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Nondestructive Evaluation of Thermal Aging in Al6061 Alloy by Measuring Acoustic Nonlinearity of Laser-Generated Surface Acoustic Waves
摘要： The structures in high-temperature environments are prone to undergo hardening and embrittlement as a result of thermal aging; this can cause variations in their mechanical properties. Because these changes occur at the microstructural level, it is difficult to evaluate them through linear ultrasonic techniques. In this work, a surface acoustic wave (SAW) was used to measure and compare the acoustic nonlinearity and mechanical properties of Al6061 alloys heat-treated at 220°C for different durations (0 min, 20 min, 40 min, 1 h, 2 h, 10 h, 100 h, 1000 h). The SAW was generated by a pulsed laser and then received by an interferometer. Moreover, the yield strength, ultimate strength, and elongation to failure were measured by tensile tests. The results demonstrate that the critical variations in the mechanical properties can be detected by monitoring the variation features in the acoustic nonlinearity. Transmission electron microscopy images were captured to observe the microstructural changes, which shows that the acoustic nonlinearity varied according to the change in the precipitation phase. This supports the acoustic nonlinearity measurement using the laser-generated SAW being an effective technique for the fully noncontact nondestructive evaluation of material degradations as well as changes in mechanical properties.
关键词： surface acoustic wave,material degradation,laser,heat treatment,mechanical property,thermal aging,nonlinear parameter,precipitation,acoustic nonlinearity
更新于2025-09-19 17:13:59
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Nd:YAG laser welding of dissimilar metals of titanium alloy to stainless steel without filler metal based on a hybrid connection mechanism
摘要： In this paper, Nd:YAG laser welding of TC4 Titanium (Ti) alloy and SUS301 L stainless steel (SS) dissimilar metal material was carried out without filler metal by laser biasing. The microstructure and fracture mode of the joint were analyzed by scanning electron microscope (SEM), energy dispersive instrument (EDS), and X-ray diffractometer (XRD). The mechanical properties of the joint were evaluated by a tensile test. The results showed that when the peak temperature was 1116?, the liquid phase existed only in the narrower region of the Ti-SS interface, and the eutectic reaction zone formed a reaction layer, which was mainly composed of (cid:2)-Ti solid solution. Ti-Fe intermetallic compound (TiFe, TiFe2) was formed at the Ti alloy-SS interface by heat conduction of the unmelted Ti alloy. The TEM analysis confirmed the presence of the (cid:2)-Ti and TiFe2 phases. The nucleation and growth of the reaction layer depended on the diffusion rate and atomic concentration of Ti and Fe atoms. The growth of the reaction layer could be effectively promoted by increasing the welding heat input, increasing the peak temperature of the Ti-SS interface and prolonging the reaction time. The tensile strength of the joint could be reached 336 MPa and an elongation was 0.13 %. The eutectic reaction method could control the thickness and size of the Ti-Fe intermetallic compound at the interface of the Ti alloy-SS and improve the mechanical properties of the joint.
关键词： Reaction layer,Microstructure,Mechanical property,SUS301L stainless steel,TC4 Ti alloy,Eutectic reaction
更新于2025-09-16 10:30:52
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Characterization of Laser-Welded Ti Alloy and Stainless Steel Joint Using Cu Interlayer
摘要： In this study, Cu was used as an interlayer to restrain the formation of brittle Ti-Fe intermetallics when joining Ti alloy to SS. Microstructures of the joint were analyzed using optical microscopy, scanning electron microscopy and x-ray diffraction. Besides, the tensile strength of the joint was also measured. The melting amount of base materials was controlled by changing thickness of Cu interlayer to control the melting proportion in weld. The melting amount of base materials in weld decreased with the thickness of Cu interlayer. The content of Cu solid solution in weld increased with the thickness of Cu interlayer. Ti-Cu compound layer was formed on the Ti alloy side. The width of the Ti-Cu compound layer increased with the increase in heat input. The tensile strength of joint was largely impacted by Ti-Cu compound layer. The tensile strength of joint ?rst increased and then decreased with the increase in width of the Ti-Cu compound layer.
