POST-FORMING TENSILE PROPERTIES OF SUPERPLASTIC TI-6AL-4V ALLOY

A study has been made of the influence of uniaxial superplastic deformation on the ambient temperature tensile properties of Ti-6Al-4V sheet. Material was deformed to various strains up to 200% at temperatures from 850 to 970 degree C at strain rates in the range 1. 1-18 multiplied by 10** minus **4 s** minus **1 (0. 7-11% min** minus **1). Tests were also performed on statically annealed material to separate the effects of high temperature exposure and superplastic deformation. Mechanical property changes were complex and depended on the relative contributions from the strengthening and softening mechanisms occurring during either superplastic deformation or heat cycling. Structural features influencing mechanical properties were phase size and morphology, dislocation density, and crystallographic texture. The strength after superplastic deformation was always less than that of as-received material but a significant reduction in strength was attributable to heat cycling. In some cases, the strength of the superplastically deformed material was greater than that after heat cycling.