Abrasive tip coating

Abstract

A method and apparatus coat an airfoil tip (105) with an abrasive (120;304) held by a matrix. The coating may be of an individual blade (20) airfoil or of multiple airfoils integral with a rotor (200). The method includes laser (910) securing an abrasive (120; 304) to a substrate (101). The abrasive is held down such as by a transparent plate (902) or a roller (300) during solidification of a powder (129, 305) melted by the laser.

Description

ABRASIVE TIP COATINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Benefit is claimed of US Patent Application No. 63 / 636,071, filed April 18, 2024, and entitled “Abrasive Tip Coating” and US Patent Application No. 63 / 662,398, filed June 20, 2024, and entitled “Abrasive Tip Coating”, the disclosures of which are incorporated by reference herein in their entireties as if set forth at length.BACKGROUND

[0002] The disclosure relates to gas turbine engines. More particularly, the disclosure relates to abrasive tip coatings for metallic substrate compressor and turbine section blades.

[0003] Gas turbine engines (used in propulsion and power applications and broadly inclusive of turbojets, turboprops, turbofans, turboshafts, industrial gas turbines, and the like) include abrasive-tipped blades.

[0004] Typical abrasive tipping is applied via electroplating in one or more stages. In some examples, there may be three basic stages: a nickel strike plating; an abrasive tack plating with abrasive particles and a thin tack layer of alloy; and a matrix plating. Each of these three plating steps is performed in a separate plating bath.

[0005] In one example of an in situ formed MCrAlY matrix, monocrystalline cBN in an MCrAlY matrix (M = Ni, or Co, or both). The MCrAlY matrix is created by co-depositing the abrasive and CrAlY or MCrAlY solid particles in a NiCo electrodeposit, then performing a diffusion heat treatment.

[0006] Various alternatives to plating have been proposed including brazing. US7718280B2 however also mentions an embodiment wherein abrasive is transferred from a carrier plate to the blade tip. The abrasive particles are secured to the carrier plate and then an MCrAlY matrix is applied by PVD. Such pre-formed abrasive is then transferred to the blade substrate in a braze process. However, it also mentions an embodiment with laser welding abrasive particles to the tip. Another embodiment involves laser welding MCrAlY matrix and then laser welding the abrasive with additional MCrAlY filler. US11795295B2 mentions a laser clad MCrAlY matrix and then an overlay.

[0007] Other art (e.g. grinding wheel manufacture) used electrostatic spray deposition of fine cBN particles (-1 micrometer), followed by matrix infill via chemical vapor deposition (CVD). Example matrix was a TiN or ZrCn-TiCN.SUMMARY

[0008] One aspect of the disclosure involves a method for coating an airfoil tip, the method comprising: applying particulate abrasive and matrix-forming material to the tip; laser melting the matrix-forming material; and rolling a roller over the abrasive so as to retain the abrasive during solidification of the melted matrix-forming material.

[0009] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the matrix-forming material is metallic.

[0010] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the matrix-forming material is an MCrAlY.

[0011] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the abrasive is cBN or SiC.

[0012] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the applying particulate abrasive and matrix-forming material to the tip comprises: during the rolling, introducing the particulate abrasive and matrix-forming material ahead of the roller.

[0013] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, during the rolling, a surface normal of the tip is within 30° of horizontal.

[0014] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the applying particulate abrasive and matrix-forming material to the tip is prior to said rolling.

[0015] A further embodiment of any of the foregoing embodiments, additionally and / or alternatively, includes laterally containing the applied particulate abrasive and matrixforming material.

[0016] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the lateral containing is via a fixture protruding past the tip on the pressure side and suction side of the airfoil; and the roller contacts the fixture.

[0017] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the solidification leaves matrix having a thickness of at least 20 micrometers.

[0018] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the matrix-forming material solidifies to form an initial matrix layer and the method further comprises applying a further matrix layer without using a roller to retain the abrasive.

[0019] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the applying the further matrix layer comprises vapor deposition.

[0020] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the initial matrix layer is applied in an amount at least 110% by weight of the further matrix layer.

[0021] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the further matrix layer is applied by PVD to a thickness of at least 40 micrometers.

[0022] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the initial matrix layer is formed from a first MCrAlY; and the further matrix layer is a second MCrAlY having lower Hf and Si, if any, than the first MCrAlY.

[0023] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the initial matrix layer is a CoCrWC; and the further matrix layer is an MCrAlY.

[0024] One aspect of the disclosure involves a method for coating an airfoil tip. The method comprises: laser tacking an abrasive to a substrate with a metallic tack; and vapor deposition of a metallic matrix material to at least partially embed the abrasive.

[0025] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the laser tacking comprises: containing metallic powder and said abrasive laterally and via a window; and directing a laser beam through the window to melt the metallic powder.

[0026] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the metallic powder is an MCrAlY.

[0027] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the lateral containing is via a fixture protruding past the tip on the pressure side and suction side of the airfoil; and the window contacts the fixture.

[0028] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the laser tacking leaves said metallic tack having a thickness of at least 20 micrometers, optionally 20 to 80 micrometers thick.

