Two-phase (α þ β) titanium alloys are widely used to made critical parts in aerospace equipment. [1-5] Usually, these critical components are manufactured by hot forming technologies, such as hot forging and heat treatment. According to the design requirements, various microstructures, including equiaxed, globular-lamellar, and basket-weave microstructures, can be obtained in this alloy by different hot forming technologies. [6-9] In general, the alloys with lamellar microstructures have the excellent fracture toughness and creep resistance, [10,11] and those with equiaxed microstructures possess good mechanical properties, especially the fatigue properties, [12,13] and the presence of coarse grains or microtextured regions in equiaxed microstructures will weaken the fatigue crack initiation resistance. [14-18] The hot workability and microstructures of titanium alloys are greatly impacted by the forming parameters, such as deformation amount, strain rate, and temperature. [19-23] Therefore, the comprehensive researches on the relationships among processing, microstructure, and properties of titanium alloys are highly necessary. [24-26] Recently, the evolutions of lamellar α microstructure in titanium alloys are investigated by some researchers. [27-29] Abbasi et al., [30] Jia et al., [31] Wang et al., [32] and Long et al. [33] investigated the dynamic or static globularization kinetics of different titanium alloys with lamellar microstructures. For titanium alloys, the dynamic or static recrystallization of α phases is traditionally called dynamic or static globularization of α phases. The dynamic recrystallization is featured by the nucleation and growth of new grains simultaneously during hot deformation. [34-37] Li et al. [38] and Shell and Semiatin [39] revealed that the dynamic spheroidization easily occurs in the initial thin lamellar α microstructure, whereas Semiatin et al. [40] predicted that the dynamic spheroidization initiates at the strain of 1.0 and completes at the strain of about 2.5 for the Ti-6Al-4V alloy. Lin et al. [41] revealed that the dynamic softening behavior of a typical two-phase (α þ β) titanium alloy (Ti-5Al-5Mo-5V-1Cr-1Fe or TC18 alloy) with thick lamellar microstructures is induced by dynamic globularization of lamellar α phases, and the globularization of lamellar α phases has an obvious influence on the hot workability and mechanical properties of titanium alloys. Except for the dynamic globularization, the static globularization can also enhance the spheroidization rate of lamellar α phases during heat treatment. Lin et al. [42] found that the spheroidization of α grains is accelerated with increasing solution temperature during the solution treatment of TC4 alloy with initial basket-weave microstructures. Also, the phase transformation behaviors and precipitation features of secondary phase of a solution-treated TC4 alloy during high-temperature aging were studied. [43] Ahmed et al. [44]
