Laser Surface Melting Research Articles

Microstructure evolution and wear behavior of AISI 304 stainless steel after Nd:YAG pulsed laser surface melting.

The microstructure and wear behavior of AISI 304 stainless steel after Nd:YAG pulsed laser surface melting (LSM) were investigated. The microstructural features of the LSM layer were characterized by field emission scanning electron microscope and high-resolution transmission electron microscope. Experimental results showed that the microstructure was obviously refined to the nano- and sub-micrometer scales on the AISI 304 stainless steel surface after LSM treatment. Fine grains with grain size of less than 200 nm were obtained when the applied laser energy densities were in the range of 1.90×107 to 3.52×107J/m2 during LSM. The results indicated that the calculated surface temperature, cooling rate, and measured grain size are closely related to the adopted laser energy densities. The lower the laser energy density is, the lower the surface temperature, and the faster the cooling rate, the finer the grain size. In addition, the microhardness and wear resistance of the stainless steel was significantly improved. Finally, the wear mechanism after LSM process was revealed.

The effect of surface laser texturing on the corrosion performance of the biocompatible β-Ti12Mo6Zr2Fe alloy

Laser materials processing is a very attractive technology, due not only to the vast number of applications in a wide range of materials and industrial segments but also due to the constant progress in the development of laser devices in terms of power, control, and costs. In metals processing technology, a high and precisely controlled density of energy concentrated in a small region imposes specific characteristics for the surface, keeping bulk properties unchanged. Alternatively, laser surface modification can result in outstanding surface properties to ordinary/low-cost metals. In the present work, the corrosion behavior of the Ti12Mo6Zr2Fe β-metastable alloy has been evaluated after laser surface melting and re-solidification under an inert atmosphere. It was found that this processing route produced significant metallurgical and chemistry changes on the surface of the alloy, including grain refinement and oxide formation. It resulted in a significant improvement in the corrosion properties in comparison to the passivated metal, as observed in potentiodynamic polarization curves and by electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). Electrical equivalent circuit (EEC) modeling of impedance data suggests that a duplex porous/dense passive layer present in the untreated alloy enables the occurrence of charge-transfer mechanisms at some extension while a thicker oxide layer present after laser texturing increases the capacitive behavior of the surface.

Softening and hardening on a Zr-based bulk metallic glass induced by nanosecond laser surface melting

The study reported here confirms that laser surface melting (LSM) can be employed to modify the hardness and the shear banding behaviour of bulk metallic glasses (BMGs). More specifically, by conducting LSM operations on the Zr-based Vitreloy 105 BMG in ambient atmosphere using a nanosecond laser, it was found that surface hardening can be achieved, in addition to the well-known surface softening effect. Besides, it was found that the presence of compressive residual stress and an increased introduction of crystalline precipitates accompanied LSM-induced surface hardening. On the contrary, tensile residual stress and a reduced fraction of crystalline precipitates were observed for a softened surface post-LSM. Finally, differences in shear-banding mechanisms were detected near the surface of the laser irradiated regions. More specifically, overall reduced serrated flow but important surface shear bands events were observed following the LSM-based introduction of compressive residual stress. In contrast, more pronounced serrated flows and the likely distribution of shear banding activity well beneath the irradiated BMG surface was promoted when LSM resulted in the introduction of tensile residual stress.

Microstructural characterization of laser surface-melted Inconel 718

In the present study, a detailed study of the effect of laser parameters on microstructure and phases of the laser surface-melted (using 2 kW continuous wave Yb-fibre laser) Inconel 718 has been carried out. Surface melting has been conducted with a power of 400 watts, scan speed of 500, 750, and 1000 mm/min and with a spot diameter of 3 mm. After laser surface melting, the microstructures, phase, surface roughness and crystallographic orientation (texture) of the melt zone has been carried out. There is refinement of microstructure and change in crystallographic texture which varied with process parameters. The effect of process parameters on the microhardness of the melt zone has been studied in detail.

