The relationship between grain size and creep deformation of nanocrystalline body-centered cubic metals

Abstract

The creep behaviors of nanocrystalline body-centered cubic metals (i.e., W, Ta and Mo) with different grain sizes were experimentally characterized via nanoindentation testing at room temperature. Distinct from coarse-grained body-centered cubic metals, the creep deformation was mediated by grain boundary-dislocation related mechanism under the high applied stress in nanoscale materials, in addition, the strain rate sensitivity and activation volume were directly dependent on the Burgers vector/grain size in this mechanism. It should be noted that the grain size exponent (P) was estimated to be about 0–1, which was different from the dislocation creep in conventional metals, i.e., P = 0. Moreover, the equation of the strain rate sensitivity and activation volume versus grain size of this mechanism were also suitable for nanocrystalline body-centered cubic, face-centered cubic even tetragonal metals.