Microstructural effect on time-dependent plasticity of nanoporous gold

Abstract

Annealed, prestrained, and ball-milled nanoporous gold (np-Au) samples were prepared. Since the microstructures of the precursor alloys, such as the crystallographic orientation and grain size, were mostly preserved during the dealloying process, prestrained np-Au is believed to have higher initial dislocation density, and ball-milled np-Au is believed to have higher densities of initial dislocation and grain boundary comparing to annealed np-Au. The time-dependent deformation behavior of np-Au samples with various microstructures was characterized with two parameters; creep strain exponent n and activation volume V∗ using spherical nanoindentation creep tests. We found that primary mechanism of time-dependent plasticity for annealed and prestrained np-Au samples is dislocation slip and that for ball-milled np-Au sample is grain boundary sliding. In dislocation slip-dominant time-dependent deformation in np-Au, a higher initial dislocation density lowers n and V∗. In grain boundary sliding-dominant time-dependent deformation in np-Au, the values of n and V∗ are similar to those for dislocation slip-dominant time-dependent deformation; however, the creep strain rate in quasi-steady-state is higher than that for dislocation slip-dominant time-dependent deformation.