Computer simulation of atomic ordering and compositional clustering in the pseudobinary Ni₃Al-Ni₃V system

The kinetics of diffusional phase transformations in the pseudobinary Ni₃Al-Ni₃V system were studied using a computer simulation technique based on microscope diffusion equations. Our focus is on the initial stages of atomic ordering and compositional clustering process during the phase transformation of an initially homogeneous disordered f.c.c. ternary alloy (Ni₇₅Al_{25 - x}V_x) into a two-phase mixture of L1₂ (Ni₃Al) and DO₂₂ (Ni₃V) ordered phases. A thermodynamic model is proposed to describe the phase equilibria in this pseudobinary system. Our computer simulations demonstrated that at small vanadium content, the L1₂ ordered domains appear first, followed by the nucleation of DO₂₂ ordered domains at the antiphase domain boundaries of L1₂, whereas at large vanadium content, precipitation of DO₂₂ precedes L1₂ domain formation. The simulation results are discussed employing the thermodynamic stability analysis. The ordering and clustering kinetics predicted from our computer simulation are consistent with recent experimental observations.