Superplastic deformation and postformed mechanical properties of high temperature titanium alloy IMI 834

Abstract

Superplastic forming is particularly attractive for high temperature Ti alloys because of the much lower forming stresses compared with those encountered during forging. The superplastic deformation parameters of IMI 834 sheet were obtained at 900, 940, and 990°C. At 990°C, IMI 834 shows low flow stresses, high values of strain rate sensitivity, and minimum strain anisotropy, however, 300% superplastic elongation was readily obtained at the lower forming temperature of 940°C but with a higher flow stress. A reduction in the room temperature and 600°C tensile properties with superplastic strain resulted from strain enhanced grain growth during superplastic deformation; this effect was greatest at 990°C. Aging of post 990°C superplastically formed material was studied. The creep performance of IMI 834 was found to be slightly reduced by superplastic forming. These properties and the changes in the microstructure and texture are compared with other Ti alloys under superplastic conditions.

MST/1822