Isothermal oxidation and hot corrosion behaviors of diffusion aluminide coatings deposited by chemical vapor deposition

Aluminization has been employed on superalloys to form dense and adhesive alumina surface layers to prolong their service life at high temperature. A chemical vapor deposited aluminizing process had been employed to deposit nickel aluminide coatings on the nickel-based single-crystal superalloys. The kinetics behavior, phase evaluation, microstructure and chemical composition of the aluminide coatings after oxidation and hot corrosion tests were studied in detail. After isothermal oxidation test, a dense and protective α-Al2O3 surface layer is formed on the aluminized superalloy and phase transformation reactions occur in the aluminide layer and interdiffusion zone. The inward diffusion of Al element toward the substrate and formation of micro-pores in the interdiffusion zone are probably the main degradation modes of the aluminide coating. Corrosive medium including of mixed of aviation fuels and artificial seawater has not serious deterioration of aluminide coating after hot corrosion at 1123 K, although large of micro-pores and few of microcracks are observed within the aluminide layer, and the typical morphology of the aluminide layer becomes corse and disorder to a certain extent.