Thermal spray powder

Abstract

Thermal spray powder, which is used to form a thermal spray layer with a friction characteristic, the thermal spray powder includes Ni alloy particles, solid lubricant particles and aluminium flakes, The oxygen content in the aluminum flakes ranges from 0.29% by mass to 4.1% by mass, and The coverage of the aluminium flakes on the surfaces of the Ni alloy particles is in a range of 60% to 100%, characterized by the fact that the mean thickness of the aluminium flakes is in a range of 0.1 µm to 2 µm and the mean particle size of the aluminium flakes is in a range of 10 µm to 100 µm, where the mean particle size of the aluminium flakes refers to the mean particle size of the aluminium flakes in a planar direction perpendicular to the thickness direction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a thermal spray powder or spray powder which is suitable for forming a thermal spray layer or spray layer having a characteristic of friability or friability. 2. Description of the state of the art

[0002] For example, the prior art knows a thermal spray coating with a characteristic of friability, which can protect various objects through self-wear (hereinafter abbreviated as "thermal spray coating"), for use in components such as gas turbines and jet engines. Furthermore, in recent years, a thermal spray coating has been developed to adjust the gap between a turbine housing on the exhaust side and a turbine wheel to improve turbocharger efficiency. The thermal spray coating is formed by thermal spraying or spraying a thermal spray powder using a material selected according to the required characteristics.

[0003] Thermal spray coatings require characteristics such as favorable machinability, allowing the coating to be easily cut through another object, for example, erosion resistance to minimize erosion caused by high-velocity gas flow, and oxidation resistance. To achieve favorable machinability among these characteristics, a process in which solid lubricant particles are blended with a thermal spray powder is used, for example, and the machinability of a thermal spray coating is thereby improved.

[0004] Regarding such thermal spray powders, for example, US Pat. No. 7,052,527 B2 describes a thermal spray powder containing solid lubricant particles such as hexagonal boron nitride (h-BN) in addition to metal particles such as a Ni alloy, and thereby capable of forming a thermal spray coating having favorable machinability, erosion resistance, oxidation resistance, and the like, and is suitable for use in gas turbines and the like. Furthermore, JP 2007-247063 A describes a thermal spray powder containing metal particles such as a Ni-Cr alloy and solid lubricant particles such as boron nitride (BN), capable of forming a spray coating having abrasion resistance.Furthermore, JP 2017-179542 A describes a thermal spray powder containing Ni-Cr alloy particles and synthetic mica particles, which can thus form a thermal spray coating that can reduce adhesive wear on another object. Furthermore, DE 102018 107 412 A1 and US 3,655,425 A describe prior art spray powders and spray coatings, respectively. SUMMARY OF THE INVENTION

[0005] However, after using the thermal spray coatings formed by thermal spraying the thermal spray powders described in US Pat. No. 7,052,057 B2, JP 2007-247063 A, and JP 2017-179542 A in a high-temperature environment, such as in a turbocharger, the metal atoms diffuse between the metal particles, and sintering occurs. Consequently, machinability is reduced. Therefore, in some cases, sufficient machinability cannot be ensured after use in a high-temperature environment.

[0006] The present invention has been made in view of the above circumstances, and the present invention provides a thermal spray powder for forming a thermal spray layer which ensures sufficient machinability after use in a high temperature environment.

[0007] In order to address the above problems, the thermal spray powder according to the present invention is a thermal spray powder which can form a thermal spray layer having a characteristic of friability, and the thermal spray powder includes Ni alloy particles, solid lubricant particles and aluminum flakes, wherein the content of oxygen in the aluminum flakes is in a range of 0.29 mass% to 4.1 mass%, and the coverage ratio isthe covering power of the aluminum flakes on the surfaces of the Ni alloy particles is in a range of 60% to 100%, characterized in that the average thickness of the aluminum flakes is in a range of 0.1 µm to 2 µm and the average particle size of the aluminum flakes is in a range of 10 µm to 100 µm, wherein the average particle size of the aluminum flakes refers to the average particle size of the aluminum flakes in a planar direction perpendicular to the thickness direction.

[0008] According to the present invention, the formation of a thermal spray layer which ensures sufficient machinability after use in a high temperature environment is possible. SHORT DESCRIPTION OF THE DRAWING

