Microstructural characteristics of the microphase Y-Ti2SC in nickel-based superalloys

• Microstructural characteristics of a minor Y-Ti2SC phase in a Ni-based superalloy.
• The interfacial structures between Y phase and MC carbide.
• Y phase can solutionize amounts of beneficial elements Hf and Zr during long-term annealing treatment.

The microstructural characteristics of microphase Y-Ti2SC in Ni-based superalloys have been studied by means of analytical transmission electron microscopy (TEM). In the standard heat treated samples, the Y phase always exhibits slab morphology forming either the sandwiched plate in MC or the side-by-side structure with MC. Moreover, the Y phase also maintains an definite crystallographic orientation relationship of [12‾10]Y//[11‾0]MC and (0 0 0 1)Y//(1 1 1)MC with the MC-type carbide. Stacking fault which results from the insertion of two Ti–C layers has been identified in the Y-Ti2SC phase. Combined with high resolution TEM (HRTEM) and first-principles calculations, we also determine the most stable interfacial structure between Y phase and MC carbide. Additionally, we find that Y-Ti2SC phase can solutionize amounts of beneficial elements Hf and Zr from the matrix during long-term annealing process, which leads to its lattice expansion. This solution phenomenon is detrimental for superalloys due to the consumption of the beneficial elements.