[0029] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the abrasive is cBN or SiC.

[0030] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the metallic matrix is applied in an amount at least 110% by weight of the metallic tack.

[0031] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the metallic matrix material is applied by PVD to a thickness of at least 40 micrometers.

[0032] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the metallic matrix material is an MCrAlY, preferably a NiCoCrAlY.

[0033] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the metallic tack is formed from a first MCrAlY; and the metallic matrix material MCrAlY has lower Hf and Si, if any, than the first MCrAlY.

[0034] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the metallic tack is a CoCrWC; and the metallic matrix material is an MCrAlY.

[0035] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively the CoCrWC has: Co as a largest by- weight constituent; and by weight percent at least 18.0 Cr, at least 2.5 W, and 0.6-2.0 C.

[0036] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the vapor deposition is accomplished from one or more metallic ingots.

[0037] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the vapor deposition is PVD, preferably EB-PVD.

[0038] A further embodiment of any of the foregoing embodiments may additionally and / or alternatively include cleaning, prior to the laser tacking, preferably laser cleaning using the same laser as used in in the laser cladding.

[0039] A further embodiment of any of the foregoing embodiments may additionally and / or alternatively include abrasive flow machining (AFM), chemical milling, or laser milling to at least partially remove matrix from the abrasive.

[0040] A further embodiment of any of the foregoing embodiments may additionally and / or alternatively include said laser milling, preferably using the same laser as the laser cladding.

[0041] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the airfoil is a blade airfoil; the substrate comprises a nickel alloy substrate, preferably SX; and the blade comprises an attachment root.

[0042] A further aspect of the disclosure involves an apparatus for coating an airfoil tip, the apparatus comprising: means for applying particulate abrasive and matrix-forming material to the tip; a laser for melting the matrix-forming material; and a roller for rolling over the abrasive so as to retain the abrasive during solidification of the melted matrixforming material.

[0043] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the means (340) for applying particulate abrasive (304) and matrix-forming material (305) to the tip comprises a nozzle. Additional embodiments are as described below.

[0044] A further aspect of the disclosure involves an apparatus for coating an airfoil tip, the apparatus comprising: means for containing particulate abrasive and matrix-forming material to the tip; a laser for melting the matrix-forming material; and a roller for rolling over the abrasive so as to retain the abrasive during solidification of the melted matrixforming material. Additional embodiments are as described below.

[0045] A further aspect of the disclosure involves an apparatus for coating an airfoil tip, the apparatus comprising: means for containing particulate abrasive and matrix-forming material to the tip; a laser for melting the matrix-forming material; and means for retaining the abrasive in the melted matrix-forming material during solidification of the melted matrixforming material.

[0046] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the means for retaining the abrasive in the melted matrix-forming material during solidification of the melted matrix-forming material comprises a roller.

[0047] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the means for retaining the abrasive in the melted matrix-forming material during solidification of the melted matrix-forming material comprises a window.

[0048] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the window is sapphire.

[0049] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the means for containing particulate abrasive and matrix-forming material to the tip comprises a weir preferably surrounding the tip.

[0050] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the roller comprises AI2O3.

[0051] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the roller comprises glass.

[0052] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the roller is spring-loaded.

[0053] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the roller is an undriven roller except for friction from the relative translation of the airfoil tip.

[0054] A further aspect of the disclosure involves an abrasive tipped airfoil comprising: a metallic airfoil substrate having a tip; and an abrasive secured to the tip via a matrix, the matrix comprising a first layer and a second layer outboard of the first layer. The first layer comprises a first MCrAlY and the second layer comprises a second MCrAlY, the first MCrAlY higher in Hf and Si than the second MCrAlY ; or the first layer is a CoCrWC and the second layer is an MCrAlY.

[0055] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the first layer comprises said first MCrAlY and the second layer comprises said second MCrAlY, the first MCrAlY higher in Hf and Si than the second MCrAlY.

[0056] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the first layer is said CoCrWC and the second layer is said MCrAlY.

[0057] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the second layer is thicker than the first layer.

[0058] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the airfoil is a blade airfoil wherein the substrate is a nickel alloy substrate, preferably SX, and the blade comprises an attachment root; or the airfoil is an integrally bladed rotor airfoil wherein the substrate is a nickel alloy substrate, preferably PM and the integrally bladed rotor comprises a circumferential array of airfoils including said airfoil.

[0059] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, a pressure side surface and a suction side surface of the airfoil bear a ceramic coating.

[0060] The features of the embodiments above may be combined in any combination unless expressly indicated otherwise or technically infeasible.

[0061] 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

[0062] FIG. 1 is a view of a gas turbine engine blade.

[0063] FIG. 2 is a sectional view of the blade showing an abrasive coating on the tip and a thermal barrier coating (TBC) on a lateral surface of the airfoil.

[0064] FIG. 3 is a view of the blade in a laser tack stage of applying the abrasive tip coating.

[0065] FIG. 4 is a view of the blade in a matrix infill stage of the laser tip coating.

[0066] FIG. 5 is a cutaway view of an integrally-bladed rotor (IBR).

