Void formation of nanocrystalline materials at the triple junction of grain boundaries

Abstract

A theoretical model of void formation at the triple junction of grain boundaries is described. Based on the combined effects of grain boundary diffusional creep and triple junction diffusional creep as well as dislocation climb, void formation time and void growth rate are derived. The results indicate that vacancy concentration increases with increasing creep strain rate and the angle of the Burgers vector to its dislocation line, and with decreasing grain size. It sharply declines at low creep strain rates, then the asymptotic behavior approaches a constant at high rates. It is also found that the dislocation density is noticeable for small grain sizes in nanocrystalline Cu, and the void growth rate decreases with creep strain rate and time, which are qualitatively consistent with the conclusions in previous work (Dongare et al 2010 J. Appl. Phys. 108 113518; Du et al 2010 Mater. Sci. Eng. A 527 4837).