THERMAL MISMATCH DISLOCATIONS PRODUCED BY LARGE PARTICLES IN A STRAIN-HARDENING MATRIX

Silver chloride containing particles of irregular form of the order of 1-mu-m in diameter is used as a model material for particle-reinforced metal matrix composites (MMCs). Matrix dislocations due to the mismatch of the coefficients of thermal expansion of the two phases are made visible to transmission optical microscopy through bulk decoration performed at room temperature. The plastic zone around the particles takes two forms, similar to what is observed around the glass microspheres: (a) rows of coaxial prismatic dislocation loops punched into the matrix and (b) a plastic zone of irregular form containing partially resolved tangled dislocations. A relationship between the inclusion volume and the volume of the plastic zone around the inclusion-developed for the geometrically tractable problem of a sphere embedded in a strain-hardening matrix deforming by slip-is found to be valid for particles of irregular form as well, which are more representative of the reinforcement used in MMCs than spheres are.