NiAl热诱发马氏体相变的分子动力学模拟

MOLECULAR DYNAMICS SIMULATION OF THERMALLY INDUCED MARTENSITIC TRANSFORMATIONS IN NiAl

运用ＮｉＡｌ合金的镶嵌原子势，进行了Ｂ２结构ＮｉＡｌ中热诱发马氏体相变的分子动力学模拟，从而研究马氏体形核和长大的微观机理．首先进行了０Ｋ等体积条件下ＮｉＡｌ的相稳定性分析，发现０Ｋ时点阵参数ｃ与ａ之比约为１．３１的ｂｃｔ结构是稳定结构，Ｂ２结构只是一种亚稳结构．在热诱发马氏体相变的模拟过程中，由于ＮｉＡｌ中Ｎｉ原子和Ａｌ原子的振动性质存在着差异，造成了马氏体的不均匀形核．对另两种不同初始构型的系统进行的模拟进一步证实了不均匀形核的存在，并通过计算Ｂ２结构ＮｉＡｌ中Ｎｉ原子和Ａｌ原子的热运动均方位移解释了其原因．模拟中，Ｂ２结构奥氏体经热诱发马氏体相变转变为ｆｃｔＬ１_０结构的马氏体．马氏体在长大过程中内部形成了若干转变孪晶．

In order to study the microscopic mechanism of martensitic nucleation and growth proeesses, molecular dynamics simulation of thermally induced martensitic transformation in stoichiometric NiAl alloy with B2 structure has been perfomied via the embedded atom method interatomic potential of NiAl alloy. The phase stability analysis of NiAl at 0 K and constant volume shows that an ordered bct structure with a ratio of lattice parameters of about 1.31 is stable while B2 structure is just metastable. The results of the simulations clearly show that only at some special sites caused by different vibrational properties of Ni and Al atoms the themially induced martensites can nucleate heterogeneously, and this has been further proved by simulations of two other systems with different initial configures. By calculating mean square displacements of Ni and Al atoms in NiAl, the reason of heterogeneous nucleation has been explained. Austenite transformed finally to fct L1_0 martensites, and during the martensite growth processes many transformation twins have formed in martensite.Correspondent: SHA Xianwei, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015