Superalloys 2016
Louis ThébaudP. VillechaiseJonathan CormierF. HamonCoraline CrozetAlexandre DevauxJean‐Michel FranchetAnne‐Laure RouffiéAntoine Organista
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Pinning of grain boundaries by second phase particles is widely used to control the grain size during forming process of superalloys.This paper presents hot corrosion results carried out systematically on the selected nickel based superalloys such as IN 738 LC, GTM-SU-718 and GTM-SU-263 for marine gas turbine engines both at high and low temperatures that represent type I and type II hot corrosion respectively. The results were compared with advanced superalloy under similar conditions in order to understand the characteristics of the selected superalloys. It is observed that the selected superalloys are relatively more resistant to type I and type II hot corrosion when compared to advanced superalloy. In fact, the advanced superalloy is extremely vulnerable to both types of hot corrosion. Subsequently, the relevant reaction mechanisms that are responsible for slow and faster degradation of various superalloys under varied hot corrosion conditions were discussed. Based on the results obtained with different techniques, a degradation mechanism for all the selected superalloys as well as advanced superalloy under both types of hot corrosion conditions was explained. Finally, the necessity as well as developmental efforts with regard to smart corrosion resistant coatings for their effective protection under high temperature conditions was stressed for their enhanced efficiency.
Degradation
High-Temperature Corrosion
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The isothermal oxidation behavior of a cast Ni-base superalloy K52 at 900 degrees C, which compared with Ni-base superalloy YC104-B-H, was investigated. The bases of the experiment and theory were provided for designing and applying superalloy K52. The results indicate that oxidation kinetics obeyed parabolic law for the two kinds of superalloys. The resistance oxidation belongs to I grade for K52 and YC104-B-H superalloys at 900 degrees C. The scales on the surface were determined by X-ray diffraction, scanning electron microscopy(SEM), and EPMA equipped with an EDAX unit. The results show that oxidation scales of K52 superalloy is similar to that of YC104-B-H one, and the oxidation scales consisted of three parts: which the external layer without protective discrete is mainly formed with TiO2, and a protective continuous compact Cr2O3 layer with a certain amount of NiCr2O4 is intermediate layer, as well as the internal layer is mainly Al2O1 with a small amount of TiO2. The oxidation resistance of the superalloy K52 is superior to that of the superalloy YC104-B-H.
Isothermal process
Base (topology)
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The current paper explains the oxidation behaviour of a newly developed nickel-based superalloy in simulating aero gas turbine engine conditions. The results showed that the new superalloy is highly susceptible to high temperature oxidation. Within three of hours of oxidation, extensive oxide scales were formed. The formed oxide scales were ana-lysed with electron dispersive spectroscopy (EDS) and morphology was studied with scanning electron microscope (SEM) for varied oxidation times. The oxidation products were determined with XRD and cross sections of all the oxi-dised superalloys were also studied. The elemental distribution of all the superalloys after oxidation was also studied with a view to understand and compare the characteristics of the new superalloy with other superalloys. Finally, an oxidation mechanism that is responsible for its faster degradation under elevated temperatures was established based on the results obtained with different techniques and presented in detail.
Degradation
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Superalloys are used at about 700 to more than 1000 and the superalloys based on nickel are used in harsh environments which general structural material can not withstand. Turbine disc is a component that is exposed to high temperature/high stress and are made of Ni-base superalloy. Ni-base superalloy has been actively studied. In this study, we observed microstructure of nickel-base superalloys by electron microscopy. It was found that the microstructure had second phase with nanometer size.
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In turbine engines, Ni or Co based alloys are used at high temperature, either as base materials, superalloys, or deposited on the surface of superalloys, as coatings. In the present study, two different MCrAlY overlay coatings, Ni and Co based, on a Ni based superalloy IN792 were aged for different times in air at three temperatures, 900°C, 1000°C and 1100°C. The aging processes were simulated by using DICTRA software by focusing on the interdiffusion behavior in the superalloy-coating systems. The results of simulation captured the main microstructural features observed and were used to analyze the diffusion behavior of alloying elements and the corresponding microstructure development. It was found that coating composition and temperature affected significantly the microstructure near the superalloy-coating interface, and their relations were mapped as a summary.
