Challenges related to elevated temperature during creep in a PM-HIP Ti-6Al-4V alloy: the role of 〈a〉 dislocations and pyramidal 〈c+a〉 dislocations

In our current study, the impact of pre-creep treatment at 300°C and 560 MPa for 1000 h on the subsequent creep behavior and properties at an elevated temperature of 400°C have been examined. The characterization of the resulting creep deformation structure, including twins and dislocation morphology, was conducted using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Additionally, we have focused on the fine crystallization behavior of the α phase during creep, as well as the study and discussion of the 〈a〉 dislocations and pyramidal 〈c+a〉 dislocations. Our findings indicate that the creep life at 400°C and 560 MPa is significantly lower, by an order of magnitude, compared to samples without pre-creep treatment. During the pre-creep process at 300°C, 〈a〉 dislocations were found to be active. Furthermore, the creep temperature was observed to reduce the critical resolved shear stress (CRSS) of pyramidal 〈c+a〉 dislocations, leading to increased dislocation activity at 400°C compared to 300°C. However, a substantial number of 〈a〉 dislocations activated during the pre-creep process were unable to accommodate the subsequent heating process, resulting in extensive intergranular fractures. Simultaneously, during the creep process, the α phase underwent marginal fine grain formation in the form of continuous dynamic recrystallization (CDRX), with its internal fine grain promoted by pyramidal 〈c+a〉 dislocations assisting 〈a〉 dislocation to form dislocation locks. These findings offer valuable insights into potential deformation mechanisms and failure causes of PM-HIP Ti-6Al-4V alloy when subjected to elevated temperatures during creep.