Patent Description:
Gas turbine engine airfoils are often manufactured by casting. The investment casing process of nickel super alloy typically includes the use of silica castings that are removed after casting to reveal voids that are useful for conducting fluid flow, for example cooling fluid flow. Current processes for removing the silica castings may be time consuming and may etch or otherwise mar the airfoil. Surface treatment of titanium parts is disclosed in <CIT>. A polishing composition for semiconductor substrates is disclosed in <CIT>. <CIT> and <CIT> discuss methods and compositions for removing scale from substrates. Removal of ceramic core from components is disclosed in <CIT>, <CIT> and <CIT>.

In an aspect of the present invention, a solution (e.g. for use in the method described herein) is provided herein comprising a strong base and a corrosion inhibitor. The corrosion inhibitor is at least one of tartaric acid, sodium tartrate, citric acid, acetic acid, oxalic acid, malic acid, maleic acid, lactic acid, glycine, L-histidine, diethylenetriaminepentaacetate or diethylenetiraminepentaacetic acid. The strong base is KOH and the KOH has a concentration of between <NUM> wt. % and <NUM> wt.

In various embodiments, the solution further comprises a solubility enhancer.

In various embodiments, the solubility enhancer is Ethylenediaminetetraacetic acid (EDTA).

In various embodiments, the corrosion inhibitor is sodium tartrate, wherein the sodium tartrate has a concentration of between <NUM>/L and <NUM>/L or between <NUM>/L and <NUM>/L.

In various embodiments, the solution further comprises a solubility enhancer comprising Ethylenediaminetetraacetic acid (EDTA), wherein the EDTA has a concentration of between <NUM>/L and <NUM>/L or between <NUM>/L and <NUM>/L.

In another aspect of the present invention, a method is provided (e.g. using the solution described herein) comprising placing a metallic aircraft part having a ceramic material disposed therein into a vessel, placing a solution into the vessel, the solution comprising, a strong base, and a corrosion inhibitor. The corrosion inhibitor is at least one of tartaric acid, sodium tartrate, citric acid, acetic acid, oxalic acid, malic acid, maleic acid, lactic acid, glycine, L-histidine, diethylenetriaminepentaacetate or diethylenetiraminepentaacetic acid. The strong base is KOH and the KOH has a concentration of between <NUM> wt. % and <NUM> wt.

In various embodiments, the method further comprises heating the vessel to an elevated temperature.

In various embodiments, the method further comprises increasing the pressure within the vessel to above atmospheric pressure.

In various embodiments, the method further comprises holding the vessel at the elevated temperature and above atmospheric pressure for between four hours and ninety six hours.

In various embodiments, the method further comprises holding the vessel at the elevated temperature and above atmospheric pressure until substantially all the ceramic material has dissolved.

In various embodiments, the method further comprises a solubility enhancer wherein the solubility enhancer is Ethylenediaminetetraacetic acid (EDTA).

In various embodiments, the corrosion inhibitor is sodium tartrate, wherein the sodium tartrate has a concentration of between <NUM>/L and <NUM>/L.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration and their best mode. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosures, it should be understood that other embodiments may be realized and that logical, chemical, and mechanical changes may be made without departing from the scope of the appended claims. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option.

Gas turbine engines may comprise a compressor, to compress a fluid such as air, a combustor, to mix the compressed air with fuel and ignite the mixture, and a turbine to extract kinetic energy from the expanding gases that result from the ignition. The compressor rotors may be configured to compress and spin a fluid flow. Stators may be configured to receive and direct the fluid flow. In operation, the fluid flow discharged from the trailing edge of stators may be turned toward the axial direction or otherwise directed to increase and/or improve the efficiency of the engine and, more specifically, to achieve maximum and/or near maximum compression and efficiency when the air is compressed and spun by a rotor.

In various embodiments, the turbine rotors may be configured to expand and reduce the swirl of the fluid flow. Stators may be configured to receive and turn the fluid flow. In operation, the fluid flow discharged from the trailing edge of stators may be turned away from the axial direction to enable the extraction of shaft power from the fluid and, more specifically, to achieve maximum and/or near maximum expansion of the fluid and efficiency when the swirled air is expanded by the turbine rotor. In various embodiments, the systems and methods described herein may be useful in the production of airfoils and related components, such as discs.

