On the microstructural behavior of titanium alloy during nonoptimal regime of superplastic deformation

Abstract

In industrial superplastic forming, maintenance of the narrow ranges of condition required for optimal superplastic flow from beginning to end is a very difficult and challenging task. When these conditions required for optimal superplastic flow lie beyond a certain limit during deformation process, non-optimal process of superplastic deformation is observed during which the microstructure of the material changes very significantly. As the microstructure changes, the stress required to deform the material changes accordingly and the response of the material becomes dependent on the history of loading in this regime of superplastic deformation. A near alpha titanium alloy has been used in this study to find out those parameters of microstructure, which are varying significantly during non-optimal regime of superplastic deformation. Superplasticity tests have been carried out on tensile specimens at 930°C with a constant strain rate of 1×10-4 s-1 successfully stopped at two different percentages of elongation. Results indicated that percentage of alpha phase, number of alpha grains per unit area, size of alpha grain, parameter of non-uniaxiality of alpha grain and grain boundary area of alpha grain, etc. varied significantly during non-optimal regime of superplastic deformation.