Thermal spray powder, method for forming a rub-off thermal spray coating using the same, and rub-off thermal spray coating

Abstract

Thermal spray powder (10) for forming a rub-off thermal spray coating (1), comprising: NiCr alloy particles (11); synthetic mica particles (12); and h-BN particles, wherein the synthetic mica particles (12) are present at 30 vol% or less based on a total volume of the thermal spray powder (10), and the h-BN particles are present at 15 vol% or less based on the total volume of the thermal spray powder (10).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a thermal spray powder used for forming a thermal spray coating having abradability, a method for forming an abradable thermal spray coating using the same, and an abradable thermal spray coating. 2. Description of the related art

[0002] Abradable thermal spray coatings (abradable thermal spray coatings) use materials that meet specific specifications based on standards for aircraft engines and the like. Abradability is a property that allows a material to be removed to protect a mating element. In recent years, abradable thermal spray coatings with heat resistance exceeding a heat-resistant temperature of, for example, 500°C have been developed for gas turbines and jet engines.

[0003] For example, Japanese Patent Application Publication No. 10-140318 (JP H10-140318 A) discloses the following method for forming an abradable thermal spray coating. In the forming method, a Ni-5Al or Ni-18.5Cr-6Al powder is first thermally sprayed onto a surface of a base material by plasma spraying. Next, a powder obtained by mixing the following first powder and second powder is thermally sprayed onto the plasma-sprayed surface by flame spraying. The first powder contains Cr at 3 to 7 wt%, Al at 3 to 7 wt%, Al2O3 and SiO2 at 6 to 14 wt%, and Ni at the remaining wt%. The second powder contains Cr at 3 to 7 wt%, Al at 3 to 7 wt%, Al2O3 and SiO2 at 15 to 30 wt% and Ni at the remaining wt%.

[0004] Furthermore, the published patent applications WO 01 / 44 533 A1 and US 2008 / 0 145 649 A1 disclose coatings from the prior art. SUMMARY OF THE INVENTION

[0005] However, in the technique in JP H10-140 318 A, when a counter member comes into contact with the formed abradable thermal spray coating, the counter member may adhere to the abradable thermal spray coating and adhesive wear of the counter member may occur.

[0006] The present invention has been made in view of the above problem, and provides a thermal spray powder capable of preventing adhesive wear of a mating member contacted with an abradable thermal spray coating, and a method for forming an abradable thermal spray coating using the same.

[0007] According to a first aspect of the present invention, a thermal spray powder for forming an abradable thermal spray coating is provided. The powder includes NiCr alloy particles, synthetic mica particles, and h-BN particles. The synthetic mica particles are contained at 30 vol% or less based on the total volume of the thermal spray powder. The h-BN particles are contained at 15 vol% or less based on the total volume of the thermal spray powder. According to the first aspect, when the synthetic mica particles remain in the abradable thermal spray coating, it is possible to prevent adhesive wear of the mating member that comes into contact with the abradable thermal spray coating.

[0008] In the first aspect, the synthetic mica particles may be contained at 20 vol% or more based on the total volume of the thermal spray powder.

[0009] The first aspect includes h-BN particles. Since h-BN is a material with solid lubricity like graphite, including h-BN particles in such a range makes it possible to further improve the abradability of the thermal spray coating.

[0010] The synthetic mica particles may be present at 20 vol% or less based on the total volume of the thermal spray powder.

[0011] In the first aspect, the synthetic mica particles may be particles made of fluorphlogopite. When particles made of fluorphlogopite are used as the synthetic mica particles, the synthetic mica particles do not readily melt when forming a thermal spray coating. Thus, it is possible to form the thermal spray coating under higher temperature conditions while some of the synthetic mica particles remain in a solid phase state.

[0012] In the first aspect, the NiCr alloy particles may contain 20 to 50 wt% Cr. Thus, it is possible to improve the oxidation resistance of the NiCr alloy particles.

[0013] In the first aspect, the NiCr alloy particles may contain 0.1 to 5 wt% Al. Thus, it is possible to increase the oxidation resistance of the NiCr alloy particles without excessively increasing the hardness of the NiCr alloy particles.

[0014] According to a second aspect of the present invention, a method for forming an abradable thermal spray coating using the thermal spray powder of the first aspect is provided. The second aspect involves forming the abradable thermal spray coating while some of the synthetic mica particles contained in the thermal spray powder remain in a solid phase state.

[0015] In the second aspect, the abradable thermal spray coating is formed using the thermal spray powder by gas flame thermal spraying. When a thermal spray powder is thermally sprayed in a gas flame thermal spraying process, some of the synthetic mica particles are likely to remain in a solid phase state when the thermal spray coating is formed.

[0016] In the second aspect, at least one of conditions including (i) a supply flow rate of a fuel gas supplied to a thermal spray gun, (ii) an air pressure of air supplied to the thermal spray gun, (iii) a thermal spray distance between a base material on which the abradable thermal spray coating is formed and the thermal spray gun, and (iv) a supply rate of the thermal spray powder to the base material is adjusted so that some of the synthetic mica particles remain in a solid phase.

[0017] According to a third aspect of the present invention, an abradable thermal spray coating is provided that includes NiCr alloy particles, synthetic mica particles, and h-BN particles. The synthetic mica particles are contained in an amount of 30 vol% or less based on the total volume of powders contained in the abradable thermal spray coating. The h-BN particles are contained in an amount of 15 vol% or less based on the total volume of the thermal spray powder.

[0018] In the third aspect, the synthetic mica particles may be contained at 20 vol% or more based on the total volume of powders contained in the abradable thermal spray coating.

