Compensation effect for grain boundary diffusion in a bicrystalline experiment

Abstract

The paper is devoted to the problem of the compensation effect for grain boundary (GB) diffusion, i.e. the linear dependence of the pre-exponential factor of the GB diffusion coefficient on the activation energy. Specific features of GB diffusion as a thermally activated process namely, the influence of segregation factor, K, and variation of the GB width, δ, on the diffusion rate are discussed. A special diffusion experiment was designed to estimate the contribution of the separate component parts of the triple product, KδDGB (DGB is the GB diffusion coefficient). The experiment was performed with Al bicrystals. The variation of the GB width δ, and a value of the segregation factor K, due to GB structure change are estimated. It is concluded that DGB is the main GB structure-sensitive parameter in the triple product. This circumstance allows us to consider the GBs in Al bicrystals as a series of uniform objects and to describe the kinetics of GB diffusion in terms of the compensation temperature Tc and a “barrier” phase. The value of Tc for GB diffusion of Zn and Ge in Al bicrystals is practically the same and equals 709 and 706 K, respectively. The character of the “barrier” phase is discussed.