MICROSTRUCTURAL CHARACTERIZATION OF METAL MATRIX COMPOSITES BY ANALYTICAL ELECTRON-MICROSCOPY

Metal Matrix Composites have several advantages over the matrix alloys, such as higher stiffness and strength, but they suffer from lower fracture toughness. This is, of course, dependent on the chemical composition of the matrix and of the reinforcement and also on the microstructure and on the processing techniques. The reactions between the different phases in the materials, in particular the matrix / reinforcement interfaces condition strength and toughness. The purpose of the present paper is to outline the potential of different analytical electron microscopy techniques (direct imaging, EDS, EELS, convergent beam diffraction) for the characterization of magnesium segregation in the case of oxide and non-oxide reinforcements. This allows to identify MgAl2O4 spinel at the interface between alumina and an aluminium base matrix, and to understand the different chemical reactions which are involved in the processing.