Hot Deformation Behavior and Microstructure Evolution of a Novel Near-α Titanium Alloy with Initial Lamellar Microstructure During Hot Compression

Abstract

The hot deformation behavior and microstructure evolution of a novel near-α Ti65 titanium alloy with an initial lamellar microstructure were investigated by isothermal compression. Compression tests were conducted at 950–1010 °C in the α + β phase region and 1050–1110 °C in the β phase region, with strain rates of 0.01–10 s−1 and deformation amounts of 30–75%. The flow behavior, strain-compensated Arrhenius constitutive model, processing map and microstructural evolution were systematically analyzed. The results indicate that the flow stress decreases with increasing temperature and decreasing strain rate, while flow softening is more pronounced in the α + β region than in the β region. The apparent activation energies are 1050.27 kJ/mol for the α + β region and 203.51 kJ/mol for the β region, indicating distinct deformation mechanisms. The established constitutive models exhibit high prediction accuracy, with R and AARE values of 0.98 and 5.97% in the α + β region and 0.99 and 4.29% in the β region, respectively. Processing-map analysis identifies two instability domains at high strain rates: 990–1020 °C/3.5–10 s−1 in the upper α + β region and 1060–1110 °C/1.65–10 s−1 in the β region. Microstructural observations reveal that dynamic spheroidization of lamellar α dominates deformation in the α + β region, whereas dynamic recovery accompanied by limited β dynamic recrystallization occurs in the β region. Increasing deformation amount at 980 °C and 0.01 s−1 promotes α-lamella fragmentation, spheroidization, grain refinement and texture weakening. The maximum pole density decreases to 6.23 mrd at a high deformation amount. By directly correlating strain-dependent processing-map characteristics with quantitative microstructural and crystallographic evolution, this work provides a microstructure-based basis for optimizing the hot-working window of Ti65 alloy with an initial lamellar microstructure.