Airfoil external masking for internal aluminization

Abstract

A masking apparatus (110; 600) for masking a part (20) during coating and comprising at least two sintered pieces (112, 114, 116, 118) of a mask material. The pieces (112, 114, 116, 118) have an assembled condition forming a compartment shaped to accommodate an airfoil (22; 608) of the part (20). The pieces (112, 114, 116, 118) have an average overall composition of: alumina and in one or more phases of a remainder nickel as a largest by-weight constituent aluminum as a second largest by-weight constituent and chromium as a third largest by-weight constituent.

Description

PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219AIRFOIL EXTERNAL MASKING FOR INTERNAL ALUMINIZATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a Continuation-In-Part of U.S. Patent Application No. 18 / 134207, filed April 13, 2023, and entitled "Airfoil External Masking for Internal Aluminization", 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 application of aluminide internal coatings for metallic substrates.

[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 internally cooled metallic components.

[0004] Typical metallic components are formed of a nickel-based superalloy. For example, nickel-based superalloys are typically used in high pressure compressor section (HPC) blades (e.g., polycrystalline forgings) and turbine blades(e.g., single crystal castings) . Other internally cooled components include vanes, struts, blade outer airseals (BOAS) , and the like. In many such internally cooled components, cooling passageways are aluminized. The aluminization prevents oxidation of the associated surfaces during operation. Gaspath-facing surfaces have multi-layer coatings typically comprising a bondcoat and one or more layers of ceramic coating serving as some combination of thermal barrier coat (TBC) , environmental barrier coat (EBC) , or, in the case of blade outer airseals, abradable coatings. Example bondcoats are MCrAlY bondcoats. In MCrAlY M stands for Ni, Co, Fe or combination of two or three of the three. However typical commercially MCrAlY used as bondcoats have little, if any, FePCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219( such as NiCrAlY, NiCoCrAlY and CoNiCrAlY with not more than 5 weight percent Fe , if any) . Minor intentional elements typically include Hf , Si , and Zr . Often, Hf , Si , and Zr are not more than 1 . 0 weight percent but Si may be up to 5 weight percent and Hf to 2 weight percent in some cases . And there may be commercial or inevitable impurities .

[0005] Internally cooled components can have cooling holes connecting the interior passages to the external gaspath surface to create a film of cooling air on the external surface . This film functions to reduce the surface temperature experienced by the thermal barrier coating . However, these cooling holes are prone to oxidation which can reduce their effectiveness by reducing the diameter of the hole . Internal aluminide coatings can reduce the oxidation and result in increased part life .

[0006] During alumini zation of the internal cooling passageways , it is known to mask exterior portions of the substrate against contamination from the alumini zat ion vapors . This can limit degradation of finished or pre-finished surfaces (e . g . , machined or pre-machined root surfaces or surfaces that are to receive subsequent bondcoat application (e . g . , along the gaspath-facing surfaces of the substrate ) ) . For example , the aluminide coating can affect the microstructure of the bond coat if present underneath .SUMMARY

[0007] One aspect of the disclosure involves a masking apparatus for masking a part during coating and comprising at least two sintered pieces of a mask material . The at least two sintered pieces have an assembled condition forming a compartment shaped to accommodate an airfoil of the part . The at least two sintered pieces have an average overall weight percent composition of : an alumina content of at least 30 ; at least 30 nickel in all phases ; an additional aluminum content of at least 3 . 5 aluminum in all phases exclusive of alumina; and a chromium content ofPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 at least 0.5 chromium in all phases and less than said additional aluminum content .

[0008] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the average overall composition by weight may be within one or more ranges of Table I below, optionally with an "Other" content as described thereafter .

[0009] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the aluminaexclusive average overall composition by weight may be within one or more ranges of Table III below, optionally with an "Other" content as described thereafter.

[0010] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the average overall composition by weight percent has: 38.5 to 55.0 alumina; 35.0 to 55.0 nickel; 4.0 to 6.0 said additional aluminum; and 1.0 to 2.5 chromium.

[0011] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the average overall composition by weight percent has: no more than 5.0 total elements other than the oxygen and aluminum of the alumina, said nickel, said additional aluminum, and said chromium; and / or no more than 1.0 elements individually other than the oxygen and aluminum of the alumina, said nickel, said additional aluminum, and said chromium.

[0012] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the at least two sintered pieces have an alumina-exclusive composition by weight percent of: 80.0 to 92.0 nickel; 5.0 to 15.0 aluminum; and 1.0 to 8.0 chromium.

