Development of Erosion-Corrosion-Resistant Cold-Spray Nanostructured Ni-20Cr Coating for Coal-Fired Boiler Applications
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M. Kumar, H. Singh, N. Singh, N.M. Chavan, S. Kumar, and S.V. Joshi (Submitted January 27, 2015; in revised form April 9, 2015) The erosion-corrosion (E-C) behavior of a cold-spray nanostructured Ni-20Cr coating was studied under cyclic conditions in a coal-fired boiler. This study was done for 15 cycles (1500 h), in which each cycle comprised 100 h of heating in the boiler environment, followed by 1 h of cooling under ambient air conditions. The E-C extent was evaluated in terms of thickness loss data of the samples. The erodedcorroded samples were characterized using XRD, SEM/EDS, and x-ray mapping analyses. The nanostructured coating offered excellent E-C protection to boiler tube material (SA 516 steel) under harsh live conditions of the boiler. This E-C resistance offered by investigated coating may be attributed to the presence of protective NiO and Cr2O3 phases in its oxide scale and its superior as-sprayed microhardness.
Keywords
boiler steel, cold-spray, erosion-corrosion, nanostructured coating, Ni-20Cr
1. Introduction Rupturing of the boiler tubes used in superheaters of the Indian coal-fired boilers under high-temperature conditions is a serious threat to economy of thermal power plants. This contributes to 50 to 75% arrest time of the boilers (Ref 1, 2). Due to these problems, protection of the boiler tubes demands critical attention of researchers to increase the service lives of the boilers (Ref 3-6). For this protection, surface coatings have been investigated, which have been deposited by several techniques. Among the different surface modification techniques, thermal spraying is one of most technically and industrially viable techniques, which can be used to deposit coatings on the boiler tubes (Ref 7). The thermal This article is an invited paper selected from presentations at the 6th Asian Thermal Spray Conference (ATSC 2014) and has been expanded from the original presentation. ATSC 2014 was held in Hyderabad, India, November 24-26, 2014, and was organized by the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI) and the Asian Thermal Spray Society. M. Kumar and H. Singh, School of Mechanical, Materials & Energy Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab, India; N. Singh, Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab, India; and N.M. Chavan, S. Kumar, and S.V. Joshi, International Advanced Research Centre for Powder Metallurgy & New Materials (ARCI), Hyderabad 500005, India. Contact e-mail: manojks@ iitrpr.ac.in.
Journal of Thermal Spray Technology
sprayed coatings offer many advantages such as on-site applications, versatility, and relatively less impact on the environment, in comparison with other surface modification techniques (Ref 8-11). Recently, a relatively younger thermal spraying process, named cold spraying, has emerged as a promising coating process (Ref 12-14), which gives several advantages such as lower porosity, high density, and high performance coatings for several applications (R
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