Thermal spray powder and method for producing thermal spray coating

Abstract

To provide a technique capable of maintaining fluidity suitable for thermal spray and supplying finer ceramic particles during thermal spray.SOLUTION: Thermal spray powder is constituted of ceramic particles. When comparing the thermal spray powder after performing atmospheric pressure plasma thermal spray in water with that before the thermal-spray on the following conditions: plasma working gas: argon (Ar) gas of 50 psi and helium (helium) gas of 50 psi, a plasma output: 36 kW, the supply rate of the thermal spray powder: 20 g / min and a thermal spray distance: 400 mm, the value of the average particle diameter (D50) of the thermal spray powder on the basis of a laser diffraction and scattering method is smaller by at least 25%.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a thermal spray powder and a method for producing a thermal spray coating using the thermal spray powder. [Background technology]

[0002] Techniques for imparting new functions by coating the surface of a substrate with various materials have been used in various fields for some time. One known example of such surface coating techniques is a thermal spraying method in which ceramic particles made of a ceramic are sprayed in a molten state onto the surface of a substrate to form a thermal spray coating made of the ceramic.

[0003] For example, in the field of semiconductor device manufacturing, microfabrication is sometimes performed on the surface of a semiconductor substrate by dry etching using plasma of a halogen-based gas such as fluorine, chlorine, or bromine. After dry etching, the interior of the chamber from which the semiconductor substrate is removed is cleaned using oxygen gas plasma. In this chamber, components exposed to highly reactive oxygen gas plasma or halogen gas plasma may be corroded. For this reason, in semiconductor device manufacturing equipment, ceramic spray coatings are provided on components exposed to oxygen gas or halogen gas plasma to prevent corrosion by the plasma.

[0004] In the thermal spraying methods disclosed in Patent Documents 1 to 3, the powder material for thermal spraying (thermal spray powder) is supplied to the thermal spraying device in a dry state. In order to stably supply the thermal spray powder to the thermal spraying device, development of thermal spray powder with improved fluidity is underway. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6811188 [Patent Document 2] Patent No. 4630799 [Patent Document 3] Patent No. 6262716 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, from the viewpoint of improving the durability of thermal spray coatings, it is desirable to form thermal spray coatings with smoother surfaces and higher density. One way to improve the smoothness and density of thermal spray coatings is to reduce the size of the ceramic particles that make up the thermal spray powder. However, simply reducing the size of the ceramic particles may result in a decrease in the flowability of the thermal spray powder. Therefore, there is still room for improvement in the design of ceramic particles.

[0007] In view of these circumstances, the present invention aims to provide a technology that maintains a fluidity suitable for thermal spraying and that can supply finer ceramic particles to a substrate (substrate) during thermal spraying. [Means for solving the problem]

[0008] The present inventors have noticed that when granulated and sintered particles are thermally sprayed, the primary particles that make up the granulated and sintered particles melt due to the thermal energy generated during the spraying process and penetrate into the gaps, thereby reducing the particle size. Furthermore, the present inventors have confirmed that in a thermal spray coating formed using granulated and sintered particles, some of the sprayed granulated and sintered particles may reach the substrate in an unmelted state and remain in the thermal spray coating. As a result of extensive research, the present inventors have found that the sprayed granulated and sintered particles can be completely melted by intentionally increasing the gaps between the granulated and sintered particles. Furthermore, the present inventors have discovered that a thermal spray coating can be produced by supplying particles to a substrate in a smaller particle size than conventional particles, which has led to the completion of the present invention.

[0009] The thermal spray powder disclosed herein is composed of ceramic particles. The thermal spray powder is prepared by subjecting the thermal spray powder to the following conditions: Plasma working gas: Argon (Ar) gas: 50 psi; and Helium (He) gas: 50 psi Plasma output: 36kW Thermal spray powder supply rate: 20g / min Spraying distance: 400mm When comparing the average particle diameter (D 50 ) is reduced by at least 25%.

[0010] The thermal spray powder having such a configuration has an average particle diameter (D 50 ) is at least 25% smaller. This allows for a finer thermal spray powder to be supplied to the substrate during thermal spraying. In addition, the particle size of the thermal spray powder can be set to achieve flowability suitable for thermal spraying.

[0011] In a preferred embodiment, the thermal spray powder disclosed herein has an angle of repose of 40 degrees or less. The angle of repose of the thermal spray powder having such a configuration is set to achieve fluidity suitable for thermal spraying.

[0012] Another preferred embodiment of the thermal spray powder disclosed herein is composed of oxide ceramic particles. By using the thermal spray powder of this composition, a thermal spray coating made of oxide ceramic can be produced.

[0013] In another preferred embodiment of the thermal spray powder disclosed herein, the ceramic particles are granulated and sintered particles of primary particles made of the ceramic. Preferably, the average ratio of the area of ​​open pores to the total area of ​​the surface, based on SEM observation of the surfaces of the ceramic particles, is 20% or more. In a thermal spray powder having such a configuration, the ratio of the area of ​​open pores is within the above range, thereby increasing the degree of thermal contraction of the thermal spray powder. This allows for the supply of finer thermal spray powder to a substrate during thermal spraying.

[0014] In another preferred embodiment of the thermal spray powder disclosed herein, the ceramic particles are granulated and sintered primary particles made of the ceramic, and when the surfaces of the ceramic particles are observed with an SEM, the ratio (Dmax / Dmin) of the maximum diameter Dmax to the minimum diameter Dmin of open pores present on the surface is 1 to 1.8. A thermal spray powder in which the shape of open pores observed on the surfaces by SEM observation is specified as described above has an increased degree of thermal shrinkage. This makes it possible to supply a more finely divided thermal spray powder to a substrate during thermal spraying.

[0015] In another preferred embodiment of the thermal spray powder disclosed herein, the average particle diameter (D 50 ) is 0.5 μm or more and 5 μm or less. This configuration makes it possible to prevent the thermal spray powder containing unmelted portions from being mixed into the thermal spray coating and to prevent defects from occurring in the thermal spray coating, thereby enabling the production of a denser thermal spray coating.

[0016] In another preferred embodiment of the thermal spray powder disclosed herein, the bulk specific gravity is 1.0 or less. This configuration further enhances the effect of micronizing the thermal spray powder by thermal spraying.

