A series of samples with yttrium alpha -SiAlON compositions and different amounts of additive has been fabricated from alpha -Si3N4, AIN, Al2O3 and Y2O3 starting powders, using gas pressure sintering and three different sintering procedures. One series of samples was heated up to 1825 degreesC and then held for 3 h, another group of samples was held at a lower temperature (1500 or 1600 degreesC) for I h and then heated up to 1825 degreesC and held for 3 h. The results of investigations using scanning electron microscopy showed the effect of composition and sintering procedure on the morphology of alpha -SiAlON grains. It was found that the amount of elongated grains increased with increasing amount of liquid phase. The mechanical tests showed that all of the samples exhibited HV10 values in the range of 1800-1976 kg/mm and K-1C values in the range of 3.9 6.3 MPam(1/2). (C) 2001 Published by Elsevier Science Ltd. All rights reserved.