Patent Application
20230227945
The present disclosure is generally directed to metal alloys with improved high-temperature oxidation and fatigue resistance for use in turbocharger applications. More particularly, the present disclosure is directed to nickel-based alloys and turbine wheels including nickel-based alloys.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine wheel to spin within the housing. The exhaust gas-driven turbine wheel is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine wheel also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
The turbine wheel, usually a cast nickel-based alloy, used in turbochargers is a high-speed rotating component that is exposed to high temperature combustion gasses between temperatures of about 750° C. to about 1050° C., depending upon the application. To withstand such a high temperature, the nickel-based alloy material should be oxidation resistant, creep resistant as well as thermo-mechanical fatigue resistant while rotating in the approximately 100,000-300,000 RPM range. Existing alloys for such applications all have various deficiencies: For example, the Mar-M-246 nickel-based alloy is relatively expensive, whereas the IN-713C nickel-based alloy exhibits inferior high-temperature properties.
Therefore, it will become apparent to those skilled in the art that there remains a present and continuing need for the provision of improved nickel-based alloys and turbine wheels that include such nickel-based alloys. Particularly, it would be desirable to provide an alloy based on Mar-M-246 but with an improved chemistry that reduces costs significantly while still retaining the desirable high-temperature oxidation and corrosion, creep and thermo-mechanical fatigue resistance, for example, of Mar-M-246. 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 disclosure.
Nickel-based alloys and turbocharger turbine wheels including nickel-based alloys are disclosed herein. In one exemplary embodiment, a nickel-based alloy includes or consists of, on a weight basis of the overall alloy: about 2.00% to about 3.00% cobalt, about 12.0% to about 14.0% chromium, about 5.75% to about 6.85% aluminum, about 5.00% to about 6.00% tungsten, about 2.25% to about 2.75% molybdenum, about 1.25% to about 2.00% titanium, about 0.55% to about 1.50% niobium, about 0.13% to about 0.17% carbon, about 0.03 to about 0.05% zirconium, about 0.01% to about 0.02 boron, and a majority of nickel, with the understanding that there may be inevitable/unavoidable impurities. Additionally, in some examples (although an amount of 0.00% of any of the following elements may be present), the nickel-based alloy may include or further consist of tantalum in an amount of less than about 0.10%, manganese in an amount of less than about 0.03%, silicon in an amount of less than about 0.03%, iron in an amount of less than about 1.00%, copper in an amount of less than about 0.02%, sulfur in an amount of less than about 10 ppm and phosphorous in an amount of less than about 50 ppm.
With regard to the foregoing alloy embodiments: the amount of cobalt may be limited to about 2.25% to about 2.75%; alternatively or additionally, the amount of chromium may be limited to about 12.00% to about 12.80%; alternatively or additionally, the amount of aluminum may be limited to about 6.40% to about 6.80%; alternatively or additionally, the amount of tungsten may be limited to about 5.25% to about 5.75%; alternatively or additionally, the amount of molybdenum may be limited to about 2.40% to about 2.60%; alternatively or additionally, the amount of titanium may be limited to about 1.35% to about 1.65%; alternatively or additionally, the amount of niobium may be limited to about 0.80% to about 1.20%.
In another exemplary embodiment, a turbocharger turbine wheel includes or consists of, at least as a part of its overall composition, a nickel-based alloy, wherein the nickel-based alloy includes or consists of, on a weight basis of the overall alloy: about 2.00% to about 3.00% cobalt, about 12.0% to about 14.0% chromium, about 5.75% to about 6.85% aluminum, about 5.00% to about 6.00% tungsten, about 2.25% to about 2.75% molybdenum, about 1.25% to about 2.00% titanium, about 0.55% to about 1.50% niobium, about 0.13% to about 0.17% carbon, about 0.03 to about 0.05% zirconium, about 0.01% to about 0.02 boron, and a majority of nickel, with the understanding that there may be inevitable/unavoidable impurities. Additionally, in some examples (although an amount of 0.00% of any of the following elements may be present), the nickel-based alloy may include or further consist of tantalum in an amount of less than about 0.10%, manganese in an amount of less than about 0.03%, silicon in an amount of less than about 0.03%, iron in an amount of less than about 1.00%, copper in an amount of less than about 0.02%, sulfur in an amount of less than about 10 ppm, and phosphorous in an amount of less than about 50 ppm. Such a turbine wheel may find application for operating at temperatures from 980° C. to 1020° C.
