Referring now to the figures, which are exemplary embodiments and wherein like elements are numbered alike:
Disclosed herein are methods of making finely structured coatings using liquid feedstocks comprising metal or cermet solid fine particles suspended in the liquid. The coatings produced by these methods have relatively high densities, uniform microstructures, high bond strengths, and high deposition efficiencies. Using a liquid carrier rather than a gas carrier allows the fine particles to be supplied to the high-velocity oxygen fuel (HVOF) flame at a relatively constant rate. As such, fine particles having smaller dimensions than those previously used in thermal spraying feedstocks can be fed to the HVOF flame to ensure that most of the particles become partially or fully melted by the flame.
As used herein, the term “liquid” is intended to encompass suspensions, colloids, and the like. Also, the term “fine particles” refers to particles having an average longest grain dimension of less than about 10 μm, more specifically less than about 1 μm, and even more specifically less than about 100 nanometers (nm). Thus, the term “finely structured” refers to a material comprising fine particles. Additionally, the term “cermet” refers to a ceramic-metal composite.
Referring now to
A HVOF flame gun 70 located downstream from the tank 10 can be equipped with a liquid injector 80 that feeds the liquid feedstock 20 into the combustion chamber of the HVOF flame gun 70 and eventually into the HVOF flame 90. The liquid feedstock 20 can be supplied to the flame 90 either in a co-axial direction or a radial direction, wherein the co-axial direction is parallel to an axis of the gun and the radial direction is parallel to a radius of the flame. The fuel used in the HVOF flame gun 70 can be, for example, propylene, hydrogen, or kerosene. The fine particles can be at least partially melted and propelled by the flame 90 to the surface of a substrate 100, such as a workpiece. HVOF parameters such as fuel-to-oxygen ratio, flow rate, and spray distance can be optimized based on coating microstructure analyses and process diagnostic methods. As a result of the particles impacting the surface of the substrate 100, a coating 110 can be deposited on that surface that exhibits a high degree of melting, a fine splat size, a fine grain size, a high density, and a high bond strength to the underlying surface.
Examples of suitable liquids for use in the liquid feedstock include but are not limited to water, organic liquids such as ethanol, acetone, glycerol, and kerosene, solutions comprising inorganic and/or organic metal salt precursors, and combinations comprising at least one of the foregoing. In embodiments in which the liquid feedstock is an organic liquid, an exothermal effect can occur in the HVOF flame, causing the particles to experience a high degree of melting and the coating deposited on the substrate surface to have a very high bond strength. In other embodiments in which the liquid feedstock is a solution comprising inorganic and/or organic metal salts, such salts can be thermally converted into metal and/or ceramic particles via chemical reactions such as pyrolysis, oxidation, and/or reduction reactions. As a result, a composite coating having good chemical homogeneity and a relatively uniform microstructure, i.e., finely structured, can be formed.
Examples of suitable metal and ceramic materials for use in the fine metal or cerment particles of the feedstock include but are not limited to aluminum (Al), transition metals such as cobalt (Co), nickel (Ni), iron (Fe), molybdenum (Mo), and chromium (Cr), alloys of such metals including Ni-based alloys such as Co—Ni and Fe—Cr based alloys, metal oxides such as alumina (Al2O3), chromia (Cr2O3), zirconia (ZrO2), titania (TiO2), and ceria (CeO2), carbides such as tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), chromium carbide (Cr3C2), tantalum carbide (TaC), and silicon carbide (SiC), nitrides such as aluminum nitride (AlN), silicon nitride (Si3N4), and zirconium nitride (ZrN), and borides such as titanium diboride (TiB2) and zirconium boride, and combinations comprising at least one of the foregoing materials.
The amount of particles present in the liquid feedstock can range from about 5 weight % (wt. %) to about 80 wt. %, specifically about 20 wt. % to about 60 wt. %, more specifically about 30 wt. % to about 60 wt. %, and even more specifically about 30 wt. % to about 50 wt. %, wherein all weight percentages are based on the total weight of the liquid feedstock.
Currently used surface preparation procedures can be applied to the substrate 100 prior to the HVOF spraying. For example, the substrate 100 can be subjected to degreasing and coarsening by sand gritting to ensure that the ensuing coating adheres to it well.
In one exemplary embodiment, the liquid feedstock is prepared by gradually adding metal or cermet fine particles to the pre-selected liquid and mechanically mixing the suspended solution that is formed. A wetting agent also can be added to the liquid feedstock to de-agglomerate the particles and maintain a thorough suspension. Examples of suitable wetting agents include but are not limited to polyvinyl alcohol, ammonium polymethacrylate, sodium methacrylate, sodium sulfamate, and combinations comprising at least one of the foregoing wetting agents. During the HVOF spray process, the liquid mixture can be continuously stirred. When the liquid feedstock is fed to the HVOF flame gun, the liquid evaporates and the fine particles at least partially melt before impacting the substrate to form a deposit coating.
