Patent Application
20240410045
The disclosure relates to gas turbine engines. More particularly, the disclosure relates to coatings for hot section piston seal rings (PSR).
Gas turbine engines (used in propulsion and power applications and broadly inclusive of turbojets, turboprops, turbofans, turboshafts, industrial gas turbines, and the like) use piston seal rings (PSR) in a variety of locations.
Coatings produced by different thermal spray techniques are being used in a wide variety of applications. They can perform different functions such as thermal barriers, abradable, corrosion and wear resistant and, for each application, different strategies and choices of materials can be used to achieve the different properties desired for the target application. When high temperature conditions are involved, the protection against wear and corrosion in elevated temperatures becomes a main engineering challenge, because oxidation and the attack by corrosive elements combined with friction and mechanical wear can damage the materials exposed to those conditions, leading to premature failure of engineered parts.
Currently, superalloy (e.g., IN718) static seals are commonly used uncoated in turbine engine hot sections and may be subject to damage by hot corrosion. Effects of hot corrosion often are reflected in weight/mass gain. Bare superalloys may have a weight gain up to 25 mg/cm2 when exposed to hot corrosion conditions such as 0.5 mg/cm2 of Na2SO4 at 900° C. for 24 hours. Such high weight gain means that the alloy is being attacked by sulfur, which could lead to premature failure of the seal and mating counterface component. Furthermore, these parts are also exposed to severe tribological conditions, which means they suffer premature wear during high temperature operation.
The use of commercially available self-lubricating coatings can increase the lifetime of these parts by improving tribological performance. However, these self-lubricating coatings (such as the NASA-developed PS304 and PS400) have shown poor resistance to hot corrosion conditions. PS304 is disclosed in U.S. Pat. No. 5,866,518 of DellaCorte et al., entitled “Self-Lubricating Composite Chromium Oxide”, issued Feb. 2, 1999. PS304 generally has NiCr binder with Cr2O3 hardener and Ag+ fluorides solid lubricant. PS400 is disclosed in U.S. Pat. No. 8,753,417 of DellaCorte et al., entitled “High Temperature Solid Lubricant Coating for High Temperature Wear Applications”, issued Jun. 17, 2014.PS400 generally has NiMoAl binder with Cr2O3 hardener and Ag+ fluorides solid lubricant.
A more recent proposal for a coating for such a PSR is found in US Patent Application Publication 2021/0270369A1 of Stoyanov et al., entitled “Wear Resistant Self-Lubricating Static Seal”, published Jan. 6, 2022, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. Another is found in US Patent Application Publication No. 2022/0325797A1 (the '797 publication), of Stoyanov et al., entitled “Low Friction, Wear Resistant Piston Seal”, published Oct. 13, 2022. The '797 publication discloses a coating with a CoCr alloy binder phase and a hard particle phase comprising Cr2O3. Application is via HVOF.
Composite coatings have been used on Fe alloy (e.g., carbon steel, stainless steel, Invar alloy) substrates for low and intermediate temperature ranges (e.g., room temperature up to about 500° C.). In such coatings, cobalt and nickel are binder metals for WC and Cr3C2 (e.g., WC—Co, WC—CoCr, Cr3C2—NiCr, or Cr3C2—WC—NiCoCr).
Another seal configuration is the W-seal of which an example is found in US Patent Application Publication 2022/0065122A1 (the '122 publication) of Stoyanov et al., entitled “Seals and Methods of Making Seals”, published Mar. 3, 2022, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. The '122 publication discloses both PSR and self-sprung compression seals. The self-sprung compression seals have cross-sections characterized by one or more cycles of a C-shape or W-shape. With such seals, sometimes because of seal orientation a different letter may be used (e.g., the letter E may be used to designate a radially compressed seal; whereas, the letter W may be used to designate an axially-compressed seal of similar cross-section but oriented 90° opposite). The '122 publication discloses both baseline seals made of conventional alloys (e.g., nickel-based superalloys) and modified seals made of HEA.
Depending on the production process, additional heat treatments or surface processing are needed to improve the mechanical properties. For example, annealing.
