Effect of sintering additives of carbon black, SiC, Al₂O₃, and Al₂O₃ + Y₂O₃ on microstructure and mechanical properties of B₄C ceramics

B₄C ceramics are widely used as structural materials in the field of engineering. B₄C ceramics are difficult to sinter; therefore, various sintering additives are added to B₄C ceramics. The mechanisms of different sintering additives that promote the sintering of B₄C ceramics are different. In this study, the effect of 3 wt % sintering additives of carbon black (CB), SiC, Al₂O₃, Al₂O₃ + Y₂O₃ on the phase compositions, microstructure, and mechanical properties of the hot-press sintered B₄C ceramics with a certain degree of porosity are studied. When CB is selected as the sintering additive, there is no free carbon in the final B₄C ceramics, which is attributed to its complete consumption with oxide film impurities existing on the B₄C starting powders. The sintering additives of SiC and Al₂O₃ exist in the form of crystals, while Y₃Al₅O₁₂ generated from the sintering additive of Al₂O₃ + Y₂O₃ exists in amorphous form in the final B₄C ceramics. In the case of the same low additive amount, the sintering additives of Al₂O₃ and Y₃Al₅O₁₂ are more conducive to promoting the sintering of B₄C ceramics than the sintering additives of CB and SiC. The difference in the average gain sizes of the B₄C ceramics with different types of sintering additives is not obvious. Different types of sintering additives determine the mechanical properties of the hot-press sintered B₄C ceramics by affecting their porosity, grain size, and grain boundary characteristics.