High Power Diode Laser (HPDL) surface treatments to improve the mechanical properties and the corrosion behaviour of Mg-Zn-Ca alloys for biodegradable implants

Biodegradability, low density and mechanical properties close to those of the bone are some of the intrinsic properties of the Mg-Zn-Ca alloys that have attracted significant attention for developing biodegradable implants. However, rapid degradation constitutes the main disadvantage of these alloys. In this work, two different alloys, Mg-1Zn-1Ca and Mg-3Zn-0.4Ca, were laser surface treated using a HPDL to increase hardness and to improve the corrosion performance. Depending on the laser parameters, a complete laser surface melting (LSM) or a selective laser surface melting (SLSM) were reached. The microstructure, mechanical properties and corrosion behaviour were established and compared. Higher laser input energies led to larger treated zones and in these cases two different regions could be distinguished: the outer zone, where the LSM took place, presented a more refined microstructure with a greater dispersion of secondary phases; the following zone suffered SLSM, in it only the secondary phases were modified by the HPDL. Hardness was 24%–27% higher than that of the untreated samples. The HPDL also reduced the corrosion rate by 21% and 37% for the Mg-1Zn-1Ca alloy and the Mg-3Zn-0.4Ca alloy, respectively, after 336 h of immersion in Hanks' solution at 37 °C.

Microstructural evolution and properties analysis of laser surface melted and Al/SiC cladded magnesium-rare earth alloys

The influence of laser surface melting and Al–SiC cladding on the microstructure, mechanical, and electrochemical properties of Mg-Gd-Y-Zn-Zr alloys was studied. The presence of α-Mg, Mg5(Gd,Y,Zn) and Mg10(Y,Gd)Zn phases in the melted layer and Al4C3, SiC, Si, Mg2Si and Mg17Al12 phases in cladded layer were confirmed from XRD results. Microstructures and chemical composition results also indicated a refined microstructure and re-distribution of the second phase. The finite element model (FEM) temperature profiles confirmed the variation in cooling rates of melted and cladded zones which supported the achieved microstructures. The microhardness values across the melted and cladded layers were significantly increased as a result of grain refinement, re-distribution of the second phases of the melted layer and the presence of hard-ceramic phases in the cladded layers. Potentiodynamic polarization studies revealed a decrease in corrosion current density (icorr) value and enhanced corrosion resistance of the laser melted alloy. The Al/SiC cladded layer showed a nobler shift in corrosion potential (Ecorr) and a significant decrease in icorr value due to the thick ceramic layer which acts as a barrier to the corrosive attack.

Microstructural characteristics of laser surface melted MoSiBTiC alloy

The microstructural characteristics of a TiC-added Mo-Si-B (MoSiBTiC) alloy fabricated by laser surface melting were investigated. The microstructure inside a melt pool consisted of many cells, and each cell was composed of an ultrafine ternary eutectic lamellar structure with Mo solid solution (Moss), Mo5SiB2, and (Mo,Ti)2C phases. The lamellar structure completely disappeared in a heat affected zone (HAZ) formed by multi tracks test, and a fine round (Ti,Mo)C phase newly precipitated in the HAZ together with other phases. The chemical composition analyses identified the elemental supersaturation of Si and Ti in the Moss phase and of Ti in the T2 phase in the lamellar structure.