[0013] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the average overall composition by weight percent has: 38.5 to 55.0 alumina,PCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-21923 . 5 to 34 . 0 intermetallic NiAlCr; and 11 . 0 to 38 . 0 additional elemental Ni .

[0014] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the at least two sintered pieces comprise : a first piece ; and a second piece . In the assembled condition the first piece and second piece form a first compartment shaped to enclose an airfoil of the part .

[0015] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the at least two sintered pieces further comprise : a third piece ; and a fourth piece . In the assembled condition : the third piece and the fourth piece form a second compartment shaped to accommodate a firtree root or root precursor of the part .

[0016] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, a coating apparatus includes the masking apparatus of and further comprises a gas manifold having spigot portions for mating with inlet ports of the part .

[0017] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively : the inlet ports are in a blade root or blade root precursor of the part ; and the spigot portions are received in the inlet ports .

[0018] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, a method for manufacturing the masking apparatus comprises : forming the at least two sintered pieces by sintering a blend of metallic powders , alumina, and a binder .

[0019] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the metallic powders comprise NiCrAl powder and Ni powder .

[0020] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, a method for using the masking apparatus comprises : assembling the at least two sintered pieces to the assembled condition over a turbinePCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219 engine airfoil element , so that the compartment accommodates an airfoil of the airfoil element ; and flowing an alumini zation vapor through the airfoil element .

[0021] The alumini zation vapor may include aluminum oxide and aluminum chloride , for example 3% by volume aluminum chloride . An alumini zation vapor may include other aluminum halide gas .

[0022] The alumini zation vapor may be flowed through the airfoil element at elevated temperatures . One non-limiting example of such an elevated temperature is between 600 ° C and 1000 ° C, but other temperatures could be used .

[0023] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the method of further comprises applying a collar around the at least two sintered pieces .

[0024] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the at least two sintered pieces further comprise : a third piece ; and a fourth piece . In the assembled condition the third piece and the fourth piece form a second compartment shaped to accommodate a firtree root of the part . The method further comprises : mating a manifold to the firtree root , the mating comprising inserting spigots of the manifold into inlet ports of the firtree root ; assembling the third piece and fourth piece to the firtree root ; and inserting the assembled third piece and fourth piece to a body of a fixture , the inserting mating an inlet of the manifold to an inlet conduit of the fixture .

[0025] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the method further comprises : removing the at least two sintered pieces ; and applying a metallic coating to an exterior surface of the part .

[0026] A further aspect of the disclosure involves , a method for manufacturing a cooled part , the method comprising : applying a pre-formed mask to a coated cast substrate having an exteriorPCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219 surface and an interior surface ; alumini z ing the interior surface ; removing the pre-formed mask; and a applying a metallic coating to the exterior surface . The mask comprises a sintered body of a mask material . The mask material comprises nickel and aluminum . Further embodiments may optionally be as described above for the first aspect or below .

[0027] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the mask material comprises at least 30_weight percent alumina and a remainder comprising in one or more phases : nickel as a largest by-weight constituent of the remainder; aluminum as a second largest by-weight constituent of the remainder; and chromium as a third largest by-weight constituent of the remainder .

[0028] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the one or more phases comprise : an NiAlCr intermetallic phase ; and an elemental nickel phase .

[0029] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the remainder comprises : no more than 5 . 0 % total all elements other than oxygen, nickel , aluminum, and chromium, optionally and no more than 1 . 0 % individually all elements other than oxygen, nickel , aluminum, and chromium .

[0030] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the applying the metallic coating is via cathodic arc deposition . Suitable voltages and temperatures may be chosen for the cathodic arc deposition, which may be performed at vacuum conditions .

[0031] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the metallic coating comprises MCrAlY .

[0032] In a further embodiment of any of the foregoing embodiments , additionally and / or alternatively, the method further comprises : forming the mask by compacting and sinteringPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 one or more powders. This may be at a temperature between 60% and 80% of the melting temperature of the mask material, and / or between 600°C and 1800°C, for example between 900°C and 1300°C or between 1000°C and 1200°C.

[0033] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the sintered one or more powders have an average overall weight percent composition of: an alumina content of at least 30; at least_30 nickel in all phases; an additional aluminum content of at least 3.5 aluminum in all phases exclusive of alumina; and a chromium content of at least 0.5 chromium in all phases and less than said additional aluminum content.

[0034] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the applying the mask is to an airfoil of the substrate; and the applying the metallic coating is to said airfoil of the substrate.

[0035] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively: the applied mask covers at least 50 percent of the airfoil of the substrate; and the applied the metallic coating is to at least 50 percent of said airfoil of the substrate including at least 50 percent of the area of the airfoil of the substrate that has been masked.

