The present research work investigates the air oxidation and hot corrosion behavior of bare and CO2 laser welded Fe-based superalloy A-286 in air and in simulated aero engine molten salt (Na2SO4–7.5%NaVO3–5%NaCl) environment at 700 °C for 50 cycles. Spalling of oxide scales is observed in laser weldment in molten salt environment during hot corrosion study which is not observed in air-oxidized weldments at the end of 50 cycles. Corrosion kinetics of the weldments is obtained using the thermogravimetric technique. Scanning electron microscope/energy-dispersive spectroscopy and X-ray diffraction method are used to characterize the surface morphology and phase identification of the oxidized and hot-corroded weldments. Also, cross-sectional investigation is performed on the hot-corroded weldments to analyze the oxide scale thickness and distribution of alloying elements by optical/SEM microscopic and X-ray mapping analysis. The results show that higher corrosion rate is observed in the base metal compared to the weld zone and weldment. The grain refinement in the fusion zone facilitates the formation of Cr2O3 resulting in improved corrosion resistance in the fusion zone. © 2019, The Indian Institute of Metals - IIM.

Arivarasu M

Department of Design and Automation

School of Mechanical Engineering

Vellore Campus

Muthu S.M

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Transactions of the Indian Institute of Metals

The hot corrosion behavior of bare and NiCoCrAlY-coated AISI 347 steel is investigated in Na2SO4-40%K2SO4-10%NaCl-10%KCl salt atmosphere at [Formula: see text]C for 10 cycles. Each cycle contains 5[Formula: see text]h heating and 30[Formula: see text]min cooling to ambient temperature. The NiCoCrAlY coating is employed on the austenitic stainless steel AISI 347 using high-velocity oxy-fuel (HVOF) coating method. Corrosion kinetics of the hot corroded steels are determined by thermo-gravimetric technique. The surface microstructures and compositions of the coating and corrosion products of the steels are characterized using a scanning electron microscope and energy dispersive spectroscopy. The phases of the coating are analyzed using X-ray diffraction method. Higher weight gain is observed on the uncoated specimen, and more oxide scale spallation is observed due to Fe2O3 oxide layer formation. In the coated specimen, there is no spallation of any oxide scales. The coating provides the resistance to the spallation of oxide scales. The EDS point analysis and elemental mapping analysis are performed on the cross-section to analyze the distribution of corrosion products with respect to depth.

Surface Review and Letters

COMPARISON OF HOT CORROSION PERFORMANCE OF BARE AND NiCoCrAlY-COATED AUSTENITIC STAINLESS STEEL AISI 347 IN AGGRESSIVE WASTE HEAT INCINERATOR ENVIRONMENT AT 650∘C

The main aim of the present work is to investigate the high-temperature corrosion behavior of bare, high-velocity oxy-fuel coated on iron-based superalloy A-286. Ni-20%Cr and Cr3C2-25%NiCr powders are deposited on the Fe based superalloy A-286 material by high-velocity oxy-fuel (HVOF) process. Surface roughness and coating thickness of the coated specimen is evaluated using surface roughness tester and optical microscope (OM). The hot corrosion study was performed on bare, and HVOF coated Fe-based superalloy A-286 in Na2SO4-50%V2O5-10%NaCl environment at 700 °C under cyclic conditions. Kinetics of corrosion has been determined by thermo-gravimetric analysis using mass change measurement; Cr3C2-25%NiCr coating shows the better corrosion resistance due to the formation of stable Cr2O3 layer. The uncoated superalloy is severely suffered by spallation and sputtering of oxide scales during hot corrosion study. The surface microstructure, chemical composition and phase identification of coatings before and after hot corrosion are analyzed using scanning electron microscope/ energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) analysis. Depth of corrosion attack and oxide scales are characterized using EDS compositional analysis and elemental mapping technique. The result of the cross-sectional image shows that uncoated material was severely suffered by hot corrosion to a depth of 200 µm. © 2019 Elsevier Ltd

Engineering Failure Analysis

Investigations of hot corrosion resistance of HVOF coated Fe based superalloy A-286 in simulated gas turbine environment

High temperature corrosion of weldments is a major obstacle in various industrial applications such as gas turbines, boilers, diesel engines and furnaces.The materials are subjected to hot corrosion when they are working at elevated temperature. The objective of this work, to investigate the high temperature corrosion on activated fiux TIG welded C-22 and AISI 316 in eutectic mixture of K2SO4-60%NaCl environment at 650°C. After hot corrosion study, the weight gain was observed from thermo gravimetric analysis and the corrosive products were identified on the scale using XRD, SEM and EDAX analysis. From the results of experiments, Cr2O3 acts as a protective oxide layer of C-22 side which protect the surface from the molten salt environment at high temperature. © 2017 Elsevier Ltd.

