Patent Application
20070111119
The present invention relates to repair and overhaul of turbine engine components. More particularly, the present invention relates to methods for repairing turbine engine components made from high-strength iron-based alloys.
Turbine engines are used as the primary power source for many types of aircrafts. 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 and the like.
Most turbine engines generally follow the same basic power generation procedure. Compressed air generated by axial and/or radial compressors 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. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, fans, electrical generators, or other devices.
Low and high pressure compressor (LPC/HPC) components such as compressor blades and impellers are primary components in the cold section for any turbine engine, and should be well maintained. The LPC/HPC components are subjected to stress loadings during turbine engine operation, and may also be impacted by foreign objects such as sand, dirt, and other such debris. The LPC/HPC components can degrade over time due to wear, erosion and foreign object impact. Sometimes LPC/HPC components are degraded to a point at which they may require replacement or repair. Since the replacement may result in significant part expense and time out of service, repair of gas turbine components is often a better option, when possible.
There are several traditional welding methods for repairing damaged turbine engine components, and each method has both advantages and limitations in terms of success. One reason for the lack of success is that the welding techniques and materials used to repair LPC/HPC components may not lend themselves to efficient and/or thorough repairs. For example, precipitation-hardened semiaustenitic stainless steel alloys are commonly used to make compressor blades because these alloys are strong and have good corrosion resistance. However, when repairing compressor blades made of these alloys using conventional welding techniques, such as plasma transferred arc (PTA) welding or tungsten inert gas (TIG) welding, it may be somewhat difficult to control heat inputs and other welding parameters. Limited control in these areas may result in complex or inefficient welding steps in order to reduce or eliminate hot cracking, part distortion, and to minimize the heat-affected zone in the weld and the base material. Also, repairing degraded compressor blades using the same filler as the base material may require relatively complex post-welding process. Furthermore, such a filler typically has a somewhat low hardness, and components that are repaired using such a filler may not perform well during subsequent operation in a sand environment.
Hence, there is a need for new repair methods for LPC/HPC components such as compressor blades. There is a particular need for new and more efficient repair methods that improve the reliability and performance of the repaired components.
The present invention provides a method for repairing an eroded surface of gas turbine compressor components. An amorphous alloy is deposited onto the eroded surface to fill material loss. First, the amorphous alloy is melted with a laser beam on the eroded surface, and then the molten amorphous alloy is re-solidified to form a welded deposit.
Other independent features and advantages of the preferred methods will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles 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 provides an improved method for repairing LPC/HPC components. The method utilizes a laser fusion welding technique to apply materials having tailored features to a worn LPC/HPC component surface. These materials can be used to repair components such as compressor blades and vanes, including impellers and blisks, which have been degraded due to wear, erosion and foreign object damage, to name several examples.
Turning now to
A welding metal powder is contained in a powder feeder 110. A powder feed nozzle 112 is in communication with the powder feeder 110 by way of a tube or other suitable conduit through which the metal powder is fed until it exits the powder feed nozzle 112 and reaches the component surface being repaired.
Other exemplary system components include a vision camera 120 and a monitor 130 that aid the system operator in viewing the repair process as performed by the laser beam and the metal powder as they impinge on the component surface being repaired. A controller 155 guides movement of the laser and powder relative to the component surface, preferably by moving the work table 140 at least in the XY plane although relative movement in the Z direction may be performed by raising and lowering either the work table 140 or the laser arm 108. An exemplary controller 155 is a computer numerically controlled (CNC) positioning system that coordinates the system components.
Under the control of the CNC positioning system, the laser is guided across the component surface being repaired while powder from the feeder 110 is directed from the nozzle 112. The laser beam and the powder pathways meet at the component surface where the energy from the laser beam melts the powder. The molten metal reacts with the component surface and then re-solidifies to form a cladding layer, as will be subsequently described in greater detail.
As previously mentioned, the laser fusion welding process can be used to repair a variety of different turbine engine components. For example, the compressor blades in the cold section of a turbine engine are particularly susceptible to wear, erosion and other degradation. Turning now to
As mentioned previously, the process of the present invention can be tailored to fit the blade's specific needs, which depend in part on the blade component where degradation has occurred. For example, degradation on the leading edge 162 and trailing edge 164 of the airfoil 152 can be repaired using the laser powder fusion welding process. The leading edge 162 and trailing edge 164 are both subject to degradation, again typically due to foreign particle impacts.
As another example, the airfoil tip 160 is particularly subject to degradation due to rubbing and other contact with the static shroud, in addition to foreign particle impacts, and the laser fusion welding process of the present invention is used to apply materials to the blade tip 160 by filling any material loss with amorphous alloys. Following the welding process, the tip 160 is machined to restore the tip 160 to the original design dimensions.
As another example, degradation on the platform 156 can be repaired using the laser fusion welding process. In some applications, wear on the platform 156 occurs at the contact surfaces 166 between adjacent compressor blades. At those locations, the friction can cause fretting and other wear. The laser powder fusion welding process can be used to fill the worn surface, cracks and other defects on the platform to restore the desired dimensions.