[0019] In the third aspect, the synthetic mica particles may include shells on surfaces of the synthetic mica particles, wherein the shells are formed by solidification of molten synthetic mica particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features, advantages, and technical and economic significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, wherein like reference numerals indicate like elements, and wherein: Fig. 1 is a schematic conceptual diagram of thermal spray powders according to an embodiment of the present invention; Fig. 2 a schematic concept diagram of one of the Fig. 1 is an abradable thermal spray coating formed from the thermal spray powders shown; Fig. 3 is a diagram describing behaviors of synthetic mica particles of the thermal spray coating when a counter element with the Fig. 2 shown abradable thermal spray coating; Fig.4 is a graph showing relations between composite indices and hardness of the thermal spray coatings according to Reference Examples 1-1 to 1-7 and Reference Examples 2-1 and 2-2; Fig. 5 is a graph showing relations between composite indices and hardness of synthetic mica particles according to Reference Examples 1-1 to 1-7 and Reference Examples 2-1 and 2-2; Fig. 6 is a graph showing relations between the hardness of the synthetic mica particles and the hardness of the thermal spray coatings according to Reference Examples 1-1 to 1-7 and Reference Examples 2-1 and 2-2; Fig. 7 shows cross-sectional images of the thermal spray coatings according to Reference Example 1-5 and Reference Example 1-6; Fig. Fig. 8 is a schematic diagram of a machinability testing apparatus; Fig.9 shows diagrams of depths to which thermal spray test pieces are shaved and wear amounts of chip-like test pieces according to Examples 1 to 4 and Comparative Examples 1 to 6; Fig. 10 is a graph showing the results obtained by analyzing the distribution of Mo in surfaces of the thermal spray test pieces according to Example 4 and Comparative Example 4 by EPMA analysis before and after a machinability test; Fig. 11 shows diagrams of depths to which thermal spray test pieces are scraped and wear amounts of chip-like test pieces according to Examples 1-1 to 1-5, Examples 2-1 to 2-5, Examples 3-1 to 3-4, and Comparative Examples 3 and 4, wherein Examples 1-1, 1-5, 2-1, 2-5, and 3-1 are no longer part of the invention; Fig.12 is a graph showing oxidation-induced increased amounts of Cr in NiCr alloy materials according to Reference Examples 3-1 to 3-4 and Reference Examples 4-1 to 4-5 after 120 hours; and Fig. 13 is a graph showing the hardness of NiCr alloy particles according to Reference Example 3-1 to 3-4 and Reference Example 4-1. DETAILED DESCRIPTION OF EMBODIMENTS

[0021] An embodiment of the present invention will be described below with reference to Fig. 1 to 3 described. 1. Thermal spray powder 10

[0022] Fig.1 is a schematic conceptual diagram of a thermal spray powder 10 according to an embodiment of the present invention. The thermal spray powder 10 according to the present embodiment is a thermal spray powder 10 for forming an abradable thermal spray coating (hereinafter referred to as a thermal spray coating). Note that the abradable thermal spray coating is a thermal spray coating that has abradability.

[0023] As in Fig.As shown in Figure 1, the thermal spray powder 10 is a powder 10 including NiCr alloy particles 11 and synthetic mica particles 12, and further including h-BN particles (to be described below). The thermal spray powder 10 is a powder 10 including particles obtained by mixing a powder 10 containing the NiCr alloy particles 11 and a powder 10 containing the synthetic mica particles 12 and granulating them using a binder such as a resin.

[0024] The thermal spray powder 10 may be a powder 10 in which the NiCr alloy particles 11 and the synthetic mica particles 12 are mixed, provided that the NiCr alloy particles 11 and the synthetic mica particles 12 in a mixed state are capable of being thermally sprayed onto a base material when the thermal spray powder 10 is thermally sprayed. Furthermore, instead of a granulated powder 10 in which the NiCr alloy particles 11 and the synthetic mica particles 12 are granulated, the thermal spray powder 10 may be a powder 10 compacted by a cladding process or the like. 1-1. NiCr alloy particles 11

[0025] The NiCr alloy particles 11 are particles made of a NiCr alloy. The Cr content is not particularly limited. However, Cr in the NiCr alloy particles 11 is preferably contained in a range of 20 to 50 mass% based on the total mass of the particles. This makes it possible to improve the oxidation resistance of the NiCr alloy particles 11.

[0026] The NiCr alloy particles 11 may further contain Al, Y, and the like. For example, if Al is added to the NiCr alloy particles 11, it is possible to improve the oxidation resistance of the NiCr alloy particles 11 regardless of the Cr content. In the NiCr alloy particles 11, Al is preferably contained in 0.1 to 5 mass% based on the mass of the total particles. Thus, it is possible to increase the oxidation resistance of the NiCr alloy particles 11 without excessively increasing the hardness of the NiCr alloy particles 11.

[0027] Furthermore, the particle size of the NiCr alloy particle 11 is not particularly limited as long as it is possible to form a thermal spray coating having a property described below. However, the particle size of the NiCr alloy particle 11 is preferably in a range of, for example, 5 to 150 μm. Note that the "particle size" herein refers to a particle size measured by a laser diffraction-type particle size distribution measurement method. Such a particle size is obtainable by classification according to, for example, JIS Z 2510:2004 (Metallic powders - determination of particle size by dry sieving). 1-2. Synthetic mica particles 12

[0028] The synthetic mica particles 12 are made of artificially synthesized mica and are different from natural mica particles. Generally, synthetic mica has a higher melting point than natural mica. The synthetic mica particles 12 are contained at 30 vol% or less based on the total volume of the thermal spray powder 10. If the synthetic mica particles 12 are contained at 40 vol% or less based on the total volume of the thermal spray powder 10, the strength of the resulting thermal spray coating can be ensured.

[0029] On the other hand, when the synthetic mica particles 12 are contained at more than 40 vol% based on the total volume of the thermal spray powder 10, as can be clearly seen from experiments conducted by the inventors to be described below, the strength of the thermal spray coating decreases and the thermal spray coating is peeled off from a base material when a counter member comes into contact with the thermal spray coating.

[0030] When the synthetic mica particles 12 are contained in the thermal spray powder 10, the lower limit of their amount is not particularly limited, as the processability of the thermal spray coating and the wear resistance of the mating element are improved. The synthetic mica particles 12 are preferably contained at 20 vol% or more based on the total volume of the thermal spray powder 10.

[0031] It should be noted that "vol%" herein refers to a volume percentage of a material of particles, calculated using a specific gravity of the particles from a mass of material constituting particles of a thermal spray powder. Volume percentages of NiCr alloy particles and synthetic mica particles are obtained by dividing the calculated volumes of the particles by the total volume of the thermal spray powder.

[0032] Synthetic micas of the synthetic mica particles 12 are synthetic micas, for example fluorphlogopite (KMg3AlSi3O 10 F2), tetrasilicate K-mica (KMg 2,5 Si4O 10 F2), tetrasilicate Na mica (NaMg 2,5 Si4O 10 F2), Na-teniolite (NaMg2LiSi4O 10 F2) and Li-teniolite (LiMg2LiSi4O 10 F2), for example.

[0033] Of these, fluorphlogopite particles are preferred as synthetic mica particles because fluorphlogopite has a higher melting point than other materials. When fluorphlogopite particles are used as the synthetic mica particles 12, the synthetic mica particles 12 do not readily melt when forming a thermal spray coating. Thus, it is possible to form the thermal spray coating under higher temperature conditions while some of the synthetic mica particles 12 remain in a solid phase state.

