Effects of Co on microstructure evolution of a 4th generation nickel-based single crystal superalloys

Microstructure, Mechanical Properties and Thermal Stability of Ni-Based Single Crystal Superalloys with Low Specific Weight

“…The calculated δ of 3Ta6.4Al1Ti, 0Ta6.4Al2Ti, 3Ta6Al1Ti, and 0Ta6Al2Ti alloys at 1050 • C are −0.37%, −0.3%, −0.27%, and −0.26%, respectively. Generally, high absolute values of the lattice misfit between the γ and γ phases indicate relatively high interphase boundary energy, which is responsible for quick coarsening/rafting during thermal exposure [38,41,42]. In the four alloys, both 6 wt.% Al alloys have lower absolute values of lattice misfit (~0.26%) than that in the 6.4 wt.% Al alloys, which is consistent with the experimental observation of relatively slow coarsening/rafting.…”

“…Coarsening is not only influenced by the lattice misfit of the alloy but also requires elemental diffusion in the γ phase, which might be slowed down by the addition of Ta. To maintain consistency with the experimental observation that replacing 1 wt.% Ti with 3 wt.% Ta is beneficial to the stability of the shape and size of γ phase during thermal exposure, replacing 1 wt.% Ti with 3 wt.% Ta increases the Re and Mo partitioning into the γ phase, which leads to a slow diffusion rate of the γ phase due to both Re and Mo being slow diffusers [42,43].…”