Superplastic properties of γ+α₂ titanium aluminide alloy Ti-43Al-(Nb,Mo,B) in cast + post-solidification heat treated condition

A novel approach to fabrication of globularized fine-grained structure in γ+α₂ titanium aluminide alloys has been proposed. The approach included the use of a specially designed alloy Ti-43 Al-X(Nb,Mo,B) and heat treatment. It was found that the ingot structure of the alloy might be partially globularized on a scale of bulk material using only globularization anneal excluding any hot working procedure. The microstructure and tensile mechanical properties of the alloy in the cast + heat treated condition were investigated. The tensile mechanical tests were performed in air in the temperature range of T=900-1130°C at an initial strain rate of ε'=1.7×10^-4 s^-1. High elongation (δ= 160-230%) and low flow stresses (σ=36-100 MPa) typical of superplastic behavior were measured at T=1050-1130°C It was demonstrated that the sheet material produced by spark cutting of the cast + heat treated alloy might be successfully hot formed.