The micro-cracking behaviors of two high-entropy alloys(HEAs) of the FeMnCoCrNi family prepared by selective laser melting were systematically studied. Residual stresses were also analyzed by X-ray diffraction techniq...The micro-cracking behaviors of two high-entropy alloys(HEAs) of the FeMnCoCrNi family prepared by selective laser melting were systematically studied. Residual stresses were also analyzed by X-ray diffraction technique. Results show that the equiatomic FeMnCoCrNi HEAs with a relatively stable single-phase face-centered cubic(FCC) structure suffered from micro-cracking with residual tensile stress after laser melting. In contrast, the metastable non-equiatomic Fe MnCoCr HEAs with reduced stacking fault energy are free of micro-cracks with residual compressive stress at various volumetric energy densities(VEDs). The displacive transformation from the FCC matrix to the hexagonal close-packed(HCP) phase during cooling prevents the micro-cracking via consuming thermal stress related internal energy. Further, the displacive transformation during tensile deformation contributes to the higher strength and ductility of the metastable dual-phase HEA compared to that of the stable single-phase HEA. These findings provide useful guidance for the design of strong, ductile, and crack-free alloys for additive manufacturing by tuning phase stability.展开更多
The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the reme...The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting(TGZM)and Gibbs−Thomson(G−T)effects can take place on secondary dendrites.Besides,the intersection angle between the primary dendrite stem and secondary branch(θ)is found to increase fromπ/3 toπ/2 as the solidification proceeds.This is the morphological feature of the HO transformation,which can change the diffusion distance of the remelting/resolidification process.Thus,a diffusion-based analytical model is established to describe this process through the specific surface area(S_(V))of dendrites.The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification.In addition,the slope of the prediction curves is changed,indicating the variation of the local remelting/resolidification rates.展开更多
A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experime...A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experimental alloy was investigated.The results indicate that the average size ofα-Mg grains decreases and spheroidizing tendency becomes more obvious with the compression ratios increasing from 0 to 40%.In addition,the eutectic Mg2Si phase in the Mg−10%Al−1%Zn−1%Si alloy transforms completely from the initial fishbone shape to globular shape by SIMA process.With the increasing of compression ratio,the morphology and average size of Mg2Si phases do not change obviously.The morphology modification mechanism of Mg2Si phase in Mg−10%Al−1%Zn−1%Si alloy by SIMA process was also studied.展开更多
A repulsive vortex\|vortex interaction model was used to numerically study the melting transition of the two\|dimensional vortex system with Monte Carlo method. Then a δ\|function\|like peak in the specific heat was ...A repulsive vortex\|vortex interaction model was used to numerically study the melting transition of the two\|dimensional vortex system with Monte Carlo method. Then a δ\|function\|like peak in the specific heat was observed and the internal energy showed a sharp drop at the melting temperature, which indicated that there exists a first\|order melting transition at finite temperatures. The Lindemann criterion was also investigated and valid, but different from previous simulation results.展开更多
This paper studies the close-contact melting around a moving, horizontal elliptical heat source thatmelts its way through a phase change material under its own weight. The heat source velocity andthe volume of the mat...This paper studies the close-contact melting around a moving, horizontal elliptical heat source thatmelts its way through a phase change material under its own weight. The heat source velocity andthe volume of the material melted are obtained by analysis. The effects of compression coefficient andtemperature distribution in the melt are investigated. The results include that for melting around amoving cylindrical heat source.展开更多
The contact melting of phase change material around a moving horizontal cylindrical heat source, which descended under its own weight, is investigated in this article. A melting model under constant surface heat flux ...The contact melting of phase change material around a moving horizontal cylindrical heat source, which descended under its own weight, is investigated in this article. A melting model under constant surface heat flux is established. The analytical results for thickness and pressure distributions inside melt layer and steady melting velocity are obtained by using contact melting theory. The melting law is discussed, and compared with that of contact melting driven by temperature difference. It is found that quasi-steady melting velocity is determined by heat flux of heat source, and the variation of heat source density has less effect on melting velocity.展开更多
