JP2008297613A - Method for forming corrosion barrier for protecting heat shield coating of workpiece, and workpiece - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a hard outer shell which is strongly bonded to a heat shield coating. <P>SOLUTION: This forming method includes depositing a corrosion barrier of the hard outer shell on the surface of the heat shield coating 52 which has been coated on a substrate such as a turbine engine component 50, by using either an electrophoretic coating process or a slurry process. The corrosion barrier can be formed from aluminum oxide, silicon carbide, silicon nitride or molybdenum disilicide. The corrosion barrier preferably has a Vickers hardness of 1,300 to 2,750 kg/mm<SP>2</SP>. An infiltration region 56 may be formed in between a coating 54 and the coating 52. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a corrosion barrier for a thermal barrier coating and a method for forming the corrosion barrier.

  Many turbine engine components include a thermal barrier coating to protect the underlying substrate. High speed particles in the gas path of the engine can cause significant corrosion damage to the thermal barrier coating. This corrosion of the thermal barrier coating leads to early damage of the coated turbine engine part.

  It would be desirable to form a hard outer shell that is strongly bonded to a thermal barrier coating.

  According to the present invention, a hard outer shell is formed that is strongly bonded to the thermal barrier coating.

One feature of the present invention is that the workpiece is generally made of a substrate, a thermal barrier coating on the surface of the substrate, and a hard corrosion barrier attached to the thermal barrier coating surface. This corrosion barrier preferably has a Vickers hardness of 140-2750 kg / mm ² . The corrosion barrier can be formed from aluminum oxide, silicon carbide, silicon nitride, and molybdenum disilicide.

A second feature of the present invention is that a method is provided for forming a corrosion barrier that protects a thermal barrier coating of a workpiece. The method generally comprises creating a suspension of ceramic particles suspended in a solvent, attaching the particles in the suspension to the thermal barrier coating surface, and a Vickers hardness of 1300-2750 kg / mm ² . Drying the particles deposited on the thermal barrier coating surface to form a corrosion barrier coating having:

  Other details and other objects and advantages of the corrosion barrier protecting the thermal barrier coatings of the present invention are set forth in the detailed description and accompanying drawings, wherein like elements are designated with like reference numerals.

  The present invention relates to forming a hard shell outer coating that acts as a corrosion barrier on a thermal barrier coating surface applied to a substrate such as a turbine engine component. This outer coating corrosion barrier can be formed by applying a slurry to remove the solvent and / or by electrophoretic deposition.

  For electrophoretic deposition, as shown in FIG. 1, a workpiece 50, which is a substrate such as a turbine engine component or part, is immersed in the suspension 10 and electrically connected to the first terminal of the voltage source 12. Connected. The second electrode 14 may be made from any suitable conductive material known in the art and is electrically connected to the second terminal of the voltage source 12.

  Prior to being immersed in the suspension, a thermal barrier coating 52, such as a zirconia-based thermal barrier coating, is generally applied to the turbine engine component 50. This thermal barrier coating 52 can be applied to turbine engine components using any suitable technique known in the art.

  The suspension 10 is composed of fine ceramic particles having a size of about 0.02 microns to 0.2 microns in the form of a sol. The size of the ceramic particles is preferably in the range of about 0.02 to 0.05 microns. The ceramic particles can be suspended in a solvent such as water, alcohol (including but not limited to ethanol or methanol), and a water-alcohol mixture. Although organic solvents such as trichloroethane can be used, the use of such organic solvents may be prohibited due to health and environmental issues.

  In the simplest embodiment, the aluminum oxide (alumina) sol is suspended in water, alcohol, or a mixture thereof and sufficient acid is added to maintain the pH of the solution below 4.25. And stabilize. As a result, the alumina particles are positively charged so that they repel each other, and agglomeration and settling of particles from the solution is avoided. Acids added to the solution include but are not limited to nitric acid, hydrochloric acid, acetic acid, and stearic acid. The pH of the solution can be lowered to 2.0, but at low pH, the acid contained in the suspension can attack the exposed metal of the part or part to be coated. The preferred pH for an alumina sol suspension in water and / or alcohol is 3.0-4.5. The part or part 50 to be coated is biased with a negative DC voltage so that the suspended particles contained in the suspension are directed to the surface of the part or part 50 to which the thermal barrier coating has been applied. It can be accelerated. A typical negative bias voltage range is about 50-2000V, preferably about 900-1100V. The higher the voltage, the faster the deposition rate, but it can be dangerous by increasing the potential energy of the system to the point of jeopardizing workplace safety.

