Patent Description:
Metals which may be prone to oxidation and/or corrosion, for example, steel and aluminum, are frequently used in aerospace applications, such as in aircraft engines and parts. To prevent oxidation and corrosion, these parts may be coated with an oxidation and corrosion resistant compound. A variety of oxidation and corrosion resistant coatings are commercially available for use; however, many of these oxidation and corrosion resistant coatings may be associated with a specific repair material. Thus, when a part's oxidation and corrosion resistant coating is damaged or in need of repair, the particular type of oxidation and corrosion resistant coating may need to be determined and the repair material specific to that type of oxidation and corrosion resistant coating obtained before any repair of the coating can be performed.

Further, environmental concerns and/or regulations may preclude the use of hexavalent chromium ("Cr(VI)") or other materials of concern in oxidation and corrosion resistant coatings and/or in the repair materials for oxidation and corrosion resistant coatings. Thus, repair materials specific to older oxidation and corrosion resistant coatings may no longer be desirable and/or may not conform to environmental regulations.

<CIT> discloses a coating process for forming a corrosion-resistant coating on a metallic surface.

<CIT> discloses a method of repairing a corrosion resistant coating in turbine components using a slurry composition comprising aluminium.

From a first aspect, a method for repairing an oxidation and corrosion resistant coating as claimed in claim <NUM> is provided. The oxidation and corrosion resistant coating may comprise hexavalent chromium. The metallic component may comprise a ferrous metal. A thickness of the first coat of the repair material may be between <NUM> (<NUM> inches) and <NUM> (<NUM> inches). In various embodiments, the method may further comprise testing a resistivity of the repair material.

In accordance with various embodiments, a method for repairing an oxidation and corrosion resistant coating of a turbine engine component may comprise identifying a damaged portion of the oxidation and corrosion resistant coating. The damaged portion of the oxidation and corrosion resistant coating exposes a metallic surface of the turbine engine component.

In various embodiments, the oxidation and corrosion resistant coating may comprise hexavalent chromium. The turbine engine component may comprise a ferrous metal. In various embodiments, the method may further comprise grit blasting the damaged portion of the oxidation and corrosion resistant coating. After the burnishing of the repair material, a resistivity of the repair material may be <NUM> ohms or less. A thickness of the first coat of the repair material may between <NUM> (<NUM> inches) and <NUM> (<NUM> inches). A thickness of the second coat of the repair material may be between <NUM> (<NUM> inches) and <NUM> (<NUM> inches).

From a further aspect, a turbine engine component as claimed in claim <NUM> is provided. In various embodiments, a thickness of the repair material may be less than a thickness of the oxidation and corrosion resistant coating. The oxidation and corrosion resistant coating may comprise hexavalent chromium. A resistivity of the repair material may be <NUM> ohms or less.

The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of the specification.

The detailed description of embodiments herein makes reference to the accompanying drawings, which show embodiments by way of illustration. While these embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical and mechanical changes may be made without departing from the scope of the invention as defined in the claims.

In various embodiments of the present disclosure, methods for coating and/or repairing an oxidation and corrosion resistant coating are described. The described methods for coating and/or repairing may be used with both oxidation and corrosion resistant coatings that contain Cr(VI) and oxidation and corrosion resistant coatings that are free or substantially free of Cr(VI).

With reference to <FIG>, a gas turbine engine <NUM> is shown according to various embodiments. Gas turbine engine <NUM> may be a two-spool turbofan that generally incorporates a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. Alternative engines may include, for example, an augmentor section among other systems or features. In operation, fan section <NUM> can drive coolant (e.g., air) along a path of bypass airflow B while compressor section <NUM> can drive coolant along a core flowpath C for compression and communication into combustor section <NUM> then expansion through turbine section <NUM>. Although depicted as a turbofan gas turbine engine <NUM> herein, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

Gas turbine engine <NUM> may generally comprise a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A-A' relative to an engine static structure <NUM> (also referred to as an engine casing structure) via several bearing systems <NUM>, <NUM>-<NUM>, and <NUM>-<NUM>. Engine central longitudinal axis A-A' is oriented in the z direction on the provided xyz axes. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided, including for example, bearing system <NUM>, bearing system <NUM>-<NUM>, and bearing system <NUM>-<NUM>.

