Microscopic phase field simulation on the nucleation incubation period of L12 and D022 phases in Ni75Cr25-xAlx alloy

Abstract

Based on the microscopic phase field dynamic model， the effect of Al concentration on the nucleation incubation period of Ni75Cr25-xAlx alloy and the relation between the incubation period and the precipitation sequence are investigated by using the atomic pictures， averaged long-range order parameters and averaged composition deviation order parameters. The simulation results show that the nucleation incubation periods of L12 and D022 phases are related not only to the Al concentration but also to the precipitation sequence. When the Al concentration is smaller than 7.5%， for the D022 phase first precipitated from the matrix, its nucleation incubation period becomes longer with the increase of Al concentration, and so is the L12 phase subsequently precipitated. When the Al concentration is larger than 7.5%， for the L12 phase first precipitated from the matrix， its nucleation incubation period become shorter with the increase of Al concentration， so is for the D022 phase subsequently precipitated. When the Al concentration is equal to 7.5%， L12 and D022 phases both precipitate almost simultaneously， and there is no obvious difference berween their nucleation incubation periods.