Effect of pre-oxidation treatment on the hot corrosion behavior of pack-cemented aluminide coatings on the K438 alloy in salt mixture

• Published in: Corrosion communications Vol. 5; pp. 1 - 13
• Main Authors: Li, Qing, Yuan, Xiaohu, Li, Dingjun, Song, Peng, Li, Zhenhua, Huang, Taihong, Wen, Lei, Liang, Yuwei, Lu, Jiansheng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2022; Elsevier
• Subjects: Alloy; Aluminide coatings; Hot corrosion; Pre-oxidation; TEM; Hot corrosion; Aluminide coatings; Pre-oxidation; Alloy; TEM
• ISSN: 2667-2669; 2667-2669
• DOI: 10.1016/j.corcom.2021.10.006

•The rod-like precipitate phase of CrS was mainly formed in the substrate of the two coatings after hot corrosion test.•The sulfur was concentrated around Cr2O3 and corrosion cavities were observed in the oxide scale formed on the as-received aluminide coatings.•Pre-oxidation could improve the hot corrosion resistance of the aluminide coatings and outward diffusion of Ti was inhibited by pre-oxidation. The hot corrosion test was carried out for the pack-cemented aluminide coatings on the K438 Ni-based alloy containing 50 wt.% NaCl + 50 wt.% Na2SO4 salt mixture at 1050 ℃ in air. This study aimed to add the salt mixture only once to the surface of the as-received and pre-oxidation aluminide coatings to investigate the influence on the subsequent and long-term hot corrosion behavior of coatings. The specimens were studied using a combination of gravimetry and several surface-analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), focused ion beam (FIB), and transmission electron microscopy (TEM). The oxide scale on the surface of the pre-oxidation aluminide coating was denser and maintained better integrity after hot corrosion. The rod-like precipitate phase of CrS was mainly formed in the substrate of the two coatings. The sulfur was concentrated around Cr2O3 and corrosion cavities were observed in the oxide scale on the surface of the as-received aluminide coatings. Furthermore, a schematic mechanism of the hot corrosion process of the aluminide coatings was proposed, emphasizing the effect of pre-oxidation.