Sprayable composition

Abstract

The present invention provides a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition, including nickel, chromium, iron, and silicon. The sprayable composition may be a composite particle, a blend, or a cored wire. The present invention further provides an abradable coating formed on a metal substrate according to a method comprising the step of depositing a bond coat on the metal substrate by thermal spraying of a bond coat composition comprising nickel, chromium and optionally aluminum and yttrium on the metal substrate and depositing the abradable coating on the bond coat by thermal spraying of a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition, including nickel, chromium, iron and silicon. The sprayable composition may be a composite particle, a blend, or a cored wire. The abradable coating may be applied to the top of the bond coat that is applied to a metal substrate such as steel, nickel-based alloys, and titanium.

Description

This is a Continuation-In-Part of patent application Ser. No. 10/490,735 filed Apr. 8, 2004 which is now pending.

FIELD OF THE INVENTION

This invention relates to sprayable compositions, particularly to sprayable compositions for use in forming abradable coatings, as well as to metal substrates coated with such abradable coatings and to a method of producing abradable coatings.

BACKGROUND OF THE INVENTION

Abradable seals have originally been developed for jet engine applications. Recently, the technology developed in the past is being adapted to land based rotating equipment, such as gas turbines and steam turbines. Further challenges are encountered in those applications. Jet engines used in aircraft applications are refurbished more often than the counterpart land based equipment. In the former case, expected service life is typically 5000-10,000 hrs., whereas in the latter case, expected service life is at least 50,000 hours, and in many cases, substantially more. This imposes new requirements on the land based coatings, namely durability. In this respect, the coatings must retain their mechanical properties, including abradability, even after long exposure at elevated temperatures.

SUMMARY OF THE INVENTION

The present invention provides a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron, and silicon.

The present invention also provides an abradable coating formed on a metal substrate according to a method comprising the step of depositing the abradable coating on the metal substrate by thermal spraying of a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron and silicon. The abradable coating may be deposited on a metal substrate.

Even further, the present invention provides an abradable coating formed on a metal substrate according to a method comprising the steps of: depositing a bond coat on the substrate by thermal spraying, and depositing an abradable coating on the bond coat by thermal spraying a sprayable composition comprising a ceramic particulate including albite, illite, and quartz and a metallic composition including nickel, chromium, iron and silicon. The abradable coating may be deposited on the metal substrate. However, a bond coat comprised of 60 to 85 wt % nickel, 15 to 25 wt % chromium, 0 to 15 wt % aluminum and 0 to 2 wt % yttrium thermally sprayed on a metal substrate has been found to provide improved performance of the abradable coating at elevated temperatures.

The present invention further provides a metal substrate including an abradable coating adhered thereto, the abradable coating becoming adhered to the metal substrate according to a method comprising the step of depositing the abradable coating on the metal substrate by thermal spraying of a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron and silicon.

The present invention also provides a metal substrate including an abradable coating adhered thereto, the abradable coating becoming adhered to the metal substrate according to a method comprising the steps of: depositing a bond coat on the substrate comprising nickel, chromium and optionally aluminum and yttrium, and depositing an abradable coating on the bond coat by thermal spraying a sprayable composition comprising a ceramic particulate including albite, illite, and quartz and a metallic composition including nickel, chromium, iron and silicon.

More particularly, the method comprises a method of producing an abradable coating adhered to a metal substrate comprising the step of depositing a bond coat on the metal substrate; by thermally spraying a sprayable composition comprising about 60 to about 85 wt % nickel, about 15 to about 25 wt % chromium, 0 to about 15 wt % aluminum and 0 to 2 wt % yttrium; and depositing an abradable coating on the bond coat by thermal spraying a sprayable composition comprising a ceramic particulate including albite, illite, and quartz; and a metallic composition including nickel, chromium, iron and silicon.

In one aspect, the sprayable composition is a powder composite, wherein the metallic composition is adhered to the ceramic particulate.

In another aspect, the sprayable composition is a powder blend, wherein the ceramic particulate is blended with the metallic composition.

In yet another aspect, the sprayable composition is a cored wire comprising an envelope including the metallic composition, wherein the ceramic particulate is disposed within the envelope.

In yet another aspect, the ceramic particulate of the invention as described above includes about 20 to about 60 wt % albite, about 15 to about 45 wt % illite, and about 15 to about 45 wt % quartz.

In another aspect, the ceramic particulate of the present invention includes about 40 wt % albite, about 30 wt % illite, and about 30 wt % quartz.

