B2-Ni_(50)Al_(50)金属间化合物的Ostwald两步法晶体生长

Ostwald Two-step Crystal Growth of B2-Ni_(50)Al_(50) Intermetallic Compound

采用分子动力学方法模拟B2型Ni_(50)Al_(50)合金的凝固结晶过程,并通过键取向序(BOO)参数和Voronoi多面体指数(VPI)来表征微观结构,采用逆向追踪法追踪大团簇,对大团簇内部结构进行分析。结果表明:B2-Ni_(50)Al_(50)合金的晶体长大过程是两步生长模式,即先由液相形成亚稳的HCP结构(壳层),再由亚稳HCP转变为稳态的BCC结构(核心)。且结晶形成的团簇壳层大多为HCP结构,核心则大多为BCC结构,典型的核-壳型结构,这一点也能佐证其符合两步生长机制。另外,同为稳定BCC相的纯金属Fe、Nb和Ti,也都为核-壳型结构,壳层主要是HCP,核心主要为BCC结构。基本可以判定,两步生长是稳定BCC相金属的共有属性。

Solidification and crystallization process of B2-Ni50Al50 alloy was simulated by using a molecular dynamics(MD),and microstructural evolution was characterized by a hybrid method of bond orientational order(BOO) and voronoi polyhedron index(VPI),then the reverse tracing method was used to track large clusters and to analyze the internal structure of large clusters.The results showed that the crystallization process of B2-Ni50Al50 alloy was a two-step growth mechanism,that is,the parent liquid structure first changed into the metastable HCP structure(shell) and then the metastable HCP structure converted into the stable BCC structure(core-shell).The cluster shell was mostly HCP structure,the core was mostly BCC structure,and the typical core shell structure proved the two-step growth mechanism too.In addition,pure metals Fe,Nb and Ti with the same stable BCC phase were all the core-shell structures,namely,the shell was mostly HCP structure,and the core was mostly BCC structure.It was basically determined that two-step growth mechanism was a common property of metals with the stable BCC phase.