Performance of Diffusion Aluminide Coatings Applied on Alloy CF8C-Plus at 800 °C

The cost effective, austenitic stainless steel CF8C plus is an attractive alloy for massive cast structures such as steam turbine casings. The microstructure stability and creep strength of this alloy are better than commercial high-performance heat-resistant steels such as NF709 and Super 304H, and are comparable to the Ni-based superalloy Inconel 617. The oxidation resistance of the alloy in atmosphere rich in water vapor is however insufficient at T>800°C, and the use of diffusion aluminide coatings is considered for potential high temperature applications.

The thermal stability and protectiveness of coatings applied on the CF8C plus substrate by pack cementation and slurry process were investigated in air + 10% H₂O environment at 800°C. Further, the coating effect on the fatigue life of the alloy was assessed via low-cycle-fatigue experiments.