[0009] Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings in which like numerals designate like elements, wherein: Fig. 1A is a schematic diagram showing examples of a thermal spray powder of the present embodiment, and Fig. 1B is a cross-sectional view schematically showing a thermal spray layer formed by thermal spraying of the Fig. 1A was formed onto a surface of a substrate; Fig. 2A is a schematic diagram showing first examples of a prior art thermal spray powder, and Fig. Figure 2B is a cross-sectional view schematically showing a thermal spray layer formed by thermal spraying the Fig.2A was formed onto a surface of a substrate; Fig. 3A is a schematic diagram showing second examples of a prior art thermal spray powder, and Fig. 3B is a cross-sectional view schematically showing a thermal spray layer formed by thermal spraying the Fig. 3A is formed onto a surface of a substrate; Fig. 4 is a schematic diagram showing the peel strength after using a thermal spray coating in a high temperature environment versus the peel strength before using a thermal spray coating. Fig. 5A shows a photograph obtained by observing the aluminum flakes contained in an aluminum powder in an example under a scanning electron microscope (SEM), and Fig.5B shows a photograph obtained by observing the aluminum particles contained in an aluminum powder of a comparative example under an SEM; Fig. 6A shows a photograph obtained by observing a thermal spray powder in Example 2-3 under an SEM, and Fig. 6B shows a photograph obtained by observing a thermal spray powder in Comparative Example 4 under an SEM. Fig. 7A is a photograph showing an oxygen distribution in the cross section of a thermal spray coating of Example 2-3 analyzed by ESMA (electron beam microanalysis), and Fig. 7B is a photograph showing an oxygen distribution in the cross section of a thermal spray layer of Comparative Example 4 analyzed by ESMA. Fig. Figure 8A shows a photograph of an automatic adhesion tester (Elcometer510) used in a peel test, and Fig. 8B shows a photo of one of the Fig. 8A using the automatic adhesion tester (Elcometer510); and Fig. 9 is a graph showing the peel strength before and after heat treatment on the thermal spray layers of the thermal spray test pieces produced in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] The embodiments of the thermal spray powders of the present invention (hereinafter abbreviated as "the present embodiment") are described below.

[0011] The thermal spray powder of the present embodiment is a thermal spray powder for forming a thermal spray layer with a characteristic of friability. The thermal spray powder includes Ni alloy particles, solid lubricant particles, and aluminum flakes, wherein the oxygen content in the aluminum flakes is in a range of 0.29 mass% to 4.1 mass%, and the coverage ratio of the aluminum flakes on the surfaces of the Ni alloy particles is in a range of 60% to 100%. The thermal spray powder is characterized in that the average thickness of the aluminum flakes is in a range of 0.1 μm to 2 μm, and the average particle size of the aluminum flakes is in a range of 10 μm to 100 μm, wherein the average particle size of the aluminum flakes refers to the average particle size of the aluminum flakes in a planar direction perpendicular to the thickness direction.

[0012] First, a design of the thermal spray powder of the present embodiment will be described with reference to the drawing. Fig. 1A is a schematic diagram showing examples of the thermal spray powder of the present embodiment, and Fig. Figure 1B is a cross-sectional view schematically showing a thermal sprayed film of the Fig. 1A shows a thermal spray layer formed on a surface of a substrate.

[0013] As in Fig.As shown in FIG. 1A, a thermal spray powder 1 of an example of the present embodiment includes Ni alloy particles 4, solid lubricant particles 6, and aluminum flakes 8, and is a granular powder including a large number of granular particles 2 in which solid lubricant particles 6 and aluminum flakes 8 are adhered to the surfaces 4a of the Ni alloy particles 4 by means of a resin binder (not shown). The Ni alloy particles 4 are, for example, particles made of a Ni-Cr-Fe alloy, and the solid lubricant particles 6 are, for example, solid lubricant particles containing hexagonal boron nitride (h-BN) and the like. Some of the aluminum flakes 8 are oxidized, and the oxygen content is in a range from 0.29 mass% to 4.1 mass%.Since the aluminum flakes 8 have the shape of flakes, the coverage of the aluminum flakes 8 on the surfaces 4a of the Ni alloy particles 4 increases to a range of 60% to 100%.

[0014] Therefore, as in Fig.1B, in a thermal spray layer 60 formed by thermally spraying the thermal spray powder 1 onto a surface of a substrate 50, in most portions where Ni alloy particles 4 are bonded together, the Ni alloy particles 4 are fused or melted by the aluminum flakes 8. At this time, solid lubricant particles 6 are filled in gaps 60a between Ni alloy particles 4. Since aluminum has high wettability to both Ni alloy particles 4 and solid lubricant particles 6, the separation of the Ni alloy particles 4 and the solid lubricant particles 6 during layer formation is limited by the aluminum flakes 8. Consequently, the solid lubricant particles 6 are likely to remain in the gaps 60a.

[0015] On the other hand, Fig. 2A is a schematic diagram showing first examples of a prior art thermal spray powder. Fig. Figure 2B is a cross-sectional view schematically showing a thermal sprayed film of the Fig. 2A shows a thermal spray layer formed on a surface of a substrate using the thermal spray powder shown. Fig. 3A is a schematic diagram showing second examples of a prior art thermal spray powder. Fig. Figure 3B is a cross-sectional view schematically showing a thermal sprayed film of the Fig. 3A shows a thermal spray layer formed on a surface of a substrate using the thermal spray powder shown. Fig. 4 is a diagram schematically showing the peel strength after using a thermal spray coating in a high temperature environment compared to the peel strength before using a thermal spray coating.

