Laser texturing of piston seal grooves

Abstract

A machine (800) has a shaft (98) having: a metallic substrate with an outer diameter surface (101) having a groove (100); a seal ring (20); and a counterface (110) to the seal ring. A coating (310) is on the shaft substrate and at least partially along at least one of the groove first (302) and second (304) axial end faces and base surface (106). The coating is atop a textured surface portion of the substrate. The seal ring is accommodated in the groove and has a seal ring substrate softer than the coating.

Description

LASER TEXTURING OF PISTON SEAL GROOVESCROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of U.S. Patent Application No. 63749360, filed January 24, 2025, and entitled “Laser Texturing of Piston Seal Grooves”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.BACKGROUND

[0002] The disclosure relates to gas turbine engines. More particularly, the disclosure relates to piston seal rings (PSR).

[0003] Gas turbine engines (used in propulsion and power applications and broadly inclusive of turbojets, turboprops, turbofans, turboshafts, industrial gas turbines, and the like) use PSR in several situations.

[0004] A PSR seals between an inner member and an outer member. The inner member and outer member may be static structure such as case components. Or, the inner member and the outer member may be rotating structure such as components of a spool or rotor. The inner member and the outer member may be subject to small excursions relative to each other. For example, torque loads may cause small rotational movements; thrust loads or differential thermal expansion may cause small axial movements. Vibration may also cause small rotational, radial, or axial movements. Such small or transient rotational movements, however, are distinguished from continuous relative rotational movement such as in face seal or shaft seal between two relatively rotating components (e.g., two different spools or a spool and a static structure).

[0005] The PSR is accommodated in an outer diameter groove in the inner member. Under dynamic and / or pressure loading, the PSR seals against a sidewall of the groove and an inner diameter surface of the outer member. In one example of such a situation involving a rotor, the inner member is a shaft and the outer member is a rotor stack of the associated spool. In a more particular example, the outer member is a seal runner protruding axially from a protuberant bore of a disk of the rotor stack. Tension in the shaft holds the rotor stack in precompression. Small rotational, axial, and / or radial displacements of the shaft and seal runner may be caused by factors including transients and changes in operational conditions such as torque and thrust loads (which will vary between one steady state condition and another steady state condition). In such an example, the PSR is accommodated in an outer diameter (OD) groove in the shaft.

[0006] PSRs are often small in cross section so as to be relatively compliant compared to the contacting structure (e.g., members forming the groove and runner). The ring is split for assembly purposes and / or to allow radial expansion under centrifugal loading. The ring circumferential ends may form an overlapping joint (e.g., a shiplap joint). The small cross section and split provide the ring with little hoop strength and twist resistance. For example, with a nickel alloy shaft and nickel alloy runner, ring material may be nickel or cobalt alloy and may have generally similar material hardness (at least of a substrate if coated). Example coatings are two-layer systems (at least along the OD surface of the PSR substrate). A base layer is metallic (e.g., copper- aluminum (CuAl)) applied by plasma spray). A second layer is a solid lubricant layer (e.g., MoS2 or graphite). An example metallic layer and sprayed or brushed solid lubricant layer extend onto the substrate axial end surfaces.

[0007] One group of examples of PSR substrates involves cobalt-basedchromium-tungsten alloys. An example alloy is AMS5894 / Cobalt Alloy 6B / UNS R30016. The PSR substrate may have a coating as discussed above.

[0008] In an example manufacture process, the substrate may be formed from forged rod stock. Ring precursors are cut / machined from the rod (e.g., on a cutting lathe or the like) to an annulus with the PSR nominal cross-sectional shape. The resulting precursor may be grit blasted, particularly on the outer diameter (OD) surface to clean and roughen in preparation for coating application. Then, the annulus may be cut (e.g., by CNC mill, wire EDM, water jet or other tool) to form a shiplap or similar joint (to allow PSR expansion / contraction). Then, the coating, if any, may be applied as discussed above.

[0009] In other known processes for other articles, laser cleaning of an article is performed prior to coating application. This removes oil and other organics. An air flow serves to cool and evacuate volatilized contaminants. One particular example is cleaning an MCrAlY bondcoat prior to ceramic thermal barrier coating application. An example of this is found in US Patent Application Publication 2022 / 0298645A1, Thayer et al., published September 22, 2022, and entitled “Laser Induced, Fine Grained, Gamma Phase Surface for NiCoCrAlY Coating Prior to Ceramic Coat”.

[0010] Smolina et al. describe laser remelt and laser clad coatings for Stellite® 6 Co-Cr alloy of Kennametal Inc., Latrobe PA. Smolina, Irina & Kobiela, Karol, “Characterization of Wear and Corrosion Resistance of Stellite 6 Laser Surfaced Alloyed (LSA) with Rhenium”, Coatings, 3 March 2021, Vol. 11 (292), MDPI, Basel, Switzerland. There are several related Stellite® family alloys. One such alloy is generically known as Cobalt Alloy 6b (wrought specification AMS 5894 - UNS R30016). Wrought microstructure is characterized by evenlydistributed isolated (rather than interconnected) carbides. Interconnected carbides of cast microstrucure contributes to brittleness. Wrought microstructure generally offers enhanced strength and wear resistance.

[0011] Separately, laser-texturing was explored in the manufacture of stainless steel / PDA / PTFE systems in Soltani-Kordshuli et al., “Laser surface texturing of both thin polytetrafluoroethylene coatings and stainless steel substrates for improving tribological properties”, Polymer Testing, January 1, 2023, Volume 117, 107852, Elsevier Science S.A., Lausanne, Switzerland. Therein, the basic system involved a stainless steel substate, PDA (polydopamine) adhesive underlayer, and PTFE (polytetrafluoroethylene) coating layer. Laser treatment was explored for the substrate and PTFE layer.SUMMARY

[0012] One aspect of the disclosure involves a machine comprising a shaft, a seal ring and a counterface to the seal ring. The shaft has: an outer diameter surface having a shaft groove having first and second axial end faces and a base surface therebetween; a metallic substrate having a shaft groove having first and second axial end faces and a base surface therebetween; and a coating on the metallic substrate and at least partially along at least one of the shaft groove first and second axial end faces and base surface, the coating atop a textured surface portion of the substrate. The seal ring is accommodated in the shaft groove and has a seal ring substrate softer than the coating.

