Effect Of Laser Surface Melting Research Articles

Effect of laser surface melting on microstructure and corrosion characteristics of AM60B magnesium alloy

Surface modification of laser surface melting (LSM) was applied to the AM60B magnesium alloy using a 10kW continuous-wave CO2 laser. The microstructure, composition and corrosion resistance of AM60B magnesium alloy after LSM treatment were investigated by using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and corrosion tests, respectively. Results showed that the LSM treatment produced a continuous and homogeneous modified layer with refined grains, enriched Al element and redistributed intermetallic compounds on AM60B alloy. The corrosion resistance of the AM60B alloy was enhanced by the LSM treatment. The enhancement of the corrosion resistance was mainly attributed to the reduced corrosion susceptibility of Al enriched α-Mg matrix and the barrier effect of uniformly distributed β-phase of the LSM modified layer.

Densification Behavior and Microstructure Evolution of Laser Surface Melting Processed Silicon-Containing Micro Arc Oxidation Coating

The present work investigated the effect of laser surface melting (LSM) process on micro arc oxidation (MAO) coating prepared in silicate electrolytes (Si-MAO) and aluminate electrolytes (Al-MAO). Plasma intensity of laser spots, element content and phase constituents of coatings were analyzed. During LSM remelting process, the formation of heat sources and micro molten pools on the surface of MAO coating were discussed. The results showed that the moderate plasma was formed more easily on the Si-MAO than Al-MAO coating, owing to the temperature threshold of melting oxide layer was decreased for silicon-containing MAO coating during LSM treatment. Besides, the Si-MAO coating of laser-treated had low porosity and smooth surface.

Laser surface melting of a complex high alloy steel

The effect of laser surface melting (LSM) on the microscopic morphology of a complex high alloy steel has been examined in single track experiments. Different combinations of power (1–4kW) and scan speed (500–1000mmmin−1) were selected in order to obtain a range of depths of melt penetration. An increase in the depth of melt penetration has correlated with rise in the estimated surface temperature induced by laser melting. Within the strongly refined structure of the laser melted alloy, the interdendritic spacing, λ varied from 0.29μm to 0.97μm with increase in the depth of melt penetration. The microhardness in the laser surface melted region has been shown to decrease linearly with λ−0.5.

MODIFICATION OF CARBON STEEL BY LASER SURFACE MELTING: PART I: EFFECT OF LASER BEAM TRAVELLING SPEED ON MICROSTRUCTURAL FEATURES AND SURFACE HARDNESS

The present study aims to improve the surface hardness of carbon steel by application of laser surface melting of effective conditions. The travelling speed of laser beam during this treatment is one of the important treatment conditions. This study aims to investigate the effect of laser surface melting with different beam speeds on macro and microstructure as well as the hardness distribution through the thickness of carbon steel. To achieve this target, three different travelling speeds (1500, 1000 and 500 mm min-1) at a constant beam power of 800 W were chosen in this study. The resulted laser treated specimens were investigated in macro and microscopically scale using optical and scanning electron microscope. Hardness measurements were also carried out through the thickness of the laser treated specimens. The laser treated areas with all used travelling speeds results in melted and solidified zone on the surface of the steel. In the same time, Plates of acicular martensite structure were observed within the upper part of the melted and solidified zone in almost all experimental conditions, while some bainite structure in ferrite grains are detected in its lower part. By increasing the travelling speed, the depth of the laser treated zone was decreases, while travelling speed has much less significant effect on the laser treated zone width. The size of the formed martensite plates was increased by decreasing the travelling speed from 1500 to 500 mm min-1. On the other hand, the travelling speed has a straight effect on the length of the acicular martensite; as the travelling speed increases, the acicular martensite became longer, while it shows fine acicular martensite at lower travelling speeds. The depth that full martensite structure can be reached is increased by increasing travelling speed. At lower travelling speed (500 mm min-1), large amount of bainite structure is observed at the center of the treated zone up to its lower end. The fast travelling speed (1500 mm min-1) show higher hardness on the free surface than that of slow travelling speed (500 mm min-1). On the other hand, the travelling speed has a reverse effect on the depth of this hardness increment; the slower travelling speed give deeper areas of high hardness than that of fast speed. The Heat Affect Zone (HAZ) areas were increased by decreasing the travelling speed. In all conditions, the heat affected zone areas were composed of partially decomposed pearlite in ferrite grains. Finally, the microstructure of the base metal far from the laser treated areas show normal ferrite-sound pearlite microstructure.

