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Determination of the limiting values of the laser parameters to heat treatment of powder carbon steels surface
摘要： The microstructure and microhardness of the surface layer of powder steels PA-ZhGr with different porosity are studied in comparison with cast steel U10 after laser treatment (LT) with a 1 kW fiber laser in argon. Using thermal modeling, the geometric dimensions of the laser exposure zones formed in the area of the laser exposure were calculated and experimentally confirmed, and the mechanisms of their formation were proposed. The boundary values of the integral criterion for the parameters of laser influence for the heat treatment of carbon powder steels are established.
关键词： thermal modeling,microstructure,laser treatment,microhardness,powder steels
更新于2025-09-23 15:19:57
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Laser Heat Treatment of Ferrocarbon Powder Steel
摘要： The laser heat treatment of sintered ZhGr ferrocarbon powder steel with different porosity is considered. The microstructure and microhardness of the steel are determined, and the defects arising in laser treatment are studied.
关键词： microhardness,ferrocarbon steel,porosity,laser heat treatment,powder metallurgy,microstructure
更新于2025-09-23 15:19:57
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Preparation, microstructure, and microhardness of selective laser-melted Wa??3Ta sample
摘要： Tungsten (W) alloy is of difficulty in processing for conventional way because of its high melting point. Here, W alloy sample with the addition of 3 wt% Ta was prepared by selective laser melting. The influence of volumetric energy density (VED) on the surface morphology and the relative density was discussed, and microstructure, phase composition, and microhardness were investigated. The results show that a smooth surface and high relative density (95.79%) can be obtained under optimal VED. The W–Ta substitutional solid solution formed because of the replacement of Ta atom. There are strip and block fine grains in the W–3Ta sample with no significant texture. In addition, subgrain structure with a size of around 1 lm formed inside the strip grain, owing to the large thermal gradient and extremely fast cooling rate. Finally, the W–3Ta alloy shows higher microhardness than that obtained by traditional methods.
关键词： tungsten alloy,volumetric energy density,microstructure,microhardness,selective laser melting
更新于2025-09-23 15:19:57
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Laser hardening of copper-iron pseudoalloy
摘要： The purpose of the study is to improve the performance characteristics of powder pseudo-alloy materials using surface heat treatment. Such materials have unique properties, for example, self-lubrication under dry friction conditions, high thermal conductivity coefficient, and high electro-erosion resistance. The disadvantage of powder pseudo-alloys is their relatively low strength. The paper considers the method of surface hardening by high-energy treatment - laser radiation. The paper describes the method of experimental research, describes the method of obtaining powder material, its chemical composition, shows the equipment used. The results of studies of the microstructure and microhardness of the surface layer of steel-copper powder pseudo-alloy after laser heat treatment (LHT) of a continuous-wave fiber laser with a maximum power of 1 kW are given, LHT modes are indicated, the influence of LHT parameters on the characteristics of the hardened layer is evaluated. It is revealed that the partial melting region in which melting occurs in the volumes of the fusible component (copper) in the initial structure and contacting segments of steel matrix is formed in the material in addition to the total melting zone. Then the quenching zone from the solid state follows, in which the maximal hardness up to 1000 HV is attained for best samples in the volume of martensite, which is formed in perlite colonies of the initial steel–copper material.
关键词： Steel–copper pseudoalloy,Microhardness,Abrasive wear,Laser heat treatment,Powder metallurgy,Microstructure
更新于2025-09-23 15:19:57
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Influence of Processing Parameters on the Microhardness Property of Laser Cladded Titanium Powder
摘要： Laser cladding techniques of additive manufacturing has been globally embraced in the most efficient means of maintenance of steel rail. Nano-composite of titanium has been used as covering layer. The processing parameters of the laser power was varied between 1.0 kW and 2.0 kW while the scanning speed, powder and gas flow rate were kept at constant. Design expert 11 software environment was used to analyze the results derived with a full factorial experiment design guide. The microhardness profiling was performed at a load of 500 g and at a dwelling time of 15 s with the microhardness indenter 20 (cid:2)(cid:3)(cid:4) (cid:5)(cid:6)stance was maintained between indentations. An almost uniform weight of Titanium powder was cladded at different variation of processing parameters. A predictive microhardness equation was generated and termss runs intercept of an orthogonal shape. The model terms were found to be significant with logical relationships. It was found that the microhardness increases as the laser power increased.
关键词： microhardness,factorial experiment,steel rail,laser cladding,nano-composite
更新于2025-09-23 15:19:57
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Polymerization pattern characterization within a resin-based composite cured using different curing units at two distances
摘要： Objectives To investigate the relationship of the irradiance-beam-profile areas from six different light-curing units (LCUs) with the degree of conversion (DC), microhardness (KH), and cross-link density (CLD) throughout a resin-based composite (RBC) cured at two clinically relevant distances, and to explore the correlations among them. Materials and methods A mapping approach was used to measure DC using micro-Raman spectroscopy, KH using a Knoop indentor on a hardness tester, and %KH reduction after ethanol exposure, as an indicator for CLD within a nano-hybrid RBC increment (n = 3) at various depths. These sample composites were cured from two distances while maintaining the radiant exposure, using six different light-curing units: one quartz-tungsten-halogen; two single and three multiple-emission-peak light-emitting-diode units. Irradiance beam profiles were generated for each LCU at both distances, and localized irradiance values were calculated. Points across each depth were analyzed using repeated measures ANOVA. Correlations across multiple specimen locations and associations between beam uniformity corresponding with polymerization measurements were calculated using linear mixed models and Pearson correlation coefficients. Results Significant non-uniform polymerization patterns occurred within the specimens at various locations and depths. At 2-mm curing distance, the localized DC = 52.7–76.8%, KH = 39.0–66.7 kg/mm2, and %KH reduction = 26.7–57.9%. At 8-mm curing distance, the localized DC = 50.4–78.6%, KH = 40.3–73.7 kg/mm2, and %KH reduction = 28.2–56.8%. The localized irradiance values were weakly correlated with the corresponding DC, KH, and %KH reduction, with only a few significant correlations (p < 0.05). Conclusions Although significant differences were observed at each depth within the specimens, the localized irradiance values for all LCUs did not reflect the polymerization pattern and did not seem to have a major influence on polymerization patterns within the RBC, regardless of the curing distance. Clinical relevance Commonly used LCUs do not produce uniform polymerization regardless of the curing distance, which may contribute to the risk of RBC fracture.
