CoCr Alloy Carbide Composite Coatings for High-Temperature Applications

Abstract

A method for applying a coating, includes: providing a mixture of powders of comprising by volume percent: 10.0 to 60.0 one or more cobalt-based alloys and 5.0 to 70.0 WCNi; 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.

Claims

1. A method for applying a coating, the method comprising: providing a mixture of powders comprising by volume percent: 10.0 to 60.0 one or more cobalt-based alloys, each having 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; and 5.0 to 70.0 WCNi; and spraying the mixture on a metallic substrate.

2. The method of claim 1 wherein 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 WCNi.

3. The method of claim 1 wherein: the mixture of powders further has by volume percent 5.0 to 85.0 Cr.sub.3C.sub.2.

4. The method of claim 3 wherein 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 WCNi; and 50.0 to 80.0 said Cr.sub.3C.sub.2.

5. The method of claim 1 wherein: the powder of WCNi is an agglomerated and sintered WCNi.

6. The method of claim 1 wherein: the spraying is HVOF spraying or HVAF spraying or cold spray.

7. The method of claim 1 wherein: the spraying is to a thickness of 75 micrometers to 130 micrometers.

8. The method of claim 1 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.

9. The method of claim 1 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.

10. The method of claim 1 wherein 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 WCNi.

11. The method of claim 10 wherein the mixture of powders comprises by volume percent: up to 20.0 Cr.sub.3C.sub.2, if any.

12. The method of claim 11 wherein the mixture of powders comprises by volume percent: up to 10.0 Cr.sub.3C.sub.2, if any.

13. The method of claim 1 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 WCNi; and 50.0 to 80.0 Cr.sub.3C.sub.2.

14. The method of claim 1 wherein: 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.

15. The method of claim 1 wherein: the substrate is a seal substrate and the spraying is at least to a contact surface portion of the substrate.

16. 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 WCNi.

17. The article of claim 16 wherein the coating further comprises by volume percent: up to 65% Cr.sub.3C.sub.2, if any and wherein at last 95% by volume exclusive of porosity is said alloy, said WCNi, and said Cr.sub.3C.sub.2, if any.

18. The article of claim 16 wherein: the coating has a thickness of 50 micrometers to 200 micrometers.

19. The article of claim 16 wherein: the substrate forms a split ring; and the coating is on an outer diameter surface of the substrate.

20. The article of claim 16 wherein: the substrate is a nickel-based superalloy or cobalt-based superalloy.

21. The article of claim 16 further comprising: a counterface in sliding engagement with the coating and comprising a nickel-based superalloy substrate.

22. The article of claim 16 wherein: 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a micrograph of a substrate coated with a CoCr alloy/WCNi coating.

[0043] FIG. 2 is a micrograph of a substrate coated with a CoCr alloy/Cr.sub.3C.sub.2/WCNi coating.

[0044] FIG. 3 is a photograph of a CoCr alloy powder particle.

[0045] FIG. 4 is a photograph of a WCNi particle.

[0046] FIG. 5 is a photograph of Cr.sub.3C.sub.2 particles.

[0047] FIG. 6 is a plot of particle diameter for the CoCr alloy powder feedstock.

[0048] FIG. 7 is a particle size distribution plot for the WCNi powder feedstock.

[0049] FIG. 8 is a particle size distribution plot for the Cr.sub.3C.sub.2 powder feedstock.

[0050] FIG. 9 is a friction coefficient plot for CoCr alloy at room temperature.

[0051] FIG. 10 is a friction coefficient plot for CoCr alloy at 300 C.

[0052] FIG. 11 is a plot of the CoCr alloy/WCNi coating at room temperature.

[0053] FIG. 12 is a plot of CoCr alloy/WCNi coating at 300 C.

[0054] FIG. 13 is a plot of the CoCr alloy/Cr.sub.3C.sub.2/WCNi coating at room temperature.

[0055] FIG. 14 is a plot of CoCr alloy/Cr.sub.3C.sub.2/WCNi coating at 300 C.

[0056] FIG. 15 is a view of a gas turbine engine.

[0057] FIG. 15A is an enlarged view of a first seal system in the engine of FIG. 15.

[0058] FIG. 15B is an enlarged view of a second seal system in the engine of FIG. 15.

[0059] FIG. 15C is an enlarged view of a third seal system in the engine of FIG. 10.

[0060] FIG. 15D is an enlarged view combustor swirler in the engine of FIG. 10.

[0061] FIG. 16 is a longitudinal sectional/cutaway view of a locating pin joint.

