Effect Of Laser Surface Melting Research Articles

Effect of laser surface melting on microstructure and hardness of Mg–4Y–2Zn–1Zr-0.6Ca alloy

To improve the performance of magnesium and enhance its mechanical properties and microstructure, a laboratory-scale Mg alloy with the composition Mg–4Y–2Zn–1Zr-0.6Ca was developed. Subsequently, the alloy was subjected to homogenization and extrusion processes to reduce casting defects and the microstructure refinement. Additionally, surface modification was performed using a pulsed Nd:YAG laser. The findings of the experiment indicate that by controlling the laser processing parameters, it was possible to attain a microstructure devoid of any defects. Moreover, an examination of the microstructure and secondary phases was conducted through the utilization of characterization techniques such as the Optical Microscope (OM), Field Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). Furthermore, the micro hardness of the samples was evaluated using the Vickers micro hardness testing method. Consequently, the microstructures of all specimens exhibited equiaxed grains, predominantly composed of (α-Mg), (Mg24Y5+α-Zr), and the W-phase (Mg3Y2Zn3). In addition, the laser-melted surface revealed a noteworthy refinement of the grain structure, with an evolution in grain morphology from the top to the bottom of the melted area. Equiaxed grains were present in the centerline, whereas columnar grains were observed in the fusion line. Additionally, as the scanning speed increased, a finer microstructure was observed. Due to the rapid heating and cooling involved in the laser surface melting (LSM) process, the secondary phase (Mg3Y2Zn3) dissolved in the microstructure, and the (Mg24Y5+α-Zr) phase was uniformly distributed throughout the LSMed area. Ultimately, the micro hardness showed a significant increase due to the dual influence of grain refinement and the homogeneous dispersion of the secondary phase.

Effect of laser surface melting on superficial morphology and properties of the electrochemical polishing Ti6Al4V alloy

Effect of laser surface melting on superficial morphology and properties of the electrochemical polishing Ti6Al4V alloy

The effect of laser surface melting on the microstructure, microsegregation and solidification path of service-aged ECY768 cobalt-based gas turbine nozzle

In this study, the laser surface melting of cobalt-based superalloy ECY768, which has been in service for 40,000 h at a temperature of 1000 °C, has been investigated. Subsequently, laser surface welding and post-welding heat treatment is performed on the samples. This study was conducted in order to restore the microstructure of the damaged service-aged gas turbine nozzle to as-cast state. The results showed that by performing laser surface remelting, the microstructure of as-cast state can be approached. Also, the results of this study have investigated the weldability, microsegregation and solidification path of this superalloy, and it can be used in the repairing this superalloy in the industry. Laser surface melting was performed using a continuous wave fiber laser at various speeds of 10, 12, 14, 20, 50, and 70 mm/s. The microstructure and phase characteristics of the samples were examined using optical and scanning electron microscopes. Upon analyzing the macrostructure of the weld metal, it was observed that the depth of the melt zone at the speed of 12 mm/s is 585 ± 40 μm. In the investigating the microstructure of the solidification modes, namely planar, cellular, columnar dendritic, and equiaxed dendritic, it was observed that microsegregation occurs during laser welding of the samples due to the presence of heavy elements such as tantalum and tungsten. The solidification distribution coefficient for tantalum was calculated to be 0.37, which increased to 0.60 after the solution annealing heat treatment, resulting in an improved segregation behavior. Characterizing the surface hardness profiles of laser-melted samples it was observed that the hardness in the melt zone significantly increased compared to the base metal. The results of the current research indicate that the weldability (resistance to various welding defects, especially hot cracks) of the cobalt-based superalloy ECY768 is acceptable, and this process can be used for rejuvenating service-aged ECY768 cobalt-based gas turbine nozzle.

Effect of laser surface melting on microstructure evolution and cavitation behavior of nickel aluminum bronze

The laser surface melting was employed on the nickel aluminum bronze to augment the cavitation performance. To investigate the effect of laser treatment, the microstructure was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. And the cavitation behavior was tested on an ultrasonic vibratory machine. The results show that the optimal process parameter with laser power of 3 kW and scanning speed of 10 mm/s contributes to the increased corrosion resistance and reduced cavitation mass loss, compared with the cast sample, respectively. The enhancement of the cavitation resistance is dominated by the synergistic mechanism of grain refinement strengthening, dislocation strengthening, and precipitate strengthening, with the homogeneous structure eliminating selective corrosion.

