Crevice Formation on the Surface of the Simple and Ti-Modified Aluminide Coatings Under a Fused Na2SO4 Salt Film

Abstract

The hot-corrosion behavior of simple and Ti-modified aluminide coatings on nickel-based superalloy B-1900 was investigated. The sodium sulfate salt deposition rate was 1 mg/cm 2 for each 32 h at 900°C. Although the mass change data showed relatively more durability for the modified coatings, morphological characterization of the specimens and corrosion products revealed similar degradation mechanisms for all coatings studied. The base of a that pit developed during hot corrosion initiation had a low oxygen pressure and the pits grew perpendicular to the surface to create deep crevices. The growth and joining of these crevices caused large pieces of the coating to be lost, exposing the bare substrate to the fused salt at longer times. The initiation and advancement of the crevices are discussed and a mechanism is proposed to explain this type of hot corrosion morphology.