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

TiAl alloys are high-temperature structural materials with excellent comprehensive properties, and their ideal service temperature range is about 700-950 degrees C. High-Nb containing the Ti-46Al-8Nb-2.5V alloy was subjected to hot compression and subsequent annealing at 900 degrees 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 alpha(2) phase exhibited a typical (0001) alpha(2) basal plane texture after hot compression, while the beta(0) and gamma phases did not show a typical strong texture. Subsequent annealing at 900 degrees C of the hot-compressed samples resulted in significant phase transformations, specifically the alpha(2) -> gamma and beta(0) -> gamma phase transformations. After 30 min of annealing, the volume fraction of the alpha(2) 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 alpha(2) -> gamma phase transformation did not follow the Blackburn orientation relationship. Multiple crystal-oriented alpha(2) phases with nanoscale widths (20 similar to 100 nm) precipitate within the gamma phase during the annealing process, which means the occurrence of gamma -> alpha(2) phase transformation. Still, the gamma -> alpha(2) phase transformation follows the Blackburn orientation relationship.

Automated summary

TiAl alloys are high-temperature structural materials. The Ti-46Al-8Nb-2.5V alloy exhibited phase transformations and texture evolution during hot compression and subsequent annealing at 900 degrees C. The volume fraction of the alpha(2) phase decreased, and the gamma -> alpha(2) phase transformation occurred during annealing.