Patent Description:
Turbine engines are used as the primary power source for various kinds of vehicles, such as aircraft. Turbine engines are also used as auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Furthermore, the power from turbine engines may be used for stationary power supplies such as backup electrical generators 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. 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 fan blades, propellers, electrical generators, or other devices, depending on the type of turbine engine.

Because 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 just 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. That is, wear of blade tips during a rub is undesirable because clearances increase, producing an associated reduction in compressor or turbine performance.

The prior art contains examples of attempted solutions to this rubbing problem by using abrasive particles embedded in the blade tip. For example, <CIT> 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, experience has shown that these abrasive tips are not durable for long-term engine use, at least in part due to limitations in the blade tip design as a result of the fabrication techniques employed.

Accordingly, it would be desirable to provide an improved method of forming an abrasive nickel-based alloy on a turbine blade tip. The method would desirably avoid fabrication methods that limit the design of the blade tip. Furthermore, other desirable features and characteristics of the disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

The present disclosure relates to a method of forming an abrasive nickel-based alloy on a turbine blade tip. As such, in one exemplary embodiment, a method of forming an abrasive nickel-based alloy on a turbine blade tip includes producing or obtaining a metal powder that is mixed with a carbon powder to form a carbon-enriched metal powder. The metal powder includes a refractory element. The method further includes bonding the carbon-enriched metal powder to the turbine blade tip. The step of bonding includes raising the temperature of the carbon-enriched metal powder past its melting point, thereby causing the carbon to combine with the refractory elements to form abrasive carbide particles.

In another exemplary embodiment, a method of forming an abrasive nickel-based alloy on a turbine blade tip includes producing or obtaining a turbine blade including the turbine blade tip. The turbine blade includes a nickel-based superalloy. The method further includes producing or obtaining a metal powder that is mixed with a carbon powder to form a carbon-enriched metal powder. The metal powder includes a nickel-based superalloy and further includes a refractory element selected from the group consisting of tungsten, tantalum, titanium, and a mixture of two or more thereof. The metal and ceramic powder mixture has a weight ratio of metal powder to carbon powder of from about <NUM>:<NUM> to about <NUM>:<NUM>. The method further includes bonding the carbon-enriched metal powder to the turbine blade tip. The step of bonding includes raising the temperature of the carbon-enriched metal powder past its melting point, thereby causing the carbon to combine with the refractory elements to form abrasive carbide particles. Bonding the carbon-enriched metal powder is performed using a laser deposition process or an electron-beam welding process.

In yet another exemplary embodiment, a method of forming an abrasive nickel-based alloy on a turbine blade tip includes producing or obtaining a turbine blade including the turbine blade tip. The turbine blade includes a nickel-based superalloy. The method further includes producing or obtaining a metal powder that is mixed with a carbon powder to form a carbon-enriched metal powder. The metal powder includes a nickel-based superalloy and further includes a refractory element selected from the group consisting of tungsten, tantalum, titanium, and a mixture of two or more thereof. The metal and ceramic powder mixture has a weight ratio of metal powder to carbon powder of from about <NUM>:<NUM> to about <NUM>:<NUM>. A variance between the mean particle size (d50) of the metal powder as compared with the mean particle size (d50) of the carbon powder is +/- <NUM>%. The method further includes bonding the carbon-enriched metal powder to the turbine blade tip. The step of bonding includes raising the temperature of the carbon-enriched metal powder past its melting point, thereby causing the carbon to combine with the refractory elements to form abrasive carbide particles. Bonding the carbon-enriched metal powder is performed using a laser deposition process or an electron-beam welding process. Still further, the method includes performing a finishing process on the turbine blade after the step of bonding. The finishing process is selected from the group consisting of: heat treating, machining, surface finishing, polishing, and coating.

This Brief Summary is provided to describe select concepts in a simplified form that are further described in the Detailed Description. This Brief Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

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

" Thus, any alloy embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. As further used herein, the word "about" means a possible variance (+/-) of the stated value of up to <NUM>%, or alternatively up to <NUM>%, or no variance at all.

The present disclosure generally provides embodiments of a method of forming an abrasive nickel-based alloy on a turbine blade tip. In accordance with these embodiments, a metal powder is prepared using an atomization process. The metal powder is an alloy that is suitable for use in a turbine blade, such as (but not limited to) a nickel-based superalloy. The metal powder includes refractory elements, such as tungsten, titanium, and/or tantalum. An amount of carbon in then mixed into the metal powder. The carbon-enriched metal powder is then bonded to the turbine blade tip using laser deposition, electron-beam welding, or any other technique that causes the carbon-enriched metal powder to melt on the turbine blade tip. During the melting of the carbon-enriched metal powder, there is a thermodynamic tendency of the carbon to combine with the refractory elements to form carbide particles. These carbide particles are very hard, and they can serve as abrasives to aid the blade tip when rubbing against the shroud.

