Yield point phenomena in TIMETAL 125 beta Ti alloy

Abstract

The yield point phenomena in TIMETAL 125 beta-Ti alloy was studied using hot compression tests in the temperature range of 680–880°C and at strain rates of 0.001–1s−1. The yield drop increased with decreasing temperature or increasing strain rate. Indeed, the yield point was sharper at high strain rates and low temperatures. The Mo equivalent was taken as a compositional index to determine the influence of chemical composition on the yield point phenomenon. There was a direct relationship between the yield drop and Mo equivalent at different deformation conditions. The total thermal–mechanical energy (Q) for yielding was determined using the power-law constitutive equation. A second-order polynomial equation was used to establish a relationship between Q and the deformation temperature. The contributions of mechanical and thermal energies (QM and QT) to Q were determined based on a semi-empirical power-law equation. The developed model showed that there is a direct relationship between the amount of mechanical energy and the yield drop. It was also found that the ratio of thermal to the total energy (QT/Q) could increase from 0.2 to more than 0.8 by increasing temperature and decreasing strain rate.