The role of partial melting on superplasticity of Si3N4p/Al-Cu-Mg composite

For metal matrix composites containing ceramic reinforcements, stress concentration during tensile deformation occurs at interfaces between the matrix and ceramic, so that, cavitation is excessively developed at interfaces, resulting in premature fracture. In a previous paper, it was suggested that the dominant deformation process of high-strain-rate superplasticity for metal matrix composites if grain boundary sliding (GBS), and that liquid phases in high-strain-rate superplasticity serve both to relax the stress concentration and to limit the appearance of internal cavitation and subsequent failure. In their experimental observation, it has been observed that a large elongation is obtained at the temperature, that is close to the onset temperature for partial melting in the superplastic composites, but the elongation significantly decreases at slightly higher temperatures, which are close to the end temperature for partial melting. This indicates that there is an optimum amount of the liquid phase for obtaining high-strain-rate superplasticity in these materials. Thus, it is important to examine the nature of ceramic-matrix interfaces of superplastic composites in order to understand the origin of superplastic flow related to liquid grain boundaries during high-strain-rate superplastic deformation. The aim of this work is to study the nature of the interfaces and surfaces of the deformedmore » specimens in Si{sub 3}N{sub 4}p/A;-Cu-Mg composites to understand GBS related with liquid phases at interfaces during superplastic flow.« less