Deformation mechanism diagram of a Ti–2.5Zr–2Al titanium alloy forged in the α+β region and grain refinement

The α+β forging is a key pass for the hot forging process of a Ti-2.5Zr–2Al titanium alloy. In this paper, the hot deformation mechanism of a Ti-2.5Zr–2Al titanium alloy was obtained by the double-cone compression test, which provides a theoretical basis for designing reasonable α+β forging process to obtain ideal microstructure. A wide range of gradient strains and corresponding microstructure were obtained by using the double-cone compression test. The double-cone compression process was simulated by the finite element software. Electron backscatter diffraction technique (EBSD) and transmission electron microscope (TEM) were used to characterize the deformed microstructure of the double-cone specimen. The hot deformation mechanism diagram in the strain range of 0.2–1.2 and the temperature range of 700 °C–850 °C was constructed. At 800 °C, in the low strain region (<0.476), the main deformation mechanism is dynamic recovery (DRV), and continuous dynamic recrystallization (CDRX) begins to occur. In the medium strain region (0.476–1.006), the deformation mechanism is mainly CDRX, accompanied by a small amount of the deformation bands (DBs). Nevertheless, in the large strain region (>1.006), a large number of the DBs occur. The ultra-fine grains with an average size of about 0.46 μm were obtained according to the hot compression under the strain of about 0.717 at 800 °C. The ultra grain refinement mechanism during hot deformation was summarized.