Low speed spool <NUM> may generally comprise an inner shaft <NUM> that interconnects a fan <NUM>, a low pressure compressor <NUM>, and a low pressure turbine <NUM>. Inner shaft <NUM> may be connected to fan <NUM> through a geared architecture <NUM> that can drive fan <NUM> at a lower speed than low speed spool <NUM>. Geared architecture <NUM> may comprise a gear assembly <NUM> enclosed within a gear housing <NUM>. Gear assembly <NUM> couples inner shaft <NUM> to a rotating fan structure. High speed spool <NUM> may comprise an outer shaft <NUM> that interconnects a high pressure compressor <NUM> and high pressure turbine <NUM>. A combustor <NUM> may be located between high pressure compressor <NUM> and high pressure turbine <NUM>. A mid-turbine frame <NUM> of engine casing structure <NUM> may be located generally between high pressure turbine <NUM> and low pressure turbine <NUM>. Mid-turbine frame <NUM> may support one or more bearing systems <NUM> in turbine section <NUM>. Inner shaft <NUM> and outer shaft <NUM> may be concentric and rotate via bearing systems <NUM> about the engine central longitudinal axis A-A', which is collinear with their longitudinal axes. As used herein, a "high pressure" compressor or turbine experiences a higher pressure than a corresponding "low pressure" compressor or turbine.

The core airflow C may be compressed by low pressure compressor <NUM> then high pressure compressor <NUM>, mixed and burned with fuel in combustor <NUM>, then expanded over high pressure turbine <NUM> and low pressure turbine <NUM>. Turbines <NUM>, <NUM> rotationally drive the respective low speed spool <NUM> and high speed spool <NUM> in response to the expansion.

Gas turbine engine <NUM> may be, for example, a high-bypass ratio geared aircraft engine. In various embodiments, the bypass ratio of gas turbine engine <NUM> may be greater than about six (<NUM>). In various embodiments, the bypass ratio of gas turbine engine <NUM> may be greater than ten (<NUM>). In various embodiments, geared architecture <NUM> may be an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system. Geared architecture <NUM> may have a gear reduction ratio of greater than about <NUM> and low pressure turbine <NUM> may have a pressure ratio that is greater than about five (<NUM>). In various embodiments, the bypass ratio of gas turbine engine <NUM> is greater than about ten (<NUM>:<NUM>). In various embodiments, the diameter of fan <NUM> may be significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> may have a pressure ratio that is greater than about five (<NUM>:<NUM>). Low pressure turbine <NUM> pressure ratio may be measured prior to inlet of low pressure turbine <NUM> as related to the pressure at the outlet of low pressure turbine <NUM> prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of various embodiments of a suitable geared architecture engine and that the present disclosure contemplates other gas turbine engines including direct drive turbofans. A gas turbine engine may comprise an industrial gas turbine (IGT) or a geared aircraft engine, such as a geared turbofan, or non-geared aircraft engine, such as a turbofan, or may comprise any gas turbine engine as desired.

With reference to <FIG>, a segment or a portion of an aircraft part <NUM> having an oxidation and corrosion resistant coating <NUM> (also referred to herein as a base coating) is illustrated, in accordance with various embodiments. In various embodiments, part <NUM> may be a part of gas turbine engine <NUM> (<FIG>). For example, part <NUM> may be a high pressure turbine shaft, a low pressure turbine shaft, an airfoil, a fan blade, a hub, etc. In various embodiments, part <NUM> may be a part outside of gas turbine engine <NUM>. For example, part <NUM> may be a brake component or a landing gear part. Part <NUM> may be any metal aircraft part which is susceptible to oxidation and/or corrosion and which may benefit from an oxidation and corrosion resistant coating.

<FIG> shows a cross-sectional view of part <NUM> taken along the line 2B-2B in <FIG>. Part <NUM> may comprise a metal substrate <NUM> comprised of, for example, steel or aluminum. In various embodiments, metal substrate <NUM> comprises a ferrous metal. Metal substrate <NUM> may be coated with base coating <NUM>. In various embodiments, base coating <NUM> may comprise an oxidation and corrosion resistant material that includes Cr(VI). In various embodiments, base coating <NUM> may comprise an oxidation and corrosion resistant material which does not include Cr(VI).

