Microstructures and properties of Al2O3/Al–AlN composites by pressureless infiltration of Al-alloys

Al alloys were infiltrated into Al2O3 preforms in N2 and N2– 2% H2 gas mixture in the temperature regime of 900–1200°C. The kinetics of nitridation during infiltration were continuously monitored by recording weight gained during infiltration of the preform. The weight gains that are attributed to the formation of AlN in the matrix were observed to increase with processing temperature. In addition, higher weight gains were recorded in N2–H2 as compared to in N2 atmosphere. Analysis of the composites indicates that controlled matrices of AlN/Al can be formed by selection of appropriate process parameters, viz. temperature and atmosphere. Based on this study it has been demonstrated that net-shaped metal matrix composites (MMCs), with varying amounts of AlN in the matrix can be fabricated by infiltrating alumina preforms at 900–1000°C in commercial nitrogen. By controlling the preform characteristics, it is possible to fabricate composites with significant variation in microstructural scale, and consequently matrix hardness and elastic modulus.