Recrystallization during Thermomechanical Processing of IMI834

Abstract

The microstructure development of the near-a titanium alloy IMI834 displaying an initial bimodal a + b microstructure has been characterized with respect to dynamic and static b recrystallization, through quantitative metallography. The investigation was supplemented by interrupted compression testing, to evaluate the applicability of fractional softening in the determination of static recrystallization kinetics for titanium alloys. Micrographs are presented that indicate that dynamic recrystallization occurred under test conditions (temperatures of 975°C, 1000°C, 1025°C, 1060°C, and 1100°C and strain rates of 0.01, 0.1, and 1 s -1 ), although complete grain refinement and homogeneity were only achieved following static recrystallization. Measurement obtained via image analysis revealed recrystallization kinetics that increased with temperature, for single-phase b predeformation microstructures (1060°C to 1100°C). However, bimodal a + b microstructures (1000°C to 1025°C) displayed more rapid recrystallization rates with decreasing temperature, which was attributed to a corresponding increase in a phase fraction. This increase yielded a more refined initial b grain size and an increase in favorable nucleation sites. In two-phase a + b microstructures (975°C) with secondary a in the b matrix, recrystallized grains could not be directly observed with optical microscopy. However, interrupted compression testing indicated that static recrystallization may be comparable to that observed at 1000°C. At all temperatures, an increasing strain rate accelerated recrystallization kinetics.

Effect of deformation inhomogeneity on the microstructure and mechanical properties of large-scale rib–web component of titanium alloy under local loading forming

“…9(d)). Similar behavior has been previously reported for near-␣ IMI834 alloy [20] and ␣ + ␤ TC11 alloy [21], which has been attributed to the dynamic recrystallization of ␣ phases [21].…”

Microstructure evolution of the transitional region in isothermal local loading of TA15 titanium alloy

“…For many two-phase titanium alloys, reported apparent activation energy above ␤ transus temperature is close to the activation energy of self-diffusion in ␤ phase [14][15][16], indicating dynamic recovery dominates ␤ working [17]. Though dynamic recrystallization is often observed in ␤ working, the volume fraction is generally small [17][18][19][20]. However, ␤ recrystallization was greatly accelerated in (␣ + ␤) working.…”

Behavior and modeling of high temperature deformation of an α+β titanium alloy

“…Higher strain rates in high temperature single ␤ phase field are often in favor of grain refinement because the rising dislocation substructures are not easily homogenized by self-diffusivity of titanium due to the insufficient recovery time [36]. The temperature 100-150 • C higher than the T ␤ was also reported beneficial to forging [5,6,37]. Thus, it can be concluded that the best forging parameter for ascast ATI 425 titanium alloy is at a strain rate greater than 0.1 s −1 at 1150 • C as shown in Fig.…”