[0067] FIG. 6 is a view of the blade in a first stage of a first alternative laser process of applying the abrasive tip coating.

[0068] FIG. 7 is a view of the blade in a second stage of the first alternative laser process of applying the abrasive tip coating.

[0069] FIG. 8 is a view of the blade in a stage of a second alternative laser process of applying the abrasive tip coating.

[0070] FIG. 9 is a view of a blade after a roller laser tack and matrix infill.

[0071] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0072] As is discussed further below, an example blade tip abrasive application for a gas turbine engine compressor or turbine blade includes laser deposition of at least a tack layer. External means are used to hold down abrasive during laser melting of matrix material. This prevents a combination of low abrasive density (if at all) and molten matrix surface tension from floating the abrasive atop the matrix yielding poor (if any) adhesion.

[0073] In some embodiments, this may be a single stage coating process providing all the matrix. In some embodiments, this may be a stage for laser tack of the abrasive and there may be a subsequent stage. An example subsequent stage is for physical vapor deposition (PVD) infill of matrix material.

[0074] In some embodiments a roller is used to hold down the grit.

[0075] Blade substrate and coating materials and manufacture techniques and configurations may be otherwise conventional or yet-developed.

[0076] FIG. 1 shows a blade 20. An example blade is a turbine blade (e.g., a first stage high pressure turbine blade in a multi-spool engine). Alternative blades (airfoils) may be portions of an integrally bladed rotor (IBR) (e.g., a compressor disk 200 with integral blades / airfoils 202 (FIG. 5)). The example blade includes an airfoil 22, an attachment root 24, and an intervening platform 26. The example attachment root extends from an inboard end of the blade to an underside of the platform and has a generally firtree convoluted profile of opposite circumferential faces and generally flat fore and aft faces forming a slightly non-right parallelogram footprint corresponding to a skew angle of the associated slot (not shown) in a blade rotor disk. The platform 26 similarly has circumferential ends and axial ends, an inboard / ID surface, and an outboard / OD or gaspath surface. The airfoil extends from an inboard end 30 at the platform gaspath surface to an outboard tip 32 and has a leading edge 34, a trailing edge 36, a pressure side 38, and a suction side 40.

[0077] The example airfoil is internally cooled with a passageway network extending from one or more inlets in the root (e.g., in the ID surface of the root) to outlets along the gaspath surfaces of the airfoil and platform. This example blade includes a tip squealer pocket 50 having outlets. A wall structure surrounds the squealer pocket on the pressure and suction sides and leading edge. Optionally, the squealer pocket may have an outlet through the wall structure typically to the pressure side near the trailing edge. The gaspath surfaces of the blade may have one or more coatings. In this example, the OD surface of the platform and the pressure and suction sides of the airfoil bear a thermal barrier coating (TBC) system and the tip (the wall surrounding the squealer pocket in the particular example) bears an abrasive tip coating.

[0078] FIG. 2 shows a TBC system 100 atop the substrate 101 on the lateral surface 103 of the airfoil and an abrasive coating system 102 on the tip 105. Example substrate materials are nickel-based superalloys such as single-crystal (SX) alloys for separate turbine blades and wrought powder metallurgical alloys for integrally bladed rotors. The TBC system includes a bond coat 104 (e.g., MCrAlY applied by PVD or thermal spray) and a ceramic thermal barrier layer 106 (e.g., one or more layers of yttria-stabilized zirconia (YSZ), gadolinium zirconate (GZO or GdZ) or the like (e.g., applied by PVD or thermal spray)). The abrasive coating system includes abrasive particles (grit) 120 embedded in a metallic matrix 122.

[0079] In a process for applying the abrasive tip coating, the exposed substrate 101 along the blade tip may be machined as part of a post-casting process and / or as part of a cleaning process after a coating (e.g., thermal barrier coating (TBC), if any) application so as to re-expose bare substrate. In other examples, the abrasive coating may be applied before TBC application. In various embodiments, the abrasive coating 102 may be applied in a repair situation and may be applied atop a buildup (e.g., weld or cladding) or preform / prosthetic that replaces lost substrate.

[0080] Additional preparation may include cleaning. An example of cleaning includes a multi-step process with an alkali cleaning (e.g., KOH or NaOH), an acid rinse to neutralize (e.g., H2SO4 - low concentration such as 0.1 to 0.5 percent solution) and a water rinse. Additionally or alternatively, there may be a laser cleaning step, optionally also followed by a water rinse. That laser cleaning may be performed using the same laser that will be used in the subsequent laser tack.

[0081] In the abrasive tip coating process, the blade may optionally be masked or shielded to protect regions away from the tip. The example masking includes hard masking / shielding 900 (FIG. 3) (e.g., which may be removed and reused) or a coating maskant (which may be sacrificially removed).