Turning now to <FIG>, an exemplary turbine blade <NUM> is illustrated. The turbine blade <NUM> 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 <NUM> 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 <NUM> includes an airfoil <NUM>. The airfoil <NUM> includes a concave curvature face and a convex face. In operation, hot gases impinge on the airfoil <NUM> concave face and thereby provide the driving force for the turbine engine. The airfoil <NUM> includes a leading edge <NUM> and a trailing edge <NUM> that firstly and lastly encounter an air stream passing around airfoil <NUM>. The blade <NUM> also includes a tip <NUM>. In some applications the tip may include raised features commonly known as squealers.

The turbine blade <NUM> may be mounted on a turbine disk that is part of a non-illustrated wheel. The blade <NUM> is attached to the disk by a fir tree or dovetail attachment <NUM> that extends downwardly from the airfoil <NUM> and engages a non-illustrated slot on the turbine wheel. A platform <NUM> extends longitudinally outwardly from the area where the airfoil <NUM> is joined to the attachment <NUM>. A number of cooling channels desirably extend through the interior of the airfoil <NUM>, ending in openings <NUM> in the airfoil surface.

In accordance with the present disclosure, for the turbine blade tip, a metal powder is prepared using an atomization process. The metal powder is an alloy that is suitable for use in a turbine blade, such as (but not limited to) a nickel-based superalloy. Within the scope of nickel-based superalloys, some compositions have proven particularly effective for turbine blade tips. For example, <CIT> discloses a nickel-based superalloy that includes, by weight, about <NUM>% to about <NUM>% chromium, about <NUM>% to about <NUM>% aluminum, about <NUM>% to about <NUM>% tantalum, about <NUM>% to about <NUM>% tungsten, less than about <NUM>% of one or more of elements selected from a group consisting of boron, zirconium, yttrium, hafnium, and silicon, and a balance of nickel. The '<NUM> Publication discloses that this alloy may be laser-welded onto the tip region of a turbine blade.

In another example, <CIT> discloses a nickel-based superalloy that includes, by weight, about <NUM>% to about <NUM>% cobalt, about <NUM>% to about <NUM>% chromium, about <NUM>% to about <NUM>% aluminum, about <NUM>% to about <NUM>% tantalum, about <NUM>% to about <NUM>% rhenium, about <NUM>% to about <NUM>% of one or more of elements selected from a group consisting of platinum, ruthenium, palladium, and iridium, about <NUM>% to about <NUM>% hafnium, about <NUM>% to about <NUM>% yttrium, about <NUM>% to about <NUM>% silicon, and a balance of nickel. The '<NUM> Publication discloses that this alloy may be cast into the shape of a blade tip, and then diffusion bonded onto a turbine blade.

Of course, other nickel-based superalloys may be suitable for use as a turbine blade tip material of the present disclosure; the foregoing examples are intended to provide but a sampling of the possible alloy compositions.

As initially noted, a metal alloy as described above is prepared in the form of a powder using an atomization process. As further noted, the metal powder includes refractory elements, such as tungsten, titanium, and/or tantalum. Thereafter, the metal powder is mixed with an amount of carbon. The carbon may be provided in powdered form, having a similar particle size mean diameter (d50) to the particles of the metal powder (e.g., a variance of +/-<NUM>%, or +/- <NUM>%). The carbon powder may be mixed with the metal powder at a suitable weight ratio such that, upon melting, there is a thermodynamic tendency in the melted, carbon-enriched alloy to form hard carbides with the refractory elements. This may be a weight ratio of the metal powder to the carbon powder of about <NUM>:<NUM> to about <NUM>:<NUM>, such as about <NUM>:<NUM> to about <NUM>:<NUM>.

As noted above, after forming the carbon-enriched metal powder, the carbon-enriched metal powder is bonded to the turbine blade tip using laser deposition, electron-beam welding, or any other technique that causes the carbon-enriched metal powder to melt on the turbine blade tip. During the melting of the carbon-enriched metal powder, there is a thermodynamic tendency of the carbon to combine with the refractory elements to form carbide particles. These carbide particles are very hard, and they can serve as abrasives to aid the blade tip when rubbing against the shroud.

Laser deposition (welding) will be described herein as a suitable melting process; however, this description should not be considered limited or exclusive of other possible processes. Referring now to <FIG> there is shown a schematic diagram of a general apparatus for laser generation and control that may be used for laser welding according to an embodiment of this disclosure. Laser generating means <NUM> generates a laser used in the welding system. A laser is directed through typical laser powder fusion welding equipment which may include beam guide <NUM>, mirror <NUM>, and focus lens <NUM>. The laser then impinges on a surface of the workpiece <NUM> (i.e., a turbine blade). Components such as beam guide <NUM>, mirror <NUM>, and focus lens <NUM> are items known in the art of laser welding. Beam guide <NUM> may include fiber optic materials such as optic fiber laser transmission lines. Furthermore, with certain laser types a laser may be directed onto workpiece <NUM> through an optic fiber line.