[0036] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the one or more powders are a blend of: a first powder being an alloy powder of NiAlCr; and a second powder being elemental Ni powder.

[0037] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the aluminizing comprises: flowing a coating vapor through the cast substrate, the coating vapor formed from source material of aluminum and chromium with an AlFa activator powder.

[0038] In a further embodiment of any of the foregoing embodiments, additionally and / or alternatively, the cooled part is a blade having an airfoil and an attachment root. The interiorPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 surface forms a cooling passageway system including one or more inlets along the root to one or more outlets along the airfoil.

[0039] The metal powder composition for the maskant power may be the same as the composition for the maskant material.

[0040] 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

[0041] FIG. 1 is a view of a turbine engine blade with a mask exploded away.

[0042] FIG. 2 is a view of the masked blade fixtured.

[0043] FIG. 3 is a radial sectional view of the fixtured masked blade .

[0044] FIG. 4 is a first transverse sectional view of the fixtured masked blade through the airfoil.

[0045] FIG. 4A is an enlarged view of a leading edge plenum of the mask.

[0046] FIG. 4B is an enlarged view of a trailing edge plenum of the mask.

[0047] FIG. 40 is an enlarged view of the pressure side and suction side of the airfoil facing the adjacent surface of the adjacent mask piece.

[0048] FIG. 4D is an enlarged view of an outlet passageway before bondcoat application.

[0049] FIG. 5 is an inward radial view of the fixtured masked blade .

[0050] FIG. 6 is a first transverse sectional view of the fixtured masked blade through the root.

[0051] FIG. 7 is a view of a base of the fixture.

[0052] FIG. 8 is a view of a manifold of the fixture.

[0053] FIG. 9 is a view of a collar of the fixture.PCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219

[0054] FIG . 10 is an enlarged view of the outlet passageway of FIG . 4D after bondcoat application .

[0055] FIG . 11 is a sectional view of an alternate mask .

[0056] Like reference numbers and designations in the various 5 drawings indicate like elements .PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219DETAILED DESCRIPTION

[0057] FIG. 1 shows a turbine engine blade 20 with a mask 110 shown exploded away. As is discussed below, the masked blade 20 is in an intermediate stage of manufacture wherein coatings are applied to a metallic substrate (e.g., single crystal (SX) nickel-based superalloy) of the blade.

[0058] The example blade is used in a turbine section of a gas turbine engine. The blade has an airfoil 22 extending from an inboard (inner diameter (ID) ) end 24 to an outboard (outer diameter (OD) ) end 26. In the example blade, the outboard end forms a free tip which may include features such as a squealer pocket, cooling outlets, and the like. Alternative blades may include shrouded tips. The airfoil includes respective pressure 28 and suction 30 sides extending between a leading edge 32 and a trailing edge 34.

[0059] At the inboard end 24 of the airfoil, the blade includes a platform 40 having an inboard face (underside) 42, an outboard face (gaspath face) 44, a leading / f orward end 46, a trailing / aft end 48, and lateral / circumferential ends 50, 52.

[0060] An attachment feature 60 depends from the underside 42 of the platform 40 (or from the airfoil inboard end if no platform) . The example attachment feature is dovetail or firtree root (or precursor thereof) having an inboard end 62, an outboard end 64 at the platform underside 42, a forward end 66, an aft end 68, and lateral faces (sides) 70, 72. The lateral sides have a parallel convolution form (or precursor thereof) providing the dovetail or firtree to be received in a complementary disk slot (not shown) . In the FIG. 1 example, the attachment feature is a precursor cast shape that will be further machined to define the firtree geometry. In an alternate example of FIG. 11 discussed below, the firtree has already been machined.

[0061] An internal cooling passageway system 80 (FIGs. 3 and 4) includes one or more inlets 82 along the root inboard end with passageways extending to one or more outlets along the airfoilPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219(typically including trailing edge outlets, leading edge outlets, surface outlets along the pressure and / or suction side, and tip outlets and platform outlets such as along the gaspath face 44 ) .

[0062] In an example process, the blade has a nickel-based superalloy substrate (e.g., cast single crystal (SX) ) . Example substrate materials are PWA 1484 and PWA 1429 among other 2ndand later generation columnar (directionally solidified (DS) ) and SX alloys.

[0063] After casting, the substrate may be machined to provide final contours in some areas. In a limited machining situation of FIG. 1, the machining may be limited to blending off excess casting material from the raw casting.

