GRAIN-BOUNDARIES AS POINT-DEFECT SOURCES OR SINKS - DIFFUSIONAL CREEP

The rate of emission and absorption of point defects at high angle grain boundaries in single phase materials is considered by means of an (intrinsic) boundary dislocation model. The emission (absorption) rate is found to depend on the boundary structure and the applied stress and/or point defect supersaturation. Ideal low energy boundaries act as point defect sources (sinks) only above a threshold stress that is proportional to the slope of the energy misorientation curve of the boundary. Boundaries deviating from ideal low energy misorientation relatíonships emit (absorb) point defects at all stresses with a rate that increases with increasing angular deviation from the ideal low energy misorientation relationship. At high stresses and/or large crystal sizes and also in the case of pure twist boundaries, extrinsic grain boundary dislocations may be important for the emission and absorption of vacancies. The results seem to agree with the experimental observations available. © 1979.