JP6126852B2 - Gas turbine component coating and coating method - Google Patents

Description

  The present invention is a protective coating for gas turbine blades or other components, depending on the aluminum bearing coating applied to the relatively hot areas of the component and the coating function required. And a coating comprising a chromium-bearing coating applied to a relatively low temperature region of the part.

  Current gas turbine designs require different coatings on different areas of the turbine component for different functional reasons. Examples of coating functions include wear, oxidation, thermal barrier, and hot corrosion. The turbine designer selects the appropriate coating depending on the specific function in the gas turbine environment.

  Hot corrosion is a form of accelerated oxidation when liquid salts are present on the surface of Ni and Co-based superalloy parts. The salt is usually sodium sulfate, and other natural components such as K, Ca, and / or Mg are present. It is well known that the resistance to hot corrosion attack increases as the Cr content of the alloy increases. A currently practiced method for increasing the surface Cr content is pack and vapor phase chromizing. This is one-step deposition and forms a Cr-enriched alloy zone by reaction with a Ni substrate alloy. The chromizing process is facilitated by a halide (Cl or F) activator, which produces Cr-halide gas at relatively high temperatures, for example, greater than 1900 ° F.

  Since packs and vapor phase chromizing require high temperatures in excess of 1900 ° F., it is difficult to apply locally to the part area of interest and when using these processes, in the early stages of the part manufacturing process, Must be applied to the entire part. Further, in these processes, masking is not effective as a means for controlling the local deposition of chromium in the target region, and as a result, has not been applied to such a high temperature process.

  The present invention, in one embodiment, provides a method of forming a protective coating on a gas turbine component that is applied as a double coating to a region of a gas turbine component that is exposed to relatively high service temperatures. An aluminum-containing coating and a chromium-containing coating applied to another area of the gas turbine blade or other component that is exposed to relatively low service temperatures and hot corrosion, thereby exposing the gas turbine component to exposure. A method is provided that can provide a coating function for different temperatures and oxidation / corrosion environments.

In an exemplary embodiment of the present invention, the method of the present invention includes forming two types of coatings on a superalloy substrate, first of all, a relatively high temperature first of the substrate. An area containing an aluminum-containing coating is applied, and then a metal coating containing chromium is applied to an adjacent relatively cold area of the substrate, followed by diffusing the chromium into the substrate to provide an adjacent relatively cold area. This is done by forming a chromium-enriched diffused coating in the region. The aluminum-containing coating is applied by high temperature deposition in the first step, and the chromium-containing coating is applied at a relatively low temperature, for example, below 500 ° F., in the next second step. The method of the present invention typically involves masking the relatively cool area before the aluminum-containing coating is applied to the relatively hot area, after which the chromium metal coating is compared. Masking the relatively hot areas prior to being applied to the hot areas.

  When the substrate is a gas turbine component, the method of the present invention first masks the base region of the component and then applies an aluminum-containing coating such as a diffusion aluminide coating to the airfoil region to remove the masking of the base portion. And then masking the already coated airfoil portion. The method of the present invention then deposits a chromium-containing metal coating on at least a portion of the relatively cold base region that is exposed to hot corrosion, removes the masking of the airfoil region, and then removes the coating portion of the base region. Diffusing chromium into the alloy to form a chromium enriched diffusion surface coating in the base region. An aluminum-containing coating can be applied over the airfoil region, as well as the intermediate platform region and the base shank region, if desired. Note that the attachment portion of the base region (e.g., the fir tree portion) is left uncoated so that the fatigue life of the base region connected to the turbine disk is reduced. Enhanced.

In certain embodiments of the present invention, the electroplating bath, the electrophoretic bath, relatively to use a low-temperature film forming process using a liquid material deposition medium liquid such as slurry (liquid deposition medium), the precursor component (precursor component ) Is formed on at least a portion of the relatively low temperature region. The chrome coating is applied as a very thin layer with a thickness of 0.0005 to 0.005 inches. The diffusion of deposited chromium into the substrate is typically done by high temperature heat treatment after removing the masking from the aluminum-containing coating already applied to the airfoil region.

