Flexural Strength, Fracture Toughness, and Hardness of Silicon Carbide and Boron Carbide Armor Ceramics

Armor‐grade B 4 C and SiC specimens were analyzed for phase assemblage, microstructure, and mechanical properties. SiC–N showed the highest four‐point fracture strength, and an ∼50% higher notched beam fracture toughness than solid‐state sintered B 4 C and SiC. This was attributed to preferential crack propagation along a weaker amorphous aluminosilicate grain‐boundary interphase, which also attenuated the effect of surface flaws on bending strength. Verco B 4 C showed the highest hardness. That material was phase pure, fully dense, and of finer grain size as compared with pressure‐assisted densification (PAD)‐B 4 C (hot pressed). Verco SiC showed a hardness equal to (Vickers) or higher than (Knoop) PAD‐B 4 C, and a comparatively narrow distribution in measured hardnesses. This was attributed to a fine‐grained, fully dense, solid‐state sintered microstructure with a fine and well‐distributed graphite second phase. Hardness of all specimens decreased with increasing applied load.