[0064] As is discussed further below, the optionally machined substrate may be coated inside and out. Example inside / interior coating is an aluminization. Example exterior coating (at least along gaspath-facing surfaces of the airfoil and platform) includes a metallic bondcoat (e.g., MCrAlY) which may be deposited such as by thermal spray or cathodic arc deposition. Example MCrAlY bondcoat is deposited by cathodic arc deposition.

[0065] In an example, the mask 110 is used during the internal aluminization before application of the bondcoat and subsequent application of a ceramic thermal barrier coat (TBC) (e.g., yttria-stabilized zirconia (YSZ) and / or gadolinium zirconate (GZO / GdZ) ) in one or more layers (e.g., via thermal spray and / or physical vapor deposition (e.g., EB-PVD) ) to the gaspath-facing surfaces .

[0066] The example mask has four main pieces 112, 114, 116, and 118. The example pieces 112 and 114 are dimensioned to, in an assembled condition, principally cover the blade root with 112 to the pressure side and 114 to the suction side having faces 120 and 122, meeting along a parting plane which may generally correspond to a central f ront-to-back and spanwise radial plane of the root.PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219

[0067] The pieces 116 and 118 generally cover the lateral surface of the airfoil and gaspath surface of the platform in the assembled condition.

[0068] The pieces 112 and 114 also have lower / inner diameter (ID) faces 124 and 126, upper or outer diameter (OD) surfaces 128 and 130, leading / f orward surfaces 132 and 134, trailing / aft surfaces 136 and 138, and lateral outboard surfaces 140 and 142 (respectively opposite inboard surfaces 120 and 122) .

[0069] The pieces 116 and 118 have lower or ID faces 150 and 152, upper or OD faces 154 and 156, circumferentially leading faces 158, 160, circumferentially trailing faces 162 and 164, axial outboard faces 166 and 168, and axial inboard faces 170 and 172. The axial inboard faces 170 and 172 mate at a parting contour. Unlike the planar parting contour (parting plane) of the root pieces 112 and 114, the example mating contour is non-planar due to considerations of needing to assemble around the airfoil.

[0070] The pieces 112 and 114 have respective pockets 180 and 182 for receiving adjacent portions of the root. The ID faces 124 and 126 have opening sections 184 (FIG. 4) and 186 (FIG. 1) open to the pocket sections to, when the mask is assembled, form a port for introduction of aluminization vapor (which may include aluminum oxide and aluminum chloride, for example 3% aluminum chloride by volume, as the usual impurities) at appropriate temperature, for example between 600°C and 1000°C. In the example discussed below, this port receives an inlet conduit for a manifold which, in turn, mates with the inlet ports of the root.

[0071] In the assembled condition, the pieces 116 and 118 closely face or contact the airfoil along the majority of the pressure side and suction side. Near the leading edge of the airfoil but shifted toward the suction side, the pieces 116, 118 diverge away from the airfoil defining a plenum 200 (FIG. 4)PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 open at the outer diameter end of the assembled mask. The axial inboard faces 170, 172 mate past this plenum 200.

[0072] In distinction, adjacent the trailing edge of the airfoil, the two pieces do not mate. This leaves a plenum 202 open both radially outward and to the circumferentially trailing faces 162, 164.

[0073] FIG. 4A shows the leading edge plenum 200 relative to leading edge cooling outlets. FIG. 4B shows the trailing edge plenum 202 relative to trailing edge discharge slot outlets.

[0074] FIG. 4G shows the pressure side and suction side of the airfoil with outlets facing the adjacent surface of the adjacent mask piece.

[0075] FIG. 4D generically shows an outlet hole / passageway in the substrate 400 with an exterior surface 404. An aluminization 410 is built up along an interior surface 412 of the substrate (e.g., one of the feed passageways) and along a surface 414 of the outlet hole / passageway. As the aluminization vapors 415 exit the outlet hole / passageway, they encounter mask material and diffuse into and react with the mask material, thereby lowering aluminization vapor concentration adjacent the exterior surface 404 of the and reducing impact. This leaves only a small exterior region 416 of aluminization on the surface 404.

[0076] After aluminizing, the mask may be disassembled. Additional machining may be performed and the MCrAlY bondcoat may be applied. In one example of subsequent machining, the tip may be ground in order to achieve the final blade length. Additionally, the root may be precision ground for fit with a disk slot.

[0077] In this example, after such machining (or before) , the bondcoat may be applied. This may be done by cathodic arc deposition on the gaspath surfaces in which non-gaspath surfaces are masked with a hard fixture (not shown) .

[0078] FIG. 10 generically shows the outlet hole / passageway in the substrate 400 with an MCrAlY bondcoat 402 atop the surfacePCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219404 of the substrate and the exterior region 416 of aluminization .