Compared to the coating formed in a current HVOF process, the coating formed in the liquid feedstock-HVOF (LF-HVOF) process described herein has much finer microstructure features, as illustrated in
In accordance with another embodiment, a multi-layered coating or a graded compositional coating, i.e., a preform, can be formed by sequentially injecting different compositional feedstocks into the HVOF flame gun. At least one of the feedstocks comprises metal or cermet solid fine particles suspended in a liquid. For example, two or more metallic or cermet layers can be deposited on a substrate by sequentially spraying multiple liquid feedstocks comprising metal or cermet solid fine particles suspended in a liquid. Alternatively, two or more layers can be deposited on a substrate by sequentially spraying very different feedstocks, wherein one of the feedstocks comprises metal or cermet solid fine particles suspended in a liquid and another of the feedstocks comprises solid particles and a flowable fluid with no suspension in a liquid (i.e., a prior art feedstock).
The LF-HVOF thermal spraying process described herein advantageously forms finely structured coatings having a higher density, more uniform microstructure, and higher bond strength relative to those coatings formed in current HVOF processes. The finely structured coatings also have superior coating integrity, surface quality, and ductility. These property improvements are a result of better melting and higher velocity of the solid fine particles in the LF-HVOF process.
Due to their relatively high corrosion resistance, wear resistance, and abrasion resistance, the finely structured coatings can be applied to components utilized in industries such as the automotives, aerospace, petrochemical, electric power, and chemical industries. They also can be used in their multi-layered forms for various applications such as in catalysts and electronic devices and for high temperature applications. As such, these coatings can be present in various end use articles such as automotive parts, boilers, superheaters, gas turbines, blades, vanes, gears, bearings, valves, pistons, pipes, and the like.
The invention is further illustrated by the following non-limiting examples.
In this example, INCONEL® 625 fine particles comprising nickel-chromium-molybdenum alloy and having a fine particle size of less than about 11 μm was used in the liquid feedstock. About 250 grams (g) of the particles were added to about 1 liter of water and continuously agitated. A wetting agent was then added to the resultant suspension. The suspension was continuously stirred for at least about 5 hours before its use. The liquid tank was pressurized to at least about 80 psi to deliver the suspension to the liquid nozzle. A HVOF system (Diamond Jet 2700 sold by Sulzer-Metco) was employed to thermally spray a coating on a carbon steel substrate. The substrate was preheated to a temperature above about 80° C. The resultant coating had a density of more than 99% and an average thickness of about 150 to about 250 millimeters (mm). The LF-HVOF process parameters for the coating are given below:
Fuel: propylene—194 standard cubic foot per hour (scfh) at 100 psi
Oxygen: 347 scfh at 150 psi
Air: 876 scfh at 105 psi
Standoff distance: 8 inches
Gun speed: traverse speed—1000 millimeters per second (mm/s); vertical
speed—8 mm/s
Feed rate: 20 to 30 grams per minute (g/min)
In this example, INCONEL® 625 fine particles were used in the liquid feedstock. About 200 g of the particles were added to about 1 liter of ethanol and continuously agitated. A wetting agent was then added to the resultant suspension. The suspension was continuously stirred for at least about 5 hours before its use. The liquid tank was pressurized to at least about 80 psi to deliver the suspension to the liquid nozzle. A Diamond Jet 2700 HVOF system was employed to thermally spray a coating on a carbon steel substrate. The substrate was preheated to a temperature above about 80° C. The resultant coating had a density of more than 99% and an average thickness of about 150 to about 250 mm. The LF-HVOF process parameters for the coating are given below:
Fuel: propylene, 194 scfh/100 psi
Oxygen: 347 scfh/150 psi
Air: 876 scfh/105 psi
Standoff distance: 9 inches
Gun speed: traverse speed—1000 mm/s; vertical speed—8 mm/s
Feed rate: 20 to 30 g/min
In this example, INCONEL® 625 fine particles were used in the liquid feedstock. About 200 g of the powder were added to a mixture of about 0.5 liters of water and about 0.5 liters of glycerol and continuously agitated. A wetting agent was then added to the resultant suspension. The suspension was continuously stirred for at least about 5 hours before its use. The liquid tank was pressurized to at least about 80 psi to deliver the suspension to the liquid nozzle. A Diamond Jet 2700 HVOF system was employed to thermally spray a coating on a carbon steel substrate. The substrate was preheated to a temperature above about 80° C. The resultant coating had a density of more than 99% and an average thickness of about 150 to about 250 mm. The LF-HVOF process parameters for the coating are given below:
Fuel: propylene, 194 scfh/100 psi
Oxygen: 347 scfh/150 psi
Air: 876 scfh/105 psi
Standoff distance: 8 inches
Gun speed: traverse speed—1000 mm/s; vertical speed—8 mm/s
Feed rate: 20 to 30 g/min
