Surface treatment method for ceramic thermal spray coating and ceramic thermal spray coating

Abstract

To provide a surface treatment method for smoothing a surface of a thermal-spray ceramic coating film, and a thermal-spray ceramic coating film with surface smoothing treatment applied thereto.SOLUTION: A surface treatment method for a thermal-spray ceramic coating film smooths a surface of the thermal-spray ceramic coating film by spraying a slurry at a pressure of 0.01-1.0 MPa using a compressed air, the slurry containing a liquid with a viscosity of 10 mPa / s or lower at 20°C and a polyhedron-shaped powdery medium with a median diameter (D50) of 1-50 μm at a content of 1-50 vol.% onto the surface of the thermal-spray ceramic coating film.SELECTED DRAWING: Figure 2a

Description

[Technical Field]

[0001] The present invention relates to a novel surface treatment method for smoothing the surface of a ceramic spray coating, and to a novel ceramic spray coating that has been subjected to a smoothing treatment. [Background technology]

[0002] Anodizing, plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, and painting are methods for coating substrates with the purpose of protecting the surface or adding functionality. Of these, thermal spraying can form a film with a thickness of several hundred microns to several millimeters in a short time, and is widely used in applications requiring thick films due to its high productivity. Thermal spraying also offers a high degree of freedom in the selection of materials used, allowing various metals and ceramics to be formed into coatings. Metal spray coatings are used as sacrificial anticorrosion coatings that protect substrates from corrosive environments by forming metal films that are more electrically base than the substrate, and to improve the wear resistance of sliding parts. Ceramic spray coatings have excellent heat resistance, wear resistance, and plasma etching resistance, and are therefore widely used as thermal insulation layers that block heat input to the substrate being sprayed, components that come into contact with other components and are worn away by etching, and components that are exposed to plasma and worn away.

[0003] However, because thermal spraying involves spraying molten material particles onto the target, the roughness of the coating surface is strongly dependent on the size of the material particles used, resulting in a higher roughness than other coating methods. For example, even if a coating has excellent abrasion resistance, if it comes into contact with another component when its surface roughness is high, it can cause the fragile structure of the coating surface to fall off, wear due to friction, or adhesion to the mating component, resulting in changes to the coating's surface roughness and coefficient of friction. For these reasons, surface treatments for thermal spray coatings to smooth them before application are being considered.

[0004] Patent Document 1 proposes a method for obtaining stable test results in a tire testing machine, in which the surface of a rotating drum simulating a road surface is coated with a steel-based metal spray coating that is stronger than the road surface substrate, and the surface is smoothed by mechanical polishing, thereby suppressing changes in roughness and friction coefficient due to tire adhesion. Furthermore, Patent Document 2 proposes a surface treatment method in which the surface of a metal spray coating formed on the surface of a building material such as concrete is polished using a jet process such as liquid honing or dry blasting, thereby obtaining a glossy finished surface similar to that of a metal surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-36750 [Patent Document 2] Japanese Patent Publication No. 04-083862 Summary of the Invention [Problem to be solved by the invention]

[0006] In the mechanical polishing method for smoothing the surface of a thermal spray coating disclosed in Patent Document 1, a processing tool is pressed directly against the coating surface to perform the grinding, generating large localized loads. Since the thermal spray coating is damaged if the substrate deforms significantly due to the load, the workpiece is required to have a structure and strength that will not deform under the load. This is particularly problematic for ceramic thermal spray coatings, which are more brittle and prone to breakage than metal thermal spray coatings.

[0007] In addition, in mechanical polishing, if the workpiece has a curved surface or a three-dimensional shape consisting of two or more surfaces, it is necessary to use a machining center, but the size of the workpiece becomes large. As the size of the workpiece increases, the dimensions of the processing equipment also become correspondingly larger, resulting in problems such as limited processing range due to interference between the processing equipment and the workpiece, and increased equipment installation costs. Furthermore, mechanical polishing requires that the tip of the processing tool be in contact with the surface of the workpiece, and detailed dimensional information about the workpiece must be grasped and taught to the processing machine so that the processing tool can be aligned over the entire processing range. However, measuring the dimensions and shape of workpieces with complex curved surfaces is difficult, and many practical challenges remain for smoothing by mechanical grinding.