[0079] The mask pieces are formed by sintering a maskant powder or mixture thereof. Example maskant powders are produced by Akron Paint & Varnish, Inc. d / b / a APV Engineered Coatings (APV) , Akron, OH under the designations M-l, M-7, M-8, M-10, and M-17. These are typically introduced as powder in a masking box. Although sintered root masking pieces have also been used. The M-l maskant broadly includes alumina, and nickel, aluminum, and chromium in one or more phases. Those phases are believed to essentially be a single NiAlCr intermetallic phase. Various sources describe similar net elemental compositions as including an intermetallic of Ni and Al mixed and optionally presintered with the Cr. Example conditions for the sintering are a temperature of 60% to 80% of the melting point of the maskant powder and at elevated pressure, for example, lOMPa to 100 MPa, or 20 to 50 MPa, or another suitable pressure and temperature.

[0080] The M-7 maskant is a 1:3 powder blend of the M-l maskant and Ni powder. This may add an elemental nickel phase. The M-17 maskant is a 3:1 weight mixture of M-l:M-7.

[0081] An example is a mixture of the M-l and M-7 powders noted above. By mixing, the resultant sintered pieces have a structure characterized by increased surface area and porosity compared to solid (e.g., cast) material. Relative to a sintered homogeneous powder, the mixture may be more manufacturable (easing compaction and creating greater structural integrity / durability ) . Specifically, the M-l principally provides the gettering of the aluminization vapor and the M-7 (due to the added nickel) aids in compaction and resulting structural integrity / durability.

[0082] The sintering process may involve blending the powder (s) with a binder (e.g., polymeric material) that facilitates compaction. This may be at a temperature between 60% and 80% of the melting temperature of the mask material, and / or betweenPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219600°C and 1800°C, for example between 900 and 1300 °C or between 1000°C and 1200°C. The mixed powder (s) and binder are compacted and then heated / sintered . The resultant sintered form may have porosity left by vaporization or decomposition of binder. This 5 porosity potentially provides increased surface area of gettering material exposed to the aluminization vapor. Table 1 below shows eight example net mask contents. Table II shows seven example M-l / M-7 combinations corresponding to the Table I examples with the first theoretically being M-17. This was based 10 on measured composition of vendor-suppled M-l. Table I Ex. 8 reflects a vendor-provided material that departed from anticipated M-17 specification. Table III discussed below has the alumina-exclusive compositions for the eight examples. The tables also show various ranges but not necessarily with the 15 same correspondence as the examples.PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219Table INet Mask Composition (wt. %)* Failure of examples to add to exactly 100.0 reflects rounding5 of individual contents. t Total all phases it Total exclusive of alumina

[0083] For the Table I ranges, example other alloyants or impurities may combine to an example at most 5.0 weight percent 10 or at most 2.0 weight percent optionally with at most 2.0 or 1.0 or 0.5 individually of each additional element. This may reference individual elements regardless of whether in elemental or compound / alloy form. One notable element is iron which isPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 often present as an artifact of the powder manufacture. Thus, an iron content of up to 1.0 weight percent may be an exception to the 0.5 number above.

[0084] Table II provides example powder mixtures:5 Table IIPowder Mixture* (wt. %)* Exclusive of fugitive binder. Failure to add to exactly 100.0 reflects rounding of individual contents.

[0085] From the Table I examples, fractional by weight elemental 10 contents of the individual Ni, Cr, Al (not in alumina) and others may be calculated excluding the alumina from the denominator. Table II Ex. 1-8 correspond to Table I Ex. 1-8 with apparent discrepancies reflecting rounding. The ranges do not correspond to the Table I ranges. These may be applied alternatively to or 15 applied concurrently with the Table I ranges (e.g., with the concurrency creating a narrower domain than either of the two ranges being combined) .PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219Table ITTAlumina-Exclusive Mask Composition (wt. %)* Failure of examples to add to exactly 100.0 reflects rounding of individual contents.5 t Total all phases it Total exclusive of alumina

[0086] For the Table III ranges (like with Table I) , the table III ranges may combine with specific limits on the "other". Example other alloyants or impurities may combine to an example 10 at most 5.0 weight percent or at most 2.0 weight percent optionally with at most 2.0 or 1.0 or 0.5 individually of each additional element. Due to alumina presence, these example ranges are inherently tighter than the same percentage appliedPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 to the Table 1 ranges. This may reference individual elements regardless of whether in elemental or compound / alloy form. One notable element is iron which is often present as an artifact of the powder manufacture. Thus, an iron content of up to 1.0 weight percent may be an exception to the 0.5 number above.