[0013] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the textured surface portion has texturing characterized by a pattern of depth of at least 0.010 millimeter.

[0014] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the pattern comprises: a first plurality of grooves; and a second plurality of grooves intersecting the first plurality of grooves.

[0015] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the coating is at least 50% by weight one or a combination of: chromium oxide; Co-based alloys; Al-Co alloys; Ni-Al alloys, Ni-Cr alloys, NiCrAl alloys and WC-Co.

[0016] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the coating is harder than the seal ring substrate.

[0017] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate has Co as a largest by-weight constituent element and at least 18.0 weight percent Cr.

[0018] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate is a split ring substrate having: an inner diameter surface; and an outer diameter surface. The seal ring has a coating having at least a first layer atop the outer diameter surface, and the outer diameter surface has texturing characterized by: a pattern of depth of at least 0.010 millimeter.

[0019] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate has Cr as a second largest by-weight constituent element.

[0020] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate has no more than 20.0 weight percent any element other than Co, Cr, and Ni.

[0021] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate has no more than 20.0 weight percent any element other than Co and Cr.

[0022] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate comprises by weight percent: <2.0 C; <2.5 Mn; <2.5 Si; <0.1 P; <0.1 S; 18.0-35.0Cr; <30.0 Ni; <8.0 max Mo; <16.0 W; <4.0 Fe; and balance Co and no more than 7.0 each other element, if any, individually and 15.0 all other elements total.

[0023] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the substrate comprises by weight percent: 0.90-1.90 C; 0.50-2.00 Mn; 0.20-2.00 Si; 0.04 max P; 0.03 max S; 28.00-32.00 Cr; 3.00 max Ni; 1.50 max Mo; 3.50-5.50 W; 3.0 max Fe; and balance Co and no more than 1.0 each other element, if any, individually and 5.0 all other elements total.

[0024] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the seal ring substrate comprises by weight percent: 0.90-1.40 C; 0.50-2.00 Mn; 0.20-2.00 Si; 0.04 max P; 0.03 max S; 28.00-32.00 Cr; 3.00 max Ni; 1.50 max Mo; 3.50-5.50 W; 3.0 max Fe; and balance Co and no more than 1.0 each other element, if any, individually and 5.0 all other elements total.

[0025] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the machine is a turbine engine wherein the shaft is a tie shaft of a spool; and the counterface is on a disk bore of the spool.

[0026] In a further embodiment of any of the foregoing embodiments, a method for manufacturing the machine comprises: laser treating the shaft substrate to form the textured surface portion; applying the coating; and installing the seal ring.

[0027] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the laser treating is in a nitrogen- or argon-enriched atmosphere.

[0028] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the applying is by thermal spray.

[0029] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, a method for remanufacturing the machine comprises: removing the seal ring; partially removing the coating; restoring removed coating by thermal spray; and installing a replacement seal ring.

[0030] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the partially removing the coating does not reach the textured surface. One aspect of the disclosure involves a machine comprising a shaft, a seal ring and a counterface to the seal ring. The shaft has: an outer diameter surface having a shaft groove having first and second axial end faces and a base surface therebetween; a metallic substrate having a shaft groove having first and second axial end faces and a base surface therebetween; and a coating on the metallic substrate and at least partially along at least one of the shaft groove first and second axial end faces and base surface. The seal ring is accommodated in the shaft groove. The machine has means for preferentially wearing the seal ring relative to the shaft.

[0031] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the means comprises laser texturing of the shaft substrate and, optionally, the coating being harder than the seal ring substrate.

[0032] Another aspect of the disclosure involves a method for manufacturing a coated machine shaft. The method comprises: laser texturing at least one surface of a groove in a substrate of the shaft to form a textured surface; and applying a coating to at least a portion of the textured surface.

[0033] A further embodiment of any of the foregoing embodiments may additionally and / or alternatively include installing a seal ring to the groove after the coating.

[0034] The various features of the aspects and embodiments identified above and as further described below may be combined in any physically possible combination to create further examples and embodiments.

[0035] 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.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a view of a piston seal ring (PSR).

[0037] FIG. 1 A is a view of joint of the PSR.

[0038] FIG. 2 is a view of a gas turbine engine containing the PSR.

[0039] FIG. 2A is an enlarged view of a rotor region of the gas turbine engine showing sealing engagement by the PSR.

[0040] FIG. 2B is an enlarged view of an OD coating on the PSR.

[0041] FIG. 2C is an enlarged view of a joint coating on the PSR.

[0042] FIG. 2D is an enlarged view of a coating on a groove surface of a shaft substrate facing or contacting the PSR.

[0043] FIG. 3 is a plan view of texturing of a substrate of the PSR.

[0044] FIG. 4 is a plan view of texturing of a metallic coating layer of the PSR.

[0045] FIG. 5 is a plan view of texturing of a substrate of the shaft at the groove surface.

[0046] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0047] Some examples discussed below reflect modification of a baseline seal having, along the OD surface of the CoCr alloy (e.g., Stellite® 6B) substrate and a sacrificial metallic coating (e.g., a plasma sprayed CuAl alloy). The modified coating has a metallic base layer and a solid lubricant outer layer. In a departure from the baseline, laser texturing is performed on the substrate and / or the base layer in lieu of grit blasting. Also or alternatively, some examples reflect modification of a baseline shaft groove having a nickel-alloy substrate, The baseline shaft substrate may be smooth and uncoated at the shaft groove that accommodates the seal. The modification involves texturing the substrate and coating the textured surface with a hard coating.