[0017] The technology disclosed herein also provides a method for producing a thermal spray coating. That is, a method is provided for producing a thermal spray coating by thermally spraying any of the thermal spray powders disclosed herein onto the surface of an object to be thermally sprayed (substrate). In this method for producing a thermal spray coating, finer thermal spray powder is supplied to the substrate during thermal spraying, making it possible to suitably produce a thermal spray coating with a dense, flat surface, for example, one having a porosity of 4% or less and a surface roughness (arithmetic mean roughness) Ra of 3.5 μm or less. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of producing a thermal spray coating using a thermal spray powder according to one embodiment. [Figure 2]FIG. 1 is a schematic diagram illustrating an example of the production of a thermal spray coating using a conventional thermal spray powder. [Figure 3] 1 is a surface SEM observation image of the thermal spray powder of Sample 1. [Figure 4] 1 is a cross-sectional SEM image of the thermal spray powder of Sample 1. [Figure 5] 1 is a surface SEM observation image of the thermal spray powder of Sample 2. [Figure 6] 1 is a cross-sectional SEM image of the thermal spray powder of Sample 2. [Figure 7] 1 is a SEM observation image of the surface of the thermal spray powder of Sample 3. [Figure 8] 1 is a cross-sectional SEM image of the thermal spray powder of Sample 3. [Figure 9] 1 is an SEM observation image of flying particles of Sample 1. [Figure 10] 10 is an SEM observation image of flying particles of Sample 2. [Figure 11] 10 is an SEM observation image of flying particles of Sample 3. [Figure 12] 1 is a cross-sectional SEM image of the thermal spray coating of Sample 1. [Figure 13] 1 is a cross-sectional SEM image of the thermal spray coating of Sample 2. [Figure 14] 1 is a cross-sectional SEM image of the thermal spray coating of Sample 3. [Figure 15] 1 is a graph showing the surface roughness Ra (μm) of the thermal spray coatings of Samples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the specification, the expression "X to Y" indicating a numerical range means "X or more and Y or less" unless otherwise specified, and it is understood that such a numerical range also includes a range "greater than X and less than Y."

[0020] <Definition> As used herein, the term "thermal spray powder" refers to a powdered material used for thermal spraying. The thermal spray powder disclosed herein is a thermal spray powder material substantially composed of ceramic particles and may contain unavoidable impurities other than the intended ceramic particles (for example, trace amounts of minute non-ceramic particulate matter). As used herein, the term "primary particle" refers to the smallest unit that can be identified as a granular material from its appearance among the morphological components that make up the thermal spray powder. When the ceramic particles that make up the thermal spray powder disclosed herein include secondary particles (e.g., granulated particles), the particles that make up the secondary particles can be referred to as primary particles. Here, "secondary particles" refers to particulate matter (in the form of particles) in which primary particles are bonded three-dimensionally and behave as a single unit. Granulated particles and granulated and sintered particles obtained by granulation are examples of "secondary particles." Note that "bonding" here refers to the direct or indirect bonding of two or more primary particles, and includes, for example, bonding between primary particles due to a chemical reaction, bonding between primary particles that attract each other due to simple adsorption, bonding that utilizes the anchor effect of allowing an adhesive or the like to penetrate into the unevenness of the primary particle surface, bonding between primary particles that utilizes the effect of electrostatic attraction, and bonding in which the surfaces of primary particles are melted and integrated. In addition, in this specification, the term "raw material particles" refers to particles that constitute the powder in the raw material stage used to produce the thermal spray powder disclosed herein.

[0021] <Method for measuring the average particle size of thermal spray powder> In this specification, the term "average particle diameter (D 50 )" refers to the average particle diameter at 50% of the cumulative value in the volume-based particle size distribution measured by a particle size distribution measuring device based on the laser scattering and diffraction method (50% volume average particle diameter). 50 )" is "D v50 It is also sometimes called ".

[0022] <Method for measuring angle of repose> In this specification, the "angle of repose" refers to the base angle calculated from the diameter and height of a cone-shaped deposit formed by dropping a thermal spray powder from a funnel of a certain height onto a horizontal substrate. The angle of repose can be measured in accordance with the provisions of JIS R9301-2-2:1999 "Methods for measuring physical properties of alumina powder - 2: Angle of repose."

[0023] <Method for measuring bulk density> In this specification, the term "bulk specific gravity" in relation to a thermal spray powder refers to the density (specific gravity) calculated from the mass of the thermal spray powder when the thermal spray powder flows naturally through an orifice with a diameter of 2.5 mm and fills a container of a predetermined volume in a natural filling state. The bulk specific gravity can be measured in accordance with the provisions of JIS Z2504:2012, "Metal powders - Measurement method for apparent density."

[0024] <Method for measuring granule strength (compressive strength)> In this specification, the "granule strength" of thermal spray powder is measured using an electromagnetic force loading compression tester. Specifically, a measurement sample is fixed between a pressure indenter and a pressure plate, and a load is applied at a constant increasing rate using electromagnetic force. Compression is performed using a constant load rate compression method, and the amount of deformation of the measurement sample during compression is measured. The measured deformation characteristics of the sample are processed using a dedicated program to calculate the strength value.

[0025] <Composition of thermal spray powder> The thermal spray powder disclosed herein is a thermal spray powder used to produce a thermal spray coating by a thermal spraying method. As described above, this thermal spray powder is composed of ceramic particles. The proportion of ceramic particles in the thermal spray powder is preferably 95 mass % or more, more preferably 99 mass % or more, and even more preferably 99.9 mass % or more, and can be, for example, 99.99 mass % or more. The type of ceramic may be appropriately selected depending on the composition of the thermal spray coating to be produced. Examples of ceramics include oxide ceramics made of oxides and non-oxide ceramics such as carbides, borides, nitrides, and apatite.

[0026] The oxide ceramic is not particularly limited and may be an oxide of various metals. Examples of metal elements or nonmetal elements constituting such oxide ceramic include semimetal elements such as boron (B), silicon (Si), germanium (Ge), antimony (Sb), and bismuth (Bi); typical elements such as magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and lead (Pb); scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Z), and the like. Examples of the metal element include one or more elements selected from transition metal elements such as magnesium (Y), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), and gold (Au); and lanthanoid elements such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Er), and lutetium (Lu). Among these, one or more elements selected from magnesium (Mg), yttrium (Y), titanium (Ti), zirconium (Zr), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), and gold (Au) are preferred.