关键词： mechanical property,microstructure,TC4 Ti alloy,laser welding,SUS301L stainless steel
更新于2025-09-12 10:27:22
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Comparative Study on Welding Characteristics of Laser-CMT and Plasma-CMT Hybrid Welded AA6082-T6 Aluminum Alloy Butt Joints
摘要： Laser-CMT (Cold Metal Transfer) and plasma-CMT hybrid welding are two promising alternative joining technologies for traditional Metal-Inert-Gas (MIG) welding of the aluminum alloy joints in the high speed trains manufacturing industry. In this work, a comparative study on the weld formation, microstructure, micro-hardness, and mechanical properties of the butt joints in the two welding methods was conducted. The results indicate that the overall quality of the laser-CMT and plasma-CMT welds were good, especially of the laser-CMT hybrid weld, and the laser-CMT hybrid welding process needed a lower heat input. The width of the partially melted zone of the laser-CMT hybrid weld was narrower than that in the plasma-CMT hybrid weld. Micro-hardness test results show that two distinct softening regions were identi?ed in the heat a?ected zone, and the micro-hardness values of each zone in the laser-CMT hybrid weld were lower than that in the plasma-CMT hybrid weld. The tensile strength of the laser-CMT hybrid welded joints was higher than that of the plasma-CMT hybrid welded joints, which could reach up to 79.4% and 73.7% of the base materials, respectively. All the fractures occurred in the softening region and exhibited a ductile shear fracture with a shear angle of approximately 45. The fractographs manifested that the laser-CMT and plasma-CMT hybrid welded joints presented ductile fracture and ductile-brittle fracture features, respectively.
关键词： laser-CMT hybrid welding,mechanical property,aluminum alloy,microstructure,plasma-CMT hybrid welding
更新于2025-09-11 14:15:04
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Characterization and analysis on micro-hardness and microstructure evolution of brass subjected to laser shock peening
摘要： In view of the temperature distribution of the high-temperature geothermal tunnels, the surrounding rock temperature was divided into four grades (40 (cid:1)C, 60 (cid:1)C, 80 (cid:1)C and 100 (cid:1)C) to simulate the hot-dry environment. Using the standard curing environment as a reference condition, the mechanical properties and pore structure characteristics of concrete for shotcrete use under hot-dry environments at different temperatures were studied by mechanical and mercury intrusion porosimetry (MIP) tests. Fractal dimension of pore structure was calculated through the fractal model based on thermodynamic method. Bivariate correlation analysis was conducted on the curing temperature and the pore structure parameters. The results show that the 40 (cid:1)C hot-dry environment is conducive to enhance the mechanical properties of concrete and optimize its pore structure at the age of 1d. However, the hot-dry environments after 7 days will deteriorate the mechanical properties and pore structure of concrete, and the higher the temperature, the more obvious the deterioration. There is a significant correlation between curing temperature and porosity of capillary pores, median pore diameter, average pore diameter and fractal dimension.
关键词： Pore structure,Surrounding rock temperature,Mechanical property,Fractal dimension,Concrete for shotcrete use,High-temperature geothermal tunnel,Hot-dry environment
更新于2025-09-11 14:15:04
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Influence of Pressure on the Mechanical and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals
摘要： The mechanical and electronic properties of two GaN crystals, wurtzite and zinc-blende GaN, under various hydrostatic pressures were investigated using first principles calculations. The results show that the lattice constants of the two GaN crystals calculated in this study are close to previous experimental results, and the two GaN crystals are stable under hydrostatic pressures up to 40 GPa. The pressure presents extremely similar trend effect on the volumes of unit cells and average Ga-N bond lengths of the two GaN crystals. The bulk modulus increases while the shear modulus decreases with the increase in pressure, resulting in the significant increase of the ratios of bulk moduli to shear moduli for the two GaN polycrystals. Different with the monotonic changes of bulk and shear moduli, the elastic moduli of the two GaN polycrystals may increase at first and then decrease with increasing pressure. The two GaN crystals are brittle materials at zero pressure, while they may exhibit ductile behaviour under high pressures. Moreover, the increase in pressure raises the elastic anisotropy of GaN crystals, and the anisotropy factors of the two GaN single crystals are quite different. Different with the obvious directional dependences of elastic modulus, shear modulus and Poisson’s ratio of the two GaN single crystals, there is no anisotropy for bulk modulus, especially for that of zinc-blende GaN. Furthermore, the band gaps of GaN crystals increase with increasing pressure, and zinc-blende GaN has a larger pressure coefficient. To further understand the pressure effect on the band gap, the band structure and density of states (DOSs) of GaN crystals were also analysed in this study.
