JP2008149712A - Heat shield oxidation resistant coating for organic matrix composite substrate and coated article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating system in which an organic matrix composite used in an aerospace industry in place of a metal part holds the capability. <P>SOLUTION: A heat shield oxidation resistant coating 14 for an organic matrix composite substrate 12 has a constitution provided with a bond coat 24 containing nanoparticles dispersed in a polyimide matrix, and a heat shield layer 22 containing a silsesquioxane or an inorganic polymer. The nonoparticle contains a clay tablet, graphite flake, or basket-like silsesquioxane. A coated article 10 can be used for a gas turbine engine, in particular, for a passage duct exposed in a high-temperature oxygen-containing environment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates generally to thermal barrier antioxidant coatings and coated articles for organic matrix composites.

  Organic matrix composites (OMC = organic matrix composites) are used in the aerospace industry because they can achieve weight reduction when used instead of metal parts. However, exposure to high temperature environments reduces the mechanical properties of OMC and causes its oxidative degradation. For this reason, current heat-resistant OMC materials using heat-resistant matrix materials such as PMR-15 and AFR-PE-4 have limited applications.

  In the industry, attempts have been made to create thick parts to solve the above problems. However, increasing the thickness increases the weight and cost of the part compared to the effects that can be achieved by reducing the thermal and oxidation effects on the part.

  Another attempt has been to delay the material degradation by providing a sacrificial layer on the part. The sacrificial layer can be a thin carbon veil impregnated with PMC resin. However, protection by the sacrificial layer is lost over time.

Currently, the use of materials with ceramic fillers carried on a polyimide matrix, which is deposited as a thermal spray coating for OMC parts, is being investigated. Thermal spray coatings are intended to improve the environmental durability and erosion resistance of organic matrix composites. However, thermal spraying is associated with environmental, health, safety, energy and labor issues. Moreover, it is difficult to obtain a fully cured coating system during the spray deposition process.
US Pat. No. 6,271,273 Vosevic et al., "Optimal Substrate Preheating Model for Therm. Spray Dep. Of Thermosets Onto Polymer Matrix Comp.," NASA Tech Memo 2003-212120 (Mar. 03), http://ntrs.nasa.gov) Erosion Coatings for High-Temp. Polymer Composites: A Collaborative Project With Allison Advanced Development Company, http // www.grc.nasa.gov / WWW / RT1999 / 5000 / 5150sutter.html Properties of PMR Polyimides Improved by Preparation of a Polyhedral Oligometric Silsesquioxane (POSS) Nanocomposites, http://www.grc.nasa.gov/WWW/RM/RM05P-compbell.html

  Accordingly, it would be desirable if the high temperature performance of a component made of an organic matrix composite could be improved by providing a coating system that improves thermal oxidation stability and mechanical performance.

  In order to meet the above-described needs, one embodiment of the present invention provides a thermal barrier antioxidant coating for an organic matrix composite structure. In this way, a coating structure formed from a heat-resistant OMC material can be used as an alternative to a metal component, for example, in an environment at a temperature higher than the maximum operating temperature of the uncoated heat-resistant OMC material. In other embodiments, a coating structure formed from a low heat resistant OMC material can be used in an environment at a temperature higher than the maximum operating temperature of the uncoated low heat resistant OMC material.

  In one embodiment, a thermal barrier antioxidant coating for an organic matrix composite substrate is provided. The coating includes a bond coat provided on at least a first surface of the substrate and one or more thermal barrier layers that substantially cover the bond coat. The bond coat includes nanoparticles dispersed in a polyimide matrix. The heat shielding layer contains silsesquioxane or an inorganic polymer.

  In another embodiment, an article is provided that comprises an organic matrix composite substrate and a thermal barrier antioxidant coating disposed on one or more surfaces of the substrate. The thermal barrier antioxidant coating includes a bond coat and one or more thermal barrier layers. The bond coat contains nanoparticles dispersed in a polyimide matrix, and the thermal barrier layer contains silsesquioxane or an inorganic polymer.

  The gist of the invention is as described in the claims. However, the present invention can best be understood with reference to the following detailed description with reference to the attached drawings.

