Pressureless sintering of (ZrB2-SiC-B4C) composites with (Y2O3Â +Â Al2O3) additions

Pressureless sintering of (ZrB2-SiC-B4C) composites with (Y2O3 + Al2O3) additions has been studied. The vol.% of SiC, B4C, and (Y2O3 + Al2O3) was varied from (26, 24, and 16) to (5, 4, and 5) respectively. Hardness of composites has been found to decrease with a decrease in B4C content. Flexural strength has been found to increase with decreasing (Y2O3 + Al2O3) content. No considerable decrease in flexural strength for composite with high vol.% of SiC, B4C, and (Y2O3 + Al2O3) has been observed up to a temperature of 1500 °C. By optimizing the composition a composite possessing a density of 4.64 g cm− 3, flexural strength of 213 MPa, and Vickers hardness of 17.3 GPa has been sintered. Conical shapes could be made by manual shaping and sintering. A complex yttria-alumina-silicate (YAG) layer was found to protect the composite from oxidation at high temperature of 1700 °C. The composites exhibited good dimensional stability and thermal shock resistance at 2200 °C in oxy-acetylene flame and at 2700 °C in plasma flame. Formation of yttria stabilized zirconia embedded in the matrix of YAG has been identified on the flame exposed surfaces. The composite could be joined to itself by gas tungsten arc welding (GTAW) with a filler material containing (ZrB2-SiC-B4C-YAG). The shear strength of the weld was about 50% of the flexural strength of the parent composite.