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5296 |
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KCl-induced corrosion behavior of HVAF-sprayed Ni-based coatings |
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Esmaeil Sadeghimeresht / University West, Sweden Reza Jafari / Tarbiat Modares University, Iran Taghi Shahrabi Farahani/ Tarbiat Modares University, Iran Nicolaie Markocsan/ University West, Sweden Shrikant Joshi/ University West, Sweden |
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It is well known that the presence of K and Cl in biomass and waste-fired boilers can lead to KCl being present in deposits on superheater tubes and be responsible for their severe corrosion and premature damage. Thermal spray coatings are often proposed as a promising solution to protect components like the boiler tubes, which are routinely exposed to such aggressive environments. By virtue of the techno-commercial benefits that it provides as a direct outcome of its ability to cost-effectively deposit coatings virtually free of porosity and in situ formed oxides, the high-velocity air fuel (HVAF) process offers a particularly attractive approach. In the present work, the influence of KCl on the oxidation behavior of four HVAF-sprayed Ni-based coatings (NiCr, NiAl, NiCrAlY, and NiCrMo) has been investigated. The coatings were deposited onto specimens of 16Mo3 steel, a widely used boiler tube material. Corrosion tests were carried out in air at 600°C, with 0.1 mg/cm2 KCl being sprayed onto the samples prior to exposure. Uncoated substrates and an identical test environment without spraying of KCl salt were used as reference. SEM/EDS and XRD techniques were utilized to characterize the as-sprayed and corroded samples. The results showed that small additions of KCl significantly accelerate damage to the coatings. It was further revealed that the NiCrAlY coating is capable of forming a more protective oxide scale compared to other coatings. The prominent results from the above study will be presented and plausible mechanisms responsible for degradation of coatings also discussed. |