[0008] On the other hand, blasting processes such as liquid honing and dry blasting, which are methods for smoothing the surface of thermally sprayed coatings disclosed in Patent Document 2, involve spraying powder media such as abrasive particles, either alone or in a mixture with a liquid, onto the target object using compressed air to scrape the surface, or creating a peening effect through impact caused by the collision of the media. Because spray guns are smaller than machining centers, they are less likely to interfere with the target object. Furthermore, the spray effect is achieved even when the distance from the spray gun to the target surface changes, making it easy to follow the spray even on surfaces with complex three-dimensional shapes. Due to these advantages, blasting processes are easier to use on larger targets and more complex shapes than smoothing processes using a machining center.

[0009] However, in Patent Document 2, the thermal spray coating is a metallic material, and ceramic thermal spray coatings are not considered. As a result of research conducted by the present inventors, when spraying onto a ceramic thermal spray coating, friction and piezoelectric effects upon collision of the media cause the ceramic coating to become charged or generate heat, resulting in destruction of the ceramic coating. In addition, when hard media such as abrasive particles are collided with the surface of a brittle ceramic material, the media are likely to penetrate the treated surface and remain, causing surface contamination. Furthermore, when the colliding media does not have a cutting effect on the ceramic spray coating surface and bounces off the surface, the treated surface of the ceramic spray coating fractures, forming a brittle structure, and fractures occur at the bonding interfaces between the sprayed particles, causing the sprayed particles to peel off, exposing a new, uncut surface on the outermost surface.

[0010] The problems that arise when spraying ceramic spray coatings as described above are avoided in fields such as semiconductor manufacturing equipment, where high levels of cleanliness and uniformity are required for the spray coating surface. Furthermore, to spray media stably, it is necessary to use media with good fluidity. Since fluidity decreases as the media particle size decreases, the media that can be used in spraying processes are limited to relatively large particle sizes. Larger particle-sized media have little smoothing effect and have a large impact on the target object, inducing surface fracture. Therefore, there is a demand for the development of a surface treatment that can stably handle smaller particle-size media.

[0011] The present invention was made under the above circumstances, and its object is to provide a new surface treatment method for smoothing the surface of a ceramic sprayed coating, and a new ceramic sprayed coating that has been subjected to a smoothing treatment. [Means for solving the problem]

[0012] The present invention has been made to achieve the above object and includes the following embodiments. (1) A surface treatment method for a ceramic spray coating, comprising spraying onto the surface of the ceramic spray coating a slurry containing a liquid having a viscosity of 10 mPa / s or less at a temperature of 20°C and powder media having a polyhedral shape and a median diameter (D50) of 1 to 50 μm, the slurry containing the powder media at a content of 1 to 50 volume %, using compressed gas at a pressure of 0.01 to 1.0 MPa, to smooth the surface of the ceramic spray coating. (2) The material of the ceramic spray coating is a rare earth oxide, a rare earth oxyfluoride, a rare earth fluoride, alumina (Al2O3), YAG (Y3Al5O 12 ), or YAP (YAlO3). (3) The surface treatment method according to (1) or (2) above, wherein the powder media is a polyhedron having four or more faces, with angles formed between the faces ranging from 10 to 135 degrees. (4) A surface treatment method according to any one of (1) to (3) above, wherein the powder media is formed from glass containing silicon oxide (SiO2) as a main component, alumina (Al2O3), silicon carbide (SiC), boron carbide (B4C), silicon nitride (Si3N4), zirconia (ZrO2), carbon steel, or stainless steel. (5) The surface treatment method according to any one of (1) to (4) above, wherein the liquid is water or an alcohol having 2 to 4 carbon atoms.

[0013] (6) The surface treatment method according to any one of (1) to (5) above, wherein the compressed gas is air, nitrogen, carbon dioxide, or argon. (7) The surface treatment method according to any one of (1) to (6) above, wherein the surface of the ceramic spray coating is smoothed so that the arithmetic mean roughness Ra is 3.0 μm or less and the skewness Rsk is 0 or less. (8) The surface treatment method according to any one of (1) to (7) above, wherein a plurality of cutting marks having a width of 0.01 to 5 μm and a length of 0.01 to 10 μm are formed on the surface of the ceramic spray coating. (9) A surface treatment method according to any one of (1) to (8) above, wherein the surface of the ceramic spray coating is smoothed so that the occupied area ratio of the newly formed surface calculated by the following formula (1) is 10% or less. New surface area ratio (%) = (new surface area / surface treatment surface area) x 100: (1) (10) A surface treatment method according to any one of (1) to (9) above, wherein the surface of the ceramic spray coating is smoothed so that the area ratio of the cutting marks calculated by the following formula (2) is 50% or more. Area ratio of cutting marks (%) = {(area of ​​cutting marks - area of ​​voids - area of ​​new surface) / area of ​​surface-treated surface} × 100: (2) (11) The surface treatment method according to any one of (1) to (10) above, wherein the ceramic sprayed coating is a sprayed coating on an inner wall member of a plasma etching apparatus for semiconductor manufacturing. (12) The surface treatment method according to any one of (1) to (10) above, wherein the ceramic sprayed coating is a sprayed coating on a sliding member such as a bearing, a piston, or a cylinder.

