Diffusion Induced Grain Boundary Motion

Several theoretical mechanisms have been proposed to explain the creep behavior for various materials these mechanisms involve stress-induced vacancy diffusion, grain boundary diffusion, dislocation motion, and grain boimdary sliding. Each leads to a different value of the stress exponent n in Equations 8.24 and 8.25. It has been possible to elucidate the creep mechanism for a particular material by comparing its experimental n value with values predicted for the various mechanisms. In addition, correlations have been made between the activation energy for creep (Qc) and the activation energy for diffusion (g Equation 5.8). 

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