Synthesis, characterization and physical properties of Al-Cu-Fe quasicrystalline plasma sprayed coatings

The phases and microstructures of Al-Cu-Fe powders and coatings were investigated in this study. Powders were prepared by grinding a chill cast ingot and by high pressure gas atomization. The contrasting solidification rates of these two processes yielded very different solidification structures. The cast ingot was very inhomogeneous and contained icosahedral ([psi]), cubic ([beta]), monoclinic ([lambda]) and tetragonal ([theta]) phases. The gas atomized powder had a finer scale of phase segregation and consisted primarily of the [psi] and [beta] phase; a small fraction of the [lambda] phase was present as well;Plasma arc sprayed (PAS) coatings were formed using the above powders. The chemical uniformity of the starting powder was carried over into the PAS coatings. Evaluation of starting powder size during PAS revealed that small powder particles (e.g., \u3c45[mu]m) tended to lose Al by vaporization. This mass loss brought the composition of the coating into a two-phase region of the Al-Cu-Fe phase diagram and produced less of the desired [psi] phase;Substitution of 1 at. pct. B for Al was done to study the effect on altering the solidification microstructure of Al63 Cu25Fe12 chill cast ingots, gas atomized powder and PAS coatings. Boron significantly altered the structure of the chill cast ingot, but had less impact on the solidification of the atomized powders or PAS coatings. Differential thermal analysis and electron microscopy indicated that B was modifying solidification by a solute-drag mechanism;Oxidation and tribological behaviors of PAS Al63 Cu25Fe12 coatings were examined. The coatings were resistant to catastrophic oxidation at 500∘ and 700∘C in flowing O2 for up to 250 hours. The weight gain of oxidized samples followed parabolic kinetics. Pin-on-disc wear tests with a Al2 O3 pm against PAS Al63 Cu25Fe12 coatings showed brittle behavior at room temperature and increasing plastic behavior at temperatures up to 600∘C. Initial coefficients of friction between the ceramic pin and the quasicrystal coatings ranged from 0.4 to 0.6 at 25∘C and 600∘C, respectively. These values increased with sliding distance. The increase in frictional force was attributed to increased contact area between the pin and coating as sliding progressed

Electrochemical Pitting And Repassivation On Icosahedral AL-CU-FE, And A Comparison With Crystalline Phases

We report the electrochemical potentials at which localized pitting and repassivation occur on icosahedral Al-Cu-Fe, and on a series of related alloys and elemental metals. The electrochemistry occurs in a buffered NaCI solution, pH 8.4. Under these conditions, pitting and repassivation appear to be controlled mainly by the chemical composition of the alloy, although the quasicrystalline phase displays an anomalous resistance to repassivation. Corrosion of this phase proceeds by dissolution of Al and Fe, leaving behind pits which are Cu-enriched

Room Temperature Oxidation of Al-Cu-Fe and Al-Cu-Fe-Cr Quasicrystals

We have investigated formation of oxides on quasicrystalline and crystalline alloy surfaces of similar composition, in different oxidizing environments. This includes a comparison between a quaternary orthorhombic approximate of Al-Cu-Fe-Cr quasicrystal and the ternary Al-Cu-Fe quasicrystalline and crystalline phases. We noted that each sample showed the following common trends: preferential oxidation of the Al, enrichment in the concentration of Al present at the surface upon oxidation, water concentration is directly related to oxide thickness, and the oxide thickness displays a strong correlation with the bulk concentration of Al in the sample

METHOD OF MAKING QUASICRYSTAL ALLOY POWDER, PROTECTIVECOATINGS AND ARTICLES

A method of making quasicrystalline alloy particulates wherein an alloy is superheated and the meltis atomized to form generally spherical alloy particulates free of mechanical fracture and exhibiting a predominantly quasicrystalline in the atomized condition structure. The particulates can be plasma sprayed to form a coating or consolidated to form an article of manufacture

