Corrosion behaviour of AIP NiCoCrAlYSiB coating in salt spray tests
TL;DR: In this paper, as-deposited and annealed/pre-oxidised NiCoCrAlYSiB coatings were studied by salt spray testing in a neutral mist of 5-wt% NaCl at 35-°C for 200h.
Abstract: NiCoCrAlYSiB coatings were deposited by arc ion plating (AIP) and annealed/pre-oxidised under various conditions. The corrosion behaviour of as-deposited and annealed/pre-oxidised coatings was studied by salt spray testing in a neutral mist of 5 wt% NaCl at 35 °C for 200 h. The results showed that the as-deposited NiCoCrAlYSiB coating behaved poorly while the annealed and pre-oxidised ones performed much better in salt spray tests. The dense microstructure in annealed coatings and formation of α-Al 2 O 3 scales on the surface during pre-oxidation improved the corrosion resistance in salt spray test. The corrosion process was investigated from the aspects of corrosion products, and its electrochemical mechanism was proposed as well.
Citations
More filters
TL;DR: In this paper, a gradient NiCoCrAlYSiB coating was prepared on a Ni-base superalloy using arc ion plating (AIP) and subsequent gaseous phase aluminisation techniques.
Abstract: A gradient NiCoCrAlYSiB coating was prepared on a Ni-base superalloy using arc ion plating (AIP) and subsequent gaseous phase aluminisation techniques. Hot corrosion of normal NiCoCrAlYSiB and the gradient coating in pure Na(2)SO(4) and Na(2)SO(4)/NaCl (75:25, wt./wt.) salts was performed at 900 degrees C in static air. The corrosion results indicated an enhanced corrosion resistance to both salts for the gradient NiCoCrAlYSiB coating, which the improved performance of it should be attributed to the beta aluminide "pool" at the surface layer. By partially sacrificing Al(2)O(3) (i.e. Al), the gradient NiCoCrAlYSiB coating specimen behaved excellently in the two kinds of salts. The grain growth during the gaseous phase aluminisation and the corrosion mechanism, including the role NaCl played in the mixture salt corrosion, are discussed. (C) 2009 Elsevier Ltd. All rights reserved.
104 citations
Cites background from "Corrosion behaviour of AIP NiCoCrAl..."
...When AlCl(g) is absorbed on the surface of normal NiCoCrAlYSiB, the major phase of c/c0 in the coating [19] will confront and react with the gaseous monochloride to start b nucleation....
[...]
TL;DR: In this article , a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion.
Abstract: Abstract Thermal barrier coatings (TBCs) can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat. However, the continuous pursuit of a higher operating temperature leads to degradation, delamination, and premature failure of the top coat. Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems. In this paper, the latest progress of some new ceramic materials is first reviewed. Then, a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion. Finally, new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar, columnar, and nanostructure inclusions. The latest developments of ceramic top coat will be presented in terms of material selection, structural design, and failure mechanism, and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance, better thermal insulation, and longer lifetime.
59 citations
TL;DR: In this article, a self-healing epoxy coating containing tetraaniline modified α-Fe2O3 (TAFe) was prepared for corrosion protection of Q235 steel.
Abstract: In this study, a self-healing epoxy coating containing tetraaniline modified α-Fe2O3 (TAFe) was prepared for corrosion protection of Q235 steel. The TAFe particles were synthesized using bio-inspired catechol chemistry and the evaluation of the corrosion resistant benefits of TAFe as additive in the epoxy coating were conducted. The time-dependent corrosion protective ability of the epoxy composite coating containing TAFe applied on Q235 carbon steel were characterized by electrochemical techniques such as EIS and LEIM. Characterization of corrosion layer was done by SEM and XRD after removing coatings after 70 days of immersion in 3.5 wt% NaCl solution. Findings of corrosion measurements confirmed the existence of a small amount TAFe (0.7 wt%) resulted in improvement of corrosion protective properties of steel during corrosion process compared with neat epoxy coating and the coating with 0.7 wt% non-modified Fe2O3. Moreover, surface techniques showed compact passivated iron oxide layer beneath the coatings and presence of different metallic oxide phases for coatings. The corrosion protective enhancement of composite coating could be ascribed to electroactive function of tetraaniline layer on α-Fe2O3.
46 citations
TL;DR: In this article, the effect of pre-oxidation on the resistance to hot corrosion was examined by corroding the CoNiCrAlYRe alloy at 900°C in molten Na2SO4.
Abstract: The effect of pre-oxidation on the resistance to hot corrosion was examined by corroding the CoNiCrAlYRe alloy at 900 °C in molten Na2SO4. Preoxidized specimens featured strong adhesion of oxide scale with uniform multi-layered structure. The time of pre-oxidation was crucial for controlling Al content sufficient for subsequent hot corrosion. However, direct corrosion yielded a defective and non-protective oxide scale, which allowed detrimental penetration of sulfur into substrate. Sulfur migrating along phase boundary was trapped by yttrium to diminish slightly sulphidation. Thus, two advantages of proper pre-oxidation treatment were presented, as keeping repairing for Al2O3 scale and inhibiting sulfur penetration.
