晶格常数变化与有序无序转变类型的关系

Relationship Between Lattice Parameter Variation and Order-Disorder Transformation Type

利用EAM势计算了Ni-Al系合金的有序无序转变,发现Ni3Al为一级相变,其晶格常数随长程有序度呈线性变化,而NiAl为二级相变,品格常数则呈非线性变化,此不同的转变规律是与相变类型有关,而不是完全由有序无序转变中原子构型力学平衡条件所决定.一级相变晶格常数变化是线性的,二级相变为非线性的.

The lattice parameter variation of stoichiometric Ni3Al and NiAl during the order-disorder transformation was studied based on the embedded atom method (EAM). The order-disorder transformation for Ni3Al is of the first order transition, and the lattice parameter changes linearly along with the long range order parameter. NiAl is in the second order transition, and the relationship between the lattice parameter and the long range order parameter is nonlinear. The lattice parameter variation during the order-disorder transformation depends on both the phase transition type and the mechanical equilibrium condition. The lattice parameter should change linearly for the first order transition and nonlinearly for the second order transition.