Influence of diamond particles content on the critical load for crack initiation and fracture toughness of SiOC glass–diamond composites

The crack initiation load and fracture toughness were characterized as a function of diamond particle content, up to 25 vol%, in silicon oxycarbide glass matrix by means of Vickers indentation and single edge notch beam (SENB) technique, respectively. The larger fracture toughness value of 3.21 ± 0.3 MPa m1/2 was reached for 20 vol% diamond content composites and the value was 4 times higher than that of the unreinforced glass. The addition of diamond particles greatly influenced the crack initiation load, which increased from 2.9 to 49.0 N. The enhancement in the fracture toughness and crack initiation load can be explained by both the intrinsic mechanical properties of diamond (especially the elastic properties; E ∼ 1100 GPa) and the diamond/SiOC glass interfacial bonding. A clear correlation was found between the fracture energy, the reinforced interparticle spacing and the residual stress arising upon cooling due to thermal expansion mismatch between the matrix and the diamond particles.