[0062] FIG. 17 is a longitudinal sectional view of a snap fastener joint.

[0063] FIG. 18 is an inward radial view of a mounting tab-in-slot joint.

[0064] FIG. 19 is a longitudinal sectional view of the joint of FIG. 18.

[0065] FIG. 20 is a longitudinal sectional view of an alternate locating pin joint.

[0066] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0067] To help improve the endurance life of next generation mechanical systems in gas turbine engines, cobalt-based alloy composite coatings with the addition of WCNi or Cr.sub.3C.sub.2 and WCNi were produced to reach low wear rate values (WR<106 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.

[0068] FIGS. 1 and 2 respectively show articles 20, 21 having a Stellite 6 alloy/WCNi (designated SW) coating 26 and Stellite 6 alloy/Cr.sub.3C.sub.2/WCNi (designated SCW) coating 27 HVOF sprayed on a surface 24 of a substrate 22. The example substrate is stainless steel. The substrate may form a seal and the coating surface 28 surface may be the tribological interface of the seal (examples discussed below and discussion in the '122 publication). The coatings 26, 27 were deposited by the HVOF and the deposition parameters of Tables 2 and 3 below.

[0069] The FIGS. 1&2 coatings are formed by: molten and semi-molten splats (which quickly solidify) of the CoCr alloy and deformed carbides. No dendrite or spike-like structure was observed. Rather, carbides and the CoCr alloy splats were homogeneously distributed across the coating with no segregation or agglomeration of a specific phase. In the images: WCNi (brightest-light grey) 32; CoCr alloy (medium grey) 34; and Cr.sub.3C.sub.2 (dark grey) 36.

[0070] In FIG. 1, it is seen that splats of both phases, CoCr alloy and WCNi, are homogeneously distributed throughout the coating.

[0071] In FIG. 2, it is seen that splats of the different phases, CoCr alloy, WCNi, and Cr.sub.3C.sub.2, are homogeneously distributed throughout the coating.

[0072] The coatings tested were produced with a mixture of powders: gas-atomized CoCr alloy (Stellite 6 CoCr alloy of Kennametal Inc., Latrobe PA) (FIG. 3); fused-crushed Cr.sub.3C.sub.2 (FIG. 5); and agglomerated and sintered WCNi (AMPERIT 547 of Hgans AB, Hgans, Sweden, nominal WC12Ni, particle size: 45/15 m) (FIG. 4). The powder particle size distribution is similar for the three powders, as shown in FIGS. 6, 7 (WCNi), and 8 (Cr.sub.3C.sub.2). As a reference, D50 of the different powders are 34 m (Stellite 6 CoCr alloy), 37 m (WCNi), and 37 m (Cr.sub.3C.sub.2), respectively. The WCNi size is of the sintered agglomerate, not the particles forming the agglomerate particles (the latter being about 1 m).

[0073] Table 1 below shows example CoCr alloy compositions. Table 2 shows two example tested powder blends that used Stellite 6 CoCr alloy as the CoCr alloy and alternative example ranges.

