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Effects of laser scanning strategies on selective laser melting of pure tungsten
摘要： Three types of scanning strategies, including the chessboard scanning strategy, the zigzag scanning strategy and the remelting scanning strategy, were conducted to study the effects of scanning strategies on surface morphology, microstructure, mechanical properties and the grain orientation of selective laser melted pure tungsten. The results showed that the pores and cracks were main defects in SLM-processed tungsten parts. The pores could be eliminated using the remelting scanning strategy. However, the cracks seemed to be inevitable regardless of the applied scanning strategies. The microstructures of SLM-processed tungsten were columnar grains and showed strong epitaxial growth along the building direction. A compressive strength of 923 MPa with an elongation of 7.7% was obtained when the zigzag scanning strategy was applied, which was the highest among the three scanning strategies. By changing the scanning strategies, the texture of SLM-processed tungsten in the direction of processing could be changed.
关键词： microstructure,texture,scanning strategy,compressive strength,pure tungsten,selective laser melting
更新于2025-09-23 15:21:01
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Controlled-Atmosphere Sintering of KNbO3
摘要： The e?ect of sintering atmosphere (O2, air, N2, N2-5% H2, and H2) on the densi?cation, grain growth, and structure of KNbO3 was studied. KNbO3 powder was prepared by solid state reaction, and samples were sintered at 1040 C for 1–10 h. The sample microstructure was studied using Scanning Electron Microscopy (SEM). The sample structure was studied using X-Ray Di?raction (XRD). H2-sintered samples showed reduced density, whereas other sintering atmospheres did not a?ect density much. Samples sintered in N2-5% H2 showed abnormal grain growth, whereas sintering in other atmospheres caused stagnant (O2, air, N2) or pseudo-normal (H2) grain growth behavior. Samples sintered in reducing atmospheres showed decreased orthorhombic unit cell distortion. The grain growth behavior was explained by the mixed control theory. An increase in vacancy concentration caused by sintering in reducing atmospheres led to a decrease in the step free energy and the critical driving force for appreciable grain growth. This caused grain growth behavior to change from stagnant to abnormal and eventually pseudo-normal.
关键词： lead-free piezoelectric,microstructure grain growth,alkali niobate
更新于2025-09-23 15:21:01
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The Average Grain Size and Grain Aspect Ratio in Metal Laser Powder Bed Fusion: Modeling and Experiment
摘要： The additive manufacturing (AM) process induces high uncertainty in the mechanical properties of 3D-printed parts, which represents one of the main barriers for a wider AM processes adoption. To address this problem, a new time-efficient microstructure prediction algorithm was proposed in this study for the laser powder bed fusion (LPBF) process. Based on a combination of the melt pool modeling and the design of experiment approaches, this algorithm was used to predict the microstructure (grain size/aspect ratio) of materials processed by an EOS M280 LPBF system, including Iron and IN625 alloys. This approach was successfully validated using experimental and literature data, thus demonstrating its potential efficiency for the optimization of different LPBF powders and systems.
关键词： laser powder bed fusion,additive manufacturing,microstructure,process optimization,analytical model
更新于2025-09-23 15:21:01
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Weldability and mechanical behavior of laser-welded TRIP 750 steel sheets
摘要： Transformation-induced plasticity steels have been developed and widely applied in the automotive and aerospace industries. They exhibit ductility and mechanical strength associated with a high formability due to their complex microstructure of bainite-associated pro-eutectoid ferrite and significant retained austenite fractions. The weldability of these steels is limited by the high content of alloying elements in the composition, causing the thermal cycle to modify the carefully designed microstructure, which in turn generates unsatisfactory weld mechanical properties. Laser welding has a relatively low thermal input, and, therefore, a narrow heat-affected zone is obtained. As known, the literature had not been definitively reported the microstructural features of the fusion and the heat-affected zones after laser welding of TRIP steels in conjunction with their mechanical behavior. The aim of the present work is to characterize the microstructure and mechanical behavior of laser-welded TRIP steel after uniaxial tensile and Erichsen formability tests. The coupons of TRIP 750 steel sheets were subjected to different laser welding conditions in order to analyze their impact on the microstructure, hardness, and mechanical strength of the material. After some preliminary tests, the laser power was fixed at 900 W and the weld speed fixed at 50 mm/s as the best choice of operating parameters. Under these conditions, the fusion zone was almost completely martensitic, while the heat-affected zone had a mixture of ferrite and martensite. The martensite transformation is corroborated by finite elements analyses as the cooling rate was 4200 °C/s for material at martensite start temperature. The average hardness of the fusion zone was 530 HV and the heat-affected zone was 550 HV, compared with 270 HVof the base material. In terms of mechanical behavior, the tensile strength of the welded coupons was found to reach 740 MPa and the ductility reached 22% in uniform deformation. The Erichsen index for the welded sheets attained 15 mm for a load of 48.5 kN, similar with the non-welded base material. Both in the case of the uniaxial tensile testing and in the Erichsen testing, the fracture occurred in the base material away from the weld, showing a good toughness of the welded component.