In this example, a LF-HVOF process was used to thermally spray INCONEL® 625 fine particles onto an aluminum bond-coat. First, an aluminum layer having a thickness of about 20 to about 50 μm was HVOF sprayed onto a steel substrate. A top layer of INCONEL® 625 alloy was then sprayed onto the aluminum bond-coat using the LF-HVOF process as described in Example 1 above. The resultant top coat layer had a density of more than 99%, a thickness of about 150 to about 250 mm, and was highly bonded to the aluminum bond-coat. The HVOF process parameters for the aluminum layer are given below:
Fuel: propylene, 176 scfh/100 psi
Oxygen: 389 scfh/150 psi
Air: 1058 scfh/105 psi
Standoff distance: 10 inches
Gun speed: traverse speed—1000 mm/s; vertical speed—8 mm/s
Powder feed rate: 2 to 3 pounds per hour (lbs/h)
In this example, a LF-HVOF process was used to thermally spray INCONEL® 625 fine particles onto a self-flux alloy bond-coat. A self-flux NiCrSiB alloy layer of about 20 to about 50 μm was HVOF sprayed onto a steel substrate. A top layer of INCONEL® 625 alloy was then sprayed onto the self-flux alloy bond-coat using the LF-HVOF process as described in Example 1 above. The resultant top coat layer had a density of more than 99%, a thickness of about 150 to about 250 mm, and was highly bonded to the NiCrSiB bond-coat. The HVOF process parameters for the self-flux layer are given below:
Fuel: propylene, 176 scfh/1100 psi
Oxygen: 289 scfh/150 psi
Air: 1058 scfh/105 psi
Standoff distance: 10 inches
Gun speed: traverse speed, 1000 mm/s; vertical speed, 8 mm/s
Powder feed rate: 2 to 3 lbs/h
In this example, INCONEL® 625 fine particles were used in the liquid feedstock. About 50 g of the powder were added to a 1 liter precursor liquid mixture comprising 7 weight % yttria stabilized zirconia based on the total weight of the liquid mixture while continuously agitating the mixture. A wetting agent was then added to the resultant suspension. The suspension was continuously stirred for at least about 5 hours before its use. The liquid tank was pressurized to at least about 80 psi to deliver the suspension to the liquid nozzle. A Diamond Jet 2700 HVOF system was employed to thermally spray a coating on a carbon steel substrate. The substrate was preheated to a temperature above about 80° C. The resultant coating had a density of more than 99% and an average thickness of about 20 to about 50 μm. The LF-HVOF process parameters for the coating are given below:
Fuel: propylene, 194 scfh/100 psi
Oxygen: 347 scfh/150 psi
Air: 876 scfh/105 psi
Standoff distance: 8 inches
Gun speed: traverse speed, 1000 mm/s; vertical speed, 8 mm/s
Feed rate: 20 to 30 g/min
In this example, Fe-20Cr alloy powder having a fine particle size of less than about 11 μm was used in the liquid feedstock. About 200 g of the powder were added to about 1 liter of water and continuously agitated. A wetting agent was then added to the resultant suspension. The suspension was continuously stirred for at least about 5 hours before its use. The liquid tank was pressurized to at least about 80 psi to deliver the suspension to the liquid nozzle. A Diamond Jet 2700 HVOF system was employed to thermally spray a coating on a carbon steel substrate. The substrate was preheated to a temperature above about 80° C. The resultant coating had a density of more than 99% and an average thickness of about 150 to about 250 μm. The HVOF process parameters for the coating are given below:
Fuel: propylene, 194 scfh/100 psi
Oxygen: 347 scfh/150 psi
Air: 876 scfh/105 psi
Standoff distance: 8 inches
Gun speed: traverse speed—1000 mm/s; vertical speed—8 mm/s
Feed rate: 20 to 30 g/min
In this example, Fe-20Cr alloy powder having a fine particle size of less than about 11 μm was used in the liquid feedstock. About 200 g of the powder were added to about 1 liter of ethanol and continuously agitated. A wetting agent was then added to the resultant suspension. The suspension was continuously stirred for at least about 5 hours before its use. The liquid tank was pressurized to at least 80 psi to deliver the suspension to the liquid nozzle. A Diamond Jet 2700 HVOF system was employed to thermally spray a coating on a carbon steel substrate. The substrate was preheated to a temperature above about 80° C. The resultant coating had a density of more than 99% and an average thickness of about 150 to about 50 μm. The HVOF process parameters for the coating are given below:
Fuel: propylene, 194 scfh/100 psi
Oxygen: 347 scfh/150 psi
Air: 876 scfh/105 psi
Standoff distance: 8 inches
Gun speed: traverse speed—1000 mm/s; vertical speed—8 mm/s
Feed rate: 20 to 30 g/min
As used herein, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Moreover, the endpoints of all ranges directed to the same component or property are inclusive of the endpoint and independently combinable (e.g., “about 5 wt. % to about 20 wt. %,” is inclusive of the endpoints and all intermediate values of the ranges of about 5 wt. % to about 20 wt. %). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and might or might not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs.
While the disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 60/826,663 filed Sep. 22, 2006, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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60826663 | Sep 2006 | US |