[0027] Examples of oxide ceramics include alumina, zirconia, yttria, chromia, titania, cobaltite, magnesia, silica, calcia, ceria, ferrite, spinel, zircon, nickel oxide, silver oxide, copper oxide, zinc oxide, gallium oxide, strontium oxide, scandium oxide, samarium oxide, bismuth oxide, lanthanum oxide, lutetium oxide, hafnium oxide, vanadium oxide, niobium oxide, tungsten oxide, manganese oxide, tantalum oxide, terbium oxide, europium oxide, neodymium oxide, tin oxide, antimony oxide, antimony-containing tin oxide, indium oxide, tin-containing indium oxide, zirconium oxide aluminate, zirconium oxide silicate, hafnium oxide aluminate, hafnium oxide silicate, titanium oxide silicate, lanthanum oxide silicate, lanthanum oxide aluminate, yttrium oxide silicate, titanium oxide silicate, and tantalum oxide silicate.

[0028] Examples of non-oxide ceramics include carbide ceramics such as tungsten carbide, chromium carbide, vanadium carbide, niobium carbide, molybdenum carbide, tantalum carbide, titanium carbide, zirconium carbide, hafnium carbide, silicon carbide, and boron carbide; boride ceramics such as molybdenum boride, chromium boride, hafnium boride, zirconium boride, tantalum boride, and titanium boride; nitride ceramics such as titanium nitride, silicon nitride, and aluminum nitride; composites such as folsterite, steatite, cordierite, mullite, barium titanate, lead titanate, lead zirconate titanate, Mn-Zn ferrite, Ni-Zn ferrite, and sialon; and phosphate compounds such as hydroxyapatite and calcium phosphate.

[0029] The above ceramics may be doped or substituted with any element. Furthermore, these ceramics may be contained alone or in combination of two or more. For example, when two or more ceramics are contained, some or all of them may form a composite. Examples of such composite ceramics include yttria-stabilized zirconia, partially stabilized zirconia, gadolinium-doped ceria, lanthanum-doped lead zirconate titanate, the above-mentioned sialon, and the above-mentioned composite oxides.

[0030] The thermal spray powder disclosed herein is prepared by subjecting the thermal spray powder to the following conditions: Plasma working gas: Argon (Ar) gas: 50 psi; and Helium (He) gas: 50 psi Plasma output: 36kW Thermal spray powder supply rate: 20g / min Spraying distance: 400mm When comparing the average particle diameter (D 50 The degree of thermal shrinkage of the thermal spray powder due to thermal spraying can be determined, for example, by reducing the average particle diameter (D 50 ) reduction rate (%) (hereinafter referred to as “D 50 The plasma output value may include a certain amount of error. The plasma output value is typically an arithmetic mean value.

[0031] The average particle diameter (D 50 ) is defined as D1, and the average particle diameter (D 50 ) is D2, then the D of the thermal spray powder 50 The reduction rate (%) is calculated using the following formula (1): D 50 Decrease rate (%)=(D1-D2) / D1×100 (1) The D of thermal spray powder can be calculated using50 The reduction rate (%) is 25% or more as described above, preferably 30% or more, and more preferably 35% or more. 50 The greater the reduction rate (%), the denser and smoother the thermal spray coating can be produced.

[0032] Alternatively, the D of the spray powder before and after the atmospheric plasma spraying (APS) 10 or D 90 The degree of thermal shrinkage of the thermal spray powder may be evaluated by comparing the values ​​of D 10 Decrease rate (%) or D 90 The reduction rate (%) may be used as an index for such evaluation. 10 D refers to the particle size at the 10% cumulative value from the smallest particle size in the volume-based particle size distribution measured using a particle size distribution analyzer based on the laser scattering and diffraction method. 90 refers to the particle size at 90% of the cumulative value from the smallest particle size in the volume-based particle size distribution measured using a particle size distribution measuring device based on the laser scattering and diffraction method.

[0033] Thermal spray powder D 10 The reduction rate (%) is calculated using the following formula (2): (The above APS pre-D 10 -D after the above APS 10 ) / D before the above APS 10 ×100 (2) The D of thermal spray powder can be calculated using 10 The reduction rate (%) is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more. 10 The greater the reduction rate (%), the denser and smoother the thermal spray coating can be produced.

[0034] Thermal spray powder D 90 The reduction rate (%) is calculated using the following formula (3): (The above APS pre-D 90 -D after the above APS 90 ) / D before the above APS 90 ×100 (3) The D of thermal spray powder can be calculated using90 The reduction rate (%) is preferably 35% or more, more preferably 40% or more, and even more preferably 45% or more. 90 The greater the reduction rate (%), the finer the thermal spray powder as a whole can be made, and in turn, the denser and smoother the thermal spray coating can be produced.

[0035] The angle of repose of the thermal spray powder disclosed herein can be 40 degrees or less. The angle of repose is one of the indicators that has traditionally been widely used to indicate the fluidity of a powder. The angle of repose of a thermal spray powder can be an indicator that reflects the fluidity of the thermal spray powder within a supply device, during transport from the supply device to the thermal spray device, etc. Therefore, specifying a smaller angle of repose makes it possible to achieve a thermal spray powder with higher fluidity, and ultimately to produce a more uniform thermal spray coating with higher productivity. The angle of repose of the thermal spray powder is preferably 39 degrees or less, more preferably 38 degrees or less, and even more preferably 37 degrees or less. There is no particular lower limit for the angle of repose, but if the angle of repose is too small, the thermal spray powder may be more likely to scatter or it may become difficult to control the supply rate of the thermal spray powder. From this perspective, the angle of repose of the thermal spray powder is preferably 20 degrees or more. Note that the angle of repose referred to here is the angle of repose before the APS.

[0036] The thermal spray powder disclosed herein has a bulk density of 3.0 g / cm 3 The bulk density of this thermal spray powder can be one of the indices for indicating the susceptibility to thermal shrinkage during thermal spraying. Therefore, the smaller the bulk density specified, the more easily the thermal spray powder can be thermally shrinked, and ultimately, the denser the thermal spray coating can be produced. The bulk density of the thermal spray powder is, for example, 2.0 g / cm 3 or less, preferably 1.5 g / cm 3 More preferably, it is 1.2 g / cm or less. 3 or less, and more preferably 1.0 g / cm 3 If the bulk density is too low, the productivity of the thermal spray coating may decrease. From this perspective, the bulk density of the thermal spray powder is set to 0.5 g / cm or less. 3The bulk density referred to here is the bulk density before the APS.

