utility concept. The response performance is analyzed based on signal-to-noise ratio and analysis of variance (ANOVA). The optimal levels of the laser process parameters were determined through the Analysis of Means (ANOM). Findings: The optimization results revealed that a combination of higher levels of scanning speed and focused position i.e., increase in defocus along with laser power in the lower level play important role in order to simultaneously minimize the heat input and to maximize the tensile strength (σ). The predicted optimal values of tensile strength and heat input of commercially pure titanium sheet produced by laser transformation hardening process are 464 N/mm 2 and 141.667 Watts, respectively, for the optimized laser process parameters with minimum LP=750 Watts, maximum SS=3000mm/min, and lower value of FP=-30mm (increase in defocus). Research limitations/implications: Research range is limited to investigation of optimization laser hardening process parameters for the simultaneous minimization and maximization of heat input and tensile strength respones.of commercially pure titanium. Hardness test responses are also be optimized in future research work. Practical implications: Laser transformation hardening is an innovative and advanced laser surface modification technique has been employed in aerospace, marine, chemical applications, heat exchangers, cryogenic vessels, components for chemical processing and desalination equipment, condenser tubing, airframe skin, and nonstructural components which introduces the advantageous residual stresses into the surface, improving the mechanical properties like wear, resistance to corrosion, tensile strength, and fatigue strength. Originality/value: Authors made an effort to optimize the laser process parameters in order to minmize the heat input and maximize tensile strength of laser transformation hardening of commercially pure titanium using Taguchi methodology and utility concept.

Development of RSM- and ANN-based models to predict and analyze the effects of process parameters of laser-hardened commercially pure titanium on heat input and tensile strength

Laser transformation hardening (LTH) is an innovative and advanced laser surface modification technique as compared to conventional transformation hardening processes and has been employed in aerospace, marine, chemical applications, heat exchangers, cryogenic vessels, components for chemical processing and desalination equipment, condenser tubing, airframe skin, and nonstructural components which introduces the advantageous residual stresses into the surface, improving the mechanical properties like wear, resistance to corrosion, tensile strength, and fatigue strength. In the present study, LTH of commercially pure titanium, nearer to ASTM grade 3 of chemical composition was investigated using continuous wave 2 kW, Nd: YAG laser. The effect of laser process variables such as laser power, scanning speed, and focused position was investigated using response surface methodology (RSM) and artificial neural network (ANN) keeping argon gas flow rate of 10 lpm as fixed input parameter. This paper describes the comparison of the heat input (HI) and ultimate tensile strength (σ) (simply called as tensile strength) predictive models based on ANN and RSM. The paper also presents the effect of laser process variables on the HI and ultimate σ. The research work also emphasizes on the effect of HI on σ. The experiments were conducted based on a three-factor, three-level Box–Behnken surface statistical design. Quadratic polynomial equations were developed for proper process parametric study for its optimal performance characteristics. The experimental results under optimum conditions were compared with the simulated values obtained from the RSM and ANN model. Adequacy of the developed models was tested by analysis of variance technique. A multilayer feed-forward neural network with a Levenberg–Marquardt back-propagation algorithm was adopted to develop the relationships between the laser hardening process parameters, HI, and ultimate σ. The performance of the developed ANN models were compared with the second-order RSM mathematical models of HI and σ. There was good agreement between the experimental and simulated values of RSM and ANN. The comparison clearly indicates that the ANN models provide more accurate prediction compared to the RSM models. It has been found that there is a trend of increased tensile strength with the decrease of hardening heat input and a trend of increased tensile strength with the increase of hardening cooling rate. As heat input decreases, there will be a faster cooling rate. Considering the effect of HI on ultimate σ, it was found that the lower the heat input, the faster cooling rate. The details of experimentation, model development, testing, validation of models, effect of laser process variables on heat input and ultimate σ, effect of HI on σ, and performance comparison of RSM and ANN models are presented in the paper. The results of Box–Behnken design of RSM and ANN models also indicate that the proposed models predict the responses adequately within the limits of input parameters being used. It is suggested that regression equations can be used to find optimum conditions for HI and σ of laser-hardened commercially pure titanium material.