  The present invention relates to a nickel-based or cobalt-based alloy having an aluminum-containing coating applied to an airfoil region and a metal coating comprising substantially pure chromium or a chromium alloy applied to at least a portion of a base region of a component. A precursor component of a turbine component is provided. The chromium coating is then diffused into the alloy to form a chromium enriched diffusion coating on the portion of the base region of the gas turbine blade. The diffuse chromium enriched coating has an outermost region that includes at least about 20%, preferably about 25%, more preferably about 30% to about 60% Cr by weight.

  Advantages, features and embodiments of the present invention will become apparent from the following description.

1 is a schematic diagram of a gas turbine blade having an aluminum-containing coating AL and a diffusion chromium-enriched coating CR, where the aluminum-containing coating AL can be used to form a protective scale or layer of alumina during use, and in the airfoil region and high temperature. A platform region facing away from the base region and the hot gas path is provided on the surface of the platform area opposite the gas path, and the diffusion chromium-enriched coating CR can form a protective scale or layer of chromium during use. And is provided.

1 is a schematic view of an intermediate gas turbine blade precursor component having an aluminum-containing coating AL and a metal chromium coating ECR, the aluminum-containing coating AL being capable of forming a protective scale or layer of alumina during use, and an airfoil region and Located on the platform region surface opposite the hot gas path, the metallic chromium coating ECR faces away from the base region and the hot gas path so that it can diffuse into the alloy to form a protective diffusion chromium enriched coating. And is provided in the platform area.

FIG. 5 is a schematic diagram of another embodiment of a gas turbine blade, showing that an aluminum-containing coating and a chromium-containing coating are provided in various illustrated areas of the turbine blade.

FIG. 6 is a further schematic diagram of another embodiment of a gas turbine blade, showing that an aluminum-containing coating and a chromium-containing coating are provided in various illustrated areas of the turbine blade.

After performing pack chromizing, masking the shank region, and performing aluminizing to form a Pt-modified diffusion aluminide (Pt-Al) coating on the airfoil, the chromium concentration profile in the shank portion of the base region (Cr concentration versus It is a graph of the distance in a CMSX-4 (trademark) nickel base superalloy base material. The base region includes the shank portion of the turbine blade and the fir tree attachment.

FIG. 6 is a graph of Cr concentration versus distance in a CMSX-4 nickel-base superalloy substrate, showing the effect of Cr plating thickness and diffusion conditions on Cr concentration in the substrate. The distance “0” is the surface of the substrate.

It is the microscope picture of the microstructure of the CMSX-4 sample which electroplated by 8.7 micrometer Cr plating, and performed the diffusion process by heating at 1975 degreeF for 4 hours after that.

It is a figure which shows the result of the hot corrosion test in 700 degreeC, and plotted the weight change with respect to exposure time about the various shown CMSX-4 samples, The test was done twice. The test was performed by applying 1 to ² mg of Na ₂ SO ₄ per cm ² to the sample surface, and sample inspection was performed every 25 hours.

CMSX- which was electroplated with 8.7 μm Cr plating and then subjected to diffusion treatment by heating at 1975 ° F. for 4 hours, and Na ₂ SO ₄ was applied to the sample surface and exposed to a high temperature corrosion state as in FIG. It is a microscope picture of four samples. The through hole provided in the sample (one shown) is not coated, indicating that it has been subjected to severe hot corrosion attack, but the coated surface is protected.

Electroplating was performed with 8.7 μm Cr plating, followed by diffusion treatment by heating at 1975 ° F. for 4 hours, and Na ₂ SO ₄ was applied to the sample surface as in FIG. 8 and exposed to high temperature corrosion at 700 ° C. It is the microscope picture of the microstructure of the CMSX-4 sample.

It is the microscope picture of the microstructure of the CMSX-4 sample which electroplated by 8.7 micrometer Cr plating, and performed the diffusion process by heating at 1975 degreeF for 4 hours after that. It is a table | surface which shows the microprobe result with respect to the sample of FIG. 11A. It is a graph plotting and showing the change of Cr content with respect to the distance in the base alloy, the open triangle symbol is a sample as plated, the open square symbol is a plated / diffusion heat treated sample, and the open diamond symbol is It is a sample subjected to plating / diffusion heat treatment / high temperature corrosion test (type I high temperature corrosion test). The distance “0” is the surface of the substrate.