The Effect of Laser Surface Melting on the Microstructure and Mechanical Properties of Low Carbon Steel

The Effect of Laser Surface Melting on the Microstructure and Mechanical Properties of Low Carbon Steel

Effect of Laser Surface Melting on Structure and Properties of a High Speed Tool Steel

The purpose of this research paper is focused on the high speed steel surface layers improvement properties using HPDL laser. The paper present laser surface technologies, investigation of structure and properties of the high speed steel alloying with carbides using high power diode laser HPDL. Investigation indicate the influence of the alloying carbides on the structure and properties of the surface layer of investigated steel depending on the kind of alloying carbides and power implemented laser (HPDL). In the effect of laser alloying with powder of carbides occurs size reduction of microstructure as well as dispersion hardening through fused in but partially dissolved carbides and consolidation through enrichment of surface layer in alloying additions coming from dissolving carbides. Introduced particles of carbides and in part remain undissolved, creating conglomerates being a result of fusion of undissolved powder grains into molten metal base. The structural mechanism was determined of surface layers development, effect was studied of alloying parameters, gas protection method, and thickness of paste layer applied onto the steel surface on structure refinement and influence of these factors on the mechanical properties of surface layer, and especially on its hardness, abrasive wear resistance, and roughness. It has the important cognitive significance and gives grounds to the practical employment of these technologies for forming the surfaces of new tools and regeneration of the used ones.

Effect of laser surface melting on intergranular corrosion behaviour of aged austenitic and duplex stainless steels

In the present study, the effect of laser surface melting (LSM) on intergranular corrosion behaviour of aged austenitic stainless steels (UNS S30400, S31603, S32100 and S34700) and aged duplex stainless steels (UNS S31803 and S32950) were investigated. LSM of the aged stainless steels was carried out using a 2.5 kW CW Nd:YAG laser. The microstructure of the aged stainless steels after LSM depends on their compositions. After LSM, the aged austenitic stainless steels mainly contain austenite (γ) with some ferrite (δ) as the minor phase, but the carbide phases are completely eliminated. For the aged duplex stainless steels after LSM, δ becomes the major phase and the δ/γ phase balance is disturbed, whereas the sigma (σ) phase is eliminated. The degree of sensitization ( DOS) and corrosion morphology of the aged stainless steels before and after LSM were determined by the double loop electrochemical potentiokinetic reactivation (DL-EPR) using a potentiostat and SEM observation, respectively. Desensitization of the aged stainless steels has been successfully achieved by LSM and their intergranular corrosion resistance is found to be significantly enhanced as reflected by the decrease in DOS due to dissolution of the carbides or σ phase, which reduced Cr depletion or the possibility of solute segregation at the grain or phase boundaries, despite the presence of δ and disturbance of δ/γ phase balance.

Effect of CO<sub>2</sub> Laser Surface Melting on the Microstructure of AZ91D Magnesium Alloy

In the present study, the effect of laser surface melting (LSM) on microstructure of AZ91D magnesium alloy was investigated with a 2kW continuous wave CO2 laser. The results indicate that both the substrate and laser melted layer mainly consisted of α-Mg and β-Mg17Al12, the amount of β-phase in laser melted layer was decreased as compared to that of the substrate. The microstructure of the laser surface melted zone consists of fine dendrites with an average grain size of less than 10m, the grain size was reduced by a factor of more than 10 times as compared to that of the substrate. The micro-hardness of the melted layer was increased to 70–85HV as compared to that of the substrate (about 53HV). Because of the grain refinement, the enhancement of the hard phase β-Mg17Al12, and the solid solution hardening of alloy elements, the micro-hardness and strength of the laser melted layer was increased significantly.