With regard to the foregoing turbine wheel embodiments: the amount of cobalt may be limited to about 2.25% to about 2.75%; alternatively or additionally, the amount of chromium may be limited to about 12.00% to about 12.80%; alternatively or additionally, the amount of aluminum may be limited to about 6.40% to about 6.80%; alternatively or additionally, the amount of tungsten may be limited to about 5.25% to about 5.75%; alternatively or additionally, the amount of molybdenum may be limited to about 2.40% to about 2.60%; alternatively or additionally, the amount of titanium may be limited to about 1.35% to about 1.65%; alternatively or additionally, the amount of niobium may be limited to about 0.80% to about 1.20%.
This brief summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description and the drawings. This summary is not intended to identify key features 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 various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.
Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 5%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. “About” can alternatively be understood as implying the exact value stated. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
Embodiments of the present disclosure provide an improved nickel-based alloy and turbocharger turbine wheels made with this nickel-based alloy. The disclosed embodiments detail an improved nickel-based alloy chemistry that is less expensive than Mar-M-246 yet has better high-temperature properties as compared with IN-713C.
With reference now to
The turbine housing 105 and turbine wheel 111 form a turbine configured to circumferentially receive a high-pressure and high-temperature exhaust gas stream 121 from an engine, e.g., from an exhaust manifold 123 of an internal combustion engine 125. The turbine wheel 111 (and thus the rotor) is driven in rotation around the axis of rotor rotation 103 by the high-pressure and high-temperature exhaust gas stream 121, which becomes a lower-pressure and lower-temperature exhaust gas stream 127 and is axially released into an exhaust system (not shown).
The compressor housing 107 and compressor wheel 113 form a compressor stage. The compressor wheel 113, being driven in rotation by the exhaust-gas driven turbine wheel 111, is configured to compress axially received input air (e.g., ambient air 131, or already-pressurized air from a previous-stage in a multi-stage compressor) into a pressurized air stream 133 that is ejected circumferentially from the compressor. Due to the compression process, the pressurized air stream is characterized by an increased temperature over that of the input air.
Optionally, the pressurized air stream may be channeled through a convectively cooled charge air cooler 135 configured to dissipate heat from the pressurized air stream 133, increasing its density. The resulting cooled and pressurized output air stream 137 is channeled into an intake manifold 139 on the internal combustion engine, or alternatively, into a subsequent-stage, in-series compressor. The operation of the system is controlled by an engine control unit (ECU) 151 that connects to the remainder of the system via communication connections 153.
The composition of an exemplary nickel-based alloy is now provided below with respect to its constituent elements (all percentages being provided on a weight basis of the overall alloy composition, unless otherwise noted). In one embodiment, elements that are associated with grain boundary cracking and embrittlement should be minimized. For example, in this embodiment, the content of silicon (Si) is maintained below or equal to about 0.03%. The content of phosphorous (P) is maintained below or equal to about 50 ppm. Further, the content of sulfur (S) is maintained below or equal to about 10 ppm. As an additional matter, to reduce cracking, the master heat alloy that is used to process the alloy to ingot form desirably does not contain any casting revert or scrap having detrimental tramp or trace elements.
Elements that are associated with grain boundary strengthening, including carbon (C), boron (B), and zirconium (Zr) are melting point depressants which can create hot cracks during solidification in a casting process (hot tearing phenomenon) and welding (solidification cracking) of alloys. Grain boundary liquation during welding of alloys is linked to carbides and borides. Since C (but not B) achieves a “carbon boil” during master alloy refining, embodiments of the nickel-based alloy retain some carbon, likely in the form of carbides (as described below) but not a significant content of borides. Zr or B does not influence the castability when added individually. However, when both Zr and B are present in the alloy, high hot tearing susceptibility was found, the effect being particularly strong if Zr concentration was high. Accordingly, the content of B is maintained in a range of about 0.01% to about 0.02%, the content of carbon is maintained in a range of about 0.13% to about 0.17%, and the content of zirconium is maintained in a range of about 0.03% to about 0.05%.
With the aforementioned relatively lower C and B content, the undesirable formation of topologically close-packed (TCP) brittle phases requires concomitant lowering of the minimum amounts of several refractory elements known to form TCP phases. For example, chromium (Cr), molybdenum (Mo), cobalt (Co), and tungsten (W) can combine to form TCP phases. Of these, reducing the Cr lower limit is desirably avoided because Cr plays a role in oxidation/sulfidation resistance. Accordingly, in one embodiment, the content of Cr is from 12.0% to about 14.0%. In another embodiment, the content of Cr is from about 12.0% to about 12.8%.