  One embodiment of the present invention provides a method for forming a protective coating on a gas turbine component wherein the formed coating is a gas turbine blade or other component that is exposed to relatively high temperatures during use. An aluminum-containing coating applied to one area and a chromium-containing coating applied to another area adjacent to the area and exposed to relatively low temperature and hot corrosion during use. Such a double coating provides a coating function for different temperatures during use and for oxidizing and corrosive environments.

  While the present invention is particularly useful for protecting different areas of gas turbine blade components from oxidation and hot corrosion during use of a gas turbine engine, the present invention is not limited to gas turbine components, This part can also be implemented to protect against oxidation and hot corrosion. The present invention can be implemented to protect nickel-base superalloy gas turbine parts, nickel-cobalt-base superalloy gas turbine parts, or cobalt-base superalloy gas turbine parts from hot corrosion, It is not limited to these alloys. The present invention is described below with respect to protecting different areas of a gas turbine engine blade made from a CMSX-4 nickel-base superalloy from oxidation and hot corrosion during use of the gas turbine engine. This is not a limitation.

  Specifically, FIG. 1 is an illustration of a gas turbine blade (10) that includes an airfoil region (12), a root region (14), an airfoil and a base region. And an intermediate platform region (20). The airfoil (12) includes a tip (12a), a leading edge (12b) and a trailing edge (12c) that are exposed to the gas path of the engine turbine section. The platform region (20) typically separates the gas path surface and the non-gas path surface, and includes a platform upper surface facing the gas path and a platform lower surface facing away from the gas path. Yes. The base region (14) includes a non-gas path surface below the lower surface of the platform region (20), and the base region includes a mounting portion (16) (e.g., a conventional fir tree), The attachments connect the turbine blades in a conventional manner to a turbine disk (not shown) and an adjacent shank (18) between the attachment (16) and the platform region (20). The fir tree typically has serrations that are machined to fit into the turbine disk, which serrations can be machined before or after coating, based on customer specifications. it can. The shank region (18) includes the region between the fir tree and the lower surface of the platform region (20), includes an as-cast surface and a machined surface, and further seals the gas path from the non-gas path region. Features can be included to assist in doing.

  The hot first region of the turbine blade (10) is exposed to relatively high temperatures in the gas turbine engine during use and is prone to oxidative degradation and faces the airfoil region (12) and the airfoil region. The platform surface (20a) is configured to operate in or near the hot gas path of the turbine section of the gas turbine engine. The airfoil region (12) and the platform surface (20a) are the hottest regions of the turbine blade and, by way of example and not limitation, are typically operating temperatures above 1900 ° F.

  When the operating temperature is relatively high, the so-called alumina production coating ( Preferably an alumina-former coating is provided.

  The relatively cool second region of the turbine blade (10) includes relatively low temperatures and other components such as sodium sulfate, K, Ca, and / or Mg during use in a gas turbine engine. ) Exposure to high temperature corrosion. The second region includes a lower surface (20b) of the platform region (20) facing away from the airfoil region and a base region (14). Thus, the second region includes a low temperature region that can be operated without the old turbine blades being coated. However, as the efficiency of the combustor increases, the operating temperature of the second region generally increases, and it extends uniformly throughout the second region. Accordingly, the first region composed of the airfoil (12) and the platform surface (20a) is also at a higher temperature. When a salt of sodium sulfate is deposited on a surface operated at 1200 ° F. to 1850 ° F., a hot corrosion attack occurs. When a high stress state and a high temperature corrosion condition overlap the base region (14) of the blade, the turbine blade in the base region is subject to a rapid corrosion attack and is likely to break. Turbine blades previously used at low temperature operating conditions are not coated in the base region, but the hot corrosion resistance can be improved by increasing the chromium content of the turbine blade alloy.

  The present invention provides a method for applying multiple coatings and coatings to protect different hot and cold regions for turbine blades that are exposed to the more aggressive temperature and hot corrosion conditions associated with modern engine designs. The present invention provides a nickel or cobalt based alloy turbine blade (10) having an aluminum containing coating AL applied to the airfoil region of the blade and a chromium containing metal coating applied to at least a portion of the base region of the blade. As such, the metal coating diffuses into the alloy to form a diffused chromium enriched coating CR in the portion of the base region. FIG. 1 shows an aluminum-containing coating AL formed on the airfoil and a chromium-containing diffusion coating CR formed on the base region. It should be noted that during operation, a thin alumina scale is formed on the coating, so the aluminum-containing coating AL includes this so-called alumina forming coating. Also, during operation, a thin chromia scale is formed on the coating, so the chromium-containing diffusion coating CR includes this so-called chromia-forming coating. In addition, a thermal barrier coating (TBC) (for example, yttria-stabilized zirconia) is applied as an outermost coating to all or a part of the airfoil region (12) and the platform surface (20a) before and after chrome coating diffusion. Provides the thermal insulation properties of TBC.

