Effect of initial alpha lamellar thickness on deformation behavior of a near-α high-temperature alloy during thermomechanical processing

The hot deformation behavior of a near-α high-temperature Ti-5.4Al-3.7Sn-3.3Zr-0.5Mo-0.4Si alloy with initial alpha lamellar thicknesses from 1 µm to 10 µm was investigated by conducting a series of isothermal hot compression tests. The effect of initial alpha lamellar thickness on the flow behavior, apparent activation energy, strain-rate sensitivity and microstructure evolution under different hot deformation conditions were analyzed based on the experimental data. The results show that the flow stress of the alloy display an overall decreasing trend with the increasing of initial alpha lamellar thickness for a given temperature and strain rate. The peak stress and the apparent activity energy during thermomechanical processing were quantitatively described as a function of alpha platelet thickness based on the Hall-Petch behavior. According to various deformation mechanisms, the variations of apparent activity energy and strain rate sensitivity associated with different initial alpha lamellar thicknesses were calculated and analyzed for the alloy, which indicate that the thin initial alpha lamellar microstructure with higher apparent activation energy and strain rate sensitivity shows easier occurrence of dynamic globularization than thick initial alpha lamellar microstructure. Furthermore, the characterization of microstructure evolution for the alpha lamellae with different thicknesses were observed and the thin lamellae was more easily fragmented into fine α phase while most of the thick lamellae were elongated or buckled at same processing conditions.