Processing, microstructure, and mechanical properties of B4C-TiB2 particulate sintered composites. II. Fracture and mechanical properties

The fracture response of pressureless sintered boron carbide ceramics containing 5-25 vol.% TiB2 phase produced via the in-situ chemical reaction between B4C, TiO2 and elemental carbon was studied. Both strength and fracture toughness depend on TiB2 volume fraction, reaching their maximum values of 500 MPa and 4.6 MPA.m(1/2), respectively, at 15 vol.% TiB2. The observed increase in strength and fracture toughness was ascribed to the interaction between the propagating crack front and local thermal mismatch stress associated with TiB2 particles. Induced circumferencial microcracking due to thermal mismatch the major toughening mechanisms. Spontaneous circumferencial microcracking due to thermal mismatch stress in TiB2 particles was found to occur when the particle size exceeds its critical value. The theoretical interpretation of spontaneous circumferencial microcracking, toughening via induced microcracking, and crack impedance was justified experimentally.