Microscopic phase field study of the antisite defect of Ni₃Al in binary Ni-Al alloys

The temporal evolution feature of a microscopic phase field model is utilized to study the antisite defects of L1₂-Ni₃Al; this is quite different from other physicist' interests. There are mainly two points in brief. Firstly, antisite defects NiAl and AlNi, which are caused by the deviation from the stoichiometric Ni₃Al, coexist in the Ni ₃Al phase. The surplus Ni atom in the Ni-rich side is prone to substitute Al thus producing the antisite defect Ni_Al that maintains the stability of the L1₂ structure. In other case, the surplus Al atom in the Al-rich side is accommodated by a Ni sublattice consequently giving rise to antisite defect Al_Ni. The calculated equilibrium occupancy probability of Ni_Al is much higher than that of Al_Ni. This point is generally in line with other theoretical and experimental works. Additionally, both Ni_Al and Al_Ni have a strong negative correlation to time step during the disorder-order transformation. Since the initial value of Ni_Al and Al_Ni on each site of the matrix is right at the concentration that we set, we can observe the decrease process of Ni_Al and Al_Ni from the initial disordered high anti-structure state to their respective equilibrium state, i.e. to the result of the ordering process further coarsening.