Abstract:The precipitation processes of the ordered phases D022 and L1 2 in Ni75Al5.5V19.5 alloy at different temperatures were studied using the microscopic phase-field method. It is found that the supercooling degree is the main factor for the phase transformation. The D022 phase precipitates at a higher temperature firstly, then the L1 2 phase precipitates at the phase boundaries of D022 and disordered phases and round the interphase of D022 forming. The L1 2 phase grew towards the disordered matrix and the D022 phase nearly at the same time. Then at a lower temperature, the L1 2 phase precipitates firstly, then the D022 phase precipitates at the ordered interphase of L1 2 phase, which transforms from a nonstoichiometric phase to a equilibrium phase through spinodal decomposition and the dimension becomes smaller. The volume fractions of the two phases are almost equal at last. With the temperature decreasing, the precipitation mechanism of L1 2 phase transforms from the mixed pattern of non-classical nucleation and spinodal decomposition of higher temperature to the spinodal decomposition of lower temperature, but the precipitation mechanism of D022 phase transforms from the mixed pattern to the non-classical nucleation.