Formation of Y2O3 nanoclusters in nano-structured ferritic alloys: Modeling of precipitation kinetics and yield strength

The solubility product of Y2O3 in ferrite and the diffusion coefficient of yttrium in ferrite have been obtained by fitting a model based on the classical nucleation–growth–coarsening theory of precipitation, as adapted to an anisothermal heat treatment, to experimental small angle neutron scattering results of Y2O3 precipitate size distributions in a mechanically alloyed and consolidated Fe–15 at.%Cr–0.13 at.%Y–0.18 at.%O ferritic alloy. This precipitation model is coupled to a dispersed barrier model of structural hardening to predict the yield strength of the alloys as a function of heat treatment. The resulting model and thermodynamic/kinetic properties are then applied to better understand how the precipitation kinetics impact the yield stress in various anisothermal heat treatments, as compared to an isothermal heat treatment. The modeling results clearly indicate that the anisothermal heat treatments can be tailored to establish a higher density and a smaller size distribution of Y2O3 precipitates, which also increase the yield stress.