关键词： Microhardness,Light-curing unit,Beam profile,Resin composite,Cross-link density,Degree of conversion
更新于2025-09-19 17:15:36
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Strengthening mechanism of Nd: Yag laser shock peening for commercially pure titanium (CP-TI) on surface integrity and residual stresses
摘要： In the present work, an attempt has been made to investigate the effect of generating shock waves through direct and con?ned ablation modes of plasma method of massive laser shock peening (MLSP) on surface integrity of cast dumbbell shaped and cylindrical cast specimens of commercially pure titanium (CP-Ti) and to compare with those of untreated CP-Ti. The MLSP is usually performed in a massively peening mode to induce uniform compressive residual stress and surface deformation across the entire specimens. After MLSP, tensile testing was carried out to obtain the tensile strength, modulus of elasticity and percentage elongation. The microstructural and surface topography investigations of the laser shock peened material were carried out using digital, optical microscopy and SEM equipped with an energy dispersive spectrometer (EDS) and XRD. The results show that laser shock peened with con?ned ablation make the surface of CP-Ti with improved change in microstructure, increase in tensile strength, microhardness (73.08%), surface roughness and compressive residual stresses ((cid:1)420 MPa) which prolongs the mastication ability and dimensional stability of dental implant restorative materials.
关键词： Massive laser peening,Direct ablation mode,Con?ned ablation mode,Microstructure,Microhardness
更新于2025-09-19 17:13:59
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The effect of temperature distribution and cooling rate on microstructure and microhardness of laser re-melted and laser-borided carbon steels with various carbon concentrations
摘要： Laser heat treatment was arranged as a laser remelting and laser boriding. Materials with different carbon concentration were used. Three zones characterized the microstructure after laser treatment: re-melted zone (MZ), heat-affected zone (HAZ) and substrate material. The differences in carbon content and physical properties of used materials influenced the obtained microstructure, temperature distribution and hardness. In case of laser re-melted specimens, the limited martensite transformation proceeded only in C20, C45 and C90 steels. As a result of laser boriding the microstructure of MZ contained additionally iron borides. The specimens with higher dilution ratio value was characterized by higher hardness of re-melted zone. The aim of this study was to indicate the possibility of predicting the microstructure and depths of MZ and HAZ with the usage of Ashby and Esterling model. The influence of carbon concentration in steel on the thickness, dilution ratio and hardness of laser-borided layers was determined.
关键词： microhardness,laser remelting,temperature distribution,laser boriding,cooling rate,microstructure
更新于2025-09-19 17:13:59
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Microstructure and microhardness of a novel TiZrAlV alloy by laser gas nitriding at different laser powers
摘要： The Ti–20Zr–6.5Al–4V (T20Z, wt%) alloy surface was treated by the process of laser surface nitriding. The evolution of microstructures and microhardness has been investigated by changing the laser power parameter from 120 to 240 W. All laser-treated T20Z samples show two regions with distinctly different microstructural features, as compared with the untreated substrate: dense TiN dendrites and (a ? b) - Ti (remelting zone, RMZ), nanoscale a laths doped with part of b phase (heat-affected zone, HAZ). The formation of TiN dendrites can be analyzed by a series of complex reactions during the process of melting and solidi?cation. The increase in laser power results in the increase in content of TiN dendrite which is mainly due to the increase in energy input. In HAZ, the self-quenching effect leads to the formation of nanoscale a laths and the residue of b phase. Microhardness pro?le of different regions was measured from the surface to the interior, and the highest microhardness was obtained (* HV 916.8) in the RMZ, as the laser power was set to 240 W. In the present study, we explained various microstructural characteristics induced by laser surface nitriding treatment.
关键词： TiZrAlV alloy,TiN dendrites,Microstructure,Laser surface nitriding,Microhardness
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Fill Factor Loss in Fielded Photovoltaic Modules Due to Metallization Failures, Characterized by Luminescence and Thermal Imaging
摘要： During irradiation UO2 nuclear fuel experiences the development of a non-uniform distribution of porosity which contributes to establish varying mechanical properties along the radius of the pellet. Radial variations of both porosity and elastic properties in high burnup UO2 pellet can be investigated via high frequency acoustic microscopy. For this purpose ultrasound waves are generated by a piezoelectric transducer and focused on the sample, after having travelled through a coupling liquid. The elastic properties of the material are related to the velocity of the generated Rayleigh surface wave (VR). A UO2 pellet with a burnup of 67 GWd/tU was characterized using the acoustic microscope installed in the hot cells of the JRC-ITU at a 90 MHz frequency, with methanol as coupling liquid. VR was measured at different radial positions. A good agreement was found, when comparing the porosity values obtained via acoustic microscopy with those determined using SEM image analysis, especially in the areas close to the centre. In addition, Young’s modulus was calculated and its radial pro?le was correlated to the corresponding burnup pro?le and to the hardness radial pro?le data obtained by Vickers micro-indentation
关键词： Nuclear fuels,piezoelectric devices,Vickers microhardness,Young’s modulus,nuclear power
更新于2025-09-19 17:13:59