Papers by Keyword: Hot Corrosion

Abstract: This research investigates the impact of heat treatment and high-temperature oxidation on the phase transformation and performance of AlCrFeCuNi-Nb high-entropy alloys (HEAs). The alloys were produced using laser deposition and methodically heat-treated to enhance their structural stability. X-ray diffraction (XRD) was employed for phase analysis to examine phase alterations resulting from Nb addition and thermal exposure. Results indicate that Nb boosts phase stability, facilitates the production of protective oxide layers, and increases resistance to high-temperature oxidation. The enhanced alloy demonstrated exceptional oxidation resistance and mechanical properties. These findings underscore the promise of Nb-doped HEAs for engineering applications that necessitate resilient, high-performance materials capable of enduring harsh temperatures and corrosive conditions.

Abstract: This work examines the phase stability during hot corrosion and the compressive strength of the AlCrFeNiCu-Nb high entropy alloy (HEA) produced using laser additive manufacturing, emphasizing its prospective uses in energy materials. The alloy's distinctive composition was chosen for its capacity to endure severe environments, including elevated temperatures and corrosive conditions, essential for energy-related applications. Phase stability was evaluated by X-ray diffraction, demonstrating remarkable preservation of critical phases despite high-temperature oxidation exposure. Compressive strength tests revealed the alloy's exceptional mechanical capabilities, underscoring its significant resistance to deformation. The AlCrFeNiCu-Nb HEA demonstrates significant promise for application in rigorous energy sectors, encompassing components for advanced power generation systems, high-temperature reactors, and corrosive conditions inside energy infrastructure.

Abstract: It is pertinent to mention here that the high temperature behaviour of CNT-reinforced NiCrAlY with CNT 3%, 5% and 7% with HVOF on T-SA213-T-11 steel at 600°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at high elevated temperatures are underwent low porosity, opaque coatings, they are more viscid in nature and are due to its low porosity, high dense coatings, more adhesive in nature and strong bond. Kinematics hot corrosion, oxidation and erosion are to be analyzed by the attainment of mass gain after each and every progression under thermogravimetric studies (1hour heating and 20 minutes cooling). Results will be achieved by using visual examination, and advanced microscopy like XRD and SEM/EDS analysis. Keywords: High temperature, hot corrosion, Thermal spray coatings HVOF, XRD and SEM/EDS analysis.

Abstract: Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na₂SO₄+5%NaCl salts at 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Meanwhile, the hot corrosion tests of Alloy 2 at 800°C were also carried out for comparison. Experimental results show that the corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr₂O₃, Al₂O₃ , NiO , Ni₃S₂ , NiCr₂O₄ and Cr₂S₃ at 800 °C. The cross-sectional morphologies and corresponding elemental maps indicate that a large amount of sulfides and oxides appeared in internal substrate. According to these results, the cooperating mechanism of oxidation and sulfuration in Na₂SO₄-NaCl salts for Alloy 1 is confirmed. Compared with Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr₂O₃ and Al₂O₃ protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect. Key words: powder metallurgy superalloy; hot corrosion; oxidation; molten Na₂SO₄-NaCl salts; sulfuration

Abstract: Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na₂SO₄+5%NaCl salts at 700 °C, 750 °C and 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Experimental results show that the average corrosion rate of Alloy 1 increases as the temperature elevates. The corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr₂O₃, TiO₂, Al₂O₃ , NiO and Ni₃S₂ at each temperature, meanwhile NiCr₂O₄ and Cr₂S₃ appeared at 750 °C and 800 °C respectively. The cross-sectional morphologies and corresponding elemental maps indicate that lots of Ni-Ni₃S₂ eutectic appeared in corrosion layers and a large amount of sulfides and oxides appeared in internal substrate. According to these results, the combined mechanism of oxidation and sulfuration in Na₂SO₄-NaCl salts for Alloy 1 is confirmed. Compared to Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr₂O₃ and Al₂O₃ protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect.

Abstract: Turbine components (blades, guides and casing) of gas turbine engine usually suffer from fatigue load in company with a HTG environment in service. The corrosive substances in HTG can deposit on the surface of turbine components and induce accelerated damage known as hot corrosion. In this study, an experimental system is designed and built up to conduct LCF tests of superalloy in HTG environment. The influence of HTG on the LCF behavior of the nickel-base superalloy GH4169 at 650°C is studied. According to the test results, the average fatigue life of the specimens in HTG environment (22270 cycles) is about 31.5% less than that in air (32496 cycles). The protective oxide film on the surface of the specimen can be destroyed by the electrochemical reaction between HTG and oxide film. Compared with the specimen tested in air, there are more fatigue sources in the specimen tested in HTG environment, and the transgranular–intergranular transition occurs in the crack growth area.