Corrosion resistance of pulsed laser modified AZ31 Mg alloy surfaces

The effect of laser surface melting on the corrosion resistance of AZ31 Mg alloy in 0.1 M NaCl solution was investigated using different laser processing conditions (energy densities of 14 and 17 J cm−2). Laser treatment induced rough surfaces primarily composed of oxidized species of Mg. XPS analysis revealed that the surface concentration of Al increased significantly as a consequence of LSM. Electrochemical impedance spectroscopy showed that the laser treatment remarkably increased the polarization resistance of the AZ31 Mg alloy and induced a passive-like region of about 100 mV, as determined by potentiodynamic polarization. Analysis of the results obtained provide solid evidence that within the immersion times used in this study, LSM treatment increased the corrosion resistance of AZ31 Mg alloy under open circuit conditions and anodic polarization.

The effect of laser surface melting on the retained austenite and wear properties of AISI D2 tool steel

In this study the effect of laser surface melting (LSM) on the amount of retained austenite, hardness and wear resistance of AISI D2 steel was investigated utilizing hardness test, X-ray diffraction (XRD), pin on disk wear test and scanning electron microscopy (SEM). In order to evaluate wear resistance, pin on disk tests at two different loads were carried out on surface treated samples including as received annealed and a quenched and tempered specimen. Surface treatment has been carried out in three different conditions; LSM, LSM with pre-heating at 300 °C and LSM with pre-cooling in liquid nitrogen which resulted in 64, 42% and 90% of retained austenite respectively, revealing that higher cooling rate led to a higher amount of retained austenite. The results showed that in spite of the presence of austenite as major phase in re-melted surface, the hardness reached to the values of up to 600 HV10 which is approximately two times of the as received steel having a lot of carbides dispersed in the ferrite matrix. In addition, at lower load, conventionally heat treated sample exhibited better wear resistance, whereas at higher load, the wear rate of laser melted specimen was the least as a result of the transformation of retained austenite into martensite. At lower load the dominant wear mechanism was abrasion while Adhesion was identified as the main wear mechanism at higher load.

Effect of Laser Surface Melting on Microstructure of Cold Sprayed Ni20Cr Coatings

Effect of Laser Surface Melting on Microstructure of Cold Sprayed Ni20Cr Coatings

Microstructure and surface texture driven improvement in in-vitro response of laser surface processed AZ31B magnesium alloy

The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy. Thermokinetic effects experienced by the material during laser surface melting were simulated using a multiphysics finite element model. Microstructure and phase evolution were examined using scanning electron microscopy, X-ray diffraction, and electron back scatter diffraction. Surface topography was evaluated using white light interferometry. The interaction of surface melted samples with simulated body fluid was monitored by contact angle measurements and immersion studies up to 7 days. Laser surface melting led to formation of a refined microstructure with predominantly basal crystallographic texture. Concurrently, the amount of β phase (Mg17Al12) increased with an increase in the laser fluence. β phase preferentially decorated the cell boundaries. In terms of topography, the surface became progressively rougher with an increase in laser fluence. As a result, upon immersion in simulated body fluid, the laser surface melted samples showed an improved wettability, corrosion resistance, and precipitation of mineral having composition closer to the hydroxyapatite bone mineral compared to the untreated sample.

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.

Effect of laser surface melting on surface integrity of Al−4.5Cu composites reinforced with SiC and MoS2

Abstract Two types of composites were prepared with Al−4.5Cu alloy as a matrix using stir casting method. One was reinforced with 10 wt.% of SiC and 2 wt.% of MoS2. The other was reinforced with 10 wt.% of SiC and 4 wt.% of MoS2. Their surfaces were remelted using a CO2 laser beam with an objective to study the influence of laser surface melting (LSM). The topography, microhardness, corrosion resistance and wear resistance of the laser melted surfaces were studied. Overall surface integrity after LSM was compared with as-cast surface. LSM enhanced the microhardness and wear resistance of the surface in each case. Porosity of the laser melted surface was low and corrosion resistance was high. Thus, LSM can be conveniently applied to enhancing the surface integrity of the aluminium composites. However, there is an optimum laser specific energy, around 38 J/m2 in this study, for obtaining the best surface integrity.

