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

摘要

The microscopic phase-field approach was applied for modeling the early precipitation process of Ni_(75)Al_XV_(25-X) alloy. Without any a prior assumption, this model can be used to simulate the temporal evolution of arbitrary morphologies and microstructures on atomic scale. Through the simulated atomic pictures, calculated order parameters and volume fraction of the θ (Ni_3V) and γ' (Ni_3Al) ordered phases, Ni_(75)Al_xV_(25-x) alloys with Al composition of 0.05, 0.053 and 0.055 (atom fraction) were studied. Results show: For these alloys, θ and γ' precipitated at the same time. With the increase of Al content, the amount of γ' phase is increasing and that of θ phase is decreasing; 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' has undergone the transition process of mixture precipitation mechanism with the characteristic of both NCNG and CO+SD mechanism. No incontinuous transition of precipitation mechanism has been found.