  Hard ceramic materials that may be suitable in addition to the alumina sol suspension are silicon nitride sol, silicon carbide sol, and molybdenum disilicide sol. The suitable pH range necessary to produce a stable suspension depends on the composition of the ceramic particulates contained in the suspension. This is due to changes in the surface chemistry, which leads to the accumulation of different charges on the surface of the particles and acts as a function of the pH of the suspension. At low pH the surface is positively charged and at high pH the surface is negatively charged. Thus, there is a pH level at which the surface charge of the particles is zero, and the pH level is known as the isoelectric point or pHiep. The pHiep of alumina is 4.5, the pHiep of silicon nitride is 9.0, the pHiep of silicon carbide is 5.4, and the pHiep of molybdenum disilicide is 2.2.

  Since the present invention can be used to form a hard shell material that adheres to a zirconia-based thermal barrier coating surface, it can be advantageously operated in a pH range that negatively charges the zirconia-based coating surface. This can be done by operating at a pH higher than 4.0, the pHiep of zirconia. When alumina particles are used in the suspension, it is considered that the lower limit of the usable pH spreads down to 3.0 because a lot of negative charges are supplied to the zirconia surface by biasing the zirconia coating.

  As mentioned above, strong acids tend to attack not only the metal coating, but also the metal that is the substrate of the part or part. For this reason, silicon nitride has an advantage over other coatings due to its high pHiep of 9.0. This system also has the advantage that it can be deposited at neutral pH, which is advantageous for health and safety.

  The pH level at which electrophoretic deposition is performed can be increased by changing the chemistry of the sol before placing it in the suspension. For example, nitriding alumina sols or aluminizing molybdenum disilicide can increase the pH level acting on the part or component 50 to minimize damage.

  Although the addition of an acid that adjusts the pH was discussed, a base may be added to the suspension to maintain the pH above 7.0. Typical added bases are ammonium hydroxide and aluminum hydroxide.

  Due to the thermal stability and excellent hardness of alumina, alumina is a suitable material for corrosion barrier coatings.

The Vickers hardness of the hard shell material at room temperature is
Alumina: about 2650 kg / mm ²
Silicon nitride: about 1900 kg / mm ²
Silicon carbide: about 2750 kg / mm ²
Molybdenum disilicide: about 1300 kg / mm ²
It is.

  The suspension can be maintained at a temperature range of approximately room temperature 68 ° F. to 120 ° F. (20 ° C. to 49 ° C.), but is preferably maintained at room temperature to minimize cost.

  The concentration of the sol (solid) in the suspension is preferably about 0.001% to 5.0% by weight. Preferably, the concentration of sol (solid) in the suspension is about 0.005 to 0.05% by weight.

  After the corrosion barrier coating is applied, once the part or part 50 is removed from the suspension, the part or part is dried using any suitable drying technique known in the art. Drying may be performed at about room temperature to 650 ° F. (343 ° C.). The drying time at room temperature may be about 1.0 to 20 hours, preferably about 3.0 to 10 hours. At drying temperatures of 250 ° F. to 650 ° F. (121 ° C. to 343 ° C.), the drying time may be reduced to about 0.5 to 5.0 hours, with a suitable drying time of about 1.0 to 2. 0 hours.

  After drying, the coated part or part may be sintered to provide a strong adhesion within the deposited corrosion barrier coating and between the corrosion barrier coating and the thermal barrier coating. In addition, the porosity in the corrosion barrier coating is reduced by sintering, and the porosity is lowered by decreasing the porosity. Sintering can be performed by any suitable technique known in the art. The sintering time at a temperature of about 1950 ° F. to 2000 ° F. (1066 ° C. to 1093 ° C.) may be about 3.0 to 4.0 hours.

  If necessary, one or more types of dispersants such as polymethyl methacrylate alcohol and ammonium stearate can be added to the suspension to prevent particle aggregation and settling. May be. The dispersant (s) may be present at a concentration of 0.01 to 1.0% by weight, preferably 0.4 to 0.8% by weight.

  In order to increase the strength of the hard shell, polyvinyl alcohol may be added to the suspension as a binder before sintering, if necessary. Polyvinyl alcohol may be added in an amount of 0.1 to 3.0% by weight, preferably 1.0 to 2.0% by weight. The purpose of adding the polyvinyl alcohol binder is to coat each particle of the suspension sol with a monolayer of the binder.

