A UNIFIED INTERPRETATION OF THRESHOLD STRESSES IN THE CREEP AND HIGH STRAIN RATE SUPERPLASTICITY OF METAL MATRIX COMPOSITES

摘要

The flow behavior of metal matrix composites is characterized by the presence of a threshold stress under both creep conditions at intermediate temperatures and in high strain rate superplasticity (HSR SP) at very high temperatures near the onset of partial melting. Experiments show the measured threshold stresses decrease with increasing temperature and this trend has been interpreted using an Arrhe- nius-type relationship incorporating an energy term, Qo. Typically, the experimental values reported for Qo are ～20-30 kJ/mol under creep conditions but up to ～100 kJ/mol in experiments associated with HSR SP. This report resolves this apparent dichotomy by demonstrating that both sets of results become consistent when the analysis is extended to incorporate an additional dependence on temperature associated with load transfer and substructure strengthening.