[0048] Regarding seal modification, the baseline grit blasting may have a number of disadvantages. Grit blasting has been observed to produce fractured carbides with refined and detached grain. These carbides become trapped near the interface of the substrate and the plasma sprayed CuAl coating. The existence of the cracked carbides with low load-carrying capacity can pose a potential risk of accelerated wear when they are liberated onto the contact point with a mating component and act as third-body abrasives. A Cu90A110 APS coating with 90% copper and 10% aluminum composition is a sacrificial coating with limited wear life. Therefore, the CuAl APS coating does not prevent liberation of such carbides which will accelerate wear when interfaced with a counterface.

[0049] Another problem with grit blasting is that, depending on the type and intensity of the abrasive material, the grit blasting process can potentially damage the substrate by leaving scratches, pitting, or roughness on the treated surface. Also, achieving uniform and even surface can be challenging with grit blasting. The blasting process can result in an uneven surface, leading to a nonuniform surface profile and non-uniform residual stress regime which in turn can negatively impact the adhesion and performance of the coating or treatment. Grit blasting can be an aggressive process, and achieving a precise or intricate surface is a major challenge. Grit blasting can be an expensive surface preparation method due to the equipment, abrasive materials, and labor. Moreover, the abrasive material might need to be replaced frequently which can add up to the overall cost.

[0050] In a specific area of modified manufacture process relative to the baseline PSR manufacture process, a laser texturing of the substrate outer diameter (OD) surface is in addition to a laser cleaning or another cleaning that may replace a laser cleaning. The laser texturing may replace a grit blasting process. The laser texturing yields an outer diameter (OD) layer or zone having regular or random pattern of high and low regions. The particularfirst example laser texturing engraves first and second groups of grooves leaving cells of relatively intact surface between adjacent pairs of grooves of the two groups. The example two groups are thus off-parallel to each other so as to intersect. However, the within each group, the grooves may be essentially parallel. For example, with a longitudinal first group and a circumferential second group, all grooves of each group are exactly parallel to each other. With such a situation, the cells are rectangular. However, if the grooves have both a longitudinal component and a circumferential component they may be essentially parallel in that each group has a single helix angle so that adjacent grooves are practically parallel whereas a segment of a groove at one circumferential location will be at an angle to a diametrically opposite groove segment of the same group. With such a situation, the cells may be rhomboidal or other quadrilateral. Alternatively to the cells being such islands, the cells may be recesses such as the dimples on a golf ball created by pulsing the laser.

[0051] Additionally, alternative patterns with regular cell shapes or irregular cell shapes are possible. These patterns may include, for example, any appropriate polygonal tiling pattern. A further example is a uniform tiling of essentially equilateral hexagons. More complex and irregular patterns may include irregular and non-equilateral and / or concave polygons and mixtures of shapes. Patterns may be formed by intersecting sets (orthogonal or otherwise transverse) of zig-zag lines (instead of intersecting sets of essentially straight lines) or intersecting sets of waveforms (e.g., sine waves). Other patterns include nature-inspired patterns such as snakeskin patterns, lotus leaf patterns, and the like.

[0052] FIG. 1 shows a piston seal ring (PSR) formed as a split ring seal 20 having a first circumferential end 24, a second circumferential end 26, an inner diameter (ID) surface 28, an outer diameter (OD) surface 30, a first axial end face 32, and a second axial end face 34. The PSR has a nominal central longitudinal axis (centerline) 500 shared with the members it seals when in a nominally centered condition. FIG. 1A shows the ID surface 28 as having a straight (circular cylindrical) central portion 35 and more frustoconical transitions 36 and 38 to the axial end faces 32 and 34, respectively. In the example, there are more radiused transitions at the extremes of the transitions 36 and 38 than centrally within those transitions. Viewed in section, junctions between the axial end faces and ID and OD surfaces are shown as radiused comers. However, other junctions are possible.

[0053] In the example, first circumferential end 24 and second circumferential end 26 form a joint or junction 40 (FIG. 1A). The example joint 40 is a shiplap joint with a projecting portion 42 of the first circumferential end received in a rebate 48 of the second circumferential end and a projecting portion 44 of the second circumferential end received ina rebate 46 in the first circumferential end. The example projecting portions have mating faces / surfaces 50, 52 which, in the example, closely face or contact along a transverse radial centerplane 502 (FIG. 2A) of the PSR.

[0054] The PSR comprises a single piece alloy substrate 200 (FIG. 2B) with one or more coating layers 202, 204 along portions of its exterior surface (and thus forming associated portions of the exterior surface of the PSR). In this example, the coating is shown as a single metallic first layer 202 (e.g., a CuAl alloy or a CrCo alloy) on the OD surface 30' of the substrate and a single solid lubricant second layer 204 (e.g., molybdenum disulfide or graphite) atop the OD surface 30" of the first layer. Thus, the coating second layer 204 outer surface locally forms the OD surface 30 of the PSR to provide lubricious engagement with the runner ID surface 110. Similarly, the coating layers 202 and 204 (or just the second layer 204) may extend along the axial end surfaces to provide lubricious engagement with groove walls 102 and 104. Example CuAl is Cu90A110. Example CrCo is Cr85Col5. Example solid lubricant layers 204 may mixtures containing at least 50% combined at least one of molybdenum disulfide and graphite. In addition to the at least one of molybdenum disulfide and graphite, mixtures may include one or more metal oxides (e.g., cobalt oxide) and / or other lubricants.

[0055] FIGs. 2B and 3 show a first texturing pattern 248 of grooves 250A (axial / longitudinal) and 250B (circumferential) in the substrate and island cells 252 therebetween. Example height of the cells (or depth of the grooves) is shown as Hi. Example on-center spacing of the grooves is shown as SAI and SBI, respectively. Example groove width is shown as WGAI and WGBI, respectively. The first texturing pattern 248 produces a complementary texturing 254 on the underside of the first layer 202.

[0056] Additionally, the first layer 202 outer surface has a second texturing pattern 258 of grooves 260A (axial / longitudinal) and 260B (circumferential) in the substrate and island cells 262 therebetween. Example height of the cells (or depth of the grooves) is shown as H2. Example on-center spacing (FIG. 4) of the grooves is shown as SA2 and SB2, respectively. Example groove width is shown as WGA2 and WGB2, respectively. The second texturing pattern 258 produces a complementary texturing 264 on the underside of the second layer 204.