One aspect of the disclosure involves a method for applying a coating. The method comprises: providing a mixture of powders comprising by volume percent: 10.0 to 60.0 one or more cobalt-based alloys, and 5.0 to 70.0 WC—Ni; and spraying the mixture on a metallic substrate. Each of the cobalt-based alloys have by weight percent: Co as a largest constituent; 20.0-35.0 Cr; up to 3.0 C, if any; and up to 4.0 Ni, if any.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders comprises by volume percent: 12.0 to 55.0 said one or more cobalt-based alloys; and 10.0 to 65.0 said WC—Ni.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders further has by volume percent 5.0 to 85.0 Cr3C2.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders comprises by volume percent: 10.0 to 30.0 said one or more cobalt-based alloys; 8.0 to 30.0 said WC—Ni; and 50.0 to 80.0 said Cr3C2.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the powder of WC—Ni is an agglomerated and sintered WC—Ni.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the spraying is HVOF spraying or HVAF spraying or cold spray.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the spraying is to a thickness of 75 micrometers to 130 micrometers.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the one or more cobalt-based alloys each comprise by weight percent: Co as said largest constituent; 25.00 to 32.00 Cr; 0.9 to 2.0 C; 3.0 to 6.0 W; 1.0-4.0 Fe; up to 1.5 Mn, if any; 0.5 to 2.0 Si; up to 0.1 P, if any; up to 0.1 S, if any; up to 2.0 Mo, if any; and 1.0-4.0 Ni.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the one or more cobalt-based alloys each comprise by weight percent: Co as said largest constituent; 28.00 to 32.00 Cr; 0.9 to 2.0 C; 3.0 to 6.0 W; up to 3.0 Fe, if any; 0.5 to 2.0 Mn; 0.2 to 2.0 Si; up to 0.04 P, if any; up to 0.03 S, if any; up to 1.50 Mo, if any; and up to 3.0 Ni, if any.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders comprises by volume percent: 30.0 to 60.0 said one or more cobalt-based alloys; and 40.0 to 70.0 said WC—Ni.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders comprises by volume percent: up to 20.0 Cr3C2, if any.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders comprises by volume percent: up to 10.0 Cr3C2, if any.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the mixture of powders comprises by volume percent: 10.0 to 30.0 said one or more cobalt-based alloys. 8.0 to 30.0 said WC—Ni; and 50.0 to 80.0 Cr3C2.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a split ring seal substrate and the spraying is at least to an outer diameter surface of the substrate.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a spring compression seal substrate and the spraying is at least to an outer an axial end surface portion of the substrate.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a HALO seal substrate and the spraying is to an inner diameter surface of the substrate.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a locating pin substrate and the spraying is to a base of the locating pin or a distal end section of the locating pin.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate interfaces with a locating pin and the spraying is to a counterface surface for the locating pin.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a snap fastener substrate and the spraying is to a shaft and a barb underside.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is of a component having a snap fit bead or groove and the spraying is to said bead or groove.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is of a component having a tab and the spraying is to a face of the tab.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is of a component having seal counterface and the spraying is to the seal counterface.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a seal substrate and the coating is to a contact surface portion of the substrate.
A further aspect of the disclosure involves an article comprising: a metallic substrate; and a coating on the metallic substrate; wherein the coating comprises by volume percent: 18.0 to 50.0 an alloy having, by weight percent, Co as a largest constituent and 20.0-35.0 Cr; and 11.0 to 70.0 WC—Ni.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the coating further comprises by volume percent: up to 65% Cr3C2, if any and wherein at last 95% by volume exclusive of porosity is said alloy, said WC—Ni, and said Cr3C2, if any.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the coating has a thickness of 50 micrometers to 200 micrometers.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate forms a split ring; and the coating is on an outer diameter surface of the substrate.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively, the substrate is a nickel-based superalloy or cobalt-based superalloy.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively: a counterface is in sliding engagement with the coating and comprising a nickel-based superalloy substrate.
In a further embodiment of any of the foregoing embodiments, additionally and/or alternatively: the substrate is a split ring seal substrate and the spraying is at least to an outer diameter surface of the substrate; or the substrate is a spring compression seal substrate and the spraying is at least to an outer an axial end surface portion of the substrate; the substrate is a HALO seal substrate and the spraying is to an inner diameter surface of the substrate; or the substrate is a locating pin substrate and the spraying is to a base of the locating pin or a distal end section of the locating pin; or the substrate interfaces with a locating pin and the spraying is to a counterface surface for the locating pin; or the substrate is a snap fastener substrate and the spraying is to a shaft and a barb underside; or the substrate is of a component having a snap fit bead or groove and the spraying is to said bead or groove; or the substrate is of a component having a tab and the spraying is to a face of the tab; or the substrate is of a component having a seal counterface and the spraying is to the seal counterface.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicate like elements.