  FIG. 2 illustrates an aluminum-containing coating AL formed on an airfoil and an as-deposited metallic chromium content formed in a base region using a method according to another embodiment of the invention described below. Figure 2 shows a gas turbine blade precursor part (intermediate part) including a coating ECR. Another embodiment of the present invention eliminates the problems and difficulties that arise when a double coating based on the required coating function is not provided, as described in the comparative examples listed below. . The chrome coating is applied as an ultra-thin layer having a thickness of from 0.000005 to 0.005 inches.

  The aluminum-containing coating is applied in an initial one-step process by high temperature deposition. For high temperature vapor deposition, for example, in addition to chemical vapor deposition at 1900 ° F. or more based on US Pat. Nos. 5,264,245, 4,132,816 and 3,486,927, a conventional above-the-pack process or other Includes those from vapor deposition processes.

  The chromium-containing coating is applied using a two-step process after the aluminum-containing coating. The two-step process uses a liquid electrolytic deposition bath or liquid carrier medium to deposit a chromium-containing metal coating on the substrate at a temperature below 212 ° F. and then diffuses the chromium into the substrate by a high temperature heat treatment. It is included. Examples of low temperature processes for depositing chromium metal coatings include, but are not limited to, electroplating or electrophoretic deposition using a liquid bath, and chromium-containing particles (eg, Cr or Cr alloy particles) in a liquid carrier. All of these can be performed at temperatures below 212 ° F. using a liquid bath or liquid slurry and dried after implementation. Other relatively low temperature deposition methods that can be used to deposit the chromium-containing metal coating include, but are not limited to, electrical spark discharges typically performed below 500 ° F. Include cladding performed at temperatures below 100 ° F., plasma sprays performed at temperatures below 500 ° F., and entrapment plating in which Cr particles are encapsulated in a Ni electroplating layer.

  If the substrate is a gas turbine component having an airfoil, a platform and a base region, one embodiment of the method is to first mask the base region of the component and then apply an aluminum-containing coating (diffusion aluminide) to the airfoil region. Coating, etc.), removing the masking of the base region and then masking the coated airfoil region. In an embodiment of this method, a chromium-containing metal coating is deposited on at least a portion of the relatively low temperature base region that will be exposed to hot corrosion, and after removing the airfoil region masking, Chromium is diffused into the coating portion alloy to form a chromium-enriched surface coating in the base region portion. If desired, an aluminum-containing coating can be applied to cover the airfoil region and the intermediate platform region and the base shank region. An attachment portion (for example, a fir tree-like portion) in the base region is a portion connected to the turbine disk, and may not be coated in order to improve the fatigue life of the base region.

  A chromium-enriched diffusion coating applied to at least a portion of the base region of a nickel-based superalloy substrate typically comprises a Cr-enriched outermost diffusion zone in a diffused state, and the outermost diffusion zone and the substrate And the Cr-enriched outermost diffusion zone contains chromium, nickel and other base alloy elements in the solid solution, and the main component of this zone is Cr (FIGS. 7, 11A, 11B), the inner diffusion zone contains nickel, chromium and other base alloy elements, in which the amount of Cr is small (FIGS. 7, 11A, 11B). There may be another diffusion or reaction zone between the inner diffusion zone and the substrate, which is a phase with a high refractory content. This diffusion or reaction zone is so thin that it cannot be seen in FIGS. 7 and 11A.

  In the implementation of the examples of the present invention, by controlling the Cr content and the Cr depth profile into the substrate, the high temperature corrosion resistance required depending on the specific use mode can be adjusted. Typically, the hot corrosion resistance is improved by increasing the Cr content on the surface of the outermost coating substrate. Increasing the Cr content can be achieved by changing the Cr metal coating thickness and diffusion heat treatment conditions.