基金financial support of the National Natural Science Foundation of China (51505166,51971248)the Huxiang Young Talents Project (2018RS3007,2019RS1001)+1 种基金the Innovation-Driven Project of Central South University,China (2020CX023)Science and Technology Project of Hunan Province (2020GK2031)。
文摘The micro-cracking behaviors of two high-entropy alloys(HEAs) of the FeMnCoCrNi family prepared by selective laser melting were systematically studied. Residual stresses were also analyzed by X-ray diffraction technique. Results show that the equiatomic FeMnCoCrNi HEAs with a relatively stable single-phase face-centered cubic(FCC) structure suffered from micro-cracking with residual tensile stress after laser melting. In contrast, the metastable non-equiatomic Fe MnCoCr HEAs with reduced stacking fault energy are free of micro-cracks with residual compressive stress at various volumetric energy densities(VEDs). The displacive transformation from the FCC matrix to the hexagonal close-packed(HCP) phase during cooling prevents the micro-cracking via consuming thermal stress related internal energy. Further, the displacive transformation during tensile deformation contributes to the higher strength and ductility of the metastable dual-phase HEA compared to that of the stable single-phase HEA. These findings provide useful guidance for the design of strong, ductile, and crack-free alloys for additive manufacturing by tuning phase stability.
基金the support from the Natural Science Foundation of China(No.51871118)Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education,Lanzhou University,China(No.LZUMMM2021005)+1 种基金the Science and Technology Project of Lanzhou City,China(No.2019-1-30)State Key Laboratory of Special Rare Metal Materials,China(No.SKL2020K003)。
文摘The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting(TGZM)and Gibbs−Thomson(G−T)effects can take place on secondary dendrites.Besides,the intersection angle between the primary dendrite stem and secondary branch(θ)is found to increase fromπ/3 toπ/2 as the solidification proceeds.This is the morphological feature of the HO transformation,which can change the diffusion distance of the remelting/resolidification process.Thus,a diffusion-based analytical model is established to describe this process through the specific surface area(S_(V))of dendrites.The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification.In addition,the slope of the prediction curves is changed,indicating the variation of the local remelting/resolidification rates.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(Nos.41807235,50674038).
文摘A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experimental alloy was investigated.The results indicate that the average size ofα-Mg grains decreases and spheroidizing tendency becomes more obvious with the compression ratios increasing from 0 to 40%.In addition,the eutectic Mg2Si phase in the Mg−10%Al−1%Zn−1%Si alloy transforms completely from the initial fishbone shape to globular shape by SIMA process.With the increasing of compression ratio,the morphology and average size of Mg2Si phases do not change obviously.The morphology modification mechanism of Mg2Si phase in Mg−10%Al−1%Zn−1%Si alloy by SIMA process was also studied.
文摘A repulsive vortex\|vortex interaction model was used to numerically study the melting transition of the two\|dimensional vortex system with Monte Carlo method. Then a δ\|function\|like peak in the specific heat was observed and the internal energy showed a sharp drop at the melting temperature, which indicated that there exists a first\|order melting transition at finite temperatures. The Lindemann criterion was also investigated and valid, but different from previous simulation results.
文摘This paper studies the close-contact melting around a moving, horizontal elliptical heat source thatmelts its way through a phase change material under its own weight. The heat source velocity andthe volume of the material melted are obtained by analysis. The effects of compression coefficient andtemperature distribution in the melt are investigated. The results include that for melting around amoving cylindrical heat source.
基金the National Natural Science Foundation of China Project No.50376074
文摘The contact melting of phase change material around a moving horizontal cylindrical heat source, which descended under its own weight, is investigated in this article. A melting model under constant surface heat flux is established. The analytical results for thickness and pressure distributions inside melt layer and steady melting velocity are obtained by using contact melting theory. The melting law is discussed, and compared with that of contact melting driven by temperature difference. It is found that quasi-steady melting velocity is determined by heat flux of heat source, and the variation of heat source density has less effect on melting velocity.