In another aspect, the metallic composition of any of the aspects of the present invention includes about 14 to about 25 wt % chromium, about 1.5 to about 4 wt % iron, and about 0.1 to about 0.6 wt % silicon, and the balance essentially nickel.

And in a further aspect of the invention, an abradable coating is provided comprising a metal substrate, a bond coat deposited on the metal substrate by thermally spraying a sprayable composition comprising about 60 to about 85 wt % nickel, about 15 to about 25 wt % chromium, 0 to about 15 wt % aluminum and 0 to about 2 wt % yttrium, and an abradable coating deposited on the bond coat by thermal spraying a sprayable composition comprising a ceramic particulate including albite, illite, and quartz and a metallic composition including nickel, chromium, iron and silicon, more particularly about 14 to about 25 wt % chromium, about 1.5 to about 4 wt % iron, and about 0.1 to about 0.6 wt % silicon, the balance essentially nickel.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a sprayable composition, for use in thermal spray applications, comprising a ceramic particulate including albite, illite, and quartz and a metallic composition including nickel, chromium, iron and silicon. The sprayable composition may be applied to, or coated or deposited upon a substrate to form an abradable coating or seal.

In another embodiment, the sprayable composition comprises a ceramic particulate including albite or a mineral possessing the characteristics of albite such as anorthite, illite or a mineral possessing the characteristics of illite, and quartz, and a metallic composition including metal, chromium, iron, and silicon.

The sprayable composition of the present invention may be applied to various substrates including those used in the thermal spray industry such as steel, nickel-based alloys and titanium.

The sprayable composition of the present invention may be applied to any of the above-enumerated substrates by thermal spraying. Preferably, a bond coat is first deposited onto the substrate to aid the adhesion of the abradable seal coating. Bond coats are well known in the art. Exemplary bond coats include Metco 450NS (trade-mark of Perkin-Elmer), nickel chromium coatings, and nickel chromium aluminum yttrium coatings.

Known bond coats such as Metco 450 NS, comprised of 95 wt % nickel and 5 wt % aluminum, are satisfactory for temperatures up to about 500° C. However, for temperatures of up to 650° C. and higher such as encountered in steam turbines, known bond coats such as Metco 450 NS have not been satisfactory due to low oxidation resistance of the bond coat. It has been found that conventional bond coats corrode under the top coat and that the top coat/bond coat system may fail by debonding from the substrate. The application of a bond coat comprised of about 60 to about 85 wt % nickel, about 15 to about 25 wt % chromium, 0 to about 15 wt % aluminum and 0 to about 2 wt % yttrium provides significantly enhanced oxidation resistance and improved performance of the bond coat/abradable top coat system at elevated temperatures.

Bond coats consisting of about 67 wt % nickel, about 22 wt % chromium, about 10 wt % aluminum for example and about 1.0 wt % yttrium, and about 80 wt % nickel and about 20 wt % chromium, are surprisingly effective to raise operating temperatures in a steam environment up to 650° C. and above.

Thermal spraying involves the softening or melting of a heat fusible material such as metal or ceramic by heat, and propelling the softened or melted material in particulate form against a surface which is to be coated. The heated particles strike the surface where they are cooled and bonded thereto. A conventional thermal spray gun may be used for the purpose of both heating and propelling the particles.

A thermal spray gun normally utilizes a combustion or plasma flame or electric arc to produce the heat for melting of the powder particles. In a powder type combustion thermal spray gun, the carrier gas, which entrains and transports the powder, is typically an inert gas such as nitrogen. In a plasma spray gun, the primary plasma gas is generally nitrogen or argon. Hydrogen or helium is usually added to the primary gas, and the carrier gas is generally the same as the primary plasma gas. Other thermal spray methods could also be used. A good general description of thermal spraying is provided in U.S. Pat. No. 5,049,450.

There is also provided an abradable coating formed on a metal substrate according to a method comprising the step of depositing the abradable coating on the metal substrate by thermal spraying of a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron and silicon. In another embodiment, an abradable coating formed on a metal substrate according to a method comprising the steps of depositing a bond coat on the substrate, and depositing an abradable coating on the bond coat by thermal spraying a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron and silicon.

In this respect, the present invention also provides a metal substrate including an abradable coating adhered thereto, the abradable coating becoming adhered to the metal substrate according to a method comprising the step of depositing the abradable coating on the metal substrate by thermal spraying of a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron and silicon. In another embodiment, the present invention provides a metal substrate including an abradable coating adhered thereto, the abradable coating becoming adhered to the metal substrate according to a method comprising the steps of depositing a bond coat on the substrate, the depositing an abradable coating on the bond coat by thermal spraying a sprayable composition comprising a ceramic particulate including albite, illite, and quartz, and a metallic composition including nickel, chromium, iron and silicon. The bond coat comprised of about 60 to about 85 wt % nickel, about 15 to about 25 wt % chromium, 0 to about 15 wt % aluminum and 0 to about 2 wt % yttrium is applied by thermal spraying onto the metal substrate.