Again, the above repair processes are just examples of how a typical compressor blade 150 can be repaired by laser fusion welding according to the present invention. It is also emphasized again that compressor blades are just one example of the type of LPC/HPC components that can be repaired. For example, many gas turbine engines include a shroud structure that surrounds a row of compressor blades at the outer radial end of the blades. The shroud, like the blade tips 160, can be subject to erosion and repaired using the welding process. Other turbine engine components that can be repaired in such a manner include compressor stator vanes, vane support structures, rotor nozzles and other LPC/HPC components.
Turning now to
After selecting a suitable and repairable workpiece for repair, any necessary pre-welding procedures are performed to prepare the worn surface for laser powder fusion welding. An exemplary pre-welding procedure includes cleaning, machining and grit blasting the repair surface as step 210, although other pre-welding procedures may also be included in step 210. Grit blasting removes contaminants that interfere with laser powder fusion welding, and improves laser energy absorption.
Next, laser powder fusion welding is performed as step 220 using any suitable laser fusion welding apparatus. One exemplary welding apparatus is a handheld laser welding device such as that disclosed in U.S. Pat. No. 6,593,540 assigned to Honeywell International, Inc. Another exemplary welding apparatus is the automated laser welding device depicted in
During laser fusion welding, the laser preferably has a power output of at least about 50 watts. The laser beam is directed onto the surface to be repaired and an amorphous alloy is fed onto the surface in the laser beam path. Energy from the laser beam melts the amorphous filler material. After the laser beam is moved from a molten pool, the molten filler material cools and re-solidifies to form a weld. Welding parameters such as laser power output, amorphous material feed rate, traverse speed, and shield gas flow rate may be manipulated to eliminate or minimize hot cracking on the workpiece and to otherwise optimize the weld formed on the workpiece surface.
The amorphous alloy that is fed onto the repair surface and melted by the laser beam energy can be selected based on various factors including the repair surface material, the normal operating environment for the component being repaired, and the needed metallurgical requirements for the weld. Amorphous powders and weld wires are just two forms which are suitable for laser powder fusion welding to repair eroded surfaces. An amorphous alloy is glass-like in structure, lacking a crystalline lattice. Amorphous alloys have certain advantages over conventional alloys. For example, amorphous alloys are capable of exhibiting high yield strength. Also, the absence of grain boundaries in amorphous alloys typically provides more resistance to corrosion than polycrystalline materials. Further, many amorphous alloys having fine boride distributions are more resistant to wear than polycrystalline materials due to their high hardness.
One example of a suitable amorphous alloy for repair of many iron-based substrates such as stainless steels, including semiaustenitic stainless steels, is developed and produced under the trademark LMC-M™ from Liquidmetal Technologies and has a nominal composition, in weight percent, of 44.5% Cr, 5.9% B, 2.0% Si, 0.17% C, balance Fe. Another suitable amorphous alloy for repair of many iron-based substrates such as stainless steels, including semiaustenitic stainless steels, is sold under the mark LMC-C from Liquidmetal Technologies and has a nominal composition, in weight percent, of 30% Cr, 19% Ni, 9.7% Co, 3.9% Mo, 3.5% B, 2.5% Cu, 1.3% Si, 0.12% C, balance Fe.
After completing a weld, the repaired surface is examined as step 230 for suitable weld buildup. Additional amorphous filler material may be needed to provide adequate buildup to the component surface. Further, excess filler will later be ground or otherwise machined from the component surface, so it may be desirable to have a minimum amount of excess weld at the point of repair. If it is determined at step 235 that at least one additional layer of weld is needed, the method returns to step 220 for additional laser fusion welding of amorphous material to the repair surface.
After amorphous alloys are laser deposited onto eroded surfaces of compressor components to provide adequate material buildup for machining, as step 240, the excess weld from the repair area is ground or otherwise machined to restore the component to its original dimensions. During machining, the weld transforms at its surface from a two-phase crystalline materials to a homogeneous amorphous structure. In addition to having high yield strength and corrosion resistance, the high transformed surface hardness provides excellent wear resistance while bulk hardness remains at a level to provide a tough support structure. In this way, repaired compressor components will perform well in a sand operational environment.
The repaired workpiece may be heat treated as step 250 to relieve welding stress while avoiding crystal growth. In an exemplary embodiment, the repaired workpiece is heat treated at a temperature of between approximately 800 to approximately 1425° F. for about 1 hour. Subsequently, the repaired workpiece may be inspected, for example, by a fluorescent penetration inspection (FPI), to determine whether it can be returned to service.
The present invention thus provides an improved method for repairing and prolonging the service life of turbine engine components such as compressor blades and other compressor components. The method utilizes a laser powder fusion welding technique to repair degradation in compressor components such as blades, impellers, blisks, and the like. These methods can be effectively used to repair eroded compressor components, and thus can improve the overall durability, reliability and performance of gas turbine engines.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
