Patent Application
20130157078
The subject matter disclosed herein relates to metallic alloy compositions suitable for use in high temperature environments, and more particularly to metallic alloy compositions suitable for use as articles or bond coat materials in high temperature environments to provide protection from oxidation and hot corrosion.
In harsh environments such as a turbine engine, metallic overlay coatings and diffusion coatings act as bond coatings (i.e. MCrAlY and/or aluminides) for thermal barrier coatings (TBCs). The coatings protect the underlying metal alloy substrate against heat and the corrosive and oxidizing environment of the hot gases. The TBC provides a heat reducing barrier between the hot combustion gases and the metal alloy substrate, and can prevent, mitigate, or reduce potential heat, corrosion, and/or oxidation induced damage to the substrate.
MCrAlY alloys are a family of high temperature coatings, wherein M is selected from one or a combination of iron, nickel and cobalt; Cr is chromium; Al is aluminum; and Y is yttrium. Sometimes other rare earth elements are substituted for Y such as lanthanum (La) or scandium (Sc). These MCrAlY coatings usually have gamma and beta phases in the alloy microstructures. Various alloying elements, such as Si, Hf, Pd and Pt, have been added to gamma/beta MCrAlY alloys to improve oxidation and/or hot corrosion resistance, but this can lead to reduction in strain tolerance of the bond coat materials and may result in a reduction of spallation life of the coating systems in which they have been employed, particularly those which include TBCs.
There is another class of overlay MCrAlY coatings which are based on gamma and gamma prime phase alloy microstructures. An advantage of gamma and gamma prime MCrAlY coatings is that they have a smaller thermal expansion mismatch with superalloys of the underlying turbine articles and the gamma prime strengthens the materials resulting in a relatively high resistance to thermal fatigue. A high thermal fatigue resistance in these bond coatings is very desirable, since thermal fatigue is a principal mode of degradation of turbine blades operated at elevated temperatures. While these coatings are desirable, they generally have operating lifetimes that are determined by their ability to maintain, or avoid the depletion of, elements such as aluminum and chromium that are essential to maintaining protective oxides and prevent spallation of TBC coatings and protective coating systems that incorporate them.
Therefore, a need exists to provide bond coat materials that improve the spallation resistance of protective coating systems in which they are employed, particularly those which employ TBCs.
According to one aspect, in an exemplary embodiment, a high temperature oxidation and hot corrosion resistant MCrAlX alloy is disclosed. The alloy includes, by weight of the alloy, M comprising nickel in an amount of at least about 30 percent and X comprising from about 0.005 percent to about 0.19 percent yttrium.
According to another exemplary embodiment, a coated article is disclosed. The article includes a substrate having a surface. The article also includes a bond coat disposed on the surface, the bond coat comprising a high temperature oxidation and hot corrosion resistant MCrAlX alloy, wherein, by weight of the alloy, M comprises at least about 30 percent nickel and X comprises about 0.005 percent to about 0.19 percent yttrium.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Referring to the Figures, a gamma-gamma prime MCrAlX alloy 100 is disclosed that is suitable for use as a bond coat 110 material and provides more than 50° F. improvement in the operating temperature capability over existing comparative gamma-beta bond coat materials, as described herein. More particularly, the MCrAlX alloy 100 comprises a NiCoCrAlY alloy 100. This material may be used as a metallic overlay bond coating that protects an underlying metallic superalloy substrate from degradation by oxidation and hot corrosion. The composition of the NiCoCrAlY alloy 100 bond coat 110 material is similar to certain Ni-based superalloy substrate compositions. Without being limited by theory, the similarity of the composition of the NiCoCrAlY alloy 100 bond coat 110 material and superalloy substrate compositions reduces the