Generation of large prismatic dislocation loops at inclusions in crystals

Two mechanisms for the generation of large climb loops at precipitates or inclusions are proposed. Both begin with the nucleation of a small prismatic loop. In one the small loop lies immediately outside the precipitate particle and its plane is perpendicular to the precipitate–matrix interface nearby. The dilations associated with the precipitate and the dislocation loop have the same sign. In the other, the small loop lies either inside the precipitate or in the interface between precipitate and matrix. The dilations associated with the precipitate and dislocation loop have the opposite sign. If conditions are suitable the small prismatic loops may grow by climb until they are much larger than the precipitates or inclusions responsible for them. The final configurations are the same as those observed in gadolinium–gallium garnet and in quenched aluminum–magnesium alloys. The mechanisms indicate that highly stressed precipitates or inclusions aid the precipitation of both vacancies and interstitial atoms. This is so whether the precipitates or inclusions are dilated or compressed by the matrix. Copyright © 1973 WILEY‐VCH Verlag GmbH & Co. KGaA