HOT-PRESSED MOSI2-PARTICULATE-REINFORCED ALPHA-SIALON COMPOSITES

MoSi2-particulate-reinforced alpha-SiAlON ceramic composites containin g 10, 20, 25, and 30 vol% were prepared by hot pressing at 1750 degree s-1800 degrees C. The (alpha-SiAlON matrix was of the composition (Y0. 48Si10.00Al2.30O1.17N15.29). The hardness for the fully dense samples changed from HV10 = 22.5 to 15.3 GPa and the toughness from 3.2 to aro und 5.2 MPa . m(1/2) when up to 30 vol% MoSi2 was present. Two interes ting microstructural features have been found, First, with an increasi ng amount of MoSi2 a pronounced coalescence of MoSi2 particles formed a ''dual phase'' material. The second effect was the growth of elongat ed alpha-SiAlON grains in the matrix with 10 vol% MoSi2 added, The oxi dation resistance has been determined to be unaffected by the addition of 20 vol% MoSi2 at 1250 degrees C in oxygen gas of 1 atm pressure.