[0087] FIG. 2 shows the mask assembled to the blade and held in a fixture 300. The example fixture comprises a base 302 having a trough-like body that receives the root-covering pieces 112, 114 to hold them assembled to each other. The example base body is formed of additively manuf actured / 3d printed nickel-based superalloy (e.g., IN718) .

[0088] The fixture further includes a manifold insert 350 (FIG.7) . The manifold insert has an inlet port (inlet) 354 and one or more outlet ports (outlets) 356, 358. The inlet port receives the aluminization vapors and the outlet (s) mate with root inlet ports to pass the vapors to the blade. The example manifold insert has fewer outlets than the root has inlets. The example blade has four inlets and the manifold has two outlets mated to the leading two inlets. In this example, the blade is a single-wall blade wherein there is communication between the various passageway legs fed by the various inlets. Thus, aluminization vapor introduced through the example two of four inlets will nevertheless circulate through substantially the entirety of the interior passageway system of the blade.

[0089] The example outlets 354, 356 are on spigots / nipples 360, 362 that are received in the blade inlets when the manifold insert is mounted to the blade. Thereafter, the root-covering pieces 112, 114 are assembled over the root and manifold insert 350 to capture and retain the manifold insert mated to the root. With the root-covering pieces 112, 114 so mated, they may be inserted into the fixture base. In the example this insertion mates the manifold insert inlet spigot 358 to a corresponding conduit 306 of the base for passing the aluminization vapors to the manifold insert. The example manifold insert may be made ofPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 nickel-based superalloy (e.g., IN718) (e.g., by additive manuf acture / 3d printing) .

[0090] The fixture also includes a ring or collar 380 (FIG. 8) for holding the airfoil-covering pieces 116, 118 secured to each other. The example collar may be made of nickel-based superalloy (e.g., IN718) (e.g., by additive manuf acture / 3d printing) .

[0091] In use, aluminization vapor is flowed through the port, into the cast substrate, through the internal passageways of the substrate, and out the outlets. Example vapor comprises an aluminide halide compound (e.g. formed by the decomposition of a mixture of an aluminum based powder and a halide activator powder in a closed furnace container or retort at an elevated temperature. Suitable temperatures for initiating the reaction range from about 1200°F (about 650°C) to about 2000° F (about 1100 °C) . The aluminum based powder (compound) may be an aluminum intermetallic compound. Examples of suitable aluminum intermetallic compounds for use in the diffusion coating process include chromium-aluminum (CrAl) alloys, cobalt-aluminum (CoAl) alloys, chromium-cobalt-aluminum (CrCoAl) alloys, and combinations thereof. Examples of suitable concentrations of the aluminum based compound in the powder mixture range from about 1% by weight to about 40% by weight.

[0092] The halide activator is a compound capable of reacting with the aluminum based compound during the diffusion coating process. Examples of suitable halide activators for use in the diffusion coating process include aluminum fluoride (AlFa) , ammonium fluoride (NH4F) , ammonium chloride (NH4CI) , and combinations thereof. Examples of suitable concentrations of the halide activator in the powder mixture range from about 1% by weight to about 50% by weight.

[0093] The powder mixture may also include inert materials such as aluminum oxide powder. The furnace container or retort may also contain one or more gases (e.g., H2 and Argon) to obtain aPCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219 desired pressure and reaction concentration during the diffusion coating process .

[0094] An example composition is by weight approximately 45% aluminum and 55% chromium with an AlFa activator powder .

[0095] The elevated temperature initiates a reaction between the aluminum based compounds and the halide activators to form gaseous aluminum halide compounds which decompose on passageway surfaces of the substrate to deposit aluminum in a molten state which then interdiffuses with the substrate . The diffusion coating process continues until a desired coating thickness is reached, e . g . , at least 25 micrometers and preferably between 25 micrometers and 125 micrometers ( inclusive ) .

[0096] FIG . 11 shows an alternate mask 600 and fixture 602 differing in several aspects but similar in others (not enumerated) . First , there are only two mask pieces 604 , 606 masking the airfoil 608 and the platform 610 gaspath surface 612 . These may be formed as in the FIG . 1 embodiment . Second, the root 614 and platform underside 616 are in a chamber 618 of the fixture . The chamber can contain conventional dry compacted M-l powder introduced to the chamber in a conventional fashion(not shown) . The root may be pre-ground . Due to the pre-ground root , it is even more important to limit or avoid alumini zation . Thus , the dry compacted powder (not shown) contacting the root will better protect the root than a closely-facing spaced-apart surface of gettering material .

