Analysis and comparison of the instability regimes in the processing maps generated using different instability criteria for Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

The isothermal compression tests of titanium alloy Ti–6.5Al–3.5Mo–1.5Zr–0.3Si with the initial Widmanstätten-type microstructure were conducted at temperature and strain rate ranges of 750–1100 °C and 0.001–10 s−1, respectively, on a THERMECMASTOR-Z hot working simulator. The flow stresses of the Ti-alloy in different conditions are obtained. The processing and instability maps based on the Prasad, Murty and Malas criteria were constructed. Through comparison and analysis of the processing maps, instability maps, and the microstructures of the deformed specimens in different conditions, it is found that: (1) the instability regimes that should be avoided are 750–880 °C, 0.004–10 s−1, 880–980 °C, 0.3–10 s−1, and 980–1100 °C, 1.8–10 s−1, and the preferable processing regimes are 790–880 °C, 0.001–0.004 s−1 and 880–1100 °C, 0.001–0.1 s−1; (2) the predicted results based on the Murty and Prasad criteria are not much different, but they are quite different from the results predicted by the Malas criterion; (3) from prediction accuracy perspective, the Murty criterion is slightly better than the Prasad criterion, and both of them are better than Malasʹ one.