  Other processes used to form the corrosion barrier coating of the present invention include slurrying processes such as dip coating, spraying, and painting. In this approach, a suspension is made as described above. Thereafter, the suspension can be applied to the part or part to which the thermal barrier coating has been applied, by dip coating, spray coating or painting as described above. Any suitable technique known in the art can be used to apply the suspension to the thermal barrier coated portion or part.

  After applying the suspension to the thermal barrier coating part or part, the part or part may be dried to remove excess reagent in the thermal barrier coating. The part or part may be dried as described above. Further, if necessary, the part or part may be sintered as described above.

  Referring to FIG. 2, the method of the present invention provides a part or portion 50 having a thermal barrier coating (TBC) 52 and a hard shell corrosion barrier coating 54 attached to the surface of the thermal barrier coating 52. An infiltrated region 56 may be formed between the coating 54 and the coating 52. The infiltration region is constituted by a thickness of 5.0 to 100% of the thickness of the TBC measured from the surface of the TBC to the inside. The thickness of the infiltration region is preferably 10 to 20% of the thickness of TBC. The part or portion 50 can be made from a suitable metallic material such as a nickel-base superalloy well known in the art.

  TBC corrosion is likely to occur in certain areas of the turbine engine component. For example, the tip of the blade, particularly the suction side, is subject to corrosion. The buttress on the outer peripheral side of the vane is also corroded by the centrifugal force. Centrifugal force acts on most of the particulates contained in the turbine gas flow outward in the radial direction of the turbine, and most of the damage caused by the particulates occurs there. The relatively steep contours of turbine engine components are subject to corrosion because the steep contours increase the local pressure on the component surface by compressing the gas flow. Increasing local pressure increases the frequency of collisions with molecules and various particulates contained in the gas stream, leading to corrosion of turbine engine components. An area known to be susceptible to corrosion in order to minimize the added weight of hard shell coatings and to minimize adverse effects such as reduced strain resistance that can be imparted to the TBC of turbine engine components. It seems better to apply a hard shell coating only to

  A hard shell coating may be applied to only a portion of the turbine engine component using a painting process, a dip coating process, or an electrophoretic approach. Organic masking agents can be applied to all surfaces that are not intended to be coated.

  The hard shell coating may be applied by applying a UV curable resin, such as a commercially available resin known as a photoresist, to the turbine engine component. Thereafter, a sheet metal mask is applied to the region where the hard coating is desired to be applied. The resin coated and masked part can then be exposed to UV light for 1.0 to 10 minutes to cure all exposed resin. After curing, the sheet metal mask is removed and the uncured resin is washed away. Thereafter, the hard coating process can proceed. When using photolithography, drying is performed at a temperature of 600 ° F. to 900 ° F. (316 ° C. to 482 ° C.) for 2.0 to 4.0 hours in order to burn off the cured resin. May be.

  The process of the present invention can be used to form a corrosion barrier coating on the surface of various types of parts and parts that have a thermal barrier coating on the surface. The part or part to be treated includes, but is not limited to, various parts having an airfoil, various parts having a seal, airfoil, seal and the like. Examples of such portions or parts include blades, vanes, stators, turbine intermediate frames, combustor panels, combustor cans, combustor partition panels, disk side plates, and fuel nozzle guides. .

Schematic diagram of an apparatus for forming a corrosion barrier on a workpiece with a thermal barrier coating. Schematic of workpiece with thermal barrier coating and corrosion barrier.

Claims (33)

