Spontaneous grain boundary swelling in irradiated copper-boron alloys

Abstract

The degeneration of grain boundaries during the annealing of copper-helium alloys has been investigated. The grain boundary bubbles are stable at temperatures below 700° C, but at higher temperatures they grow spontaneously by absorbing vacancies generated in the grain boundaries. Resistivity measurements are particularly sensitive to grain boundary degeneration and can be used to investigate the process in its earliest stages. Increasing the temperature after bubbles have reached an equilibrium size causes breakaway growth of grain boundary bubbles at temperatures below those at which it would normally occur. Gas concentrations as low as 46 ppm are sufficient to cause spontaneous grain boundary degeneration at 800° C. The ultimate failure of grain boundaries is caused by the growth of bubbles until they touch and the conditions which contribute to this growth in the absence of an applied stress are examined.