Method and tool for applying abrasive and protective armor coating

Abstract

The invention relates to a method for producing a metallic coating (7, 7 ', 7' ', 7 ''') having secondary particles (19), in particular grinding-active ceramic particles (19), in which a separate supply device (16) is used to inject the secondary particles (19) from the outside into a spray (10) of an HVOF gun (13).

Description

[0001] The present invention relates to a method for applying a grinding and protective armor coating, in particular, to the tip of a rotating component of a gas turbine engine, and a corresponding tool.

[0002] In a gas turbine engine, clearance control is extremely important for improving engine efficiency and reducing harmful emissions.

[0003] A clearance control method involves applying a grinding and protective coating to the tip of a blade that cuts into a stationary mating surface coating during a friction event, which is well known:

[0004] D. B. Allen US 2005 / 0129522 A1;

[0005] D. B. Allen WO 2014 / 074370 A2;

[0006] Burton A. Kushner, Anthony J. Rotolico, John E. Nerz, Lawerence A.Saia, US 5,059,095;

[0007] J.D. Shell and H.J. Farr US 5,952,110;

[0008] J. R. Faughnan et al.US 2016 / 0024942 A1;

[0009] X-T Luo, and C-J. Li, “Thermal Stability of Microstructure andHardness of Cold-Sprayed cBN / NiCrAl Nanocomposite Coating” JTST, Vol. 21, pp. 578-585 (2012).

[0010] Cubic boron nitride (cBN) in a superalloy or MCrAlY matrix is the most commonly selected option.

[0011] There are several methods for applying cBN to the tip of a blade, including electroplating, hard brazing, and laser welding.

[0012] For power turbines where commissioning control is not as perfect as in aircraft engines or inevitably requires long-term high-temperature operation, electroplated or hard-brazed cBN particles cannot form a suitable coating.

[0013] This is because the coating thickness of the electroplated and brazed versions is limited to single-layer abrasives and a substrate of a few tens of micrometers.

[0014] On the other hand, welded claddings may result in multi-layer abrasives and a cladding with a substrate thickness in the millimeter range.

[0015] Therefore, for powder turbines, a more common method is by the laser powder welding method: US 8,647,073 B2 by Hoebel et al. or US 10,259,720 B2, by Balbach et al...

[0016] In laser powder welding (LPW, sometimes also referred to as laser cladding and laser metal forming), a laser beam creates a molten pool on the substrate surface. Abrasive and substrate material powders are transported by a carrier gas and injected into the molten pool around the laser beam. The abrasive and substrate materials are pre-mixed in a hopper for single injection in the desired ratio, or in the case of dual injection, the ratio is achieved by controlling the mass feed rates of the two components. LPW can be used to economically and repeatedly build thick protective and abrasive claddings on tips with complex shapes.

[0017] However, like any welding process, the LPW process tends to create a heat-affected zone in the base alloy when depositing the abrasive layer. This can lead to tip cracking, especially if the blade is not made of single crystal, unlike in US '073 B2 by Hoebel et al. In addition, the heat input to cBN particles in existing LPW processes may result in loss of cBN particles due to high-temperature oxidation or decomposition, or may reduce the size of the cBN particles that ultimately end up in the welded cladding. The reduction in the number and / or size of cBN particles has an adverse effect on the cutting behavior of the blade.

[0018] This problem has not been fully solved.

[0019] For brazing and electroplating, the coating thickness is quite limited, restricted to single crystal grains and a few tens of micrometers, which may provide too low wear resistance when the rotor and stator components come into contact.

[0020] In contrast, if welding is considered, the layer thickness may be high enough.

[0021] However, the high heat of the process causes internal cracking in the base alloy, which is addressed to some extent by applying a buffer layer. This only partially solves the cracking problem. In addition, the problem of loss or size reduction of cBN particles has not been solved during the welding process.

[0022] Therefore, the technical problem to be solved by the present invention is to overcome these problems.

[0023] This technical problem is solved by the method according to claim 1 and the tool according to claim 8.

[0024] Additional advantages are listed in the dependent claims, and these advantages can be combined arbitrarily to produce further advantages.

[0025] In the drawings:

[0026] Figure 1 A schematic diagram showing the tool for the method is presented.

[0027] Figures 2 to 4 An example of a coating produced by the method is shown.

[0028] These figures and descriptions are merely examples of the present invention.

[0029] The present invention proposes the use of a High-Velocity Oxygen Fuel (HVOF) thermal spraying process technology to simultaneously spray a matrix material and an abrasive material in a dual-injection (non-premixed powder form) setup.

[0030] Figure 1 An exemplary tool 1 is shown, including an HVOF spray gun 13 that uses powder and generates a spray 10 with the matrix material.

[0031] The matrix material is deposited on the substrate 4 to form a coating 7.

[0032] The abrasive particles 19 bypass the spray gun 13 through a separate and distinct supply device 16 that uses a carrier gas to transport the abrasive particles 19.

[0033] The supply device 16 is preferably fixed to the spray gun 13.

[0034] The end of the supply device 16 is at a certain length from the end of the spray gun and is used at a certain distance 22 from the substrate 4.

[0035] However, the length of the supply device 16 and thus the distance from the surface or substrate 4 can also be adjusted.

[0036] The key technical features of the present invention for solving the problem are the use of HVOF technology for spraying and the use of a special setup to separate the abrasive particles from the matrix and away from the flame jet.

[0037] Advantages of using HVOF compared to the LPW process:

[0038] - Different from the LPW process, the HVOF process has a minimum heat input to the substrate 4 made of a base alloy.

[0039] - Different from the LPW process, the HVOF process produces a shot peening effect on the surface of the substrate 4. The above features can reduce the tendency of tip cracking.