[0016] As in Fig.As shown in FIG. 2A, a thermal spray powder 11 of the first prior art example includes Ni alloy particles 4 and solid lubricant particles 6, and is a granular powder including a large number of granular particles 12 in which solid lubricant particles 6 are adhered to the surfaces 4a of the Ni alloy particles 4 by means of a resin binder (not shown). The Ni alloy particles 4 and the solid lubricant particles 6 are the same as in the example of the present embodiment.

[0017] Therefore, as in Fig.2B, in a thermal spray layer 70 formed by thermally spraying the thermal spray powder 11 onto a surface of the substrate 50, the Ni alloy particles 4 are directly fused together in all the portions where the Ni alloy particles 4 are bonded together. Therefore, when the thermal spray layer 70 is used in a high-temperature environment, metal atoms diffuse between the Ni alloy particles 4 in all the bonding portions, and sintering occurs, thereby increasing the bonding strengths between the Ni alloy particles 4. Therefore, as shown by a dot-dashed line in the diagram in Fig.4, the peel strength before use of the thermal spray layer 70 is 3 MPa or more, which is a lower limit at which it is possible to ensure erosion resistance, minimizing erosion caused by, for example, a high-speed gas flow, for example, in a turbocharger. However, after use of the thermal spray layer 70 in a high-temperature environment, it exceeds 8 MPa, which is an upper limit at which it is possible to ensure sufficient machinability, for example, in a turbocharger. At this time, solid lubricant particles 6 are filled in gaps 70a between the Ni alloy particles 4.

[0018] As in Fig.As shown in Fig. 3A, a thermal spray powder 21 of a second prior art example includes Ni alloy particles 4, solid lubricant particles 6, and aluminum particles 28, and is a granular powder including a large number of granular particles 22 in which solid lubricant particles 6 and aluminum particles 28 are adhered to the surfaces 4a of the Ni alloy particles 4 by means of a resin binder (not shown). The Ni alloy particles 4 and the solid lubricant particles 6 are the same particles as in the example of the present embodiment. Although some of the aluminum particles 28 are oxidized, they have a granular shape, unlike the aluminum flakes 8 in the example of the present embodiment.Therefore, the coverage ratio of the aluminum particles 28 on the surfaces 4a of the Ni alloy particles 4 is 20%, which is lower than the coverage ratio of the aluminum flakes 8 on the surfaces of the Ni alloy particles 4 in the example of the present embodiment.

[0019] Therefore, as in Fig. As shown in Fig. 3B, in a thermal spray layer 80 formed by thermally spraying the thermal spray powder 21 onto a surface of a substrate 50, in most portions in which Ni alloy particles 4 are bonded together, while aluminum particles 28 are interposed between Ni alloy particles 4, the Ni alloy particles 4 are directly fused together. Therefore, when the thermal spray layer 80 is used in a high-temperature environment, there is almost no difference from the thermal spray layer 80 shown in Fig. Fig.2B, metal atoms diffuse between the Ni alloy particles 4 in most of the bonding portions, and sintering takes place, and thereby the bonding strength between the Ni alloy particles 4 increases. Consequently, as shown by the two-dot dashed line in the diagram in Fig. 4, the peel strength before use of the thermal spray coating 80 is 3 MPa or more, then the peel strength after use of the thermal spray coating 80 in a high-temperature environment exceeds 8 MPa. At this time, the solid lubricant particles 6 are filled in gaps 80a between the Ni alloy particles 4, and the aluminum particles 28 facilitate the solid lubricant particles 6 to remain in the gaps 80a.

[0020] On the other hand, in the thermal spray layer 60 according to the example of the embodiment, unlike the two prior art examples, in most portions where the Ni alloy particles 4 are bonded together, the Ni alloy particles 4 are fused together by means of the aluminum flakes 8. Therefore, when the thermal spray layer 60 is used in a high-temperature environment, the oxygen contained in the aluminum flakes 8 restricts the diffusion of the metal atoms between the Ni alloy particles 4 in most bonding portions, and the progress of sintering can be slowed down. Therefore, it is possible to minimize an increase in the bonding strength between the Ni alloy particles 4. Consequently, as shown by the solid line in the diagram in Fig.As stated in Figure 4, even if the peel strength before use of the thermal spray layer 60 is 3 MPa or more, the peel strength after use of the thermal spray layer 60 in a high-temperature environment should be 8 MPa or less. Therefore, sufficient machinability can be ensured in the thermal spray layer 60 after use in a high-temperature environment, for example, in a turbocharger.

[0021] As in the example of the present embodiment, the thermal spray powder of the present embodiment includes Ni alloy particles, solid lubricant particles, and aluminum flakes, wherein the oxygen content of the aluminum flakes is in a range of 0.29 mass% to 4.1 mass%, and the coverage ratio of the aluminum flakes on the surfaces of the Ni alloy particles is in a range of 60% to 100%. Therefore, in a thermal spray layer formed by thermal spraying the thermal spray powder of the present embodiment, in most portions where Ni alloy particles are bonded together, the Ni alloy particles are fused together by the aluminum flakes.Therefore, when the thermal spray coating is used in a high-temperature environment, the oxygen contained in the aluminum flakes 8 restricts the diffusion of metal atoms between the Ni alloy particles in most of the bonding portions, and the progress of sintering can be slowed down. Therefore, according to the present embodiment, it is possible to form a thermal spray coating that ensures sufficient machinability after use in a high-temperature environment, for example, in a turbocharger.

