The growth of grain-boundary voids under stress

Abstract The effect of combined hydrostatic pressure, P, and of uniaxial tension, [sgrave], on the rupture time of polycrystalline copper wire in the temperature range 400° to 500°c has been determined. All the specimens broke by intergranular fracture, due to the growth of voids along grain boundaries. Preliminary experiments indicated that the voids grow by the addition of vacancies under the action of the applied stress. A theory has been developed assuming that failure results from the growth of void nuclei on the grain boundary, which requires that the activation energy for failure is that of grain boundary diffusion and that the rupture time, tr, depends only on ([sgrave]-P). The experiments show that the activation energy is close to the expected value, and provided that [sgrave] is constant tr agrees with theory. Changes in [sgrave], when ([sgrave] - P) is constant, affect tr appreciably, and the results suggest that many of the void nuclei are stress induced.