The present invention further provides a metal substrate including an abradable coating adhered thereto or onto a bond coat, the abradable coating comprising a matrix including a metallic composition including nickel, chromium, iron and silicon, and a ceramic particulate including albite, illite, and quartz, wherein the ceramic particulate is dispersed within the matrix.

In one embodiment, the sprayable composition is a blend of a ceramic particulate including albite, illite, and quartz and a metallic composition, such as a particulate, including nickel, chromium, iron, and silicon.

In another embodiment, the sprayable composition is a cored wire comprising an envelope including the metallic composition, wherein the ceramic particulate is disposed within the envelope.

In another embodiment, the sprayable composition is a composite powder, wherein the metallic composition is adhered to a surface of the ceramic particulate. In one aspect, the metallic composition encapsulates the ceramic particulate.

By including albite, illite, and quartz, the ceramic particulate imparts desirable mechanical properties to the abradable coating, such as good erosion resistance combined with good abradability.

In another embodiment, the ceramic particulate includes about 20 to about 60 wt % albite, about 15 to about 45 wt % illite, and about 15 to about 45 wt % quartz. In a further embodiment, the ceramic particulate includes about 40 wt % albite, about 30 wt % illite, and about 30 wt % quartz.

In a further embodiment, the ceramic particulate consists essentially of albite, illite and quartz. Other materials may be present in the ceramic particulate in small quantities. These other materials are present as impurities introduced into the ceramic particulate as by-products arising during processing or from the raw materials. These other materials are present in amounts which are not sufficiently significant to affect the desirable properties of the ceramic particulate. In particular, the impurities are present in amounts which do not compromise the desired abradability and long term stability of the abradable coating.

In another embodiment, the metallic composition or particulate includes about 14 to about 25 wt % chromium, about 1.5 to about 4.0 wt % iron, and about 0.1 to about 0.6 wt % silicon, and the balance essentially nickel.

In a further embodiment, the metallic composition or particulate includes about 15.0 to about 18.1 wt % chromium, about 2.45 to about 2.71 wt % iron, about 0.43 to about 0.45 wt % silicon, and the balance essentially nickel. The coating derived from this embodiment particularly provides superior coating oxidation resistance in air up to about 650° C. The oxidation weight gain stabilizes at about 8000 hours in air. The mechanical properties of the coating derived from this composition are also stable under the same conditions. The resultant coating has a combination of excellent mechanical properties and oxidation resistance. Nevertheless, such specific intrinsic properties are not critical or necessary for the practice of each of the embodiments of this invention.

In a further embodiment, the metallic composition or particulate consists essentially of nickel, chromium, iron, and silicon. When the term “essentially” is used with respect to any of the above-described embodiments of the metallic composition or particulate of the present invention, this means that other materials may be present in the metallic composition in small quantities. These other materials are present as impurities introduced into the metallic composition as by-products arising during processing or from the raw materials. These other materials are present in amounts which are not sufficiently significant to effect the desired properties of the metallic composition. In particular, the impurities are present in amounts which do not compromise oxidation resistance and mechanical properties of the resultant coating.

The sprayable composition of the present invention is sufficiently flexible to provide coatings tailored to a specific application. When a coarser powder particle size is used, say, −80 mesh +115 mesh (−180 micrometers +125 micrometers), soft coatings can be produced to rub against hardware that are susceptible to damage by interaction with softer coatings. Examples of such hardware are blades and knife edges. If more robust hardware is used, then harder, more erosion-resistant coatings can be produced using finer powder where most of the particles are in the −100 mesh +325 mesh range (−150 micrometers +44 micrometers).

The ceramic particulate can be produced by agglomerating individual fine ceramic particle constituents (albite, illite, and quartz) using organic or inorganic binders and then milling the individual components in an attrition mill. Suitable organic binders include Derakane 470-36™ produced by Dow Chemical. The ceramic-binder mixture is then cured at room temperature for about 18 hours and the particles are subsequently screened to the desired particle size or size range required for the application.

