Asphaltene deposition in petroleum refineries is known to be problematic as it reduces efficiency and may lead to structural failure or production downtime. Though several successful approaches have ...been utilized to limit deposition through the addition of dispersants and inhibitors to petroleum, these methods require constant intervention and are often expensive. In this study, we demonstrate an innovative technique to engineer the surface chemistry of pipeline steels to inhibit asphaltene deposition. Pack aluminization, a standard industrial-scale chemical vapor deposition process, is employed at a low temperature of 600 °C to aluminize API 5L X65 high strength pipe steel substrates. The results showed deposit-free steel surfaces after high-pressure and high-temperature fouling experiments. The improvement is attributed to the formation of an aluminide intermetallic phase of Fe2Al5, which changes the native oxide chemistry to favor alumina over hematite. The continuous passivating oxide scale, acting as a protective barrier, mitigates asphaltene deposition and sulfidic corrosion. Because this process is based on alloying the surface of the steel and is not a coating with a weakly adhered interface, it is not prone to delamination, and it can be re-formed when damaged within the aluminized region. The combination of low-cost processing and improved antifouling characteristics makes surface chemistry modification of steel a promising preventative approach against asphaltene deposition.
The Fe–Mn–Al–C lightweight steel has been widely studied due to its higher strength-to-weight ratio and potential applications for automotive vehicles, energy, transportation and mining industries. ...In general, the strength and ductility of the Fe–Mn–Al–C lightweight steel can be improved by the formation of nano-sized (Fe,Mn)3AlCx κ-carbide precipitates by a proper heat treatment below 800 °C. In this work, a unique micrometer scale κ-carbide phase transformation phenomenon induced by the pack aluminization in the Fe–29Mn–9Al–0.9C lightweight steel was firstly reported.
Extremely large columnar-like (Fe,Mn)3AlCx κ-carbide grains with average length of 18.1 μm embedded in the Fe3Al matrix were discovered in the interdiffusion zone of aluminization layer, which were totally different from these nanoscale κ-carbides precipitated in the austenitic steel matrix. The increased Al content in the pack aluminide coating/substrate interface reduced the chemical potential of carbon and became the driving force for carbon diffusion toward the coating/substrate interface. Therefore, due to the extremely low solubility of carbon in the Fe3Al phase and the inward diffusion of carbon atoms, very long columnar-like (Fe,Mn)3AlCx κ-carbide phases were thus produced in the interdiffusion zone. The average chemical concentration of the κ-carbide was 43.9Fe–27.3Mn–20.3Al–8.5 C (in at.%). The average hardness, elastic modulus and the lattice parameter of κ-carbide were 8.8 ± 0.3 GPa, 285 ± 10 GPa and 0.3764 nm, respectively. This study provided detailed chemical compositions, hardness and elastic modulus of (Fe,Mn)3AlCx κ-carbide phase for better understanding the carbide precipitation and strengthening mechanism of Fe–Mn–Al–C lightweight steel.
Pack aluminization of high pressure turbine nozzle guide vane of an aero gas turbine engine has been carried out following a well defined systematic procedure. The process parameters are first ...optimized on dummy vanes and optimized process is followed for the actual vanes for evaluation and testing. Visual and binocular examination followed by metallurgical evaluation have been carried out to validate the process and to establish the adequacy and correctness of the coating. The coated vanes are then evaluated through engine level tests for performance and durability. The results of engine level tests and inspection post accelerated mission test cycles ensure that the vanes with aluminide coating can withstand severe engine operating cycles without any damage or failure which would otherwise would have happened without the coating. The condition of vanes post endurance test is also an indication of enhanced life of the vanes with coating.
The Ni-base superalloys facing high temperature require further protection against high temperature oxidation. One of the most common methods providing high temperature oxidation resistance is the ...production of aluminide layers (NiAl-coatings). It is known that the thickness of produced diffusion layer can be controlled by the temperature and time of aluminization process. However, no research on the effect of surface roughness on aluminization kinetics was conducted so far. Then, to elucidate the effect of surface roughness on aluminization kinetics, diffusion layers were obtained by an in-pack aluminization method on the IN 617 alloy with differently prepared surfaces, namely polished, ground using 220 grit SiC paper and 80 grit SiC paper. The obtained results revealed that different surface preparation does not affect the chemical and phase composition of produced layers. However, a strong influence of surface preparation method on aluminide layers thicknesses was observed. Namely, it was found that the increase in substrate surface roughness results in an increase of aluminization kinetics. The dependence between surface roughness and thickness of aluminide layers was found to be logarithmic. Moreover, it was found that the aluminization kinetics is influenced, especially at early stages of the aluminization process.