[0022] Next, the configuration of the thermal spray powder according to the present embodiment will be described in detail. 1. Aluminum flakes

[0023] Aluminum flakes are flaky aluminum which is partially oxidized, and the oxygen content is in a range of 0.29 mass% to 4.1 mass%.

[0024] The shape of the aluminum flakes is not particularly limited, as long as it is flake-like, so the coverage ratio of the aluminum flakes on the surfaces of the Ni alloy particles can be in a range of 60% to 100% by adjusting the contents of Ni alloy particles, solid lubricant particles, and aluminum flakes in the thermal spray powder within a desired range. The aluminum flakes have a shape with an average thickness in a range of 0.1 μm to 2 μm and an average particle size in a range of 10 μm to 100 μm, with a shape with an average thickness in a range of 0.3 μm to 1 μm and an average particle size in a range of 20 μm to 50 μm being preferable.

[0025] The "average thickness of aluminum flakes" refers to the thickness of an aluminum foil, for example, when aluminum flakes are produced by pulverizing aluminum foil. Furthermore, the "average particle size of aluminum flakes" refers to the average particle size of the aluminum flakes in a planar direction perpendicular to the thickness direction, and refers, for example, to a mean particle size of 50% (D50) of the equivalent circular diameter obtained from the area of ​​the plane perpendicular to the thickness direction of the aluminum flakes. Furthermore, the average thickness and average particle size of the aluminum flakes can be measured using, for example, a scanning electron microscope (SEM).

[0026] The average particle size of the aluminum flakes can be adjusted according to the pulverization conditions. For example, aluminum flakes are produced by pulverizing aluminum foil. Furthermore, if aluminum flakes are produced by pulverizing aluminum foil, the thickness of the aluminum flakes can be adjusted by the thickness of the aluminum foil.

[0027] The oxygen content in the aluminum flakes is not particularly limited, as long as it is within the upper range, and is preferably in a range of 0.29 mass% to 1 mass%. This serves to ensure the erosion resistance of the thermal spray coating upon initial use, for example, in a turbocharger.

[0028] The oxygen content in aluminum flakes can be measured using an oxygen-nitrogen analyzer.

[0029] An aluminum flake manufacturing method is not particularly limited, and a general method can be used, examples of which include a manufacturing method in which an aluminum foil is pulverized by the use of a ball mill or the like.

[0030] Regarding a method of adjusting the oxygen content in the aluminum flakes, for example, a method in which the oxygen content is adjusted by controlling a pulverization time in a process for producing aluminum flakes by pulverizing an aluminum foil can be exemplified. 2. Ni alloy particles

[0031] Ni alloy particles are particles made of a Ni alloy.

[0032] The Ni alloy is not particularly limited, and examples thereof include Ni-Cr alloy, Ni-Al alloy, Ni-Cr-Fe alloy, and Ni-Cr-Al alloy.

[0033] The Ni-Cr alloy is not particularly limited, and preferred is a Ni-Cr alloy with a Cr content in a range of 20 mass% to 50 mass%. This serves to improve the oxidation resistance of the Ni alloy particles. The Ni-Al alloy is not particularly limited, and preferred is a Ni-Al alloy with an Al content in a range of 4 mass% to 20 mass%. The Ni-Cr-Fe alloy is not particularly limited, and preferred is a Ni-Cr-Fe alloy with a Cr content in a range of 14 mass% to 18 mass% and an Fe content in a range of 7 mass% to 10 mass%. The Ni-Cr-Al alloy is not particularly limited, and preferred is a Ni-Cr-Al alloy with a Cr content in a range of 18 mass% to 22 mass% and an Al content in a range of 6 mass% to 10 mass%. The Ni content in such a Ni alloy can be expressed as the balance, exclusive, or total content.without Cr, Al and Fe.

[0034] The particle size of the Ni alloy particles is not particularly limited and is, for example, preferably in a range of 38 µm to 150 µm and more preferably in a range of 45 µm to 125 µm.

[0035] Here, “the particle size” refers to a particle size measured by using a laser diffraction particle size distribution measuring device, and such a particle size can be obtained by classification according to, for example, JISZ2510. 3. Solid lubricant particles

[0036] The solid lubricant particles are not particularly limited, and examples thereof include those containing one or two or more selected from hexagonal boron nitride (h-BN), graphite (C), resins such as polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2), tungsten disulfide (WS2), and the like. Preferred are those containing one or two or more selected from hexagonal boron nitride, graphite, and resins such as polytetrafluoroethylene. This is because they have high lubricity.