To help improve the endurance life of next generation mechanical systems in gas turbine engines, cobalt-based alloy composite coatings with the addition of WC—Ni or Cr3C2 and WC—Ni were produced to reach low wear rate values (WR<10−6 mm3/Nm) of the coating as well as the counterface at room temperature and elevated temperature (300° C.) during reciprocating/fretting wear. Particular tests were conducted on coatings that, for the CoCr alloy feedstock used Stellite® 6 gas atomized alloy of Kennametal Inc., Latrobe Pennsylvania.
The
In
In
The coatings tested were produced with a mixture of powders: gas-atomized Co—Cr alloy (Stellite® 6 CoCr alloy of Kennametal Inc., Latrobe PA) (
Table 1 below shows example Co—Cr alloy compositions. Table 2 shows two example tested powder blends that used Stellite® 6 CoCr alloy as the Co—Cr alloy and alternative example ranges.
The first four rows are taken from different industry sources. The powders were mixed according to the ratio shown in Table 2 (which ignores voids in the mixture) and were deposited by high-velocity oxygen-fuel (HVOF) spray using the spraying parameters in Table 3 to a thickness of coating 26 of 248±12 micrometers and coating 27 of 230±40 micrometers. The substrate was stainless steel. The coating containing the CoCr alloy and WC—Ni is identified as “SW” and the coating containing the CoCr alloy in addition to WC—Ni and Cr3C2 is identified as “SCW”.
As additional variations, optionally any of these ranges may include impurity levels of other elements, compounds, and the like, In further examples these other materials may represent up to 5.0 volume percent aggregate and up to 2.0 or 1.0 volume percent individually. In yet other examples, additions include pre-formed lubricious oxides. For example, cobalt oxides and tungsten oxides may be included initially so that one does not have to wait for in-service oxidation of cobalt and tungsten. These may be included in said small aggregate amounts but possibly above the individual.
The spraying was by using a Diamond Jet™ 2700 gun of Oerlikon Metco, Pfaeffikon, Switzerland.
Table 4 shows: deposition efficiency (DE); volume fraction of matrix, carbide, and porosity; and Vickers hardness. Retention of Cr3C2 in the coating is lower than WC—Ni, decreasing the DE of SCW compared to SW. Vickers hardness was tested at room (RT) and elevated temperature (300° C.). Hardness values are higher for the SCW coating at both RT and HT. Table 5 shows wear rate measured as V/(FN×L) where V is the wear volume (mm3), FN is the applied load (N) and L represents the length (m).
The Table 5 wear tests were conducted in a ball-on-flat configuration in reciprocating motion at room temperature and elevated temperature (300° C.) on an alumina (Al2O3) counterface with the three identified coatings on stainless steel substrates.
As mentioned above, the two coatings were produced to achieve low wear rate values (WR<10−6 mm3/Nm) of the coating as well as the counterface at room temperature and high temperature (300° C.) during reciprocating sliding. Low wear values can translate into increasing the lifecycle of materials during operation, particularly between room temperature and 300° C. or more at relatively low loads (e.g., 5N). An example seal substrate is a nickel-based superalloy such as IN 718 (e.g., equiaxed). An example counterface is a nickel-based superalloy such as IN 718 (e.g., equiaxed). Such superalloy may be essentially uncoated (no added coating), but may form an alumina scale in service.
The composite coatings may be put into service without any post-treatment. This is distinguished from Aoh (2001) and Tan, (2018) wherein there is a post-coating heat treatment involving annealing and aging. J. N. Aoh and J. C. Chen, “On the Wear Characteristics of Cobalt-based Hard-facing Layer after Thermal Fatigue and Oxidation”, Wear, October 2001, Vol 250 (1-12), pp. 611-620, Elsevier Science B.V., Amsterdam, Netherlands; J. Tan et al., “High performance Co—Cr3C2 composite coating by jet electrodeposition”, Surface Engineering, December 2018, Vol. 34:11, pp. 861-869, Taylor & Francis Group, London, England.
HVOF allows forming high-density coatings and low decomposition of the carbides (due to melting or decarburization as in APS). The combination of the production process (HVOF) and the ratio of the metallic matrix (Stellite™ 6) to carbides showed good wear resistance (low wear rate). Additionally, high velocity air-fuel (HVAF) and cold spray are candidates. Of these three non-plasma techniques, HVOF generally has higher operating temperature and lower particle velocity than HVAF and cold spray. Cold spray generally has the lowest operating temperature and highest particle velocity. HVAF is generally intermediate in both parameters.