[0040] - The HVOF process is capable of generating an extremely dense and highly oxidation-resistant coating / cladding 7.

[0041] Advantages of the jet using the improved abrasive particles 19 compared to the standard jet in the HVOF process (and LPW process):

[0042] - The abrasive particles 19 are less exposed to a high-temperature oxidation atmosphere before deposition, so there is less loss of cBN particles and less reduction in the size of the abrasive particles (such as cBN particles).

[0043] - Generally for the standard HVOF process, the powder particles 19 are smaller in size, which helps to accelerate the particles. Fine abrasive particles are not ideal for cutting applications such as gas turbine blades. In contrast, in the setup of the present disclosure, a properly selected injector will allow the spraying of the required coarse particles 19 with a size up to 250 µm.

[0044] - The abrasive particle feed rate can be independently controlled and adjusted during the deposition of the entire coating thickness. This will allow for a free change in the microstructure of the composite coating throughout the thickness.

[0045] Figures 2 to 4 Schematic diagram showing different thickness microstructure variations that may be achieved by a powder feedstock using a spray gun 13 through the disclosed tool 1.

[0046] Figure 2 Showing a staggered structure 7' where the particles 19 are not in the area directly on or near the substrate 4.

[0047] Figure 3 Showing a graded structure 7'' where the abrasive particles 19 have a higher density near the outer surface 25 of the coating 7''.

[0048] In Figure 2 、 Figure 3 In two examples, the abrasive particles 19 can also protrude from the outer surface 28, as shown by the coating 7''' in Figure 4 .

[0049] The disclosed method can be applied to both liquid fuel and gas fuel versions of the HVOF spray gun 13.

[0050] Furthermore, although the present disclosure uses cBN particles as an example of the abrasive material, it is by no means limited to this material and can be applied to any suitable combination of abrasive and matrix materials. Possible abrasive materials include but are not limited to SiC, TaC, VC, B4C, Si3N4, AlN, Al2O3, ZrO2, zirconia toughened alumina (ZTA), etc...

[0051] In the research, HVOF has been used to spray premixed Inconel 718 / cBN feedstock, which was either centrally injected in a gas-dynamic HVOF or through the injection ports of a liquid-fuel HVOF system [K. Shivalingaiah, “HVOFsprayed Inconel 718 / cubic boron nitride composite coatings: microstructure,microhardness and slurry erosive behaviour” in Mater. Res. Express 6 (2019)1265i8]. In that research, the feedstock material used was smaller cBN grains smaller than 10 µm in size, which were typically alloyed with the matrix powder through a ball-milling process. As such, the abrasive grains were not large and, due to their small size, did not protrude beyond the sprayed coating through the process.

[0052] Luo and Li used the cold-spray method to prepare samples of cBN / NiCrAl nanocomposite coatings for their research [X-T Luo, and C-J. Li, “Thermal Stability of Microstructure and Hardness ofCold-Sprayed cBN / NiCrAl Nanocomposite Coating” JTST, Vol. 21, pp. 578-585(2012)]. However, nanostructured composites are not suitable for high-temperature applications, and the fine abrasive particles do not provide optimal cutting behaviour. Additionally, cold spraying is not suitable for superalloys that do not have sufficient ductility.

[0053] The present invention proposes the use of larger particles 19 of 50 µm to 250 µm, which are fed separately from the matrix and injected outside the spray gun 13 ( Figure 1 ).

[0054] This procedure has advantages over standard HVOF spraying: the larger cBN particle size provides a more efficient wear (cutting) process. Additionally, the heat-induced degradation of the abrasive 19 is significantly reduced. Another advantage is the customization of the coating structure itself to suit the requirements ( Figures 2 to 4 ).

[0055] The bonding (buffer) layer can be sprayed using only the matrix material, and subsequently the graded structure or even the cBN layer can be sprayed on the matrix according to the separation of the two materials in the powder jet. Overall, the coatings provided by liquid fuel HVOF have compressive stress, which is beneficial to suppressing the cracking tendency of the base alloy. Compared with the LPW process, the low heat input and compressive stress in the present disclosure are particularly beneficial to components made of polycrystalline base alloys.

Claims

1. A method for producing a metallic coating (7, 7', 7'', 7''') having secondary particles (19), in particular abrading ceramic particles (19), wherein, The secondary particles (19) are ejected from the outside into the spray (10) of the HVOF gun (13) using a separate supply device (16).

2. The method according to claim 1, wherein, The secondary particles (19) are applied at a distance (22) that is 50% to 75% of the distance from the gun (13) to the substrate (4).

3. The method according to any one of claims 1 or 2, wherein cBN, SiC, TaC, VC, B4C, Si3N4, AlN, Al2O3, ZrO2, zirconia toughened alumina (ZTA), or a mixture thereof are used for the secondary particles (19).

4. The method according to any one of claims 1, 2, or 3, wherein The particle size of the secondary particles (19) is between 50 µm and 250 µm.

5. The method according to any one of claims 1, 2, 3 or 4, wherein A buffer layer without the secondary particles (19) is applied on the substrate (4).

6. The method according to any one of claims 1, 2, 3, 4 or 5, wherein A graded structure of the abrasive particles (19) is generated.

7. The method according to any one of claims 1, 2, 3, 4, 5 or 6, wherein The particles (19) protrude from the outer surface (28) of the coating (7, 7', 7'', 7'''), in particular by increasing the supply of the abrasive particles (19) by the supply device (16).

8. A tool (1) for performing the method according to any one of claims 1, 2, 3, 4, 5, 6, or 7, comprising an HVOF gun (13), a separate supply device (16) for the secondary particles (19) outside the region of the spray (10), the supply device (16) being attached in particular to the gun (13).

9. The tool according to claim 8, wherein The length of the supply device (16) is adjustable.

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