[0037] The particle size of the solid lubricant particles is not particularly limited and is preferably smaller than that of the Ni alloy particles. This serves to completely cover the Ni alloy particle surfaces with solid lubricant particles. The particle size of the solid lubricant particles is preferably, for example, in a range of 3 µm to 30 µm, and particularly preferably in a range of 3 µm to 10 µm. This serves to completely and uniformly cover the Ni alloy particle surfaces with solid lubricant particles with the content described below. 4. Thermal spray powder

[0038] The thermal spray powder is a thermal spray powder for forming a thermal spray layer with a characteristic of friability and includes Ni alloy particles, solid lubricant particles and aluminum flakes, and the coverage ratio of the aluminum flakes on the surfaces of the Ni alloy particles is in a range of 60% to 100%.

[0039] Here, "the coverage of aluminum flakes on the surfaces of the Ni alloy particles" refers to the ratio of the area of ​​the region covered by aluminum flakes on the Ni alloy particle surfaces (expressed as a percentage). The coverage of aluminum flakes on the surfaces of the Ni alloy particles can be measured, for example, using a scanning electron microscope (SEM).

[0040] The coverage ratio of the aluminum flakes on the surfaces of the Ni alloy particles is not particularly limited as long as it is within the upper range, and preferably within a range of 60% to 80%. When the coverage ratio is within the lower limit of the range or more, it is easy to slow down the progress of sintering while maintaining a high temperature. When the coverage ratio is within the upper limit of the range or less, it is easy to ensure the required strength for a thermal spray coating.

[0041] The content of aluminum flakes in the thermal spray powder is not particularly limited and is preferably in a range of, for example, 3 mass% to 5 mass%. Since aluminum has high wettability compared to Ni alloy particles and solid lubricant particles containing, for example, hexagonal boron nitride, if the thermal spray powder contains aluminum flakes in such a range, it is possible to restrict the separation of the Ni alloy particles and the solid lubricant particles during film formation. Meanwhile, if the aluminum flake content is too low, it is not possible to expect a sufficient wettability effect of the Ni alloy particles and the solid lubricant particles according to the aluminum flakes in the thermal spray layer. On the other hand, if the aluminum flake content is too high, the machinability in the thermal spray layer will deteriorate.

[0042] The content of solid lubricant particles in the thermal spray powder is not particularly limited and is preferably in a range of, for example, 4% to 8% by mass. This serves to reduce the adhesive wear of the thermal spray layer and further improve the friability characteristics. On the other hand, if the content of solid lubricant particles is too low, sufficient lubricity cannot be exerted, and adhesive wear of the thermal spray layer is likely to occur. In addition, since fewer solid lubricant particles are interposed between the Ni alloy particles of the thermal spray layer, the number of metal bonds between the Ni alloy particles increases. Therefore, the hardness of the thermal spray layer increases, and the machinability of the thermal spray layer deteriorates.On the other hand, if the content of solid lubricant particles is too high, the thermal spray layer becomes brittle due to an increase in solid lubricant particles.

[0043] The content of Ni alloy particles in the thermal spray powder can be considered as the residual content, excluding solid lubricant particles and aluminum flakes. The contents of Ni alloy particles, solid lubricant particles, and aluminum flakes in the thermal spray powder are calculated without taking into account the binder content, which is added as a resin binder during granulation of the thermal spray coating.

[0044] A method for producing a thermal spray powder is not particularly limited, and examples thereof include a production method in which an alloy powder containing Ni alloy particles, a solid lubricant powder containing solid lubricant particles, and an aluminum powder containing aluminum flakes are mixed together, and the solid lubricant particles and the aluminum flakes are adhered to the surfaces of the Ni alloy particles by means of a binder such as a resin binder for granulation. Incidentally, when the thermal spray powder is thermally sprayed, the thermal spray powder may be a powder in which Ni alloy particles, solid lubricant particles, and aluminum flakes are mixed, insofar as the Ni alloy particles and the solid lubricant particles and the uniformly mixed aluminum flakes can be thermally sprayed. Furthermore, the thermal spray powder may be coated according to a coating method.a cladding process or similar. 5. Further

[0045] A thermal spraying method for a thermal spray powder is not particularly limited insofar as a thermal spray layer can be formed, and examples thereof include a gas flame thermal spray method and a plasma thermal spray method. A gas flame thermal spray method is particularly preferable. Compared with other thermal spray methods, such as a plasma thermal spray method, it allows the thermal spray powder to be thermally sprayed at a low temperature. Therefore, because more solid lubricant particles can be inserted between the Ni alloy particles during thermal spray layer formation, the number of metal bonds between the Ni alloy particles can be reduced, and the machinability of the thermal spray layer can be improved.

[0046] The thermal spray powder according to the present embodiment will be described in more detail below with reference to examples and comparative examples. [Example 1-1]

[0047] A Ni alloy powder (gas-atomized powder) including Ni alloy particles made of a Ni-Cr-Fe alloy containing 77 mass% Ni, 15 mass% Cr, and 8 mass% Fe, with a particle size ranging from 45 µm to 125 µm, was prepared. Next, a solid lubricant material including hexagonal boron nitride (h-BN)-containing solid lubricant particles with a particle size ranging from 3 µm to 10 µm was prepared.