  Referring to the drawings, FIG. 1 shows a component 10 for use in a high temperature environment, particularly a gas turbine engine, although other applications are envisioned within the scope of the present invention. The component 10 includes a substrate 12 and a thermal barrier antioxidant coating 14 on at least a first surface 16 thereof. The first surface 16 is located on the “hot side” 18 of the part 10. The operating temperature on the high temperature side 18 of the component 10 can be about 725 ° F (385 ° C) or less.

  One embodiment envisions the use of a thermal barrier antioxidant coating for heat resistant OMC in turbine engine applications. A thermal barrier antioxidant coating is provided on at least the high temperature side of the composite part to lower the maximum exposure temperature of the underlying substrate and to form a barrier to oxidation of the structural composite matrix. Applications for thermal barrier antioxidant coatings include application to ducts that define various flow paths within the engine.

  Thermal protection systems in the form of thermal barrier coatings (TBCs) have been used on metals for many years. In such cases, the surface of the part is coated with a low thermal conductivity material to establish a thermal gradient between the environment of use and the part so that the subsurface material is not exposed to temperatures above its maximum operating temperature. . However, the characteristics and goals of OMC are different from those of metal substrates and are unique. Therefore, the coating of the present invention is referred to as “thermal oxidative barrier coating” in order to distinguish it from the thermal barrier coating used for the metal substrate.

  In one embodiment, the OMC matrix material is a heat resistant polyimide system such as AFR-700B, PETI-375, PMR-II-50, HFPE, AFR-PE-4 and PMR-15. However, the thermal barrier oxidation-preventing coating of the present invention is a bismaleimide-based polyimide material (BMI) (BMI), which is lower in cost and easier to process than a resin material having a lower heat resistance, for example, typically a heat-resistant polyimide material. For example, it can be used together with Cycom 5250-4 (registered trademark). By providing a thermal barrier anti-oxidation coating, it is possible to use low heat resistant materials in higher temperature environments than previously possible.

  The thermal barrier antioxidant coating 14 includes an outer thermal barrier layer 22 and a bond coat 24. The bond coat 24 functions as an oxide barrier in addition to the adhesion of the outer heat shield layer 22. In one embodiment, since the bond coat 24 is protected by the thermal barrier layer 22, the polymer matrix of the bond coat 24 can be the same as or similar to the polymer matrix of the substrate 12.

  In one embodiment, the material intended for use as the thermal barrier layer 22 is a material having thermal stability, specific gravity, bending strength and modulus measured as a function of thermal conductivity, coefficient of thermal expansion (CTE), weight loss. To evaluate. In one embodiment, it is desirable to reduce the difference between the CTE of the substrate 12 and the CTE of the thermal barrier layer 22. For example, the CTE of the OMC substrate is about 1 ppm / ° F (1.8 ppm / ° C), while the CTE of the thermal barrier layer is about 3.5-6 ppm / ° F (6.3-10.8 ppm / ° C). ). In one embodiment, the desired density of the thermal barrier layer 22 is less than or equal to the density of the OMC substrate 12. However, the highest acceptable density usually depends on the thermal conductivity of the material. The thermal conductivity of the thermal barrier layer affects the thickness required to achieve the required thermal effect.

  In one embodiment, the coating thickness is sufficient to provide a temperature drop of at least 100 ° F. (56 ° C.) at the substrate / coating interface 26. Thus, in one embodiment, if the use temperature is about 725 ° F. (385 ° C.), the exposure temperature at the substrate / coating interface 26 is about 625 ° F. (329 ° C.) or less. In one embodiment, the coating 14 has a thickness of about 0.030 inches (0.76 mm) to about 0.060 inches (1.5 mm). With the method and coating of the present invention, it is believed that the coated organic matrix composite substrate can be used at higher service temperatures, i.e., greater than 725 ° F (385 ° C).