After the ceramic particulate is sized, a metal composition is deposited thereon. As a first step, the ceramic particulate may be clad with Ni via hydrometallurgical processing. In this respect, dissolved Ni complexes are precipitated out of solution onto nucleation sites on the ceramic particulate via hydrogen reduction cycles at about 180° C. and 500 psig H₂. After the Ni is precipitated onto the ceramic particulate, the resultant particles are washed and dried. The Ni-clad ceramic particulate is then alloyed with Cr using any one of a number of diffusion processes, such as chemical vapor deposition. Without wishing to be bound by theory, it is believed that Fe and Si diffuse from the ceramic particulate core, and particularly the illite constituent, into the metal composition during the heat treatment.

It will be understood, of course, that modifications can be made in the embodiments of the invention described herein without departing from the scope and purview of the invention as defmed by the appended claims.

Claims

1. A method of producing an abradable coating adhered to a metal substrate comprising the steps of:

depositing a bond coat on the metal substrate by thermally spraying a sprayable composition comprising about 60 to about 85 wt % nickel, about 15 to about 25 wt % chromium, about 0 to about 15 wt % aluminum and about 0 to about 2 wt % yttrium; and

depositing an abradable coating on the bond coat by thermal spraying a sprayable abradable composition comprising: a ceramic particulate including albite, illite, and quartz; and a metallic composition including nickel, chromium, iron and silicon.

2. The method as claimed in claim 1, in which the bond coat comprises about 67 wt % nickel, about 22 wt % chromium, about 10 wt % aluminum and about 1.0 wt % yttrium.

3. The method as claimed in claim 1, in which the bond coat comprises about 80 wt % nickel and about 20 wt % chromium.

4. The method as claimed in claims 1, 2 or 3, wherein the sprayable abradable composition is a composite powder and the metallic composition is adhered to a surface of the ceramic particulate.

5. The method as claimed in any one of claims 1 to 4, wherein the ceramic particulate consists essentially of albite, illite, and quartz.

6. The method as claimed in any of claims 1 to 4, wherein the ceramic particulate includes about 20 to about 60 weight percent albite, about 15 to about 45 weight percent illite, and about 15 to about 45 weight percent quartz.

7. The method as claimed in any of claims 1 to 4, wherein the ceramic particulate includes about 40 weight percent albite, about 30 weight percent illite, and about 30 weight percent quartz.

8. The method as claimed in any one of claims 1 to 7, wherein the metallic composition includes about 14 to about 25 weight percent chromium, about 1.5 to about 4 weight percent iron, and about 0.1 to about 0.6 weight percent silicon, and the balance essentially nickel.

9. The method as claimed in any one of claims 1 to 7, wherein the metallic composition comprises 15.0 to 18.1 wt % chromium, 2.45 to 2.71 wt % iron, 0.43 to 0.45 wt % silicon, and the balance essentially nickel.

10. A metal substrate including an abradable coating adherently bonded to the metal substrate comprising a bond coat deposited on the metal substrate, said bond coat comprising about 60 to about 85 wt % nickel, about 15 to about 25 wt % chromium, about 0 to about 15 wt % aluminum and 0 to about 2 wt % yttrium, and the abradable coating adherently bonded to the bond coat, said abradable coating comprising:

a matrix including a metallic composition, the metallic composition including nickel, chromium, iron and silicon; and

a ceramic particulate, including albite, illite, and quartz;

wherein the ceramic particulate is dispersed within the matrix.

11. The metal substrate as claimed in claim 10, in which the bond coat comprises about 67 wt % nickel, about 22 wt % chromium, about 10 wt % aluminum and about 1.0 wt % yttrium.

12. The metal substrate as claimed in claim 10, in which the bond coat comprises about 80 wt % nickel and about 20 wt % chromium.

13. The metal substrate as claimed in any one of claims 10 to 12, wherein the ceramic particulate consists essentially of albite, illite, and quartz.

14. The metal substrate as claimed in any one of claims 10 to 12, wherein the ceramic particulate includes about 20 to about 60 weight percent albite, about 15 to about 45 weight percent illite, and about 15 to about 45 weight percent quartz.

15. The metal substrate as claimed in any one of claims 10 to 12, wherein the ceramic particulate includes about 40 weight percent albite, about 30 weight percent illite, and about 30 weight percent quartz.

16. The metal substrate as claimed in any one of claims 10 to 15, wherein the metallic composition includes about 14 to about 25 weight percent chromium, about 1.5 to about 4 weight percent iron, and about 0.1 to about 0.6 weight percent silicon, and the balance essentially nickel.

17. The metal substrate as claimed in any one of claims 10 to 15, wherein the metallic composition comprises 15.0 to 18.1 wt % chromium, 2.45 to 2.71 wt % iron, 0.43 to 0.45 wt % silicon, and the balance essentially nickel.