32 citations
TL;DR: Al2O3 diffusion barriers of various thicknesses have been fabricated by filtered arc ion plating between the NiCrAlY coating and the O-Ti2AlNb alloy as mentioned in this paper.
Abstract: Al2O3 diffusion barriers of various thicknesses have been fabricated by filtered arc ion plating between the NiCrAlY coating and the O-Ti2AlNb alloy. Isothermal oxidation tests and three-point bend tests have been conducted to investigate the influence of the Al2O3 diffusion barriers on the oxidation and interfacial fracture behaviour of the coatings. The results indicate that the Al2O3 diffusion barrier defers interdiffusion and gives oxidation resistance of the NiCrAlY coatings. The thickness of the Al2O3 interlayer not only influences the oxidation behaviour but also affects the interfacial fracture properties. Additionally, thermal exposure affects the critical load in three-point bend tests.
30 citations
References
More filters
TL;DR: In this paper, electrochemical impedance spectroscopy, potentiodynamic polarization and E(corr)-t curve were used to investigate the corrosion behavior of Mg alloy AZ91D.
Abstract: Electrochemical behavior in aerated 3.5 wt.% NaCl solution of Mg alloy AZ91D anodized or not has been investigated by using electrochemical impedance spectroscopy, potentiodynamic polarization and E(corr)-t curve. Their microstructures before and after corrosion have been examined under scanning electron microscope. Testing results from E(corr)-t and polarization curves indicate that the corrosion behavior of Mg alloy makes significant, characteristic changes due to anodization. Impedance spectra obtained show a regular evolution with exposure time revealing the development of corrosion damage. SEM micrographs confirm that there are pores, defects and microcracks in anodic film which determine the existence of film-vulnerable regions. Electrochemical data are combined with micrographs to explain protection mechanism of anodic film and corrosion mechanism of Mg alloy. (c) 2005 Elsevier Ltd. All rights reserved.
274 citations
TL;DR: In this paper, a variety of surface coatings and deposition processes available for the protection of blade and vane components in aero gas turbines are reviewed and the performance of various coating systems is discussed, where possible, with reference to the behaviour of engine-tested components.
Abstract: The variety of surface coatings and deposition processes available for the protection of blade and vane components in aero gas turbines is reviewed. Diffusion, overlay and thermal barrier coatings are described and deposition processes such as pack and vapour metallizing, plasma spraying processes and PVD techniques outlined. The performance of various coating systems is discussed, where possible, with reference to the behaviour of engine-tested components.
149 citations
TL;DR: In this article, high-temperature oxidation experiments with vacuum-plasma-sprayed (VPS) and high-velocity-oxygen-fuel (HVOF)-sprayed MCrAlY coatings showed that the transient stage of oxidation for HVOF coatings is very short.
Abstract: Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion. They consist of a MCrAlY bond coating and a ceramic top layer. The oxidation resistance of MCrAlY coating is based on the formation of α-Al2O3 in the steady-state stage of oxidation. The α-Al2O3 grows very slowly between the metallic bond coating and the ceramic top coating and is thermodynamically stable. High-temperature oxidation experiments with vacuum-plasma-sprayed (VPS) and high-velocity-oxygen-fuel (HVOF)-sprayed MCrAlY coatings showed that the transient stage of oxidation for HVOF coatings is very short. Moreover, in contrast to the VPS coatings, where also Cr2O3, NiO or CoO are identified, on HVOF coatings, only metastable modifications of alumina were observed. The transformation of metastable alumina modifications to α-Al2O3 is very fast. Oxidation experiments in a high-temperature chamber attached to a X-ray diffractometer were carried out. The morphology and the structure of the formed oxide scale were characterized by X-ray diffraction and scanning electron microscopy (SEM).
134 citations
TL;DR: In this article, an attempt has been made to identify hot corrosion resistant coatings which can produce a thermodynamically stable and inert oxide scale during exposure to a hot corrosion environment and thereby enhance the coating life significantly.
Abstract: In the current paper, an attempt has been made to identify hot corrosion resistant coatings which can produce a thermodynamically stable and inert oxide scale during exposure to a hot corrosion environment and thereby enhance the coating life significantly. The results obtained from hot corrosion tests of a variety of MCrAlY-type coatings with different alloying elements and traces of silicon and hafnium in the presence of sodium chloride and vanadium containing environments revealed that a NiCoCrAlY coating exhibits maximum life time among the coatings studied. The results also revealed that presence of trace elements in the coating reduces coating life significantly. Based on the results, a novel electrochemical mechanism has been proposed. It has been shown that the hot corrosion of protective coatings is an electrochemical phenomena and hence the electrochemical techniques appear to be quite useful in evaluating coatings for hot corrosion resistance.
125 citations