Application of aluminum diffusion coatings to mitigate the KCl-induced high-temperature corrosion

Abstract

Pack cementation was used to produce Fe1−xAl and Fe2Al5diffusion coatings on ferritic-martensitic steel P91 and a Ni2Al3diffusion coating on pure nickel. The performance of diffusion coatings against high-temperature corrosion induced by potassium chloride (KCl) was evaluated by exposing the samples at 600 °C for 168 h in static lab air under KCl deposit. In addition, a salt-free experiment was performed for comparison. Microstructure, chemical and phase composition of the samples were analyzed with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD) before and after the exposures. It was found that all the diffusion coatings formed protective oxides under salt-free exposure in air. Under the salt deposit, Fe1−xAl showed local failure while on large parts of the sample a protective layer had formed. Fe2Al5was attacked over the entire surface and the dominant mode of attack was selective aluminum removal. Ni2Al3showed excellent performance and no sign of attack was observed anywhere on the sample.