[0037] The granular strength (compressive strength) of the thermal spray powder disclosed herein is 0.7 kgf / mm 2 The granule strength is preferably 0.9 kgf / mm 2 More preferably, it is 1.0 kgf / mm 2 That's all. By setting the granule strength (compressive strength) within this range, it is possible to prevent the thermal spray powder from scattering or collapsing when being fed to a thermal spraying device or during thermal spraying, which in turn makes it possible to produce a uniform thermal spray coating with higher productivity. On the other hand, if the granule strength is too high, it may be difficult to sufficiently melt the thermal spray powder. From this perspective, the granule strength of the thermal spray powder should be set to 500 kgf / mm 2 The appropriate value is less than 400 kgf / mm 2 More preferably, it is 200 kgf / mm 2 The granule strength referred to here is the granule strength before the APS.

[0038] The average particle diameter (D 50 The average particle size (D 50 ) is preferably 14 μm or more, more preferably 18 μm or more, and even more preferably 22 μm or more. 50 By setting the average particle diameter (D) in this range, the flowability of the thermal spray powder can be made suitable for supplying the powder, which in turn makes it possible to produce a uniform thermal spray coating with higher productivity. 50 The average particle diameter (D) is, for example, 55 μm or less, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less. 50 By setting the average particle diameter (D) in this range, the thermal spray powder can be sufficiently melted during thermal spraying. 50It is particularly preferable to set the average particle diameter (D) to 20 μm to 30 μm. This makes it possible to produce a dense thermal spray coating with a smooth surface while realizing the desired flowability for the thermal spray powder. 50 ) is the average particle diameter before APS (D 50 )

[0039] The particle size distribution of the thermal spray powder disclosed herein can be appropriately set depending on the type and conditions of the apparatus used for thermal spraying to produce a thermal spray coating. 90 It is advisable to set the D of the thermal spray powder to 60 μm or less (for example, 50 μm or less). 10 It is advisable to set D to 20 μm or less. 90 and D 10 The above APS pre-D 90 and D 10 is.

[0040] When the ceramic particles constituting the thermal spray powder disclosed herein are secondary particles, the average particle diameter D of the ceramic primary particles constituting the secondary particles is 50 The average particle size D may be 10 μm or less. 50 The average particle diameter D is preferably 9 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less. 50 By setting the average particle diameter D in this range, the heat from the heat source can easily reach the center of the primary particles during thermal spraying of the thermal spray powder, which makes it possible to prevent the thermal spray powder containing unmelted portions due to insufficient heating from being mixed into the thermal spray coating, thereby enabling the production of a denser thermal spray coating. 50 The average particle diameter D is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. 50 By setting the temperature within this range, it is possible to suppress the occurrence of defects in the thermal spray coating that are thought to be caused by overheating, and to produce a denser thermal spray coating.

[0041] From the viewpoint of thermal shrinkage as described above, the thermal spray powder disclosed herein is preferably a granulated and sintered powder. This thermal spray powder is, for example, a thermal spray powder formed by mixing and granulating raw ceramic particle particles (primary particles), followed by sintering, and is composed of granulated and sintered particles as secondary particles formed by three-dimensionally bonding the primary particles with gaps between them. In other words, the ceramic particles that make up the thermal spray powder can be granulated and sintered particles of primary particles made of ceramic. Below, an example of a granulation and sintering method for suitably producing such granulated and sintered particles will be described, but it is not intended to be limited to this method.

[0042] <Method of manufacturing thermal spray powder> The granulation sintering method is a technique in which raw material particles (primary particles) are granulated into secondary particles and then sintered to firmly bond (sinter) the raw material particles together. In this granulation sintering method, granulation can be carried out using a granulation method such as dry granulation or wet granulation. Examples of granulation methods include tumbling granulation, fluidized bed granulation, stirring frame granulation, crushing granulation, melt granulation, spray granulation, and microemulsion granulation. Among these, spray granulation is a preferred granulation method.

[0043] Using the spray granulation method, a thermal spray powder can be produced, for example, by the following procedure. First, raw material particles having a desired composition are prepared, and their surfaces are stabilized with a protective agent or the like, as needed. The stabilized raw material particles are then dispersed in an appropriate solvent, along with spacer particles made of an organic material or the like, and optional binders and various additives (e.g., dispersants), as needed, to prepare a spray liquid. Dispersion of the raw material particles in the solvent can be carried out using, for example, a mixer or disperser, such as a homogenizer or a blade stirrer. The spray liquid is then sprayed using an ultrasonic atomizer or the like to form droplets. Granulated particles can be formed by, for example, passing the droplets through an airflow in a spray-drying device (spray dryer). The resulting granulated particles are introduced into a predetermined firing furnace and fired, thereby sintering the raw material particles. In this way, a thermal spray powder can be obtained that is composed of granulated and sintered particles in the form of secondary particles, in which primary particles are bonded together with gaps between them. The primary particles may have substantially the same size and shape as the raw material particles, or the raw material particles may have grown and bonded together by firing.

[0044] To impart a predetermined thermal shrinkage to the granulated and sintered particles (thermal spray powder) produced in this manner, it is preferable to use spacer particles in the preparation of the spray liquid. In this way, when the droplets are dried in the above-mentioned production process, the raw material particles, spacer particles, and binder are in a uniformly mixed state. The raw material particles and spacer particles are bound by the binder to form mixed particles. When these mixed particles are fired, the spacer particles and binder disappear (burn out), and the raw material particles are sintered. In this way, secondary particles are formed in which primary particles are bonded together with gaps. Note that during sintering, some of the raw material particles may become liquid, depending on their composition and size, and contribute to bonding with other particles. As a result, the average particle size of the primary particles may be larger than that of the raw material particles of the starting material. Furthermore, during the drying and firing processes, due to the disappearance of components other than the raw material particles and the densification of the raw material particles by firing, the average particle size of the resulting secondary particles becomes significantly smaller than the size of the droplets. The average particle size of the secondary particles and primary particles, and the size and proportion of the gaps formed between the primary particles can be appropriately designed according to the desired shape of the secondary particles.

