High-Temperature Exposure Studies of HVOF-Sprayed Cr 3 C 2 -25(NiCr)/(WC-Co) Coating

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Harpreet Singh, Manpreet Kaur, and Satya Prakash (Submitted April 15, 2015; in revised form May 2, 2016) In this research, development of Cr3C2-25(NiCr) + 25%(WC-Co) composite coating was done and investigated. Cr3C2-25(NiCr) + 25%(WC-Co) composite powder [designated as HP2 powder] was prepared by mechanical mixing of [75Cr3C2-25(NiCr)] and [88WC-12Co] powders in the ratio of 75:25 by weight. The blended powders were used as feedstock to deposit composite coating on ASTM SA213-T22 substrate using High Velocity Oxy-Fuel (HVOF) spray process. High-temperature oxidation/corrosion behavior of the bare and coated boiler steels was investigated at 700 °C for 50 cycles in air, as well as, in Na2SO4-82%Fe2(SO4)3 molten salt environment in the laboratory. Erosion-corrosion behavior was investigated in the actual boiler environment at 700 ± 10 °C under cyclic conditions for 1500 h. The weight-change technique was used to establish the kinetics of oxidation/corrosion/erosion-corrosion. Xray diffraction, field emission-scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/ EDS), and EDS elemental mapping techniques were used to analyze the exposed samples. The uncoated boiler steel suffered from a catastrophic degradation in the form of intense spalling of the scale in all the environments. The oxidation/corrosion/erosion-corrosion resistance of the HVOF-sprayed HP2 coating was found to be better in comparison with standalone Cr3C2-25(NiCr) coating. A simultaneous formation of protective phases might have contributed the best properties to the coating.


coatings, Cr3C2-25(NiCr) + 25%(WC-Co), corrosion, HVOF-spray, oxidation


1. Introduction High-temperature oxidation/corrosion and erosioncorrosion of coal-fired boiler tubes are the key material issues in steam generating plants since it affects the thermal efficiency and hence the electricity production (Ref 15). The maintenance costs for replacing broken tubes in these installations are also high. High-temperature oxidation and erosion caused by the impact of fly ashes and unburnt carbon particles are the main problems in these applications, especially in those regions where the component surface temperature is above 600 °C. The hot corrosion of a boiler steel/alloy usually occurs in the 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. Harpreet Singh, Indian Institute of Technology Ropar, Roopnagar, India; Manpreet Kaur, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, India; and Satya Prakash, Indian Institute of Technology Roorkee, Roorkee, India. Contact e-mail: [email protected]

Journal of Thermal Spray Technology

environments where molten salts such as sulfates (Na2SO4), chlorides (NaCl), or ox