Influences of laser surface melting on microstructure, mechanical properties and corrosion resistance of dual-phase Cr–Fe–Co–Ni–Al high entropy alloys

In this paper, a laser surface melting (LSM) method was utilized on CrFeCoNiAlx (x = 0.5, 0.6, 0.7) high entropy alloys (HEAs) with FCC + BCC structure, and the effects of LSM on their microstructure, mechanical properties and corrosion behavior were systematically investigated. It is intriguing that, a layer with BCC + B2 structure formed on the surface of CrFeCoNiAl0.6 and CrFeCoNiAl0.7 substrates after LSM, while a monolithic FCC layer formed on that of CrFeCoNiAl0.5 substrate under the same condition. LSM influences the mechanical properties of CrFeCoNiAlx HEAs to varying degrees including hardness and tensile properties decided by the phase formation in laser-treated surfaces and the substrates. In addition, compared to the substrates, obvious increase in self-corrosion potential and pitting potential were found in the laser-treated surface layers of CrFeCoNiAl0.6 and CrFeCoNiAl0.7. Interestingly, the corrosion resistance of laser-treated surface layers has positive correlation with Al content, while that of the substrates shows negative correlation with the concentration of Al, which is possibly resulted from the difference in corrosion mechanism. This work provides a new route for significantly improving surface properties of dual-phase HEAs, which would be very beneficial to their further application as advanced materials.

Effect of Laser Surface Melting on Microstructure and Performance of Super 13Cr Stainless Steel

Effect of Laser Surface Melting on Microstructure and Performance of Super 13Cr Stainless Steel

The effect of laser surface melting on grain refinement of phase separated Cu-Cr alloy

Grain refinement and homogenization of Cr phase were achieved by laser surface melting (LSM) method, and the properties of Cu-Cr alloy were significantly improved. In this study, LSM of Cu-50Cr alloy (wt.%) was conducted with a high power density (106–107 W/cm2) laser beam, the microstructure and the properties of melt layer were investigated. The size of Cr phase was effectively refined from hundreds of micron scale to several micron scale, and the average size of Cr particles decreased to a few hundred nanometers. High cooling rate effectively inhibited coarsening effect on the Cr particles during liquid phase separation. Spherical Cr particles were dispersed in the melt layer with a thickness of 165 ± 20 μm. Microhardness was obviously enhanced and the maximum hardness was 232HV, which was 2.8 times that of the substrate. Arc duration of the LSM treated contacts increased up to 18%. The withstanding voltage of the fixed and the moving contact increased to 28.7% and 35.4%, respectively. The results show that LSM is an effective method to refine the microstructure of Cu-Cr alloy, and it is a promising modification method for electrical Cu-Cr vacuum contacts.

Effect of Laser Surface Melting on Chromium Carbide of 304 Stainless Steels

In the present study, the effects of laser surface melting (LSM) on chromium carbide of heat treated (AISI 304) austenitic stainless steels (ASS) was studied with the aim to suppress sensitization of 304SS. Austenitic stainless steels were heated (aging) up to (800) oC at constant holding time for two hours. LSM was conducted by using a (600 W) Yb-YAG laser. The microstructure was characterized by using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results shows, refined and homogeneous microstructure which contains austenite (γ) as basically phase and delta ferrite (δ) as the secondary phase, however, chromium carbide (Cr23C6) phase are fully dissolved. Desensitization of heat treated ASS has been successfully achieved by LSM which reduced Cr depletion at the grain boundaries.

Effect of laser surface melting and subsequent re-aging on microstructure and corrosion behavior of aged S32950 duplex stainless steel

In the present study, the microstructure and corrosion behavior of duplex stainless steel (DSS, S32950) after aging, laser surface melting (LSM) without and with subsequent re-aging were investigated. After LSM, the pitting corrosion resistance of the aged DSS was restored. It is attributed to re-dissolution and removal of M23C6, σ and γ2 phases. The purpose of re-aging is to investigate the phase balance and hence corrosion performance of the laser-melted DSS after subjected to isothermal aging at 800 °C, a condition which might be encountered during application. Results of the present study show that the laser-melted specimens after re-aging is less susceptible to pitting corrosion because the content of γ2 (the anode) is close to that of σ and δ (the cathodes).

Effect of laser surface melting on bulk metallic glass: Investigation of microstructure, microhardness, friction and wear properties

10 × 3 × 80 mm3 fully dense crack-free plate-like Cu46Zr42Al7Y5 bulk metallic glass (BMG) samples were successfully prepared by a copper mold casting method in an argon atmosphere and subjected to surface laser surface melting (LSM) under different laser frequencies. X-ray diffraction patterns showed that the degree of crystallization is determined by the crystalline phase in the heat-affected zone and the welding fusion zone; the heat-affected zone is easier to crystallize than the welding fusion zone at the same laser frequency. The microhardness of the welding fusion zones reached a maximum of 508.2 Hv at a laser frequency of 16 Hz. However, the microhardness of the heat-affected zone declined drastically with increasing laser frequency. In addition, the average frictional coefficient dramatically increased and then decreased with an increase in sliding velocity, and the values reached a maximum at the sliding velocity of 500 mm/min. The property of wear resistance was moderately improved at laser frequencies of 12, 14, and 16 Hz. Moreover, the grinding trace widths slightly increased with increasing sliding velocity. The friction and wear mechanisms and morphological representations were completely different under different sliding velocities.