[0097] Also , the example FIG . 11 blade i s a multi-wall casting wherein the root inlets feed fully separate passageways . Thus , the manifold 620 has outlets to all four root inlets so as to alumini ze all passageways . The fixture body comprises a base 630 with an inlet conduit mated to the manifold and a sidewall piece 632 extending upward from the base with a lower end of the sidewall piece received in the base and an upper end having a shoulder with an inner pocket receiving the platform . An outerPCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219 portion of the shoulder separated from the pocket by a short wall supports the lower ends of the mask pieces .

[0098] The example FIG . 11 fixture pieces , manifold, and collar may be formed of additively manuf actured / 3d printed nickel-based superalloy (e . g . , IN718 ) .

[0099] In either the FIG . 1 or FIG . 11 embodiments , the example mask pieces may cover at least 50 percent of the airfoil surface area of the substrate or at least 90 percent . Additionally or alternatively, the example mask pieces may cover at least 50 percent of the combined airfoil and platform gaspath / OD surface area of the substrate or at least 90 percent . In turn, the applied the bondcoat is to at least 50 percent of said airfoil surface of the substrate ( or combined airfoil surface and platform gaspath / OD surface ) including at least 50 percent of the area of the airfoil surface of the substrate ( or combined airfoil surface and platform gaspath / OD surface ) that has been masked .

[0100] The alloys discussed herein may have the usual impurities , unless expressly indicated herein .

[0101] Where percentages are mentioned herein without an indication of the type of percentage (e . g . , by weight or by volume ) the percentage is to be understood as a weight percentage .

[0102] Where a blend of materials or powders is referred to this is to be understood as the materials listed and a balance of the usual impurities .

[0103] The use of "first" , "second" , and the like in the following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order . Similarly, the identification in a claim of one element as "first" ( or the like ) does not preclude such "first" element from identifying an element that is referred to as "second" ( or the like ) in another claim or in the description .PCT / US24 / 51547 16 October 2024 (16.10.2024)174156WOO l-U-22-219

[0104] One or more embodiments have been described . Nevertheless , it will be understood that various modifications may be made . For example , when applied to an existing baseline part configuration and / or process , details of such baseline may 5 influence details of particular implementations . Accordingly, other embodiments are within the scope of the following claims .

Claims

PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219CLAIMSWhat is claimed is:

1. A masking apparatus (110; 600) for masking a part (20) during coating and comprising at least two sintered pieces (112, 114, 116, 118; 604, 606) of a mask material wherein: the at least two sintered pieces (112, 114, 116, 118; 604, 606) have an assembled condition forming a compartment shaped to accommodate an airfoil (22; 608) of the part (20) ; and the at least two sintered pieces (112, 114, 116, 118; 604, 606) have an average overall weight percent composition of : an alumina content of at least 30; at least 30 nickel in all phases; an additional aluminum content of at least 3.5 aluminum in all phases exclusive of alumina; and a chromium content of at least 0.5 chromium in all phases and less than said additional aluminum content .

2. The masking apparatus of claim 1 wherein the average overall composition by weight percent has:38.5 to 55.0 alumina;35.0 to 55.0 nickel;4.0 to 6.0 said additional aluminum; and1.0 to 2.5 chromium.

3. The masking apparatus of claim 1 wherein the average overall composition by weight percent has: no more than 5.0 total elements other than the oxygen and aluminum of the alumina, said nickel, said additional aluminum, and said chromium; and / orPCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 no more than 1.0 elements individually other than the oxygen and aluminum of the alumina, said nickel, said additional aluminum, and said chromium.

4. The masking apparatus of claim 1 wherein the at least two sintered pieces have an alumina-exclusive composition by weight percent of:80.0 to 92.0 nickel;5.0 to 15.0 aluminum; and1.0 to 8.0 chromium.

5. The masking apparatus of claim 1 wherein the average overall composition by weight percent has:38.5 to 55.0 alumina;23.5 to 34.0 intermetallic NiAlCr; and11.0 to 38.0 additional elemental Ni.

6. The masking apparatus of claim 1 wherein the at least two sintered pieces (112, 114, 116, 118; 604, 606) comprise: a first piece (116; 604) ; and a second piece (118; 606) , wherein in the assembled condition: the first piece (116; 604) and second piece (118; 606) form a first compartment shaped to enclose an airfoil (22;608) of the part (20) .

