Effect of cobalt on micro-structural parameters of Ni-base single crystal superalloys

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 degrees C, Cr, Mo and W partitioned more into the gamma matrix; in contrast, Al and Ti partitioned into the gamma' precipitates. Increase in partitioning of Cr, Mo and W to the gamma phase resulted in an increase in the lattice parameter of gamma phase. Thus, lattice misfit of 0Co tend to more negative value than that of TMS-82 +.