[0034] Furthermore, the particle size of the synthetic mica particles 12 is not particularly limited as long as a thermal spray coating having a property to be described below can be formed, and the particle size of the synthetic mica particles 12 is preferably in a range of 5 to 150 μm, for example. 1-3. h-BN particles

[0035] The Fig. The thermal spray powder 10 shown in Figure 1 contains h-BN particles. The h-BN particles are made of hexagonal boron nitride. When the thermal spray powder 10 is granulated, the h-BN particles can be bonded to the NiCr alloy particles 11 and the synthetic mica particles 12 using a binder.

[0036] The thermal spray powder 10 is a powder 10 in which the NiCr alloy particles 11, the synthetic mica particles 12, and the h-BN particles are mixed, provided that thermal spraying can be performed on a base material, while the h-BN particles are uniformly mixed with the NiCr alloy particles 11 and the synthetic mica particles 12 when the thermal spray powder 10 is thermally sprayed. Alternatively, instead of a granulated powder in which the NiCr alloy particles 11, the synthetic mica particles 12, and the h-BN particles are granulated, the thermal spray powder 10 may be a powder compacted by a cladding process or the like.

[0037] Since the thermal spray powder 10 contains h-BN particles, a total volume of the thermal spray powder 10 is a total value of the volumes of the NiCr alloy particles 11, the synthetic mica particles 12, and the h-BN particles. Assuming that the synthetic mica particles 12 are contained at 30 vol% or less based on the total volume of the thermal spray powder, the h-BN particles are contained at 15 vol% or less based on the total volume of the thermal spray powder. Since h-BN is a material with solid lubricity like graphite, if the h-BN particles are contained in such a range, it is possible to further improve the abradability of the thermal spray coating.

[0038] Here, when the synthetic mica particles are contained at 30 vol% or less and the h-BN particles at 15 vol% or less based on the total volume of the thermal spray powder, it is possible to ensure the strength of the formed thermal spray coating while maintaining abradability, as clearly demonstrated by experiments conducted by the inventors to be described below. Similarly, when the synthetic mica particles are contained at 20 vol% or less and the h-BN particles at 15 vol% or less based on the total volume of the thermal spray coating, it is possible to ensure the strength of the formed thermal spray coating while maintaining abradability.Furthermore, if the proportions of synthetic mica particles and h-BN particles are outside such a range, the strength of the thermal spray coating decreases and the thermal spray coating may be peeled off from the base material when the counter member comes into contact with the thermal spray coating.

[0039] If a thermal spray coating having a property to be described later can be formed, the particle size of the h-BN particles is not particularly limited, and the particle size of the h-BN particles is preferably in a particle size range of 3 to 30 μm, for example. 2. Method for forming a thermal spray coating 1 and properties of the thermal spray coating 1

[0040] A method for forming a thermal spray coating 1 and properties of the thermal spray coating 1 are described below with reference to Fig. 2 and Fig. 3 described. Fig. 2 is a schematic concept diagram of the Fig. 1 shown thermal spray powder 10 formed thermal spray coating 1. Fig. 3 is a diagram for describing behaviors of synthetic mica particles 12A of the thermal spray coating 1 when a counter element 4 having the Fig. 2 comes into contact with the thermal spray coating 1 shown.

[0041] In the present embodiment, the Fig. 1 is added to a thermal spraying device (not shown), and the thermal spray coating 1 is applied using the method shown in Fig.2 is formed on a surface of a base material 3, such as a turbine housing of a turbocharger. When the thermal spray powder 10 is thermally sprayed, the thermal spray coating 1 is formed on the base material 3 while some of the synthetic mica particles 12 contained in the thermal spray powder 10 remain in a solid phase state.

[0042] The thermal spraying method is not particularly limited, as long as some of the synthetic mica particles 12 can remain in a solid phase. Thermal spraying methods include a thermal gas flame spraying method, which allows the thermal spray powder 10 to be sprayed onto the base material 3 at lower temperatures than other thermal spraying methods, such as plasma thermal spraying. When the thermal spray powder 10 is thermally sprayed in the thermal gas flame spraying method, some of the synthetic mica particles 12 are likely to remain in a solid phase when the thermal spray coating 1 is formed.

[0043] Furthermore, as clearly understood from a determination test 1 to be described below, in the thermal gas flame spraying method, by setting the following conditions (1) to (4) when the thermal spray powder 10 is sprayed, it is possible to form the thermal spray coating while some of the synthetic mica particles 12 remain in a solid phase state. (1) A supply flow rate of a fuel gas to be supplied (for example, a supply flow rate of C2H2 gas) (2) an air pressure around the outer circumference of a nozzle for increasing a flow rate of a fuel gas (3) a thermal spray distance between a base material and a thermal spray gun (4) a feed rate of the thermal spray powder.

[0044] As in Fig.2, during the formation, NiCr alloy particles 11A in which the NiCr alloy particles 11 of the thermal spray powder 10 are melted, and synthetic mica particles 12A in which some of the synthetic mica particles 12 of the thermal spray powder 10 are melted are deposited on a surface 3 of the base material and form the thermal spray coating 1.

[0045] More specifically, during formation, synthetic micas are melted on the outermost surfaces of the synthetic mica particles 12 and then solidified to form shells 12b formed on surfaces of synthetic mica base materials 12a. As a result, as shown in Fig.2, it is possible to weld the synthetic mica particles 12A with the NiCr alloy particles 11A and form the thermal spray coating 1 in which the synthetic mica particles 12A are arranged between the NiCr alloy particles 11A.

[0046] If here, as in Fig. 2, the counter element (for example, a turbine wheel blade) 4 comes into contact with a thermal spray element 5 (for example, a turbine housing of a turbocharger) in which the thermal spray coating 1 is formed on the base material 3, then the thermal spray coating 1 is scraped off by the counter element 4.

[0047] In this case, as in Fig.As shown in Figure 3, the shells 12b are crushed together with the synthetic mica base material 12a of the synthetic mica particles 12A. Since the synthetic mica base material 12a is a (mechanically) splittable material, it becomes scale-like synthetic mica particles 12c upon crushing, and the synthetic mica particles 12c spread like a lubricant on a surface in contact with the counter element 4. Therefore, even if the counter element 4 continues to come into contact with the thermal spray coating 1, it is possible to prevent adhesive wear of the counter element 4 opposite the thermal spray coating 1 because the scale-like synthetic mica particles 12c are interposed therebetween. [Identification Test 1]

[0048] First, according to the following Reference Examples 1-1 to 1-7 and Reference Examples 2-1 and 2-2, the following determination test was conducted, and then conditions for forming a thermal spray coating using a thermal spray powder were determined. Specifically, a gas flame thermal spraying device (TERO-DYN3000, commercially available from Castolin Eutectic) was used, and the following thermal spray powder was thermally sprayed onto a surface of a base material (JIS Standard: S45C) having a width of 25 mm, a length of 50 mm, and a thickness of 6 mm to form a thermal spray coating.