Studies on laser surface melting of tool steel—Part I: Surface characterization and it's electrochemical behavior

In the present study, the effect of laser surface melting of a tool steel (SAE 52100 steel) on the characteristics (microstructures, phases and residual stress) and the corrosion property of the treated surface has been undertaken. Laser surface melting is carried out using a high power (2 kW) continuous wave CO 2 laser (with a beam diameter of 3 mm) with a linear scan speed of 1–2 m/min, using different proportions of argon (Ar) and nitrogen (N 2) as shrouding atmosphere. The gas flow rate was maintained constant at 6 l/min. Laser surface melting in argon (Ar) atmosphere significantly refined the microstructure (grain size) with the presence of lath martensite. Laser surface melting in 50%Ar + 50% N 2 and 100% N 2 atmosphere led to the formation of thin nitride (consisting of Fe 4N and Fe 2N and Cr 2N) layer. Laser surface melting in 100% N 2 atmosphere developed a microstructure consisting of primary ferrite and eutectic mixtures of α-Fe and Fe 4N, Fe 3N, Fe 2N and Cr 2N. There is introduction of residual tensile micro-stress in laser surface melted surface. However, residual stress in the range of (− 800 to − 400 MPa) and (− 300 to + 100 MPa) were observed when surface melted in 100% N 2 and 50%Ar–50% N 2 atmosphere. Improvement in general and pitting corrosion resistance in a 3.56 wt.% NaCl solution was noticed after laser surface melting.

Studies on laser surface melting of tool steel — Part II: Mechanical properties of the surface

In the present study, the effect of laser surface melting using different proportions of argon and nitrogen as shrouding atmosphere on microhardness and wear resistance properties of a low alloy high carbon tool steel (SAE 52100 steel) has been undertaken. Laser surface melting in argon (Ar) atmosphere significantly refined the microstructure (grain size) with the presence of carbides (both iron and chromium) and martensites and improved microhardness (350–500 VHN) as compared to as-received SAE 52100 steel (280 VHN). Laser surface melting in 100% N 2 atmosphere led to formation of thin nitride (consisting of Fe 4N and Fe 2N and Cr 2N) layer with improved microhardness to as high as 1050 VHN. Wear studies showed a significant enhancement in wear resistance against hardened steel ball, a maximum improvement was achieved when lased using 100% N 2. The mechanism of wear was studied in details.

Effect of laser surface melting on corrosion behaviour of AZ91D Mg alloy in simulated-modified body fluid

High corrosion rate in physiological environment of the body is the major drawback of magnesium alloys for their successful applications as biodegradable orthopaedic implants. In the present study, corrosion behaviour of AZ91D magnesium alloy after laser surface melting (LSM) was studied in modified-simulated body fluid at 37 °C. The improved corrosion resistance of AZ91D alloy using LSM was found to depend on the solidification microstructure in the laser-melted zone. The general and pitting corrosion resistance of laser-treated surface was significantly enhanced due to the refined continuous network of β-Mg17Al12 phases and the increased Al concentration in the laser-melted zone.

Rapid solidification of M 2 high-speed steel by laser melting

The effects of laser surface melting and rapid solidification on the microstructure of M2 high-speed steel (HSS) have been investigated. A solid state pulse Nd-YAG laser of wavelength 1.06 μm, maximum power of 100 W, beam diameter ∼1 mm, and pulse duration of 0.8 and 2.5 ms. Optical, scanning electron microscopy, and X-ray diffraction techniques were used to evaluate the microstructure and identify the phases. Results show that laser surface melting has led to a complete dissolution of the carbides and re-solidification of cellular/dendritic structure of a very fine scale surrounded by a continuous interdendritic (or intercellular) network of carbides eutectic. The phases appeared were mainly δ ferrite and M 6C and small amount of austenite γ. Laser surface melting leads to a refinement of the microstructure and altering the morphology and the distribution of the phases. The microhardness of this material was not increased after laser melting.

Effect of laser surface melting on friction and wear behavior of AM50 magnesium alloy

In the present study, an attempt has been made to enhance tribological properties of AM50 magnesium alloy by laser surface melting (LSM) with a 2 kW continuous wave CO 2 laser. The microstructure of the laser surface melted zone consists of fine columnar dendrites growing epitaxially from the liquid–solid interface. Microhardness of the melted zone was improved to 55–75 HV as compared to 40 HV of the substrate. The friction and wear behavior of the laser surface melted layer were investigated using a ball-on-flat apparatus under dry sliding condition. It was found that the friction coefficient curve of the laser surface melted layer was similar to that of substrate. They showed a lower initial friction coefficient about 0.18 that after the running-in period increased up to about 0.38. Furthermore, compared with the AM50 substrate, the wear volume of the laser surface melted layer was decreased by 42%, the wear resistance of the laser surface melted layer was improved.