TABLE-US-00001 TABLE 1 CoCr alloy Composition (Weight %) Alloy C Mn Si P S Cr Ni Co Mo W Fe Other Cobalt Alloy 1- 1- 27- 3- bal 4- 3- 6 nom range 2 2 32 4 6 4 Cobalt Alloy 0.90- 0.50- 0.20- 0.04 0.03 28.00- 3.00 bal 1.50 3.50- 3.0 6b 1.40 2.00 2.00 max max 32.00 max max 5.50 max AMS 5894 (wrought) Cobalt Alloy 1.15 1.25 1.10 30 bal 4.5 6b nom. (wrought) Cobalt Alloy 1.40- 0.50- 0.20- 0.04 0.03 28.00- 3.00 bal 1.50 3.50- 3.0 6k (wrought) 1.90 2.00 2.00 max max 32.00 max max 5.50 max Tested alloy 0.9- 0.5 0.7- 0.030 0.030 27.0- 3.0 bal 1.0 3.5- 3.0 0.5 max vendor spec. 1.4 max 1.5 max max 30.0 max max 5.5 max total Tested alloy 1.2 0.5 1.3 0.003 0.003 28.0 2.1 bal 0.2 4.8 2.1 0.06N.sub.2; sample assay 0.02O.sub.2 Range 1 2.0 2.5 2.5 0.1 0.1 27.0- 4.0 bal 2.0 6.0 4.0 max max max max max 32.0 max max max max Range 2 2.0 2.5 2.5 0.1 0.1 27.0- 4.0 bal 2.0 3.00- 4.0 max max max max max 32.0 max max 6.00 max Range 3 0.90- 0.50- 0.20- 0.04 0.03 28.00- 3.00 bal 1.50 3.00- 3.0 2.00 2.00 2.00 max max 32.00 max max 6.00 max Range 4 0.90- 0.50- 0.20- 0.04 0.03 28.00- 3.00 bal 1.50 3.50- 3.0 1.90 2.00 2.00 max max 32.00 max max 5.50 max Range 5 0.90- 0.50- 0.20- 0.04 0.03 25.00- 3.00 bal 1.50 3.50- 3.0 1.90 2.00 2.00 max max 35.00 max max 5.50 max Range 6 0.90- 0.50- 0.20- 0.04 0.03 28.00- 3.00 bal 1.50 3.50- 3.0 1.40 2.00 2.00 max max 32.00 max max 5.50 max Range 7 0.90- 0.50- 0.20- 0.04 0.03 25.00- 3.00 bal 1.50 3.50- 3.0 1.40 2.00 2.00 max max 35.00 max max 5.50 max Range 8 2.0 2.5 2.5 0.1 0.1 20.0- 4.0 bal 2.0 6.0 4.0 max max max max max 35.0 max max max max Range 9 0.5- 2.5 2.5 0.1 0.1 25.0- 4.0 bal 2.0 6.0 4.0 2.0 max max max max 35.0 max max max max Range 10 0.9- 1.5 2.0 0.1 0.1 25.0- 4.0 bal 2.0 6.0 4.0 2.0 max max max max 35.0 max max max max Range 11 0.9- 1.5 0.5- 0.1 0.1 25.0- 1.0- bal 2.0 3.0- 1.0- 2.0 max 2.0 max max 32.0 4.0 max 6.0 4.0 15.0 Other total; 7.0 other individually 5.0 Other total; 1.0 other individually 2.0 Other total; 0.50 other individually

[0074] 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 24812 micrometers and coating 27 of 23040 micrometers. The substrate was stainless steel. The coating containing the CoCr alloy and WCNi is identified as SW and the coating containing the CoCr alloy in addition to WCNi and Cr.sub.3C.sub.2 is identified as SCW.

TABLE-US-00002 TABLE 2 Tested Coating Feed Powder Composition Powder mixture (vol %) Coating CoCr Alloy Cr.sub.3C.sub.2 WCNi SW Bal. 55 SCW Bal. 70 10 Range 1A 10.0-60.0 85.0 5.0-70.0 Range 1B 12.0-55.0 78.0 10.0-65.0 Range 1C 12.0-55.0 78.0 8.0-65.0 Range 2A 30.0-60.0 20.0 40.0-70.0 Range 2B 30.0-50.0 10.0 50.0-70.0 Range 2C 30.0-50.0 5.0 50.0-65.0 Range 3A 10.0-30.0 50.0-80.0 8.0-30.0 Range 3B 10.0-30.0 60.0-80.0 10.0-25.0 Range 4A 10.0-60.0 5.0-85.0 5.0-70.0 Range 4B 12.0-55.0 5.0-85.0 10.0-65.0

[0075] 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.

TABLE-US-00003 TABLE 3 HVOF spraying parameters Powder Oxygen Propylene Air flow Spraying Feed Rate Flow rate flow rate rate distance Parameter (g/min) (LPM) (LPM) (LPM) (mm) Value 23 304 79 422 150

[0076] The spraying was by using a Diamond Jet 2700 gun of Oerlikon Metco, Pfaeffikon, Switzerland.

[0077] Table 4 shows: deposition efficiency (DE); volume fraction of matrix, carbide, and porosity; and Vickers hardness. Retention of Cr.sub.3C.sub.2 in the coating is lower than WCNi, 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/(F.sub.NL) where V is the wear volume (mm.sup.3), F.sub.N is the applied load (N) and L represents the length (m).

