Atomic-scale computer simulation for early precipitation process of Ni_(75)Al_xV_(25-x) alloy with intermediate Al composition

摘要

The microscopic phase-field approach is applied to model the early precipitation process of Ni_(75)Al_xV_(25-x) alloy. Without any prior assumptions, this model can be used to simulate the temporal evolution of arbitrary morphologies and microstructures on atomic scale. By simulating the atomic pictures, and calculating the order parameters and volume fraction of the θ(Ni_3V) and γ'(Ni_3Al) ordered phases, we study Ni_(75)Al_xV_(25-x) alloys with Al composition of 0. 05, 0. 053 and 0.055 (atom fraction). Our calculated results show that, for these alloys, θ and γ' phases precipitate at the same time; with the increase of Al content, the amount of γ' phase increases and that of θ phase decreases; the precipitation characteristic of γ' phase transforms from Non-Classical Nucleation and Growth (NCNG) to Congruent Ordering + Spinodal Decomposition (CO+SD) gradually; otherwise, the precipitation characteristic of θ phase transforms from Congruent Ordering + Spinodal Decomposition (CO + SD) to Non-Classical Nucleation and Growth (NCNG) mechanism gradually. Both θ and γ' phases have undergone the transition process of mixture precipitation mechanism characterized by both NCNG and CO + SD mechanisms. No incontinuous transition of precipitation mechanism has been found.