[0082] An example first stage is the laser tack of abrasive (e.g., cBN and / or SiC) with a thin layer of tack metal or alloy 130 (FIG. 3) that will become a portion of the final matrix. cBN is commonly used as an abrasive on turbine blades and compressor blades. The cBN may be monocrystalline or polycrystalline or a combination. SiC is typically used on turbine blades only. Further alternatives include oxide ceramics. The tacking may use the aforementioned fixture 900 as a weir to contain a mixture of tack precursor alloy (e.g., initially a powder 129) and abrasive grit. Example weir material is metal (e.g., aluminum or an aluminum alloy which may have advantages of durability / rigidity and low susceptibility to near IR lasers). This may surround the tip, continuing from surrounding the pressure and suction sides adjacent the tipand protruding upward to form the weir. In the case of a squealer pocket, the masking may include a plug in the pocket and protruding therefrom. The material may be sprinkled into the weir and then a window (glass or sapphire) 902 (shown as a plate transparent to the laser) placed atop the weir to enclose the material and retain the grit 120 and tack during direction of the laser beam 910 from a laser 912 (e.g., a near infrared (IR) laser) through the window to melt the tack precursor. The weir height may be just larger than grit size so that the plate holds grit close against the substrate so that the grit does not float atop the molten tack and fail to be secured. FIG. 3 shows a traversal of the beam in a direction 500 progressively melting precursor powder 129 and leaving a solidifying wake as the tack 130. The illustration is schematic only and there will be additional movement transverse to the cut plane.

[0083] An example tack material 130 is an MCrAlY (M is Ni, Co or combinations thereof, e.g., a NiCoCrAlYHfSi alloy discussed further below) in powder form. An example composition is Ni 22Co 17Cr 12A10.5Hf 0.5Y 0.4Si (commercially available as Amdry™ 386 by Oerlikon Metco of Pfaffikon Switzerland. The Amdry™ 386 family is designated as having 20-26% Co, 14-21% Cr, 11-14% Al, 0.2-0.8% Y, 0.1-0.5% Hf, 0.1-0.7% Si, and the balance Ni with < 1.0 other. This may be pre-blended with the abrasive particles or there may be separate feeders from separate sources (e.g., hoppers). The result of this stage is to produce a thin tack layer 130 holding abrasive particles in place. The tack layer may have some degree of diffusion with the substrate. MCrAlY may have an advantage over pure nickel in that it has superior resistance to oxidation and does not promote diffusion of alloying elements of the blade alloy into the pure Ni deposit. The NiCoCrAlYHfSi has a further advantage over NiCoCrAlY (without Hf and Si) in oxidation life and resistance to hot corrosion, allowing use at higher temperatures. Specifically, the Hf and Si promote the formation of an alpha alumina protective thermally grown oxide. This protects against further oxidation of material below.

[0084] Example tack thickness Ti (FIG. 3) is approximately 40 micrometers, more broadly, 5 micrometers to 80 micrometers or 20 micrometers to 60 micrometers or 20 micrometers to 80 micrometers.

[0085] Example characteristic abrasive particle size is 120 mesh, more broadly 100 - 240 mesh.

[0086] The blade with tacked abrasive may proceed directly to a subsequent matrix-forming stage or there may be some intermediate cleaning or prep. Such may include a diffusion heat treat in a protective atmosphere (e.g., vacuum or nitrogen or argon) although this may be after the second stage below.

[0087] The example second matrix-forming stage is a physical vapor deposition process such as cathodic arc deposition or electron beam physical vapor deposition (EB-PVD) or plasma-assisted PVD (PA-PVD) or sputtering (e.g., high power impulse magnetron sputtering). A further option is the BALORA™ PVD arc technology of Oerlikon Balzers Coating AG, Balzers, Liechtenstein.

[0088] The deposition builds up a second matrix layer (sublayer) 140’ at least partially further embedding the abrasive particulate (FIG. 4). Example second matrix layer thickness T2' as-applied is 80 micrometers, more broadly at least 40 micrometers or 40 micrometers to 120 micrometers. FIG. 4 shows this PVD matrix layer or sublayer 140’ as being applied with the masking / weir 900 still in place although there are various other options.

[0089] The mass of matrix 140’ applied by PVD may be greater than the mass of metal or alloy of the tack. For example, at least at least 110% or at least 300% or an example 110% to 2300% or 300% to 2300% or 400% to 1000%. Layer thickness ratios may be similar or less if cross-sectional area occupied by grit is biased away from the substrate.

[0090] Example matrix-forming material for PVD is an MCrAlY such as NiCoCrAlY. A particular example NiCoCrAlY is 20Co-18Cr-12Al-0.2Y-balance Ni. Relative to the tack MCrAlY, the PVD matrix MCrAlY source material may have lower or zero Hf and Si content due to the difficulty of adding elements with relatively low vapor pressures to EB-PVD deposits. Example Hf and Si, if any, in the source material (e.g., ingot and melt pool) for the PVD has not more than 50% or not more than 25% or not more than 10% the Hf and / or Si in the laser tack source powder. Similarly, the as-deposited layer 140' may have such or even lower proportions (due to preferential attrition of Hf and Si in PVD) relative to the as-applied layer 130. Use of EB-PVD MCrAlY without the Hf and Si additions is worthwhile relative to the tack MCrAlYHfSi due to the superior microstructure of the PVD deposit. As a further candidate, the Amdry™ 365 family is designated as having 20-26% Co, 14-20% Cr, 11-14% Al, 0.1-0.8% Y, and the balance Ni with < 1.0 other.

