Microscopic Phase-Field Simulation of the Structure Transformation from DO22 to L10(M=1) Phase in Ni64Al21V15 Alloy

Abstract

Abstract 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.