Wear Characteristics of Aluminide Blend for Thermal Barrier Coatings Bond Coat (original) (raw)
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Structural Modification of Aluminide Blend for Thermal Barrier Coatings
The structural properties of conventional bond coats were modified to improve thermal barrier coating properties. Silicon-carbide was blended with aluminum, nickel and chromium in an aluminide bond coat and deposited on various metallic substrates via oxyacetylene flame spray in a neutral flame. Wear test was conducted on the surface modified substrates. Microstructural analysis reveals different levels of interfacial diffusion in the various modified substrates resulting in differential wear co-efficient. Among the substrates coated, mild steel exhibited the greatest resistance to wear followed by Compacted Graphite Iron (CGI). This suggests that the generated aluminide blend can be used to enhance the surface of mild steel preparatory to the application of thermal barrier coating.
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Materials Science and Engineering: A, 2005
The mechanisms governing the failure of multi-layer thermal barrier systems based on Pt-modified nickel aluminide bond coats and electron beam deposited thermal barrier coatings (TBCs) have been studied. The primary experimental variable is the morphology of the bond coat surface prior to application of the TBC, at constant multi-layer chemistry. The durability of these systems in a furnace cycle test has been measured and compared. The failure mechanisms, as well as the thickening of the thermally grown oxide (TGO), have been characterized for each of the surface morphologies. The major findings are that the durability is enhanced by removing imperfections on the surface of the bond coat, as well as by surface pre-treatments that diminish subsequent TGO thickening and by incorporating a reactive-element in the substrate that strengthens the bond coat upon inter-diffusion during manufacture. These effects are consistent with the expectations of a TGO instability mechanism, driven by a combination of growth and thermal expansion misfit strains in the TGO. The grain structure of the bond coat also affects failure through its influence on the TGO instability sites.
Aluminide protective coatings on high–temperature creep resistant cast steel
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The thermal cyclic durability of a TBC is thought to be strongly dependent on the physical and mechanical properties of the bond coat layer. A novel high temperature microsample tensile testing technique has been employed to characterize the mechanical behavior of a platinum modified nickel aluminide bond coat at 0% and 28% of cyclic life in the temperature range of 25 to 1150°C. Values for the coefficient of thermal expansion and the Young's modulus are reported. The bond coat exhibits a ductile to brittle transition temperature at approximately 600°C, and above this temperature the yield and creep strength decreases rapidly with temperature. A power law description of elevated temperature stress relaxation is developed. The intermediate temperature strength was found to increase with thermal cycling, while the high temperature strength remained the same. This evolution in properties has been related to the development of a martensitic transformation that occurs during each thermal cycle.
Deposition of Aluminide Coatings onto AISI 304L Steel for High Temperature Applications
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The nickel aluminides are commonly employed as a bond coat material in thermal barrier coating systems for the components of aeroengines operated at very high temperatures. However, their lifetime is limited due to several factors, such as outward diffusion of substrate elements, surface roughness at high temperatures, morphological changes of the oxide layer, etc. For this reason, inter-diffusion migrations were studied in the presence and absence of nickel coating. In addition, a hot corrosion study was also carried out. Thus, on one set of substrates, nickel electrodeposition was carried out, followed by a high activity pack aluminizing process, while another set of substrates were directly aluminized. The microstructural, mechanical, and oxidation properties were examined using different characterization techniques, such as SEM-EDS, optical microscopy, XRD, optical emission spectroscopy, surface roughness (Ra), and adhesion tests. In addition, the variable oxidation temperatures...
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In this paper, aluminide coatings of various thicknesses and microstructural uniformity obtained using chemical vapor deposition (CVD) were studied in detail. The optimized CVD process parameters of 1040 °C for 12 h in a protective hydrogen atmosphere enabled the production of high density and porosity-free aluminide coatings. These coatings were characterized by beneficial mechanical features including thermal stability, wear resistance and good adhesion strength to MAR 247 nickel superalloy substrate. The microstructure of the coating was characterized through scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. Mechanical properties and wear resistance of aluminide coatings were examined using microhardness, scratch test and standardized wear tests, respectively. Intermetallic phases from the Ni-Al system at specific thicknesses (20–30 µm), and the chemical and phase composition were successfully evaluated at optimiz...
