Superplastic deformation characteristics of microduplex Ti–6Al–4V alloy

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Abstract
A study has been made of the superplastic tensile behaviour of a microduplex Ti–6AI–4V alloy in the temperature range 760–940°C. Maximum superplastic elongations were obtained for a temperature of 880°C at which the volume fraction of β–phase was approximately 0·4. At temperatures below about 850°C, the main microstructural changes which occurred involved dynamic grain refinement and cavitation. The cavities, which occurred at α/α and α/β boundaries, interlinked parallel to the tensile axis at high strains. However, the volume fractions of cavities observed, although not quantitatively assessed, were always relatively small and had no significant effect on the fracture behaviour of tensile specimens, all of which pulled down to a fine point or chisel edge at failure. At temperatures greater than 850°C, no cavities were observed except near the fracture surface, and the most important structural change was grain growth. At all the temperatures examined, the structural changes which occurred during superplastic deformation were accompanied by strain hardening. MST/323