[0014] (13) A ceramic spray coating that has been subjected to a smoothing surface treatment, the arithmetic mean roughness Ra of the treated surface being 3 μm or less, and the skewness Rsk being 0 or less. (14) The ceramic spray coating according to (13) above, wherein the occupied area ratio of the newly formed surface calculated by the following formula (1) is 10% or less. New surface area ratio (%) = (new surface area / surface treatment surface area) x 100: (1) (15) The ceramic spray coating according to (13) or (14) above, wherein the area ratio of the cutting marks calculated by the following formula (2) is 50% or more. Area ratio of cutting marks (%) = {(area of ​​cutting marks - area of ​​voids - area of ​​new surface) / area of ​​surface-treated surface} × 100: (2) [Effects of the Invention]

[0015] The present invention provides a novel surface treatment method capable of smoothing a ceramic spray coating, and a ceramic spray coating that has been subjected to a smoothing surface treatment. In particular, the present invention provides a novel ceramic spray coating that is useful for inner wall members of plasma etching equipment used in semiconductor manufacturing, which require high cleanliness, because it has less brittle, fractured layers that are prone to falling off after the smoothing treatment. [Brief explanation of the drawings]

[0016] [Figure 1]1 shows an SEM image of the surface of a ceramic spray coating before the surface treatment of the present invention. [Figure 2a] 1 is an SEM image (×1000 magnification) of the surface of a ceramic spray coating obtained by a surface treatment method according to an embodiment of the present invention, particularly showing the state of the newly formed surface b and voids c. [Figure 2b] 1 is an SEM image (×1000 magnification) of the surface of a ceramic spray coating obtained by a surface treatment method according to an embodiment of the present invention, and particularly shows the state of cutting marks in each 10 μm×10 μm section. [Figure 2c] 1 shows an SEM image (×5000 magnification) of the surface of a ceramic spray coating obtained by a surface treatment method according to an example of the present invention. [Figure 2d] 1 shows an SEM image of the surface of a ceramic spray coating obtained by the surface treatment method of Comparative Example 1. [Figure 2e] 1 shows an SEM image of the surface of a ceramic spray coating obtained by the surface treatment method of Comparative Example 2.

[0017] [Figure 3a] 1 shows an SEM image of the adhesive surface of an adhesive tape that was attached to the surface of a ceramic spray coating obtained by a surface treatment method according to an embodiment of the present invention and then peeled off. [Figure 3b] 1 shows an SEM image of the adhesive surface of an adhesive tape that was attached to the surface of the ceramic spray coating obtained by the surface treatment method of Comparative Example 1 and then peeled off. [Figure 3c] 1 shows an SEM image of the adhesive surface of an adhesive tape that was attached to the surface of a ceramic spray coating obtained by the surface treatment method of Comparative Example 2 and then peeled off. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes in detail the embodiments of the present invention. In this specification, when a numerical range is expressed as "X to Y," the lower limit (X) and the upper limit (Y) are included. When the upper and lower limits have the same unit, the unit of the lower limit may be omitted.

[0019] [Ceramic spray coating] The ceramic spray coating material that is the target of the surface treatment of the present invention includes inorganic solid materials that are mainly composed of non-noble metals, such as ceramics such as oxides, fluorides, silicides, nitrides, carbides, borides, and carbon. Examples include zirconia (ZrO2), silicon dioxide (SiO2), alumina (Al2O3), yttria (Y2O3), calcium fluoride (CaF2), yttrium fluoride (YF3), tungsten silicide (WSi2), tungsten carbide (WC), and zirconium boride (ZrB2). Also included are complex oxides, complex fluorides, oxyfluorides, and carbonitrides containing two or more types of anions or cations. Examples include YAG (Y3Al5O 12 ), potassium zirconium fluoride (K2ZrF6), yttrium oxyfluoride (YOF), soda glass whose main component is silicon oxide, and borosilicate glass are examples.