关键词： first principle,electronic property,GaN,pressure,mechanical property
更新于2025-09-10 09:29:36
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Influence of Island Scanning Strategy on Microstructures and Mechanical Properties of Direct Laser-Deposited Ti–6Al–4V Structures
摘要： To investigate the influence of island scanning on the microstructures and mechanical properties of direct laser-deposited Ti–6Al–4V structures, two samples are prepared using island scanning and orthogonal successive scanning, respectively. The microstructures, relative density, and mechanical properties of the samples prepared using these two scanning strategies are compared. Each sample exhibits columnar β-grain morphology and basket-weave microstructure characterization. The grains of the sample prepared using island scanning are significantly finer than that prepared by orthogonal successive scanning due to faster cooling during deposition. However, the relative density of the sample prepared using island scanning was slightly smaller due to the concentration of lack-of-fusion pores at the overlap zone of the island. Tensile testing at room temperature indicates that the ultimate tensile strength and yield strength of the sample prepared using island scanning is enhanced due to finer grains, while the ductility of the sample is weakened due to defects.
关键词： Ti–6Al–4V,Defects,Direct laser deposition,Scanning strategies,Mechanical property,Microstructure
更新于2025-09-10 09:29:36
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Tensile mechanical properties and fracture behavior of monolayer InSe under axial tension
摘要： Based on a newly developed interatomic potential, the mechanical properties and fracture behavior of monolayer InSe are investigated by using the classical molecular dynamics method. We ?nd that monolayer InSe exhibits excellent mechanical properties comparing with other two-dimensional materials. Especially, it can sustain an axial tensile strain of 27% in the zigzag direction at room temperature 300 K. Furthermore, the numerical results indicate that the monolayer InSe has an isotropy in the mechanical behaviors with the Youngs modulus being about 43 N/m both in the armchair and zigzag directions. We also discuss the e?ects of temperature and strain rate on the mechanical properties of monolayer InSe and ?nd the high temperature-sensitivity. It’s found that the mechanical properties signi?cantly decrease as the increasing temperature. In contrast, the mechanical properties has a relatively weak dependence on the strain rate. As the strain rate increases from 0.0002 to 0.0008 ps?1, Young’s modulus nearly keeps a constant. The fracture stress and strain in armchair direction only increase by 3.6% and 8.3%, respectively.
关键词： Tensile strain,Monolayer InSe,Molecular dynamics simulation,Two-dimensional materials,Mechanical property
更新于2025-09-10 09:29:36
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Performance Consistency of AlSi10Mg Alloy Manufactured by Simulating Multi Laser Beam Selective Laser Melting (SLM): Microstructures and Mechanical Properties
摘要： Multi-laser beam selective laser melting (SLM) technology based on a powder bed has been used to manufacture AlSi10Mg samples. The AlSi10Mg alloy was used as research material to systematically study the performance consistency of both the laser overlap areas and the isolated areas of the multi-laser beam SLM manufactured parts. The microstructures and mechanical properties of all isolated and overlap processing areas were compared under optimized process parameters. It was discovered that there is a raised platform at the junction of the overlap areas and the isolated areas of the multi-laser SLM samples. The roughness is significantly reduced after two scans. However, the surface roughness of the samples is highest after four scans. As the number of laser scans increases, the relative density of the overlap areas of the samples improves, and there is no significant change in hardness. The tensile properties of the tensile samples are poor when the overlap area width is 0, 0.1, or 0.2 mm. When the widths of the overlap areas are equal to or greater than 0.3 mm, there is no significant difference in the tensile strength between the overlap and the isolated areas.
关键词： selective laser melting,AlSi10Mg,microstructure,multi-laser manufacturing,mechanical property
更新于2025-09-09 09:28:46
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Mechanical property modeling of photosensitive liquid resin in stereolithography additive manufacturing: Bridging degree of cure with tensile strength and hardness
摘要： Owing to the unique layer-wise production method, additive manufacturing technologies have been widely adopted in rapid prototyping and tooling areas, which often require superior mechanical properties such as tensile strength and hardness. In current literature, most mechanical property studies focusing on additive manufactured materials mainly adopt experimental or simulation-based approaches, and therefore cannot be directly used to accurately estimate and predict the achieved mechanical properties. In addition, information regarding the mechanical properties of photosensitive liquid resin used in the Stereolithography additive manufacturing process is limited. Hence, in this paper, mathematical models are established to quantify the tensile strength and hardness of Stereolithography fabricated materials by estimating the solidification levels of both green parts and Ultraviolet post-cured parts. The established degree of cure model is shown to have an average prediction accuracy of around 94%. In addition, the mechanical property models have an average accuracy of 88% and 90% for tensile strength prediction, and 98% and 95% for hardness prediction of green parts and post-cured parts, respectively. It is also observed that the Ultraviolet post-curing process has the capability of significantly enhancing the studied mechanical properties.
关键词： degree of cure,tensile strength,Additive manufacturing,hardness,photosensitive liquid resin,mechanical property
更新于2025-09-09 09:28:46