Elevated Temperature Corrosion Studies of AlCrN and TiAlN Coatings by PAPVD on T91 Boiler Steel
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JMEPEG (2017) 26:5481–5494 DOI: 10.1007/s11665-017-2972-4
Elevated Temperature Corrosion Studies of AlCrN and TiAlN Coatings by PAPVD on T91 Boiler Steel Lucky Goyal, Vikas Chawla, and Jasbir Singh Hundal (Submitted October 26, 2016; in revised form August 2, 2017; published online October 2, 2017) The present investigation discusses the hot corrosion behavior of AlCrN and TiAlN nano-coatings on T91 boiler steel by PAPVD process subjected to molten salt of Na2SO4-60%V2O5 at 900 °C for 50 cycles. Surface and cross-sectional studies were performed by AFM, SEM/EDS and XRD techniques to understand the corrosion kinetics and mechanism. T91 bare boiler steel as well as TiAlN-coated specimen has shown higher internal oxidation as well as weight gain. The better corrosion resistance of AlCrN-coated specimen has been observed by virtue of higher availability of Cr and Al in the oxide scale as well as adherent and dense coating. The betterment of AlCrN coating can be attributed to low internal oxidation as well as movement of Cr and Al toward oxide scale to form protective corrosion barriers. Keywords
hot corrosion, nano-coatings, PAPVD, SEM/EDS
1. Introduction Degradation of materials at elevated temperature has been reported to be a precarious issue in various industrial operations as in steam generators, turbines, engines and industrial incinerators, etc. (Ref 1). Boiler tubes of power plants have been exposed to elevated temperature degradation. Attempts have been initiated, and methods have been recommended to curb the high-temperature degradation of materials (Ref 2). The boiler components have frequent failures by virtue of overheating, erosion, corrosion or other factors (Ref 3). High-temperature corrosion of structural materials in coal-fired boilers, in particular of heat exchanger tubes, has become a very important issue in the design and operation of thermal power plants and is recognized as one of the main causes of down time in these installations (Ref 4). S and V are common impurities present in the fuel used in boilers of coal-fired plants, and Na is ingested from air (Ref 5). At high temperature, these species are reported to react with each other and form low melting eutectic mixture of Na2SO4-60%V2O5, which directs to cause the corrosion of materials (Ref 6). Hot corrosion resistance of the metals and alloys used in high-temperature regions of power plants can be improved by the application of protective coatings (Ref 6). Reportedly, various types of protective coatings have been used and their betterment at various applications has been available in the reported literature (Ref 1). The primary aim of the coating/surface treatment is to produce a stable, slow-growing surface oxide capable of providing a barrier between the coated alloy and the environment (Ref 7). Reportedly, nano-structured Lucky Goyal and Vikas Chawla, I. K. Gujral Punjab Technical University, Kapurthala, Punjab, India; and Jasbir Singh Hundal, Maharaja Ranjit Singh Punjab Technical University, Bathinda, Punjab, India. Contact e-mail: lu
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