Wear behaviour of Al–Mo–Ni composite coating at elevated temperature
Wear, 2005
The wear behaviour of the Al-Mo-Ni coating on piston ring material against gray cast iron was investigated under dry and lubricated conditions at elevated temperatures. AISI 440C steel material, widely used in manufacturing piston ring for two-cycle engines, was coated by plasma spraying method including Al-Mo-Ni powders. Wear tests were carried out on a universal wear tester with a loading of 83, 100, 200 and 300 N, and at elevated temperatures of 25, 100, 200 and 300 • C under dry and lubricated conditions. In conclusion, the material loss of the Al-Mo-Ni composite coating is increased with elevated temperatures under dry and lubricated sliding conditions. The material loss is sharply increased up to temperature point of 100 • C under dry sliding condition while it is nearly constant after this point with test loading of 100 N. Under lubricated conditions, the same tendency can be obtained for loading of 83 N. The wear mechanism is mixed mode such as abrasion, scuffing, delamination for dry conditions. Under lubricated conditions, for the lower temperature, the absorbed oil inclusions in the porosities postpone the wear in progress, resulting in easy friction. The wear mechanism of Al-Mo-Ni coating is predominantly abrasive, and delamination also occurs under heavy loading. The wear of the coating under lubricated conditions is nearly 10 times lower than that of dry conditions.
Materials Today: Proceedings, 2019
Stabilized zirconia ceramic top coats were synthesized by Air Plasma Spray coating process on flat plates machined from Al-11Si alloy diesel engine pistons. Coating process parameters and qualifications that were followed were based on previous studies made on the same substrates. The ceramic coatings were subjected to various thermal treatments such as (a) thermal shock cycling tests and (b) continuous heating in a furnace. Uncoated Al-Si samples were simultaneously subjected to the same thermal treatments and used as reference to study the protection offered by the coatings to the base metal substrates. Thermal shock cycles tests involved subjecting the coated and uncoated Al-Si plates to oxy-acetylene flame to allow the ceramic surface to be maintained at 500°C for 1000 cycles (one cycle comprised of heating for 60 s, withdrawal from flame and forced cooling in ambient air for 60 s) and similar thermal shock cycles in an electric furnace. The specimen were also heated in a furnace at 300°C for 1000 continuous hours. Stresses induced during thermal shock cycles and oxidation of bond coat-ceramic coat interface during the exposure to heat are the main reasons for the coating's failure. Details of an investigation on the microstructural changes and oxidation behaviour of the substrate and the ability of the coatings to protect the metal substrates from oxidation are presented. Microstructural studies were carried out by employing a Scanning Electron Microscope attached with Energy Dispersive X-ray spectroscopy facility. The findings were compared on (a) uncoated Al-Si alloy and (b) thermal barrier coated Al-Si alloy with a goal to understand the capability of the coatings to protect the metal from the influences of thermal treatments, at temperatures lower than the melting point of the Al-Si alloy.
The effect of silicon on thermal shock performance of aluminide-thermal barrier coatings
Corrosion Science, 2013
The failure of air-plasma-sprayed thermal barrier coatings (APS TBCs) with conventional pack aluminide and slurry Si-modified aluminide bond coats on superalloy In-738LC was investigated during a thermalshock test. Thermal shock experiments consisted of rapid thermal cycling between 1100°C and 300°C for 120 times. It was found that the lifetime of APS TBCs on aluminide bond coats can be extended by introducing silicon into aluminide structure. Silicon improved the bond coat oxidation resistance as well as the stability of b-NiAl phase, which is critical to the coating life enhancement.