[0020] The ceramic spray coating material in the present invention may be a rare earth oxide, a rare earth oxyfluoride, a rare earth fluoride, alumina (Al2O3), YAG (Y3Al5O 12 ), YAP (YAlO3), etc. Among these, yttria (YO3), yttrium oxyfluoride (YOF), and yttrium fluoride (YF3) are preferred. This is because thermal spray coatings made of these materials are suitable for semiconductor manufacturing equipment, etc., which require high surface smoothness as well as high cleanliness and uniformity. The substrate material on which the ceramic spray coating is formed may be a known material such as an aluminum alloy, a stainless steel alloy, quartz, an alumina sintered body, etc. The method for forming the ceramic spray coating may be a known method such as atmospheric plasma spraying or low-pressure plasma spraying.

[0021] An SEM image of the surface of a ceramic spray coating before the surface treatment of the present invention is shown in Figure 1. As can be seen in Figure 1, the surface of the ceramic spray coating before the surface treatment has an uneven surface roughness, which indicates that the molten ceramic particles collided with the substrate during the spraying process, flattening the particles or scattering as droplets.

[0022] [Surface treatment method] In the surface treatment method of the present invention, a slurry containing polyhedral powder media is blasted (sprayed) onto the surface of the above-mentioned ceramic spray coating using a compressed gas such as compressed air. The slurry, blasting equipment, and blasting conditions used in the surface treatment are described below.

[0023] (slurry) The slurry used in the surface treatment method of the present invention is formed in a state in which powder media are suspended in a liquid. The content (concentration) of powder media in the slurry is preferably 1 to 50% by volume, in volume percent. If the content of powder media is less than 1% by volume, the amount of grinding is reduced, which increases the time required for surface treatment and is inefficient. On the other hand, if the content of powder media is more than 50% by volume, the powder media will not disperse in the liquid and will settle, making it impossible to obtain a suitable slurry. The content of powder media is more preferably 5 to 45% by volume, and even more preferably 10 to 40% by volume.

[0024] The liquid constituting the slurry preferably has a viscosity of 10 mPa / s or less at a temperature of 20°C. If the viscosity is greater than 10 mPa / s, it becomes difficult to spray the liquid. The viscosity of the liquid is more preferably 1 to 5 mPa / s, and particularly preferably 1 to 3 mPa / s. The liquid is preferably water or a hydrophilic solvent. Preferred examples of the hydrophilic solvent include alcohols having 2 to 4 carbon atoms, such as ethyl alcohol and isopropyl alcohol.

[0025] The powder media constituting the slurry has a polyhedral shape. In the present invention, the term "polyhedron" in the media refers to a solid body formed by straight edges connecting multiple vertices and faces enclosed by those edges. The polyhedron has, for example, four or more faces, preferably five or more faces, and for example, 20 or fewer faces, preferably 15 or fewer faces. The polyhedron may be an irregular polyhedron or a regular polyhedron (such as a regular hexahedron (cube) or regular octahedron). The powder media may also be a mixture containing two or more of these irregular polyhedrons and / or regular polyhedrons. In particular, the angle between the faces of the polyhedron is preferably an acute angle of 10 to 135 degrees, more preferably 10 to 90 degrees, and particularly preferably 30 to 80 degrees. By having an angle within the above range, when the polyhedron collides with the surface of the thermal spray coating during blasting (spraying) treatment, cutting marks are easily formed on the surface of the thermal spray coating.

[0026] In the present invention, the term "polyhedron" does not include spheres or ellipsoids (rugby balls) that have no vertices (corners). When using powder media that are spherical or ellipsoidal and have no vertices, the media that collide with the treated surface of the ceramic spray coating bounces off without being able to cut into the surface, and the kinetic energy of the collision acts as an impact on the treated surface rather than cutting. As a result, the surface of the ceramic spray coating is not cut, and the impact can result in the formation of a brittle layer that is fractured or the spray particles falling off due to fractures between the spray particles. In the surface treatment method of the present invention, by using polyhedral powder media, the tips of the media, such as the vertices of the polyhedrons that collide with the surface of the ceramic sprayed coating, cut into and cut the treated surface of the sprayed coating, thereby smoothing the coating while suppressing fracture of the surface of the sprayed coating and peeling of the sprayed particles due to breakage between the sprayed particles.

