COLD SPRAYING METHOD FOR COATING COMPRESSOR AND TURBINE BLADE TIPS WITH ABRASIVE MATERIALS

Abstract

A method for coating compressor or turbine blade tips of a bladed disk with abrasive particles includes installing the blades onto a disk, and then cold gas-dynamic spraying the abrasive particles onto the blade tips while the blades are installed in the disk. According to another embodiment, a method for coating compressor and turbine blade tips of a bladed wheel with abrasive particles includes grinding the blade tips to bring the bladed wheel to a predetermined diameter. Then, surfaces of the bladed wheel not requiring coating are masked. After masking the surface not to be coated, the abrasive particles are cold gas-dynamic sprayed onto the blade tips. For both embodiments, an oxidation resistant layer may be cold gas-dynamic sprayed on the blade tips prior to spraying the abrasive particles.

Description

FIELD OF THE INVENTION

The present invention generally relates to gas turbine engine components that function in high pressure and elevated temperature environments. More particularly, the present invention relates to methods for coating turbine engine components such as compressor or turbine blades to prevent or minimize wear during rubs with adjacent abradable shrouds.

BACKGROUND OF THE INVENTION

Turbine engines are used as the primary power source for various kinds of aircraft. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators for hospitals and the like.

Most turbine engines generally follow the same basic power generation procedure. Compressed air is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Gas turbine engines use the power created by the rotating turbine disk to power a bladed compressor that draws more air into the engine and to energize propellers, electrical generators, or other devices.

Since turbine engines provide power for many primary and secondary functions, it is important to optimize the operating efficiency of compressors and turbines. One way to maximize compressor and turbine efficiency is to minimize high-pressure air leakage between the tips of the blades and the adjacent shroud. In order to accomplish this objective, compressor or turbine blade dimensions are tightly controlled and blade tips can be machined so the installed blades span a diameter that is slightly smaller than the shroud inner diameter. Improvements in compressor or turbine performance are possible when compressor or turbine blade tips can tolerate interference rubs with the adjacent shroud without experiencing significant blade tip wear. Wear of titanium, steel or superalloy blade tips during a rub is undesirable because clearances increase, producing an associated reduction in compressor or turbine performance.

In order to minimize the escape of high pressure air between compressor blade tips and the mating shroud, abrasive blade tip coatings may be applied to machined compressor blades. Further, a porous and abradable ceramic coating may be applied to the shroud as taught by Draskovich in U.S. Pat. No. 5,704,759. The primary function of such coatings is to provide rub-tolerant shroud and blade surfaces that minimize blade damage in the event a compressor blade rubs the surrounding shroud surface. For example, U.S. Pat. No. 5,704,759 discloses a turbine blade body having a tip portion that is coated with an abrasive material. The abrasive material includes a dispersion of discrete particles of cubic boron nitride (CBN) that are formed on the blade tip by an entrapment plating method wherein the CBN particles are entrapped in electroplated nickel with their tips (cutting edges) exposed. However, entrapment plating is difficult to perform on large turbine components such as a compressor impeller. Furthermore, entrapment plating is a somewhat cumbersome process since each turbine blade must be individually coated. Because CBN is very hard and difficult to grind, each of the uncoated blades must be inserted into slots in a hub. Then, the blades are ground at their outer diameters to conform to blue print dimension. Finally, the blades are removed from the hub and individually coated with CBN, and then reinserted into the slots in the hub. The steps of disassembling and reassembling the turbine wheel and its blades are burdensome and inefficient.

Entrapment electroplating of abrasive particles, such as CBN, into a co-deposited NiCoCrAlY matrix has also been applied to turbine blade tips as taught by Wride in U.S. Pat. No. 5,076,897. The hard CBN abrasive particles can cut into porous stabilized zirconia shroud coatings for short periods of up to a few hours until the cubic boron nitride particles are lost due to oxidation.

Accordingly, it is desirable to provide turbine engine components such as compressor and turbine blades that are coated and machined to prevent air leakage between a gas turbine engine shroud and wheel blades. In addition, it is desirable to provide an efficient method for producing such components. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.

BRIEF SUMMARY OF THE INVENTION

According to one embodiment of the invention, a method is provided for coating compressor or turbine blade tips of a bladed disk with abrasive particles. The method includes installing the blades onto a disk, and then cold gas-dynamic spraying the abrasive particles onto the blade tips while the blades are installed in the disk.