[0057] As is discussed below, upon initial application of the first layer the first texturing pattern 248 may print / transfer through to the first layer outer surface at least partially.Depending on technique, this printed-through pattern may be somewhat smoother relative to the first texturing pattern 248. Additionally, cleaning, polishing, or other preparation of thefirst layer to receive the second layer may further diminish artifacts of the first texturing pattern 248. The second laser texturing to produce the second texturing pattern 258 may further obscure or obliterate these artifacts. However, some of these artifacts may yet be discernible within the texturing pattern 258.

[0058] Overall coating thickness is shown as T and individual layer thicknesses are shown as Ti and T2. These may be measured as thickness centrally in cells and as an average among cells.

[0059] Example thickness Ti is 25 micrometers to 130 micrometers, more broadly 15 micrometers to 200 micrometers or 15.0 micrometers to 250 micrometers. Example thickness T2 is 8.0 micrometers to 18.0 micrometers, more broadly 5.0 micrometers to 30.0 micrometers or 5.0 micrometers to 40.0 micrometers.

[0060] The coating with its relevant composition noted above may thus exist on the entirety or at least a majority (at least 50%) of the OD surface of the substrate or of the OD and axial end surfaces. And in this or other applications such layer / zone may be on at least an example 10% of total surface area. An example ratio of Ti to T2 is about 6:1, more broadly, about 3:1 to 10:1 or 1.4:1 to 17:1.

[0061] Example spacings SAI and SBI or SA2 and SB2 in both directions for a given texturing 248 or 258 are the same. Also, example spacings for the two texturings are the same.Example spacings are 10.0 micrometers to 20.0 micrometers, more broadly, 6.0 micrometers to 30.0 micrometers.

[0062] Example groove depths Hi or H2 in both directions for a given texturing 248 or 258 are the same. However, example groove depths for the two texturings differ generally in association with differences in the thicknesses of the associated coating layers 202 or 204. Example depths Hi are 20.0 micrometers to 35.0 micrometers, more broadly, 10.0 micrometers to 50.0 micrometers. Example depths H2 are 4.0 micrometers to 10.0 micrometers, more broadly, 1.0 micrometers to 30.0 micrometers.

[0063] Example groove widths WGAI and WGBI or WGA and WGB2 in both directions for a given texturing 248 or 258 are the same. However, example groove widths for the two texturings differ generally in association with differences in the thicknesses of the associated coating layers 202 or 204. Example widths WGAI and WGBI are 3.0 micrometers to 10.0 micrometers, more broadly, 2.0 micrometers to 20.0 micrometers. Example widths WGA2 and WGB2 are 1.0 micrometers to 3.0 micrometers, more broadly, 1.0 micrometer to 20.0 micrometers.

[0064] With example spacings of 6.0 micrometers in each direction and example groove widths of 3.0 micrometers, ignoring curvature the cell area is 9.0 square micrometers of ungrooved material. With spacings of 30.0 micrometers in each direction and groove widths of 1.0 micrometers, the corresponding cell area is 841 square micrometers. Accordingly, there can be a broad range of cell sizes. A broad range may thus be dictated by the extremes of spacings and widths given above with narrower ranges such as 10.0 square micrometers to 800 square micrometers or 20 square micrometers to 600 square micrometers or 30 square micrometers to 500 square micrometers.

[0065] Where the surface is grooved, an example fraction of surface area occupied by the grooves is 68% using example spacings of 15 micrometers and example groove widths of 6.5 micrometers. This may represent a flat plane simplification for corresponding measurements along the ungrooved / original surface of the OD surface (of substrate or first coating layer) or other relevant curved surface. Similarly, using the same spacing but a groove width of 2.0 micrometers, the grooves would occupy 25% of the relevant surface. More broadly, example grooves may represent 10% to 95% or 20% to 80% of the relevant area (e.g. the OD surface discussed above or other regions discussed below).

[0066] In some embodiments, such area may be measured based upon the full groove width. In others, it may be measured as an area of the portions of the grooves that meet or exceed a given depth such as the depths Hi and H2 discussed above (or the lower ends of ranges or fall within ranges).

[0067] Alternative characterizations of groove extent may involve the linear amount of grooves (e.g., meeting the threshold depths as discussed above) per area of the relevant portion of the surface. As with the area ratios, example density ranges of the linear extent relative to area may be those corresponding to the ranges of groove spacings identified. For example, with spacings of 10.0 micrometers in the square grid of grooves, there would be in a 1. Oxl.O millimeter square one hundred grooves in each direction. Thus, there would be two hundred grooves in that 1. Ox 1.0 millimeter square. Each of these grooves would be 1.0 millimeter long, for a density of two hundred linear millimeters of groove per square millimeter of surface.

[0068] As noted above, the relevant area for some embodiments may be substantially the entire OD face. Or it may be an example of at least 50% of the OD face. Or it may be at least 50% of the other relevant surface such as the joint surfaces discussed below.

[0069] In a further variation, the texturing may be internal to the shiplap joint. The texturing may be at least along the faces / surfaces 50, 52 but also, optionally, along the distal ends 54,56 of the projecting portions 42, 44 and / or along the bases 58, 60 of the rebates 46, 48. The coating layers along these surfaces may be the same as noted for the OD surface or may differ. One example of a difference is that if both faces / surfaces 50, 52 are coated there is a like-on-like interaction and the coating may be optimized for that relative to the hypothetical interaction of OD coating with an uncoated ID surface of a counterface. FIG. 2C shows an example where both mating faces have the same two layers and texturings as the OD so that there, at least initially is solid lubricant to solid lubricant contact.

[0070] In yet a further variation, only one of the faces / surfaces 50, 52 may have such coating(s) and texturing(s). In yet a further possible variation, only the joint may have such texturing(s) such as in a situation where the OD is conventionally coated. In such hypothetical joint coatings, the grooves may be near parallel such as concentric circumferential grooves intersecting with radial grooves. The radial grooves thus have slight angular departure one to the other.