[0048] Next, an aluminum powder was prepared including aluminum flakes with an average thickness of 0.5 µm, an average particle size of 30 µm, and an oxygen content of 0.29 mass%. Specifically, an aluminum foil (commercially available from Minalco Co., Ltd.) was pulverized for 10 minutes using a ball mill to prepare an aluminum powder. Fig. 5A is a photograph obtained by observing the aluminum flakes contained in an aluminum powder in an example under a scanning electron microscope (SEM).

[0049] Next, the Ni alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 3 mass%, and the NiCr alloy powder: the rest, and the solid lubricant particles and the aluminum flakes were adhered to the surfaces of the Ni alloy particles by means of a resin binder, and a thermal spray powder was produced by granulation.

[0050] Next, the thermal spray powder was thermally sprayed onto a substrate surface, thereby producing a thermal spray test piece on which a thermal spray layer with a layer thickness of 0.8 mm was formed. Specifically, the thermal spray powder was thermally sprayed onto a substrate surface with a width of 50 mm, a length of 50 mm, and a thickness of 5 mm (nickel alloy (Inconel 600)) using a gas flame thermal spray device (commercially available from Oerlikon Metco 6P-II), thereby forming a thermal spray layer. The gas pressure of the gases supplied to the thermal spray gun was oxygen gas: 42 psi, hydrogen gas (fuel gas): 34 psi and air: 60 psi, and the gas flow rates of the supply gases were oxygen gas: 461 slpm, hydrogen gas: 149 slpm and air: 110 slpm.A feed amount of the thermal spray powder supplied to the thermal spray gun during film formation was 90 g / min, a distance between the tip of the thermal spray gun and the substrate was 230 mm, the moving speed of the thermal spray gun was 30 m / min, and the pitch was 6 mm. [Example 1-2]

[0051] First, a thermal spray powder was prepared in the same manner as in Example 1-1 except that an aluminum foil was pulverized for 20 minutes to prepare an aluminum powder enclosing aluminum flakes with an oxygen content of 0.94 mass%.

[0052] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 1-3]

[0053] First, a thermal spray powder was prepared in the same manner as in Example 1-1 except that an aluminum foil was pulverized for 50 minutes to prepare an aluminum powder enclosing aluminum flakes with an oxygen content of 4.1 mass%.

[0054] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison example 1]

[0055] First, a thermal spray powder was prepared in the same manner as in Example 1-1 except that an aluminum foil was pulverized for 160 minutes to prepare an aluminum powder including aluminum flakes with an oxygen content of 5.0 mass%.

[0056] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 2-1]

[0057] First, a thermal spray powder was prepared in the same manner as in Example 1-1, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 4 mass%, and the NiCr alloy powder: the remainder.

[0058] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 2-2]

[0059] First, a thermal spray powder was prepared in the same manner as in Example 1-2, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 4 mass%, and the NiCr alloy powder: the remainder.

[0060] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 2-3]

[0061] First, a thermal spray powder was prepared in the same manner as in Example 1-3, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 4 mass%, and the NiCr alloy powder: the remainder.

[0062] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison example 2]

[0063] First, a thermal spray powder was prepared in the same manner as in Comparative Example 1, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 4 mass%, and the NiCr alloy powder: the remainder.

[0064] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 3-1]

[0065] First, a thermal spray powder was prepared in the same manner as in Example 1-1, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 5 mass%, and the NiCr alloy powder: the remainder.

[0066] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 3-2]

[0067] First, a thermal spray powder was prepared in the same manner as in Example 1-2, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 5 mass%, and the NiCr alloy powder: the remainder.

[0068] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Example 3-3]

[0069] First, a thermal spray powder was prepared in the same manner as in Example 1-3, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 5 mass%, and the NiCr alloy powder: the remainder.

[0070] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison example 3]

[0071] First, a thermal spray powder was prepared in the same manner as in Comparative Example 1, except that the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material: 4.5 mass%, the aluminum powder: 5 mass%, and the NiCr alloy powder: the remainder.

[0072] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison example 4]

[0073] First, a thermal spray powder was prepared in the same manner as in Example 1-1, except that aluminum powder (#600F, commercially available from Minalco Co., Ltd.) including aluminum particles with a particle size in the range of 5 μm to 7 μm with an oxygen content of 0.37 mass% was prepared, and the NiCr alloy powder, the solid lubricant material, and the aluminum powder were mixed such that the solid lubricant material accounted for 4.5 mass%, the aluminum powder for 4 mass%, and the NiCr alloy powder for the remainder. The particle size of the aluminum particles indicates an equivalent spherical diameter. Fig. 5B is a photograph obtained by observing the aluminum particles contained in the aluminum powder in the comparative example under an SEM.

[0074] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison Example 5]

[0075] First, a thermal spray powder was prepared in the same manner as in Comparative Example 4 except that the aluminum powder prepared in Comparative Example 4 was heated to prepare an aluminum powder including aluminum particles having an oxygen content of 0.89 mass%.