关键词： Transformation-induced plasticity steels,Microstructure,Hardness,Tensile testing,Erichsen testing,Laser welding
更新于2025-09-23 15:21:01
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Selective laser melting 316L/CuSn10 multi-materials: Processing optimization, interfacial characterization and mechanical property
摘要： Adopting selective laser melting (SLM), a typical technology of additive manufacturing (AM), to form multi-material metallic composites is a challenging and promising field. In this study, SLM 316L/CuSn10 multi-material composites was an innovative attempt to develop functional and structural materials with excellent properties of steel and copper alloys. Dense 316L/CuSn10 specimens with no interfacial macrocracks were successfully fabricated. Results showed that the Vickers microhardness gradually decreased from 329.5±12.5 HV in 316L region to 172.8HV±7.4 in CuSn10 region. The ultimate tensile strength and flexural strength of 316L/CuSn10 sample was 210 MPa, which was higher than the steel/copper alloys fabricated by other methods. It indicated an ideal interfacial bonding condition of 316L/CuSn10 multi-material, which was benefited from sufficient agitation of the molten pools and elements diffusion in the term of continuous distribution of elements and the enrichment of the heterogeneous alloy phases. Also, the grain refinement by re-melting and recrystallization upgraded the bonding performance at the interface. Finally, the 316L/CuSn10 lattice structure was formed by SLM, hinting at the prospects for industrial applications of steel/copper multi-material by SLM in future.
关键词： Selective laser melting (SLM),Mechanical properties,Interface,316L/CuSn10,Multi-material,Microstructure
更新于2025-09-23 15:21:01
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Gradient microstructure and vibration fatigue properties of 2024-T351 aluminium alloy treated by laser shock peening
摘要： To investigate the improvement in vibration fatigue and the strengthening mechanism of laser shock peening, a nanosecond laser was used to strengthen the 2024-T351 aluminium alloy. Accordingly, the microstructure, residual stress, nanohardness and surface roughness of the treated alloy were measured. Subsequently, the vibration fatigue damage and fatigue life were evaluated, and the vibration fracture morphology was observed. The results showed that the grains in the peened surface were re?ned. A residual stress of ?141 MPa and a nanohardness of 3.1 GPa were obtained by laser shock peening. Based on the relationship between the peened microstructure and fracture morphology, it was deduced that an increase in the grain boundaries led to a lower crack initiation rate and a higher crack initiation life. The compressive residual stress decreased the crack growth rate and increased the crack growth life. Therefore, laser shock peening increases the total vibration fatigue life by about 63.5%.
关键词： Laser shock peening,Vibration fatigue,2024-T351 aluminium,Compressive residual stress,Microstructure
更新于2025-09-23 15:21:01
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Effect of Scanning Strategy During Selective Laser Melting on Surface Topography, Porosity, and Microstructure of Additively Manufactured Ti-6Al-4V
摘要： The effect of the scanning strategy during selective laser melting (SLM) of Ti-6Al-4V was investigated. An optimized cellular scan strategy (island scan modeled) was compared to a simple cellular scan strategy (island scan stripes) and a simple antiparallel line scanning strategy (line scan). Surface texture was investigated by optical three-dimensional (3D) surface measurements, which when combined with light optical microscopy (LOM), revealed deflections caused by the thermal stresses during the build process. Elevated edges caused by the edge-effect dominate the surface texture of all investigated specimens. The scanning strategy determines the surface texture, and the lowest surface roughness was obtained by the line scan strategy. Porosity was investigated with X-ray computed tomography-imaging. Mainly spherical porosity was observed for the line scan and island scan modeled specimens, while the island scan stripes strategy showed more lack-of-fusion defects and a higher total porosity amount. Microstructure was investigated with LOM and scanning electron microscopy (SEM). The microstructure in Ti-6Al-4V was largely martensitic α’ and prior β grains. The morphology is different for the various scan strategies, and decomposition of α’ into lamellar α/β was observed in the bottom part of the island scan specimen. Accordingly, the hardness decreased in the decomposed part of the specimen.
