A Constitutive Model and Processing Maps Describing the High-Temperature Deformation Behavior of Ti-17 Alloy in the β-Phase Field

In the present study, the hot deformation behavior and microstructural evolution of Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy are examined at temperatures above the beta-transus (1153 K). The true stress-true strain curves obtained during hot compression testing (temperature region 1173-1373 K, strain rates from 10(-3) to 1 s(-1)) all exhibited steady-state flow behavior. The constitutive equations, considering applied strain as the main parameter, revealed that the apparent activation energy of the hot deformation process monotonously decreases with increasing applied strain. Its value obtained at a true strain of 0.6 is equal to 190 +/- 52 kJ mol(-1), which is close to the activation energy of self-diffusion in beta-Ti. Processing maps based on the dynamic materials model shows that the power dissipation efficiency generally decreases with increasing strain rate and applied strain. The domain with the peak efficiency of approximately 60% is located at a temperature of 1173 K and strain rate of 10(-3) s(-1). Furthermore, flow instabilities are observed only at strain rates higher than 0.1 s(-1) regardless of temperature. The obtained results can be correlated with the dynamic recovery process, representing a dominant mechanism for the hot deformation of Ti-17 alloy at beta-stable temperatures.