Investigation of Element Effect on High-Temperature Oxidation of HVOF NiCoCrAlX Coatings (original) (raw)
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Investigation of Element Effect on High Temperature Oxidation of HVOF NiCoCrAlX Coatings
MCrAlX (M: Ni or Co or both, X: minor elements) coatings have been widely used to protect hot components in gas turbines against oxidation and hot corrosion at high temperatures. Understanding the influence of the X-elements on oxidation behaviour is important in the design of durable MCrAlX coatings. In this study, NiCoCrAlX coatings doped with Y+Ru and Ce, respectively, were deposited on Inconel-792 substrate by HVOF. The samples were subjected to isothermal oxidation test in laboratory air at 9000, 1000, 1100 ºC and cyclic oxidation test between 100 ºC and 1100…
Some aspects of elemental behaviour in HVOF MCrAlY coatings in high-temperature oxidation
Surface and Coatings Technology, 2015
MCrAlY coatings are widely used to protect superalloys against oxidation and corrosion at high temperature in gas turbine engines. To design a durable MCrAlY coating, the behaviour of alloying elements in coating-superalloy system needs to be better understood. After oxidation tests in temperature range between 900 °C to 1100 °C, the development of the microstructures in the samples was analysed at the coating surface or in areas near the coatingsuperalloy interface. Some interdiffusion simulations were also done to model the diffusion behaviour of alloying elements in different coating-superalloy couples. The results show that both oxidation at the coatings' surface and the elements' diffusion inside of the materials were temperature-and chemical-composition dependent. The behaviour of some minor elements like Y, Hf, Ru and Ir in the oxidation processes was particularly studied by tracking their position and composition in the materials. Abbreviations high-velocity oxy-fuel (HVOF) coating-substrate interface (CSI) inner-β-depletion zone (IBDZ) γ'-depletion zone (GPDZ) secondary β phase (SBP)
Proceedings of the Asian Pacific Conference on Fracture and Strength and International Conference on Advanced Technology in Experimental Mechanics
Aoba-ku, 980-8550, Jap an Recently, thermal barrier coatings CIrBC) have been used in advanced gas turbine plants to improve the durability and perfbrmance of turbine blades, Usually, TBCs consist of an inner layer of meta11ic bond coating (MCrAIY) and an outer layer of ceramic top coating. According to several studies, the failure of such coatings is induced by thermal stress due to the formation of thermally grown oxide (TGO) at the interface between the TBC and MCrAIY, Therefore, it is important to investigate the oxidadon behavior of the interface at high temperatures, In this work, the TGO, which forms at the interface, is characterized in detail. Moreover, for the purpose of understanding oxide formation at the interface, the oxidation behavior of specimens with and without TBC are compared. The TBC specimens are therrnally aged at high temperature to simulate the surface temperature of the first rotating blades of 1500deg.C class gas turbine plants, After aging, TGO formed at the interface. The TGO formed is observed to consist of two different oxide layers, The thickness of the two oxide layers inereases with the aging time. As a result ofa comparison between the specimens with and without TBC, the TGO thickness of the specimen with TBC is observed to be thicker than for the specimen without TBC. These specimens exhibited different oxidation behaviors, which are caused by specimen dependent preferential growth ofone ofthe oxide layers for the specimen with TBC.
