SINTERING, MICROSTRUCTURE, AND MECHANICAL-PROPERTIES OF ALON-ALN PARTICULATE COMPOSITES

Particulate composites prepared by sintering compacts of Al2O3 and AlN powders,with a small addition of Y2O3, in 1 atm of nitrogen at 1650-1 900 degrees C have been characterised in terms of microstructure and m echanical properties. Aluminum oxynitride (AlON-5AlN.9Al(2)O(3)), 27R AlN pseudopolytype, and AlN were identified by XRD as the main phases in the sintered material. With increasing Al2O3, content, the sintered bulk density for comparable sintering conditions increased. The sinte red bulk density of AlON matrix materials showed a maximum at 1750 deg rees C, while that of the AlN matrix materials decreased with increasi ng sintering temperature. A liquid phase was formed mainly by the reac tion of AlN with Al2O3, aided by the presence of Y2O3, above 1850 degr ees C. Densification of the AlON matrix materials was mainly governed by the formation of liquid phase and grain growth of AlON. In the AlN matrix materials, liquid was formed at 1650 degrees C and little AlN g ain growth occurred with increasing sintering temperature up to 1900 d egrees C. With 5 mol.-%Al2O3, secondary AlON phase separated at the Al N grain boundaries during sintering. The room temperature bend strengt h and fracture toughness of AlON material containing dispersed AlN par ticles were higher than those of AlON. The high temperature bend stren gth of materials containing 50 and 64.3 mol.-%Al2O3 was approximately constant up to 1000 degrees C, at similar to 290 and 420 MPa, respecti vely, but abruptly decreased at 1200 degrees C. With 5 and 30 mol.-%Al 2O3, the bend strength increased by similar to 14% at 1000 degrees C c ompared with the loom temperature value, before falling again to the r oom temperature value at 1200 degrees C. BCT/266.