Systematic approach to microstructure design of Ni-base alloys using classical nucleation and growth relations coupled with phase field modeling

Abstract

To analyze the formation of bimodal particle size distributions during precipitation, the dynamic competition for supersaturation by growth of existing precipitates and nucleation of new particles was studied under continuous cooling conditions with constant cooling rates. The nucleation rate was calculated according to classical nucleation theory as a function of local supersaturation and temperature. The depletion of matrix supersaturation by growth of existing particles was calculated from fully diffusion-controlled precipitate growth in an infinite matrix. Phase field simulations of γ precipitation in a binary Ni-Al alloy were performed under continuous cooling conditions. Then the average and maximum matrix supersaturations were calculated and plotted onto the contours of nucleation rate and growth rate in concentration and temperature space. These methods were used iteratively to identify the window for bimodal particle size distributions. © The Minerals, Metals & Materials Society and ASM International 2008.