[0076] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison example 6]

[0077] First, a thermal spray powder was prepared in the same manner as in Comparative Example 4 except that the aluminum powder prepared in Comparative Example 4 was heated to prepare an aluminum powder including aluminum particles having an oxygen content of 3.8 mass%.

[0078] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. [Comparison Example 7]

[0079] First, a thermal spray powder was prepared in the same manner as in Comparative Example 4 except that the aluminum powder prepared in Comparative Example 4 was heated to prepare an aluminum powder including aluminum particles having an oxygen content of 4.9 mass%.

[0080] Next, in the same manner as in Example 1-1, a thermal spray test piece in which a thermal spray layer was formed by thermally spraying the thermal spray powder onto a surface of a substrate was prepared. <Betrachtung des thermischen Spritzpulvers unter einem REM>

[0081] The thermal spray powders produced in the examples and comparative examples were observed under an SEM. Fig. Figure 6A shows a photograph obtained by observing the thermal spray powder of Example 2-3 under an SEM, and Fig. 6B shows a photograph obtained by observing the thermal spray powder of Comparative Example 4 under an SEM.

[0082] As in Fig. 6A and Fig.6B, the coverage of the aluminum flakes on the surfaces of the Ni alloy particles contained in the thermal spray powder of Example 2-3 was larger than the coverage of the aluminum particles on the surfaces of the Ni alloy particles contained in the thermal spray powder of Comparative Example 4. < Degree of coverage of aluminum on the surfaces of the Ni alloy particles >

[0083] Regarding the thermal spray powders produced in the examples and comparative examples, the coverage of aluminum (aluminum flakes or aluminum particles) on the surfaces of the Ni alloy particles was measured. Specifically, the thermal spray powder was observed under an SEM, image processing was performed, and the coverage was measured. The measurement results are shown in Table 1 below, along with the type of aluminum powder blended with the thermal spray powder, the aluminum content in the thermal spray powder, and the oxygen content in the aluminum. Table 1 Type of aluminum powder Aluminum content in thermal spray powder [mass%] Oxygen content in aluminum [mass%] Degree of aluminum coverage on the surface of the Ni alloy particles [%] Example 1-1 aluminum flakes 3 0,29 60 Example 1-2 aluminum flakes 3 0,94 60 Examples 1-3 aluminum flakes 3 4,1 60 Comparison example 1 aluminum flakes 3 5,0 60 Example 2-1 aluminum flakes 4 0,29 80 Example 2-2 aluminum flakes 4 0,94 80 Example 2-3 aluminum flakes 4 4,1 80 Comparison example 2 aluminum flakes 4 5,0 80 Example 3-1 aluminum flakes 5 0,29 100 Example 3-2 aluminum flakes 5 0,94 100 Example 3-3 aluminum flakes 5 4,1 100 Comparison example 3 aluminum flakes 5 5,0 100 Comparison example 4 aluminum particles 4 0,37 20 Comparison example 5 aluminum particles 4 0,89 20 Comparison example 6 aluminum particles 4 3,8 20 Comparison example 7 aluminum particles 4 4,9 20

[0084] As shown in Table 1, in the examples where aluminum flakes were used as the aluminum powder blended with the thermal spray powder, the aluminum coverage ratio was higher as the aluminum content was higher. Specifically, when aluminum was contained in the thermal spray powder in a range of 3 mass% to 5 mass%, the aluminum coverage ratio was in a range of 60% to 100%. Furthermore, although the aluminum content was 4 mass% in Examples 2-1 to 2-3 using aluminum flakes and Comparative Examples 4 to 7 using aluminum particles, the aluminum coverage ratio in Examples 2-1 to 2-3 was significantly higher than that in Comparative Examples 4 to 7. < Oxygen distribution in cross-sections of thermal spray coatings>

[0085] The oxygen distributions in the cross sections of the thermal spray coatings of the thermal spray test pieces produced in the examples and the comparative examples were analyzed by ESMA. Fig. 7A is a photograph showing an oxygen distribution in the cross section of the thermal spray layer of Example 2-3 analyzed by ESMA, and Fig. 7B is a photograph showing an oxygen distribution in the cross section of the thermal spray layer of Comparative Example 4 analyzed by ESMA.

[0086] As in Fig. 7A and Fig. As shown in Figure 7B, the oxygen content present on the surface of the Ni alloy particles in the cross section of the thermal spray layer of Example 2-3 is larger than that in the cross section of the thermal spray layer of Comparative Example 4. <Abziehfestigkeit der thermischen Spritzschicht>

[0087] The thermal spray coatings of the thermal spray test pieces produced in the examples and comparative examples were subjected to a peel test in which the peel strength was evaluated before and after a heat treatment in which the thermal spray test piece was placed in an atmospheric furnace at 850 °C for 200 hours. Fig. 8A is a photograph of an automatic adhesion tester (Elcometer510) used in a peel test, and Fig. Figure 8B shows a photograph of a pull test procedure, which Fig. The automatic adhesion tester shown in Figure 8A was used.