The carbon-enriched metal powder may be provided in powder feeder <NUM>. In such an embodiment, the powder is fed onto the workpiece through powder feed nozzle <NUM>. A coaxial or off-axis arrangement may be used with powder feed nozzle <NUM> with respect to the main laser.

Other components of the system include vision camera <NUM> and video monitor <NUM>. The image taken by the camera can also be fed-back to the controller screen for positioning and welding programming. The workpiece <NUM> is held on a work table <NUM>. An inert gas shield (not shown) is fed through guides (not shown) onto the workpiece <NUM>. The inert gas shield is directed onto a portion of the surface of the workpiece <NUM> during laser welding.

Controller <NUM> may be a computer numerically controlled (CNC) positioning system. CNC controller <NUM> coordinates components of the system. As is known in the art the controller may also include a digital imaging system. The controller guides movement of the laser and powder feed across the face of the workpiece <NUM>. In a preferred embodiment, movement of the workpiece in the XY plane is achieved through movement of the worktable <NUM>. Movement in the up and down, or Z-direction is achieved by control of the laser arm; i.e., pulling it up or lowering it.

In a preferred embodiment, the power of the laser is between about <NUM> to about <NUM> watts and more preferably between about <NUM> to about <NUM> watts. The powder feed rate of powder filler material is between about <NUM> to about <NUM> grams per minute and more preferably about <NUM> to about <NUM> grams per minute. Traveling speed for relative motion of the substrate positioning table <NUM> relative to the laser beam is <NUM> to <NUM> per minute ( about <NUM> to about <NUM> inches per minute) and more preferably <NUM> to <NUM> per minute ( about <NUM> to about <NUM> inches per minute). The size of the main spot cast by the laser onto the work surface is <NUM> to <NUM> ( about <NUM> to about <NUM> inches) in diameter and more preferably <NUM> to <NUM> (about <NUM> to about <NUM> inches).

The laser-welded bead width that results through the laser is thus <NUM> to <NUM> (about <NUM> to about <NUM> inches) and more preferably <NUM> to <NUM> (about <NUM> to about <NUM> inches) in width.

In this manner, the blade tip can be provided with the abrasive alloy of the present disclosure within virtually unlimited design constraints. Namely, because it is the melting of the carbon-enriched metal powder (and subsequent solidification) that causes the hard carbides to form, the act of laser welding itself creates the carbide particles. Thus, any design shape that can be produced by the laser can also include the hard carbide particles. The blade tip design may thus be optimized for any turbine engine configuration.

Once the alloy of the present disclosure is bonded on to the blade tip, the turbine blade may be finished using convention processes. These processes may include, but are not limited to, further heat treatments, machining, and surface finishing treatments such as polishing and coatings.

In accordance with the foregoing, a method <NUM> of forming an abrasive nickel-based alloy on a turbine blade tip. is illustrated in <FIG>. At step <NUM>, a metal powder is prepared using an atomization process. The metal powder is an alloy that is suitable for use in a turbine blade, such as (but not limited to) a nickel-based superalloy. The metal powder includes refractory elements, such as tungsten, titanium, and/or tantalum. At step <NUM>, an amount of carbon in mixed into the metal powder. At step <NUM>, the carbon-enriched metal powder is bonded to the turbine blade tip using laser deposition, electron-beam welding, or any other technique that causes the carbon-enriched metal powder to melt on the turbine blade tip. During the melting of the carbon-enriched metal powder, there is a thermodynamic tendency of the carbon to combine with the refractory elements to form carbide particles. These carbide particles are very hard, and they can serve as abrasives to aid the blade tip when rubbing against the shroud. The method <NUM> may contain additional steps not recited herein. The method <NUM> may have the method steps performed in an alternative order than as described.

As such, the present disclosure has provided embodiments of an improved method of forming an abrasive nickel-based alloy on a turbine blade tip. The method desirably avoids fabrication methods that limit the design of the blade tip by bonding the abrasive alloy to the tip using a melting technique (such as laser welding) that can accommodate virtually any design, where it is the step of melt itself (and subsequent re-solidification) of the alloy that causes the abrasive particles to be formed there-within and distributed throughout.

Claim 1:
A method of forming an abrasive nickel-based alloy on a turbine blade tip, comprising:
producing or obtaining a metal powder that is mixed with a carbon powder to form a carbon-enriched metal powder, wherein the metal powder comprises a refractory element; and
bonding the carbon-enriched metal powder to the turbine blade tip, wherein the step of bonding comprises raising the temperature of the carbon-enriched metal powder past its melting point, thereby causing the carbon to combine with the refractory elements to form abrasive carbide particles.