composition gradient of certain of the coating or substrate alloy constituents, thereby also reducing the potential for diffusion processes that might tend to deplete the coating or substrate of certain essential constituents, such as, for example, aluminum and chromium, that provide surface oxides associated with oxidation and hot corrosion protection, or enrichment in constituents that do not promote oxidation or hot corrosion protection, particularly by reducing interdiffusion at the substrate/coating interface. With reduced chemical constituent gradients, the bond coating/substrate alloys can sustain their original compositions for prolonged times; depletion of essential elements such as Al, Cr in the bond coat 110 material, as well as enrichment with elements that were not in the original bond coat, becomes more gradual. For example, the bond coat 110 material can sustain a thin, continuous, protective alumina scale for longer intervals at high operating temperatures, which in turn promotes improved spallation lifetimes of thermal barrier coatings (TBC) proximate the bond coat 110 material, as described herein. The NiCoCrAlY alloys 100 are substantially Si-free, thereby preventing the potential formation of brittle TixSiy intermetallic phases, which can reduce the spallation lifetimes of TBC coatings disposed on bond coat materials that include silicon, particularly when the substrate alloy includes titanium, such as GTD111, which has a nominal composition, in weight percent of the alloy, of 14% chromium, 9.5% cobalt, 3.8% tungsten, 1.5% molybdenum, 4.9% titanium, 3.0% aluminum, 0.1% carbon, 0.01% boron, 2.8% tantalum, and the balance nickel and incidental impurities, or Rene N4, which has a nominal composition, in weight percent of the alloy, of 7.5% cobalt, 9.75% chromium, 4.20% aluminum, 3.5% titanium, 1.5% molybdenum, 4.8% tantalum, 6.0% tungsten, 0.5% columbium (niobium), 0.05% carbon, 0.15% hafnium, 0.004% boron, and the balance nickel and incidental impurities. In certain embodiments, the NiCoCrAlY alloys 100 described herein may include up to 1.25% germanium, particularly the high temperature ductility. The NiCoCrAlY alloys 100 described herein may be used in various turbine engine applications to enable higher engine operating temperatures, improved operating efficiencies and/or longer inspection intervals.
Referring to
In an exemplary embodiment, a surface 30 of a component 10, such as a turbine blade 50, is protected by the bond coat 110 material as a metallic protective coating layer, as illustrated in greater detail in
Protective system 130 may include bond coat 110 as an under layer as part of a combination of coating layers that also includes one or more thermal barrier coating (TBC) layer 140, or one or more aluminide coating layer 150, or one or more other bond coat layers, or a combination thereof. In an exemplary embodiment, as illustrated in
In another exemplary embodiment, as illustrated in
In yet another exemplary embodiment, as illustrated in
In a further exemplary embodiment, as illustrated in
Protective system 130 may also include bond coat 110 as an inner layer as part of a combination of coating layers that also includes one or more thermal barrier coating (TBC) layer 140, or one or more aluminide layer 150, or a combination thereof. For example, in exemplary embodiments, the protective systems 130 of
In yet another exemplary embodiment, as illustrated in
In a further exemplary embodiment, as illustrated in
In an exemplary embodiment, the MCrAlX alloy 100 comprises a nickel-based MCrAlX alloy having a microstructure that includes gamma and gamma prime phases wherein, by weight of the alloy, M comprises nickel in an amount of at least about 30 percent and X comprises from about 0.005 percent to about 0.19 percent yttrium. In another exemplary embodiment, the MCrAlX alloy 100 comprises a nickel-cobalt-based MCrAlX (NiCoCrAlX) alloy 100 having a microstructure that includes gamma and gamma prime phases wherein, by weight of the alloy, M comprises nickel in an amount of at least about 30 percent and cobalt in an amount of about 5.0 percent to about 15.0 percent, and X comprises yttrium in an amount from about 0.005 percent to about 0.19 percent. The MCrAlX alloy 100 may also include germanium in an amount, by weight of the alloy, up to about 1.25 percent.
