摘要
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.
在定向凝固Sn−Ni包晶合金中发现六方−正方相变,即自β-Ni_(3)Sn_(2)(六方)向α'-Ni_(3)Sn_(2)(正方)相的转变。研究表明,二次枝晶臂上发生由温度梯度区域熔化(TGZM)与吉布斯−汤姆森(G−T)效应引起的重熔/再凝过程。此外,一次枝晶干与二次分枝间夹角(θ)随凝固过程进行由π/3增至π/2,这一现象为六方−正方转变的组织特征,并会改变重熔/再凝过程中的扩散距离。因此,建立扩散控制唯象模型,重熔/再凝过程由枝晶的比表面积(S_(V))进行表征。模型预测表明,包晶凝固过程中发生六方−正方相变后可抑制重熔/再凝过程。另外,预测曲线的斜率变化表明重熔/再凝过程局域速率发生改变。
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)
the Science and Technology Project of Lanzhou City,China(No.2019-1-30)
State Key Laboratory of Special Rare Metal Materials,China(No.SKL2020K003)。
