SUPERPLASTIC DEFORMATION AND POSTFORMED MECHANICAL-PROPERTIES OF HIGH-TEMPERATURE TITANIUM-ALLOY IMI-834

Superplastic forming is particularly attractive for high temperature T i alloys because of the much lower forming stresses compared with thos e encountered during forging. The superplastic deformation parameters of IMI 834 sheet were obtained at 900, 940, and 990-degrees-C. At 990- degrees-C, IMI 834 shows low flow stresses, high values of strain rate sensitivity, and minimum strain anisotropy, however, 300% superplasti c elongation was readily obtained at the lower forming temperature of 940-degrees-C but with a higher flow stress. A reduction in the room t emperature and 600-degrees-C tensile properties with superplastic stra in resulted from strain enhanced grain growth during superplastic defo rmation; this effect was greatest at 990-degrees-C. Aging of post 990- degrees-C superplastically formed material was studied. The creep perf ormance of IMI 834 was found to be slightly reduced by superplastic fo rming. These properties and the changes in the microstructure and text ure are compared with other Ti alloys under superplastic conditions. ( C) 1993 Crown Copyright.