High-temperature flow characterization and microstructural evolution of Ti6242 alloy: Yield drop phenomenon

The hot deformation behavior of Ti6242 alloy holding a duplex microstructure (primary α+transformed β) was investigated. This was performed through hot compressing the experimental material at temperatures in the range of 1000 °C to 1100 °C, where the alloy was in its single-phase β region. The hot deformations were conducted under different strain rates of 0.003, 0.03 and 0.3 s−1 up to the true strain of 0.7. The microstructural examinations reveal newly recrystallized grains, which were formed in the vicinity of initial β grain boundaries under all testing conditions. A yield drop phenomenon is observed during straining at the strain rates of 0.003 and 0.03 s−1. However, a continuous yielding at early stages of deformation is characterized for the case of 0.3 s−1. In the former condition, the yield drop phenomenon is considered to mask the typical flow softening behavior, which is commonly attributed to the occurrence of dynamic recrystallization (DRX). A numerical approach was employed to determine the effective alloying element in dislocation pinning and yield drop. The results indicate that the hot deformation activation energy at the upper yield points varies between 222 and 301 kJ/mol. The activation energy at lower strain rates is found to be equal to that of Al diffusion in β titanium. The atom distribution maps reveal that the aluminum atoms in the form of atom clusters play an important role in yield drop phenomenon.