[0091] A more highly alloyed MCrAlY is a MCrAlYHfSi such as that used for the tack, which may preferably be applied by PA-PVD (which may offer less Hf and Si attrition v. EB- PVD).

[0092] The tack plus PVD can offer several advantages. The PVD deposit may be denser, lower in oxide content, and / or more environmentally resistant than the laser tack portion. Additionally, a number of factors may influence the thickness of the tack to be more than the minimum for tack purposes. At least to a point, the laser tack process may build thickness fasterthan the PVD. At the upper end, tack thickness may be limited by microstructural considerations such as excessive unmelts and porosity in the finished coating.

[0093] An optional further stage is a finishing stage. One group of example finishing stages includes further partially removing matrix. This is useful to eliminate the amount of excess matrix material atop the abrasive. Thus, this stage or step will remove a surface sublayer of the material 140’ to leave material 140 (FIG. 2) with exposed grit. Advantageously, the amount of material removal may be small so that the ratios of material 140 to 130 may be generally similar to those given for 140’ to 130. This may result from preferential accumulation of PVD atop the material 130 relative to atop exposed grit. The desirability of such removal may depend on issues of the particular grits and the particular matrix application techniques because both may influence the affinity of the grits for accumulation of matrix.

[0094] Example finishing can include abrasive polishing, electrochemical machining (e.g., anodic dissolution of matrix material by electrochemical machining using a conductive fluid between the tool and workpiece), chemical milling (e.g., etching), or laser milling (ablation). This may have the effect of removing matrix material from the intended cutting surfaces of the grits, thereby improving the abrasive performance of the deposit. Particularly in a situation where the tack and matrix-forming stages are performed at a single station, the laser milling might be performed with the same laser as used in the laser tack.

[0095] Example post-removal PVD matrix thickness T2 as-applied (as opposed to after service) is 75 micrometers, more broadly at least 35 micrometers or 35 micrometers to 115 micrometers. The mass of matrix post-removal may be greater than the mass of metal or alloy of the tack. For example, at least 100% or an example or 100% to 2300% or 250% to 2300% or 300% to 2300%. Example combined thickness T (FIG. 2) is 125 micrometers, more broadly at least 80 micrometers or 80 micrometers to 150 micrometers or 80 micrometers to 200 micrometers.

[0096] Nevertheless, the thicknesses T2 and T2' may be less than Ti. And the mass ratios may be similar or less still. This may involve thicker tack than described above and thinner PVD. Even then, the PVD material microstructure may offer potential environmental benefits. Particular balances between the techniques for the two stages may depend on economics which may be influenced by particular laser tack and PVD apparatus available.

[0097] In a polishing example (of abrasive flow machining (AFM)), an abrasive media is forced past the blade tip under high pressure to polish the surface. This may be performed with a protective maskant on all portions of the airfoil other than the tip, or it may be used to polish the airfoil surface at the same time as the thin MCrAlY layer is removed from the grits (e.g.,particularly for tip coatings applied prior to TBC). The part is de-masked upon completion. Such polishing may be performed either to reduce the thickness of the MCrAlY layer on the grits to an acceptable level for the application, or to remove it entirely.

[0098] In a laser ablation example, the laser is rastered over the blade tips at sufficient power to ablate the MCrAlY layer off the abrasive grits without resulting in extensive oxidation of the grits. This may be performed in a standard pattern for all blade tips. The specific method of water-guided laser machining is anticipated to minimize thermal damage to the abrasive grits.

[0099] In a chemical milling (aka etching) example, after a cleaning process and masking of all surfaces other than the blade tip, the part is immersed in a temperature-controlled bath of chemical etchant which attacks and removes the MCrAlY. The part is de-masked upon completion. This method is better suited to individual blades rather than IBRs. Due to the waste stream and potentially lengthy processing times (dependent on etching rate), this may be a lesser preferred option.

[0100] Depending upon the implementation, there may be one or more of several advantages compared with traditional baseline plating processes that may be replaced. For example, the laser tack and subsequent non-plating matrix application provide relatively smaller waste / recycling stream(s) and / or the recycling stream(s) may be more easily processed. For example, in plating processes there is nickel salt waste that needs to be treated. In the PVD process, the salt is eliminated. There may be some need to retrieve or recycle overspray and there may be some liquid waste associated with chemical milling (if used). But these may be of smaller scale and / or smaller chemical complexity.

[0101] Relative to electrostatic spray coating (ESC), the laser tack and PVD infill may allow much larger grit and MCrAlY instead of nitride coatings as the matrix. MCrAlY may offer superior oxidation resistance and significantly higher useful operating temperatures.

[0102] The coating and layer thickness, composition, and properties may be measured at a single location or across an area. Such area may be a total or continuous area (e.g., truly continuous or continuous ignoring cooling hole outlets). With an area, that may be at all locations or an average (mean, median, or mode). A representative area is at least 0.1 square centimeters.

[0103] Or, a representative area may be a fraction or percentage of a relevant area. For example with a blade tip, the relevant area may be the tip surface excluding the squealer pocket, if any. A representative such fraction or percentage is at least 10% or at least 50% or at least 90%.

