Preparation of calcium stabilized alpha-sialon ceramic and their (cBN/SiC) composites by spark plasma sintering

Abbas Saeed Hakeem

Abstract

Numerous compositions of calcium alpha and alpha/beta sialon ceramics represented by the chemical formula of Cam/2Si12-(m+n)Alm+nOnN16-n were sintered at 1500 °C by employing spark plasma sintering tech-nique and nano-size oxi-nitride powder precursors. The identification of the al-pha/alpha + beta phase boundary (Figure 1) was followed by the synthesis of alpha-silaon cBN and alpha-silaon/SiC compo-sites. Ultrasonic probe sonication resulted in the homogenous dispersion of both the reinforcing particles (cBN and SiC) in the alpha-sialon matrices. Single phase alpha sialon sample depicted the Vicker’s hard-ness of 19.22 GPa whereas Vickers hard-ness (HV10) of 24.0 GPa was achieved for composite reinforced with cBN particles. However, a notable combination of hard-ness 24.53 GPa and fracture toughness 11.0 MPa m1/2 was achieved (HV10) for the sialon composite reinforced with 30 wt% SiC. Crack deflection and bridging by the finely dispersed SiC particles were seen to be the primary mechanisms involved in the enhanced fracture toughness.