Evaluation of the hot workability and deformation mechanisms for a metastable beta titanium alloy prepared from powder

Abstract

Ti-5Al-5V-5Mo-3Cr (Ti-5553) is a metastable beta titanium alloy and has excellent combined properties for extensive applications, but the hot workability and deformation mechanisms of powder metallurgy (PM) metastable beta titanium alloys are seldom reported. This study prepared the Ti-5553 alloy from powder using thermomechanical powder consolidation approach and investigated its hot deformation behaviour at 800 °C to 1150 °C and 0.001 s−1 to 10 s−1 through thermal physical simulation using the Gleeble®-3800 simulator. The hot processing map of the Ti-5553 alloy was successfully established based on the dynamic materials model. Various material characterization techniques, including optical microscopy (OM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD), were used to reveal the related deformation mechanisms. The calculated apparent activation energies for the Ti-5553 alloy are 323.8 kJ/mol in (α + β) region and 227.0 kJ/mol in β region, and four primary optimum efficiency domains and one instability domain are identified in the hot processing map. The deformation mechanisms for the Ti-5553 alloy processed at the different optimum efficiency domains are governed by various deformation mechanisms including α phase globalization, superplastic deformation, discontinuous dynamic recrystallization (DDRX) and dynamic recovery (DRV), while the deformation mechanism in the instability domain is mainly dominated by flow localization. Also, the Ti-5553 alloy in this study exhibits a wider processing window and lower deformation resistance than its counterpart and/or other similar metastable beta titanium alloys produced by ingot metallurgy (IM) approach, suggesting that the Ti-5553 alloy we produced from powder has better hot workability.