Non-equilibrium grain-boundary segregation of Bi in Cu bicrystals

The observations of grain-boundary segregation of Bi in Cu bicrystals were analyzed. According to equilibrium grain boundary segregation (EGS) model and non-equilibrium grain-boundary segregation (NGS) model, respectively, the segregation kinetics of isothermal annealing at 500 °C and that of isochronal annealing for 24 h of Bi in Cu bicrystals were investigated. By qualitative analysis and quantitative analysis, it is concluded that the grain-boundary segregation of Bi agrees well with the theory of NGS. Based on the kinetics model of NGS, some parameters that are useful to predicting and controlling the Bi-induced embrittlement in Cu alloys are calculated as follows: the diffusion coefficient of Bi-vacancy complexes Dc=7.8×10−5exp[–1.46/(kT)]; the apparent diffusion coefficient of Bi atoms DiA=7.66×10at+bexp[–1.76/(kT)], where a=8.45×10−8 and b=–13.37.