In order to improve the oxidation resistance in air and mechanical properties of Fe foam prepared by electrodeposition on polyurethane foam, a surface aluminizing layer of Fe foam was obtained by a ...convenient pack cementation method. Phase evolution, microstructure, compressive strength of the as-fabricated Fe foams and surface aluminized Fe foams (SA-Fe foam) were investigated and characterized by XRD, SEM, EDS and compression testing. The SEM results showed that the SA-Fe foams maintain the overall porous architecture inherited from the Fe foam and polyurethane foams. A key factor for enhancing the mechanical properties of the Fe foam was a high temperature heat treatment in H2 atmosphere. A porous and sponge-like structure appeared on the surface of the strut of SA-Fe foams after surface aluminization. With increasing aluminizing time, main phase on the surface changed from Fe–Fe2Al5/FeAl/Fe–FeAl/Fe3Al. Maximum compressive strength of the SA-Fe foams was obtained for 10min aluminization and had a value of about 12MPa, which is more than 2.5 times that of Fe foams. The deformation characteristic of the porous materials changed from ductile to brittle deformation with increasing pack aluminization time.
Pack aluminization of low-pressure turbine blade of an aero gas turbine engine has been carried out following a well-defined systematic procedure. The process parameters are first optimized on dummy ...blades, and optimized process is followed for the actual blades for evaluation and testing. Visual and binocular examination followed by metallurgical evaluation has been carried out to validate the process and to establish the adequacy and correctness of the coating. The coated blades are then evaluated through component-level test and engine-level test followed by field evaluation trials for performance and durability. The results of engine-level tests and inspection post-accelerated mission test cycles ensure that the blades with aluminide coating can withstand severe engine operating cycles without any damage or failure which otherwise would have experienced. The failure-free operation for an equivalent TBO life and post-AMT condition of blades are an indication of enhanced life of aluminide blades and prevention of failure of the turbine blades through pack aluminization.
This study aims to apply pack aluminization which contains ZrO2 powder to develop NixAly layers on the surface of pure Ni substrate to investigate the effect of ZrO2 content on phase development and ...oxidation behavior of the aluminized Ni. The surface of pure Ni substrate was aluminized at 1,000 °C for 6.25 hrs using a pack-cementation with three ZrO2 contents in the pack mixture. Aluminized specimens were subjected to cyclic oxidation with air-cooling in ambient air at 1,000 °C. A scanning electron microscope equipped with energy-dispersive X-ray spectroscopy and an X-ray diffractometer (XRD) were used for phase analyses. Layers of coatings consisted β-NiAl, γ’-Ni3Al and Al-alloyed γ-Ni. Thicknesses decreased with increasing ZrO2 contents. Incorporated Zr was in the forms of intermetallics. The absence of δ-Ni2Al3 indicated a reduction of diffusing Al activity. While the specimen with moderate ZrO2 content showed parabolic oxidation kinetics, the multiple linear kinetics along with the high-exponent power-law oxidation were observed in the oxidized specimens prepared at other conditions. The addition of ZrO2 in pack aluminization enables a modification of the thermodynamic Al activity. The stable αAl2O3 formation was found to be promoted by the Zr addition rather than a higher Al concentration of aluminides.
This paper deals with the use of a pack aluminization process for the transformation of stainless steel wires and three-dimensional (3-D) interconnected fibres into intermetallic compounds. The ...decomposition of the pack was first investigated using differential thermal analysis. For both sample geometries, wires and interconnected fibres, the influence of trace amounts of oxygen in the processing atmosphere on intermetallic formation is shown. In a normal furnace atmosphere with Ar-flow, aluminium deposited from the pack on the sample surface but did not diffuse inside because a surface oxidation layer appeared. Upon active limitation of the oxygen partial pressure, Al was able to diffuse into the sample, up to 100 μm after 4 hours at 1000°C for the stainless steel wire, and resulting in complete transformation of the 3-D fibre network.
Nickel–aluminide protective coatings on the surface of TiAl alloys were produced by pack aluminization of preliminarily nickel-coated samples. The deposition of the nickel layer from a solution was ...carried out initially by an electroless, and subsequently by an electrolytic process, providing good adhesion of Ni to the TiAl alloy surface. Two bed regimes were used: a high-activity one (with pure aluminum as the coating source) and a low-activity one (with Fe
2Al
5 as the source). The effect of the bed composition and of the thickness of the preliminary Ni layer was examined. The layers were examined by optical microscopy, SEM with EDS and X-ray analysis. The coatings obtained with the high-activity bed contained Al-rich phases of low symmetry, making for high brittleness and poor adhesion of the surface layers; those obtained with the low-activity bed, with NiAl as the outermost layer, are oxidation resistant at high temperatures and have a ductile structure with good adhesive properties.
Aluminum diffusion coatings on Armco iron were produced by a pack aluminization technique. Two different beds were applied: a high-activity bed containing pure aluminum as the coating source, and a ...low-activity bed containing Fe
2Al
5 as the source. In this work, the master alloy itself was also prepared by a pack aluminization procedure using aluminum and iron powders. The effect of the bed content on the coating was examined. With the low-activity bed, the desired FeAl was formed as the outermost coating layer. A set of complementary examination methods—XRD, SEM, EDX, RBS and CEMS—were employed, providing detailed information on the coating produced.
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