From size-dependent strengthening to softening in nanolaminated Cu/Cu-Zr crystalline/amorphous micropillars

Microcompressive tests were performed to investigate the intrinsic modulation effect and extrinsic diameter effect on strength and deformation behaviors of nanolaminated Cu/Cu-Zr crystalline/amorphous micropillars within a diameter D range from 300 to 1500 nm as well as a modulation ratio η range from 0.1 to 3.0. Experimental results revealed a transition of D-dependent deformation mode from homogeneous-like to shear localization at large η while D-independent homogeneous extrusion of Cu at small η. Furthermore, the flow strength increased with raising D at small η but decreased at large η exhibiting a D-insensitive strength at a critical η* ~ 0.5. These unusual results were rationalized in terms of a coupling effect of dislocation actions and shear transformation zone mediated operations.