[0104] The table below identifies alternatives for tack material and PVD matrix material.Table ITack and PVD Matrix Combinations

[0105] A first example MCrAlY for both layers if the same is NiCoCrAlYHfSi source material with some differential attrition particularly for EB-PVD.

[0106] When differing MCrAlY are used for the two layers, an example difference is NiCoCrAlYHfSi for the tack layer and NiCoCrAlY (without Hf and Si) for the PVD layer as discussed above.

[0107] Example CoCrWC alloys include the Stellite™ alloy family of Kennametal Inc., Pittsburgh, Pennsylvania, such as Stellite™ 6 and Stellite™ 694. Stellite™ alloys are known as a laser clad material. Thus, developed fields exist regarding laser parameters associated with such cladding. Use as a tack may offer greater ease of application at a sacrifice of temperature performance.

[0108] An example by weight composition based on Stellite™ 694 is 27-30% Cr, 18- 21% W, 4-6% Ni, 0.5-1.5% V, 0.6-1.4% C, balance Co with up to, if any, 3% Fe, 1% Mn, 1% Si, 1% Mo, 0.02% B and impurities.

[0109] One published by weight composition for Stellite™ 6 is 27-32% Cr, 3-6% W, 0.9- 1.4% C, base Co with Ni, Fe, Si, Mn, Mo listed but with unspecified content.

[0110] In general, key such Stellite™ and other relevant CoCrWC alloys may have Co as a largest by-weight constituent, at least 18.0 weight percent Cr (e.g., 18.0-35.0 or 20.0 to 32.0), at least 2.5 W (e.g. 2.5 to 22.0), 0.6-2.0 C, up to, if any, one or more of 11.0 Ni, 5.0 Fe, 2.0 Mn, 2.0 Si, 2.0 Mo, 2.0 V, 1.0 B, and up to impurity levels of yet others (e.g. up to 0.5 or 1.0 individually and 2.0 or 5.0 aggregate others). Cr may be the second largest by weight constituent.

[0111] Heat treatment and service use may alter compositions such as via interdiffusion of the two layers and substrate and oxidation or other environmental reaction.

[0112] As noted above, some embodiments may involve use of a roller 300 (FIG. 7) to hold down the abrasive. FIG. 6 shows a full volume of matrix-forming powder (304) and grit (305) combination 302 atop a blade tip.

[0113] FIG. 7 shows the blade tip during laser melting. The roller has a peripheral surface 310 and is held for rotation about a roller axis 520. The blade is traversed relative to the roller in a direction 522 causing rotation in direction 524 about the axis while maintaining contact with the applied matrix-forming powder and grit. FIG. 7 also shows a local surface normal 530 of the tip as being close to vertically upward (e.g., within 30°, preferably 0° to 20°, of upward 510).

[0114] In various embodiments using a roller, the matrix applied may be the entirety of the matrix or may be a sublayer (even just a tack (130 of FIG. 9) such as discussed above) with subsequent infill 140 such as discussed above. In some embodiments of either the plate or roller implementations, the depth of the matrix melted by the laser may be greater than half of the effective cBN grit diameter. If it is less, the grit is more likely to mask the matrix powder and prevent the matrix from capturing the grits. The effective diameter may be measured via a mesh size. Typically in the field, grit diameter determined by the grit or mesh size is listed by the supplier, using a standard ANSI chart. For example, 100 grit is the same as 100 mesh, which gives an average diameter of 122 micrometers or 0.0048 inches. 240 grit is the same as 200 mesh which gives an average diameter of 50 micrometers or 0.002 inches. Thus, example grit diameter is 100-150 micrometers, with a target of 125 micrometers.

[0115] Example roller material is high density AI2O3 (e.g., densely sintered) or heat resistant glass. For horizontal orientation, steel could be used, but only if grit size and matrix amount is such that the matrix powder is not in contact with the roller.

[0116] Example roller mounting and relative roller-blade movement is by a spring-loaded axle that holds the roller against the matrix material and cBN mix with a desired force and associated contact pressure. The roller may be driven such as directly by a motor or by a belt which is linked to the mechanism (e.g., motor driven) that moves the blades, or it may be driven by friction from the relative translation of the blades. More complex actuators (e.g., industrial robots) may hold the roller and / or blade and provide a desired contact force throughout the movement.

[0117] Additionally, means may be provided for lateral containment of matrix such as masking / fixturing (e.g., 900 of FIG. 3) described above. In such a case, the masking may be configured to contact the roller or may be configured to protrude shy of contact with the roller. In one example, the height of the powder retaining fixture may be 60% to 90% of the average diameter of the cBN grits. This allows the roller to maintain grit in contact with the substrate (or closer to the substrate for smaller grits). Nevertheless, particularly for relativelyuniform grit, the fixture height may be selected to exceed the grit effective diameter so that the roller can at least partially contact the fixture.

[0118] The laser is directed to slightly lead the roller movement in the blade frame of reference. For example, within 1.0 millimeter of the contact point so that the matrix cannot eject the cBN before it is held down and refreezes.