[0071] FIG. 2A shows the PSR 20 seated in an outer diameter groove 100 in an inner member (e.g., shaft or shaft section) 98 and sealing against an ID surface 110 of an outer member 112 (e.g., a seal runner). The groove 100 has a first sidewall or end wall 102, a second sidewall or end wall 104, and a base 106 joining the two. The groove has a transverse centerplane 503 which may be coincident with the PSR centerplane 502 when the PSR is centered in the groove. In the example gas turbine engine, the first sidewall is an aft sidewall and the second sidewall is a forward sidewall. Example junctions between the sidewalls and the base are shown as quarter-rounds, chamfers, or bevels 108. However, right angle junctions or other transitions are possible. The groove 100 extends radially inward from an outer diameter (OD) surface section or portion 101 of the inner member.

[0072] FIG. 2A shows the PSR in a gas turbine engine rotor 150 including the shaft section 98. Such a situation is discussed as background above. The example rotor is the high pressure compressor (HPC) portion of a high pressure spool of a two-spool engine. The rotor includes a stack of blade disks 152. Each blade disk includes a protuberant inner diameter (ID) bore 154 having an ID surface 156. A radial web 158 extends outward from the bore to a rim structure 160. A circumferential array of blades 162 (shown with airfoil tips cut away) may be mounted to the rim (e.g., via fir tree or dovetail mounting). Or, blade airfoils may be unitarily formed with the rim and the rest of the disk (e.g., an integrally bladed rotor (IBR)).

[0073] The example PSR seals between the rotor shaft section 98 and one of the disk bores 154 as they rotate as a unit. The PSR accommodates small excursions between the two members it seals due to dynamic or static loading, thermal effects, and the like. The exampleseal runner 112 is unitarily formed with the particular disk bore and protrudes axially from the disk bore near the ID surface thereof to a free distal end / rim of the seal runner. This is one non-limiting example of one baseline.

[0074] The example PSR has a relaxed condition wherein the circumferential ends 24 and 26 are not completely nested / bottomed against each other (there is a slight circumferential gap 124 (FIG. 1A). When assembled over the shaft and seated in the groove, there may be a small ID gap 120 FIG. 2A). However, the PSR OD surface 30 may be close to flush and even potentially sub-flush to the adjacent shaft OD surface 101. Thus, when the seal runner is assembled over the shaft and PSR, there is an at least local OD radial gap between the PSR OD surface 30 and the seal runner ID surface 110. However, when the shaft rotates, centrifugal action will radially expand the PSR, closing the OD gap and expanding the ID gap 120 (or creating the ID gap) and expanding the circumferential gap 124. This centrifugal action biases the PSR OD surface 30 into sealing engagement with the ID surface 110 of the seal runner.

[0075] One difference among various Stellite® family alloys is the carbon content that impacts the carbide volume fraction. With about 1 wt.% carbon in Stellite® 6B, the carbides constitute approximately 13 wt% of the material. Additionally, the carbides are predominantly primary carbides. Primary carbides are large in size and of the formulas: MC (where M = W, Ta, Nb, Zr, and / or Ti); or M7C3 (where M = Cr, W, and / or Mo). Secondary carbides are small in size and of the formulas: M23C6 (where M = Cr and / or Mo); or M6C (where M = Mo and / or W).

[0076] Stellite® 6B is capable of operating well (e.g., low wear) at a wide range of temperatures. It has carbide strengthening at low temperature to provide wear resistance and oxide glaze layer formation at elevated temperature to provide act as a friction mitigator to limit wear.

[0077] Other Sellite® grades are more suitable either for high temperatures or for low temperatures, but not both.

[0078] Stellite® 6B has higher hardness compared to solid solution Stellite® alloy grades (e.g., Stellite® 21) providing sufficient wear resistance and lower hardness compared to the carbide -rich grades (e.g., Stellite® 12, 1, 20, 100) limiting the wear on the counterface). Most other Stellite® grades are typically cast. Wrought Stellite® 6B may be advantageous in terms of manufacturability and / or lower brittleness compared to cast Stellite® grades.

[0079] As noted above, example Stellite® 6B total carbide content is about 13 wt.%. More broadly for a range of candidate alloys, example total carbides are about 10% to 16% byweight, more broadly 10% to 20% by weight. Lower carbide content may decrease wear resistance. Higher carbide content may increase wear on the counterface.

[0080] Table I below gives candidate substrate alloys (examples as nominal values and specifications and additional ranges) including specific Stellite® family examples and others.Table ISubstrate Alloys (weight percentages)< < < < < < < < << < < < < < < < << < < < < < < < < < < < < < < < << < < < < < <t < 15.0 Other total; < 7.0 other individuallyft < 5.0 Other total; < 1.0 other individuallyttt < 2.0 Other total; < 0.50 other individually

[0081] Generally, these example alloys are all cobalt-based with cobalt as the largest by-weight constituent element. These alloys all then have chromium as the second largest by-weight constituent element. The three “other” ranges marked with one or more daggersmay be substituted for each other in the table and added to the examples to create other ranges. Or impurities may be as discussed below.

[0082] In general, for high temperature cobalt-based alloys, chromium is known to add oxidation and sulfidation resistance and to serve as a carbide former for M7C3 and M23C6 carbides. Molybdenum and tungsten are known solid solution strengtheners and carbide formers for M6C and for forming Co3M intermetallic s. Nickel is known to stabilize fee matrix and for forming Ni3Ti intermetallic to facilitate working. Carbon provides for formation of carbides (MC, M7C3, M6C, M23C6). Yttrium and lanthanum provide oxidation resistance.

[0083] Tantalum and niobium are also known solid solution strengtheners and carbide formers for MC and M6C and for forming Co3M intermetallic s. Aluminum is known for oxidation resistance and CoAl intermetallic s. Titanium is known as a carbide former for MC and for forming Co3Ti (and Ni3Ti with sufficient Ni). Boron and zirconium increase stressrupture strength.

[0084] Thus, there may be intentional levels of various such additions. Any of the examples or ranges above may optionally include impurity levels (e.g., commercial impurities or inevitable impurities) of any element not listed of for which a specific value is not given.