Aircraft components such as discs may be cast by pouring molten metal over a ceramic material. The molten metal materials are often nickel superalloys, for example, austenitic nickel-chromium-based superalloys, such as that sold under the mark INCONEL. In various embodiments, the ceramic material may comprise silica (SiO<NUM>), alumina (Al<NUM>O<NUM>), zircon (ZrSiO<NUM>), magnesia (MgO), and/or mixtures of two or more of the same, though in various embodiments other mixtures of oxides and other ceramics may be used. The ceramic material may then be dissolved or otherwise removed to leave voids in the aircraft component. These voids may be used as pathways for cooling liquid during operation. For example, a strong base is used to dissolve the ceramic material, for example under temperatures and pressures that may exceed typical room temperature (~<NUM>°F) (~<NUM>), and pressures (-<NUM> psi) (-<NUM> kPa). However, use of high concentrations of strong bases may lead to undesirable etching or other damage to the surfaces of the aircraft component. For example, a corrosion inhibitor is used to protect the aircraft component from damage typically associated with strong bases, thus allowing for use of higher concentrations of strong bases, and, in various embodiments, at higher temperatures and pressures.

With reference to <FIG> and <FIG>, a method of dissolving a ceramic material in a metallic aircraft component <NUM> is illustrated. Metallic aircraft part <NUM> may comprise any metallic aircraft component, including cast and forged metallic aircraft components, though in various embodiments the metallic aircraft component is cast. Metallic aircraft part <NUM> may comprise an airfoil body <NUM> and one or more ceramic inserts, including insert <NUM> and insert <NUM>. During casting, insert <NUM> and insert <NUM> may be surrounded by molten metal. After the metal solidifies, it is desirable to remove insert <NUM> and insert <NUM> to leave voids, voids which may be used to conduct cooling fluid. Insert <NUM> and insert <NUM> may comprise any suitable ceramic, though in various embodiments, insert <NUM> and insert <NUM> comprise silicon dioxide. Vessel <NUM> may comprise any vessel capable of providing heat to the contents of the interior and, in various embodiments, be configured to be sealed from the atmosphere and configured to withstand interior pressures of greater than <NUM> kPa. Vessel <NUM> may comprise any suitable geometry, including rectangular and cylindrical. Vessel <NUM> may comprise an autoclave. A solution, as described herein, may be placed into vessel <NUM>. In step <NUM>, the metallic aircraft part <NUM> is placed into vessel <NUM>. In step <NUM>, a solution is added into the vessel <NUM> to at least partially cover and/or submerge the metallic aircraft part <NUM>. In step <NUM>, heat is applied to elevate the temperature within the vessel <NUM>. In various embodiments, pressure is increased within the vessel <NUM>. This pressure increase may be the result of the heating of the solution within a closed space.

With reference to <FIG> and <FIG>, process <NUM> is illustrated. In step <NUM>, a solution is added into the vessel <NUM>. In step <NUM>, the metallic aircraft part <NUM> is placed into vessel <NUM>, becoming at least partially or totally submerged in the solution. In step <NUM>, heat is applied to elevate the temperature within the vessel <NUM>. In various embodiments, pressure is increased within the vessel <NUM>. This pressure increase may be the result of the heating of the solution within a closed space.

The solution comprises a strong base and a corrosion inhibitor. The strong base is potassium hydroxide (KOH). The solution comprises KOH in a concentration of <NUM> (<NUM> wt. %) to <NUM> (<NUM> wt.

The solution comprises a corrosion inhibitor The corrosion inhibitor is at least one of tartaric acid, sodium tartrate, citric acid, acetic acid, oxalic acid, malic acid, maleic acid, lactic acid, glycine, L-histidine, or diethylenetriaminepentaacetate or diethylenetriaminepentaacetic acid. For example, in various embodiments, the corrosion inhibitor has a concentration of at least one of <NUM> ppm, between <NUM>/L and <NUM>/L, between <NUM>/L and <NUM>/L, and between <NUM>/L and <NUM>/L. In various embodiments, the corrosion inhibitor comprises sodium tartrate at a concentration of at least one of between <NUM>/L and <NUM>/L, between <NUM>/L and <NUM>/L, between <NUM>/L and <NUM>/L, between <NUM>/L and <NUM>/L and between <NUM>/L and <NUM>/L. In various embodiments, the corrosion inhibitor has a concentration at least <NUM> ppm.

In various embodiments, the solution further comprises a solubility enhancer. The solubility enhancer may comprise Ethylenediaminetetraacetic acid (EDTA). For example, in various embodiments, the solubility enhancer comprises solubility enhancer at a concentration of at least one of between <NUM>/L and <NUM>/L, between <NUM>/L and <NUM>/L, between <NUM>/L and <NUM>/L, and between <NUM>/L and <NUM>/L. In various embodiments, the solubility enhancer has a concentration at least <NUM> ppm.