TABLE-US-00004 TABLE 4 Hardness of as-Sprayed (pre-use and without Heat Treat) Coatings and Example Composition Ranges Percentage in Coating (vol %) Hardness (HV0.3) Coating DE (%) CoCr alloy Cr.sub.3C.sub.2 WCNi Porosity RT 300 C. SW 75 37 4 61 4 3 0.3 800 123 693 96 SCW 40 24 2 58 2 17 1 1 0.7 918 114 820 64 Range 1A NA 18.0-50.0 70.0 11.0-70.0 8.0 NA NA Range 1B NA 19.0-45.0 65.0 15.0-70.0 8.0 NA NA Range 2A NA 25.0-50.0 20.0 35.0-70.0 8.0 NA NA Range 2B NA 30.0-50.0 10.0 40.0-70.0 8.0 NA NA Range 3A NA 18.0-40.0 45.0-70.0 11.0-30.0 8.0 NA NA Range 3B NA 19.0-30.0 45.0-65.0 15.0-25.0 8.0 NA NA

TABLE-US-00005 TABLE 5 Wear Rate of as-Sprayed (pre-use and without Heat Treat) Coatings Average of Wear Average of Wear Temperature volume rate Coating ( C.) (10.sup.3 mm.sup.3) (10.sup.6 mm.sup.3/N .Math. m) Stellite 6 RT 34.96 2.86 69.93 5.7 CoCr alloy 300 86.64 6.99 173.27 14 SW RT 0.81 0.23 1.61 0.45 300 1.23 0.23 2.46 0.46 SCW RT 1.16 0.47 2.32 0.94 300 17.56 2.97 35.13 5.9

[0078] 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 (Al.sub.2O.sub.3) counterface with the three identified coatings on stainless steel substrates.

[0079] FIGS. 9-14 show the average value of the coefficient of friction plotted against the number of cycles at room temperature (25 C.) and 300 C. for the CoCr alloy, SW, and SCW coatings on the stainless steel. At room temperature, the SW and SCW coatings showed a lower coefficient of friction than the CoCr alloy. At 300 C., the SCW coating showed a coefficient of friction behavior and values similar to the reference Stellite 6 CoCr alloy coating, whereas the SW coating showed a higher coefficient of friction. This is because WC particles are harder, and more abrasive compared to chromium carbide (Cr.sub.3C.sub.2). Additionally, the thermal softening of the metallic binder (the CoCr alloy) can cause the WC particles to protrude and create more asperities on the coating surface, resulting in a higher CoF. Table 5 shows the wear rate and wear volume values at room temperature and 300 C. The SW and SCW had lower wear rates than the reference HVOF Stellite 6 alloy. This is because the carbides offer a load bearing capacity to the coating modifying the contact area and distribution of the stresses, in addition of being more resistant to abrasion compared to the metallic matrix (Stellite 6 alloy). The 300 C. wear rate and friction coefficient of SCW are higher than those of SW. However, SCW may have advantages at yet higher temperatures (e.g., in the range of 550 C. to 800 C.) due to higher temperature stability of chromium carbide relative to tungsten carbide. Relative to the '797 publication, the addition of WCNi is believed to increase the hardness of the resultant coating to improve abrasive wear resistance. Despite testing the present parameters only on steel, the parameters are believed to transfer to nickel-based superalloy substrates and cobalt-based superalloy substrates in applications such as described above and below.

[0080] As mentioned above, the two coatings were produced to achieve low wear rate values (WR<10.sup.6 mm.sup.3/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.

[0081] 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 CoCr.sub.3C.sub.2 composite coating by jet electrodeposition, Surface Engineering, December 2018, Vol. 34:11, pp. 861-869, Taylor & Francis Group, London, England.

[0082] 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.

[0083] FIG. 15 schematically illustrates a gas turbine engine 120. The example gas turbine engine 120 is a two-spool turbofan that generally includes a fan section 122, a compressor section 124, a combustor section 126, and a turbine section 128. The fan section 122 drives air along a bypass flow path B in a bypass duct defined within a housing 115, such as a fan case or nacelle. The fan section also initially drives air along a core flow path C for compression through the compressor section and communication into the combustor section 126 then expansion through the turbine section 128. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines.

[0084] 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.

[0085] 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.

[0086] 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

[0087] FIG. 15A shows one example seal in the engine as a piston seal 160. The example seal 160 (and its metallic substrate) has an inner diameter (ID) surface 161, an outer diameter (OD) surface 162, and axial end surfaces 164 and 165. The seal follows a constant cross-sectional shape and forms a split ring with a shiplap or similar joint (not shown).

[0088] 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.

[0089] 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.

[0090] 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 (FIG. 15B) is a bellows or similar type seal with convoluted cross-section effective to be deformed under compression to self-spring-bias engagement with the counterface members. The cross-section generally has a generally inner diameter (ID) surface 221, a generally outer diameter (OD) surface 222 generally parallel and spaced apart from the ID surface by a material thickness T.sub.S, and end surfaces 224 and 225. In an installed axially compressed state, axial ends 226, 227 of the seal are formed by portions of one of the surfaces 221, 222 (both 221 in the example). The illustrated seal is a W-seal although other configurations are possible (e.g., more or fewer cycles of the cross-sectional wave form) as are radial seals (e.g., an E-seal).