[0045] When the spacer particles disappear from the mixed particles due to sintering of the granulated particles, pores are generated in the mixed particles where the spacer particles were previously present. Therefore, the use of spacer particles can increase the porosity of the granulated and sintered particles. Increasing the porosity of the granulated and sintered particles can increase the degree of thermal contraction of the granulated and sintered particles (i.e., thermal spray powder) during thermal spraying. The porosity of the granulated and sintered particles can be appropriately adjusted by the amount of spacer particles added, their particle size, shape, etc. For example, the mixing ratio of raw material particles to spacer particles (volume of raw material particles:volume of spacer particles) is preferably 80:20 to 10:90. The higher the mixing ratio (volume ratio) of spacer particles, the higher the porosity of the granulated and sintered particles, and ultimately the more dense and smooth the thermal spray coating can be produced. From this perspective, when the total volume of the raw material particles and the volume of the spacer particles is taken as 100 volume%, the volume fraction of the spacer particles is more preferably 30 volume% or more, and even more preferably 40 volume% or more. On the other hand, in order to improve the physical stability and handleability of the thermal spray powder and produce a uniform thermal spray coating with higher productivity, the volume fraction of such spacer particles is appropriately 80 mass % or less, and preferably 70 volume % or less.

[0046] The particle size of the spacer particles is, for example, 0.1 μm to 10 μm, preferably 1 μm to 5 μm. The spacer particles can be any pore-forming material (e.g., resin particles such as acrylic resin particles, epoxy resin particles, polyimide resin particles, and polyolefin particles) used to produce this type of granulated and sintered particles, without any particular limitations. The shape of the spacer particles is not particularly limited, but may be, for example, spherical or nearly spherical, plate-like, fibrous, or the like.

[0047] In the above manufacturing process, the concentration of raw material particles in the spray liquid is preferably adjusted to 10% by mass to 50% by mass. The amount of binder added is preferably adjusted to a ratio of 0.05% by mass to 10% by mass (for example, 1% by mass to 5% by mass) relative to the mass of the raw material particles. Examples of binders that can be added include carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP).

[0048] In the above manufacturing process, firing can be carried out in air, vacuum, or an inert gas atmosphere. To remove the spacer particles and binder, firing is preferably carried out in an oxygen-containing atmosphere. The firing temperature is preferably set to, for example, 600°C or higher and 1600°C or lower. After firing, the produced secondary particles may be crushed and / or classified, if necessary.

[0049] When the surface of a thermal spray powder composed of granulated and sintered particles produced as described above is observed using an SEM, it is found that the granulated and sintered particles have a ceramic matrix portion (the white portion in Figure 3) and open pores (the black portion in Figure 3). These open pores are independent of each other and are formed when the spacer particles are burned away during firing from the mixed particles of raw material particles and spacer particles formed in the above-mentioned production process. As described in the Examples below, the matrix portion and the independent open pore portion in the granulated and sintered particles can be separated using commercially available image analysis software.

[0050] The independent open pores may be substantially circular. "Substantially circular" means that the ratio (Dmax / Dmin) of the maximum diameter Dmax to the minimum diameter Dmin of the independent open pores is 1 to 1.8. The ratio (Dmax / Dmin) can be determined by observing the surface of the thermal spray powder with an SEM and analyzing the surface SEM image obtained. For example, five or more (e.g., ten or more) ceramic particles are randomly selected from the surface SEM image, and the ratio (Dmax / Dmin) is calculated for the independent open pores that occupy the interior of an imaginary circle drawn from the center of each particle and having a diameter equal to half the particle diameter of the particle. In addition, when calculating, a 1 μm binarization is performed. 2 It is desirable to exclude minute regions less than this value. By doing this, it is possible to obtain an arithmetic mean value that is closer to the actual value. The arithmetic mean value calculated here is used to evaluate the shape of the independent open pores.

[0051] The closed open pores may have approximately the same diameter. "Almost the same diameter" means, for example, that the Dmax and Dmin used in measuring the ratio (Dmax / Dmin) are both within 20% (preferably within 10%) of the average diameter of the closed open pores. The diameter of the closed open pores may be -20% to +20% of the size of the spacer particles used in the manufacturing process.

[0052] An average of 20 or more independent open pores may be present per granulated and sintered particle. The greater the number of independent open pores present on the surface of the granulated and sintered particles, the greater the degree of thermal shrinkage of the thermal spray powder, and ultimately, the more dense and smooth the thermal spray coating that can be produced. The average number of independent open pores per granulated and sintered particle is preferably 30 or more, more preferably 40 or more, and even more preferably 50 or more. Considering the flowability and granular strength of the thermal spray powder, the average number of independent open pores per granulated and sintered particle should be 200 or less (e.g., 150 or less, or 100 or less). The number of independent open pores may be counted for five or more (e.g., 10 or more) ceramic particles randomly sampled from a surface SEM image, and the arithmetic mean value may be calculated.

[0053] Alternatively, the thermal spray powder produced by the above-described production method may have an average porosity of 20% or more on the surface of the granulated and sintered particles. This porosity refers to the average value of the ratio of the total area of ​​open pores (independent open pores) to the area (projected area) of any number of particles (e.g., 1 to 5 particles per image) that are the subject of analysis when multiple (e.g., 5 to 10) SEM images of the surface of the granulated and sintered particles are observed. Note that, although only roughly half of the particle is observed in a surface SEM image, the area of ​​this half surface and the pore area can be conveniently doubled to determine the area and pore area of ​​the entire particle surface. Porosity is an index for evaluating the porosity of granulated and sintered particles, and is preferably 25% or more, and more preferably 30% or more. The higher the porosity, the greater the degree of thermal shrinkage of the thermal spray powder, and ultimately the more dense and smooth the thermal spray coating can be produced. On the other hand, taking into consideration the physical stability and handleability of the thermal spray powder, the porosity is, for example, 70% or less, preferably 60% or less, and more preferably 50% or less. Specific methods for measuring porosity are as described in the Examples below.

[0054] The mechanism by which the thermal spray powder disclosed herein exhibits a higher degree of thermal shrinkage than conventional methods will be described below with reference to FIGS. 1 and 2 . However, the mechanism by which the effects of the thermal spray powder disclosed herein are realized is not intended to be limited to the following. As shown in FIG. 1 , when ceramic particles 11 constituting the thermal spray powder disclosed herein are sprayed, the ceramic particles 11 are melted into flying particles 12 by the thermal energy generated during the spraying. When the flying particles 12 reach the substrate S, a thermal spray coating L1 is formed. When the ceramic particles 11 melt, the molten ceramic penetrates into the gaps P1 (open pores and closed pores). In other words, the volume of the gaps decreases. Therefore, the flying particles 12 shrink during spraying compared to before spraying. In this way, the flying particles 12 that have shrunk due to the spraying form the thermal spray coating L1, which can increase the density of the thermal spray coating L1 and further improve the smoothness of the surface of the thermal spray coating.

