The influence of stress levels on the creep behavior of Ti–42Al–6Nb–0.05Y2O3 alloy

The paper studied the creep behavior of Ti–42Al–6Nb–0.05Y2O3 alloy. Short-term creep tests were performed at the temperature range of 750–900 °C and the stress range of 100–300 MPa. The results reveal that the stress exponent varies from 1.85 to 5.01 when the creep stress increases from 100 to 300 MPa at 850 °C. Interface sliding and dislocation climb are the main creep mechanisms at 100 and 300 MPa, respectively. Formation of intergranular cracks is the major cause of the failure above 150 MPa. Instead, under 100 MPa, nucleation of cracks along lamellar interfaces plays a dominant role in the rupture. There is a critical temperature at which the apparent activation energy (Qc) increases suddenly. For the lamellar alloy, the increase of Qc has a close association with the dislocation movement in minority α2 laths. Below the activation energy transition temperature (AETT), the deformation of α2 phase is mainly governed by a→ type dislocations. Whereas above the AETT, the activation of 2c→+a→ type dislocations plays a dominant role. Moreover, the AETT at 300 MPa is determined to be 800–850 °C, whereas that at 100 MPa is 850–900 °C. There is an increase of AETT with the decrease of creep stress. At the low stress (100 MPa), the AETT depends on lattice resistance rather than long-range internal stress, since the flow stress may be less than Peierls-Nabarro force for slipping of 2c→+a→ type dislocations, resulting in a high AETT.