The effects of Nb content on microstructure and fracture behavior of near α titanium alloys

The microstructure and fracture behavior of as-cast Ti-1100 alloys with different contents of Nb were systematically investigated. The results demonstrate that the Nb element added to titanium alloys changes the lattice parameters of α phase. Microstructural observations indicate an obvious reduction in the prior β grain size, α-laths spacing, as well as the thickness of β phase, with the increase of Nb content. It is also observed that Nb addition promotes the formation of ternary (TiZr)6Si3 (S2 type) silicides. The fracture toughness KIC of the alloy increases with increasing content of Nb element, which is primarily attributed to the improved propensity for crack-tip tortuousity caused by the fracture behaviors of the α/β colonies. The fracture morphologies of these alloys reveal cleavage fracture mode.