Metal-Ceramic composites via "in situ" methods

Several "in situ" methods for obtaining composite materials with ceramic particles were developed in order to overcome some of the inherent problems associated with conventional processes. This paper reviews the obtaining processes of composite materials with a greater emphasis on nitriding and oxidation by directed melting. These obtaining methods provide microstructures with different combinations of metal–ceramic. Metal matrix composites with controlled amounts of dispersed ceramic particles are obtained by "in situ" processes. The composite materials obtained are having different properties by controlling various processing variables such as temperature, time, the reactant phases and the reinforcing material. The properties of the "in situ" obtained materials depend mainly on the matrix and volume fraction of constituent phase. Briefly are reviewed the mechanical properties, hardness mechanisms and possible applications of these composite materials. Nitridation is much more attractive because with the variation of process parameters is obtained a wider range of microstructures and properties. The activation energy for the formation of AlN (A1N ∼ 100 kJ/mole) is smaller than that of oxidation (Al₂O₃ ∼ 400 kJ/mole) and growth rates (3 × 10^-2 gm/cm²/s) are at least three times higher for oxidation. (paper)