Effect of Prior Cyclic Oxidation on the Creep Behavior of Bare and Pt-Aluminide Coated Directionally Solidified CM-247LC Alloy

摘要

Bare and Pt-aluminide coated creep specimens fabricated out of a directionally solidified Ni-based superalloy, CM-247 LC, were subjected to cyclic oxidation at 1100°C in air for 750 h and their creep properties were evaluated at 980°C and 220 MPa. It was observed that cyclic oxidation exposure causes degradation in the creep behavior of both bare and coated superalloy leading to increase in the minimum creep rate and decrease in time to fracture. The deterioration in creep behavior of the bare alloy can be ascribed to the surface damage as well as microstructural degradation induced in the alloy during cyclic oxidation and the associated variation in the rafting behavior during creep testing. The application of the coating prevents surface damage in the alloy during oxidation. However, deterioration in the substrate microstructure during thermal exposure adversely affects the creep behavior of the coated alloy.