Hot corrosion behavior of NiCrAl-NiC sealing coating in thiochlorate

Abstract

To investigate the corrosion behavior of NiCrAl-NiC sealing coating in high-temperature molten salt environments，NiCrAl-NiC sealing coating was prepared using atmospheric plasma spraying technology. By measuring the weight loss of NiCrAl-NiC sealing coating，the dynamic changes of the coating were studied. The thermal corrosion behavior of NiCrAl-NiC sealing coating in a mixture of thiochlorate（75% Na2SO4 + 25% NaCl）at 650 ℃ was discussed using scanning electron microscopy（SEM），X-ray diffraction（XRD），laser confocal microscopy，and other methods. The results show that after 10 h of hot corrosion experiments，the NiCrAl-NiC sealing coating exhibites a rapid weight gain state，with a weight gain rate of 32.041 mg2·cm–4·h–1. After conducting a 20 h hot corrosion experiment，the coating experienced weight loss due to the detachment of the surface oxide film. After 30 h of hot corrosion，the growth of the facial mask on the coating surface covers the entire coating. The surface morphology of the coating is uniform，and the surface pores are reduced，which can play a good role in protecting the substrate. Under the protection of a complete oxide film，the mass change rate of the NiCrAl-NiC sealing coating after a 40 h hot corrosion experiment is 0.064 mg2·cm–4·h–1. Through XRD testing，it is found that the composition of the oxide film on the surface of the coating after hot corrosion is mainly NiO and NiCr2O4. During the hot corrosion process，the spinel structure of NiCr2O4 hinders the hot corrosion of the coating，which is the main reason for the slow corrosion process of the coating.

Keywords

• sealing coating
• nicral-nic
• hot corrosion
• corrosion mechanism