Quasi-in-situ investigation on microstructure degradation of a fully lamellar TiAl alloy during creep

Abstract

Microstructure degradation of a fully lamellar TNM alloy during creep has been investigated by using the quasi-in-situ creep tests, which were conducted at 750 °C under 250 MPa, for (1–5.4) % creep strain. The results indicated that the fully lamellar structure exhibited gradual microstructure degradation during creep. At the primary creep region, dynamic recrystallization of the γ phase occurred at the colony boundary and a massive proportion phase transformation occurred, these caused microstructure instability and a relatively large primary strain. Within the steady-state creep region, the steady creep strain rate was 8.89E-8 s−1. The fine (α2+γ) clusters with more interface provided obstacles for the dislocation movement because of α2 parallel decomposition. Moreover, the interfacial β0 phase precipitation was suppressed the α2 → γ transformation and remained the integrity and continuity of the lamellae structure, which was attributed to the steady-state creep resistance. At the tertiary creep region, many cavities nucleated at the colony boundary or γg/β0 phase boundaries due to the local stress concentration. The dynamic recrystallized of the γg area was extended and damaged the integrity of the fully lamellar structure. Moreover, the partial dissolution of α2 lamellae caused discontinuous lamellae and reduced the creep resistance. It concluded that microstructure stability has a strong influence on creep resistance.

Keywords

• TiAl alloy
• Hot isostatic pressing
• Microstructure
• Phase transformation
• Creep