A method of forming a corrosion barrier that protects a thermal barrier coating on a workpiece, comprising:
Creating a suspension of ceramic particles suspended in a solvent;
Attaching particles in the suspension to the thermal barrier coating surface;
Drying the particles adhered to the thermal barrier coating surface to form a corrosion barrier coating having a Vickers hardness in the range of 1300-2750 kg / mm ² ;
Including methods.   The step of creating the suspension includes adding an acid or base to the suspension such that the pH of the suspension is 9.0 or less, and the step of attaching comprises the step of blocking. The particles in the suspension are biased using a sufficient direct current voltage to accelerate the suspended particles in the suspension toward the surface of the workpiece. The method of claim 1, comprising depositing a surface of the thermal barrier coating.   The method of claim 1, further comprising maintaining the suspension in a temperature range from room temperature to 120 ° F.   The method of claim 1, further comprising making the suspension such that the ceramic particles are present at a concentration of 0.001 to 5.0 wt%.   The method of claim 1, further comprising making the suspension such that the ceramic particles are present at a concentration of about 0.005 to 0.05 wt%.   Removing the work piece containing the deposited particles from the suspension, and the drying step removes the work piece in a temperature range from room temperature to 650 ° F. The method of claim 1, further comprising drying for a period of time.   The method of claim 6, wherein the drying step comprises drying the workpiece at room temperature for 1 to 20 hours.   The method of claim 6, wherein the drying step comprises drying the workpiece at room temperature for 3 to 10 hours.   The method of claim 6, wherein the drying step comprises drying the workpiece at a temperature range of 250 ° F. to 650 ° F. for 0.5 to 5.0 hours.   The method of claim 6, wherein the drying step comprises drying the workpiece at a temperature range of 250 ° F. to 650 ° F. for 1.0 to 2.0 hours.   The method of claim 6, further comprising sintering the workpiece at a temperature range of 1950 ° F. to 2000 ° F. for 3.0 to 4.0 hours.   In order not to agglomerate and settle the particles, 0.01 to 1.0% by weight of a dispersant selected from the group consisting of polymethyl alcohol methacrylate and ammonium stearate is further added to the suspension. The method of claim 1 comprising.   The method of claim 1, further comprising adding 0.1 to 3.0 wt% binder to the suspension to enhance the strength of the shell formed by the corrosion barrier.   14. The method of claim 13, wherein the step of adding a binder comprises adding 1.0-2.0% by weight polyvinyl alcohol.   Making the suspension of ceramic particles comprises making the suspension with ceramic particles selected from the group consisting of aluminum oxide, silicon nitride, silicon carbide, and molybdenum disilicide. Item 2. The method according to Item 1.   The method of claim 1, wherein making the suspension comprises making the suspension using ceramic particles having a particle size of 0.02 to 0.2 microns.   The method of claim 2, wherein the acid adding step comprises adding an acid that maintains a pH of the suspension below 4.25.   3. The method of claim 2, wherein the step of adding acid comprises adding an acid that maintains the pH of the suspension in the range of 2.0 to 4.25.   The method of claim 2, wherein the step of adding acid comprises adding an acid selected from the group consisting of nitric acid, hydrochloric acid, acetic acid, and stearic acid.   The method of claim 2, wherein the step of adding a base comprises adding a base selected from the group of aluminum hydroxide and ammonium hydroxide to raise the pH of the suspension.   The method of claim 2, wherein the depositing step comprises applying a voltage of 50-2000V to the workpiece.   The method of claim 2, wherein the depositing step comprises applying a voltage of 900-1100 V to the workpiece.   The method of claim 1, wherein the step of making a suspension comprises adding a solvent selected from the group consisting of water, alcohol, and mixtures thereof.   The method of claim 1, wherein depositing the particles comprises applying the suspension to the thermal barrier coating surface of the workpiece using a slurrying process technique.   25. The method of claim 24, wherein the applying step comprises applying the suspension using a technique selected from the group consisting of dip coating, spray coating, and painting. A substrate;
A thermal barrier coating on the substrate surface;
A hard corrosion barrier attached to the thermal barrier coating surface and having a Vickers hardness of 1300-2750 kg / mm ² ;
Workpiece with 27. The workpiece of claim 26, wherein the hard corrosion barrier comprises a layer of alumina having a Vickers hardness of 2650 kg / mm < ² >. 27. The workpiece of claim 26, wherein the hard corrosion barrier comprises a layer of silicon nitride having a Vickers hardness of 1900 kg / mm < ² >. 27. The workpiece of claim 26, wherein the hard corrosion barrier comprises a layer of silicon carbide having a Vickers hardness of 2750 kg / mm < ² >. 27. The workpiece of claim 26, wherein the hard corrosion barrier comprises a layer of molybdenum disilicide having a Vickers hardness of 1300 kg / mm < ² >.   27. The workpiece of claim 26, wherein the thermal barrier coating comprises a zirconia-based thermal barrier coating.   27. The workpiece of claim 26, further comprising an infiltration region between the thermal barrier coating and the corrosion barrier.   27. The workpiece of claim 26, wherein the workpiece comprises a turbine engine component.

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