According to another embodiment of the invention, a method is provided for coating compressor and turbine blade tips of a bladed wheel with abrasive particles. First, the blade tips are ground to bring the bladed wheel to a predetermined diameter. Then, surfaces of the bladed wheel not requiring coating are masked. After masking the surface not to be coated, the abrasive particles are cold gas-dynamic sprayed onto the blade tips.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and

FIG. 1 is a perspective view of a blade for a turbine engine power wheel according to an embodiment of the invention;

FIG. 2 is a side view of a compressor blisk that is an integrally bladed rotor having a tip that is coated with cold sprayed abrasive particles according to an embodiment of the invention;

FIG. 3 is a cross-sectional view depicting the tip of a compressor or turbine blade including a surface that is embedded with particles by a cold gas-dynamic spraying process according to an embodiment of the present invention;

FIG. 4 is a cross-sectional view depicting the tip of a compressor or turbine blade including a thin oxidation resistant coating that is embedded with particles by a cold gas-dynamic spraying process according to an embodiment of the present invention;

FIG. 5 is a schematic view of an exemplary cold gas-dynamic spray apparatus;

FIG. 6 is a side view of a gas turbine engine turbine wheel beside a cold spraying nozzle that is spraying a turbine blade tip with abrasive particles according to an embodiment of the invention; and

FIG. 7 is a flow diagram of a coating method in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention.

The present invention includes methods for coating the machined tip of any compressor or turbine blade. The methods are particularly advantageous when the compressor or turbine rotor is fully bladed and machined. The rotor may be an integral bladed disk or a disk with inserted blades. When manufacturing a compressor or turbine wheel that incorporates inserted compressor or turbine blades, the blades are inserted into slots in a disk.

Turning now to FIG. 1, an exemplary turbine blade 150 is illustrated. The turbine blade 150 is exemplary of the type of turbine blades that are used in the turbine engines. Turbine blades commonly have a different shape, dimension and size depending on gas turbine engine models and applications. In a typical turbine engine, multiple turbine blades 150 are positioned in adjacent circumferential position along a hub or rotor disk. The turbine blades are typically made from advanced superalloys such as IN713, IN738, IN792, MarM247, GTD111, Rene142, Rene N5, SC180 and CMSX4 to name several non-exclusive examples.

The turbine blade 150 includes an airfoil 152. The airfoil 152 includes a concave curvature face and a convex face. In operation, hot gases impinge on the airfoil 152 concave face and thereby provide the driving force for the turbine engine. The airfoil 152 includes a leading edge 162 and a trailing edge 164 that firstly and lastly encounter an air stream passing around airfoil 152. The blade 150 also includes a tip 160. In some applications the tip may include raised features commonly known as squealers.

The turbine blade 150 is mounted on a turbine disk 146 that is part of a wheel 20 depicted in FIG. 6. The blade 150 is attached to the disk 146 by a fir tree or dovetail attachment 154 that extends downwardly from the airfoil 152 and engages a non-illustrated slot on the turbine hub 146. A platform 156 extends longitudinally outwardly from the area where the airfoil 152 is joined to the attachment 154. A number of cooling channels desirably extend through the interior of the airfoil 152, ending in openings 158 in the airfoil surface.

As previously discussed, the turbine blade 150 depicted in FIG. 1 is designed to be inserted into the wheel 20. However, turbine blades commonly have different shapes, dimensions, and sizes depending on gas turbine engine models and applications. The present invention also is directed to coating methods for compressor blades having an inserted design similar to that of the turbine blade 150. Furthermore, the turbine and compressor blades may be components of an integral bladed disk. Turning now to FIG. 2, an exemplary integral compressor blisk 250 is illustrated. In an exemplary turbine engine, multiple compressor blades 252 are circumferentially positioned adjacent to one another along the outer surface of a hub 246. According to an exemplary embodiment, compressor and impeller blades are made from titanium, steel, and superalloys, such as Ti-6A1-4V, M350, and IN718. Each compressor blade 252 includes an airfoil having a concave face and a convex face. Each airfoil includes a leading edge 256 and a trailing edge 258 that firstly and lastly encounter an air stream passing around the airfoil. Each blade 252 also includes a tip 254.

