Superplasticity in Aeroengine Titanium Alloy VT-9 and its Modified Compositions

Abstract

The alloy (Ti-6.5AL-3.3 Mo-1.6Zr-O.3Si) is a Soviet composition designated VT-9. Excellent superplastic characteristics found by us in this alloy prompted us to explore the possibility of use of Si-free VT-9 in sheet form for superplastic forming. An optimum thermomechanical processing produced a microstructure that resulted in an elongation of 1700 per cent at a fairly high deformation rate (2 X 10-3 set-1). Thus, the same aeroengine alloy (VT-9) can be used for superplastically formed airframe parts in the Si-free condition. The present study also shows that for making the forming process commercially viable, deformation temperature could be lowered by temporarily alloying with hydrogen in a particular concentration range (0.1 to 0.2 wt per cent).