关键词： scanning strategy,porosity,surface topography,selective laser melting,powder bed fusion,microstructure,SLM,Ti-6Al-4V
更新于2025-09-23 15:21:01
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Over 6% Efficient Cu(In,Ga)Se2 Solar Cell Screen-Printed from Oxides on FTO
摘要： A new approach to fabricate copper, indium, gallium diselenide (CIGSe) solar cells on conductive fluorine-doped tin oxide (FTO) reached an efficiency of over six per cent for champion photovoltaic device. Commercial oxide nanoparticles are formulated into high-quality screen printable ink based on ethyl cellulose solution in terpineol. The high homogeneity and good adhesion properties of the oxide ink play an important role in obtaining dense and highly crystalline photoabsorber layers. This finding reveals that solution-based screen printing from readily available oxide precursors provides an interesting cost-effective alternative to current vacuum- and energy-demanding processes of the CIGSe solar cell fabrication.
关键词： screen-printing,ink formulation,photovoltaics,CIGSe,microstructure,oxides nanoparticles
更新于2025-09-23 15:21:01
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Microstructure characteristics of non-monodisperse quantum dots: On the potential of transmission electron microscopy combined with X-ray diffraction
摘要： Although the concept of quantum confinement was introduced more than thirty years ago, a wide application of the quantum dots is still limited by the fact that monodisperse quantum dots with controlled optoelectronic properties are typically synthesized on a relatively small scale. Larger scale synthesis techniques are usually not able to produce monodisperse nanoparticles yet. In this contribution, we illustrate the capability of the combination of transmission electron microscopy and X-ray diffraction to reveal detailed and scale-bridging information about the complex microstructure of non-monodisperse quantum dots, which is the first step towards a further upscalling of the techniques for production of quantum dots with controlled properties. As a model system, CdSe quantum dots synthesized using an automated robotic hot-injection method at different temperatures were chosen. The combined microstructure analytics revealed the size and shape of the CdSe nanocrystals and the kind, density and arrangement of planar defects. The role of the planar defects in the particle coarsening by oriented attachment and the effect of the planar fault arrangement on the phase constitution, on the crystallographic coherence of the counterparts and on the optoelectronic properties are discussed.
关键词： microstructure,optoelectronic properties,planar defects,transmission electron microscopy,X-ray diffraction,quantum dots,oriented attachment,CdSe
更新于2025-09-23 15:21:01
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Study on the Microstructure and Properties of Al/Cu Laser Filled Solder Joint
摘要： Using IPG-YLS-4000 fiber laser to weld T2 copper plate and LY16 aluminum alloy plate, using Zn-10%Al flux cored wire as filler material, the microstructure of the joint was observed and analyzed by SEM and EDS, and the effects of laser power, welding speed and welding line energy on the mechanical properties of the joint were studied. The results show that the joints are mainly divided into copper side brazing area, weld center area and aluminum side fusion welding area. Among them, there are two interface reaction layers composed of intermetallic compound (IMC) in the copper side brazing area, the first layer is CuZn compound in the form of strip, and the second layer is Al2Cu phase in the form of shoot. The central area of the weld is mainly composed of massive α-Al phase and branched β-Zn phase. The tensile strength of the joint increases first and then decreases with the increase of laser power, welding speed and welding line energy. The thickness of IMC layer grows linearly with the increase of line energy. The best process parameters: when the laser power is 2200 W, the welding speed is 0.9 m/min, the welding line energy is 1446.67 J/cm, the IMC layer thickness is 10.11 μm, and the tensile strength reaches the maximum value, 252.6 MPa.
关键词： intermetallic compound,Al/Cu laser welding,microstructure,mechanical properties,Zn-10%Al flux cored wire
更新于2025-09-23 15:21:01