Wear and corrosion behavior of P20 steel surface modified by gas nitriding with laser surface engineering

Gas nitriding and laser surface engineering are popular technologies to improve the surface performance of steels. This study evaluates the effect of duplex treatment of gas nitriding and laser surface engineering on surface hardness, wear and corrosion resistance of P20 plastic mold steel. It is found that gas nitriding at 550 °C for 20 h with nitrogen potential of 0.18 generates a nitrided layer without nitrides, which drastically improves the wear resistance. Simultaneously, the corrosion resistance is also marginal improved by the gas nitriding. Laser surface hardening further elevates the surface hardness and wear resistance of the nitrided layer due to the formation of martensite. Besides, a small amount of austenite retains in surface layer after laser surface hardening, which may lead to the galvanic attack at the phase interface between martensite and retained austenite and deteriorate the surface corrosion resistance. Laser surface melting results in the denitrification of nitrided layer and the formation of holes at the bottom of melted layer, thus reducing the surface hardness and wear resistance. Meanwhile, the denitrified surface layer also exhibits a degraded corrosion resistance owe to the decreasing nitrogen content and the formation of mixed structure of martensite and retained austenite.

Developing of nano sized fibrous eutectic silicon in hypereutectic Al\u2013Si alloy by laser remelting

Laser surface melting followed by rapid solidification is an effective means to produce very fine microstructures with desirable surface properties because of the high rates of cooling associated with it. In the present study, the effect of rapid cooling on the silicon particle size, distribution, and morphology of hypereutectic Al–17wt.%Si and Al–20wt.%Si alloys have been investigated. A continuous-wave CO2 laser of wavelength 10.6 μm and a Trumpf Yb-YAG disk laser of wavelength 1.030 μm were used with a beam diameter of 1 mm and scanning speeds ranging from 5 to 100 mm/s. Rapid solidification increased the solubility of silicon in aluminum to approximately 5wt% and induced non-equilibrium hypoeutectic microstructures comprising large volume fractions of primary α-Al dendrites and ultrafine Al–Si eutectic of lamellar morphology. Both α-Al dendrites and the silicon particle sizes were significantly reduced from micron to nanoscale level. The morphology of silicon particles is modified from massive polygonal and plate-like to a mixture of fine flakes with round corners, feathery and fibrous, or a coral-like and thread-like structure. The eutectic silicon size and the interlamellar spacing were reduced to 30 and 10 nm, respectively. Furthermore, most of the silicon crystals in the eutectic region and the aluminum dendrites contained a significant number of twins which were considered as an essential contributor to the mechanism of growth and branching. Microhardness values increased two to threefold due to the refinement of the microstructural constituent.

Laser processing of Mg-10Li-3Al-3Zn alloy：Part II- Improving corrosion resistance of multi-phase Mg alloys by laser surface processing

In Part Ⅰ of this series, it can be found that the corrosion resistance of metals in the welded seam zone (WSZ) was far higher than that of the base metal (BM) of MBLS10A-200 Mg-Li alloy. Therefore, the feasibility of improving the corrosion resistance of MBLS10A-200 Mg-Li alloy through laser surface melting (LSM) was further explored. Meanwhile, laser shock peening (LSP) treatment was also used for contrast. The results showed that the surface melted zone with the corrosion resistance through LSM superior to that of metals in WSZ of MBLS10A-200 alloy through laser welding can be prepared by controlling heat input through increasing the scanning speed of laser beam, while LSP has limited impact on the electrochemical corrosion resistance of MBLS10A-200 alloy. The corrosion current density (Jcorr) of the samples subjected LSM declined by two orders of magnitude compared with the base metal (BM) while the charge transfer resistance increased by 17 times compared with BM. An analysis indicated that owing to the fast cooling rate during laser processing, the multi-phase microstructures (i.e. α phase, β phase and Li2MgAl) of BM were transformed into β single-phase microstructure in WSZ and surface melted zone. In this way, not only solid solution strengthening of the metals in WSZ was realized but also the micro-galvanic coupling generated due to the difference of electric potentials of multi-phase microstructures were reduced, thus improving the corrosion resistance of surface melted zone.