Co is a solid solution strengthening element, but it can contribute to TCP phase formation. Accordingly, permitting a lower Co content has been discovered to be beneficial from lower risk of TCP formation, lower density and lower cost point of view. Thus, in one embodiment, the content of Co is from about 2.00% to about 3.00%. In another embodiment, the content of Co is from about 2.25% to about 2.75%.
Furthermore, W is known to be an element that forms carbides, that acts as a solid solution strengthening element, and that forms TCP phases especially in case of high percentage of gamma prime in alloys. W is also a relatively expensive element and increases density of alloys. Accordingly, permitting a lower W content has been discovered to be beneficial. Thus, in one embodiment, the content of W is from about 5.00% to about 6.00%. In another embodiment, the content of W is from about 5.25% to about 5.75%.
Titanium (Ti) is both a carbide and gamma-prime phase forming element. The gamma-prime phase is favorable for high-temperature oxidation resistance. Gamma-prime phase volume fraction and its thermal stability at high temperature is key for alloys for higher mechanical properties, creep and thermo-mechanical fatigue resistance during severe thermal-shock loading conditions. Accordingly, in some embodiments, titanium is provided in a range of about 1.25% to about 2.00%. In other embodiments, titanium is provided in a range of about 1.35% to about 1.65%.
Mo is a solid solution strengthening element and increases the Al partitioning to the gamma-prime phase by reducing the solubility of Al in the γ matrix which increases gamma-prime volume fraction. Moreover, Mo is known to be an element that forms primary MC carbides and that forms detrimental phases like TCP phases or M6C carbides, in some instances, the formation of M6C is an intragranular Widmanstatten precipitates. Alloy tends to precipitate M6C carbides if the alloy has a sufficiently high molybdenum+tungsten content (Mo+½W≥6 wt %). There is evidence in the art that Mo may be detrimental to hot corrosion or oxidation resistance. Mo oxide volatility may also be a negative factor. moderate-strength cast alloys such as IN-738 and higher-strength cast alloys such as IN-792 have achieved greatly improved corrosion resistance with low levels of molybdenum and tungsten, and beneficial levels of chromium (12 to 15%). Accordingly, the content of Mo is desirably maintained within a range of about 2.25% to about 2.75%. In another embodiment, the content of Mo is maintained with a range of about 2.40% to about 2.60%.
Continuing with the description of an exemplary embodiment of the nickel-based alloy, niobium (Nb) is known to be an element that forms carbides and a solid solution strengthening element that also partitions to the gamma-prime phase. The phase fraction and stability of γ′ increases with niobium content. Allowing a higher content of Nb will favor Nb-rich carbides and make up for the absence of Ti in the gamma-prime phase while contributing to solid solution strengthening. Moreover, Nb is preferred MC carbide former because titanium-rich MC carbides are less stable and introduce deleterious M6C reactions. Accordingly, in an embodiment, the content of Nb is from about 0.55% to about 1.50%. In another embodiment, the content of Nb is from about 0.80% to about 1.20%.
Al, as a gamma-prime phase forming element, is also included in the alloy composition of the present disclosure. In one embodiment, the content of Al is from about 5.75% to about 6.85%. In another embodiment, the content of Al is from about 6.40% to about 6.80%.
Other elements that may be present in small amounts (or possibly 0%) in some embodiments include tantalum (Ta) in an amount of less than about 0.10%, manganese (Mn) in an amount of less than about 0.03%, iron (Fe) in an amount of less than about 1.00%, and copper (Cu) in an amount of less than about 0.02%.
Moreover, as the described alloys are nickel-based, it will be appreciated that nickel (Ni) forms a majority of the content (i.e., greater than about 50%) of the described alloy. That is, nickel typically accounts for the balance of the content not otherwise described above, while accounting for inevitable/unavoidable impurities not otherwise set forth above as are commonly understood in the art.
Table 1, set forth below, provides the elemental content of a nickel-based alloy of the present disclosure in accordance with the description provided above, while also specifying the maximum content of additional detrimental tramp or trace elements commonly encountered in nickel-based alloys. Each weight percentage included in Table 1 is understood to be preceded by the term “about.” In addition, a minimum of zero, signified by “<”, means “low as possible”, not to exceed the maximum. It should be acknowledged that trace amounts of inevitable/unavoidable impurities may be present (in trace amounts), although not explicitly listed in Table 1, as is known in the art.
