The Mechanism of Cavity Growth in Copper during High-Temperature Fatigue

AbstractDuring the fatigue of copper at elevated temperatures cavities form on grain boundaries and cause a decrease in density. The fractional change in density is directly proportional to time for tests in which the plastic strain amplitude remains constant. In constant-stress tests, when the stress is sufficient to cause appreciable hardening, the fractional change in density is approximately proportional to (time)⅔. For the majority of the tests the activation energy of the growth process is 24.2 kcal.mole−1; this and other evidence suggests that growth depends on a grain-boundary diffusion mechanism as well as on the migration of vacancies created by fatigue. The results are interpreted on the basis of a model in which defects absorbed by grain-boundary migration contribute to cavity growth.