Base coating <NUM> may comprise a damaged portion <NUM>. Damaged portion <NUM> may expose a surface <NUM> of metal substrate <NUM>. In various embodiments, damaged portion <NUM> may be a portion of base coating <NUM> that is scratched, eroded, abraded, worn, or otherwise damaged. Damaged portion <NUM> may comprise an opening in base coating <NUM> that exposes metal substrate <NUM>, though in various embodiments damaged portion <NUM> does not expose metal substrate <NUM>. Damaged portion <NUM> may make part <NUM> susceptible to further damage including oxidation, corrosion, cracking, breaking, or other damage that may lead to failure of part <NUM>.

With reference to <FIG>, <FIG>, aircraft part <NUM> having a repaired base coating <NUM> is illustrated, in accordance with various embodiments. <FIG>, <FIG> illustrate a cross sectional view of part <NUM> taken along the line BCD-BCD in <FIG>. In accordance with various embodiments, damaged portion <NUM> of base coating <NUM> may be repaired by replacing the eroded or lost material with a repair material <NUM> (also referred to herein as a repair coating). The repair material <NUM> comprises an oxidation and corrosion resistant paint or sealant that does not include Cr(VI) (i.e., a "chromate-free" material). For example, a suitable chromate-free repair material <NUM> comprises, in weight percent to within ±<NUM>%, <NUM>% aluminum powder (<NPL>), <NUM>% water (<NPL>), and <NUM>% metal silicates (<NUM>-<NUM>-<NUM>), and is available from Coating For Industry, Inc. , <NUM> Township Line Road, Souderton, PA (U. ) under the tradename ALSEAL® <NUM>.

Repair material <NUM> may be applied to damaged portion <NUM> of base coating <NUM> by brushing, spraying, painting, or any other suitable application method. Repair material <NUM> may be applied and used to repair multiple types of base coating <NUM>. For example, repair material <NUM>, comprising a chromate-free material, demonstrates a compatibility with base coatings <NUM> that are chromate-free and an unexpected compatibility with base coatings <NUM> that include Cr(VI).

In various embodiments, base coating <NUM> may include Cr(VI) and is repaired with chromate-free repair material <NUM> and exhibits the same corrosion resistance and/or structural properties as an undamaged base coating <NUM> and/or a base coating <NUM> repaired with a repair material comprising Cr(VI). The part <NUM> coated with a base coating <NUM> comprised of, by weight percent to within ±<NUM>%, <NUM>% to <NUM>% water (<NPL>), <NUM>% to <NUM>% phosphoric acid-reaction products with aluminum hydroxide and chromium oxide (CrO3) (<NPL>), and <NUM>% to <NUM>% uncoated aluminum powder (<NPL>). The base coating <NUM> is repaired with a repair material <NUM> comprising, in weight percent to within ±<NUM>%, <NUM>% aluminum powder (<NPL>), <NUM>% water (<NPL>), and <NUM>% metal silicates (<NPL>). The repaired base coating <NUM> exhibits the same corrosion resistance and/or structural properties as an undamaged base coating <NUM> and/or a base coating <NUM> repaired with a repair material comprising Cr(VI). In various embodiments, structural properties may include corrosion resistance, oxidation resistance, fatigue life, color match, strength, toughness, ductility, and/or durability. In various embodiments, structural properties may include yield strength, ultimate strength, Young's modulus, and/or Poisson's ratio.

In various embodiments, not part of the present invention, the base coating <NUM> may be comprised of, by weight percent to within ±<NUM>%, <NUM>% to <NUM>% aluminum (<NPL>), <NUM>% to <NUM>% phosphoric acid (<NPL>), <NUM>% or less chromium (VI) trioxide (<NPL>), and <NUM>% or less chromium hydroxide (<NPL>), and may be repaired with chromate-free repair material <NUM>, as described above. The repaired base coating <NUM> may exhibit the same corrosion resistance and/or structural properties as an undamaged base coating <NUM> and/or a base coating <NUM> repaired with a repair material comprising Cr(VI). In various embodiments, structural properties may include corrosion resistance, oxidation resistance, fatigue life, color match, strength, toughness, ductility, and/or durability. In various embodiments, structural properties may include yield strength, ultimate strength, Young's modulus, and/or Poisson's ratio.