The example engine 120 generally includes a low speed spool 130 and a high speed spool 132 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 136 via several bearing systems 138. It should be understood that various bearing systems 138 at various locations may alternatively or additionally be provided, and the location of bearing systems 138 may be varied as appropriate to the application.
The low speed spool 130 generally includes an inner shaft 140 that interconnects, a first (or low) pressure compressor 144 and a first (or low) pressure turbine 146. The inner shaft 140 is connected to the fan 142 through a speed change mechanism, which in the example gas turbine engine 120 is illustrated as a geared architecture 148, to drive a fan 142 at a lower speed than the low speed spool 130. The high speed spool 132 includes an outer shaft 150 that interconnects a second (or high) pressure compressor 152 and a second (or high) pressure turbine 154. A combustor 156 is between the high pressure compressor 152 and the high pressure turbine 154. A mid-turbine frame 157 of the engine static structure 136 may be arranged generally between the high pressure turbine 154 and the low pressure turbine 146. The mid-turbine frame 157 further supports one or more of the bearing systems 138 in the turbine section 128. The inner shaft 140 and the outer shaft 150 are concentric and rotate via bearing systems 138 about the engine central longitudinal axis A which is collinear with their longitudinal axes.
The core airflow is compressed by the low pressure compressor 144 then the high pressure compressor 152, mixed and burned with fuel in the combustor 156, then expanded over the high pressure turbine 154 and low 146 pressure turbine. The example mid-turbine frame 157 includes airfoils 159 which are in the core airflow path C. The turbines 146, 154 rotationally drive the respective low speed spool 130 and high speed spool 132 in response to the expansion. It will be appreciated that each of the positions of the fan section 122, compressor section 124, combustor section 126, turbine section 128, and fan drive gear system 148 may be varied. For example, gear system 48 may be located aft of the low pressure compressor, or aft of the combustor section 26 or even aft of turbine section 128, and fan 142 may be positioned forward or aft of the location of gear system 48
In the illustrated example, the piston seal 160 is partially accommodated in a radially outwardly open groove 170 in an inner member and its OD surface is engaged to an inner diameter (ID) surface 171 of an outer member. The example inner member is a vane structure (e.g., circumferential vane array) of the mid turbine frame 157. The example outer member is a seal runner of the static structure 136. The example groove is formed by the interior surfaces 174, 175 of wall sections 172, 173 and a base surface 176. The example walls have OD rims and outboard axial faces opposite the respective faces 174, 175.
Principal contact between the seal and the contacting members is between the seal OD surface 162 and the runner ID surface 171. Additional contact may be between the seal axial end surfaces and the adjacent groove wall surface. Wear and damage may occur at any of these. Typically, the counterface members nay be uncoated alloy at the interfaces (e.g., uncoated at the surfaces 171, 174, 175). Thus, the seal substrate surface at the seal OD and/or axial end faces (or the entire cross-sectional perimeter surface) may be coated as above.
Another example is a spring compression static seal. For example, as in the '122 publication baseline, stainless steel or nickel- or cobalt-based superalloy or other seal substrates may be formed by deforming sheetmetal or may be cast or otherwise formed. Example seals include axial compression seals such as a bellows seal or a W-seal, or for radial compression seals, such as C-seals or E-seals. For example, seal 220 (
For the example seal 220, forward counterface members engaging the axial end 226 are a radially extending end surface portions 230 of a circumferential array of blade outer air seals (BOAS) 232. BOAS ID surfaces closely surround tips of airfoils 240 of a stage of blades 242. For the example seal 220, aft counterface members engaging the axial end are a radially extending end surface portions 250 of the OD shrouds 254 of a circumferential array of vanes 252. Example vanes are in clusters with multiple airfoils 253 per cluster.
