Computer simulation for the precipitation process of Ni_(75) Al_(7.5) V_(17.5) alloy

摘要

The precipitation mechanism of Ni_(75) Al_(7.5) V_(17.5) alloy above the L1_2 instability line, between the L1_2 and D0_(22) instability lines and below the D0_(22) 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 Ll2 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 L1_2 and D0_(22) instability lines. The mechanism below the D0_(22) instability line is similar to that between the L1_2 and D0_(22) instability lines Withthe 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 0 phase becomes large and the shape transforms from strip to circle.