Microstructure and corrosion behavior of laser surface-melted high-speed steels

Three high-speed steels (HSSs) M2, ASP23, ASP30 were surface-melted by a CW 2.5-kW Nd:YAG laser. The microstructure of the laser surface-melted HSSs was investigated by optical microscopy, scanning electron microscopy and X-ray diffractometry, and the hardness profiles of the laser surface-melted layers were determined by a Vickers hardness tester. The corrosion behavior in 0.6 M NaCl and 0.5 M NaHCO 3 solutions at 25 °C was studied by potentiodynamic polarization technique. Metallographical as well as electrochemical corrosion studies illustrated the beneficial effects of laser surface melting (LSM) in refining the microstructure and in enhancing the corrosion resistance of the HSSs. The large carbide particles of annealed HSSs were dissolved after LSM and ultrafine dendrites of austenite and martensite with submicroscopic carbide precipitation were formed in the melt zones of the laser surface-melted HSSs. LSM of M2, ASP23 and ASP30 produced surface layers of hardness 615, 580 and 665 Hv, respectively. The hardness of the laser surface-melted ASP23 and ASP30 reached about 0.75 to 0.80 that of the conventionally hardened ones, while the hardness of laser-melted M2 was comparable to that of conventionally hardened M2. The corrosion resistance of all laser surface-melted HSSs in both solutions was significantly improved, as evidenced by a noble shift of the corrosion potential and a reduction in the corrosion current density. Among the HSSs, laser surface-melted ASP23 possessed the highest corrosion resistance in both solutions. The presence of cobalt in ASP30 has no beneficial effect on enhancing its corrosion resistance. The enhancement in the corrosion resistance of the laser surface-melted HSSs is attributable to the combined effects of dissociation and refinement of large carbides and the increase of the passivating alloying elements such as Cr, Mo and W in solid solution.

Reassessment of the effects of laser surface melting on IGC of SUS 304

Laser surface remelting (LSM) experiments were conducted on surface of 304 stainless steel using a 2 kW CW Nd: YAG laser and the effects of LSM on the intergranular corrosion (IGC) resistance of 304 stainless steel were reassessed from view point of grain boundary engineering (GBE). LSM could make the sensitized microstructures locally desensitize, and could improve the IGC resistance. The improved IGC resistance of the laser-surface-melted specimens could be attributed in part to Cr redistribution at the boundaries of the cells and grains and in part to existence of a large amount of low energy Σ(1 ≤ Σ ≤ 29) boundaries and the formation of 〈0 0 1〉(1 0 0) texture. However, the laser-surface-melted specimens became much more susceptible to IGC in the sensitization temperature region, and the corrosion rate of the resensitized specimen was even higher than that of the base materials under the same sensitization condition. A subsequent annealing treatment changed the grain boundary character distribution (GBCD) remarkably and the IGC resistance of the processed specimens was improved.

Microstructure analysis of magnesium alloy melted by laser irradiation

The effects of laser surface melting (LSM) on microstructure of magnesium alloy containing Al8.57%, Zn 0.68%, Mn0.15%, Ce0.52% were investigated. In the present work, a pulsed Nd:YAG laser was used to melt and rapidly solidify the surface of the magnesium alloy with the objective of changing microstructure and improving the corrosion resistance. The results indicate that laser-melted layer contains the finer dendrites and behaviors good resistance corrosion compared with the untreated layer. Furthermore, the absorption coefficient of the magnesium alloy has been estimated according to the numeral simulation of the thermal conditions. The formation process of fine microstructure in melted layers was investigated based on the experimental observation and the theoretical analysis. Some simulation results such as the re-solidification velocities are obtained. The phase constitutions of the melted layers determined by X-ray diffraction were β-Mg 17Al 12 and α-Mg as well as some phases unidentified.

