Pressureless sintering of LPS-SiC (SiC-Al2O3-Y2O3) composite in presence of the B4C additive

Abstract One limitation of using silicon carbide (SiC) is the materials’ intrinsic brittleness. The mechanical properties of these ceramics can be improved through the use of additives during the sintering process. This research investigated the addition of boron carbide (B4C) on the Liquid Phase Sintered (LPS) SiC-Al2O3-Y2O3 system. The aim was to determine the effects on both the mechanical properties and microstructure of the LPS-SiC composite with varying levels of B4C as an additive. The Silicon Carbide preparation was composed of a 10 wt% mixture of Alumina (Al2O3) and Yttria (Y2O3) at a 3:2 M ratio, with different concentrations of boron carbide between 0 - 6 wt%. In addition, 1 wt% of carbon powder was added to the precursors to prevent oxidation during sintering. All precursors were milled for 2 h at 200 rpm and then samples were sintered by the pressureless technique for 1 h at 1900 °C in an argon atmosphere. A relationship was observed between the measured mechanical properties, the porosity and various phases formed in within the structure of the ceramic composite. The grain size and distribution of the B4C reinforcement phase provides a mechanism for the observed strengthening and increase in fracture toughness. Increasing the B4C content up to 5 wt% enhanced the strength and fracture toughness of the composite samples, however increasing beyond 5 wt% led to a decrease in these properties. Furthermore, a microstructural explanation of the grain-effects is proposed by considering the crack-growth micro-patterns. This work clarifies the link between the mechanical properties and microstructural characteristics of the SiC-Al2O3-Y2O3 composite with B4C additive. The strengthening mechanism of B4C additives was also explored in the microscopic scale.