The effect of laser surface melting of stainless steel grade AISI 316L welded joint on its corrosion performance in molten Solar Salt

Whereas there are numerous studies dedicated to the corrosion performance of different grades of austenitic stainless steel (ASS) exposed to the conditions of thermal storage of solar energy, there is no data concerning the resistance of the welding joints, which are unavoidable when fabricating large structures. Because the microstructure of a weld bead can significantly differ from that of the base metal and the heat-affected zone (HAZ), increased susceptibility to localized corrosion can be expected. This work explores corrosion resistance of a welding joint of ASS grade 316 L when exposed to molten Solar Salt (60% NaNO3 – 40% KNO3) at 565 °C. Further, the application of laser surface melting (LSM) is proposed as a method to modify the microstructure of the weld bead and HAZ to enhance the corrosion resistance of the joint. Isothermal exposure to molten Solar Salt was implemented in static immersion, in the presence of atmospheric air, for the duration of up to 1008 h (6 weeks). The gravimetric analysis revealed a corrosion rate of 54 μm/y at the weld joint, which is at least twice as high as that expected for the same non-welded alloy in similar conditions. Although LSM reduces the rate of uniform corrosion in the first 2 weeks, there is no long term benefit in this regard. However, the onset of localized corrosion of the intergranular type is effectively prevented, presenting a potential approach for diminishing the risk of catastrophic failure of HAZ by fracture.

Degradation, wettability and surface characteristics of laser surface modified Mg-Zn-Gd-Nd alloy.

This work evaluates the effects of laser surface modification on Mg-Zn-Gd-Nd alloy which is a potential biodegradable material for temporary bone implant applications. The laser surface melted (LSM) samples were investigated for microstructure, wettability, surface hardness and in vitro degradation. The microstructural study was carried out using scanning and transmission electron microscopes (SEM, TEM) and the phases present were analyzed using X-ray diffraction. The in vitro degradation behaviour was assessed in hank's balanced salt solution (HBSS) by immersion corrosion technique and the effect of LSM process parameters on the wettability was analyzed through contact angle measurements. The microstructural examination showed remarkable grain refinement as well as uniform redistribution of intermetallic phases throughout the matrix after LSM. These microstructural changes increased the hardness of LSM samples with an increase in energy density. The wetting behaviour of processed samples showed hydrophilic nature when processed at lower (12.5 and 17.5 J/mm2) and intermediate energy density (22.5 and 25 J/mm2), which can potentially improve cell-materials interaction. The corrosion rate of as cast Mg-Zn-Gd-Nd alloy decreased by ~83% due to LSM.

Effect of laser surface melting on nanoparticles dispersion and tensile properties of in-situ nano-ZrB2p/6061Al composite

Laser surface melting (LSM) were successfully applied in in-situ 10 vol% ZrB2(np)/6061Al composites. Formation of nano-sized ZrB2 phase is confirmed by FESEM, EDS and HRTEM. Due to the minimization of porosity defects, one-way laser scanning is evaluated as optimum scan route strategy. After LSM, nanoparticle aggregations in composites are largely eliminated by melt vortex and matrix grain growth pushing force. Nanoparticles are uniformly dispersed near matrix grain boundaries and agglomerations showed an explosive orientation dispersion. After LSM, the average matrix grain size decreased by 87.5% to 3.4 μm. Nanoparticle dispersion uniformity and toughness of composites are proportional to laser power density. Both strength and elongation are enhanced as the matrix grain refinement and better uniformity of the nanoparticle dispersion after LSM. When LSM for 420 NW/mm2 was performed, the optimal improvements of tensile strength and elongation are 33.54% and 72.51% respectively.

Influence of Solidification Conditions on the Microstructure of Laser-Surface-Melted Ductile Cast Iron.

The thermal conditions in the molten pool during the laser surface melting of ductile cast iron EN-GJS-700-2 were estimated by using infrared thermography and thermocouple measurements. The thermal data were then correlated with the microstructure of the melted zone. Additionally, the thermodynamic calculations of a Fe-C-Si alloy system were performed to predict the solidification path of the melted zone. It was found that increasing the cooling rate during solidification of the refined ledeburite eutectic but also suppressed the martensitic transformation. A continuous network of plate-like secondary cementite precipitates and nanometric spherical precipitates of tertiary cementite were observed in regions of primary and eutectic austenite. The solidification of the melted zone terminated with the Liquid → γ-Fe + Fe3C + Fe8Si2C reaction. The hardness of the melted zone was affected by both the fraction of the retained austenite and the morphology of the ledeburite eutectic.