7. The masking apparatus of claim 6 wherein the at least two sintered pieces (112, 114, 116, 118) further comprise: a third piece (112) ; and a fourth piece (114) , wherein in the assembled condition: the third piece (112) and the fourth piece (114) form a second compartment shaped to accommodate a firtree root (60) or root precursor of the part (20) .PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-2198. A coating apparatus including the apparatus of any previous claim and further comprising: a gas manifold (350; 620) having spigot portions (360, 362) for mating with inlet ports of the part (20) .

9. The coating apparatus of claim 8 wherein: the inlet ports are in a blade root (60; 614) or blade root precursor of the part (20) ; and the spigot portions (360, 362) are received in the inlet ports .

10. A method for manufacturing the masking apparatus (110; 600) of any previous claim, the method comprising: forming the at least two sintered pieces (112, 114, 116, 118; 604, 606) by sintering a blend of metallic powders, alumina, and a binder.

11. The method of claim 10 wherein: the metallic powders comprise NiCrAl powder and Ni powder.

12. A method for using the masking apparatus (110; 600) of any previous claim, the method comprising: assembling the at least two sintered pieces (112, 114, 116, 118; 604, 606) to the assembled condition over a turbine engine airfoil element (20) , so that the compartment accommodates an airfoil (22; 608) of the airfoil element (20) ; and flowing an aluminization vapor (415) through the airfoil element (20) .

13. The method of claim 12 further comprising: applying a collar (380) around the at least two sintered pieces (116, 118; 604, 606) .PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-21914. The method of claim 12 wherein: the at least two sintered pieces (112, 114, 116, 118) further comprise: a third piece (112) ; and a fourth piece (114) , wherein in the assembled condition the third piece (112) and the fourth piece (114) form a second compartment shaped to accommodate a firtree root (60; 614) of the part; and the method further comprises: mating a manifold (350; 620) to the firtree root (60; 614) , the mating comprising inserting spigots (360, 362) of the manifold (350; 620) into inlet ports of the firtree root (60; 614) ; assembling the third piece (112) and fourth piece (114) to the firtree root (60; 614) ; and inserting the assembled third piece (112) and fourth piece (114) to a body of a fixture (300) , the inserting mating an inlet (358) of the manifold (350; 620) to an inlet conduit (306) of the fixture (300) .

15. The method of claim 12 further comprising: removing the at least two sintered pieces; and applying a metallic coating to an exterior surface of the part .

16. A method for manufacturing a cooled part (20) , the method comprising : applying a pre-formed mask (110; 600) to a cast substrate (400) having an exterior surface (404) and an interior surface (412) ; aluminizing the interior surface (412) ;PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-219 removing the pre-formed mask (110) ; and applying a metallic coating to the exterior surface (404) , wherein : the mask (110; 600) comprises a sintered body of a mask material; and the mask material comprises nickel and aluminum.

17. The method of claim 16 wherein the mask material comprises : at least 30_weight percent alumina; and a remainder comprising in one or more phases: nickel as a largest by-weight constituent of the remainder; aluminum as a second largest by-weight constituent of the remainder; and chromium as a third largest by-weight constituent of the remainder.

18. The method of claim 17 wherein the one or more phases comprise : an NiAlCr intermetallic phase; and an elemental nickel phase.

19. The method of claim 17 wherein the remainder comprises: no more than 5.0 % total all elements other than oxygen, nickel, aluminum and chromium; and no more than 1.0 % individually all elements other than oxygen, nickel, aluminum and chromium.

20. The method of claim 16 wherein: the applying the metallic coating is via cathodic arc deposition .PCT / US24 / 5154716 October 2024 (16.10.2024)174156WOO l-U-22-21921. The method of claim 16 wherein the metallic coating comprises :MCrAlY.

22. The method of claim 16 further comprising: forming the mask (110; 600) by compacting and sintering one or more powders .

23. The method of claim 22 wherein the sintered one or more powders have an average overall weight percent composition of: an alumina content of at least 30; at least 30 nickel in all phases; an additional aluminum content of at least 3.5 aluminum in all phases exclusive of alumina; and a chromium content of at least 0.5 chromium in all phases and less than said additional aluminum content.

24. The method of claim 16 wherein: the applying the mask (110; 600) is to an airfoil (22; 608) of the substrate (400) ; and the applying the metallic coating is to said airfoil (22; 608) of the substrate (400) .

25. The method of claim 24 wherein: the applied mask (110; 600) covers at least 50 percent of the airfoil (22; 608) of the substrate (400) ; and the applied the metallic coating is to at least 50 percent of said airfoil (22; 608) of the substrate (400) including at least 50 percent of the area of the airfoil (22; 608) of the substrate (400) that has been masked.

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