In step <NUM> and/or step <NUM>, the solution may be heated to a desired temperature of at least one of between <NUM> degrees Fahrenheit (<NUM>) to <NUM> degrees Fahrenheit (<NUM>), between <NUM> degrees Fahrenheit (<NUM>) to <NUM> degrees Fahrenheit (<NUM>), and between <NUM> degrees Fahrenheit (<NUM>) to <NUM> degrees Fahrenheit (<NUM>). In various embodiments, the solution is heated at <NUM> degrees Fahrenheit (<NUM>). The vessel may be kept at the desired temperature for a period of time ranging from at least one of one half hour to <NUM> hours, one hour to <NUM> hours, and <NUM> hours to <NUM> hours. In various embodiments, the vessel is kept at the desired temperature for <NUM> hours.

In step <NUM> and/or step <NUM>, the solution may be subjected to a desired pressure of at least one of between <NUM> psi (<NUM> kPa) and <NUM> psi (<NUM> kPa), <NUM> psi (<NUM> kPa) and <NUM> psi (<NUM> kPa), and <NUM> psi (<NUM> kPa) and <NUM> psi (<NUM> kPa). In various embodiments the desired pressure may be <NUM> PSI (<NUM> kPa). In various embodiments, step <NUM> may be repeated in a number of cycles. In various embodiments, the number of cycles ranges between <NUM> cycles and <NUM> cycles, between <NUM> cycles and <NUM> cycles, in between <NUM> cycles and <NUM> cycles. Step <NUM> and/or step <NUM> may include holding the vessel at the elevated temperature and above atmospheric pressure until substantially all the ceramic material has dissolved.

The processes <NUM> and <NUM> offer various improvements over conventional methods. For example, reduced process time may be achievable in accordance with various embodiments. With reference to <FIG>, the results of several tests are shown to illustrate control data. Samples of ceramic material (e.g., silicon dioxide, i.e., silica, i.e., SiO<NUM>) disposed in contact with thermally and chemically stable materials (here, an epoxy material) were placed into an autoclave and mixed with <NUM> milliliters of potassium hydroxide solution. The autoclave was heated to <NUM> degrees Fahrenheit (<NUM>). After <NUM> hours at <NUM> degrees Fahrenheit (<NUM>), the samples were removed, and the depth of etching was determined. <FIG> shows each sample and the average attack depth in mm in bar graph form here. The data is also shown in TABLE <NUM>. With reference to <FIG>, a <NUM> dimensional view of etching is depicted.

The chemistry of this reaction proceeds generally by the reaction:.

4OH + <NUM> SiO<NUM>(s) -> SiO<NUM> + Si<NUM>O<NUM> +<NUM><NUM>O.

It is theorized that by making the resultant silicon product more soluble in the solution, the reaction kinetics may be enhanced. Thus, in various embodiments a solubility enhancer is used in the solution.

With reference to <FIG>, additional tests were performed using solutions in accordance with various embodiments (not according to the invention). As <FIG> shows, tests were run by submerging ceramic material samples disposed in contact with a nickel alloy material in a <NUM> solution of sodium hydroxide at a concentration of <NUM>/L. The solution also contained EDTA at <NUM>/L and sodium tartrate at <NUM>/gL. The solution was brought to <NUM> degrees Fahrenheit (<NUM>) in an autoclave and maintained at that temperature for <NUM> hours. TABLE <NUM>, below, illustrates the depth of attack achieved in four different tests. As shown in <FIG>, the average depth of attack exceeds that of the control shown in <FIG>, yielding an average depth of attack of <NUM> vs. <NUM> in the control. It is noted that the control test was performed over <NUM> hours and the test shown in <FIG> was performed in <NUM> hours, resulting in a <NUM> increase in average depth of attack yet a reduction of one third (<NUM>%) of the process time.

<FIG> shows the surface of a nickel alloy after being subjected to a <NUM>% KOH solution for <NUM> hours at <NUM> degrees Fahrenheit (<NUM>). The surface of the nickel alloy exhibits a dark brown color surface, evidence that the surface has been attacked and chemically altered, for example by oxide formation. <FIG> shows the surface of a nickel alloy after being subjected to a <NUM>% KOH solution for <NUM> hours at <NUM> degrees Fahrenheit (<NUM>), wherein the KOH solution further comprised EDTA at <NUM>/L and sodium tartrate at <NUM>/gL. As illustrated, the nickel alloy in <FIG> exhibits a shiny metallic color. This is evidence of no surface attack or oxide formation.

With reference to <FIG> and <FIG>, the nickel alloy sample shown in <FIG> was placed under a scanning electron microscope to produce the micrographs shown in <FIG>. The images in <FIG> were taken at 1000x and 5000x, respectively. The state of the surface of the nickel alloy sample is evidenced in <FIG>. With reference to <FIG>, an elemental analysis was performed on the surface of the nickel alloy sample. Notably, the presence of oxygen (O) is shown. This is evidence of oxides that form part of the coating of the nickel alloy sample. Such oxides would be detrimental to the functioning of a nickel alloy aircraft part.

