LOW-CYCLE FATIGUE BEHAVIOR OF A PLASMA-SPRAYED COATING MATERIAL

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma-sprayed coating for oxidation and hot corrosion resistance. These coatings may also effect fatigue life of the superalloy substrate. As part of a larger program to understand the fatigue behavior of coated single crystals, fully reversed, total-strain controlled fatigue tests were run on a 'free standing' NiCoCrAlY coating alloy, PWA 276, at 0. 1 Hz. Fatigue tests were conducted at 650 degree C, where the NiCoCrAlY alloy has modest ductility, and at 1050 degree C, where it is extremely ductile, showing tensile elongation in excess of 100%. At the lower test temperature, deformation-induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two-phase microstructure. Fatigue life of the NiCoCrAlY was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, left bracket 001 right bracket -oriented PWA 1480 single crystals at 1050 degree C, but at 650 degree C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.