Effect of Y₂O₃-RE₂O₃ (RE= Nd, Sm, Tb, Dy, Tm) -MgO additives on mechanical and thermal properties of silicon carbide ceramics

The mechanical and thermal properties of SiC ceramics with 1.5 vol.% Y₂O₃-RE₂O₃ (where RE is Nd, Sm, Tb, Dy, and Tm) -MgO additives hot-pressed at 1900 °C under an applied pressure of 35 MPa for 3 h in nitrogen atmosphere were investigated. All the samples show the relatively high relative density of equal to or higher than 99.1 % of theoretical density. The SiC ceramics with Y₂O₃-Dy₂O₃-MgO additives show the highest flexural strength of 943.8 ± 101.5 MPa and Vickers hardness of 29.2 ± 2.3 GPa at room temperature, owing to smaller cationic radii in RE₂O₃, which leads to a stronger intergranular phase. And the highest thermal conductivity was obtained from the sample with Y₂O₃-Tb₂O₃-MgO, due to the fully crystallized junction phase and grain boundary without an intergranular phase, inducing enhanced lattice continuity.