Patent Application
20100279148
The inventive subject matter generally relates to alloys, and more particularly relates to nickel-based alloys and turbine components.
Turbine engines are used as the primary power source for various kinds of aircraft. Turbine engines may also serve as auxiliary power sources that drive air compressors, hydraulic pumps, and industrial electrical power generators. Most turbine engines generally follow the same basic power generation procedure. Compressed air is mixed with fuel and burned to form expanding hot combustion gases, which are directed against stationary turbine vanes in the turbine engine. The stationary turbine vanes turn the gas flow partially sideways to impinge onto turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at a 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, electrical generators or other devices.
Many turbine engine blades and vanes are fabricated from high temperature materials, such as nickel-based or cobalt-based superalloys. Although nickel-based and cobalt-based superalloys have good high temperature properties and many other advantages, they may be susceptible to corrosion, oxidation, thermal fatigue, and/or erosion damage in the high temperature environment of an operating turbine engine. These limitations are undesirable as there is a constant drive to increase engine operating temperatures in order to increase fuel efficiency and to reduce emissions. Additionally, replacing damaged turbine engine components made from nickel-based and cobalt-based superalloys is expensive.
Accordingly, it is desirable to fabricate turbine engine components that are more robust than conventionally-fabricated components. Moreover, it is desirable to have more cost-effective ways to repair the components, if they become damaged or degraded. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.
Nickel-based alloys and turbine components are provided.
In an embodiment, by way of example only, a nickel-based alloy includes, by weight, about 29.5 percent to about 31.5 percent aluminum, about 0.20 percent to about 0.60 percent hafnium, about 0.08 percent to about 0.015 percent yttrium, and a balance of nickel.
In another embodiment, by way of example only, a nickel-based alloy includes, by weight, about 9.7 percent to about 10.3 percent of cobalt, about 15.5 percent to about 16.5 percent of chromium, about 6.6 percent to about 7.2 percent of aluminum, about 5.7 percent to about 6.3 percent of tantalum, about 2.7 percent to about 3.3 percent of tungsten, about 1.8 percent to about 2.3 percent of rhenium, about 0.20 percent to about 1.2 percent of hafnium, about 0.20 percent to about 0.60 percent of silicon, and a balance of nickel.
In still another embodiment, by way of example only, a component includes a substrate comprising a first alloy and a welded portion on the substrate, the welded portion comprising a second alloy that is different in formulation than the first alloy and selected from a group consisting of a first formulation and a second formulation. The first formulation comprises, by weight about 29.5 percent to about 31.5 percent aluminum, about 0.20 percent to about 0.60 percent hafnium, about 0.08 percent to about 0.015 percent yttrium, and a balance of nickel. The second formulation comprises, by weight about 9.7 percent to about 10.3 percent of cobalt, about 15.5 percent to about 16.5 percent of chromium, about 6.6 percent to about 7.2 percent of aluminum, about 5.7 percent to about 6.3 percent of tantalum, about 2.7 percent to about 3.3 percent of tungsten, about 1.8 percent to about 2.3 percent of rhenium, about 0.20 percent to about 1.20 percent of hafnium, about 0.20 percent to about 0.60 percent of silicon, and a balance of nickel.
In still another embodiment, by way of example only, a turbine component includes a substrate comprising a first alloy and a bond coat over the substrate. The bond coat comprises a second alloy including about 31.0 percent aluminum, about 0.25 percent to about 0.5 percent hafnium, about 0.01 percent yttrium, and a balance of nickel.
The inventive subject matter will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description is merely exemplary in nature and is not intended to limit the inventive subject matter or the application and uses of the inventive subject matter. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
In an embodiment, the base material 202 comprises a first alloy, such as a nickel-based superalloy including, but not limited to IN738, IN792, C101, MarM247, Rene80, Rene125, ReneN5, SC180, CMSX 4, and PWA1484. In other embodiments, the base material 202 may comprise a cobalt-based superalloy or another superalloy conventionally employed for the fabrication of turbine engine components.