[0088] In the pull-off test, shot blasting was first performed on the adhesive surface of a 20 mm diameter punch. 0.050 g to 0.060 g of a two-component epoxy resin adhesive (Araldite (registered trademark) Standard) was then applied to the adhesive surface of the punch. The adhesive surface of the punch was adhered to the thermal spray coating of the thermal spray test piece and cured by standing at room temperature for 24 hours. Next, a connecting coupling and a quick-connect coupling of the tester were lifted or pulled up, respectively, and the test head was attached to the punch. Then, the connecting coupling was released and the punch was fitted. Next, the tester was turned on, and the punch diameter, measuring unit, and pull-off speed were set to 20 mm, MPa, and 0.20 MPa / s, respectively.Then the tester’s start button was pressed to start the test.

[0089] After starting the test, the pressure and peeling position during the peeling of the punch from the thermal spray layer were recorded in the tester as the pressure increased at the set peeling speed until the punch was peeled off the thermal spray layer. The peeling test was performed on two or more sections before and after heat treatment of the thermal spray layer of each thermal spray test piece. The pressure and peeling position (at the interface between the substrate and the thermal spray layer, within the thermal spray layer, and on the adhesive surface) during the peeling of the punch from the thermal spray layer were recorded for the sections in the peeling test. The average of the pressures during the peeling of the punch from the thermal spray layer in the peeling test for the sections was obtained as the peel strength of the thermal spray layer.

[0090] Fig.9 is a graph showing the peel strength before and after heat treatment on the thermal spray coatings of the thermal spray test pieces formed in the examples and the comparative examples.

[0091] As in Fig.As shown in Figure 9, in the thermal spray coatings of Comparative Examples in which aluminum particles were used as aluminum powder, the peel strength after heat treatment was significantly higher than that before heat treatment, and none of the peel strengths before and after heat treatment were within a range of 3 MPa to 8 MPa. The presumable reason for this is described below. First, in these thermal spray coatings, while aluminum particles were interposed between the Ni alloy particles, the Ni alloy particles were directly fused together in most parts where the Ni alloy particles were bonded together. Therefore, during the heat treatment, in most bonding portions, the metal atoms diffused between the Ni alloy particles, and sintering occurred, thereby increasing the bonding strength between the Ni alloy particles.It was assumed that this resulted in the above results.

[0092] On the other hand, among the thermal spray coatings of the examples in which aluminum flakes were used as aluminum powder, in the thermal spray coatings in which the oxygen content in the aluminum flakes ranged from 0.29 mass% to 4.1 mass%, the peel strength after heat treatment was in a range of 3 MPa to 8 MPa. Therefore, according to these thermal spray coatings, it was possible to ensure erosion resistance and sufficient machinability after use in a high-temperature environment, for example, in a turbocharger. The presumable reason for this is described below. First, in these thermal spray coatings, in most parts where the Ni alloy particles were bonded together, the Ni alloy particles were directly fused together by means of the aluminum flakes.Therefore, during heat treatment, the oxygen contained in the aluminum flakes limited the diffusion of metal atoms between the Ni alloy particles in most joint sections, thus slowing down the progression of sintering. Therefore, it was possible to minimize any increase in the bond strength between the Ni alloy particles. Consequently, it was considered that the peel strength did not increase after heat treatment, and the above results were obtained.

[0093] Furthermore, in the thermal spray coating in which the oxygen content in the aluminum flakes ranged from 0.29% to 0.94%, the peel strength before heat treatment ranged from 3 MPa to 8 MPa. Therefore, according to these thermal spray coatings, it was possible to ensure erosion resistance from the beginning of use, for example, in a turbocharger. The presumable reason for this is described below. First, in these thermal spray coatings, the oxygen content in the aluminum flakes was not too high, and thus, the diffusion of metal atoms between the Ni alloy particles during the coating formation process was not excessively restricted due to the oxygen contained in the aluminum flakes. Therefore, the fusion of the Ni alloy particles progressed appropriately. Consequently, it was considered that the above results were obtained without any reduction in the peel strength before heat treatment.

Claims

[1] Thermal spray powder used to form a thermal spray coating with a characteristic of friability, wherein the thermal spray powder includes Ni alloy particles, solid lubricant particles and aluminum flakes, the oxygen content in the aluminium flakes is in a range of 0.29 mass% to 4.1 mass%, and the degree of coverage of the aluminum flakes on the surfaces of the Ni alloy particles is in a range of 60% to 100%, characterized by , that the mean thickness of the aluminum flakes is in a range of 0.1 µm to 2 µm and the mean particle size of the aluminum flakes is in a range of 10 µm to 100 µm, wherein the mean particle size of the aluminum flakes refers to the mean particle size of the aluminum flakes in a planar direction perpendicular to the thickness direction. [2] The thermal spray powder according to claim 1, wherein the oxygen content in the aluminum flakes is in a range of 0.29 mass% to 1 mass%.

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