The thermal barrier layer 22 contains, for example, one or more of the commercially available system variants known as Thermablock® coatings. This coating is a two component silsesquioxane / titanate material developed as a heat resistant coating by MicroPhase Coatings. Silsesquioxane is represented by the general formula: (RSO _1.5 ) _n and each silicon atom is bonded to an average of 1.5 (sesqui) oxygen atoms and one (ane) hydrocarbon group. It is a compound. Silsesquioxanes can exist in the form of polycyclic oligomers, ladder polymers and linear polymers. Such coatings are said to adhere tightly to various substrates including thermoset OMC. The two component coating system cures at 50-100 ° F. (10-38 ° C.). This material is resistant to acids and bases and has a maximum continuous use temperature of 2000 ° F. (1093 ° C.). The CTE of the various coatings is in the range of about 3.5-5 ppm / ° F. (6.3-9 ppm / ° C.) and the thermal conductivity is 560 ° F. (293 ° C.), such as 0.15 W / m · K. Very low.

  In another embodiment, the thermal barrier layer may comprise a developing material known as the Sialite® poly (sialate) material currently being developed by the Cornerstone Research Group. Poly (sialate) is an inorganic polymer having a group of basic structures (—Si—O—Al—O—). The actual structure and properties of poly (sialate) depend on the atomic ratio of Si to Al. CTE is typically about 5 ppm / ° F. (9 ppm / ° C.) in the case of genuine resin, and is adjusted by adding a filler. Fully cured and dried cast samples withstand 1650 ° F. (899 ° C.) before significant strength loss due to phase transformation occurs. In published data for unfilled poly (sialate), the thermal conductivity is in the range of 0.2 to 0.4 W / m · K.

  In one embodiment, the bond coat 24 can be composed of a polyimide matrix containing nanoparticles. Examples of nanoparticles include caged silsesquioxanes, graphite flakes and clay platelets. The respective amounts of polyimide and nanoparticles are determined by factors such as processability, CTE, oxygen barrier performance and bond strength.

  Two examples of polyimide resins include uncrosslinked MVK-19, which is a fluorinated high thermal stability resin, and Kapton (registered trademark) polyimide, which is a high Tg thermoplastic polyimide. The first MVK-19 system contains expanded nanoclay filler. The second MVK-19 system contains expanded graphite flakes. The polyimide system contains a cage silsesquioxane nanofiller. Cage-like silsesquioxane (POSS = polyhedral oligomeric silsesquioxane) is commercially available from Hybrid Plastics, Inc. 15 wt. Of premixed poly (amic acid) and cage-like silsesquioxane into N-methylpyrrolidone (NMP) % Solution. Each of these three systems is optimally adjusted as a solution, tested as a film, and finally tested with a selected thermal barrier material.

  Processability is measured as a function of system viscosity and particle distribution uniformity. The relationship between viscosity and temperature is evaluated for coating processability. Filler dispersion is measured by various diffraction and microscopy methods. CTE is measured by the expansion test method over a temperature range of -65 ° F to 800 ° F (-53 ° C to 426 ° C).

  The oxygen penetration resistance is measured by measuring the oxygen diffusivity of a film formed from a predetermined formulation. Coated OMC substrate samples are exposed to a thermal oxidation environment and evaluated for thermal protection. For example, in a thermal oxidation stability test, a sample is placed in a chamber and a constant flow of air is passed through the chamber at a flow rate sufficient to update the chamber volume at a rate of 5 times / hour. The test temperature, pressure, and time are selected so that degradation can be measured with an unprotected OMC substrate sample. The oxygen barrier capacity of the coating is determined by the weight loss of the protected OMC substrate compared to the unprotected OMC substrate. The primary role of the bond coat 24 is to adhere the outer heat shield layer 22 and the oxygen barrier capability is a secondary advantage.

  Bond strength is tested at room temperature and elevated temperature. Since the bond coat and the polyimide of the OMC substrate are chemically similar, and the bond coat polyimide and the thermal barrier layer are not chemically similar, the initial bond strength is evaluated at the bond coat / thermal barrier layer interface. It is done about adhesion of. Bond strength is measured by a plane tensile test.