[0049] Here, the following thermal spray powders A and B were prepared as the thermal spray powder. Specifically, for NiCr alloy particles of the two thermal spray powders A and B, particles were prepared whose particle size was classified as 125 µm or less and which included a Ni-20Cr alloy (with 20 wt% Cr and the remainder Ni and unavoidable impurities).

[0050] In the thermal spray powder A, fluorphlogopite (KMg3AlSi3O 10 F2), whose average particle size was classified as 5 µm, was used as the synthetic mica particles. It should be noted that fluorphlogopite has a melting point of 1375°C. In thermal spray powder B, tetrasilicate K mica (KMg 2,5 Si4O 10F2), whose average particle size was classified as 5 µm, was used as the synthetic mica particles. Furthermore, tetrasilicate K mica (KMg 2,5 Si4O 10 F2) has a melting point of 1250°C.

[0051] The thermal spray powders A and B were both granulated from NiCr alloy particles and synthetic mica particles in such a way that the synthetic mica particles of the thermal spray powders A and B were contained at 40 vol% based on a volume of a combination of NiCr alloy particles and synthetic mica particles, that is, on the total volume of the thermal spray powder.

[0052] In Reference Examples 1-1 to 1-7, thermal spray powder A was used. In Reference Examples 2-1 and 2-2, thermal spray powder B was used. In the Reference Examples, a thermal spray gun was provided such that a thermal spraying distance between the base material and the thermal spray gun was 150 mm when a thermal spray coating was formed. Next, a mixed gas in which oxygen gas and C2H2 gas were mixed was supplied to the thermal spray gun, the gas was burned at a tip of the thermal spray gun to generate a flame, and thermal spray powders A and B were supplied to the flame. Note that in the Reference Examples, as shown in Table 1, a supply flow rate of oxygen gas, a supply flow rate of C2H2 gas, and a supply flow rate of a thermal spray powder were adjusted during formation.

[0053] Here, (1) a feed flow rate of C2H2 gas, (2) an air pressure around the outer circumference of a nozzle, (3) a thermal spray distance between the base material and the thermal spray gun, and (4) a feed rate of the thermal spray powder were closely related to the melting state of the thermal spray powder. Therefore, these values ​​were defined as the following indexes 1 to 4, corresponding to the energy fraction applied to the thermal spray powder by the flame during thermal spraying.

[0054] The index 1 is a index defined for the feed flow rate of C2H2 gas. The flame energy depends on the feed flow rate of C2H2 gas. As the feed flow rate increases, the flame energy increases, and the thermal spray powder is readily melted. The index 1 was set to 1 when the feed flow rate of C2H2 gas was 60 l / min. The index 1 was calculated based on the feed flow rate of C2H2 gas of the reference examples. The results are shown in Table 1.

[0055] The index number 2 is a value defined for the air pressure around the outer circumference of the nozzle. The flame energy depends on the air pressure around the outer circumference of the nozzle. As the air pressure increases, the flame burning temperature decreases, and the thermal spray powder does not melt easily. The index number 2 was set to 1 when the air pressure for supplying the thermal spray powder was 2.8 kg / cm³. 2Since the air pressure in the reference examples was 2.8 kg / cm 2 was, the key figures 2 were all 1.

[0056] The index 3 is a index specified for the thermal spray distance between the base material and the thermal spray gun. In the gas flame thermal spraying device described above, as the thermal spray distance between the base material and the thermal spray gun increases in a range of 100 to 200 mm, the time for the thermal spray powder to contact the flame increases. Thus, the thermal spray powder is easily melted. The index 3 was set to 1 when the thermal spray distance between the base material and the thermal spray gun was 200 mm, and the index 3 was set to 0.85 when the thermal spray distance between the base material and the thermal spray gun was 150 mm. Since the thermal spray distance between the base material and the thermal spray gun was 150 mm in the reference examples, the index 3 was all 0.85.

[0057] The index 4 is a parameter defined for the feed rate of the thermal spray powder fed into the flame. As the feed rate of the thermal spray powder decreases, the amount of thermal spray powder contacting the flame decreases, and the thermal spray powder is easily melted. The index 4 was set to 1 when the feed rate of the thermal spray powder was 58 g / min. The index 4 was calculated by dividing the feed rates of the reference examples by the feed rate of 58 g / min. The results are shown in Table 1.

[0058] A value obtained by multiplying the specified indexes 1 to 4 was defined as a composite index. The results are shown in Table 1. The composite index is an index indicating the ease of melting of a thermal spray powder during thermal spraying.

[0059] The Vickers hardness (Hv: 200 g) of the NiCr alloy particles of the thermal spray coatings of the reference examples was measured at five locations, and an average value was set as the hardness (coating hardness) of the thermal spray coating. The Vickers hardness (Hv: 5 g) of the synthetic mica particles (including molten particles) of the thermal spray coatings of the reference examples was measured at five locations, and an average value was set as the hardness (mica hardness in coating) of the synthetic mica particles. The results are shown in Table 1.

[0060] Fig. Figure 4 is a graph showing relations between the composite indices and the hardness of the thermal spray coatings according to the reference examples. Fig.Figure 5 is a graph showing relations between the composite indices and the hardness of the synthetic mica particles according to the reference examples. Fig. Figure 6 is a graph showing relations between the hardness of the synthetic mica particles and the hardness of the thermal spray coatings according to the reference examples.

[0061] Cross sections of the thermal spray coatings according to Reference Examples 1-5 and 1-6 were observed under a scanning electron microscope (SEM). Fig. Figure 7 shows cross-sectional images of the thermal spray coatings according to Reference Example 1-5 and Reference Example 1-6. [Table 1] Thermal spray powder gas Thermal spray distance Powder feed rate Composite key figure E Coating hardness Mica hardness in coating Oxygen flow rate C2H2 flow rate Gas pressure (air around outer circumference) Hv0.2 Hv5 L / min L / min Key figure 1 kg / cm 2 Key figure 2 mm Key figure 3 g / min Key figure 4 Reference example 1-1 A 25 45 0,75 2,8 1 150 0,85 77 0,75 0,48 25 19 Reference examples 1-2 A 25 45 0,75 2,8 1 150 0,85 55 1,05 0,67 44 18 Reference examples 1-3 A 30 50 0,83 2,8 1 150 0,85 58 1,00 0,71 43 19 Reference examples 1-4 A 30 50 0,83 2,8 1 150 0,85 55 1,05 0,74 46 18 Reference examples 1-5 A 40 55 0,92 2,8 1 150 0,85 58 1,00 0,78 47 197 Reference examples 1-6 A 40 60 1,00 2,8 1 150 0,85 58 1,00 0,85 51 457 Reference examples 1-7 A 40 75 1,25 2,8 1 150 0,85 58 1,00 1,06 80 650 Reference Example 2-1 B 40 50 0,83 2,8 1 150 0,85 58 1,00 0,71 101 988 Reference Example 2-2 B 40 45 0,75 2,8 1 150 0,85 89 0,65 0,41 93 960 (Results 1)

