The role of microstructural stability on compression creep of fully lamellar γ-TiAl alloys

The microstructural stability of fully lamellar γ-TiAl alloys was studied under thermal exposure and creep conditions. Retention of metastable α2 during creep leads to dislocation generation, degradation of the lamellar microstructure and formation of recrystallized γ grains. Dynamic recrystallization is driven by the need to accommodate the volume increase associated with α2 loss. While loss of α2, recrystallization and coarsening of the lamellar microstructure are the main sources of tertiary creep under compression, the role of twinning as a recovery mechanism cannot be ruled out. The addition of C and Si has a substantial effect on reducing strain rates at all stages of creep by precipitation hardening. Stabilizing the microstructure prior to creep significantly improves creep properties by removing metastable α2, reducing the driving force for dynamic recrystallization and by the generation of precipitates in alloys containing C and Si.