In these example embodiments, wear may notably occur at counterface surfaces 171, 174, 175, 230, and 250. Example PSR (or other seal) substrate material is nickel- or cobalt-based superalloy (e.g., wrought). Example, nickel-based superalloy legacy alloys are IN-718 (UNS N07718/W.Nr. 2.4668, Inconel® alloy 718 Huntington Alloys Corp., Huntington WV), X750 (UNS N07750/W. Nr. 2.4669, Inconel® alloy X750 Huntington Alloys Corp., Huntington WV), and Waspaloy (alloy 685, N07001). However, new alloys are continually being proposed. Each example counterface member (or other member to be coated or not described above or below) may be formed of a nickel- or cobalt-based based alloy or superalloy alloy (e.g., uncoated). Example nickel-based superalloys are Inconel® 718 (IN-718; UNS N07718; AMS 5662), Inconel® 100 (IN-100; UNS N13100; AMS 5397), and Inconel® 713C (IN-713C; Alloy 713C), each of (Huntington Alloys Corp., Huntington WV) and Mar-M247. An example cobalt-based superalloy is Haynes® 188 (UNS R30188) of Haynes International, Kokomo, Indiana. Thus, the seal substrate surface at least at the axial ends 226, 227 (forming contact surfaces) (or the entire cross-sectional perimeter surface) may be coated as above. However, new alloys are continually being proposed. In the seal relaxed/extended pre-installation condition, the areas to be coated may be other than axial ends (e.g., shifted along the surface 221).
Additional seal applications include brush seal systems, namely coating the brush seal counterface (e.g., runner). Typical brush seals have radially inwardly extending bristles engaging the OD surface of the counterface. U.S. Pat. No. 6,170,831B1 (the '831 patent), of Bouchard, Jan. 9, 2001, and entitled “Axial Brush Seal for Gas Turbine Engines”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length, discloses a double-ended axial static brush seal system partially re-presented as 400 in
Other examples involve locating pins. A typical locating pin 420 (
Along a distal end portion 514 of the shaft, the shaft exterior surface 512 is in sliding engagement with a second component. An example engagement is with the inner diameter surface 520 of a boss 522 of the second component acting as a socket for said pin distal end portion. In the example, the second component is an annular combustion chamber liner 526 held spaced apart from the case (e.g., radially inward). The boss may be separately formed from and welded to a main section of the liner. Example wearing movement is between the OD surface 512 and ID surface 520. Relative movement is parallel to the axis 501 and typically results from differential thermal expansion and engine vibration. Thus, one or both of these surfaces (surface 512 along the distal portion and surface 520) may be coated via the present methods.
Another snap example is a separate snap fastener 440 (
Among additional locations for the coating are in snap fit interfaces 460 (
Additional examples involve tabs 481 (
Additional seal applications include examples involve knife edge seals (not shown). A typical knife edge seal has hardened knife edges. Thus, the runner (usually an OD surface of an inner member but optionally an ID surface of an outer member) may be the counterface coated by the present methods. An example knife edge seal is shown in U.S. Pat. No. 10,167,729B2 (the '729 patent), of Aiello et al., Jan. 1, 2019, and entitled “Knife Edge with Increased Crack Propagation Life”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.
Additional seal applications involve finger seals (e.g., of steel or other alloys discussed above). With finger seals, the contacting portions of the seals themselves and/or the counterface surface may be coated via the present methods. Example finger seals are shown in U.S. Pat. No. 10,094,389B2 (the '389 patent), of Chuong et al., Oct. 9, 2018, and entitled “Flow Diverter to Redirect Secondary Flow”, and U.S. Pat. No. 9,845,695B2 (the '695 patent), of Budnick et al., Dec. 19, 2017, and entitled “Gas Turbine Seal Assembly and Seal Support”, the disclosures of which are incorporated by reference herein in their entireties as if set forth at length.
Additional seal applications involve so-called HALO seals (not shown). One example is shown in U.S. Pat. No. 10,221,714B2 (the '714 patent), of Peters et al., Mar. 5, 2019, and entitled “Secondary Seal Device(s) with Alignment Tab(s)”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. The ID surface of the HALO seal may be coated by the present methods as may be the OD surface of the inner member or shaft. Additionally, alignment or mounting tabs are typical in such seals and may be coated as noted above.
The use of “first”, “second”, and the like in the following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as “first” (or the like) does not preclude such “first” element from identifying an element that is referred to as “second” (or the like) in another claim or in the description.
One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing baseline configuration, details of such baseline may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.
Benefit is claimed of U.S. Patent Application No. 63/472,263, filed Jun. 9, 2023, and entitled “CoCr Alloy Carbide Composite Coatings for High-Temperature Applications”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.
| Number | Date | Country | |
|---|---|---|---|
| 63472263 | Jun 2023 | US |
