Chemical compound formation and diffusion – as parallel processes in grain boundary

Abstract

The Fischer’s model1 is the base of the standard description of the diffusion along grain boundary (GB) with leakage to grain bulk. Various versions of calculation diffusant concentration field were realized: for self diffusion and hetero diffusion, with a grain boundary segregation2,3 and formation of atomic complexes in GB,4‒6 for various temperature areas7 and various structural types of GBs.8 It may seem strange, but the model describing influence of chemical processes in GB, which bind a part of diffusing atoms, on the rate of their moving in GB wasn’t developed. Though the experimental fact of grain boundary diffusion (GBD) delay due to precipitation of nanoparticles in GB is well-known, it is usually connected with the idea that fine particles which are formed in GB reduce the section of boundary and diffusive flux. The direction of this investigation is the development the Fisher’s model of GBD taking into account simultaneous chemical interaction of diffusive and matrix atoms in GB. The events of this kind – parallel carrying out two processes with participation of the same atoms – are well-known in heterogeneous kinetics.9 As a typical example of those processes it can be considered the steel nitration process.