[0119] The relative movement of the roller and blade is slow enough to allow solidification of the matrix while the roller is still holding the grit down toward the substrate. For example, 2.0 millimeter per second to 10.0 millimeter per second should allow the laser to melt the powder, and for the resulting metal matrix to refreeze before the restraining pressure is removed from the grits.

[0120] In an alternative implementation, the laser beam may trail the roller. In this case, the fused material and wetting by already-melted material may help retain the material about to be melted.

[0121] FIG. 8 shows a further variation on the process of FIGs. 6 and 7 but wherein the application of the matrix-forming powder and grit is during the roller rolling and laser melting. In the example, the mixture of matrix-forming powder and grit is dropped into the region between roller 300 and tip ahead of the relative roller movement.

[0122] Example delivery of the mixture is via air jet or mechanical conveyor. FIG. 8 shows a nozzle 340 that entrains the matrix powder and grits in a stream of air of other gas such as Ar or N2.

[0123] In the illustrated example, the surface normal 530 is close to horizontal (e.g., within 45°, preferably 0° to 30° or 0° to 20°). The traversal direction 522 is thus generally upward (e.g., within 45° of upward, preferably 0° to 30° or 0° to 20°).

[0124] 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.

[0125] 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 blade configuration and coating and substrate composition, 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 method for coating an airfoil (22) tip (105), the method comprising: laser tacking an abrasive (120) to a substrate with a metallic tack (130); and vapor deposition of a metallic matrix (140) material to at least partially embed the abrasive.

2. The method of claim 1 wherein the laser tacking comprises: containing metallic powder (129) and said abrasive laterally and via a window (902); and directing a laser beam (910) through the window to melt the metallic powder.

3. The method of claim 1 wherein: the metallic powder is an MCrAlY.

4. The method of claim 1 wherein: the lateral containing is via a fixture (900) protruding past the tip on the pressure side and suction side of the airfoil; and the window contacts the fixture.

5. The method of claim 1 wherein: the laser tacking leaves said metallic tack having a thickness of at least 20 micrometers.

6. The method of claim 1 wherein: the abrasive is cBN or SiC.

7. The method of claim 1 wherein: the metallic matrix material is applied in an amount at least 110% by weight of the metallic tack.

8. The method of claim 1 wherein: the metallic matrix material is applied by PVD to a thickness of at least 40 micrometers.

9. The method of claim 1 wherein:the metallic matrix material is an MCrAlY, preferably a NiCoCrAlY.

10. The method of claim 1 wherein: the metallic tack is formed from a first MCrAlY ; and the metallic matrix material MCrAlY has lower Hf and Si, if any, than the first MCrAlY.

11. The method of claim 1 wherein: the metallic tack is a CoCrWC; and the metallic matrix material is an MCrAlY.

12. The method of claim 1 wherein the CoCrWC has:Co as a largest by-weight constituent; and by weight percent at least 18.0 Cr, at least 2.5 W, and 0.7-2.0 C.

13. The method of claim 1 wherein: the vapor deposition is from one or more metallic ingots.

14. The method of claim 1 wherein: the vapor deposition is PVD, preferably EB-PVD.

15. The method of claim 1 further comprising prior to the laser tacking: cleaning, preferably laser cleaning using the same laser as used in in the laser cladding.

16. The method of claim Ifurther comprising: abrasive flow machining (AFM), chemical milling, or laser milling to at least partially remove matrix from the abrasive.

17. The method of claim 1 comprising: said laser milling, preferably using the same laser as the laser cladding.

18. The method of claim 1 wherein: the airfoil is a blade airfoil; the substrate is a nickel alloy substrate, preferably SX; and the blade comprises an attachment root.

19. A method for coating an airfoil tip (105), the method comprising: applying particulate abrasive (305) and matrix-forming material (304; 129) to the tip; laser (910) melting the matrix-forming material; and rolling a roller (300) over the abrasive so as to retain the abrasive during solidification of the melted matrix-forming material.

20. The method of claim 19 wherein: the matrix-forming material is metallic.

21. The method of claim 19 wherein: the matrix-forming material is an MCrAlY.

22. The method of claim 19 wherein: the abrasive is cBN or SiC.

23. The method of claim 19 wherein the applying particulate abrasive and matrix-forming material to the tip comprises: during the rolling, introducing the particulate abrasive and matrix-forming material ahead of the roller.

24. The method of claim 23 wherein: during the rolling, a surface normal (530) of the tip is within 30° of horizontal.

25. The method of claim 19 wherein the applying particulate abrasive and matrix-forming material to the tip is prior to said rolling.

26. The method of claim 19 further comprising: laterally containing the applied particulate abrasive and matrix-forming material.

27. The method of claim 26 wherein: the lateral containing is via a fixture (900) protruding past the tip on the pressure side and suction side of the airfoil; and the roller contacts the fixture.

28. The method of claim 19 wherein: the solidification leaves matrix having a thickness of at least 20 micrometers.

29. The method of claim 19 wherein the matrix-forming material solidifies to form an initial matrix layer and the method further comprises: applying a further matrix layer without using a roller to retain the abrasive.