Surface and Coatings Technology, 2018
For nuclear safety issues, there is an international effort to develop innovative "Enhanced Accident Tolerant Fuels" (EATF) materials. EATF cladding tubes are of particular interest because they constitute the first barrier against radioactive fission species dispersal in case of accidental scenario such as LOCA (LOss of Coolant Accident). Actual nuclear fuel claddings are made from Zr-based alloys and to increase safety margins, both mechanical strength and resistance to high-temperature oxidation have to be improved. Several alternatives using high-temperature oxidation resistant coatings for outer-wall protection have been proposed worldwide but there is currently no solution for the inner-wall protection. In order to resist to high temperature steam environment upon LOCA transients, internal Cr-based coatings deposited by DLI-MOCVD (Direct Liquid Injection of MetalOrganic precursors) were investigated. These hard metallurgical coatings could also be used in hightemperature corrosive environments as those encountered in aeronautics and other industries to protect 3D complex components. Thanks to a suitable chemistry of the liquid Cr precursor, bis(ethylbenzene)chromium, different coatings were deposited including: metal Cr, chromium carbides Cr x C y and mixed carbides Cr x Si z C y. The high-temperature behavior of these Cr-based coatings under oxidizing atmospheres has been studied using several techniques and various oxidation tests including pure steam environment followed by water quenching down to room temperature to be representative of LOCA situations. Amorphous Cr x C y coatings showed the most promising properties. For instance compared to uncoated substrate, they shift the catastrophic oxidation towards higher temperatures and delay the complete oxidation of the substrate at 1473 K of > 2 h. The results are discussed in terms of oxidation mechanisms and protection of the fuel claddings inner surface deduced from fine characterizations of the samples before and after oxidation tests.
Microstructure, Processing, Performance Relationships for High Temperature Coatings
2008
HVOF coating have shown high resistance to corrosion in fossil energy applications and it is generally accepted that mechanical failure, e.g. cracking or spalling, ultimately will determine coating lifetime. The high velocity oxygen-fuel method (HVOF) of applying coatings is one of the most commercially viable and allows the control of various parameters including powder particle velocity and temperature which influence
Cyclic oxidation characteristics of HVOF thermal-sprayed NiCoCrAlY and CoNiCrAlY coatings at 1000 C
Thermal-sprayed MCrAlY coatings have become widespread in various industries such as power plants, aeronautics, and oil and gas firms. High-temperature oxidation behavior of these coatings is therefore of significance. Spraying of two prevalent MCrAlY powders (NiCoCrAlY and CoNiCrAlY) on Hastelloy substrate by high velocity oxygen and fuel method and exposing them to 1000 C air for resolving of their cyclic oxidation behavior are presented in this paper. The coatings were characterized by x-ray diffraction, scanning electron microscopy and energy-dispersive x-ray spectroscopy. The obtained oxidation kinetic indicated that at 1000 C, the thermally sprayed NiCoCrAlY coating has greater resistance to oxidation than CoNiCrAlY. While oxidation rate of the former follows a parabolic rate equation with specific rate of 5.1 Â 10 À3 (mm) 2 h À1 at 1000 C, the oxidation rate for the latter has a specific rate of 12.1 Â 10 À3 (mm) 2 h À1 .
Isothermal Oxidation Behavior of HVAF-Sprayed NiCoCrAlY Coatings: Effect of Surface Treatment
Thermal spray, 2017
The formation of a protective chromia scale on stainless steels is known to be suppressed by the presence of water vapor in reducing conditions. Thermal spray coatings present a promising approach to improve the durability of steels by transferring the first line of oxidation attack from the bulk steel to the coating. In the present work, isothermal oxidation behavior of Ni and NiCr coatings deposited by High-Velocity Air Fuel (HVAF) process on 304L stainless steel was investigated at 600°C for 168h. Ar-10%H 2-20%H 2 O was selected as the oxidation environment to study the oxidation behavior of the coatings in a low pO 2 environment containing H 2 and H 2 O. BIB/SEM, EDS, and XRD techniques were used to characterize the as-sprayed coatings and to investigate the oxidation mechanisms in the coated samples. Results showed that both Ni and NiCr coatings imparted oxidation protection to the 304L substrate. The chromia-forming 304L steel presented a duplex but non-protective oxide scale comprising of an outer Fe 3 O 4 layer on an inner (Fe,Cr) 3 O 4-spinel oxide. In contrast, the NiCr coating presented superior oxidation behavior due to the formation of a continuous, thin, and slow-growing Cr 2 O 3 scale. The Ni coating, too, protected the substrate owing to limited nucleation and growth of the deleterious NiO scale in the low-oxygen-activity environment.