Materials Today: Proceedings

Hot Corrosion Studies on Dissimilar Weldments C-22 and AISI 316L in the Molten Salt K2SO4 + 60%wt NaCl Environment

High temperature corrosion resistance of welded components in power plant industry, hot sections of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces and petrochemical installations is one of the serious necessity. The failure of hot sections of welded component is due to the deposition of molten salt which accelerates the hot corrosion reactions in the weld joint. In this research work, the oxy-chlorination of dissimilar weldments between AISI 304L austenitic stainless steel and AISI 4340 alloy steel at 600°C in eutectic mixture of K2SO4 + 60% NaCl under molten salt conditions was investigated. Corrosion kinetics for this dissimilar joints calculated from the thermogravimetric charts were represented. Corrosion on the dissimilar joint employing E309L filler in pulsed current gas tungsten arc welding process is found to be very aggressive, due to the fragmented delta ferrites at numerous locations resulting in the formation of the micro electrochemical cells, which act as sites for corrosion initiation and thus leading to higher corrosion rate. However, in the case of continuous current, the joint is able to protect itself better in this environment due to lower amounts of delta ferrites in weld zone, which is attributed to the higher temperature available in continuous mode leading to austenisation of delta ferrites in the multipass welding. © 2017 Institute of Materials, Minerals and Mining Published by Taylor &amp; Francis on behalf of the Institute.

Corrosion Engineering, Science and Technology

Hot-corrosion resistance of dissimilar AISI 4340 and AISI 304L weldments in the molten salt environment at 600°C

Understanding the behavior of weldment at elevated temperatures and especially the corrosion behavior has become an object of scientific investigation recently. Investigation has been carried out on friction welded AISI 4140 and AISI 304 in molten salt of K2SO4–60% NaCl environment at 550, 600 and 650 °C under cyclic condition. The resulted oxide scales in the weldment have been characterized systematically by surface analytical techniques. From the results of the experiments, it is observed that the scale thickness on low alloy steel side was higher than that on stainless steel side. Furthermore, weld interface has been found to be more susceptible to degradation than base metals due to inter diffusion of element across the interface and the formation of intermetallic compound. The influences of welding parameters and the temperature of exposure on the hot corrosion behavior of the weldment were discussed in this paper.

Journal of Materials Science & Technology

Hot Corrosion Behavior of Friction Welded AISI 4140 and AISI 304 in K2SO–60% NaCl Mixture

The investigation on high-temperature corrosion resistance of the weldments is necessary for prolonged service lifetime of the components used in corrosive environments. This paper reports on the performance of friction welded low alloy steel AISI 4140 and stainless steel AISI 304 in air as well as molten salt environment of Na2SO4–60%V2O5 and NaCl–50%Na2SO4 at 650&nbsp;°C. This paper reports several studies carried out for characterizing the weldments corrosion behavior. Initially thermogravimetric technique was used to establish the kinetics of corrosion. For analyzing the corrosion products, X-ray diffraction, scanning electron microscopy/energy-dispersive analysis and electron probe micro analysis techniques were used. From the results of the experiments, it is observed that the weldments suffered accelerated corrosion in NaCl–Na2SO4 environment and showed spalling/sputtering of the oxide scale. Furthermore, corrosion resistance of weld interface was found to be lower than that of parent metals in molten salt environment. Weight gain kinetics in air oxidation studies reveals a steady-state parabolic rate law while the kinetics with salt deposits displays multi-stage growth rates. Moreover NaCl is the main corrosive species in high temperature corrosion, involving mixtures of NaCl and Na2SO4 which is responsible for formation of internal attack.

Journal	Data powered by TypesetTransactions of the Indian Institute of Metals
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ISSN	0972-2815
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