[0027] The particle size of the powder media is preferably 1 to 50 μm in median diameter D50. If the particle size is less than 1 μm, the amount of grinding will be reduced, which will increase the time required for surface treatment and make it less efficient. On the other hand, if the particle size is larger than 50 μm, the amount of grinding increases and smoothing becomes difficult. The particle size is more preferably 5 to 40 μm, and particularly preferably 5 to 30 μm. When powder media with a particle size within this range is used, the impact effect on the ceramic thermal spray coating is reduced, and peeling of the spray particles due to fracture of the coating surface and breakage between the spray particles can be further suppressed. The median diameter D50 is the particle size at the 50% point of the cumulative height according to JIS R6002-1998.

[0028] The powder media can be made of either ceramic or metal. Ceramics include glass primarily composed of silicon oxide (SiO2), alumina (Al2O3), silicon carbide (SiC), boron carbide (B4C), silicon nitride (Si3N4), and zirconia (ZrO2). Of these, alumina (Al2O3) and silicon carbide (SiC) are preferred. Metals include carbon steel and stainless steel. Of these, stainless steel (SUS304, SUS430, etc.) is preferred.

[0029] The polyhedral powder media used in the present invention can be obtained by crushing or molding the original lumps of the powder media, but are also available as commercially available products. Examples of powder media include alumina (manufactured by Wanami Co., Ltd., trade name: White Alundum), silicon carbide (manufactured by Fuji Manufacturing Co., Ltd., trade name: Fuji Alundum C), and alumina zirconia (manufactured by Saint-Gobain, trade name: NorZon NV).

[0030] In the surface treatment of the present invention, media with small particle diameters and poor fluidity that cannot be sprayed stably by dry blasting can be made into a slurry and then sprayed onto the surface of the ceramic spray coating, thereby smoothing the spray coating while suppressing heat generation and charging of the workpiece. In addition, by using a slurry containing polyhedral powder media, the media exert a strong cutting effect on the coating surface, making it possible to smooth the coating surface by cutting while preventing the coating surface from being fractured by the impact effect or the thermal spray particles from peeling off due to breakage between the thermal spray particles. As a result, the surface of a ceramic thermal spray coating smoothed using a slurry containing polyhedral powder media according to the present invention contains almost no untreated areas that have not been cut off due to the peeling of the thermal spray particles or fragile fractured layers that are prone to falling off.

[0031] (Blasting equipment and processing conditions) The slurry containing powder media can be sprayed onto the surface of the ceramic thermal spray coating using compressed gas, that is, using a known wet blasting device that sprays both compressed gas and slurry. The compressed gas may be air, nitrogen, carbon dioxide, argon, etc. Among these, air is preferable because it is inexpensive and inert.

[0032] Blasting is performed by spraying a slurry containing powder media onto the surface of the ceramic spray coating using compressed gas, preferably at a spray pressure of 0.01 to 1.0 MPa (gauge pressure). If the spray pressure is less than 0.01 MPa, the amount of grinding is reduced, which increases the time required for surface treatment and is inefficient. On the other hand, if the spray pressure is greater than 1.0 MPa, the amount of grinding increases, making smoothing difficult. Among these, a spray pressure of 0.1 to 0.5 MPa is more preferable.

[0033] [Surface of surface-treated ceramic spray coating] The surface of the ceramic spray coating treated in the present invention preferably has an arithmetic mean roughness Ra of 3.0 μm or less, more preferably 0.1 to 2.5 μm, and even more preferably 0.1 to 2.5 μm. The arithmetic mean roughness Ra is 2.0 μm. If the arithmetic mean roughness Ra is 3.0 μm or less, the surface will have a small difference in unevenness, but if it is greater than 3.0 μm, the surface will be rough with a large difference in unevenness, and the treated surface will be more susceptible to wear due to abrasion in the usage environment. The smaller the arithmetic mean roughness Ra, the less likely it is to be worn, making it more preferable.

[0034] Furthermore, the surface of the ceramic spray coating surface-treated in the present invention preferably has a skewness Rsk of 0 or less, more preferably -1.0 or more and -0.01 or less. If the skewness Rsk is greater than 0, the surface will have many fine peaks with sharp protrusions, making it more susceptible to wear. On the other hand, if the skewness Rsk is less than 0, the surface will have many fine valleys, in other words, fewer fine peaks, making the surface less susceptible to wear, which is preferable. In the present invention, the arithmetic mean roughness Ra is measured in accordance with JIS B0601, 1994. The skewness Rsk is also measured in accordance with JIS B0601, 1994.

