Effect of microstructure on creep deformation of 45XD TiAl alloy at low and high stresses

A stabilized fully lamellar (stabilized FL) structure and a nearly lamellar (NL) structure were prepared by selected heat treatments in a Ti–45Al–2Nb–2Mn (wt.%) + 0.8 vol.% TiB2 (45XD) alloy. Tensile creep tests were performed at 760 °C using applied stresses of 138 and 207 MPa. The stabilized FL structure exhibits a lower minimum creep rate and a longer rupture life compared to the NL structure at both stress levels. More γ grains in the NL structure hasten dynamic recrystallization and the onset of grain boundary sliding (GBS), especially at high creep stress. GBS further accelerates microstructural degradation and increases the creep strain rate. However, dynamic recrystallization and GBS are greatly delayed in the stabilized FL structure. The finer lamellar spacing also decreases the creep strain rate. These results demonstrate that the γ grains have a great effect on microstructural instability and creep resistance of TiAl alloys.