Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings. (March 2018)

• Record Type: Journal Article
• Authors: Sadeghimeresht, Esmaeil; Reddy, Liam; Hussain, Tanvir; Markocsan, Nicolaie; Joshi, Shrikant
• Is Part Of: Corrosion science. Volume 132(2018)
• Page Start: 170
• Page End: 184
• Publication Date: 2018-03
• Subjects: A. Thermal spray coating -- A. NiCr -- A. NiAl -- B. High-velocity air fuel (HVAF) -- B. Biomass-/waste-fired boiler -- C. Fireside corrosion; Corrosion and anti-corrosives -- Periodicals; 620.11223
• DOI: 10.1016/j.corsci.2017.12.033
• Languages: English
• ISSNs: 0010-938X

Abstract

Highlights: HVAF-sprayed coatings were exposed to HCl atmosphere with and without KCl deposit. Corrosion kinetics and mechanisms were studied. The corrosion of NiCr was based on "electrochemical mechanism" at the beginning. The corrosion mechanism was followed by "chlorine-active corrosion" process. The NiAl coating showed much higher corrosion resistance than the NiCr coating. Abstract: Chlorine-induced corrosion of HVAF-sprayed Ni21Cr and Ni5Al coatings was investigated in 5 vol.% O2 + 500vppm HCl + N2 with and without KCl at 600 °C up to 168 h. Both coatings were protective in the absence of KCl. With KCl, Ni21Cr degraded through a two-stage mechanism: 1) formation of K2 CrO4 followed by diffusion of Cl − through the oxide grain boundaries to yield chlorine and a non-protective oxide, and 2) inward diffusion of chlorine though defects in the non-protective oxide, leading to breakaway oxidation. Cl − /Cl2 could not diffuse through the protective alumina scale formed on Ni5Al, hence the corrosion resistance increased.