The investigation of the influence of laser re‐melting on density, surface quality and microstructure of selective laser melting parts

PurposeSelective laser melting (SLM) is a powder metallurgical (PM) additive manufacturing process whereby a three‐dimensional part is built in a layer‐wise manner. During the process, a high intensity laser beam selectively scans a powder bed according to the computer‐aided design data of the part to be produced and the powder metal particles are completely molten. The process is capable of producing near full density (∼98‐99 per cent relative density) and functional metallic parts with a high geometrical freedom. However, insufficient surface quality of produced parts is one of the important limitations of the process. The purpose of this study is to apply laser re‐melting using a continuous wave laser during SLM production of 316L stainless steel and Ti6Al4V parts to overcome this limitation.Design/methodology/approachAfter each layer is fully molten, the same slice data are used to re‐expose the layer for laser re‐melting. In this manner, laser re‐melting does not only improve the surface quality on the top surfaces, but also has the potential to change the microstructure and to improve the obtained density. The influence of laser re‐melting on the surface quality, density and microstructure is studied varying the operating parameters for re‐melting such as scan speed, laser power and scan spacing.FindingsIt is concluded that laser re‐melting is a promising method to enhance the density and surface quality of SLM parts at a cost of longer production times. Laser re‐melting improves the density to almost 100 per cent whereas 90 per cent enhancement is achieved in the surface quality of SLM parts after laser re‐melting. The microhardness is improved in the laser re‐molten zone if sufficiently high‐energy densities are provided, probably due to a fine‐cell size encountered in the microstructure.Originality/valueThere has been extensive research in the field of laser surface modification techniques, e.g. laser polishing, laser hardening and laser surface melting, applied to bulk materials produced by conventional manufacturing processes. However, those studies only relate to laser enhancement of surface or sub‐surface properties of parts produced using bulk material. They do not aim at enhancement of core material properties, nor surface enhancement of (rough) surfaces produced in a PM way by SLM. This study is carried out to cover the gap and analyze the advantages of laser re‐melting in the field of additive manufacturing.

Laser hardening techniques on steam turbine blade and application

Different laser surface hardening techniques, such as laser alloying and laser solution strengthening were adopted to perform modification treatment on the local region of inset edge for 2Cr13 and 17-4PH steam turbine blades to prolong the life of the blades. The microstructures, microhardness and anti-cavitation properties were investigated on the blades after laser treatment. The hardening mechanism and technique adaptability were researched. Large scale installation practices confirmed that the laser surface modification techniques are safe and reliable, which can improve the properties of blades greatly with advantages of high automation, high quality, little distortion and simple procedure.

Diffusion bonding of laser-surface-modified gamma titanium aluminide alloy to nickel-base casting alloy

γ-TiAl alloy was bonded to Ni-base casting alloy using a laser surface modification technique, and the effects of Ni–Cr–Ti–Al clad coatings on TiAl alloy/Ni-base alloy bonds were investigated. Interfacial defects in joints were restricted by Ni–Cr–Ti–Al clad coatings. The compositions and microstructures of Ni–Cr–Ti–Al clad coatings have significant effects on the thickness and shape of interfacial reaction layers, and sound joints with the high shear strength are achieved between laser-surface-remelted TiAl alloy and Ni-base alloy laser clad with a Ni 56 Cr 7 Ti 15 Al 22 coating.

Laser surface engineering of steel for hard refractory ceramic composite coating

Laser surface modification technique is applied to deposit ultrahard ceramic (TiB 2) coating on 1010 steel. A uniform, continuous and crack free coating with a metallurgically sound interface is obtained. Coating is “composite” in nature comprising TiB 2 particles and Fe in the laser melt zone. Polygonal and needle shaped boride particles are uniformly distributed in the laser melted zone. The interfacial microstructure consists of cellular dendrites and fine equiaxed dendrites. Metastable phase(s) such as Fe x B y and Ti m B n are also observed which is a characteristic feature of non-equilibrium synthesis by laser energy. Laser melt zone has a high hardness. However, hardness is not uniform in the layer.

Laser melting of plasma nitrided Ti6A14V alloy

A laser surface modification technique can be used as a part of a dublex treatment process to improve the surface properties of Ti6A14V alloy. The present study is conducted to investigate the surface properties of the Ti6A14V alloy due to laser melting prior to a plasma nitriding process. Consequently, nitriding is carried out to obtain the depth of the nitride zone of 30 μm. A CO 2 laser with 1.6 kW output power was used to melt the nitride layers. The wear properties of the plasma nitrided and nitrided/melted surfaces were investigated using pin-on-disc equipment while the friction coefficient was determined using a ball-on-disc machine. The nitride depth profile was measured using a nuclear analysis reaction and elemental distribution in the melted zones was investigated using μ-PIXE. Scanning electron microscopy and optical microscopy were carried out to analyze the microstructures developed before and after the laser melting process. In addition, heating and cooling rates were predicted through the electron-kinetic theory approach.

Laser Surface Modification for Structural Materials.

Much attention is recently paid to laser surface modification (LSM) techniques forproviding an approach in controlling compositions and structure of matal surface. IHI has been performing reseach activity for bringing LSM techniques to a degree of development such that they can be used industrially. One of these LSM techniques was actually applied to austenitic stainless steel pipes put in practical use to prevent stress corrosion cracking.In this paper, our recent laser beam technology related to LSM and details of LSM technique applied to actual component in our company are introduced.