States-of-the-arts of dynamic recrystallization behavior of Ti alloys and its implications on the thermo-mechanical processing: a critical review

Renowned for their exceptional specific strength and excellent corrosion resistance, titanium (Ti) alloys are extensively utilized across numerous industrial sectors. Thermo-mechanical processing (TMP) is crucial for optimizing their engineering performance to meet the specific demands for practical application. One of the most essential metallurgical focuses during TMP is the occurrence of dynamic recrystallization (DRX), which is crucial for microstructure refinement. Recent studies revealed that the DRX of Ti alloys involves distinct mechanisms and their mutual interactions, rendering the TMP design difficult. This review systematically examines the different DRX mechanisms responsible for Ti alloys subjected to TMP, including discontinuous DRX (DDRX), continuous DRX (CDRX), geometric DRX (GDRX), and twin-assisted DRX (TDRX) under various TMP conditions. Moreover, the effects of key TMP parameters such as deformation temperature, strain rate, and strain level on the DRX behavior in Ti alloys during TMP are discussed. Meanwhile, the effects of initial microstructure, second-phase particles, and deformation modes on the DRX behavior of Ti alloys are also assessed. Besides, the impacts of conventional TMP techniques are evaluated on the DRX behavior in Ti alloys, such as surface modification approaches and material joining processes. Moreover, recent advancements in the numerical modeling and multi-scale simulation methods for predicting DRX behavior in Ti alloys are summarized. Finally, challenges and future research directions including advanced characterization and machine learning enabled TMP design of Ti alloys are proposed and discussed.