Recrystallization during Thermomechanical Processing of IMI834

Abstract

The microstructure development of the near-α titanium alloy IMI834 displaying an initial bimodal α + β microstructure has been characterized with respect to dynamic and static β 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 β predeformation microstructures (1060 °C to 1100 °C). However, bimodal α + β microstructures (1000 °C to 1025 °C) displayed more rapid recrystallization rates with decreasing temperature, which was attributed to a corresponding increase in α phase fraction. This increase yielded a more refined initial β grain size and an increase in favorable nucleation sites. In two-phase α + β microstructures (975 °C) with secondary α in the β 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.