30. The method of claim 29 wherein the applying the further matrix layer comprises: vapor deposition.

31. The method of claim 30 wherein: the initial matrix layer is applied in an amount at least 110% by weight of the further matrix layer.

32. The method of claim 30 wherein: the further matrix layer is applied by PVD to a thickness of at least 40 micrometers.

33. The method of claim 30 wherein: the initial matrix layer is formed from a first MCrAlY ; and the further matrix layer is a second MCrAlY having lower Hf and Si, if any, than the first MCrAlY.

34. The method of claim 30 wherein: the initial matrix layer is a CoCrWC; and the further matrix layer is an MCrAlY.

35. The method of claim 34 wherein the CoCrWC has:Co as a largest by-weight constituent; and by weight percent at least 18.0 Cr, at least 2.5 W, and 0.6-2.0 C.

36. The method of claim 30 wherein: the vapor deposition is from one or more metallic ingots.

37. The method of claim 30 wherein: the vapor deposition is PVD, preferably EB-PVD.

38. The method of claim 19 further comprising prior to the applying: cleaning, preferably laser cleaning using the same laser as used in in the laser cladding.

39. The method of claim 19 further comprising: abrasive flow machining (AFM), chemical milling, or laser milling to at least partially remove matrix from the abrasive.

40. The method of claim 39 comprising: said laser milling, preferably using the same laser as the laser cladding.

41. The method of claim 19 wherein: the airfoil (22) is a blade (20) airfoil; the substrate (101) is a nickel alloy substrate, preferably SX; and the blade comprises an attachment root (24).

42. An apparatus for coating an airfoil tip, the apparatus comprising: means (900) for containing particulate abrasive (120; 304) and matrix-forming (129; 305) material to the tip; a laser (900) for melting the matrix-forming material; and means (902; 300) for retaining the abrasive in the melted matrix-forming material during solidification of the melted matrix-forming material.

43. The apparatus of claim 42 wherein: the means (902) for retaining the abrasive in the melted matrix-forming material during solidification of the melted matrix-forming material comprises a window.

44. The apparatus of claim 43 wherein: the window is sapphire.

45. The apparatus of claim 42 wherein:the means (900) for containing particulate abrasive (120; 304) and matrix-forming (129;305) material to the tip comprises a weir preferably surrounding the tip.

46. The apparatus of claim 42 wherein: the means (300) for retaining the abrasive in the melted matrix-forming material during solidification of the melted matrix-forming material comprises a roller.

47. An apparatus for coating an airfoil tip, the apparatus comprising: means (340) for applying particulate abrasive (304) and matrix-forming material (305) to the tip; a laser (912) for melting the matrix-forming material; and a roller (300) for rolling over the abrasive so as to retain the abrasive during solidification of the melted matrix-forming material.

48. The apparatus of claim 47 wherein: the means (340) for applying particulate abrasive (304) and matrix-forming material (305) to the tip comprises a nozzle.

49. An apparatus for coating an airfoil tip, the apparatus comprising: means (900) for containing particulate abrasive (304) and matrix-forming material (305) to the tip; a laser (912) for melting the matrix-forming material; and a roller (300) for rolling over the abrasive so as to retain the abrasive during solidification of the melted matrix-forming material.

50. The apparatus of claim 49 wherein: the roller (300) comprises AI2O3.

51. The apparatus of claim 49 wherein: the roller (300) comprises glass.

52. The apparatus of claim 49 wherein: the roller (300) is spring-loaded.

53. The apparatus of claim 49 wherein: the roller (300) is an undriven roller except for friction from the relative translation of the airfoil tip.

54. An abrasive-tipped airfoil comprising: a metallic airfoil substrate (101) having a tip (105); and an abrasive (120; 304) secured to the tip via a matrix (122), the matrix comprising a first layer (130) and a second layer (140) outboard of the first layer, wherein: the first layer comprises a first MCrAlY and the second layer comprises a second MCrAlY, the first MCrAlY higher in Hf and Si than the second MCrAlY ; or the first layer is a CoCrWC and the second layer is an MCrAlY.

55. The abrasive-tipped airfoil of claim 54 wherein: the first layer comprises said first MCrAlY and the second layer comprises said second MCrAlY, the first MCrAlY higher in Hf and Si than the second MCrAlY.

56. The abrasive-tipped airfoil of claim 54 wherein: the first layer is said CoCrWC and the second layer is said MCrAlY.

57. The abrasive-tipped airfoil of claim 54 wherein: the second layer is thicker than the first layer.

58. The abrasive-tipped airfoil of claim 54 wherein: the airfoil is a blade airfoil wherein: the substrate is a nickel alloy substrate, preferably SX; and the blade comprises an attachment root.

59. The abrasive-tipped airfoil of claim 54 wherein: the airfoil is an integrally bladed rotor airfoil wherein: the substrate is a nickel alloy substrate, preferably PM; and the integrally bladed rotor comprises a circumferential array of airfoils including said airfoil.

60. The abrasive-tipped airfoil of claim 54 wherein: a pressure side surface and a suction side surface of the airfoil bear a ceramic coating.

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