Effect of Y2O3 and Al2O3 sintering additives during fabrication of Si3N4–Mo–Si cermet by conventional pressure-less sintering

Abstract

Abstract The present paper reports the individual and combined effect of Y2O3 and Al2O3 as sintering additives during fabrication of Si3N4–Mo–Si cermet by powder metallurgy route. Si3N4 + Mo + Si cermet composition is prepared and different proportions of yttria (Y2O3) and alumina (Al2O3) are added to that composition as sintering additives. Powder mixture is cold compacted and finally sintered by conventional pressure-less sintering at 1500 °C for 1 h in Argon gas atmosphere. The effect of the additives on the mechanical properties as well as microstructure of cermet has been investigated. Hardness and fracture toughness are found to be improved with combined addition of both the additives than that of individual addition. The maximum hardness and fracture toughness values are found in case of 5 wt. % Y2O3 and 10 wt. % Al2O3 added cermet with 11.41 ± 0.43 GPa and 7.005 ± 0.58 MPa m1/2 respectively. However, the optimal results are found in case of 7.5 wt % Y2O3 and 7.5 wt % Al2O3 added cermet with relative density of 62.25%, micro-hardness of 8.07 ± 0.55 GPa and fracture toughness of 4.57 ± 0.44 MPa m1/2. From microscopic study it is observed that initial α- Si3N4 transforms to β-Si3N4 after sintering.