[0062] As in Fig.As shown in Figure 4, the hardness of the thermal spray coatings of Reference Examples 1-6 and 1-7, whose composite indexes were greater than the composite indexes of Reference Examples 1-1 to 1-5, was greater than that of Reference Examples 1-1 to 1-5. The hardness of the thermal spray coatings of Reference Examples 2-1 and 2-2 was greater than that of Reference Examples 1-1 to 1-7.

[0063] As in Fig. As shown in Figure 5, the hardness of the synthetic mica particles of Reference Examples 1-6 and 1-7, whose composite indexes were greater than the composite indexes of Reference Examples 1-1 to 1-5, was greater than that of Reference Examples 1-1 to 1-5. The hardness of the synthetic mica particles of Reference Examples 2-1 and 2-2 was greater than that of Reference Examples 1-1 to 1-7.

[0064] As in Fig.6, the hardness of the thermal spray coating increased with increasing hardness of the synthetic mica particles. As shown in Fig. As shown in Figure 7, the thermal spray coating of Reference Example 1-5 retained a flaky texture characteristic of synthetic mica particles, and a cross-section of the thermal spray coating was slightly porous. In contrast, in Reference Example 1-6, the flaky texture characteristic of synthetic mica particles was not present, but the synthetic mica melted and solidified, forming a dense mass.

[0065] It is understandable that based on the results in Fig. 6 the hardness of the thermal spray coating depends on the hardness of the synthetic mica particles, and that the synthetic mica particles were melted during formation, so that based on the results in Fig.7 the hardness of Reference Examples 1-6 and 1-7 was greater than that of Reference Examples 1-1 to 1-5.

[0066] Furthermore, in Reference Examples 2-1 and 2-2, the synthetic mica particles contained in thermal spray powder B were tetrasilicate K mica. Tetrasilicate K mica has a melting point (1250°C) lower than the melting point (1375°C) of fluorphlogopite contained in thermal spray powder A used in Reference Examples 1-1 to 1-7. Therefore, in Reference Examples 2-1 and 2-2, whose composite characteristics were also lower than those of Reference Example 1-6, it was assumed that the synthetic mica particles were melted during formation. As a result, it can be understood that the hardness of the (melted and solidified) synthetic mica particles and the hardness of the thermal spray coatings of Reference Examples 2-1 and 2-2 were higher than those of Reference Examples 1-1 to 1-5.

[0067] Based on the above findings, it is understandable that when fluorphlogopite, which has a high melting point, is used for the synthetic mica particles of the thermal spray powder, a flaky texture of the synthetic mica particles is likely to remain during formation, and this texture may prevent an increase in the hardness of the thermal spray coating. Consequently, as described in the following examples, it is understandable that abradability can be imparted to a thermal spray coating in a more suitable manner.

[0068] Also, in Reference Examples 2-1 and 2-2, tetrasilicate K mica was used for the synthetic mica particles, but tetrasilicate K mica has a melting point that is 125°C lower than the melting point of fluorphlogopite. Therefore, it is understandable that if thermal spraying conditions are determined such that the composite index becomes lower, for example, along the imaginary line (the dashed line) in Fig. 5, a scale-like texture of synthetic mica particles may remain while the synthetic mica particles remain in a solid phase state even when tetrasilicate K mica is used.

[0069] Examples of the present invention will now be described based on the results of the determination test described above. [Example 1 (no longer part of the invention)]

[0070] Under conditions (see Table 1) shown in Reference Example 1-5 in the above-described evaluation test, a thermal spray test sample in which a thermal spray coating was formed on a surface of a base material was prepared. This example differed from that of Evaluation Test 1 in that a thermal spray powder composed of NiCr alloy particles and synthetic mica (fluorphlogopite) particles was granulated such that the synthetic mica particles were contained at 10 vol% or less based on the total volume of the thermal spray powder, which was a volume of a combination of the NiCr alloy particles and synthetic mica particles contained in the thermal spray powder. Also, 10 vol% corresponded to-% of a content of synthetic mica particles of 2.5 mass% based on the mass of the combination of the NiCr alloy particles and synthetic mica particles contained in the thermal spray powder (the total mass of the thermal spray powder). [Examples 2 to 4 (no longer part of the invention)]

[0071] Thermal spray test samples were prepared in the same manner as in Example 1. These examples differed from Example 1 in that, as shown in Table 2, the content of the synthetic mica particles was successively 20 vol%, 30 vol%, and 40 vol% based on the total volume of the thermal spray powder. Also, 20 vol%, 30 vol%, and 40 vol% of the synthetic mica particle content corresponded successively to 3.5 wt%, 7.4 wt%, and 17.7 wt% based on the total mass of the thermal spray powder. [Comparison examples 1 and 2]

[0072] Thermal spray test samples were prepared in the same manner as in Example 1. These examples differed from Example 1 in that, as shown in Table 2, no synthetic mica particles were contained in Comparative Example 1 (0 vol%) and a content of the synthetic mica particles in Comparative Example 2 was 50 vol%. [Comparison examples 3 to 5]

[0073] Thermal spray coatings were formed in the same manner as in Example 1. These examples differed from Example 1 in that, as shown in Table 2, the h-BN particles were added instead of the synthetic mica particles, and the h-BN particles were sequentially included at 20 vol%, 25 vol%, and 30 vol% based on a volume of a combination of the NiCr alloy particles and h-BN particles contained in the thermal spray powder (the total volume of the thermal spray powder). [Comparison example 6]

[0074] A thermal spray coating was formed in the same manner as in Example 1. This example differed from Example 1 in that iron alloy particles of Ni: 13 mass%, Cr: 8 mass%, and the balance of Fe and unavoidable impurities were used instead of the NiCr alloy particles, h-BN particles and Al particles were used instead of the synthetic mica particles, and the h-BN particles were contained at 19.2 vol% and the Al particles at 8.8 vol% based on a total volume of a combination of the iron alloy particles, h-BN particles, and Al particles contained in the thermal spray powder (the total volume of the thermal spray powder). [Editability check]

[0075] The thermal spray test samples from Examples 1 to 4 and Comparative Examples 1 to 6 were tested using a Fig.A machinability test was conducted using the machinability testing apparatus shown in Figure 8. Specifically, a chip-like test piece 51 made of the same material (Ni-13Cr-4Mo-2Nb-6Al-0.8Ti-0.1Zn-0.01B) as a turbine wheel of an automotive turbocharger was prepared as a counter member, and two pieces were attached to a rotor 53 in an electric furnace 52. Next, while a thermal spray test piece 55 attached to a movable jig 54 was in contact with the chip-like test piece 51, a position of the thermal spray test piece 55 was fixed. Next, a temperature inside the electric furnace 52 was increased to 500°C, a rotation speed of the rotor 53 was set to 1200 rpm, a feed rate of the chip-like test piece 51 was set to 0.05 mm / s, and the rotor 53 was rotated for 10 seconds.

