Robust bulk silicon carbide polymorphs sintered from collapsed hollow mesoporous structure

Bulk silicon carbide (SiC) ceramics are important for extreme-environment applications, but conventional synthesis demands densification temperature above 2100 °C or additives. This work introduces a straightforward strategy utilizing hollow mesoporous powder, achieving nearly full densification (99.2 ± 0.49% relative density) at 1750 °C through spark plasma sintering. The hollow structure induces intense stress accumulation around mesopores, causing instantaneous structural collapse into nanofragments (~6 nm) that greatly accelerate the densification kinetics. The resulting SiC ceramics feature fine grains (200–300 nm), clean grain boundaries, and coexisting 2H, 4H, and 3 C polytypes. These structural characteristics yield good mechanical properties: nanoindentation hardness > 35.0 GPa, Vickers hardness of 31.8 ± 1.6 GPa, and flexural strength of 625.32 ± 22.3 MPa—all exceeding conventional pure SiC. Theoretical and experimental analysis demonstrate that high-density stacking faults, nano-twins, and polytypic boundaries create substantial lattice distortions and atomic strain fields, effectively pinning dislocations and suppressing plastic deformation.