Abstract: Alloy 617 OCC, a variant of INCONEL 617 with optimised chemical composition, has been produced in India for manufacture of superheater and reheater tubing in boilers operating in advanced ultrasupercritical (A-USC) power plants. The tubing encounters intense hot corrosion conditions during service. The present study deals with hot corrosion behaviour of 617 OCC in A-USC environment. The environment occurring in A-USC plants was simulated in the laboratory by exposing the material coated with a mixture of salts at 700°C in a flowing gas mixture. For use in A-USC boiler technology, the metal loss due to fireside corrosion of the material should be less than 2 mm in 200,000 hours. The loss obtained in the present study was nearly 5 times this value. The corrosion processes were studied using SEM/EDAX, XRD and thermogravimetry. The degradation mechanisms coming into play, disqualifying the material for use in A-USC plants, would be discussed.

Abstract: Current development in power generation industry leads to search of new technologies and ways how to protect surface against aggressive corrosion environment. Suitable method leading to enhancement of surface properties is application of protective coatings on surface. This approach allows to use components composed from less quality materials. The current development in steam turbines leads to increasing operating temperatures for the purpose to enhance performance. This process results in elevation of operating temperature reaching the potential limits of commonly used materials. One of the key areas of protection in such environment is protection against hot temperature corrosion. Possible solution can be found in application of coatings based on alloys and cermets prepared by HVOF (High Velocity Oxygen Fuel) technology. This paper examines local mechanical and microstructural properties of Cr₃C₂-25%NiCr coating after exposition to extremely severe hot corrosion environment. Furthermore, the nanoindentation measurements of this coating were performed before and after the corrosion test. The test environment composition was based on mixture of salts 59% Na₂SO₄ with 34.5% KCl and 6.5% NaCl. Test temperature was 525°C and 575°C. Duration of the exposition to hot corrosion environment was 168 hours in autoclave. The results confirmed that the coating matrix is deteriorated during the exposition to such aggressive environment. The deterioration is localized at surface of coating and is characterized by creation of oxide layer which decreases the speed further speed of matrix dissolution and stabilizes the coating.

Abstract: An investigation of distress of hot section nozzle guiding vane (NGV) was carried out. Thermal barrier coatings (TBCs) were applied to the components of gas turbine engines to operate at higher temperatures i.e. up to 1200°C. The cause of failure was hot corrosion of TBCs by chemical entities from atmosphere like oxides of Al, Ca, Si and Mg (CMAS). Source of CMAS was dust, which was ingested to airfoil engine components. Different techniques like scanning electron microscope, boroscopy, optical microscopy, X-ray Diffraction and optical emission spectroscopy were utilized to investigate the failure of nozzle guiding vanes.

Abstract: Since gas turbine blades in engines suffer centrifugal stress and gas corrosion during service, a good creep resistance in hot corrosion environment is one of the important considerations to evaluate service performance of the blade materials. In this work, the creep rupture behaviors of the directionally solidified superalloy DZ466 with and without salt deposition at 760°C/765MPa, 850°C/500MPa and 950°C/220MPa are preliminarily investigated based on the creep properties measurement and microstructure observations. The effects of hot corrosion on the creep properties and fracture mode are examined. The results show that the creep-rupture life in salt-deposit environment is lower than that in air-exposure environment at different temperatures. The creep-rupture life reduction caused by hot corrosion is increased with increase of the creep temperature. The fracture mode is exhibited by transgranular fracture in all crepted specimens. The propagation directions of all the secondary cracks are almost perpendicular to the crept specimen surface or the stress axis. The surface cracks are mainly produced in air-exposure environment at low temperature or in salt-deposited environment at high temperature. Induced by the stress concentration, the internal cracks are initiated surrounding the carbides in both air-exposure and salt-deposit environments. The creep-rupture life is dependent on the crack initiation at low temperature but on the crack propagation at high temperature. The reduction of the active load bearing area in transversal direction is the main reason why the creep-rupture life is decreased at 950°C.