[0085] FIG. 2A shows the sealing between a first region or volume 600 and a second region or volume 602. In an example dynamic operating condition, the first region is a high pressure region and the second region is a low pressure region.

[0086] Regarding the shaft groove modifications noted above, FIG. 2D shows the shaft comprising a substrate 300 and a hard coating 310 along one or more of the three faces of the shaft groove (fore, aft, and ID / base). Example shaft substrate is nickel alloy / superalloy (e.g. IN 718). Example hard coatings include chromium oxide wear resistant coatings (e.g., essentially pure C Oa such as 99.0 weight percent or greater or a deliberate blend with an example 80.0 or 90.0 plus C Oa such as 4.5 SiO2-2.5 TiO2-bal Cr20a), or Co alloy (e.g., Co base 25Cr-10Ni-7.5W or Co base 23Cr-13Al-0.65Y or Co-Al / Al-Co), or Ni alloy coatings (e.g., Ni-Cr alloy (e.g., 80Ni-20Cr), or Ni-Al alloy (e.g., 80Ni20Al orNi5Al), or NiCrAl alloy (e.g., Ni40Cr3Al, or Nil8.5Cr6Al, or Ni22CrlOAl)), or WC-Co. FIG. 2D schematically shows a substrate surface 302 / 304 / 306 respectively along the aft groove surface, fore groove surface and base / ID surface. The exposed coating 310 surface thus includes associated portions 312 / 314 / 316.

[0087] For adhesion of the coating, the corresponding substrate surface is roughened.Example roughening is by laser texturing. Example laser texturing forms a regular or irregular positive or negative cellular pattern. The FIG. 5 example is a rectangular groove array similar to that of FIG. 3. Thus, the shaft has a third texturing pattern 318 of grooves 320A and 320B in the shaft substrate and island cells 322 therebetween. Example height of the cells (or depth of the grooves) is shown as H3. Example on-center spacing (FIG. 5) of the grooves is shown as SA3 and SB3, respectively. Example groove width is shown as WGA3 and WGB3, respectively. The third texturing pattern 318 produces a complementary texturing 324 on the underside of the coating 310.

[0088] Example spacings SA3 and SB3 in both directions are the same. Example spacings are 10.0 micrometers to 20.0 micrometers, more broadly, 6.0 micrometers to 30.0 micrometers.

[0089] Example groove depths H3 in both directions are the same. Example depths H3 are 20.0 micrometers to 35.0 micrometers, more broadly, 10.0 micrometers to 50.0 micrometers.

[0090] Example groove widths WGA3and WGB3 in both directions are the same. Example widths WGA3 and WGB3 are 3.0 micrometers to 10.0 micrometers, more broadly, 2.0 micrometers to 20.0 micrometers.

[0091] The hard coating 310 may be applied essentially directly after the laser texturing (e.g., without any intervening polishing, etching, or the like). Example coating thickness T3 is 7.5 micrometers to 510 micrometers, more particularly 50 micrometers to 300 micrometers. This may be measured from the untextured / intact surface or substrate peaks.

[0092] Example hard coating is harder than at least the PSR substrate. For example, the Stellite® 6 seal substrate has a HRC hardness of about 33 to 43; whereas, a cobalt alloy coating 310 has a hardness of about 65 HRC. Example IN-718 shaft substrate hardness is at least 35 HRC. Example PSR substrate hardness is 33-43 HRC. Thus, example coating hardness is at least 50 HRC or at least 60 HRC.

[0093] Relative to the shaft substrate 300 material, the coating need not necessarily be harder. The coating may be selected for sprayability properties to facilitate subsequent restoration. For example, in operation, the hardness of the coating may cause preferential wear of the PSR axial end faces and ID surface. At a service internal (or otherwise) the PSR will be replaced with a new PSR. At such service interval, the hard coating thickness will have been partially worn down. Based upon expected wear rate of the hard coating, at every such PSR replacement interval or at select PSR replacement intervals, the wear coating may be restored.

[0094] An example restoration involves a cleaning and preparation process such as chemical degreasing, sand blasting or other abrasive process, chemical etching or other chemical process, and / or an air or gas purge / cleaning. After the cleaning and preparation, application may be by thermal spray. The substrate areas adjacent the area(s) to be coated may be masked.

[0095] An example post-spray processing includes abrasive blast so as to modify surface roughness. Advantageously, the intervals and processing parameters are selected so that each refurbishment of the groove hard coating does not disturb shaft substrate.

[0096] FIG. 5 shows a square grid patterning of grooves leaving undisturbed lands therebetween. Thus, such grooves and lands have components that face both radially and circumferentially for the shaft groove sidewalls or axially and circumferentially for the shaft groove base. An alternative variation may be radial lines intersecting circumferential lines for the shaft groove sidewalls. Other more complex patterns may increase surface area exposure and may be regular or random / irregular patterns. Alternative patterns involve arrays of negative cells such as dimples. This is distinguished from the intersecting grooves in that it reverses the nature of the isolated versus the interconnecting regions between disturbed and undisturbed.

[0097] Alternatively to sealing a disk bore to a shaft, such a seal and / or groove may be applied to static structures such as cases.

[0098] Alternatively, applications beyond gas turbine engines include pumps, turbochargers, and other turbomachines.

[0099] FIG. 2 shows an example gas turbine engine 800 as a two-spool turbofan engine. Although shown as a high bypass turbofan, a low bypass turbofan may have similar features. The engine 800 has an engine case 822 surrounding a centerline or central longitudinal axis 500. An example engine has a fan section 824 including a fan 826 within a fan case 828. The example engine includes an inlet 830 at an upstream end of the fan case receiving an inlet flow along an inlet flowpath 520. The fan 826 has one or more stages 832 of fan blades (typically one in a high bypass turbofan and more in a low bypass turbofan). Downstream of the fan blades, the flowpath 520 splits into an inboard portion 522 being a core flowpath and passing through a core of the engine and an outboard portion 524 being a bypass flowpath exiting an outlet 834 of the fan case.

