A layer model for the kinetics of segregation in planar defects in multi-component materials

Abstract

Suzuki segregation and local phase transformations are widely observed across materials with extended planar defects, offering opportunities to design novel high-temperature and functional materials enabled by the nanoscale two-dimensional defects. However, the kinetics of the segregation process are not well understood despite intensive efforts have been made to investigate the segregation profiles at equilibrium and non-equilibrium conditions. In this work, a new model is proposed to study the temperature- and time-dependent segregation process to facilitate the research of this phenomenon. The model is established from the segregation energy landscape across the planar defects and the interlayer diffusion process. The model is applied to the Co-Ni binary alloys, Co-based superalloys, and Ni-based superalloys to understand the characteristics of segregation at equilibrium, the timescale required to reach equilibrium, and the influence of solute–solute interactions in the process. The kinetic model can be implemented with the thermodynamic models of segregation energy, which is demonstrated for a Ni-Co-Cr system. Based on the findings, a time–temperature–segregation diagram is proposed to determine the heat treatment parameters or thermal exposure profiles to achieve Suzuki segregation and local phase transformation for material design.