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

Al alloys were infiltrated into Al2O3 preforms in N-2 and N-2- 2% H-2 gas m ixture in the temperature regime of 900-1200 degrees C. The kinetics of nit ridation during infiltration were continuously monitored by recording weigh t gained during infiltration of the preform. The weight gains that are attr ibuted to the formation of AlN in the matrix were observed to increase with processing temperature. En addition, higher weight gains were recorded in N-2-H-2, as compared to in N-2 atmosphere. Analysis of the composites indic ates that controlled matrices of AlN/Al can be formed by selection of appro priate process parameters, viz. temperature and atmosphere. Based on this s tudy it has been demonstrated that net-shaped metal matrix composites (MMCs ), with varying amounts of AN in the matrix can be fabricated by infiltrati ng alumina preforms at 900-1000 degrees C in commercial nitrogen. By contro lling the preform characteristics, it is possible to fabricate composites w ith significant variation in microstructural scale, and consequently matrix hardness and elastic modulus. (C) 1999 Elsevier Science S.A. All rights re served.