[0076] The depths to which the thermal spray coatings of the thermal spray test pieces of Examples 1 to 4 and Comparative Examples 1 to 6 were scraped off were measured using a micrometer. Wear amounts of the chip-like test pieces of Examples 1 to 4 and Comparative Examples 1 to 6 were measured using an electronic balance. The results are shown in Table 2 and Fig. 9. Furthermore, the distribution of Mo in surfaces of the thermal spray coatings of Example 4 and Comparative Example 4 was measured before and after the machinability test using an EPMA. The results are shown in Fig. 10 shown. [Table 2 (Examples 1 to 4 are no longer part of the invention)] Added particles Depth to which thermal spray test piece was scraped (mm) Amount of wear of a chip-like test piece (mg) Content of synthetic mica particles (vol%) Content of other particles (vol%) Comparison example 1 0 0,010 -90 Example 1 10 0,056 -75 Example 2 20 0,230 -21 Example 3 30 0,312 -14 Example 4 40 0,340 -11 Comparison example 2 50 0.120 (peeled) -13 (peeled) Comparison example 3 20 (h-BN) 0,180 -36 Comparison example 4 25 (h-BN) 0,250 -29 Comparison example 5 30 (h-BN) 0.04 (peeled) -9 (peeled) Comparison example 6 19.2 (h-BN) 8.8 (Al) 0,17 -45 [Results 2]

[0077] As in Fig.As shown in Figure 9, the thermal spray test piece of Comparative Example 1, which did not contain synthetic mica particles, was hardly scraped off, and the wear amount of the chip-like test piece was greater than that of Examples 1 to 4. Here, in Examples 1 to 4, since the thermal spray coating was formed under the conditions of Reference Examples 1-5 of the above-described evaluation test, the splittable synthetic mica particles (having a scaly texture of mica) remained in the thermal spray coating. Therefore, it can be understood that in Examples 1 to 4, when the thermal spray coating was scraped off, the synthetic mica particles with a scaly texture were crushed and became scaly and fine synthetic mica particles.As a result, as described below, it is understood that in Examples 1 to 4, it is possible to suppress adhesive wear of the chip-like test piece serving as a counter member while increasing the workability of the thermal spray coating of the thermal spray test piece.

[0078] Furthermore, in the thermal spray test piece of Comparative Example 2, the strength of the thermal spray coating was insufficient, and the thermal spray coating peeled off during the machinability test. It is understood that in Comparative Example 2, when the synthetic mica particles were contained at 50 vol%, the strength of the thermal spray coating decreased because there were too many synthetic mica particles relative to the thermal spray coating. Accordingly, it is understood that it is possible to ensure the strength of the resulting spray coating when the synthetic mica particles were contained at 40 vol% or less based on the total volume of the thermal spray powder.

[0079] Furthermore, comparing Example 1 and Comparative Example 1, it is understandable that when - as in Example 1 - the synthetic mica particles were included, since the amount of wear of the chip-like test piece decreased, such an effect can be simply due to the inclusion of a small amount of the synthetic mica particles. Also, as in Fig. As shown in Figure 9, the wear amounts of the chip-like test piece in Examples 2 to 4 were stable and small. Accordingly, the synthetic mica particles may preferably be contained at 20 vol% or more based on the total volume of the thermal spray powder.

[0080] Furthermore, as in Fig. 9, the wear amounts of the chip-like test pieces of Comparative Examples 3 and 6, in which the same amount of h-BN particles as in Example 2 was contained instead of the synthetic mica particles, were larger than that of Example 2. In addition, as shown in Fig.As shown in Figure 10, Mo adhered to the thermal spray coating of Comparative Example 4 after the test, but Mo hardly adhered to the thermal spray coating of Example 4 after the test.

[0081] Accordingly, it can be understood that Mo, a component of the chip-like test piece, adhered to the thermal spray coatings of Comparative Examples 3, 4, and 6, and the wear amounts of the chip-like test pieces of Comparative Examples 3, 4, and 6 due to adhesive wear were larger than those of the chip-like test piece of Example 2. As in Examples 1 to 4, it can be understood that by containing the synthetic mica particles of the thermal spray coating, when the thermal spray coating was scraped off, the synthetic mica particles having a scale-like texture became fine and scale-like synthetic mica particles and dispersed on a surface, acting as a lubricant, and thus adhesive wear of the chip-like test piece was suppressed.

[0082] Furthermore, in the thermal spray test piece of Comparative Example 5, the strength of the thermal spray coating was insufficient, and the thermal spray coating peeled off during the machinability test. It is understandable that, as in Comparative Example 5, when the h-BN particles were contained at 30 vol%, the strength of the thermal spray coating decreased because the content of the h-BN particles was too large relative to the thermal spray coating. Here, as described above, in Example 4, the strength of the thermal spray coating was ensured despite the synthetic mica particle content of 40 vol% (more than 30 vol%). It is understandable that during thermal spraying, parts of the outer periphery of the synthetic mica particles were melted and welded to the NiCr alloy particles, and the synthetic mica particles supported the NiCr alloy particles.However, since h-BN sublimates without melting, the h-BN particles were unable to support the NiCr alloy particles as the synthetic mica particles did. Therefore, it is possible to ensure the strength of the thermal spray coating even when the content of synthetic mica particles is greater than that of h-BN particles. [Examples 1-1 to 1-5 (Examples 1-1 and 1-5 are no longer part of the invention)]

