The production of AlN-rich matrix composites by the reactive infiltration of Al alloys in nitrogen

Abstract

Aluminium nitride (AlN)-Al matrices reinforced with Al₂O₃ particulate have been fabricated by reactive infiltration of Al-2% Mg alloy into Al₂O₃ preforms in N₂ in the temperature range of 900-1075 °C. The growth of composites of useful thickness was facilitated by the presence of a Mg-rich external getter, in the absence of which composite growth is self-limiting and terminates prematurely. Successful growth of composites has been attributed to the reduction in residual oxygen partial pressure brought about by the reaction with oxygen of highly volatile Mg in the getter alloy. The microstructure of the matrix consists of AlN-rich regions contiguous with the particulate with metal-rich channels in-between, thereby suggesting that nitridation initiates by preferential wicking of alloy along the particle surfaces. The increase in nitride content of the matrix with temperature is consistent with hardness values that vary between ~3 and 10 GPa.