Pitting corrosion of the laser surface melted Alloy 600

The effect of laser surface melting (LSM) on the resistance to pitting corrosion of Ni-base Alloy 600 was investigated by a potentiodynamic polarization test in 1M NaCl solutions at pH values of 4 and 10 at temperatures of 30, 60 and 90°C. The pitting potentials of Alloy 600 were markedly increased by the LSM process, when compared with those of the non-laser treated Alloy 600. From the microscopic examination after the corrosion test, it was found that the pitting was initiated at the junction between a TiN inclusion and the matrix, possibly at the site of a sulfide physically associated with the TiN inclusion. The homogeneous micro-structure associated with the reduction of the inclusion size during the LSM process could be attributed to the improvement of the pitting corrosion properties in the LSM Alloy 600.

Effect of laser surface melting on the corrosion and cavitation erosion behaviors of a manganese–nickel–aluminium bronze

Abstract Manganese–nickel–aluminium bronze (MAB) samples were treated with a high-power Nd:YAG laser system to achieve laser surface melting. Under proper laser processing conditions, the cavitation erosion–corrosion rate of laser-treated MAB in 3.5 wt.% NaCl solution was reduced by more than five times compared with that of as-received MAB. To elucidate the mechanism leading to enhancement in resistance, pure corrosion in 3.5 wt.% NaCl solution and pure cavitation erosion behaviors were studied separately. Pure corrosion behavior was studied using electrochemical technique and immersion method under quiescent condition, while pure cavitation erosion behavior was studied using deionized water as a non-corrosive medium. Both the corrosion resistance and the erosion resistance benefited from a homogeneous single-phase microstructure resulting from laser surface melting, while the relatively low resistance of as-received MAB was mainly attributable to its heterogeneous and multi-phase microstructure. The increase in erosion resistance was more significant than that in corrosion resistance, probably due to the increase in hardness as an additional favorable factor for erosion resistance. For laser-treated MAB, erosion–corrosion synergism constituted a significant contribution to the overall cavitation erosion–corrosion in 3.5 wt.% NaCl solution. The shift in corrosion potential under cavitation revealed the difference in the relative dominance of the effect of cavitation on the cathodic and anodic reactions on laser-treated and untreated MAB samples.

Effect of laser surface melting upon the devitrification of plasma sprayed cordierite

Devitrification behavior of plasma sprayed cordierite (2MgO–2Al 2O 3–5SiO 2) modified by addition of 6.3 wt.% TiO 2 was studied in the as-sprayed condition and after laser surface melting. Laser treatment was performed using a pulsed Nd:YAG laser and the melt depth was maintained within the plasma sprayed coating. Laser surface melting produced a chemically homogeneous glass surface that contained extensive microcracks in both the melted and unmelted portions of the coating. Laser surface melting was found to be effective in reducing porosity and surface roughness. Roughness of the as-sprayed surface was reduced to R a 2.5 μm or better from a roughness of R a 14 μm. Devitrification of as-sprayed cordierite was dependent upon TiO 2 distribution in the coating, whereas crystallization in the laser melted coating was dominated by nucleation at microcracks. Microcrack density was significantly reduced by viscous glass flow and transformation induced volume expansion during devitrification.

Effect of laser surface melting on corrosion and wear resistance of a commercial magnesium alloy

Among the light metals, Mg and its alloys occupy a prominent position due to its low density, excellent machinability, and high specific strength. However, a relatively poor resistance to corrosion and wear are serious impediments against wider application of Mg alloys. In the present study, an attempt was made to enhance pitting corrosion resistance and microhardness of a commercial Mg alloy, MEZ (Zn 0.5%, Mn 0.1%, Zr 0.1%, rare earth elements 2%, Mg remaining percentage) by laser surface melting. The study included a detailed characterization of laser surface melted zone in terms of microstructure, phase analysis and its correlation with process parameters to optimize the laser processing routine. Mechanical properties like microhardness, wear, and electrochemical properties like pitting corrosion resistance of the surface melted layer were studied in detail. Microhardness of the laser surface melted layer was improved to 85–100 VHN as compared to 35 VHN of the as-received MEZ. Pitting corrosion resistance of the laser surface melted MEZ, significantly improved in a 3.56 wt.% NaCl solution because of grain refinement and redistribution of the intermetallic phases following rapid quenching associated with the process. The wear resistance of laser surface melted layer was also improved as compared to as-received MEZ.