  Two candidate materials for the thermal barrier layer 22 are selected and adhered to the two OMC substrates 12 with the three candidate materials for the bond coat 24. The OMC substrate 12 includes a cured panel of AFR-PE-4 prepreg and BMI (Cycom® 5250-4) prepreg. These 12 combinations are subjected to a thermal cycle test to evaluate the bond coat / thermal barrier interface. Evaluation of cracking and peeling of the thermal barrier layer during the thermal cycle test. The cold cycle test is performed by rapidly heating to the isothermal maximum temperature (about 750 ° F. (398 ° C.)) and then rapidly cooling to room temperature. A plane tensile test is performed at room temperature on an equivalent sample immediately after formation and after a thermal test to measure the effect on bond strength. The selected bond coat is evaluated for thermal cycling performance, oxygen diffusion into the OMC, and protection of the OMC from thermal oxidative degradation.

  Twelve combination panels are evaluated for the effect of isothermal oxidation aging on a given mechanical property. The bending strength and the mechanical properties of the modulus are measured according to ASTM C1161.

  Using thermodynamic calculations, measured material properties and oxidative aging analysis, the thickness of the bond coat 24 and the thermal barrier layer 22 is determined to be necessary for the coating 14 to achieve the desired level of performance at the specific use conditions. .

  In one embodiment, the nanoparticle modified bond coat precursor is applied (coated) as a liquid to a selected substrate, and then the inorganic thermal barrier layer precursor is applied as a liquid, molding compound, prepreg or thermal spray, The exact method is determined by the particular part to be protected. The prepreg can be supported by, for example, a non-woven veil or woven fabric (eg, quartz fiber cloth).

  Therefore, the provision of the thermal barrier oxidation prevention coating makes it possible to use the organic composite matrix substrate in a high temperature environment.

  In the above description, the present invention including the best mode is disclosed with specific examples, and those skilled in the art can reproduce and use the present invention. The patentable scope of the invention is as defined in the claims, and may include other examples that occur to those skilled in the art. If such other embodiments also have structural elements that do not differ from the language of the claims, or equivalent structural elements that have only substantial differences from the language of the claims, this embodiment It is within the scope of the gist of the invention.

It is sectional drawing which shows a part of components containing the base material which has a thermal-insulation antioxidant coating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Component 12 Base material 14 Thermal barrier oxidation prevention coating 16 First surface 18 High temperature side 22 Thermal barrier layer 24 Bond coat 26 Base material / coating interface

Claims (10)

A thermal barrier antioxidant coating (14) for an organic matrix composite substrate (12) comprising:
A bond coat (24) provided on at least a first surface (16) of an organic matrix composite substrate (12) comprising nanoparticles dispersed in a polyimide matrix;
One or more thermal barrier layers (22) substantially covering the bond coat, the thermal barrier layer (22) comprising one or more selected from silsesquioxane and an inorganic polymer. Antioxidant coating (14). The thermal barrier antioxidant coating according to claim 1, wherein the nanoparticles contain one or more selected from clay platelets, graphite flakes, and caged silsesquioxanes. The thermal barrier antioxidant coating of claim 1, wherein the coating acts to reduce the exposure temperature of one or more surfaces of the substrate by at least 56 ° C. in an operating temperature environment of about 385 ° C. or less. An organic matrix composite substrate (12);
An article (10) comprising a thermal barrier antioxidant coating (14) provided on one or more surfaces (16) of the substrate, wherein the thermal barrier antioxidant coating (14) is a bond coat (24). And a thermal barrier layer (22), wherein the bond coat (24) includes nanoparticles dispersed in a polyimide matrix, and the thermal barrier layer (22) is selected from silsesquioxane and an inorganic polymer. Article (10) containing one or more. The article of claim 4, wherein the organic matrix composite substrate comprises a heat resistant polyimide resin system. The organic matrix composite base material contains one or more materials selected from the group consisting of AFR-700B, PETI-375, PMR-II-50, HFPE, AFR-PE-4, PMR-15 and BMI. The article according to claim 4. The article according to any one of claims 4 to 6, wherein the nanoparticles contain one or more selected from clay platelets, graphite flakes, and cage silsesquioxanes. The article according to any one of claims 4 to 7, wherein the inorganic polymer comprises a poly (sialate) material. The article according to any one of claims 4 to 8, wherein the article includes a flow duct for use in a gas turbine engine. The article of any one of claims 4 to 9, wherein the coating acts to reduce the exposure temperature of one or more surfaces of the substrate by at least 56 ° C in an operating temperature environment of about 385 ° C or less.