Residual stress effects on toughening of ultrafine-grained B₄C-SiC ceramics

The attainment of both enhanced toughness and super hardness is crucial for B₄C ceramics. Refining grains to the nanoscale is known to be an effective strategy to address the above issue, but remains a great challenge. In this work, B₄C and SiC nanoparticles were synthesized and used for the preparation of ultrafine-grained B₄C-SiC ceramics. The grain size effect on the mechanical properties of composites was systematically investigated. It is found that, contrary to the conventional view that there is almost no residual thermal stress in the B₄C-SiC interface, residual stress arises as B₄C grains reach a nanostructured state, and the toughness can be considerably improved to 5.13 MPa m^1/2. The B₄C-SiC composite also demonstrates excellent hardness of 36.6 GPa, even superior to that of monolithic B₄C ceramics. This study has important implications for the development of toughening mechanisms for B₄C-SiC ceramics and presents a new strategy for producing high-performance ceramics.