FIGS. 3 and 4 are a cross-sectional views depicting the tip of a compressor or turbine blade. The blade tip depicted in FIG. 3 includes a substrate 10 and a surface 13 that is coated with particles 14 by a cold gas-dynamic spraying process. The substrate 10 may be formed from various metals such as steel alloys, structural aluminum alloys, titanium alloys such as Ti-6A1-4V, and superalloys such as a nickel-based superalloy IN718, MarM247 or SC180. According to an exemplary embodiment, the substrate 10 is sufficiently oxidation resistant to provide the surface 13 into which a single layer or a plurality of layers of particles 14 is partially imbedded by high velocity impaction during cold gas-dynamic spraying. The substrate 10 for the blade tip depicted in FIG. 4 has a thin oxidation resistant metallic coating 12 that formed thereon, and the coating 12 has a surface 15 into which a single layer of particles 14 are partially imbedded by high velocity impaction during cold gas-dynamic spraying. The cold gas-dynamic spraying process includes accelerating the abrasive particles at a velocity that is sufficient for the particles to be embedded into the surface. However, the abrasive particles are only partially embedded so the abrasive particles protrude above the metallic substrate 10 or the coating 12.

According to an exemplary embodiment, the abrasive particles are cubic boron nitride (CBN). The CBN preferably has an average particle diameter ranging between 25 and 100 microns. Other abrasive materials may also be suitably applied by a cold gas-dynamic spraying process. Some exemplary abrasive materials include diamond, silicon carbide (SiC), yttrium aluminum garnet (YAG), and cubic zirconia. Diamond and CBN are harder than SiC, YAG and cubic zirconia. However, these and other suitable abrasive materials may be selected based on their high temperature oxidation resistance properties. The abrasive coating composition also may vary depending on the type of blades that are being coated and the intended operational conditions for the blades.

As previously discussed, a single layer of abrasive particles 14 are imbedded into compressor and turbine blade tips using a cold gas-dynamic spraying process which accelerates the particles to supersonic velocities. Turning now to FIG. 5, an exemplary cold gas-dynamic spray system 100 is illustrated diagrammatically. The system 100 is illustrated as a general scheme, and additional features and components can be implemented into the system 100 as necessary. The main components of the cold-gas-dynamic spray system 100 include a powder feeder for providing abrasive powder, a carrier gas supply (typically including a heater) for heating and accelerating powder particles, a mixing chamber and a nozzle. In general, the system 100 transports the abrasive powder with a suitable pressurized gas to the mixing chamber. The particles are accelerated by the pressurized carrier gas, such as air, helium, nitrogen, or mixtures thereof, through the specially designed nozzle and directed toward a targeted surface on the turbine component. When the particles strike the target surface, converted kinetic energy of the particle causes plastic deformation in the target metallic substrate (the blade tip surface), which permits the particles to partially embed the surface. Thus, the cold gas-dynamic spray system 100 can bond the powder materials to a turbine blade tip surface and thereby form a protective coating on the tip.

The cold gas dynamic spray process is referred to as a “cold spray” process because the particles are applied at a temperature that is well below their melting point. The kinetic energy of the particles on impact with the target surface, rather than particle temperature, causes the substrate to plastically deform and bond the particles with the target surface.

A variety of different systems and implementations can be used to perform the cold gas-dynamic spraying process. For example, U.S. Pat. No. 5,302,414, entitled “Gas-Dynamic Spraying Method for Applying a Coating” describes an apparatus designed to accelerate materials and to mix particles of the materials with a process gas to provide the particles with a density of mass flow between 0.05 and 17 g/s·cm². Supersonic velocity is imparted to the gas flow, with the jet formed at high density and low temperature using a predetermined profile. The resulting gas and powder mixture is introduced into the supersonic jet to impart sufficient acceleration to ensure a particle velocity ranging between 300 and 1200 m/s.

According to the present invention, the cold gas-dynamic spray system 100 applies abrasive particles onto a compressor or a turbine blade tip. Although the process is referred to as “cold spraying,” some warming of the gas and/or particles may be advantageous in order to provide the abrasive particles with sufficient energy to embed into a turbine blade tip. The system typically uses gas pressures of between 5 and 20 atm, and at a temperature ranging between about 300 and 1000° F. Furthermore, the abrasive particles may be warmed to a temperature of up to about 500° F. However, any warming of the particles and/or the propellant gas is tailored to maintain the particle temperatures well below their melting points. As non limiting examples, the gases can comprise air, nitrogen, helium and mixtures thereof. Again, this system is but one example of the type of system that can be adapted to cold spray powder materials to the target surface. The system 100 is typically operable in an ambient external environment.

