Metal-matrix composites, comprising strong particles, whiskers or fibres in a ductile metal matrix, are becoming widely accepted for speciallized applications where properties such as a high strength-to-weight ratio, high stiffness or a low coefficient of thermal expansion, are needed. However, the manufacture of such materials always requires heating to high temperatures, which may result in unwanted reactions between the strengthening phase and the metal matrix. The processing route must therefore be chosen to minimize such reactions.
In many practical situations, these interactions result in additional phases that can only be observed and analyzed using transmission electron microscopy (TEM). The illustration shows such as example, where graphite fibres coated with a layer of TiB_2 were incorporated in an aluminum alloy matrix. Such materials are used for such applications because of their high stiffness. In order to study the reaction products, a thin (about one ten thousandth of a millimetre) cross-section was prepared for TEM using ion-beam sputtering. A number of different phases could be identified at the interface between the coated fibre and the metal matrix, the most important being the reaction product Al_4C_3 MAGNIFICATION X37,000