Coble Creep In Polycrystalline Materials Induced By Stress And Electromigration

Coble creep is a classical problem originally. It means the creep induced by grain boundary diffusion under the condition of high temperature. Superplastic behavior has been researched in a variety of metallic systems during high temperature deformation. As the progress of technologies, especially the appearance of new materials, the possibility of superplasticity in nanometer-crystalline materials at low temperatures, even at room temperature, is reported in molecular-dynamics simulations and in experimental evidences. It has been verified that the mechanism of the superplasticity in nanometer-crystalline materials was generated by the grain boundary diffusion (Coble Creep). One of the recurring questions in superplasticity behavior is the manner by which the polycrystalline aggregate as a whole deforms plastically without changing grain shape and size, especially when an elongation of 5,000% was observed in nanocrystalline copper at room temperature. This novel behavoir could not be explained by present models and theories.In this paper we present a model and derive analytical solutions for stress and electromigration-induced Coble creep in polycrystalline metallic materials to explain the observed novel superplasticity behavior. The creep driven by uniaxial stress has been extensively researched, but in practice most of creep occurs in complex stress states. In this paper, we consider the creep not only in uniaxial stress but also in biaxial stress states based on an extended Lee model. In addition, Electromigration driven atomic diffusion in metals has been generating tremendous research interest both as a mechanism of plastic deformation and as a failure mechanism of interconnects in integrated circuits. An analytical solution for the Coble creep induced by electromigration is, at the first time, established in this paper.