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Ni-base superalloy is a kind of the most complex alloy,it was used widely as higher temperature components.Its relative applied temperature is the highest in common alloy series.From the developing history of superalloy,it experienced four steps:wrought superalloy、C.C.superalloy、D.S. superalloy、S.C.superalloy.The development and research method of the alloy design was presented.In this paper,and the effect of material physical properties due to elements deflection was discussed too.
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Purpose To characterise the high temperature oxide scales for some plasma sprayed NiCrAlY coated Ni‐ and Fe‐based superalloys. Design/methodology/approach Ni‐22Cr‐10Al‐1Y metallic coatings were deposited on two Ni‐based superalloys; Superni 601 and Superni 718 and one Fe‐based superalloy; Superfer 800H by the shrouded plasma spray process. Oxidation studies were conducted on uncoated as well as plasma spray coated superalloys in air at 900°C under cyclic conditions for 50 cycles. Each cycle consisted of 1 h heating followed by 20 min of cooling in air. The thermogravimetric technique was used to approximate the kinetics of oxidation. X‐ray diffraction, SEM/EDAX and EPMA techniques were used to analyse the oxide scales. Findings All of the coated, as well as the uncoated, superalloys followed an alnost‐parabolic rate of oxidation. The NiCrAlY coating was found to be successful in maintaining its continuous contact with the superalloy substrates in all the cases. The oxide scales formed on the exposed NiCrAlY coated superalloys were found to be intact and spallation‐free. The main phases analysed for the coated superalloys were oxides of nickel, chromium and aluminium and spinel of nickel and chromium, which are expected to be useful for developing oxidation resistance at high temperatures. Practical implications The coated superalloys showed remarkable cyclic oxidation resistance under simulated laboratory conditions. However, it is suggested that these coated superalloys also should be tested in actual industrial environments of boilers and gas turbines, etc. so as to obtain more practical and reliable oxidation data. Originality/value The knowledge of the reaction kinetics and the nature of the surface oxide scales formed during oxidation is important for evaluating the alloys for their use and degradation characteristics in high temperature applications such as steam boilers, furnace equipment, heat exchangers and piping in chemical industry, reformer, baffle plates/tubes in fertilizer plants, jet engines, pump bodies and parts.
Thermogravimetric analysis
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The importance of understanding and controlling the basic solidification process in high temperature alloy technology as applied to gas turbine engine production is discussed. Resultant tailoring of the superalloy macro- and microstructure offers significant potential for continued advances in superalloy use temperatures in turbine engines. Atomized superalloy powders, rapidly solidified superalloys, microstructural control, and advanced superalloys are discussed.
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In this paper superalloys, their processing and application areas have been researched. The superalloys are widely used in the industrial production elds such as aircraft, nucleer, space industry and so on due to superior properties at high temperature and resistance to metallurgical and structural variations. The most important groups of the superalloys is Ni, Fe and Co-based superalloys. Also processing of the superalloys are investigated and another goal of the present paper is to investigate microstructure and mechanical properties of IN718 subjected to strength ening heat treatment.
Inconel
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Superalloys are indispensable for the superior perfomance and efficie n of jet engine turbine disks,turbine blades,combustors,roket shells and many other devices and components used in various industries, i n Cluding nuclear, space and aeronautics. Over the last thirty years,nickel-base superalloys has undergone more structural studies than any other superalloy as a result of attempts to correlate its properties to microstructure and heat treatment. To avoid contradictory or inconsistent findings, it is also necessary a carefully microstructural observation of the employed starting materials. In the present paper,we report morphologies relating to the as cast , forged and heat-treated Ni-base superalloy by transmission and scanning electron microscopy. This superalloy contain intermettallic compounds and carbides. The alloy in study was an as cast and also forged Ni-Fe based superalloy with the following chemical composition:
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