<Comparative example>
This comparative example is described to show that it is difficult to form the two types of coatings on the gas turbine blade by a method other than the present invention.

Coating to protect two environments using, for example, a pack or vapor phase chromizing process at temperatures above 1900 ° F. or a pack, vapor phase or CVD aluminizing process at temperatures above 1700 ° F. Turbine blades with (two types of coatings) can be made. However, it has been found that there is a problem in maintaining the high Cr surface by treating the surface to be high Cr. Due to the masking used for aluminizing, Cr may be removed from the chromium plated shank during the high temperature aluminizing process. That is, to coat a turbine blade with two types of coatings, the turbine blade must be entirely chromium plated by a hot pack or vapor phase process, and the resulting Cr-enriched layer can be Before applying the aluminizing or protective coating on the surface, it must be removed from the gas path surface (12) (12a). In order to prevent the base region (14) from being aluminized, the base region is placed in a containment vessel containing masking powder (eg, alumina powder, NiO powder, etc.) and masked. However, this step is not preferable because the Cr content of the Cr-enriched layer already applied to the base region is reduced and the high temperature corrosion resistance is lowered. This will be clarified in the following explanation.

  With the airfoil, platform, and base features of FIG. 1, a CMSX-4 nickel-base superalloy (nominal composition is about 9.6% Co, about 6.6% Co, about 0.6% Mo, and about 0.60 Mo) %, W about 6.4%, Re about 3.0%, Ta about 6.5%, Al about 5.6%, Ti about 1.0%, Hf about 0.1%, balance Ni and inevitable impurities) The entire cast turbine blade is made of chrome and then grit blasted to remove the Cr-enriched coating from the hot first region containing the airfoil region (12) and platform surface (20a). did. A high temperature first region was electroplated to form a Pt metal layer and then aluminized by CVD to form a Pt modified diffusion aluminide coating in the first region. Next, the cold second region (including platform surface (20b) and base region (14)) was masked using a commercially available powder maskant M1 (Akron Paint & Varnish Co., 1390 Firestone Parkway, Akron Ohio).

The pack parameters used to carry out the chromizing process are as follows: Pure chromium powder was treated with aluminum oxide and NH ₄ Cl activator for 5 hours at 1950 ° F.

Pt electroplating was performed using the parameters described in US Pat. No. 5,788,823, and 0.3 mil Pt was deposited on the substrate. This patent is hereby incorporated by reference. The aluminizing process used the parameters described in US Pat. No. 5,264,245 and was processed in a H ₂ / AlCl ₃ atmosphere at a temperature of 1975 ° F. for 1440 minutes. This patent is hereby incorporated by reference.

  FIG. 5 shows the Cr concentration depth profile in the shank portion (18) of the turbine blade, as it is chromium plated (pack Cr), and after masking and aluminizing (pack Cr + aluminizing cycle). A Pt-modified diffusion aluminide coating is formed in the first region including the airfoil and the platform surface (20a).

  In the case of a chrome-plated coating in the second region shown in FIG. 5, enrichment of Cr content is a desirable and desirable chemistry in terms of resistance to hot corrosion attack. However, as the graph shows, Cr enriched by the pack chromizing process prevents aluminum from depositing on the shank (18) and mounting (16) even when the base is masked. To reduce) after the aluminizing step. The Cr content of the shank portion is reduced to be less than the Cr content of the CMSX-4 superalloy (nominal Cr composition of the alloy: 6.4% by weight). This is completely opposite to the direction of Cr content desired to improve hot corrosion resistance. This comparative double coating process failed to produce turbine blades with Cr-enriched coatings that are favorable for hot corrosion attack resistance.

In accordance with an embodiment of the method of the present invention, continuous processing steps used to produce two types of coatings (sequence processi n g steps) is intended to eliminate the proven above problems and difficulties in Comparative Example is there.

<Example 1>
In an exemplary embodiment of the invention, the following processing steps are used:

  1. When platinum modified diffusion aluminide coatings are formed on gas path surfaces (12) (20a), these surfaces are optionally electroplated with a layer of Pt as described in US Pat. No. 5,788,832. This patent has already been incorporated herein by reference. Also, this step can be omitted if only the diffusion aluminide coating is to be formed.