In various embodiments, base coating <NUM> may be comprised of, by weight percent to within ±<NUM>%, <NUM>% to <NUM>% aluminum(<NPL>), <NUM>% to <NUM>% phosphoric acid and reaction products of aluminum hydroxide and chromium oxide (CrO3) (<NPL>), and <NUM>% to <NUM>% water(<NPL>), and may be repaired with chromate-free repair material <NUM>, as described above. The repaired base coating <NUM> may exhibit the same corrosion resistance and/or structural properties as an undamaged base coating <NUM> and/or a base coating <NUM> repaired with a repair material comprising Cr(VI). In various embodiments, structural properties may include corrosion resistance, oxidation resistance, fatigue life, color match, strength, toughness, ductility, and/or durability. In various embodiments, structural properties may include yield strength, ultimate strength, Young's modulus, and/or Poisson's ratio.

In accordance with various embodiments, accelerated oxidation and corrosion testing was performed on six sets of steel substrates, each set of steel substrate having a different oxidation and corrosion resistant coating. Five of the six sets of steel substrate were coated with oxidation and corrosion resistant coatings that included an aluminum ceramic compound containing Cr(VI). One of the six sets of steel substrates was coated with oxidation and corrosion resistant coatings that did not include an aluminum ceramic compound containing Cr(VI).

A first damaged area was formed in each of the oxidation and corrosion resistant coatings. The first damaged area was formed by placing a piece of tape on the steel substrate prior to applying the oxidation and corrosion resistant coating. After applying the oxidation and corrosion resistant coating, the tape was removed to expose the surface of the steel substrate. A second damaged area was formed in each of the oxidation and corrosion resistant coatings by scratching or otherwise cutting through the oxidation and corrosion resistant coating to expose the steel substrate.

The first damaged area and the second damage area were both repaired using a chromate-free repair material comprised of, in weight percent to within ±<NUM>%, <NUM>% aluminum powder (<NPL>), <NUM>% water (<NPL>), and <NUM>% metal silicates (<NUM>-<NUM>-<NUM>). An accelerated oxidation and corrosion test, meeting American Society for Testing and Materials (ASTM) B117 test requirements, was then performed by exposing the steel substrates, with repaired oxidation and corrosion resistant coatings, to neutral salt fog conditions that consisted of <NUM>% NaCl at <NUM>° F (<NUM>° C), in an environment of <NUM>% relative humidity. After <NUM> hours of exposure to the neutral salt fog conditions, all substrates remained free of corrosion, demonstrating an unexpected compatibility between the Cr(VI) containing oxidation and corrosion resistant coatings and the chromate-free repair material.

After the <NUM> hours of exposure to the neutral salt fog conditions, an adhesion and/or resistance to delamination and/or resistance to cracking of the repair material was tested by bending the substrates around a <NUM> (<NUM> inch) mandrel. Chromate-free material <NUM> demonstrated adhesion, resistance to delamination, and resistance to cracking with all oxidation and corrosion resistant coatings.

With reference to <FIG>, in various embodiments, repair material <NUM> may be applied to damaged portion <NUM> such that a thickness T1 of repair material <NUM> may be about equal to a thickness T2 of base coating <NUM>; as used herein the phrase "about equal" mean ±<NUM> micrometers (µm) (i.e., ±<NUM> inches). In various embodiments, T1 may a total thickness of repair material <NUM> after application of a second coat of repair material <NUM>.

With reference to <FIG>, in various embodiments, a thickness T3 of repair material <NUM> may be greater than the thickness T2 of base coating <NUM> such that a portion or lip <NUM> of repair material <NUM> extends over a surface <NUM> of base coating <NUM>.

With reference to <FIG>, in various embodiments, a thickness T4 of repair material <NUM> may be less than the thickness T2 of base coating <NUM> and still provide a viable repair. In various embodiments, repair material <NUM> does not need to reestablish the thickness T2 of base coating to be compatible with base coating <NUM>. The accelerated corrosion test, as previously described, revealed that repair material <NUM> provided corrosion protection even when a thickness T4 of repair coating was less than a thickness T2 of base coating <NUM>. A thickness of repair material <NUM> may selected such that repair material <NUM> covers exposed surface <NUM>.

