Evolution of nanoscale Cr-rich phase in a Fe-35 at.% Cr alloy during isothermal aging

A quantitative investigation of phase decomposition in Fe-35 at.% Cr alloy aged at 773 K was performed by using atom probe tomography (APT) and phase-field simulation. The kinetics of the alpha' phase formation via spinodal decomposition was studied by the variation of volume fraction, average particle radius and particle size distribution of alpha' phase at 700, 725 and 750 K. The simulated morphology and composition are in good agreement with the APT and transmission electron micrograph (TEM) results, demonstrating that the thermodynamic parameters used in the simulation were optimized. The growth and coarsening of the alpha' phase were promoted by the increasing aging temperature. Also, the coarsening rate increases and induces a larger slope for the number density of particles at the steady-state coarsening stage. The time exponent of the average radius of the alpha' phase shows a three-stages variation from about 0.31 to 0.20 and larger than 0.33 for the initial phase decomposition, growth and coarsening, and the steady-state coarsening stages, respectively. The particle size distribution of the alpha' phase is similar with the Brailsford-Wynblatt's (BW) predication at early stage of phase decomposition, and becomes lower than BW's value at coarsening stage. The kinetics of nanoscale alpha' phase from initial decomposition to coarsening is useful for the composition design and properties prediction of Fe-Cr alloys working at high temperature. (C) 2017 Elsevier B.V. All rights reserved.