  2. The second region of the turbine blade (ie, the base region (14) and the platform surface (20b) is masked with the M1 maskant powder contained in the containment vessel, ie, the base region (14) and the platform surface (20b) are Embedded in maskant powder in a containment vessel.

  3. Diffusion aluminide coating (e.g., if step 1 was performed, Pt modified) with aluminizing the first region (i.e. airfoil 12 and platform surface 20a) at the high temperature and masking the second region A diffusion aluminide coating).

  4). Mask the diffusion aluminide coating in the first region.

  5. In a state where the diffusion aluminide coating formed in Step 3 is covered with the masking in Step 2, Cr electroplating is performed on the low temperature second region. Cr electroplating is performed using a liquid (eg, water) electroplating bath, for example, below 212 ° F. Since the masking of the first region is effective under low temperature plating bath conditions, local film formation by Cr electroplating is possible.

  6). Cr plating is diffused into the CMSX-4 substrate alloy to form a Cr-enriched hot corrosion resistant coating. The diffusion of Cr plating improves the bond with the superalloy substrate and improves the resulting ductility of the Cr-enriched layer.

  The plating conditions used in the chrome electroplating process comply with AMS (Aerospace Material Specification) 2438B for hard chrome coating of steel materials for aerospace materials, and is a hexavalent high hardness high density chromium which is substantially pure Cr. This is the condition under which plating can be formed. This AMS 2338B is incorporated herein by reference to achieve this goal.

  In this example, high hardness, high density, and substantially pure chromium electroplating was done commercially by the Illinois electroplater Armoloy (118 Simonds Ave., Dekalb, Illinois). The deposited thickness of the Cr electroplating was 8.7 micrometers or 3.5 micrometers. The electroplating layer is substantially pure Cr, for example, 99.9 wt% Cr, with the balance being plating impurities. The present invention includes electroplating of Cr alloy in addition to pure Cr, and also includes plating of alternating layers of Cr and Ni.

Chromium electroplating can be performed using any suitable parameter. Although the plating conditions which can be used are shown below, it is for illustration and is not limited.
1. The surface to be plated is cleaned by vapor honing the surface with an alumina slurry.
2. The surface to be plated is activated by immersion in a plating bath at 52 to 63 ° C. containing 250 to 400 g / L chromic acid and 2.5 to 4 g / L sulfate catalyst (sulfuric acid). 30 to 54 A / dm ² ) at ˜12 volts for 30 seconds to 2 minutes to make the part the anode (the reverse of the Cr plating layer).
3. The surface to be plated is immersed in a plating bath and Cr plated, and a current is applied for 4 to 30 minutes to make the part a cathode. The time for passing the current may be the time necessary to obtain the desired Cr plating thickness.
4. Rinse in 120 ° F. deionized water to remove most of the plating bath.
5. Rinse in hot deionized water to remove remaining plating bath and dry.

The CVD aluminizing process is performed using the following parameters:
Based on US Pat. No. 5,264,245, treated in a 1975 ° F. H ₂ / AlCl ₃ atmosphere for 1440 minutes. This patent is hereby incorporated by reference to achieve this goal. Other aluminizing processes that can be used include pack, vapor phase, sputtering, physical vapor deposition, diffusion heat treatment performed after slurry, diffusion heat treatment performed after electrophoresis, etc. It is not limited.

  In this example, the Cr diffusion heat treatment is performed at 1975 ° F. for 4 hours or at 2050 ° F. for 2 hours, and in an Ar partial pressure atmosphere to prevent oxidation.

  FIG. 6 is a graph showing the relationship between the Cr concentration and the distance into the CMSX-A nickel-base superalloy substrate, and shows the effect of Cr plating thickness and diffusion conditions on the Cr concentration in the substrate. . In FIG. 6, the distance “0” is the surface of the substrate. FIG. 6 shows that the surface Cr content can be controlled to a minimum of 15 atomic% and a maximum of 63 atomic%. FIG. 6 also shows that the Cr enrichment depth can be controlled similarly. The Cr content and enrichment depth are typically adjusted so that hot corrosion resistance can be tolerated while minimizing the fatigue effects of strain experienced by components during use in a turbine engine. FIG. 6 shows the range of Cr enrichment results for two types of Cr plating thickness and two types of diffusion heat treatment conditions.

