Specimen size and shape dependent yield strength in micropillar compression deformation of Mo single crystals

The deformation behavior of _[1-25] oriented Mo micropillars with rectangular cross-sections having the [111] primary slip direction parallel to one of the two orthogonal side-surfaces has been investigated as a function of specimen size and shape (with varying ratios for two side-edge lengths of the cross-section). Micropillars with square-shaped cross-sections exhibit a size dependence of the critical resolved shear stress τCRSS approximated by τCRSSL-m with a power-law exponent of m ∼0.5 (L: cross-section side length). For a series of micropillars with a fixed length for the side-edge perpendicular to [111] (CE series), the CRSS also exhibit a power-law relationship with a relatively small exponent of m = 0.3. In contrast, an unexpected size-dependence is observed with two strength plateaus being connected by a strongly size dependent region (m ∼ 1) for a series of micropillars having a fixed length for the other cross-section side (CS series). The observed specimen size and shape dependence of CRSS of Mo micropillars is discussed based on the stochastic dislocation source length model and the dislocation kinetics model.