High-Temperature Behavior of a High-Velocity Oxy-Fuel Sprayed Cr 3 C 2 -NiCr Coating
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HIGH-TEMPERATURE oxidation, corrosion, and erosion-corrosion are serious problems in steam-generation plants, gas turbines, internal combustion engines, fluidized bed combustors, industrial waste incinerators, and black liquor boilers. Erosive, high-temperature wear of heat-exchanger tubes and other structural materials in coal-fired boilers has become a key material issue in the design and operation of thermal power plants and is recognized as one of the main causes of downtime in these installations.[1] 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 873 K (600 °C). The hot corrosion of a boiler steel/alloy usually occurs in the environments where molten salts such as sulfates (Na2SO4), chlorides (NaCl), or oxides (V2O5) are deposited onto the surfaces. The Na2SO4-82 pct Fe2(SO4)3 environment is found usually in coal-fired boilers where the coal ash corrosion is induced by the deposition of complex iron-alkali MANPREET KAUR, Assistant Professor, is with the Department of Mechanical Engineering, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, 140 407 Punjab, India. Contact e-mail: [email protected] HARPREET SINGH, Assistant Professor, is with the School of Mechanical, Material and Energy Engineering, Indian Institute of Technology Ropar, Roopnagar, 140001 Punjab, India. SATYA PRAKASH, Professor Emeritus, is with Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee, Roorkee, 247667 Uttarakhand, India. Manuscript submitted August 15, 2011. Article published online March 9, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
sulfates, (Na, K)3Fe(SO4)3.[2] Therefore, the development of wear-protection and high-temperature oxidation protection systems in industrial boilers is an important topic from both engineering and an economic perspective. Protective coatings are used on the structural alloys in energy-conversion and energy-utilization systems to protect the surfaces from oxidation and erosion.[3,4] Three methods are used widely for depositing coatings, which include chemical vapor deposition (CVD) from a pack, physical vapor deposition (PVD), and thermal spraying (metal spraying). Illavsky et al.[5] reported that often, thermally sprayed deposits have superior properties with potentially lower application costs or less environmental issues as and when compared with other industrially used coatings such as CVD, PVD, and hard chromium plating. Thermal spray techniques such as plasma spray, high-velocity oxy-fuel (HVOF), and detonation-gun spray processes are considered for coating the boiler and gas turbine materials. The coatings enhance the life of these materials by making them resistant to erosion and corrosion. A much thicker coating thickness can be achieved by thermal spraying, which is another r
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