Ni64Al21V15沉淀过程DO22向L10(M=1)结构转变的微观相场模拟(英文)

Microscopic Phase-Field Simulation of the Structure Transformation from DO_(22) to L1_0 (M=1) Phase in Ni_(64)Al_(21)V_(15) Alloy

基于微观相场模型,研究了Ni64Al21V15合金在1150K时效过程中相结构演化。结合微观组织演化图像和各个格点上原子占位几率的演化,分析了DO22结构向L10(M=1)结构转变机制。合金沉淀中期,在相界处析出L10(M=1)结构。研究发现,L10(M=1)结构形成可分为3类:在DO22与L12相界处形核,沿[001]方向排列,向DO22相扩张;在DO22结构90°有序畴界处形核,沿[001]方向排列,向DO22扩张;在2个[100]向排列的DO22结构交界处形核,沿[100]方向排列,向DO22结构扩张。DO22相中,V主要占据β位,Ni主要占据α2和α3位,Al主要占据α1位;随后,V向α2位跃迁,在(002)面富聚且发生有序化,逐渐占据β和α2位,Ni原子发生面间跃迁,由α2位跃迁至α1位,逐渐占据α1和α3位,Al原子向相外扩散。DO22结构最终转变为高度有序的L10(M=1)结构。

The structure transformation from DO22 to L10 （M=1） phase in Ni64Al21V15 alloy at 1150 K was studied by the microscopic phase-field kinetic model. The results show that L10 （M=1） structure precipitates at interphase during the middle stage of the aging process with three types of the formation mechanism. Firstly, the L10 （M=1） structure which aligns along [001] direction and nucleates at the interphase of L12 and DO22 grows towards DO22 phase. Secondly, the L10 （M=1） structure which aligns along [001] direction nucleates at 90° ordered domain boundary of DO22 phase and expands to the [001] direction of DO22 phase. Thirdly, the L10 （M=1） structure which aligns along [100] direction nucleates at the interphase of two [100] aligned DO22 structure, and expands towards DO22 phase. The phase transformation from DO22 structure to L10 （M=1） structure is accomplished by atomic diffusion. In a perfect DO22 phase, the β site is mainly occupied by V atoms, while the α2 and α3 sites by Ni atoms and the α1 site by Al atoms. As the aging process proceeds, V atoms which migrate to α2 site, leading to the atomic ordering on （002） plane takes the place of both β and α2 sites ultimately, and the Ni atoms migrate from α2 to α1 site and occupy both α1 and α3 sites lastly, while Al atoms diffuse towards outside of DO22 structure facilitating the formation of highly ordered L10 （M=1） structure finally.