Strong and plastic near-α titanium alloy by Widmanstätten structure spheroidization

Abstract

The spheroidization of the Widmanstätten structure through thermo-mechanical processes, leading to the formation of fine recrystallized and sub-grain structures, is crucial for achieving a balance between strength and plasticity. This study systematically examined the spheroidization mechanism of the Widmanstätten structure in Ti-25Zr-4Al-1.5Mn (wt.%, TiZrAlMn) alloy under varying rolling temperatures and its influence on microstructure and mechanical properties. After rolling at 900 °C, the specimen exhibited a mixed morphology of Widmanstätten and Basket-weave structures, with a high yield strength of approximately 1038 MPa but low plasticity (∼5.2%). While the rolling temperature was reduced to 850 °C, the specimen exhibited refined prior-β grains, discontinuous grain boundaries and a small amount of equiaxed α grains, which collectively enhanced plasticity (∼12.4%) while preserving yield strength. As the rolling temperature further decreased, the dynamic recrystallization mechanism shifted from the discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX). Specimens rolled at 800 °C and 750 °C showed excellent strength-plasticity synergy, with yield strengths of 1070 MPa and 1110 MPa, respectively, and total elongations of 15% and 18%, respectively. The enhanced yield strength is attributed to both fine-grain and sub-grain strengthening. Furthermore, the lower degree of recrystallization in the 750-AC specimen preserved a relatively high dislocation density, offering additional strengthening. The favorable plasticity results from a combination of equiaxed α grains, “soft” barrier sub-grains, and a small number of twins. Additionally, the 750-AC specimen retained 6.4% of the fine β grains and the weak basal texture. These characteristics contribute to the enhanced plasticity. Therefore, 750 °C is the optimal rolling temperature for achieving the best strength-plasticity synergy in the hot-rolled TiZrAlMn alloy. These findings demonstrate that selecting the appropriate temperature during thermomechanical processing to optimize recrystallized grains and sub-grain content ensures excellent plasticity at high yield strength. This offers valuable guidance for developing near-α Ti alloys with superior mechanical properties.