The welded portions 204, 206 include a second alloy, which may comprise a nickel-based alloy or a nickel-based superalloy having a composition that is different than the composition of the first alloy. As used herein, the term “nickel-based alloy” may include “nickel-based superalloy”. In an embodiment, the second alloy may have a first formulation that has oxidation-resistance properties that are greatly improved over those of the first alloy. The first formulation of the nickel-based alloy includes nickel, aluminum, hafnium, and yttrium, which may form an intermetallic phase such as a β-NiAl phase. In still another embodiment, the first formulation of the nickel-based alloy may include incidental impurities (e.g., trace amounts of additional elements that are not intentionally included in the composition), but does not include other elements other than those listed previously (e.g., nickel, aluminum, hafnium, yttrium, and/or chromium). For example, the first formulation of the nickel-based alloy may include, by weight, aluminum in a range of about 29.5 percent to about 31.5 percent, hafnium in a range of about 0.20 percent to about 0.60 percent, yttrium in a range of about 0.08 percent to about 0.015 percent, and a balance of nickel. In still another embodiment, the first formulation of the nickel-based alloy may include about 31.0 percent aluminum, about 0.25 percent to about 0.5 percent hafnium, about 0.01 percent yttrium, and a balance of nickel. Inclusion of a greater percentage of aluminum as compared with conventional nickel-based superalloys promotes formation of a protective oxide layer on a surface of the welded portion (e.g., blade tip 206), which protects the outer surface of the welded portion (e.g., blade tip 206) against oxidation. The hafnium atoms diffuse into grain boundaries of the aluminum oxides within the nickel-based alloy to decrease a rate at which the protective oxide layer grows over the welded portion (e.g., blade tip 206) so that the protective oxide layer remains relatively thin. As a result, spallation of the protective oxide layer may be minimized, and the presence of the protective oxide layer may provide additional oxidation resistance for the alloy. Yttrium is included in the composition of the nickel-based alloy to react with sulfur that may be present in the turbine engine component 200. The yttrium forms stable sulfides with the sulfur to prevent the sulfur from diffusing to the surface of the nickel-based alloy. This may also improve the adherence of protective oxide layer to the alloy.
In another embodiment in which increased oxidation-resistance is desired, the first formulation of the nickel-based alloy may further include chromium. In an example, chromium may be present in the first formulation of the nickel-based alloy in a range of about 4.7 percent to about 5.3 percent, by weight. In another embodiment, the first formulation may include about 5.0 percent chromium, by weight. By including about 5.0 percent, by weight, of chromium, the chromium may contribute to the formation of a chromium oxide scale over the welded portion (e.g., blade tip 206).
In any case, although the first formulation of the nickel-based alloy may provide oxidation-resistance at elevated temperatures (e.g., temperatures greater than about 1100° C.), it may be relatively brittle. Thus, in an embodiment, the first formulation of the nickel-based alloy may be employed for the blade tip 206 as a coating having a thickness in a range of about 75 microns to about 250 microns. In other embodiments, the coating may be thicker or thinner.
In another embodiment, the second alloy may have environmental-resistance properties that are greatly improved over those of the first alloy. In such a case, the second alloy may be employed for repairing cracks 204 and blade tip 206 and may have a second formulation that includes, in addition to nickel, elements selected from cobalt, chromium, aluminum, tantalum, tungsten, rhenium, hafnium, silicon, carbon, boron, and yttrium. For example, the second formulation of the nickel-based alloy may include, by weight, cobalt in a range of from about 9.7 percent to about 10.3 percent, chromium in a range of from about 15.5 percent to about 16.5 percent, aluminum in a range of from about 6.6 percent to about 7.2 percent, tantalum in a range of from about 5.7 percent to about 6.3 percent, tungsten in a range of from about 2.7 percent to about 3.3 percent, rhenium in a range of from about 1.8 percent to about 2.3 percent, hafnium in a range of from about 0.20 percent to about 1.2 percent, silicon in a range of from about 0.20 percent to about 0.60 percent, and a balance of nickel (and incidental impurities). In another embodiment, the second formulation of the nickel-based alloy may include, by weight, about 10.0 percent cobalt, about 16.0 percent chromium, about 6.8 percent aluminum, about 6.0 percent tantalum, about 3.0 percent tungsten, about 2.0 percent rhenium, about 0.25 percent hafnium, about 0.4 percent silicon, and a balance of nickel (and incidental impurities).
As noted above, by including aluminum and chromium in the second formulation of the nickel-based alloy, oxidation resistance properties of the alloy may be improved over conventional nickel-based superalloys because the aluminum and chromium may react with oxygen to form a protective alumina and chromia scales over the nickel-based alloy, and the protective scales may protect the second alloy against oxidation. Additionally, because the percentage of chromium in the second formulation of the nickel-based alloy is relatively high as compared to conventional nickel-based superalloys, corrosion-resistance properties may be imparted to the alloy. Moreover, the silicon in the alloy reacts with oxygen to form silica, which contributes to the formation of a protective oxide scale. In order to prevent the oxide layer from becoming undesirably thick, hafnium is included. In an embodiment, the hafnium also may contribute to the environment-resistance properties of the nickel-based alloy by diffusing to the grain boundaries of alumina scale to slow down its growth rate This may improve the adherence of the thin protective layer to the base material 202. Cobalt may increase solubility of the gamma matrix of the alloy to prevent topologically close-packed (“TCP”) phases from forming. Cobalt also enhances corrosion-resistant properties of the alloy. Tungsten is included to strengthen the gamma matrix of the alloy to improve its mechanical properties. Rhenium may be included to partition to the gamma matrix of the alloy to enhance the negative lattice misfit between the gamma matrix and gamma prime phases, which may improve creep resistance of the alloy. Rhenium may also prevent gamma prime particles from coarsening, which may greatly improve the elevated-temperature properties of the alloy. Tantalum may mainly partition to the gamma prime phase to improve the elevated-temperature properties of the alloy.