Experimental and Numerical Analysis of Laser Surface Melting by Using Enthalpy Method

In this study, experimental and numerical applied of heat distribution due to pulsed Nd: YAG laser surface melting. Experimental side was consists of laser parameters are, pulse duration1.3ms, wavelength 1064nm, laser energies 1.5, 2. 6 and 4.3 J, laser beam diameter is 0.6 mm and spot diameter 0.78 mm was applied a low carbon steel type St37 with a dimension 10, 10, 3 mm, length, width and thickness respectively. Numerical analysis side consist of a mathematical model and calculating a thermal cycle by using equation in the enthalpy method applied to determine the cooling rate in fusion zone. The simulation by using the enthalpy method, applied on conduction heat transfer to estimate the cooling rate model in fusion zone and heat affected zones. Cooling rates models are helping to estimate the microstructure and micro hardness distribution in fusion and heat affected zones. The complication of the heat transfer in laser surface melting process, because at in rapid solidification, therefore the enthalpy model is more appropriate for this case. The result shows that increases of laser energy lead to decrease cooling rates and increase width and penetration of fusion zone, also decrease micro hardness in fusion zone and we found an increase in the pool size of fusion and heat affected zones.

Casting and Laser Surface Melting of 316L Stainless Steel from Scrap Resources

316L stainless steel is used in various industrial applications including chemical, biomedical and mechanical industries due to its good mechanical properties and corrosion resistance. Recycling of 316L stainless steel scrap without significantly reducing its value has received recently great attention because of the environmental regulations. In the current work, 316L stainless steel scrap was recycled via casting using Skull induction melting technique. The casted products subsequently subjected to laser surface melting process to improve its surface properties to be used for harsh environment. The results showed defect free surfaces with homogeneous microstructures. Nano size grains were also obtained due to rapid solidification process. Such nano size grains are preferred for extending the usage of the 316L stainless steel in new applications.Corresponding author: E-Mail: elgazzar.ha@gmail.com

Rejuvenation of Inside Surface of Intergranular Corrosion-Damaged Type 304 Stainless Steel Tube through Laser Surface Melting

The present paper describes an experimental study aimed at rejuvenation of internal surface of intergranular corrosion-damaged type 304 stainless steel tube through laser surface melting. In the present investigation, effectiveness of laser surface melting technique was experimentally demonstrated on the inside surface of type 304 SS tubular specimens, which is often the requirement in most of the industrial applications as the process fluid flows through tubes/pipes. The results of the study demonstrated that laser surface melting treatment of inner surface of intergranular corrosion-damaged type 304 stainless steel not only erased previous IGC damage, but also restored its degree of sensitization close to that of untreated condition. Laser surface-melted specimens successfully passed ASTM A262 practice E test, thereby not displaying susceptibility to intergranular corrosion. However, subsequent exposure to susceptible temperature (973 K) brought about enhancement in IGC susceptibility of laser rejuvenated surface of 304 stainless steel tube. As a logical extension of the experimental corrosion study, a laser beam maneuvering system was designed to carry out in situ laser surface melting treatment on the internal surface of tubular components. To the authors’ best knowledge, this type of laser beam maneuvering system has been designed first time to carry out laser surface melting for repair of intergranular corrosion inside the tubular parts. The results are important for rejuvenation of IGC-damaged in-service austenitic stainless steel components.

