Coating-associated microstructure evolution and elemental interdiffusion behavior at a Mo-rich nickel-based superalloy

Substituting Mo for W in superalloy (SA) design can effectively decrease the alloy density and improve thrust-to-weight ratio of aero engines. However, the outer diffusion of Mo was proved to deteriorate the oxidation resistance and mechanical properties of the coated alloys. In this paper, single phase Ni[sbnd]Al alloys (Ni/Al = 50/50 and 60/40, marked as Ni[sbnd]50Al and Ni[sbnd]40Al) and two-phase Ni[sbnd]Al alloys (Ni/Al = 70/30, marked as Ni[sbnd]30Al), which always worked as coatings for superalloy, were prepared and employed to form diffusion couples with a Mo-rich superalloy. The average effective interdiffusion coefficients were measured to describe the interdiffusion behavior, and the Ni-30Al/SA diffusion couple showed the lowest average effective interdiffusion coefficients for all elements. Besides, distinct congregation of refractory elements (Mo, Cr, Re, Ta) was observed at the superalloy side in Ni-50Al/SA and Ni-40Al/SA diffusion couples. The different interface phase structure was thought to cause the results, and the initial coating compositions – interface microstructure – elemental interdiffusion behavior relationship was established. This should provide insight into the coat-superalloy interaction and usefully guide designing suitable coats for Mo-rich single crystal superalloy.