As such, described herein are embodiments of improved nickel-based alloys and turbocharger turbine wheels made with such nickel-based alloys. The described embodiments provide a high-temperature oxidation and corrosion resistance, creep and thermo-mechanical fatigue resistant and very good castable (due to lower freezing range and density) nickel-based alloy that is achieved, in part, with increased in chromium and aluminum, significantly decreased tungsten and cobalt, addition of niobium, with no tantalum, in comparison to Mar-M-246. The resultant alloy has a reduced cost, wherein the raw material is about 15% less than Mar-M-246. Thus, the novel alloy described herein will have good mechanical properties, better creep and thermo-mechanical fatigue resistance, better oxidation/hot corrosion resistance and better castability with lesser density and cost, and will be a suitable alternative to the prior art options. As such, the alloy of the present disclosure can be used to make turbine wheels for applications reaching temperatures from 980° C. to 1020° C. with lower cost than existing commercial alloys.
All of the nickel-based alloys described herein may be understood as either: (1) “comprising” the listed elements in their various percentages, in an open-ended context or (2) “consisting of” the listed elements in their various percentages, in a closed-ended context. Alternatively, the alloys described herein may be understood as (3) “consisting essentially of” the listed elements in their various percentages, wherein other elements may be present in amounts not effecting the novel/nonobvious characteristics of the alloy. Thus, as used herein, the terms “comprising,” “consisting of,” and “consisting essentially of” should be understood as applicable to all of the ranges of alloy compositions disclosed herein.
The present disclosure is now illustrated by the following non-limiting examples. It should be noted that various changes and modifications can be applied to the following examples and processes without departing from the scope of this invention, which is defined in the appended claims. Therefore, it should be noted that the following examples should be interpreted as illustrative only and not limiting in any sense.
Hot tearing (HTR) phenomenon, also referred to as hot cracking or hot shortness, represents the formation of an irreversible failure (crack) in the still semisolid casting during formation via casting of a metal alloy part. Hot tearing arises from a complex combination of thermal-mechanical and solidification phenomena, basically being associated with the incomplete liquid feeding and tensile stress generated in coherent regions of mushy zones, more specifically, in areas with a high solid fraction of 0.9 and beyond. It is generally believed that hot tearing occurs above the solidus temperature when the volume fraction of solid is, for example, 85% to 95% and the solid phase is organized in a continuous network of grains and propagates in the interdendritic and/or intergranular liquid film. “Time spend” in mushy zone during solidification is possible to influence by the chemical composition of the alloy.
As illustrated, due to the complexity of the turbine wheel, particularly the changes of cross-sectional dimensions of the blades, cracks can occur in the blades by casting turbine wheels. There may be multiple factors that could be involved in the formation of cracks at supersolidus temperatures, however a primary cause is inadequate compensation of solidification shrinkage by melt flow in the presence of thermal stresses. These cracks can be difficult to detect visually or by non-destructive analysis (NDA) and, as such, can result in some cast parts being used in the field, which may have a shorted “use life.”
Example metal alloys (referred to herein as “MarM246” and “G246UL”) with the following compositions were used in the examples presented below in Table 2 with respect in
ThermoCalc software was used for computation of the freezing range of Mar-M-246, Inconel 713C and G246UL. Precision of computation was reviewed by experimental measurement of Mar-M-246 and Inconel 713C by DSC (Differential scanning calorimetry) equipment. Correlation between computation and experimental measurement was found to be very good.
As illustrated, G246UL exhibits similar, but slightly lower, computed values of freezing range to Inconel 713C and much lower in comparison to Mar-M-246. Further, it was observed that Inconel 713C castability is better and HTR occurrence is much lower in comparison to Mar-M-246. As such, castability of G246UL is better and HTR occurrence is much lower in comparison to Mar-M-246 and correspondingly improved over Inconel 713C.
Further, the computed density of G246UL is lower than MM246, which can provide a benefit in the case of turbine wheel inertia and will be beneficial in case of material castability. It is believed that lower density is better for castability.
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 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 as set forth in the appended claims and their legal equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202211002807 | Jan 2022 | IN | national |
This application is related to and claims all available benefit of Indian Provisional Patent Application IPA: 202211002807 filed Jan. 18, 2022, the entire contents of which are herein incorporated by reference.
