Effect of Cobalt on micro-structural parameters, such as the lattice misfit and partitioning behaviors of alloying elements, of Re-bearing Ni-base single crystal superalloys have been investigated. The second-generation single crystal superalloys, TMS-82+(Ni-7.8Co-4.9Cr-1.9Mo-8.7W-5.3Al-6.0Ta-2.4Re-0.1Hf, in mass%), was compared to a Co-free (0Co) alloy which had the same chemical composition as TMS-82+ except that Co was removed.
The lattice misfit of 0Co alloy was found to be more negative value than that of TMS-82+ at any temperature. Additionally, when 0Co alloy was equilibrated at 1100°C, Cr, Mo and W partitioned more into the γ matrix; in contrast, Al and Ti partitioned into the γ′ precipitates. Increase in partitioning of Cr, Mo and W to the γ phase resulted in an increase in the lattice parameter of γ phase. Thus, lattice misfit of 0Co tend to more negative value than that of TMS-82+.