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
In order to understand the influence of supergravity on the microstructure of materials,crystal nucleation,dendritic growth,and polycrystal solidification under supergravity are investigated by using the modified nucl...In order to understand the influence of supergravity on the microstructure of materials,crystal nucleation,dendritic growth,and polycrystal solidification under supergravity are investigated by using the modified nucleation theory and phase field models.Firstly,supergravity is considered in the nucleation theory by using pressure-dependent Gibbs free energy.It is found that the critical radius decreases and the nucleation rate increases when supergravity rises.Secondly,anisotropic heat transport is proposed in the phase field model to investigate the influence of supergravity on dendritic growth.Phase field simulations show that supergravity promotes the secondary dendritic growth in the direction parallel to supergravity.Finally,a multiply phase field model with pressure-dependent interfacial energy is employed to simulate the polycrystalline solidification under supergravity.Due to the depth-dependent pressure by supergravity,crystal grains are significantly refined by high pressure.In addition,gradient distribution of grain size is obtained in the solidification morphology of polycrystalline,which is consistent with previous experimental observations.Results of this work suggest that supergravity can be used to tune the microstructures and properties of materials.展开更多
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This work was supported by the Basic Science Center Program for Multiphase Evolution in Hypergravity of the National Natural Science Foundation of China(Grant No.51988101)the National Natural Science Foundation of China(Grant Nos.12192214 and 11972320)the Key Research Project of Zhejiang Laboratory(Grant No.2021PE0AC02).
文摘In order to understand the influence of supergravity on the microstructure of materials,crystal nucleation,dendritic growth,and polycrystal solidification under supergravity are investigated by using the modified nucleation theory and phase field models.Firstly,supergravity is considered in the nucleation theory by using pressure-dependent Gibbs free energy.It is found that the critical radius decreases and the nucleation rate increases when supergravity rises.Secondly,anisotropic heat transport is proposed in the phase field model to investigate the influence of supergravity on dendritic growth.Phase field simulations show that supergravity promotes the secondary dendritic growth in the direction parallel to supergravity.Finally,a multiply phase field model with pressure-dependent interfacial energy is employed to simulate the polycrystalline solidification under supergravity.Due to the depth-dependent pressure by supergravity,crystal grains are significantly refined by high pressure.In addition,gradient distribution of grain size is obtained in the solidification morphology of polycrystalline,which is consistent with previous experimental observations.Results of this work suggest that supergravity can be used to tune the microstructures and properties of materials.
