On the formation of adiabatic shear bands in titanium alloy Ti17 under severe loading conditions

Abstract

For metallic materials, fabrication processes (e.g. machining and forging) may involve important strain rates and high temperatures. For such severe loading conditions, the development of damage is often associated with the formation of Adiabatic Shear Bands (ASB). In this work, the impact of loading conditions (strain rate, temperature) on the formation of ASB in a beta rich titanium alloy (Ti17) is investigated. In this perspective, uniaxial compression tests have been conducted on cylindrical samples with a Gleeble-3500 thermo-mechanical simulator at temperatures ranging from 25◦C to 800◦C and strain rates ranging from 0.1 to 50 s−1 with axial strains of approximately 50 %. According to the experimental results, the flow curves exhibit hardening from 25◦C to 550◦C and softening from 600◦C to 800◦C. When looking at the evolution of flow stress, the strain rate sensitivity is found to increase significantly with increasing temperatures. Also, adiabatic shear bands are preferably observed for high strain rates and low temperatures. The formation of ASB thus seems to be quite dependent on the evolution of the strain rate sensitivity of Ti17. Finally, metallographic observations have been carried out to better understand the process leading to the formation of ASB. Such observations demonstrate that the average width of ASB increases with increasing temperatures and decreasing strain rates. However, such observations do not allow for identifying whether some specific microstructural transformations (e.g. recrystallization or phase transformation) could explain the formation of ASB or not.