[0055] Comparing the thermal spray powder disclosed herein with a conventional thermal spray powder, conventional ceramic particles 21 shown in FIG. 2 also have voids P2. However, the volume of the voids in ceramic particles 21 is smaller than the volume of the voids in ceramic particles 11. Therefore, the degree of thermal contraction of ceramic particles 21 when they become flying particles 22 is smaller than the degree of thermal contraction of ceramic particles 11. Furthermore, compared to ceramic particles 11, the interior of ceramic particles 21 is more solid, and even if the particle surface is melted by thermal spraying, the interior of the particle may reach substrate S in an unmelted state (unmelted particles 23). For these reasons, it is believed that the density and surface smoothness of thermal spray coating L1 produced by thermal spraying ceramic particles 11 are greater than those of thermal spray coating L2 produced by thermal spraying ceramic particles 21.

[0056] The thermal spray powder disclosed herein can be sprayed by various thermal spraying methods to produce thermal spray coatings on various substrates. The thermal spray powder disclosed herein can be particularly preferably used to produce thermal spray coatings by plasma spraying methods such as atmospheric plasma spraying (APS), low pressure plasma spraying (LPS), and high pressure plasma spraying. This thermal spray powder can also be suitably used for high velocity flame spraying, such as high velocity oxygen flame (HVOF) thermal spraying, warm spray thermal spraying, and high velocity air flame (HVAF) thermal spraying. The thermal spray powder may be supplied to a thermal spraying device in the form of a powder, or in the form of a slurry in which the powder is dispersed in an appropriate dispersion medium.

[0057] The type of substrate used to produce the thermal spray coating is not particularly limited. Examples of substrates include aluminum, aluminum alloys, iron, steel, copper, copper alloys, nickel, nickel alloys, gold, silver, bismuth, manganese, zinc, and zinc alloys. Among these, preferred examples include substrates made of widely used metallic materials, such as steels typified by various SUS materials (which may be so-called stainless steels) used as corrosion-resistant structural steels, aluminum alloys typified by 1000 series to 7000 series aluminum alloys useful as lightweight structural materials, and Ni-, Co-, or Fe-based corrosion-resistant alloys typified by Hastelloy, Inconel, Stellite, and Invar. [Example]

[0058] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in the following examples.

[0059] <Production example> [Sample production] (Sample 1) As raw material powder, the average particle diameter D 50 Yttrium oxide powder (primary particles) with an average particle diameter of 0.9 μm and 50A mixed powder was prepared by mixing the above powder with yttrium oxide powder (primary particles) having a particle size (particle diameter) of 3.0 μm. Acrylic resin spacer particles (hereinafter also referred to as "acrylic particles") having a particle size (particle diameter) of approximately 3 μm (MX-300, manufactured by Soken Chemical & Engineering Co., Ltd.) were prepared as spacer particles. A spray liquid was prepared by blending 70 volume % of the above mixed powder and 30 volume % of acrylic particles and dispersing the blend in an aqueous solution containing 2 weight % of binder. The spray liquid contained 90.7 weight % of yttrium oxide particles and 9.3 weight % of acrylic particles. This spray liquid was sprayed into an airflow using a spray granulator and dried to produce granulated particles. The resulting granulated particles were fired at 1600°C to sinter the primary particles, and then crushed and classified to produce a thermal spray powder composed of granulated and sintered particles (secondary particles). This thermal spray powder was designated Sample 1 according to this production example. Average particle size D of sample 1 50 was 27 μm.

[0060] (Sample 2) The blending ratio was 40% by volume of the above mixed powder and 60% by volume of acrylic particles. In the spray liquid, the content of yttrium oxide particles was 73.5% by weight, and the content of acrylic particles was 26.5% by weight. Except for this, the thermal spray powder of Sample 2 was manufactured using the same materials and process as Sample 1. The average particle diameter D of Sample 2 50 was 27 μm.

[0061] (Sample 3) As raw material powder, the average particle diameter D 50 The thermal spray powder of Sample 3 was manufactured using the same materials and process as Sample 1. The average particle diameter D of Sample 3 was 2.4 μm. 50 was 27 μm.

[0062] (Sample 4) A fused and pulverized powder of yttrium oxide was prepared as Sample 4. First, raw material powders were blended so as to obtain the target yttrium oxide (YO). The raw material powder was heated to melt, and then cooled to prepare a solidified product (ingot). This solidified product was pulverized by mechanical means and classified as necessary to obtain the fused and pulverized powder of Sample 4. The average particle diameter D of Sample 4 was 50 was 29 μm.

[0063] [Measurement of particle size distribution] The volumetric particle size distribution of the thermal spray powders of Samples 1 to 4 was measured using a laser diffraction / scattering particle size analyzer (Malvern Panalytical, Mastersizer 3000). v10 ,D v50 , and D v90 Indicates the value of

[0064] [Angle of repose] The angle of repose of the thermal spray powders of Samples 1 to 4 was measured in accordance with JIS R9301-2-2:1999. The angle of repose was measured by subjecting each thermal spray powder to an ABD powder property measuring instrument (Model ABD-72, manufactured by Tsutsui Rikakikai Co., Ltd.). The corresponding column in Table 1 shows the measured angle of repose values.

[0065] [Measurement of bulk density] The bulk density (g / cm) of the thermal spray powders of Samples 1 to 4 was 3 ) was measured in accordance with JIS Z2504:2012. 3 The bulk density (g / cm) measured in the corresponding column in Table 1 is the value obtained by subjecting each thermal spray powder to a JIS bulk density measuring instrument for metal powders (manufactured by Tsutsui Scientific Instruments Co., Ltd.). 3 ) value.

[0066] [SEM observation] Planar and cross-sectional images of the thermal spray powders of Samples 1 to 4 were obtained using a benchtop SEM (Phenom ProX, manufactured by Phenom-World). The observation magnification was 5000x. For reference, Figures 3 to 8 show surface and cross-sectional SEM images of Samples 1 to 3. The scale bars in Figures 3 to 8 indicate 10 μm.

