Hot deformation and microstructure evolution of TiZrAlHf Ti-based medium entropy alloy

Abstract

In order to optimize the hot working window of the novel TiZrAlHf Ti-based medium entropy alloy, the thermal deformation characteristics and microstructural evolution during thermal deformation were investigated by using hot compression simulation experiments and microstructural characterization methods. The results show that the microstructure of TiZrAlHf alloy ingot primarily consists of lamellar α phase and Widmanstatten structure at grain boundaries. The β transformation temperature (Tβ) of TiZr-AlHf alloys is 895 ℃. Within the α/α+β phase region (700-850 ℃) during deformation, an instability zone is identified within the temperature range of 700-750 ℃. The thermal deformation activation energy in the α/α+β phase region is 827.514 kJ/mol, the deformation microstructure predominantly comprised globular α phase, with the softening mechanism involving the globularization of lamellar α phase. When the alloy is deformed in the β phase region (900-1100 ℃) test process range, there is no instability zone in hot processing map, all samples remain intact without any signs of cracking. Consequently, free forging can be employed for roughing and finish forging operations. The hot deformation activation energy is 113.909 kJ/mol, and the deformation microstructure is mainly elongated β grains and acicular martensite α'. The softening mechanism in the region is dynamic recovery. The underlying nature of both deformation softening mechanisms lies in the proliferation of dislocations, slip and the evolution of cellular structures.

Keywords

• ti-based medium entropy alloy
• hot deformation
• microstructural evolution
• α phase globula-rization
• dynamic recovery