<FIG> illustrates a method <NUM> for repairing a damaged oxidation and corrosion resistant coating, in accordance with various embodiments. Method <NUM> may comprise applying a repair material to a damaged oxidation corrosion resistant coating (step <NUM>). In various embodiments, the repair material comprises, in weight percent to within ±<NUM>%, <NUM>% aluminum powder, <NUM>% water, and <NUM>% metal silicates. Method <NUM> may comprise heat curing the repair material (step <NUM>), and burnishing the repair material (step <NUM>).

In various embodiments, with combined reference to <FIG> and <FIG>, step <NUM> of method <NUM> may comprise applying repair material <NUM> to damaged portion <NUM> of oxidation and corrosion resistant coating <NUM>. Repair material <NUM> may be applied by brushing, rolling, spraying, painting, or any other suitable application method. Repair material <NUM> may be applied to damaged portion <NUM> regardless of the Cr(VI) content of base coating <NUM>. In other words, repair material <NUM> may be used without regard to the identity of the particular type of the material used for base coating <NUM>. Step <NUM> may include heat curing repair material <NUM>. In various embodiments, the heat curing of repair material <NUM> may comprise drying repair material <NUM> at room temperature (e.g., <NUM>° F/<NUM>° C) for between <NUM> minutes and <NUM> hours, baking part <NUM> to a metal surface temperature of between <NUM>° F and <NUM>° F (i.e., between <NUM>° C and <NUM>° C) for between <NUM> minutes and <NUM> hours, and heating part <NUM> to a surface temperature of between <NUM>° F and <NUM>° F (i.e., between <NUM>° C and <NUM>° C) for between <NUM> minutes and <NUM> hours. Step <NUM> may comprise burnishing repair material <NUM>. Repair material <NUM> may be burnished to cause repair material <NUM> to become electrically conductive. In various embodiments, repair material <NUM> may be burnished by rubbing, polishing, or any other suitable sliding contact. In various embodiments, repair material <NUM> may be burnished by glass bead peening, or application of aluminum oxide.

With reference to <FIG>, according to the invention, applying the repair material (i.e., step <NUM> of method <NUM>) comprises applying a first coat of the repair material (step <NUM>), drying the first coat of the repair material (step <NUM>), and applying a second coat of the repair material (step <NUM>).

In the inventive method, with combined reference to <FIG> and <FIG>, step <NUM> comprises applying a first coat of repair material <NUM>. The first coat of repair material <NUM> may be applied by brushing, rolling, spraying, painting, or any other suitable application method. In various embodiments, a thickness of the first coat of repair material <NUM> may be between <NUM> and <NUM> (i.e., between <NUM> inches and <NUM> inches). In various embodiments, thickness of the first coat of repair material <NUM> may be between <NUM> and <NUM> (i.e., between <NUM> inches and <NUM> inches).

Step <NUM> comprises drying the first coat of repair material. In various embodiments, drying the first coat of repair material <NUM> may comprise allowing the first coat of repair material <NUM> to dry at room temperature (e.g., <NUM>° F/<NUM>° C) for between <NUM> minutes and <NUM> hours. In various embodiments, drying the first coat of repair material <NUM> may further comprise baking part <NUM> to a metal surface temperature of between <NUM>° F and <NUM>° F (i.e., between <NUM>° C and <NUM>° C) for between <NUM> minutes and <NUM> hours.

