Hot deformation behavior and processing maps of Ti–15Al–12Nb alloy

Abstract

The isothermal hot compression tests of Ti–15Al–12Nb alloy under wide range of strain rates (0.01–10.00 s⁻¹) and deformation temperatures (950, 1000, 1050, and 1100 °C) were carried out using Gleeble-3500 thermo-simulation machine. A constitutive equation represented as a function of temperature, strain rate and true strain was developed, and the hot deformation apparent activation energy is calculated to be about 453 kJ·mol⁻¹. By employing dynamic material model (DMM), the processing maps of Ti–15Al–12Nb alloy at various strains were established. Maximum efficiency of about 57 % for power dissipation is obtained at high temperature and low strain rate. Owing to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization (DRX) zone for metal material, the optimum processing conditions are selected as the temperature range of 1050–1100 °C and the strain rate range of 0.01–0.10 s⁻¹. Using transmission electron microscopy (TEM) studies, it is found that the dislocation density is directly associated with the value of processing efficiency. It is observed that when the processing efficiency is about 22 %, the dislocation density is reasonably large. The flow instability region occurs at strain rate of 10.00 s⁻¹ with cracks, which should be avoided during hot processing to obtain the required mechanical properties.