Microstructure Evolution of the Ti-46Al-8Nb-2.5V Alloy during Hot Compression and Subsequent Annealing at 900 °C.

Abstract

TiAl alloys are high-temperature structural materials with excellent comprehensive properties, and their ideal service temperature range is about 700-950 °C. High-Nb containing the Ti-46Al-8Nb-2.5V alloy was subjected to hot compression and subsequent annealing at 900 °C. During hot compression, work-hardening and strain-softening occurred. The peak stresses during compression are positively correlated with the compressive strain rates and negatively correlated with the compression temperatures. The α2 phase exhibited a typical (0001)α2 basal plane texture after hot compression, while the β0 and γ phases did not show a typical strong texture. Subsequent annealing at 900 °C of the hot-compressed samples resulted in significant phase transformations, specifically the α2 → γ and β0 → γ phase transformations. After 30 min of annealing, the volume fraction of the α2 phase decreased from 39.0% to 4.6%. The microstructure characteristics and phase fraction after 60 min of annealing were similar to those after 30 min. According to the calculation of Miller indexes and texture evolution during annealing, the α2 → γ phase transformation did not follow the Blackburn orientation relationship. Multiple crystal-oriented α2 phases with nanoscale widths (20~100 nm) precipitate within the γ phase during the annealing process, which means the occurrence of γ → α2 phase transformation. Still, the γ → α2 phase transformation follows the Blackburn orientation relationship.