Isothermal oxidation behavior of HVAF-sprayed Ni and NiCr coatings in H 2 -H 2 O environment
Surface and Coatings Technology, 2017
The formation of a protective chromia scale on stainless steels is known to be suppressed by the presence of water vapor in reducing conditions. Thermal spray coatings present a promising approach to improve the durability of steels by transferring the first line of oxidation attack from the bulk steel to the coating. In the present work, isothermal oxidation behavior of Ni and NiCr coatings deposited by High-Velocity Air Fuel (HVAF) process on 304L stainless steel was investigated at 600°C for 168h. Ar-10%H 2-20%H 2 O was selected as the oxidation environment to study the oxidation behavior of the coatings in a low pO 2 environment containing H 2 and H 2 O. BIB/SEM, EDS, and XRD techniques were used to characterize the as-sprayed coatings and to investigate the oxidation mechanisms in the coated samples. Results showed that both Ni and NiCr coatings imparted oxidation protection to the 304L substrate. The chromia-forming 304L steel presented a duplex but non-protective oxide scale comprising of an outer Fe 3 O 4 layer on an inner (Fe,Cr) 3 O 4-spinel oxide. In contrast, the NiCr coating presented superior oxidation behavior due to the formation of a continuous, thin, and slow-growing Cr 2 O 3 scale. The Ni coating, too, protected the substrate owing to limited nucleation and growth of the deleterious NiO scale in the low-oxygen-activity environment.
Study of Wear Resistance of Coatings Deposited by High Velocity Oxygen Fuel (Hvof) Technology
2012
The contribution deals with the evaluation of wear resistance three types thermally sprayed coatings deposited by HVOF spraying. The wear resistance of these coatings was evaluated by simulation of erosive wear. Erosive wear was simulated by abrasive blast cleaning process using abrasive - brown corundum. Simultaneously there was studied influence of various impact angles on wear resistance of HVOF coatings. Study of properties the coatings was supplied also by measuring thickness, adhesion, microhardness and by EDX analysis. Construction and structure of coatings were studied using optical and electron microscopy. The research results showed that all coatings exhibit comparable resistance against erosive wear, greater weight loss was observed at impact angle 75°. v Adhesion of coatings after heat load slightly decreased, but within 10 thermal cycles stayed relatively stable. Despite these results, it is not possible to recommend to the operational conditions with high and fluctuati...
Effect of surface condition on the oxidation behaviour of MCrAlY coatings
Surface and Coatings Technology, 2006
Coatings of the MCrAlY type (M = Ni, Co) are commonly used as overlay coatings and as bond coats (BC's) for ceramic thermal barrier coatings (TBC's) in industrial gas turbines. During high temperature service the MCrAlY coatings form aluminium based surface oxide scales. The technologically most relevant properties of the oxide scales, growth rate and adherence do not only depend on the exact MCrAlY composition but also on the surface condition after coating manufacturing. Depending on the coating manufacturing process, the MCrAlY surfaces may substantially differ in roughness. In addition the coatings may be subjected to surface treatments (e.g. shot peening, grinding or smoothening prior to deposition of TBC). In the present work the effect of the surface roughness commonly prevailing in the case of vacuum plasma sprayed MCrAlY coatings on the morphology and composition of the alumina scales formed during high-temperature oxidation was studied. For this purpose free standing coatings with rough and polished surfaces were oxidised in the temperature range from 800 to 1100°C with exposure times up to 1000 h. The surface scale composition and morphology were analysed by optical metallography and SEM. Fluorescence spectroscopy was used for stress measurements in the oxide scales. It has been found that the oxide scales formed on rough surfaces of MCrAlY coatings have an intrinsically different morphology and growth rate compared to those formed on the flat ground surfaces.