Search

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 α 2 and α 3 sites by Ni atoms and the α 1 site by Al atoms. As the aging process proceeds, V atoms which migrate to α 2 site, leading to the atomic ordering on (002) plane takes the place of both β and α 2 sites ultimately, and the Ni atoms migrate from α 2 to α 1 site and occupy both α 1 and α 3 sites lastly, while Al atoms diffuse towards outside of DO22 structure facilitating the formation of highly ordered L10 (M=1) structure finally. [Copyright &y& Elsevier]