Step <NUM> comprises applying a second coat of repair material <NUM>. The second coat of repair material <NUM> may be applied by brushing, rolling, spraying, painting, or any other suitable application method. In various embodiments, a thickness of the second coat of repair material <NUM> may be between <NUM> and <NUM> (i.e., between <NUM> inches and <NUM> inches). In various embodiments, thickness of the second coat of repair material <NUM> may be between <NUM> and <NUM> (i.e., between <NUM> inches and <NUM> inches). In the inventive method, after applying the second coat or repair material <NUM>, repair material <NUM> is heat cured (step <NUM>), with momentary reference to <FIG>. In other words, after applying the second coat of repair material <NUM> the second coat of repair material <NUM> may be dried at room temperature (e.g., <NUM>° F/<NUM>° C) for between <NUM> minutes and <NUM> hours, part <NUM> may then be baked to a metal surface temperature of between <NUM>° F and <NUM>° F (i.e., between <NUM>° C and <NUM>° C) for between <NUM> minutes and <NUM> hours, and the part <NUM> may be heated to a surface temperature of between <NUM>° F and <NUM>° F (i.e., between <NUM>° C and <NUM>° C) for between <NUM> minutes and <NUM> hours.

With reference to <FIG>, in various embodiments, prior to applying the repair material, method <NUM> may include inspecting a part to identify oxidation and corrosion resistant coating damage (step <NUM>), grit blasting the part and/or damaged area of the oxidation and corrosion resistant coating (step <NUM>), and wiping the part to remove any residue left over the from the grit blast (step <NUM>).

In various embodiments, with combined reference to <FIG>, <FIG>, and <FIG>, step <NUM> may comprise inspecting part <NUM> and identifying damaged portion <NUM> in oxidation and corrosion resistant coating <NUM>. Step <NUM> may comprise grit damaged portion <NUM> and the portion of surface <NUM> exposed by damaged portion <NUM>. The grit blasting may remove rust or corrosion that may have begun to accumulate on the portion of surface <NUM> exposed by damaged portion <NUM>. Grit blasting may be used to roughen or otherwise prepare exposed surface <NUM> for receiving repair material <NUM>. Step <NUM> may comprise wiping part <NUM> to remove any residue left over the from the grit blast. In various embodiments, part <NUM> may be wiped down by hand.

With reference to <FIG>, in various embodiments, method <NUM> may include testing a resistivity of the repair material (step <NUM>). In various embodiments, with combined reference to <FIG> and <FIG>, step <NUM> may comprise testing a resistivity of repair material <NUM>. The resistivity testing may be performed after burnishing repair material <NUM>. In various embodiments, after burnishing, a resistivity of repair material <NUM> may be less than <NUM> ohms. In various embodiments, after burnishing, a resistivity of the repair material <NUM> may be less than <NUM> ohm.

The scope of the inventions is accordingly to be limited by nothing other than the appended claims.

Claim 1:
A method for repairing an oxidation and corrosion resistant coating (<NUM>), comprising:
applying a first coat of a repair material (<NUM>) to a damaged portion (<NUM>) of the oxidation and corrosion resistant coating (<NUM>), wherein the repair material (<NUM>) consists of, in weight percent to within ±<NUM>% , <NUM>% aluminum powder, <NUM>% water, and <NUM>% metal silicates, wherein the damaged portion (<NUM>) of the oxidation and corrosion resistant coating exposes a portion of a metallic substrate (<NUM>);
drying the first coat of repair material (<NUM>);
applying a second coat of the repair material (<NUM>) in the damaged portion (<NUM>) of the oxidation and corrosion resistant coating (<NUM>);
heat curing the repair material (<NUM>); and
burnishing the repair material (<NUM>);
wherein the oxidation and corrosion resistant coating (<NUM>) comprises at least one of:
a first material comprised of, by weight percent to within ±<NUM>%, <NUM>% to <NUM>% water, <NUM>% to <NUM>% phosphoric acid and reaction products with aluminum hydroxide and chromium oxide (CrO3), and <NUM>% to <NUM>% uncoated aluminum powder;
a second material, different from the first material, and comprised of, by weight percent to within ±<NUM>%, <NUM>% to <NUM>% aluminum powder, <NUM>% to <NUM>% phosphoric acid, <NUM>% or less chromium (VI) trioxide, and <NUM>% or less chromium hydroxide; or
a third material, different from the first material and the second material, and comprised of, by weight percent to within ±<NUM>%, <NUM>% to <NUM>%, aluminum, <NUM>% to <NUM>% phosphoric acid and reaction products of aluminum hydroxide and chromium oxide (CrO3), and <NUM>% to <NUM>% water; and
wherein the repair material (<NUM>) is chromate-free.