In one exemplary embodiment, the MCrAlX alloy 100 comprises, by weight of the alloy, from about 5.0 to about 15.0 percent cobalt, from about 12.0 to about 28.0 percent chromium, from about 6.5 to about 11.0 percent aluminum, up to about 1.25 percent germanium, from about 4.0 to about 8.0 percent tantalum, from about 0.005 to about 0.05 percent zirconium, from about 0.005 to about 0.8 percent hafnium, from about 0.005 to about 0.19 percent yttrium, and the balance nickel and incidental impurities. In another embodiment, the MCrAlX alloy 100 comprises, by weight of the alloy, from about 8.5 percent to about 12.0 percent cobalt, from about 16.0 percent to about 21.0 percent chromium, from about 6.5 percent to about 8.5 percent aluminum, from about 4.5 percent to about 7 percent tantalum, from about 0.001 percent to about 0.1 percent zirconium, from about 0.1 percent to about 0.65 percent hafnium, from about 0.005 percent to about 0.19 percent yttrium, up to about 1.25 percent germanium, and the balance nickel and incidental impurities. These MCrAlX alloys 100 have more aluminum than the existing gamma-gamma prime bond coat alloy described herein. Without being limited by theory, this may provide additional aluminum that may avoid depletion of aluminum in the bond coat 110 material during high temperature exposure in an oxidizing environment, and thus promote improved oxidation, hot corrosion and spallation resistance. The addition of The MCrAlX alloys 100 described herein are substantially silicon-free and substantially rhenium-free (i.e., contain substantially no silicon or rhenium other than as an incidental impurity). As used herein, substantially silicon-free means that even where silicon may be present, such as by incorporation as an incidental impurity, it will comprise, by weight of the alloy, about 0.1 percent or less. The absence of silicon avoids the possibility of the formation of brittle TixSiy intermetallic phases in or adjacent to the bond coat/substrate interface, particularly where the materials proximate the MCrAlX alloy 100 include titanium. As used herein, substantially rhenium-free means that even where Re may be present, such as by incorporation as an incidental impurity, it will comprise, by weight of the alloy, about 0.1 percent or less. Avoidance of the use of rhenium improves the strain tolerance (
This is illustrated in
The above tests demonstrated the ability of the protective system 130 employing MCrAlX alloy 100 bond coating to prevent or at least significantly delay the onset of crack initiation. From another perspective, the use of the MCrAlX alloys 100 disclosed herein also enabled the protection system 130 described, i.e., bond coat 110/TBC coating layer 140, to achieve about the same spallation resistance at an average operating temperature that was at least about 50° F. higher than that of a protective system comprising the existing bond coat alloys described herein and TBC layer 140. Therefore, the MCrAlX alloys 100 described herein improve the spallation resistance sufficiently to enable longer operating lifetimes at the same operating temperature or the similar operating lifetimes at reduced cooling rates, therefore at improved efficiency. For example, for a given spallation life of a protective system 130 employing a TBC layer 140, the protective systems 130 disclosed herein employing bond coat 110 materials may be used at bond coat/TBC interface temperatures that are at least about 50° F. higher than a similar protective system employing the comparative gamma-beta bond coat alloy disclosed herein, for example, which provides higher operating temperature capabilities and improved operating efficiencies and/or longer inspection intervals of the turbine engines employing them. Without being limited by theory, yttrium in the amounts prescribed herein improves oxidation resistance by delaying alumina spallation. Lower Y concentrations in the MCrAlX alloy reduce segregation of Y-rich phases in the coating that can lead to failure. The use of aluminum in the amounts described may also provide additional aluminum that may avoid depletion of aluminum in the bond coat 110 material during high temperature exposure in an oxidizing environment, and thus may also promote improved oxidation, hot corrosion and spallation resistance.
In another exemplary embodiment, the MCrAlX alloys 100 disclosed herein may also include, by weight of the alloy, germanium in an amount up to about 1.25 percent, and more particularly about 0.001 percent to about 1.25 percent.
The incidental impurities may include those incidental to the processing of the individual alloy constituents described herein, particularly those known to be incidental to nickel-based alloys comprising these constituents, and more particularly, to nickel-cobalt-based superalloys comprising these constituents. An example of an incidental impurity is sulfur. The amount of sulfur will preferably be controlled to 8-100 ppm sulfur by weight.