[0100] The core flowpath 522 proceeds downstream to an engine outlet 836 through one or more compressor sections, a combustor, and one or more turbine sections. The example engine has two axial compressor sections and two axial turbine sections, although otherconfigurations are equally applicable. From upstream to downstream there is a low pressure compressor section (LPC) 840, a high pressure compressor section (HPC) 842, a combustor section 844, a high pressure turbine section (HPT) 846, and a low pressure turbine section (LPT) 848. Each of the LPC, HPC, HPT, and LPT comprises one or more stages of blades which may be interspersed with one or more stages of stator vanes. In many low bypass turbofan configurations, the core and bypass flows rejoin to exit a nozzle (e.g., a variable nozzle).

[0101] In the example engine, the blade stages of the LPC and LPT are part of a low pressure spool mounted for rotation about the axis 500. The example low pressure spool includes a shaft (low pressure shaft) 850 which couples the blade stages of the LPT to those of the LPC and allows the LPT to drive rotation of the LPC. In the example engine, the shaft 850 also drives the fan. In the example implementation, the fan is driven via a transmission (not shown, e.g., a fan gear drive system such as an epicyclic transmission) to allow the fan to rotate at a lower speed than the low pressure shaft.

[0102] The example engine further includes a high pressure shaft 852 (of which the shaft section 198 forms a section) mounted for rotation about the axis 500 and coupling the blade stages of the HPT to those of the HPC to allow the HPT to drive rotation of the HPC. In the combustor 844, fuel is introduced to compressed air from the HPC and combusted to produce a high pressure gas which, in turn, is expanded in the turbine sections to extract energy and drive rotation of the respective turbine sections and their associated compressor sections (to provide the compressed air to the combustor) and fan.

[0103] In an example seal manufacture process, the substrate is formed into a ring by conventional methods.

[0104] There then may be an optional polishing (e.g., abrasive) of the surface of the substrate (e.g., at least the OD surface) to achieve a mirror-finished surface. This will remove large peaks and valleys and leave a very smooth surface which will result in a more uniform pre-texturing surface and easier laser surface texturing process due to consistent focal distance between the laser beam and the surface. Thus, it will result in a more uniformly textured surface.

[0105] An optional cleaning the polished surface eliminates polishing residue. An example is sonication. Alternatives include plasma treatment or laser cleaning.

[0106] The substrate (e.g., polished cleaned) may be placed in a fixture for the laser texturing (e.g., sample fixed in the fixture and laser moved responsive to g-code coordinates).

[0107] The laser program is run to control the beam (e.g., based on the g-code coordinates) to texture the surface. The laser texturing may be performed in air with suction drawn from an evacuation pipe kept near the laser spot to evacuate ablated material.Optionally, to limit oxidation, the laser texturing may involve a relatively oxygen-lean atmosphere (compared to air) so as to limit oxidation. For example, nitrogen and / or argon may be used to dilute oxygen content to at or below about 0.1 atm (10 kPa) oxygen partial pressure.

[0108] The PSR is removed / defixtured and inspected (visual or optical microscopy) to verify the uniformity of the pattern all over the surface area.

[0109] The textured surface may be cleaned such as by using DI water rinse, alcohol rinse, and / or wipe as necessary.

[0110] Optionally, the textured surface may be polished gently such as with nano-sized polishing suspensions to remove the (attached) laser debris if any. However, in some applications, the attached laser debris may be left in place to increase the surface roughness and interlock the substrate with the metallic coating layer 202.

[0111] The laser textured surface may be further cleaned (e.g., by sonication) prior to applying the metallic coating 202.

[0112] The metallic coating is applied (e.g., by thermal spray such as air plasma spray) to the laser textured substrate surface.

[0113] Optionally, the metallic coated substrate may be cleaned (e.g., by sonication).

[0114] The metallic coating may then be polished (e.g., by fine diamond disk) prior to laser texturing. Some coatings have very rough surface and might need to be polished to permit uniform texturing (such as noted above with the substrate).

[0115] The metallic coating is then laser textured such as was the substrate (but with laser parameters appropriate to the material difference (coating v. substrate) and any difference in texturing pattern parameters).

[0116] The metallic coating may be polished (e.g., by fine diamond disk) to remove the laser debris.

[0117] The laser textured metallic coating surface may be further cleaned (e.g., by sonication) prior to applying the dry film lubricant (DFL) 204.

[0118] The DFL may then be applied (e.g., by spraying, brushing, immersion, dipping, and / or swabbing).

[0119] Notably, if the initial cleaning is laser cleaning, the texturing of the substrate differs from the laser cleaning in that the laser power and energy for texturing would be much greater in order to ablate the surface and create textures.

[0120] The coating texturing differs from the substrate texturing in that the pattern shape and size can be the same or different. The depth of the textures must be different because the DFL coating is thinner than the APS coating. Thus, for the shallower and narrower grooves expected, power may be lower for the coating grooves than the substrate grooves.

[0121] In various embodiments, the texturing and / or associated coating may be applied to only one of the groove and PSR. In such situations, the other may be as in the prior art or in a yet-developed form.

[0122] 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.

[0123] 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.

Claims

CLAIMSWhat is claimed is:

1. A machine (800) comprising:a shaft (98) comprising:an outer diameter surface (101) having a shaft groove (100) having first (102) and second (104) axial end faces and a base surface (106) therebetween;a metallic substrate (300) having a shaft groove having first (302) and second (304) axial end faces and a base surface (306) therebetween; and a coating (310) on the metallic substrate and at least partially along at least one of the shaft groove first and second axial end faces and base surface, the coating atop a textured surface portion of the substrate;a seal ring (20) accommodated in the shaft groove and having a seal ring substrate (200) softer than the coating; anda counterface (110) to the seal ring.

2. The machine of claim 1 wherein:the textured surface portion has texturing characterized by a pattern of depth of at least 0.010 millimeter.

3. The machine of claim 2 wherein the pattern comprises:a first plurality of grooves; anda second plurality of grooves intersecting the first plurality of grooves.

