Computer simulation for the precipitation process of Ni₇₅Al_7.5V_17.5 alloy

The precipitation mechanism of Ni₇₅Al_7.5V_17.5 alloy above the L1₂ instability line, between the L1₂ and D0₂₂ instability lines and below the D0₂₂ instability line are studied using microscopic phase-field kinetic equation. This paper is aimed at investigating the effect of temperature on precipitation mechanism and morphological evolution of the alloy. Our simulations demonstrate that the precipitation is a mixed mechanism of non-classical nucleation growth and spinodal decomposition above the L1₂ instability line. It needs certain thermal fluctuations for nucleation and the number of θ phases is small at this temperature. The precipitation mechanism of γ' phase is congruent ordering followed by spinodal decomposition, and θ phase is a mixed mechanism of non-classical nucleation growth and spinodal decomposition between the L1₂ and D0₂₂ instability lines. The mechanism below the D0₂₂ instability line is similar to that between the L1₂ and D0₂₂ instability lines. With the decrease of the temperature, ordering and phase separation becomes fast, the dimension of γ' phase becomes small, the shape transforms from equiaxed to block, the dimension of θ phase becomes large and the shape transforms from strip to circle.