[0083] Thermal spray test pieces in which a thermal spray coating was formed on a surface of a base material were prepared in the same manner as in Example 1. Example 1-1 was the same as Example 1. Examples 1-2 to 1-5 differed from Example 1 in that h-BN particles whose average particle size was classified as 5 μm were additionally contained in the thermal spray powder. Specifically, as shown in Table 3, the h-BN particles in Examples 1-2 to 1-5 were sequentially contained at 5 vol%, 10 vol%, 15 vol%, and 20 vol% based on a volume of a combination of the NiCr alloy particles, the synthetic mica particles, and the h-BN particles, which was the total volume of the thermal spray powder. Also, 5 vol%, 10 vol%, 15 vol% and 20 vol% of the h-BN particle content corresponded successively to 1.5 wt%, 3.3 wt%, 4.9 wt% and 6.9 wt% based on the total mass of the thermal spray powder. [Comparison example 1-1]

[0084] A thermal spray test piece in which a thermal spray coating was formed on the surface of a base material was prepared in the same manner as in Example 1-1. Comparative Example 1-1 differed from Example 1-1 in that h-BN particles, whose average particle size was classified as 5 µm, were additionally contained in the thermal spray powder. Specifically, as shown in Table 3, the h-BN particles in Comparative Example 1-1 were contained at 25 vol% based on the total volume of the thermal spray powder. [Examples 2-1 to 2-5 (Examples 2-1 and 2-5 are no longer part of the invention)]

[0085] Thermal spray test pieces in which a thermal spray coating was formed on a surface of a base material were prepared in the same manner as in Example 2. Example 2-1 was the same as Example 2. Examples 2-2 to 2-5 differed from Example 2 in that h-BN particles whose average particle size was classified as 5 μm were additionally contained in the thermal spray powder. Specifically, as shown in Table 3, the h-BN particles in Examples 2-2 to 2-5 were sequentially contained at 5 vol%, 10 vol%, 15 vol%, and 20 vol% based on the total volume of the thermal spray powder. Also, 5 vol%, 10 vol%, 15 vol% and 20 vol% of the h-BN particle content corresponded successively to 1.6 wt%, 3.4 wt%, 5.4 wt% and 7.5 wt% based on the total mass of the thermal spray powder. [Comparison example 2-1]

[0086] A thermal spray test piece in which a thermal spray coating was formed on the surface of a base material was prepared in the same manner as in Example 2-1. Comparative Example 2-1 differed from Example 2-1 in that h-BN particles, whose average particle size was classified as 5 µm, were additionally contained in the thermal spray powder. Specifically, as shown in Table 3, the h-BN particles in Comparative Example 2-1 were contained at 25 vol% based on the total volume of the thermal spray powder. [Examples 3-1 to 3-4 (Example 3-1 is no longer part of the invention)]

[0087] Thermal spray test pieces in which a thermal spray coating was formed on a surface of a base material were prepared in the same manner as in Example 3. Example 3-1 was the same as Example 3. Examples 3-2 to 3-4 differed from Example 3 in that h-BN particles whose average particle size was classified as 5 μm were additionally contained in the thermal spray powder. Specifically, as shown in Table 3, the h-BN particles in Examples 3-2 to 3-4 were sequentially contained at 5 vol%, 10 vol%, and 15 vol% based on the total volume of the thermal spray powder. Also, 5 vol%, 10 vol%, and 15 vol% of the h-BN particle content sequentially corresponded to 1.8 mass%, 3.7 mass%, and 5.9 mass% based on the total mass of the thermal spray powder. [Comparison examples 3-1 and 3-2]

[0088] Thermal spray test pieces in which a thermal spray coating was formed on a surface of a base material were prepared in the same manner as in Example 3-1. Comparative Examples 3-1 and 3-2 differed from Example 3-1 in that h-BN particles, whose average particle size was classified as 5 μm, were additionally contained in the thermal spray powder. Specifically, as shown in Table 3, the h-BN particles were contained in Comparative Example 3-1 and Comparative Example 3-2 sequentially at 20 vol% and 25 vol% based on the total volume of the thermal spray powder. [Editability check]

[0089] Analogously to Example 1, the machinability test was conducted on the thermal sprayed test pieces of Example 1-1 to 1-5, Comparative Example 1-1, Example 2-1 to 2-5, Comparative Example 2-1, Example 3-1 to 3-4, and Comparative Example 3-1 and 3-2. The results are shown in Table 3 and Fig. 11. In addition, Fig. 11 also the results of comparative examples 3 and 4. [Table 3 (Examples 1-1, 1-5, 2-1, 2-5, and 3-1 are no longer part of the invention)] Content of synthetic mica particles (vol%) Content of BN particles (vol%) Depth to which a thermal spray test piece was scraped (mm) Amount of wear of a chip-like test piece (mg) Example 1-1 10 0 0,06 -90 Example 1-2 10 5 0,13 -25 Examples 1-3 10 10 0,28 -15 Examples 1-4 10 15 0,34 -10 Examples 1-5 10 20 0,46 -10 Comparison example 1-1 10 25 peeled peeled Example 2-1 20 0 0,23 -29 Example 2-2 20 5 0,35 -13 Example 2-3 20 10 0,35 -10 Example 2-4 20 15 0,44 -4 Example 2-5 20 20 0,49 -1 Comparison example 2-1 30 25 peeled peeled Example 3-1 30 0 0,31 -19 Example 3-2 30 5 0,39 -9 Example 3-3 30 10 0,42 -6 Example 3-4 30 15 0,48 -2 Comparison example 3-1 30 20 peeled peeled Comparison example 3-2 30 25 peeled peeled (Results 3)

[0090] As in Fig. As shown in Figure 11, in Examples 1-1 to 1-5, Examples 2-1 to 2-5, and Examples 3-1 to 3-4, as the content of h-BN particles increased, the depth to which the thermal spray test piece was scraped increased, and the amount of wear of the chip-like test piece decreased. This is believed to be because h-BN in the h-BN particles is a material with solid lubricity like graphite.

[0091] Furthermore, as shown in Table 3, in the thermal spray specimens of Comparative Example 1-1, Comparative Example 2-1, and Comparative Example 3-1 and 3-2, the strength of the thermal spray coating was insufficient, and the thermal spray coating peeled off during the machinability test. In these comparative examples, it is clear that the strength of the thermal spray coating decreased due to the presence of too many h-BN particles relative to the thermal spray coating.

[0092] Therefore, as in Fig.11 and Table 3, it is understood from the determination based on the results of Examples 1-1 to 1-4, Examples 2-1 to 2-4, and Examples 3-1 to 3-4 that it is possible to ensure the strength of the thermal spray coating to be formed when the synthetic mica particles are contained at 30 vol% or less and the h-BN particles at 15 vol% or less based on the total volume of the thermal spray powder. On the other hand, it is understood from the determination based on the results of Examples 1-1 to 1-5 and Examples 2-1 to 2-5 that it is possible to ensure the strength of the thermal spray coating to be formed when the synthetic mica particles are contained at 20 vol% or less and the h-BN particles at 20 vol% or less based on the total volume of the thermal spray powder.