One-piece, composite crucible with integral withdrawal/discharge section

A one-piece, composite open-bottom casting mold with integral withdrawal section is fabricated by thermal spraying of materials compatible with and used for the continuous casting of shaped products of reactive metals and alloys such as, for example, titanium and its alloys or for the gas atomization thereof

Synthesis, characterization and physical properties of Al-Cu-Fe quasicrystalline plasma sprayed coatings

The phases and microstructures of Al-Cu-Fe powders and coatings were investigated in this study. Powders were prepared by grinding a chill cast ingot and by high pressure gas atomization. The contrasting solidification rates of these two processes yielded very different solidification structures. The cast ingot was very inhomogeneous and contained icosahedral ([psi]), cubic ([beta]), monoclinic ([lambda]) and tetragonal ([theta]) phases. The gas atomized powder had a finer scale of phase segregation and consisted primarily of the [psi] and [beta] phase; a small fraction of the [lambda] phase was present as well;Plasma arc sprayed (PAS) coatings were formed using the above powders. The chemical uniformity of the starting powder was carried over into the PAS coatings. Evaluation of starting powder size during PAS revealed that small powder particles (e.g., <45[mu]m) tended to lose Al by vaporization. This mass loss brought the composition of the coating into a two-phase region of the Al-Cu-Fe phase diagram and produced less of the desired [psi] phase;Substitution of 1 at. pct. B for Al was done to study the effect on altering the solidification microstructure of Al63 Cu25Fe12 chill cast ingots, gas atomized powder and PAS coatings. Boron significantly altered the structure of the chill cast ingot, but had less impact on the solidification of the atomized powders or PAS coatings. Differential thermal analysis and electron microscopy indicated that B was modifying solidification by a solute-drag mechanism;Oxidation and tribological behaviors of PAS Al63 Cu25Fe12 coatings were examined. The coatings were resistant to catastrophic oxidation at 500∘ and 700∘C in flowing O2 for up to 250 hours. The weight gain of oxidized samples followed parabolic kinetics. Pin-on-disc wear tests with a Al2 O3 pm against PAS Al63 Cu25Fe12 coatings showed brittle behavior at room temperature and increasing plastic behavior at temperatures up to 600∘C. Initial coefficients of friction between the ceramic pin and the quasicrystal coatings ranged from 0.4 to 0.6 at 25∘C and 600∘C, respectively. These values increased with sliding distance. The increase in frictional force was attributed to increased contact area between the pin and coating as sliding progressed.</p