[0067] [Particle surface porosity] The ratio of the area of ​​open pores to the total area of ​​the particle surface (porosity (%) of the particle surface) was measured for the thermal spray powders of Samples 1 to 4. The surface SEM images of each sample obtained in the above [SEM observation] were binarized by specifying only the particle portion of the surface SEM image using image analysis software (Image-Pro Plus, manufactured by Nippon Roper Co., Ltd.). Specifically, a contrast threshold was determined, and the white areas were designated as the matrix (yttrium oxide) areas, and the black areas were designated as open pores. The ratio of the area of ​​open pores was then calculated when the area (projected area) subject to image analysis was taken as 100%. This measurement was performed on 10 randomly selected ceramic particles. The obtained arithmetic mean value was taken as the particle surface porosity (%) for each thermal spray material. The measured particle surface porosity (%) values ​​are shown in the corresponding columns in Table 1.

[0068] [Table 1]

[0069] As shown in Figures 3 to 8 and Table 1, which show the results of this production example, open and closed pores were observed in the thermal spray powders (Samples 1 and 2) obtained by granulating and sintering using a spray solution containing yttrium oxide particles and a predetermined amount of spacer particles (acrylic particles). These samples exhibited surface porosity of 20% or more, and the porosity increased depending on the amount of spacer particles. Meanwhile, the particle size distributions of Samples 1 to 3, which were composed of granulated and sintered particles, were similar regardless of whether spacer particles were used. Furthermore, the angles of repose of Samples 1 to 4 were all 40° or less, confirming that the thermal spray powders had fluidity suitable for thermal spraying. Furthermore, the use of spacer particles to produce granulated and sintered particles reduced the bulk density of the thermal spray powder.

[0070] <Creating flying particles> The thermal spray powders of Samples 1 to 4 produced in the above Production Examples were subjected to atmospheric plasma spraying (APS) in water under the following thermal spraying conditions to produce flying particles of each sample. [Thermal spraying conditions] Thermal spray machine: SG-100 (Praxair) Powder feeder: Model 1264 (Praxair) Plasma working gas: Argon (Ar) gas (50 psi (0.34 MPa)); and Helium (He) gas (50 psi (0.34 MPa)) Plasma output: 36kW Plasma generation voltage: 40V Plasma generation current: 900A Thermal spray powder supply rate: 20g / min Spraying distance: 400mm

[0071] To produce flying particles, Ar gas (primary gas) and He gas (secondary gas) were first supplied to the thermal spray gun at atmospheric pressure as plasma working gases, and a voltage was applied between the cathode and anode to generate plasma. The plasma generation conditions during thermal spraying were as described above. The plasma generation current was set to 900 A, and the plasma generation voltage accordingly varied between 38 and 42 V, resulting in a plasma output ranging from 34 to 38 kW. Each sample of thermal spray powder was supplied into this plasma using the powder feeder, and the powder was then injected into cold water. The plasma irradiation angle relative to the water surface was 90 degrees. Note that the "spraying distance" mentioned above for producing flying particles refers to the distance from the tip of the thermal spray gun to the water surface.

[0072] As described above, the water after the spray powder was sprayed by atmospheric plasma spraying was collected. The spray powder (ceramic particles) contained in the collected water was dried to form the flying particles for each sample. For reference, Figures 9 to 11 show SEM observation images (1000x magnification) of each sample. The scale bars in Figures 9 to 11 indicate 80 μm.

[0073] [Measurement of particle size reduction rate] The particle size distribution of the flying particles in each example was measured on a volume basis in the same manner as in the measurement of the particle size distribution of the thermal spray powder in the above production examples. v10 ,D v50 , and D v90 and the D of the thermal spray powder before APS. v10 ,D v50 , and D v90 The reduction rate (%) of each particle size due to APS was calculated for each sample of thermal spray powder. Specifically, the reduction rate (%) of D before and after APS was calculated based on the above formulas (1) to (3). v10 ,D v50 , and D v90 Calculate the reduction rate (%) of D v10% Decrease rate (%), D v50% Decrease rate (%), and D v90% The corresponding column in Table 2 shows the reduction rate (%) of D after APS. v10 ,D v50 , and D v90, and the reduction rate (%) of each particle size are shown.

[0074] [Table 2]

[0075] As shown in Table 2, the D of ceramic particles in both samples was significantly different before and after APS. v10 ,D v50 , and D v90 It was confirmed that the D of sample 4 was small. v10 When comparing thermal spray powders made of granulated and sintered particles produced using spacer particles (samples 1 and 2) with thermal spray powders that did not use spacer particles (samples 3 and 4), it was confirmed that the particle size reduction rate (%) in samples 1 and 2 was greater than that in samples 3 and 4.

[0076] <Making of thermal spray coating> Thermal spray coatings were produced by APS using the thermal spray powders of Samples 1 to 4 produced in the above Production Example. In this example, the substrate was an aluminum alloy (Al6061) plate (70 mm × 50 mm × 2.3 mm) whose surface was roughened by blasting with brown alumina abrasive (A#40). The equipment, plasma generation conditions, and thermal spray powder supply rate used in this example were the same as those in the "Production of Flying Particles" section above. In this example, the thermal spray powder of each sample was supplied into the plasma generated by the thermal spray gun. The thermal spray gun was moved at a speed of 400 mm / s, with the plasma irradiation angle to the substrate set at 90 degrees, to produce the thermal spray coatings of Samples 1 to 4. The thermal spray distance was set to 90 mm to 130 mm. The "spraying distance" used in the production of thermal spray coatings refers to the distance from the tip of the thermal spray gun to the substrate. For reference, Figures 12 to 14 show cross-sectional SEM images (observation magnification: 1000x) of the thermal spray coatings of Samples 1 to 3. The scale bars in Figures 12 to 14 indicate 80 µm.

[0077] [Deposition rate] The coating rate (μm / pass) in producing the above thermal spray coating was calculated using the thermal spray powders of Samples 1 to 4. The coating rate (μm / pass) is the thickness (μm) of the thermal spray coating produced in one thermal spraying operation (1 pass) performed by the thermal spraying device (thermal spray gun) along the direction of travel of the thermal spraying device. Representative coating rates (μm / pass) for each sample are shown in the corresponding column in Table 3. The values ​​listed in the "Spraying Distance" column in Table 3 are the spraying distances at which the coating rate, density (described below), and surface roughness (described below) were measured.

