Shear and distensile fracture behaviour of Ti-based composites with ductile dendrites

The room-temperature deformation and fracture behaviour of Ti-based composites with ductile dendrites, prepared by copper mold casting and arc-melting techniques, was investigated. Under compressive loading, the Ti-based composites display high fracture strength (about 2000 MPa) and good ductility (about 4 or 10%). The yield strength of the Ti-based composites is relatively low (about 565-923 MPa). However, they have a large strain-hardening ability before failure, due to the interactions between shear bands and dendrites. For the arc-melted Ti-based composites, fracture often occurs in a shear mode with a high plasticity ( about 10%). In contrast, the cast Ti-based composites break or split into several parts with a compressive plasticity of 4%, rather than failing in a shear mode. A new fracture mechanism, i.e. distensile fracture, is proposed for the first time to elucidate the failure of the as-cast Ti-based composites. Based on the difference in the fracture modes of the differently prepared composites, the relationships between shear and distensile fracture mechanisms and the corresponding fracture criteria are discussed.