Effects of Ta on the high temperature creep behavior and deformation mechanism of a Ni-based single crystal superalloy

The effects of Ta on the high temperature creep behavior and deformation mechanism in a Ni-based single crystal (SX) superalloy were investigated at 1120 degrees C/137 MPa. Ta was regarded as an essential strengthening element of the gamma' phase in the alloy, and the results indicated that the increase of Ta prolonged the creep rupture life. In this work, the addition of Ta increased the volume fraction of the gamma' phase and narrowed the gamma channels, making the dislocation bowing out at the primary stage of creep more difficult. As creep continued, with a lower effective diffusion coefficient of alloying elements and larger gamma' raft thickness, the alloy with 6.5 wt% Ta addition was considered to possess the lower dislocation climbing rate, which reduced the minimum creep rate of the alloys. Subsequently, it was noted that the density of superdislocations in gamma' phase was clearly reduced with the increase of Ta. This was supposed to be the elevated Ta content in the alloy, which increased the lattice misfit and led to the formation of a denser dislocation network, thereby enhancing the interfacial strengthening effect and effectively preventing the cutting of superdislocations. The Ta effect on high-temperature creep was systematically summarized in this study, which was an important guideline for further composition design and optimization of Ni-based SX superalloys.