[0078] [Denseness] The density of the thermal spray coatings of Samples 1 to 4 formed as described above was evaluated by measuring the porosity (%) of the thermal spray coating. The porosity was determined by image analysis of cross-sectional SEM images taken approximately perpendicular to the substrate. First, the thermal spray coating was cut perpendicular to the substrate surface together with the substrate, and an arbitrary cross section in the thickness direction was extracted. The cross-sectional SEM image of the thermal spray coating at this cross section was analyzed using image analysis software (Image-Pro Plus, manufactured by Nippon Roper Co., Ltd.) to perform binarization to separate the pores and solid phase, and the porosity (%), defined as the ratio of the pore area to the total cross-sectional area, was calculated. The representative porosity (%) of each sample is shown in the corresponding column in Table 3.

[0079] [Surface roughness measurement] The surface roughness (arithmetic mean roughness) Ra of the thermal spray coatings of Samples 1 to 4 was measured in accordance with JIS B0601:2013. The surface roughness Ra was determined by measuring the surface roughness at five random points on each thermal spray coating using a surface roughness measuring instrument "SV-3000S CNC" (manufactured by Mitutoyo Corporation) and calculating the arithmetic mean value of these measurements. Representative surface roughness Ra (μm) for each sample is shown in the corresponding column of Table 3. For reference, FIG. 15 shows the surface roughness Ra (μm) of the thermal spray coatings produced by spraying the thermal spray powders of Samples 1 to 3 at a spraying distance of 90 mm or 100 mm. The vertical axis "Ra / μm" in the graph of FIG. 15 represents the surface roughness Ra (μm). The horizontal axis "spraying distance / mm" in the graph of FIG. 15 represents the spraying distance (mm). In the graph of FIG. 15, in each section divided by spraying distance, the left bar is Sample 1, the center bar is Sample 2, and the right bar is Sample 3.

[0080] [Table 3]

[0081] As shown in Table 3, the coating rate was similar when using the thermal spray powder of each sample, regardless of the method of preparation of the thermal spray powder. Furthermore, when comparing the thermal spray coatings produced using the thermal spray powders prepared using spacer particles (Samples 1 and 2) with those produced using the thermal spray powders not using spacer particles (Samples 3 and 4), it was confirmed that the surface roughness Ra (μm) of the thermal spray coatings of Samples 1 and 2 was smaller than that of Samples 3 and 4. Furthermore, the porosity (%) of the thermal spray coating of Sample 2 was smaller than that of the other samples, indicating that the use of spacer particles can contribute to the production of thermal spray coatings with flatter and denser surfaces.

[0082] As is clear from the above results, when a thermal spray powder containing ceramic particles is sprayed under predetermined conditions into water and the powder is compared before and after atmospheric plasma spraying, the average particle diameter (D 50It was found that by using thermal spray powders (Samples 1 and 2) characterized by a value of σ (σ) that is at least 25% smaller, it is possible to supply finer particles to the substrate and produce a thermal spray coating. By using such thermal spray powders, it is possible to produce a thermal spray coating with a smoother surface. Furthermore, such thermal spray powders are suitable for producing denser thermal spray coatings. [Explanation of symbols]

[0083] 11,21 Ceramic particles 12,22 Flying particles 23 Unmelted particles L1, L2 spray coating S base material

Claims

1. A thermal spray powder comprising: It is composed of ceramic particles, The thermal spray powder was subjected to the following conditions: Plasma working gas: Argon (Ar) gas: 50 psi; and Helium (He) gas: 50 psi Plasma output: 36 kW Supply rate of thermal spray powder: 20 g / min Spraying distance: 400 mm When comparing the average particle diameter (D) of the thermal spray powder based on a laser diffraction scattering method after atmospheric pressure plasma spraying in water with that before the thermal spraying, ５０ ) is reduced by at least 25%; the ceramic particles are granulated and sintered particles of primary particles made of the ceramic, A thermal spray powder characterized in that the average ratio of the area of ​​open pores to the total area of ​​the surface, based on SEM observation of the surface of the ceramic particles, is 20% or more.

2. A thermal spray powder, It is composed of ceramic particles, The thermal spray powder was subjected to the following conditions: Plasma working gas: Argon (Ar) gas: 50 psi; and Helium (He) gas: 50 psi Plasma output: 36 kW Supply rate of thermal spray powder: 20 g / min Spraying distance: 400 mm when comparing the average particle size (D 50 ) of the thermal spray powder after atmospheric pressure plasma spraying in water with the value before the spraying, the average particle size (D 50 ) of the thermal spray powder determined by a laser diffraction scattering method is reduced by at least 25%; the ceramic particles are granulated and sintered particles of primary particles made of the ceramic, the ratio (Dmax / Dmin) of the maximum diameter Dmax to the minimum diameter Dmin of open pores present on the surface of the ceramic particles is 1 to 1.8 when the surfaces of the ceramic particles are observed with an SEM.

3. A thermal spray powder, comprising: It is composed of ceramic particles, The thermal spray powder was subjected to the following conditions: Plasma working gas: Argon (Ar) gas: 50 psi; and Helium (He) gas: 50 psi Plasma output: 36 kW Supply rate of thermal spray powder: 20 g / min Spraying distance: 400 mm when comparing the average particle size (D 50 ) of the thermal spray powder after atmospheric pressure plasma spraying in water with the value before the spraying, the average particle size (D 50 ) of the thermal spray powder determined by a laser diffraction scattering method is reduced by at least 25%; A thermal spray powder having an angle of repose of 40 degrees or less.

4. 3. The thermal spray powder according to claim 1, having an angle of repose of 40 degrees or less.

5. the ceramic particles are granulated and sintered particles of primary particles made of the ceramic, 4. The thermal spray powder according to claim 2, wherein the average ratio of the area of ​​open pores to the total area of ​​the surface of the ceramic particles, based on SEM observation of the surface, is 20% or more.

6. the ceramic particles are granulated and sintered particles of primary particles made of the ceramic, 4. The thermal spray powder according to claim 1, wherein, when the surfaces of the ceramic particles are observed with an SEM, the ratio (Dmax / Dmin) of the maximum diameter Dmax to the minimum diameter Dmin of open pores present on the surfaces is 1 to 1.

8.

7. The average particle diameter (D ５０ 7. The thermal spray powder according to claim 1, wherein the average particle size is 0.5 μm or more and 5 μm or less.

8. A thermal spray powder described in any one of claims 1 to 7, which is composed of oxide ceramic particles.

9. The thermal spray powder according to any one of claims 1 to 8, having a bulk specific gravity of 1.0 or less.

10. A method for producing a thermal spray coating by thermally spraying the thermal spray powder according to any one of claims 1 to 9 onto the surface of a substrate.

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