It has been well documented that when a large difference in the coefficients of thermal expansion (CTE) exist between the matrix and reinforcement in metal-matrix composites (MMCs) internal stresses can develop which are sufficiently high to generate dislocations at the reinforcement/matrix interface. Numerous observations have been made of this phenomenon via TEM which have shown a variety of different dislocation substructures and dislocation punching mechanisms. An important consequence of this phenomenon is that the metal matrix becomes strain hardened as the dislocation density increases, thereby reducing subsequent plastic flow of the matrix. One notable feature of the dislocation punching mechanism is that prismatic dislocation loops are commonly observed emanating from the interface. In two recent studies it was found that dislocations were not emitted immediately upon cooling, but rather at some lower critical temperature. A number of microstructural and processing parameters can affect the thermally-induced dislocation substructure such as: a) differences in CTEs, b) lattice frictional stress, c) vol.% particulate, d) particle/matrix interface morphology, e) quench temperatures (ΔT effect), and f) thermal-cycling (e.g. reheating and requenching).
Impact of irradiation induced dislocation loops on thermal conductivity in ceramics
