HOT ISOSTATIC PRESSING AND POST-HOT ISOSTATIC PRESSING OF SIC-BETA-SIALON COMPOSITES

SiC-beta-sialon two-phase composites with various compositions were fo rmed by hot isostatic pressing (HIP) and treated by post-hat isostatic pressing (post-HIP). The bending strength of the HIP specimens reache d the highest values when the Z-value (Si6-ZAlZOZN8-Z) of the second p hase, beta-sialon, was 2.0, while the highest values of hardness were reached at Z = 1.5. Scanning electron microscopy (SEM) observations of the fracture surface revealed that a fine and homogeneous microstruct ure was obtained by HIP. Surface nitriding of the HIP specimens by pos t-HIP in a N-2 atmosphere resulted in significant improvement in the b ending strength. The maximum value of bending strength reached 950 MPa at Z = 1.0 for beta-sialon. The formation of a dense microstructure, with rod-like grains in the surface layer, and other strengthening mec hanisms may be responsible for the improvement.