Superplastic Properties of y+a2 Titanium Aluminide Alloy Ti-43AI-(Nb,Mo,B) in Cast + Post-Solidification Heat Treated Condition

A novel approach to fabrication of globularized fine-grained structure in y+a2 titanium aluminide alloys has been proposed. The approach included the use of a specially designed alloy Ti-43Al-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 deg C at an initial strain rate of s'=1.7x10-4 s-1. High elongation (6=160-230%) and low flow stresses (6=36-100 MPa) typical of superplastic behavior were measured at T=1050-1130 deg C. It was demonstrated that the sheet material produced by spark cutting of the cast + heat treated alloy might be successfully hot formed.