Impact of the initial microstructure and the loading conditions on the deformation behavior of the Ti17 titanium alloy

In this work, the impact of the microstructure and the loading conditions on the mechanical behavior of a beta-rich Ti17 titanium alloy is investigated. For this purpose, two different initial microstructures are considered : (i) a two-phase lamellar alpha + beta microstructure and (ii) a single-phase equiaxed beta-treated microstructure. First, compression tests are performed at different strain rates (from 10(-1) to 10 s(-1)) and different temperatures (from 25 to 900 degrees C) for both microstructures. Then, optical microscopy, scanning electron microscopy, EBSD and X-ray diffraction analyses of deformed specimens are carried out. Whatever the loading conditions are, the flow stress of the as-received alpha + beta Ti17 is higher than that of the b-treated Ti17. Also, because of a higher strain-rate sensitivity, the beta-treated Ti17 is less prone to shear banding. At low temperatures (i.e., T <= 450 degrees C), the deformation behavior of both the as-received alpha + beta and the beta-treated Ti17 is controlled by strain hardening. For the b-treated Ti17 alloy, martensitic transformation is systematically detected in this temperature range. The softening behavior of the as-received alpha + beta Ti17 observed at high temperatures is due to the joint effect of dynamic recrystallization, dynamic transformation, adiabatic heating and morphological texture evolution. For the beta-treated Ti17 alloy, when the temperature exceeds 700 degrees C, stress-strain curves display a yield drop phenomenon, which is explained by dynamic recrystallization.