  FIGS. 7 and 11A include micrographs of microstructures of CMSX-4 samples electroplated with 8.7 μm Cr plating and then subjected to a diffusion treatment that was heated at 1975 ° F. for 4 hours. FIG. 11B shows the microprobe data of the Cr-enriched diffusion coating as a table, and FIG. 11C plots the change in Cr content against the distance in the base alloy. The distance “0” is the surface of the substrate.

  The results of FIGS. 7, 11A and 11B (microprobe table) and 11C (plot) show that the chromium-enriched diffusion coating is between the Cr-enriched outermost (top) diffusion zone and the outermost diffusion zone and the substrate. An inner diffusion zone (diffusion), and the Cr-enriched outermost diffusion zone contains chromium, nickel and other base alloy elements in the solid solution, the main component of this top zone is Cr, and the inner diffusion zone is This indicates that the amount of Cr is small in this diffusion zone, including nickel, chromium and other base alloy elements. There may be another diffusion or reaction zone between the inner diffusion zone and the substrate, which is a phase with a high refractory content. This diffusion or reaction zone is so thin that it cannot be seen in FIGS. 7 and 11A.

FIG. 8 is a diagram showing the results of the hot corrosion test at 700 ° C., in which the change in weight with respect to the exposure time is plotted for the various CMSX-4 samples shown, and the test was performed twice. In the test, 1 to ² mg of Na ₂ SO ₄ was applied to 1 cm ² of the sample surface, and sample inspection was performed every 20 hours. The salt treated sample was then placed in a furnace heated to 700 ° F. In the furnace, 1000 ppm of SO ₂ / O ₂ gas was flowing in the heated Pt catalyst, and the sample was exposed to the furnace to generate SO ₃ . SO ₃ reacts with the salt at the test temperature to attack the corrosion.

  FIG. 8 shows that the coated test sample of the inventive example had essentially the same weight change over time, regardless of Cr electroplating thickness and Cr diffusion parameters. . The uncoated CMSX-4 sample had substantial weight loss during the test.

FIG. 9 is a micrograph of the CMSX-4 sample. The sample was electroplated with 8.7 μm Cr plating and then subjected to diffusion treatment by heating at 1975 ° C. for 4 hours. As shown in FIG. It has been exposed to a hot corrosive environment with Na ₂ SO _{4 at} a temperature exceeding ° F. The through-holes (only one shown) through the sample are uncoated and have been subjected to severe hot corrosion attack, indicating that the coated surface is protected.

  FIG. 9 shows that these test conditions are aggressive for uncoated CMSX-4 alloy substrates, and that the coated sample surface is resistant to hot corrosion attack. Show.

FIG. 10 is a micrograph of the microstructure of the CMSX-4 sample. The sample was electroplated with 8.7 μm Cr plating and then subjected to diffusion treatment by heating at 1975 ° F. for 4 hours, as shown in FIG. Thus, it has been exposed to a high temperature corrosive environment with Na ₂ SO _{4 at} a temperature exceeding 700 ° F.

  FIG. 11C is a graph plotting the change in Cr content with respect to distance in the base alloy, where the open triangle symbol indicates the as-plated sample, the open square symbol indicates the plated / diffusion heat-treated sample, white The open diamond symbol is a sample subjected to plating / diffusion heat treatment / high temperature corrosion test (type I high temperature corrosion test). The distance “0” is the surface of the substrate.

  Comparing the latter two samples of FIG. 11C, the Cr content after the hot corrosion test is virtually unchanged.

<Example 2>
In another exemplary embodiment of the invention, the following processing steps are used:

  1. When platinum modified diffusion aluminide coatings are formed on gas path surfaces (12) (20a), these surfaces are optionally electroplated with a layer of Pt as described in US Pat. No. 5,788,832. This patent has already been incorporated herein by reference. Also, this step can be omitted if it is desired to form a simple diffusion aluminide coating.

  2. A high temperature first and second regions are aluminized to form a diffusion aluminide coating (eg, Pt modified diffusion aluminide coating if step 1 is performed). Masking for protecting the second region is not performed.

  3. The diffusion aluminide coating is selectively removed from the second region by grit blasting, machining or other techniques to expose the base alloy. Note that the diffusion aluminide coating in the first region remains.

