Atomic Mechanisms of Flow and Fracture at Metal-Ceramic Interfaces and Their Rolein the Design of Metal Matrix Composites

摘要

This report describes new and significant results that can be applied in themicrostructure design for optimum mechanical performance of metal-ceramic composites and laminates. There are three elements to these recommendations: (1) the design of the atomic structure of metal-ceramic interfaces, (2) identification of the critical length scale in the two phase microstructure, and (3) prediction of the microstructural conditions under which the thermal conductivity of the composite becomes significantly influenced by the thermal boundary resistance of interfaces. In the first topic we show that the beneficial effect of titanium interlayers at a copper/alumina interface is accomplished with only about one monolayer; with further increase in the titanium interlayer thickness having an insignificant effect on the interfacial strength. In the second topic we show that the metal ligament size is the key microstructural parameter in controlling the flow stress, the fracture stress and the fracture toughness of metal-ceramic composites. The metal ligament size is important because dislocation activity in the metal, which produces pile ups against the interface, is the critical event in flow and fracture of composites. In the third area we show that the interfacial thermal boundary resistance plays a dominant role in the overall thermal conductivity of the composite when the microstructural scale becomes smaller than about 1um.