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 conta ining 5-25 vol.% TiB2 phase produced via the in-situ chemical reaction betw een 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 in crease in strength and fracture toughness was ascribed to the interaction b etween the propagating crack front and local thermal mismatch stress associ ated with TiB2 particles. Induced circumferencial microcracking due to ther mal mismatch the major toughening mechanisms. Spontaneous circumferencial m icrocracking due to thermal mismatch stress in TiB2 particles was found to occur when the particle size exceeds its critical value. The theoretical in terpretation of spontaneous circumferencial microcracking, toughening via i nduced microcracking, and crack impedance was justified experimentally.