A new strategy for microstructural programming and toughening of α-SiC ceramics

Achieving both high densification and intrinsic toughening remains a fundamental challenge for SiC and other strongly covalent ceramics. A new strategy is proposed to promote the densification of SiC ceramics via spark plasma sintering. The direct addition of uncrosslinked polysilazane (PSZ) into 6H-SiC powders introduces nitrogen (N) during pyrolysis, which may locally modify the chemical environment and may be associated with changes in the relative stability of α-SiC polytypes and the observed 6H-SiC→4H-SiC transformation. This transformation is accompanied by anisotropic grain growth and controllable microstructural evolution from equiaxed to columnar grains, resulting in the formation of interlocking structures. By adjusting the PSZ content, both fine equiaxed and interlocking microstructures exhibit high fracture toughness (∼6.9 MPa m^1/2), representing an improvement of approximately 72.5% compared with monolithic SiC (∼4 MPa m^1/2). This strategy provides an effective solid-state sintering route for microstructural design and mechanical enhancement in strongly covalent ceramics.