[0091] 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.

[0092] 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).

[0093] 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 FIG. 15C. The brush 402 has two protruding bristle sections 406, 407 (e.g., of a single cluster of bristles) engaging respective counterfaces (a case segment and a blade outer air seal segment). FIG. 15C shows the coating may be applied by the present methods to the counterface surface 408, 409 of the counterface substrate 410, 411 to engage the bristles.

[0094] Other examples involve locating pins. A typical locating pin 420 (FIG. 16) has, forming opposite axial end sections of the pin, a base section or shank 422 for press-fit or threading into a hole or socket 428 in a first component 426 and a head 424 for accommodation in a hole or socket 432 of a second component 430. A flange 434 (if present) may separate the base or shank from the head. The head will typically have a tapered portion for guidance into the receiving socket 432. With a press-fit pin, the OD surface of the press-in base or shank may be coated by the present methods. Additionally, the head and flange faces may be coated. With a threaded pin, it is more likely that only the flange and head may be coated and not the threaded shank.

[0095] FIG. 20 shows an alternate locating pin joint having a locating pin 500. FIG. 20 shows the joint and pin as having a common axis 501. Forming a first/proximal end of the pin in this example is a head or terminal flange 502. A shaft generally extends from an underside of the head to a distal end 504. A proximal portion 506 of the shaft mounts to a first component 508. An example first component is an engine case. An example mounting is via press-fit or threading into a boss of the case either directly or to an insert in the boss. In this example, the shaft exterior surface 512 along a proximal portion 510 of the shaft is so externally threaded to mate with an internal thread of the case boss or insert.

[0096] 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.

[0097] Another snap example is a separate snap fastener 440 (FIG. 17) (e.g., holding two (or more) generally flat sections (pieces) of material 442 and 444 against each other as if a rivet). In one example, the fastener has a head 446 with an underside 448 against the outer face 443 of one terminal piece 442 of the stack of mated pieces. A shaft or shank 450 extends from the underside to a tip/end 452. Adjacent the tip, the shaft has a barbed backlocking surface 454 (underside) facing the head and backlocked against the outer face 445 of the opposite terminal piece 444 in a sandwich of two or more pieces. Example fasteners have longitudinally split areas near the tip allowing insertion through holes in the pieces with the insertion compressing the slot 456 to allow passage of the barbs 458 and then relaxing once the barbs pass out of engagement with the members so as to back lock surfaces 454 to 445. Due to the relatively higher engagement pressures along the barb undersides 454 versus the head underside, the barb underside region and transition to shank main body 456 is a particular area for coating. With the snap fastener, the shaft/shank main body may also be coated by the present methods to limit wear of the holes in the mated components.

[0098] Among additional locations for the coating are in snap fit interfaces 460 (FIG. 15D) (e.g., either fully backlocked or detented). One example of a snap fit between two components involving a bead and groove interaction for mounting a swirler is shown in U.S. Pat. No. 10,101,031B2 (the '031 patent), of Williams et al., Oct. 16, 2018, and entitled Swirler Mount Interface for Gas Turbine Engine Combustor, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. The '031 patent discloses an OD (relative to swirler/injector axis 470) projection or bead 464 on a swirler 462 captured in an ID groove 468 in a bulkhead support shell 466. The coating may be applied by the present methods to one or both of the inner member (e.g., swirler) and outer member (e.g., bulkhead support shell) at the bead or groove and adjacent contacting OD and ID surface regions respectively. Often, case of spraying may make it easiest to just apply to the OD surface of the inner member. But, with a large diameter and relatively small axial extent, it may be easy to also have normal spray access to the bulkhead ID surface to coat both pieces.

[0099] Additional examples involve tabs 481 (FIGS. 18&19) of a first component 480 in slots 483 in a second component 482 For example, in many annular mounting situations, tabs may protrude radially (inward or outward depending on the situation) and be received in associated slots. Example such tabs have first and second axial end faces 484, 485 facing or contacting slot end faces 486 and 487 and tab circumferential end faces (ends) 488, 489 contacting or facing slot circumferential end faces (ends) 490, 491. Typically, pressure or spring loading will bias one axially facing face 484 of the tab against the adjacent axially facing face 486 of the slot. Particularly that axial end face of the tab may be coated via the present methods. But also, circumferential end faces will typically provide some locating function and may also be coated. Spray access makes it easier to coat the tab faces (with a normal angle of incidence than coating slot faces (where the angle will be more off normal).

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.