Abstract:The precipitation processes of γ′ and θ phases in Ni₇₅Al_6.5V_18.5 alloy were simulated at different temperatures and the precipitation sequence of two phases and morphological evolution were investigated. The simulation demonstrates that the two phases precipitate simultaneously at high temperature and γ′ phase precipitates earlier than θ phase at 1000K and 1120K. With the temperature decreasing, the velocity of precipitation quickens, the quantity of θ phase increases and the size reduces; but the volume fraction increases, the quantity of phase increases and the size reduces as well. The two phases nucleate and grow independently at high temperature and the θ phase precipitates from the boundaries of γ′ phase at 1000K and 1120K. We also find that there are many kinds of domain boundaries between the same and different phases. The results of average deviation of composition and average absolute long range order parameter show that the ordering and compositional clustering of γ′ phase happen simultaneously at high temperature, the congruent ordering occurs prior to spinodal decomposition at 1000K and 1120K and the ordering advances and quickens as the temperature decreases. Ordering and compositional clustering of θ phase occur simultaneously at each temperature and are quickened with temperature decreasing.

Key words: microscopic phase-field; precipitation; atomic configuration; ordering; spinodal decomposition; simulation