Characterization of strain-rate sensitivity and grain boundary structure in nanocrystalline gold-copper alloys

Abstract

The power-law dependence of strength on strain rate provides a measure of the strain-rate sensitivity. In general, strength increases as grain size decreases from the microscale into the nanoscale regime for many cubic metals. The method of microscratch testing is used to measure microhardness in order to evaluate material strength. The strain-rate dependence of hardness is measured by varying the microscratch velocity. New results for nanocrystalline gold alloys show that the exponent (m) of the power-law dependence of stress on strain rate increases to 0.20 as grain size decreases to values less than 10 nm. A high-resolution electron microscopy examination of grain boundary structure reveals that an increase in the strain-rate sensitivity exponent (m) is found with an increase in the grain boundary misorientation. © 2009 The Minerals, Metals & Materials Society and ASM International.