A unique advantage provided by cold gas-dynamic spraying abrasive particles is the ability to deposit the abrasives onto the tips of blades that are installed on a disk. As previously discussed, many conventional methods of coating compressor and turbine blades with abrasives are somewhat cumbersome processes since the methods require that each turbine blade be individually coated. Because CBN and other suitable abrasives are very hard and difficult to grind, each of the uncoated blades are inserted into slots in a disk using conventional methods, and the blades are then ground at their outer diameters to conform to the bladed disk's blue print dimension. The blades are thereafter removed from the disk and individually coated with the abrasive material, and then reinserted into the slots in the disk. The steps of disassembling and reassembling the turbine wheel and its blades are burdensome and inefficient. Returning now to FIG. 6, a side view is depicted of the gas turbine engine bladed disk 20 beside a cold spraying nozzle 34 that is spraying a compressor or turbine blade tip 160 with abrasive particles according to an embodiment of the invention. Because the blades are inserted into the hub during deposition of the abrasive particles, the disassembling and reassembling steps from the conventional process are eliminated. Sheet metal or rubber masking (not shown) protects the other non-blade tip surfaces of the bladed disk from deposition of the abrasive powder. Only the blade tip surfaces are exposed to the high-velocity flux of abrasive coating powder.

According to the embodiment depicted in FIG. 6, the cold spraying apparatus 100 includes the nozzle 34 that is communicatively coupled to a propellant gas heater 32 by way of a main gas passage 36. A premix chamber 38 is in line with the main gas passage 36 upstream of the nozzle 34, and is upstream of the nozzle 34. The gas is transferred from the premix chamber 38 into a mixing chamber 40 where the gas is combined with the abrasive particles and any other metal powders. The particles are transferred to the mixing chamber 40 using an injection tube 50 that is in communication with a powder feeder that supplies the particles. The gas-dynamic spraying is enabled by using a nozzle that includes a throat 58 or other aperture that is sized to optimize the gas pressure and, in turn, the particle velocity as it passes through the nozzle 34.

Turning now to FIG. 7, a flow diagram outlines an exemplary coating method in accordance with an embodiment of the invention. As step 60, a bladed wheel having an inserted blade design is assembled by installing the compressor or turbine blades onto the disk. The hub includes slots that are sized to receive and secure the blades. An exemplary blade is attached to the hub by a dovetail that extends downwardly from the blade's airfoil and engages the slot on the hub. As previously discussed, according to another embodiment a compressor or turbine blisk having an integrally bladed rotor is used. According to such an embodiment, no assembly of the blades into a disk is performed.

With the blades installed on the hub, the blade tips are ground to predetermined or blueprint dimensions as step 62. During operation of a gas turbine engine, the turbine wheel blades are surrounded by a shroud. Engine power and operational efficiency are optimized by forming the compressor or turbine wheel to have a diameter that minimizes the blade tip to shroud clearance, which prevents wasteful high pressure air leakage between the blades and the shroud.

As step 64, a protective mask is applied to protect surfaces of the bladed disk where the deposition of abrasive particles is not permitted. The protective mask may include strips of rubber or sheet metal with airfoil shaped slots to expose the tips of the blades.

As step 66, the tips of the installed compressor or turbine blades are coated with abrasive particles by a cold gas-dynamic spraying process. According to the exemplary embodiment depicted in FIG. 6, the tips are sprayed by positioning the spraying nozzle radially in line with, and directly opposing, the blade tips so the abrasive particles are sprayed substantially normal to the blade tip surface. However, other nozzle positions with respect to the blade tips may be employed to ensure adequate blade tip coating. A mask that leaves the blade tips exposed but covers or otherwise shields the remainder of the wheel may be employed when spraying the abrasive particles. According to one embodiment, the abrasives are constantly sprayed toward the blade tips while the turbine wheel is continuously spun. According to another embodiment, spinning of the wheel is intermittently halted when each individual blade reaches a position to receive a coating of abrasive materials. Spraying may also be intermittent in order to avoid waste of abrasive material when the blade tips are not aligned with the spraying nozzle. In order to further increase manufacturing efficiency, the hub may be installed on a shaft 144, depicted in FIG. 6, while cold gas-dynamic spraying the abrasive materials onto the turbine blade tips.

