Correlation Between Pressureless Sintering, Microstructure, and Properties of ZrB₂-SiC-Y₂O₃ Composites

The influence of Y₂O₃ addition on densification, physical, mechanical, thermal, and oxidation properties of ZrB₂-20 vol.%SiC- (0-15 vol.%Y₂O₃) composites was investigated in the present study. Powders of ZrB₂-SiC-Y₂O₃ were cold compacted uniaxially, and green compacts were densified by pressure-less sintering. Results indicate that Y₂O₃ addition improves the sinterability and mechanical properties, whereas it diminishes the electrical and thermal conductivities of the investigated composites. Removal of surface oxides by the additives and segregation of Y₂O₃ particles at the triple junction of the ZrB₂ grains enhances densification. Reduction in porosity (9.5-4.2%) through Y₂O₃ addition (0-15 vol.%) improves hardness (up to 52%), relative elastic modulus (up to 9%), and fracture toughness (up to 26%) of the investigated composites. The electrical conductivity has been observed to vary in the range of 2.67-1.92 10⁶ S/m, and thermal diffusivity values decrease with an increase in Y₂O₃ content and temperature. Oxidation studies indicate that the ZrB₂-SiC composite shows better oxidation resistance than other investigated composites. Characterization of oxidized scales confirms the formation of a thicker oxide layer over the samples containing Y₂O₃.