Effect of Laser Surface Melting on the Microstructure and Pitting Corrosion Resistance of 304L SS Weldment

The manuscript presents the effect of laser surface melting (LSM) on the microstructural variations and pitting corrosion resistance of 304L SS weldment fabricated by gas tungsten arc welding of 304L SS plates using 308L SS filler wire. The weld region was examined by X-ray radiography for defect detection. LSM of 304L SS weldment was performed using Nd:YAG pulsed laser. Microstructural evaluation was carried out using optical and electron back scatter diffraction techniques. The microstructure of 304L SS base was found to be austenitic, while the weld region of 304L SS weldment contained delta ferrite distributed in austenite matrix. The microstructure of LSM 304L SS weldment was found to be homogeneous austenite matrix with sparsely distributed ferrite. Ferrite measurements showed a decrease in the percentage ferrite in the fusion zone of 304L SS weldment after LSM. A profound enhancement in the pitting corrosion resistance was observed after LSM, which could be attributed to the homogeneous microstructure and decrease in the ferrite content. Pit density was found to be higher in the heat-affected zone of the weldment. Very few pits were observed in the LSM 304L SS weldment compared to the as-weldment.

Microstructure and mechanical properties of Cr12MoV by ultrasonic vibration-assisted laser surface melting

ABSTRACTThe effects of laser surface melting assisted by ultrasonic vibration on the microstructure and mechanical properties of Cr12MoV were investigated. Results indicated that the original coarse columnar dendrite can be converted into a fine dendritic and equiaxed. The average microhardness increase from 389HV0.2 to 427HV0.2 resulted from the effect of grain refinement. The friction coefficient was lower than the melted layer without ultrasonic vibration and substrate. Under the same experimental conditions, the width and depth of wear scar were decreased by 19% and 25% than that of without ultrasonic vibration, respectively. The wear mechanism from severe adhesive wear into slight abrasive wear under the action of ultrasonic vibration. Experimental results revealed that melted layer fabricated by ultrasonic vibration exhibit finer and more uniform microstructure as well as superior tribological properties.

The effect of laser surface melting on microstructure and corrosion behavior of friction stir welded aluminum alloy 2219

This study aimed to explore the electrochemical properties and microstructure of friction stir welds to understand the correlation between their properties and processing. Friction stir welding is a promising solid-state joining process for high-strength aluminum alloys (AA). Although friction stir welding (FSW) eliminates the problems of fusion welding due to the fact that it is performed below Tm, it causes severe plastic deformation in the material. Some AA welded by FSW exhibit relatively poor corrosion resistance. In this research, the corrosion resistance of such welds was enhanced through laser surface melting. A friction stir weld of AA 2219 was laser melted. The melt depth and microstructure were observed using optical and scanning electron microscopy. The melt zone exhibited epitaxially grown columnar grains. The redistribution of elemental composition was analyzed using energy-dispersive spectroscopy. The anticorrosion properties of both laser-melted and original welds were studied in aqueous 3.5% NaCl solution using cyclic potentiodynamic polarization. The results indicated a noticeable increase in the pitting corrosion resistance after the laser treatment on the surface. The repassivation potential was nobler than the corrosion potential after the laser treatment, confirming that the resistance to pitting growth improved.

Microstructure and Corrosion Behavior of Laser Melted 304L SS Weldment in Nitric Acid Medium

The manuscript presents the effect of laser surface melting on the corrosion property of 304L SS weldment in nitric acid medium. 304L SS weldment was prepared by gas tungsten arc welding process and subsequently laser surface melted using Nd:YAG laser. The microstructure and corrosion resistance of laser surface melted 304L SS weldment was evaluated and compared with that of 304L SS as-weldment and 304L SS base. Microstructural evaluation was carried out using optical and scanning electron microscopes attached with energy-dispersive x-ray spectroscopy. Corrosion investigations were carried out in 4 and 8 M nitric acid by potentiodynamic polarization technique. From the results, it was found that laser surface melting of the weldment led to chemical and microstructural homogeneities, accompanied by a substantial decrease in delta ferrite content, that enhanced the corrosion resistance of the weldment in 4 and 8 M nitric acid. However, the enhancement in the corrosion resistance was not substantial. The presence of small amount of delta ferrite (2-4 wt.%) in the laser surface melted specimens was found to be detrimental in nitric acid. X-ray photoelectron spectroscopy studies were carried out to investigate the composition of the passive film.