As necessary or useful, an optional heat treatment may be performed as step 68 after cold gas-dynamic spraying the abrasive particles onto the turbine blade tips and before installing the compressor or turbine wheel into an engine. A heat treatment may improve metallurgical bonding between the abrasive particles and the turbine blade material.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It is understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A method for coating compressor or turbine blade tips of a bladed disk with abrasive particles, comprising the steps of:

installing the blades onto a disk; and

cold gas-dynamic spraying the abrasive particles onto the blade tips while the blades are installed in the disk.

2. The method according to claim 1, further comprising the step of:

grinding the blade tips, after installing the blades onto the disk and before cold gas-dynamic spraying the abrasive particles onto the blade tips, until the bladed disk is brought to a predetermined diameter.

3. The method according to claim 1, further comprising the step of:

masking surfaces of the bladed disk not requiring the abrasive coating before performing the cold gas-dynamic spraying step.

4. The method according to claim 1, wherein the method excludes any grinding of the blade tips after cold gas-dynamic spraying the abrasive particles.

5. The method according to claim 1, further comprising the step of:

heat treating the blade tips after cold gas-dynamic spraying the abrasive particles.

6. The method according to claim 1, wherein the method excludes removing of the turbine blades from the disk after cold gas-dynamic spraying the abrasive particles.

7. The method according to claim 1, wherein the step of cold gas-dynamic spraying the abrasive particles onto blade tips comprises spraying abrasive particles selected from the group consisting of cubic boron nitride, diamond, silicon carbide, yttrium aluminum garnet, and cubic zirconia.

8. The method according to claim 7, wherein the step of cold gas-dynamic spraying the abrasive particles onto the blade tips comprises spraying cubic boron nitride particles.

9. The method according to claim 7, wherein the step of cold gas-dynamic spraying the abrasive particles onto the blade tips comprises spraying particles having an average diameter ranging between 25 and 100 microns.

10. The method according to claim 8, further comprising the step of:

forming a MCrAlY oxidation resistant layer on the blade tips prior to cold gas-dynamic spraying the abrasive particles.

11 The method according to claim 10, wherein the MCrAlY oxidation resistant layer is formed using a cold gas-dynamic spraying process.

12. The method according to claim 1, wherein the step of cold gas-dynamic spraying the abrasive particles onto the turbine blades comprises partially embedding the particles into the tips of the blades.

13. The method according to claim 1, wherein the step of cold gas-dynamic spraying the abrasive particles onto the turbine blades comprises spraying only tip portions of the blades with the abrasive particles.

14. The method according to claim 1, wherein the step of cold gas-dynamic spraying the abrasive particles onto the turbine blades comprises the step of spraying the abrasive particles while spinning the bladed disk.

15. The method according to claim 14, wherein the step of spraying the abrasive particles while spinning the bladed disk comprises constantly spraying the abrasive particles until each blade tip is coated with the abrasive particles.

16. The method according to claim 14, spraying the abrasive particles while spinning the bladed disk comprises intermittently halting the spinning when each individual blade reaches a position to receive a coating of abrasive materials.

17. A method for coating compressor and turbine blade tips of an integrally bladed wheel with abrasive particles, comprising the steps of:

grinding the blade tips to bring the bladed wheel to a predetermined diameter;

masking surfaces of the bladed wheel not requiring coating; and

cold gas-dynamic spraying the abrasive particles onto the blade tips.

18. The method according to claim 17, wherein the bladed wheel is selected from the group consisting of an integral axial compressor wheel, an impeller, and an integral turbine wheel.

19. The method according to claim 17, wherein the step of cold gas-dynamic spraying the abrasive particles onto the turbine blades comprises the step of spraying the abrasive particles while spinning the bladed disk.

20. The method according to claim 19, wherein the step of spraying the abrasive particles while spinning the bladed disk comprises constantly spraying the abrasive particles until each blade tip is coated with the abrasive particles.

21. The method according to claim 19, wherein the step of spraying the abrasive particles while spinning the bladed disk comprises intermittently halting the spinning when each individual blade reaches a position to receive a coating of abrasive materials.