Fracture characteristics and microstructures of intermetallic compound Ti-24Al-11Nb (at%)

Abstract

Fracture characteristics of Ti-24Al-11Nb(at%) were related to microstructures based on the results of tensile tests and fracture toughness tests. Fracture mechanisms were also investigated. Fracture toughness, JIc, increased when microcracks were formed at the interfaces of colonies or acicular α2 in β solutionized and furnace cooled materials. The microcracks were formed by the coarse and big slip bands which were activated widely near the crack tip as a result of the formation of colonies. The crack propagation resistance, Tmat, increased with increasing crack deflection and shear ligaments in addition to microcracks. JIc and Tmat decreased with increasing precipitations of fine α2 in β during air cooling in α2 + β solutionized and air cooled materials. The blunting of the crack tip was inhibited because the deformability of β was inhibited by the finely precipitated α2. The microstructure of equiaxed α2 which is obtained by the solutionizing at 1313 K for 7.2 ks followed by water quenching gave the best balance among strength, elongation and fracture toughness.