With reference to <FIG> and <FIG>, the nickel alloy sample shown in <FIG> was placed under a scanning electron microscope to produce the micrographs shown in <FIG>. The images in <FIG> were taken at 1000x and 5000x, respectively. The state of the surface of the nickel alloy sample is evidenced in <FIG>. With reference to <FIG>, an elemental analysis was performed on the surface of the nickel alloy sample. Notably, there is no evidence of oxygen (O). This is evidence that no oxides are part of the coating of the nickel alloy sample. Such lack of oxides would be beneficial to the functioning of a nickel alloy aircraft part.

With reference to TABLE <NUM>, additional tests were performed using solutions in accordance with various embodiments.

As TABLE <NUM> shows, tests were run by submerging ceramic material samples disposed in contact with a nickel alloy material in a <NUM> solution of potassium hydroxide. The control was performed with <NUM>% wt KOH without a corrosion inhibitor or solubility enhancer. Tests <NUM>, <NUM>, and <NUM> were performed with <NUM>/L EDTA + <NUM>/L sodium tartrate at concentrations of KOH of <NUM> wt% wt, <NUM> wt%, and <NUM> wt %, respectively. The solution was brought to <NUM> degrees Fahrenheit (<NUM>) in an autoclave and maintained at that temperature for <NUM> hours. TABLE <NUM>, above, illustrates the depth of attack achieved in four different tests. As shown in TABLE <NUM>, the average depth of attack exceeds that of the control, yielding an increase in efficiency of <NUM>% against the control. <FIG> and <FIG> illustrate the etch depth obtained in test <NUM>.

<FIG> shows the surface of a nickel alloy after being subjected to a <NUM>% KOH solution for <NUM> hours at <NUM> degrees Fahrenheit (<NUM>). The surface of the nickel alloy exhibits a dark brown color surface, evidence that the surface has been attacked and chemically altered. <FIG> shows the surface of a nickel alloy after being subjected to a <NUM>% KOH solution for <NUM> hours at <NUM> degrees Fahrenheit (<NUM>), wherein the KOH solution further comprised EDTA at <NUM>/L and sodium tartrate at <NUM>/gL. As illustrated, the nickel alloy in <FIG> exhibits a shiny metallic color. This is evidence of no surface attack or oxide formation.

With reference to <FIG> and <FIG>, the nickel alloys samples shown in <FIG> was placed under a scanning electron microscope to produce the micrographs shown in <FIG>. The images in <FIG> were taken at 1000x and 5000x, respectively. The state of the surface of the nickel alloy is evidenced in <FIG>. With reference to <FIG>, an elemental analysis was performed on the surface of the nickel alloy. Notably, the presence of oxygen (O) is shown. This is evidence of oxides that form part of the coating of the nickel metal alloy. Such oxides would be detrimental to the functioning of a nickel alloy aircraft part.

With reference to <FIG> and <FIG>, the nickel alloys sample shown in <FIG> was placed under a scanning electron microscope to produce the micrographs shown in <FIG>. The images in <FIG> were taken at 1000x and 5000x, respectively. The state of the surface of the nickel alloy is evidenced in <FIG>. With reference to <FIG>, an elemental analysis was performed on the surface of the nickel alloy. Notably, there is no evidence of oxygen (O). This is evidence of that no oxides are part of the coating of the nickel metal alloy. Such lack of oxides would be beneficial to the functioning of a nickel alloy aircraft part.

As shown herein, use of the solution and process in various embodiments may significantly and unexpectedly reduce the time associated with dissolving a ceramic material (e.g. a silica casting core, an alumina casting core, a zircon casting core, a magnesia casting core, and/or a casting core comprising mixtures of two or more of silica, alumina, magnesia and zircon), while preventing metallic aircraft part surfaces from damage due to, among other things, oxide formation. With reference to TABLE <NUM>, etching attack depth may be increased nearly threefold by doubling concentration. Not only is this unexpected, the use of a corrosion inhibitor allows this large increase in attack depth to occur without harming the metallic aircraft part.

The scope of the disclosures is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more. " Moreover, where a phrase similar to "at least one of A, B, or C" is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, Band C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C.

Claim 1:
A solution comprising:
a strong base; and
a corrosion inhibitor,
wherein the corrosion inhibitor is at least one of tartaric acid, sodium tartrate, citric acid, acetic acid, oxalic acid, malic acid, maleic acid, lactic acid, glycine, L-histidine, diethylenetriaminepentaacetate or diethylenetriaminepentaacetic acid, and
wherein the strong base is KOH and the KOH has a concentration of between <NUM> wt.% and <NUM> wt.%.