Influence of Heat Treatment and Sealing on Hot Corrosion Behavior of 80Ni-20Cr Coatings
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Influence of Heat Treatment and Sealing on Hot Corrosion Behavior of 80Ni-20Cr Coatings Harkulvinder Singh1
•
Sukhpal Singh Chatha1 • Hazoor Singh Sidhu1
Submitted: 1 May 2019 / in revised form: 26 July 2019 ASM International 2019
Abstract The present work aims to examine the influence of heat treatment and sealing on high-temperature hot corrosion performance of HVOF-deposited 80Ni-20Cr coating on T347H austenite steel. The high-temperature corrosion performance of T347H, 80Ni-20Cr, 80Ni-20Cr heat-treated and 80Ni-20Cr sealed coatings has been investigated in Na2SO4-60V2O5 atmosphere at 750 C for 50 cycles. Corrosion kinetics were measured by weight change calculations after each cycle. Bare T347H steel experienced severe spallation of the oxide scale indicating weak resistance toward high-temperature hot corrosion. 80Ni-20Cr coatings have given a significant protection to austenite steel due to the development of oxides and spinels of Ni and Cr. Further, the post-treated by way of heat treatment and sealing improved the corrosion resistance of 80Ni-20Cr coating. Both the post-treatments lead to choking the interconnected porosity of the 80Ni-20Cr coating, which resulted in better performance of posttreated coatings. Keywords 80Ni-20Cr characterization coating hot corrosion HVOF post-treatment
Introduction Modern industrial components operate at high temperature and pressure in corrosive environment. One of the severe environments produces after burning of coal fuel in thermal & Harkulvinder Singh [email protected] 1
Yadavindra College of Engineering, Punjabi University Guru Kashi Campus, Talwandi Sabo, Punjab, India
power plants. Coal comprises impurities, i.e., sodium sulfate (Na2SO4), vanadium pentoxide (V2O5) and Cl, which makes a sodium vanadyl vanadate salt film on the surface of components, and reaction that takes place at high temperature is known as ‘hot corrosion’ (Ref 1–3). These salts (Na2SO4, V2O5, K2SO4, KCl, and NaCl) reduce the ability of the material to withstand high temperature, resulting in failure of the components (Ref 4). After the revolution in technology, the innovations of superior materials or alloys are considered with a prospect of increasing the lifetime of boilers, waste incinerators, turbines, etc., by corrosion-resistant properties (Ref 5, 6). Hot corrosion resistance of metals and alloys can be enhanced by the application of protective coatings. The primary aim of the coating is to provide stable barrier between the base material and the harsh environment. Thermal spray coatings (TSCs) are prepared by heating feedstock material in the presence of hot gaseous medium and at the same time propelled toward the substrate material with high velocity to build up a layered structure (Ref 7, 8). Nowadays, various TSC techniques such as plasma, D-gun, flame spray, cold spray, and high-velocity oxy fuel (HVOF) are used to protect the substrate material from high-temperature degradation. HVOF spray is the best process due to its flexibility to deposit
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