[0093] Furthermore, as in Fig.As shown in Figure 11, all the thermal spray coatings of Examples 1-5, 2-5, and Comparative Example 3 contained the h-BN particles of the thermal spray powder at 20 vol%. However, it can be understood that the depth to which the thermal spray test piece was scraped was greater and the wear amount of the chip-like test piece was lower than those of Comparative Example 3 because the thermal spray test pieces of Examples 1-5 and 2-5 contained the synthetic mica particles. [Identification Test 2]

[0094] The following Determination Test 2 was conducted on materials of the following Reference Examples 3-1 to 3-4 and Reference Examples 4-1 to 4-5, and thus a preferable composition of NiCr alloy particles used in Example 1 was determined. [Reference example 3-1 to 3-4]

[0095] In Reference Examples 3-1 to 3-4, NiCr alloy materials containing Cr contents of 10 mass%, 20 mass%, 30 mass%, and 50 mass% in sequence, and the balance of Ni and unavoidable impurities were prepared as the materials of the NiCr alloy particles. [Reference example 4-1 to 4-5]

[0096] In Reference Examples 4-1 to 4-5, as materials of NiCr alloy particles, NiCrAl alloy materials were prepared which included an Al content of 5 mass%, a Cr content of 9.5 mass%, 18 mass%, 19 mass%, 33.2 mass% and 47.5 mass% in sequence, and the balance of Ni and unavoidable impurities. [High-temperature oxidation test]

[0097] The alloy materials of Reference Examples 3-1 to 3-4 and Reference Examples 4-1 to 4-5 were placed in a heating furnace and heated for 120 hours at 850°C in an oxygen gas atmosphere, and the oxidation-induced increased amounts of the alloy materials were measured. Note that the oxidation-induced increased amounts are values ​​obtained by dividing the difference between the weights of the alloy materials before and after the test by the surface areas of the alloy materials. The results are shown in Fig. 12 shown. [Hardness test]

[0098] The Vickers hardness of the alloy materials of Reference Example 3-1 to 3-4 and Reference Example 4-1 was measured under temperature conditions of 20°C, 500°C, and 850°C. Also, the Vickers hardness of the same material as the chip-like test piece, which served as a counter element, was measured under temperature conditions of 20°C and 500°C as Reference Example 5. The results are shown in Fig. 13 shown.

[0099] As in Fig.As shown in Figure 12, the oxidation-induced increase in the alloy material of Reference Example 3-1 was greater than that of the alloy materials of Reference Examples 3-2 to 3-4. Therefore, it can be understood that when the amount of Cr contained in the NiCr alloy particles is in a range of 20 to 50 mass %, the NiCr alloy particles are hardly oxidized when the element is used during and after formation. In contrast, in Reference Examples 4-1 to 4-5 containing Al, the oxidation-induced increase was small regardless of the Cr content.

[0100] As in Fig.As shown in Figure 13, in Reference Examples 3-1 to 3-4, the Vickers hardness also increased with increasing Cr content. Since the hardness of the alloy materials of Reference Examples 3-1 to 3-4 and Reference Example 4-1 was lower than the Vickers hardness of the material of Reference Example 5, which was a counter element material, such alloy materials are suitably usable for the NiCr alloy particles of the thermal spray powder. Furthermore, based on the results of changes in the Vickers hardness of the alloy materials of Reference Examples 3-1 to 3-4 at 500°C and the hardness of the alloy material of Reference Example 4-1 at 500°C, it can be understood that the Vickers hardnesses of Reference Examples 4-2 to 4-5 were lower than that (at 500°C) of the material of Reference Example 5.

[0101] Although the embodiments of the present invention have been described in detail above, specific configurations are not limited to the embodiments.

Claims

[1] Thermal spray powder (10) for forming an abradable thermal spray coating (1), comprising: NiCr alloy particles (11); synthetic mica particles (12); and h-BN particles, where the synthetic mica particles (12) are contained at 30 vol.% or less based on a total volume of the thermal spray powder (10), and the h-BN particles are contained at 15 vol.% or less based on the total volume of the thermal spray powder (10). [2] Thermal spray powder (10) according to claim 1, wherein the synthetic mica particles (12) are contained at 20 vol% or more based on the total volume of the thermal spray powder (10). [3] Thermal spray powder (10) according to claim 1, wherein the synthetic mica particles (12) are contained at 20 vol% or less based on the total volume of the thermal spray powder (10). [4] Thermal spray powder (10) according to one of claims 1 to 3, wherein the synthetic mica particles (12) are particles made of fluorphlogopite. [5] Thermal spray powder according to one of claims 1 to 4, wherein the NiCr alloy particles (11) contain Cr at 20 to 50 mass%. [6] Thermal spray powder according to one of claims 1 to 5, wherein the NiCr alloy particles (11) contain Al at 0.1 to 5 mass%. [7] A method for forming an abradable thermal spray coating (1) using the thermal spray powder (10) according to any one of claims 1 to 6, comprising: Forming the abradable thermal spray coating (1) while some of the synthetic mica particles (12) contained in the thermal spray powder (10) remain in a solid phase state, wherein the formation of the abradable thermal spray coating (1) using the thermal spray powder (10) is carried out by thermal gas flame spraying, and at least one of conditions including (i) a supply flow rate of a fuel gas supplied to a thermal spray gun, (ii) an air pressure of air supplied to the thermal spray gun, (iii) a thermal spray distance between a base material on which the abradable thermal spray coating is formed and the thermal spray gun, and (iv) a supply rate of the thermal spray powder to the base material is adjusted so that some of the synthetic mica particles remain in a solid phase state. [8] Abradable thermal spray coating (1) comprising: NiCr alloy particles (11A); synthetic mica particles (12A); and h-BN particles, where the synthetic mica particles (12A) are contained at 30 vol.% or less based on a total volume of powders (10) contained in the abradable spray coating (1), and the h-BN particles are contained at 15 vol.% or less based on the total volume of the thermal spray powder (10). [9] Abradable thermal spray coating (1) according to claim 8, wherein the synthetic mica particles (12A) are contained at 20 vol% or more based on the total volume of powders (10) contained in the abradable spray coating (1). [10] Abradable thermal spray coating (1) according to claim 8 or 9, wherein the synthetic mica particles (12A) include shells (12b) on surfaces of the synthetic mica particles (12A), the shells (12b) being formed by solidification of molten synthetic mica particles (12A).

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