4. The machine of any of claim 1 to claim 3 wherein:the coating (310) is at least 50% by weight one or a combination of:chromium oxide;Co-based alloys; Al-Co alloys;Ni-Cr alloys;Ni-Al alloys;NiCrAl alloys; andWC-Co.

5. The machine of any of claim 1 to claim 3 wherein the coating (310) is at least 50% by weight chromium oxide.

6. The machine of any of claim 1 to claim 3 wherein the coating (310) is at least 50% by weight Co-based alloys.

7. The machine of any of claim 1 to claim 3 wherein the coating (310) is at least 50% by weight Al-Co alloys.

8. The machine of any of claim 1 to claim 3 wherein the coating (310) is at least 50% by weight Ni-Cr alloys.

9. The machine of any of claim 1 to claim 3 wherein the coating (310) is at least 50% by weight NiCrAl alloys.

10. The machine of any of claim 1 to claim 3 wherein the coating (310) is at least 50% by weight WC-Co.

11. The machine of any of claim 1 to claim 3 wherein:the coating is harder than the seal ring substrate12. The machine of any of claim 1 to claim 3 wherein:the seal ring substrate has Co as a largest by- weight constituent element and at least 18.0 weight percent Cr.

13. The machine of claim 12 wherein:the seal ring substrate is a split ring substrate having:an inner diameter surface (35); andan outer diameter surface (210);the seal ring has a coating (202, 204) having at least a first layer (202) atop the outer diameter surface, andthe outer diameter surface has texturing characterized by a pattern (248) of depth of at least 0.010 millimeter.

14. The machine of claim 12 wherein the seal ring substrate has Cr as a second largest byweight constituent element.

15. The machine of claim 12 wherein the seal ring substrate has no more than 20.0 weight percent any element other than Co, Cr, and Ni.

16. The machine of claim 12 wherein the seal ring substrate has no more than 20.0 weight percent any element other than Co and Cr.

17. The machine of claim 12 wherein the seal ring substrate comprises by weight percent:<2.0 C;<2.5 Mn;<2.5 Si;<0.1 P;<0.1 S;18.0-35.0Cr;<30.0 Ni;<8.0 max Mo;<16.0 W;<4.0 Fe; andbalance Co and no more than 7.0 each other element, if any, individually and 15.0 all other elements total.

18. The machine of claim 12 wherein the seal ring substrate comprises by weight percent:0.90-1.90 C;0.50-2.00 Mn;0.20-2.00 Si;0.04 max P;0.03 max S;28.00-32.00 Cr;3.00 max Ni;1.50 max Mo;3.50-5.50 W;3.0 max Fe; andbalance Co and no more than 1.0 each other element, if any, individually and 5.0 all other elements total.

19. The machine of claim 12 wherein the seal ring substrate comprises by weight percent:0.90-1.40 C;0.50-2.00 Mn;0.20-2.00 Si;0.04 max P;0.03 max S;28.00-32.00 Cr;3.00 max Ni;1.50 max Mo;3.50-5.50 W;3.0 max Fe; andbalance Co and no more than 1.0 each other element, if any, individually and 5.0 all other elements total.

20. The machine of any of claim 1 to claim 3 being a turbine engine wherein:the shaft is a tie shaft of a spool; andthe counterface is on a disk bore (154) of the spool.

21. A method for manufacturing the machine of any of claim 1 to claim 3, the method comprising:laser treating the shaft substrate to form the textured surface portion;applying the coating; andinstalling the seal ring.

22. The method of claim 21 wherein:the laser treating is in a nitrogen- or argon-enriched atmosphere.

23. The method of claim 21 wherein:the applying is by thermal spray.

24. A method for remanufacturing the machine of any of claim 1 to claim 3, the method comprising:removing the seal ring;partially removing the coating;restoring removed coating by thermal spray; andinstalling a replacement seal ring.

25. The method of claim 24 wherein:the partially removing the coating does not reach the textured surface.

26. A machine (800) comprising:a shaft (98) comprising:an outer diameter surface (101) having a shaft groove (100) having first (102) and second (104) axial end faces and a base surface (106) therebetween;a metallic substrate (300) having a shaft groove having first (302) and second (304) axial end faces and a base surface (306) therebetween; and a coating (310) on the metallic substrate and at least partially along at least one of the shaft groove first and second axial end faces and base surface;a seal ring (20) accommodated in the shaft groove;a counterface (110) to the seal ring; andmeans (310) for preferentially wearing the seal ring relative to the shaft.

27. The machine of claim 26 wherein:the means comprises a coating.

28. The machine of claim 27 wherein:the coating is atop a textured surface portion of the substrate.

29. The machine of claim 27 wherein:the coating is harder than a seal ring substrate.

30. The machine of claim 29 wherein:the seal ring substrate has Co as a largest by- weight constituent element and at least 18.0 weight percent Cr.

31. The machine of claim 29 being a gas turbine engine wherein the means is on a forward axial end surface of the shaft groove.

32. A method for manufacturing a coated machine (800) shaft (98), the method comprising:laser texturing at least one surface of a groove in a substrate (300) of the shaft to form a textured surface; andapplying a coating (310) to at least a portion of the textured surface.

33. The method of claim 32 further comprising:installing a seal ring (20) to the groove after the coating.

34. The method of claim 32 wherein:the coating is applied to only one of two axial end faces of the groove.

35. The method of claim 32 wherein:the applying is by thermal spray.

36. The method of claim 32 wherein:the laser texturing is in a nitrogen- or argon-enriched atmosphere.

37. The method of claim 32 wherein the laser texturing forms:a first plurality of grooves; anda second plurality of grooves intersecting the first plurality of grooves.

38. The method of claim 32 wherein:the laser texturing forms a pattern of depth of at least 0.010 millimeter.

39. The method of claim 32 wherein the machine is a gas turbine engine.

40. The method of claim 39 wherein:the laser texturing is on a forward face of the shaft groove.

41. The method of claim 39 wherein:the shaft is a tie shaft of a spool; andthe counterface is on a disk bore (154) of the spool.

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