Microscopic phase-field simulation for formation of pre-precipitation phase in Ni ₇₅Al _25-xMn _x alloy

The microscopic phase-field model was used to simulate the formation of pre-precipitation phase in Ni ₇₅Al _25-xMn _x alloy. The results of the microscopic morphology evolution of alloys, the volume fraction curves, order parameter curves and occupation probability show that L1 ₀ phase precipitates from the Ni ₇₅Al _25-xMn _x alloy first and then transforms into L1 ₂phase inside of L1 ₀ phase in the following time. With the increase of Al concentration, the nucleation incubation periods of L1 ₀and L1 ₂ phases and structure transformation time obviously become shorter. The ordering of Al and Mn atoms takes place in (001) and (002) planes simultaneously. As followed, the atom order degree begins to decrease in (002) planes and the structure is changed. Al atoms preferentially occupy the β site and Mn atoms preferentially occupy the α _II site. Finally, the L1 ₀ pseudobinary structure precipitates in the alloy system.