  4). The diffusion aluminide coating in the first region is masked as described in Example 1.

  5. Cr electroplating is performed on the exposed low-temperature second region. The diffusion aluminide coating formed in step 2 is coated with the masking in step 4. Cr electroplating is performed using a liquid electroplating bath, for example, at temperatures below 212 ° F. Since the masking of the first region is effective under a low temperature plating bath condition at room temperature, film formation by Cr electroplating can be performed locally.

  5. Cr plating is diffused into the CMSX-4 substrate alloy to form a Cr-enriched hot corrosion resistant coating. Due to the diffusion of the Cr plating, the bonding with the superalloy substrate is improved, and the ductility of the obtained Cr-enriched layer is improved.

  The chrome electroplating process is performed by the electroplating company of Example 1. The CVD aluminizing process is performed using the parameters of Example 1. The Cr diffusion heat treatment is performed using the parameters of Example 1.

<Other embodiments>
3 and 4 show another embodiment of the present invention. In FIG. 3, an aluminized layer (which may or may not be modified by Pt) AL ′ is applied to the upper region of the shank portion (18). From the platform surface (20b) to a predetermined distance or plane below the platform (20), there are other coatings AL, CR, as shown. In FIG. 4, the base region is provided with an uncoated mounting portion (17) in a lower temperature region near the turbine disk of the turbine blade. The attachment portion (17) is masked during aluminizing and Cr plating. The attachment portion (17) includes an uncoated base alloy. This mounting portion (17) cannot accept any coating including other coatings AL and CR due to the blade design.

  The present invention allows for many combinations of Al, Al / Cr, Cr, and uncoated areas in a turbine blade, and the desired coating required to adapt to various usage conditions of a gas turbine engine. Provide functionality.

  While the invention has been described in terms of several detailed embodiments, those skilled in the art will recognize that various modifications can be made to the embodiments and details without departing from the spirit and scope of the claimed invention. It will be understood that it can be done.

Claims (10)

A method of forming different types of coatings on a substrate having a first region and a second region different from the first region ,
(A) forming a diffusion aluminide coating on the first region of the substrate,
(B) after step a, the second region of the substrate, a step of depositing a metal containing chromium to form a chromium-containing metallic coating,
(C) formed the chromium chromium-containing metal coating is diffused into the substrate, steps and, the including a method for forming a chromium enriched diffusion layer in the second region of the substrate. Prior to step a, the masking is facilities in the second region, the method of claim 1. Prior to step b, the masking is facilities diffusion aluminide coating formed on the first region, the method of claim 1. A method of forming different types of coatings on a substrate having a first region and a second region different from the first region,
(A) forming a diffusion aluminide in the first region and the second region of the substrate;
(B) removing the diffusion aluminide coating formed on the second region of the substrate;
(C) after step b, depositing chromium-containing metal on the second region of the substrate to form a chromium-containing metal coating;
(D) performing a diffusion heat treatment on the formed chromium-containing metal coating to diffuse chromium into the substrate to form a chromium-enriched diffusion layer in the second region of the substrate. . The method of claim 4 , wherein the diffusion aluminide coating formed in the first region is masked prior to step c . The method of claim 1 or 4 , wherein the chromium-containing metal coating is formed by electroplating or electrophoretic deposition . The method of claim 1 or 4 , wherein the chromium-containing metal coating is formed by a slurry coating process comprising chromium-containing particles in a liquid carrier . The base material is a turbine blade made of a nickel-based or cobalt-based alloy, and the first region is an airfoil side surface (20a) of an airfoil region (12) and a platform region (20), The method according to claim 1 or 4, wherein the second region is a base region side surface (20b) of the base region (14) and the platform region (20) . Chromium-containing metallic coating method of claim 1 or 4 is formed by electroplating a lower temperature than 212 ° F (100 ℃). A turbine component comprising a nickel-based or cobalt-based alloy and comprising an airfoil region (12), a platform region (20) and a base region (14),
  A diffusion aluminide coating is formed in a first region including the airfoil region (12) and the airfoil-side surface (20a) of the platform region (20);
  A chromium-containing metal coating is formed on the second region including the base region (14) and the base region side surface (20b) of the platform region (20);
  The turbine region, wherein the second region includes a chromium enriched diffusion layer.

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