The bond coat 110 material may have a composition different from that of the substrate 120, or may have the same composition. The bond coat 110 may have any suitable thickness. In an exemplary embodiment, the bond coat 110 material may have a thickness of 0.003 inch to about 0.03 inch. In other embodiments, the thicknesses may be greater. The MCrAlX alloys 100 disclosed herein may be used in any suitable form, including as alloy used to form an entire article of the types disclosed herein, or as a bond coat 110 material. The MCrAlX 100 alloys may be formed by any suitable method, including various vacuum melting methods, and particularly melting methods employed for various superalloys, particularly nickel-cobalt-based superalloys. The bond coat 110 material may be applied by any thermal spray process including but not limited to high velocity oxygen fuel spraying (HVOF), high velocity air fuel thermal spray (HVAF), vacuum plasma spray (VPS), air plasma spray (APS), and cold spray methods. Further, the bond coat 110 material can be deposited by various physical vapor deposition (PVD) processes, including cathodic arc physical vapor deposition, electron beam-physical vapor deposition (EBPVD), and ion plasma deposition (IPD).
The protective system 130 may also include an aluminide layer 150 disposed relative to the bond coat 110 material and other coatings as described herein. The aluminide layer 150 may include any suitable aluminide, including a diffusion aluminide such as a simple diffusion aluminide or a complex diffusion aluminide, such as a platinum aluminide. The aluminide layer 150 may have any suitable thickness, and in an exemplary embodiment, may have a thickness from about 0.0005 inch to about 0.0045 inch thick.
The protective system 130 may also include a TBC layer 140 disposed relative to the bond coat 110 material and other coatings as described herein. Any suitable TBC layer 140 may be used, including a dense vertically microcracked (DVM) ceramic TBC layer 140, a porous TBC layer 140 or a hybrid structure. The TBC layer 140 may have any suitable thickness, and in an exemplary embodiment, may have a thickness from about 0.005 inch to about 0.1 inch. An example of a suitable TBC layer 140 includes a TBC which is chemically bonded, for example to the bond coat 110 or aluminide layer 150, as described herein, a strain-tolerant columnar grain structure as may be achieved by depositing the TBC layer 140 using physical vapor deposition techniques as are known in the art (e.g., EBPVD), or by using a plasma spray technique to deposit a non-columnar TBC layer 140. Suitable materials for TBC layer 140 include yttria-stabilized zirconia (YSZ), a preferred composition being about 6 to about 8 weight percent yttria, optionally with up to about 20 weight percent of an oxide of a lanthanide-series element to reduce thermal conductivity. Other ceramic materials may also be used, such as yttria, nonstabilized zirconia, or zirconia stabilized by magnesia, gadolinia, ytterbia, calcia, ceria, scandia, and/or other oxides.
The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). Furthermore, unless otherwise limited all ranges disclosed herein are inclusive and combinable (e.g., ranges of “up to about 25 weight percent (wt. %), more particularly about 5 wt. % to about 20 wt. % and even more particularly about 10 wt. % to about 15 wt. %” are inclusive of the endpoints and all intermediate values of the ranges, e.g., “about 5 wt. % to about 25 wt. %, about 5 wt. % to about 15 wt. %”, etc.). The use of “about” in conjunction with a listing of constituents of an alloy composition is applied to all of the listed constituents, and in conjunction with a range to both endpoints of the range. Finally, unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments.
It is to be understood that the use of “comprising” in conjunction with the alloy compositions described herein specifically discloses and includes the embodiments wherein the alloy compositions “consist essentially of” the named components (i.e., contain the named components and no other components that significantly adversely affect the basic and novel features disclosed), and embodiments wherein the alloy compositions “consist of” the named components (i.e., contain only the named components except for contaminants which are naturally and inevitably present in each of the named components).
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