In another embodiment, the second formulation of the nickel-based alloy additionally may include yttrium at about 0.01 percent, by weight. Yttrium may contribute to the environment-resistant properties of the nickel-based alloy by reacting with sulfur and forming stable sulfides. In still another embodiment, the nickel-based alloy may further include carbon at about 0.06 percent, by weight and/or boron at about 0.01 percent, by weight. Carbon and boron are included to strengthen grain boundaries.
To further protect the turbine engine component 200 from the harsh operating environment of an engine, the turbine engine component 200 may include a protective coating system 210, in an embodiment.
According to an embodiment, the bond coating 302 may be a diffusion aluminide coating. For example, the diffusion aluminide coating may be formed by depositing an aluminum layer over the base material 202 (
The thermal barrier coating 304 may be formed over the bond coating 302 and may comprise, for example, a ceramic. In one example, the thermal barrier coating 304 may comprise a partially stabilized zirconia-based thermal barrier coating, such as yttria stabilized zirconia (YSZ). In an embodiment, the thermal barrier coating may comprise yttria stabilized zirconia doped with other oxides, such as Gd2O3, TiO2, and the like. In another embodiment, the thermal barrier coating 304 may have a thickness that may vary and may be, for example, in a range from about 50 μm to about 300 μm. In other embodiments, the thickness of the thermal barrier coating 304 may be in a range of from about 100 μm to about 250 μm. In still other embodiments, the thermal barrier coating 304 may be thicker or thinner than the aforementioned ranges.
The thermally-grown oxide layer 306 may be located between the bond coating 302 and the thermal barrier coating 304. In an embodiment, the thermally-grown oxide layer 306 may be grown from aluminum in the above-mentioned materials that form the bond coating 302. For example, after a heat treatment during deposit of bond coating 302, oxidation may occur thereon to result in the formation of the oxide layer 306. In one embodiment, the thermally-grown oxide layer 306 may be relatively thin, and may be less than 5 μm thick.
To fabricate or refurbish the turbine engine component, a method 400, depicted in a flow diagram provided in
In another embodiment of step 402, the turbine engine component may be mechanically prepared. Examples of mechanical preparation include, for example, pre-repair machining, degreasing surfaces in proximity to the target surface in order to remove any oxides, dirt or other contaminants, mechanically grinding the target surfaces, and/or grit-blasting the target surfaces. In another embodiment, additional or different types and numbers of preparatory steps can be performed, such as visual and/or fluorescent penetrant inspections. It will be appreciated that the present embodiment is not limited to these preparatory steps, and that additional, or different types and numbers of preparatory steps can be conducted.
Once the turbine engine component has been prepared, a nickel-based alloy may be applied thereto, step 404. In an embodiment, the nickel-based alloy may be laser-welded onto the target surfaces. In an example, the nickel-based alloy may comprise any one of the above-described alloy compositions used for welded portions 204, 206 (
In another embodiment, applying the nickel-based alloy to the target surfaces may include plasma transfer arc (PTA), micro plasma, and tungsten inert gas (TIG) welding methods. In still other embodiments, the step of applying the nickel-based alloy may include performing a thermal spray process such as high velocity oxygen fuel (HVOF), argon-shrouded plasma spraying or low pressure plasma spraying (LPPS) methods.
Returning to the flow diagram of
After the post-deposition step 406 is completed, at least one inspection process can be performed, step 408. In an embodiment, the inspection process may be employed to determine whether any surface defects exist, such as cracks or other openings, step 410. The inspection process may be conducted using any well-known non-destructive inspection techniques including, but not limited to, a fluorescent penetration inspection and a radiographic inspection. If an inspection process indicates that a surface defect exists, the turbine blade is subjected to an additional deposition process, and the process may return to either steps 402, 404, or 406. If an inspection process indicates that a surface defect does not exist, the process ends and the turbine engine component may be ready to be implemented into a turbine engine or other system.
Novel nickel-based alloys and improved methods for refurbishing turbine engine components have now been provided. Some embodiments of the novel nickel-based alloys may provide improved oxidation-resistance over conventional nickel-based alloys when subjected to typical engine operating temperatures. Other embodiments of the novel nickel-based alloys may provide improved corrosion-resistance over conventional nickel-based superalloys when subjected to typical engine operating conditions. Additionally, the methods by which the novel nickel-based alloys are applied may be employed not only on blades, but also on other turbine components, including, but not limited to, vanes and shrouds. The alloys and the methods of applying the alloys may also improve the durability of the turbine component over conventional superalloys and application methods, thereby optimizing the operating efficiency of a turbine engine, and prolonging the operational life of turbine blades and other engine components.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the inventive subject matter, 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 inventive subject matter 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 inventive subject matter. It being 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 inventive subject matter as set forth in the appended claims.