Energy Reductions Using Next-Generation Remanufacturing Techniques

The goal of this project was to develop a radically new surface coating approach that greatly enhances the performance of thermal spray coatings. Rather than relying on a roughened grit blasted substrate surface for developing a mechanical bond between the coating and substrate, which is the normal practice with conventional thermal spraying, a hybrid approach of combining a focused laser beam to thermally treat the substrate surface in the vicinity of the rapidly approaching thermally-sprayed powder particles was developed. This new surface coating process is targeted primarily at enabling remanufacturing of components used in engines, drive trains and undercarriage systems; thereby providing a substantial global opportunity for increasing the magnitude and breadth of parts that are remanufactured through their life cycle, as opposed to simply being replaced by new components. The projected benefits of a new remanufacturing process that increases the quantity of components that are salvaged and reused compared to being fabricated from raw materials will clearly vary based on the specific industry and range of candidate components that are considered. At the outset of this project two different metal processing routes were considered, castings and forgings, and the prototypical components for each process were liners and crankshafts, respectively. The quantities of parts used in the analysis are based on our internal production of approximately 158,000 diesel engines in 2007. This leads to roughly 1,000,000 liners (assuming a mixture of 6- and 8-cylinder engines) and 158,000 crankshafts. Using energy intensity factors for casting and forgings, respectively, of 4450 and 5970 Btu-hr/lb along with the energy-induced CO2 generation factor of 0.00038 lbs CO2/Btu, energy savings of over 17 trillion BTUs and CO2 reductions of over 6.5 million lbs could potentially be realized by remanufacturing the above mentioned quantities of crankshafts and liners. This project supported the Industrial Technologies Program's initiative titled 'Industrial Energy Efficiency Grand Challenge.' To contribute to this Grand Challenge, we. pursued an innovative processing approach for the next generation of thermal spray coatings to capture substantial energy savings and green house gas emission reductions through the remanufacturing of steel and aluminum-based components. The primary goal was to develop a new thermal spray coating process that yields significantly enhanced bond strength. To reach the goal of higher coating bond strength, a laser was coupled with a traditional twin-wire arc (TWA) spray gun to treat the component surface (i.e., heat or partially melt) during deposition. Both ferrous and aluminum-based substrates and coating alloys were examined to determine what materials are more suitable for the laser-assisted twin-wire arc coating technique. Coating adhesion was measured by static tensile and dynamic fatigue techniques, and the results helped to guide the identification of appropriate remanufacturing opportunities that will now be viable due to the increased bond strength of the laser-assisted twin-wire arc coatings. The feasibility of the laser-assisted TWA (LATWA) process was successfully demonstrated in this current effort. Critical processing parameters were identified, and when these were properly controlled, a strong, diffusion bond was developed between the substrate and the deposited coating. Consequently, bond strengths were nearly doubled over those typically obtained using conventional grit-blast TWA coatings. Note, however, that successful LATWA processing was limited to ferrous substrates coated with steel coatings (e.g., 1020 and 1080 steel). With Al-based substrates, it was not possible to avoid melting a thin layer of the substrate during spraying, and this layer re-solidified to form a band of intermetallic phases at the substrate/coating interface, which significantly diminished the coating adhesion. The capability to significantly increase the bond strength with ferrous substrates and coatings may open new remanufacturing opportunities that were previously not considered due to concerns with the limits of the mechanical bonding of conventional TWA coatings. However, the limited results obtained within this one-year program are not sufficient to move the LATWA into a production environment. Additional work will be needed engineer the process to coat components with more complex geometries than the flat specimens studied in this work. In addition part-specific bench testing and relevant field tests will be required to fully establish the necessary confidence for introducing the LATWA process. These are typical constraints and requirements for most any new production process, and it is quite possible this new process will continue to be a viable approach for extending the usage of remanufacturing, and in turn capturing the resulting energy savings and green house gas emission reductions

Abrasion Resistant Coating and Method of making the same

An abrasion resistant coating is created by adding a ductile phase to a brittle matrix phase during spray coating where an Al-Cu-Fe quasicrystalline phase (brittle matrix) and an FeAl intermetallic (ductile phase) are combined. This composite coating produces a coating mostly of quasicrystal phase and an inter-splat layer of the FeAl phase to help reduce porosity and cracking within the coating. Coatings are prepared by plasma spraying unblended and blended quasicrystal and intermetallic powders. The blended powders contain 1, 5, 10 and 20 volume percent of the intermetallic powders. The unblended powders are either 100 volume percent quasicrystalline or 100 volume percent intermetallic; these unblended powders were studied for comparison to the others. Sufficient ductile phase should be added to the brittle matrix to transform abrasive wear mode from brittle fracture to plastic deformation, while at the same time the hardness of the composite should not be reduced below that of the original brittle phase material

Microstructure and wear behavior of quasicrystalline thermal sprayed

An Al-Cu-Fe alloy coating which forms a quasicrystalline phase is a potential candidate for replacing electro-deposited chromium on various components in the Space Shuttle Main Engine. Coatings were deposited by air and vacuum plasma spraying and by high-velocity oxygen-fuel spraying. Finer starting powders tended to lose Al during spraying, which affected the phase equilibrium of the coatings. Coatings which retained the starting powder composition were richer in the desired quasicrystalline phase. Ball-on-disk wear tests between 440 C stainless steel ball and the Al-Cu-Fe coatings were performed. Coefficients of friction ranged from 0.60 to 1.2 for the different coatings