Comparative study of laser melting and pre-placed Ni–20% Cr alloying over nodular iron surface

In this study, two techniques such as laser surface melting (LSM) and laser surface alloying (LSA) were performed to protect the surface layers of nodular cast iron as it is used to manufacture different machine parts like cams, beds, camshafts, crankshafts, cylinders and engine blocks. The main objective of this research work is to examine the effects of LSM and LSA processes on phases, microstructure, hardness, wear resistance and surface roughness. The outcomes of both LSM and LSA specimens show a homogeneous structure, effective bonding of alloy powders with the base metal and crack-free surfaces. The hardness was improved 4 times (LSM) and 2.62 times (LSA) when compared with the base material. The tribological test shows improved wear resistance of LSM (8.82 × 10−7 kN) and LSA (1.32 × 10−6 kN) samples compared to the base material (4.36 × 10−6 kN). The examined wear tracks indicate that mild abrasion, adhesion and delamination were the major wear mechanisms. The reason for the enhancement of wear resistance is the refinement of microstructure, the solid solution strengthening effect and good bonding between alloy powders and base material. The LSM technique is a potential method to improve the tribological properties of industrial materials.

Mechanical Properties and Hydrogen Embrittlement of Laser-Surface Melted AISI 430 Ferritic Stainless Steel

In the present study, the feasibility of laser surface melting (LSM) of AISI 430 ferritic stainless steel to minimize hydrogen embrittlement (HE) was investigated. LSM of AISI 430 steel was successfully achieved by a 2.3-kW high power diode laser (HPDL) with scanning speeds of 60 mm/s and 80 mm/s (the samples are designated as V60 and V80, respectively) at a power of 2 kW. To investigate the HE effect on the AISI 430 steel without and with LSM, hydrogen was introduced into specimens by cathodic charging in 0.1 M NaOH solution under galvanostatic conditions at a current density of 30 mA/cm2 and 25 °C. Detail microstructural analysis was performed and the correlation of microstructure with HE was evaluated. By electron backscatter diffraction (EBSD) analysis, the austenite contents for the laser-surface melted specimens V60 and V80 are found to be 0.6 and 1.9 wt%, respectively. The amount of retained austenite in LSM specimens was reduced with lower laser scanning speed. The surface microhardness of the laser-surface melted AISI 430 steel (~280 HV0.2) is found to be increased by 56% as compared with that of the substrate (~180 HV0.2) because of the presence of martensite. The degree of embrittlement caused by hydrogen for the charged and non-charged AISI 430 steel was obtained using slow-strain-rate tensile (SSRT) test in air at a strain rate of 3 × 10−5 s−1. After hydrogen pre-charging, the ductility of as-received AISI 430 steel was reduced from 0.44 to 0.25 while the laser-surface melted AISI 430 steel showed similar tensile properties as the as-received one. After LSM, the value of HE susceptibility Iδ decreases from 43.2% to 38.9% and 38.2% for V60 and V80, respectively, due to the presence of martensite.

Effect of laser surface melting pretreatment on the growth behavior and mechanical properties of microarc oxidation coating on Ti6Al4V alloy

Porous TiO2 ceramic coatings with high contents of Si and P were fabricated on a Ti6Al4V alloy using hybrid processing of laser surface melting (LSM) and microarc oxidation (MAO). The effect of LSM pretreatment on the growth behavior and mechanical properties of the MAO coating was studied. The results showed that the MAO coating on LSM pretreatment Ti6Al4V (LSM-MAO) had quite different surface morphologies, thickness, and compositions compared to the MAO coating on as-received titanium alloy. Grain refinement and dislocation in the LSM-treated Ti6Al4V alloy provided extra energy and more numbers of discharge channels during the MAO process. LSM–MAO coating exhibited a more uniform pore distribution, relatively small pores, and larger thickness compared to the MAO coating. The LSM-MAO coating had higher hardness and better wear resistance than the MAO coating. LSM is deduced to be an appropriate and efficient pretreatment method for achieving a high-quality MAO coating on titanium alloy.