DIVISION OF THE HARDNESS OF MOLYBDENUM INTO RATE-DEPENDENT AND RATE-INDEPENDENT COMPONENTS

The hardness, H, and rate sensitivity of the hardness, m = partial der ivative ln H/partial derivative ln epsilon(eff)\x(p), where epsilon(ef f) is an effective strain rate and x(p) the plastic depth, are measure d in molybdenum at room and low temperature (160 and 170 K) using as-r eceived and annealed specimens. Based on these measurements it is foun d that H separates into two components: one depending on indentation r ate and temperature, and the other depending on the starting state of the material. An activation volume is defined, v() = 9kT/mH, which fa lls within the range of values derived from other experimental techniq ues. The values of rn obtained from indentation creep, indentation loa d relaxation, and indentation rate-change experiments agree closely wi th each other provided a consistent analysis is used. The results of t hese experiments suggest that the rate- and temperature-dependence of the hardness can be used to discriminate between strengthening mechani sms at low temperature.