[0035] Figures 2a and 2b are both SEM images taken at 1000x magnification of the surface of a ceramic spray coating after being subjected to the surface treatment method in an example of the present invention, and Figure 2c is an SEM image taken at 5000x magnification. As shown in Figure 2a, after the surface treatment method of the present invention is applied, numerous cutting marks, a newly formed surface indicated by arrow b, and voids indicated by arrow c are formed on the surface of the ceramic spray coating, although these are not shown.

[0036] Arrow a in Figure 2b and area a in Figure 2c illustrate cutting marks. By the blasting treatment of the present invention, powder media cuts the treated area on the surface of the ceramic spray coating, leaving cutting marks 0.01 to 5 μm wide and 0.01 to 10 μm long on the surface of the ceramic spray coating after surface treatment (treated surface). The surface of the ceramic spray coating has countless cutting marks as described above, resulting in a uniform surface texture. In addition, multiple 10 μm × 10 μm sections are shown in Figure 2b. These sections are used when identifying the cutting mark area, which will be described later. In Figure 2b, only the cutting mark present in one section is indicated by arrow a. Although cutting marks are not shown in the other sections, this does not mean that cutting marks are not present in the other sections.

[0037] The ceramic spray coating obtained by the surface treatment of the present invention is characterized by the small amount of newly formed surface on the treated surface. Here, the newly formed surface refers to the surface that is exposed when the spray particles are broken down and peeled off from the surface during the surface treatment, as shown by the arrow b in Figure 2a and the area b in Figures 2d and 2e. It is preferable that the occupied area ratio of the newly formed surface is small, but in the present invention, the occupied area ratio of the newly formed surface can be made smaller than 10%, which can sufficiently reduce the occurrence of surfaces with uneven roughness. In the present invention, the occupied area ratio of the newly formed surface can be made 5% or less, and even 1% or less. When the occupied area ratio of the newly formed surface is within these ranges, the occurrence of surfaces with uneven roughness can be greatly reduced.

[0038] In the present invention, the occupied area ratio (%) of the newly formed surface is calculated by the following formula (1). New surface area ratio (%) = (new surface area / surface treatment surface area) x 100: (1) In the above formula (1), the area ratio of the newly formed surface can be determined by identifying the position of the newly formed surface by observing the surface-treated surface with an SEM at 1,000x magnification, and then calculating the proportion of the area of ​​the newly formed surface in the observed area using image analysis software.

[0039] Furthermore, on the surface of the surface-treated ceramic spray coating of the present invention, a number of cutting marks caused by the collision of the polyhedral media can be seen. This can suppress the occurrence of new surfaces exposed due to peeling of the sprayed particles that form the thermal spray coating on the surface of the thermal spray coating.

[0040] In the present invention, cutting marks refer to depressions with short sides of 0.01 to 5 μm, long sides of 0.01 to 10 μm, and an aspect ratio of short sides to long sides of 1.5 or more, which are visible when the treated surface of a thermal spray coating is observed with an SEM, as shown by arrow a in Figure 2b and area a in Figure 2c. The area coverage ratio (%) of these cutting marks is calculated using the following formula (2). Area ratio of cutting marks (%) = {(total area of ​​cutting marks - area of ​​voids - area of ​​newly formed surface) / area of ​​surface-treated surface} × 100: (2)

[0041] In the above formula (2), as shown in Figure 2b, the total area of ​​the cutting mark region is the total area of ​​the sections containing five or more cutting marks (each section is referred to as a "cutting mark region"), where the treated surface of the thermal spray coating is divided into 10 μm x 10 μm sections in a 1,000x SEM image. The voids are voids that are formed during the production of the thermal spray coating and remain after surface treatment. These voids correspond to the black areas seen in SEM observation, as indicated by arrows c in Figures 2a, 2d, and 2e. The area of ​​the voids can be calculated using image analysis software.

[0042] As mentioned above, the area of ​​the newly formed surface in equation (2) refers to the surface that is exposed and created when the sprayed particles are broken down and peeled off during surface treatment, and corresponds to areas such as arrow b in Figure 2a and area b in Figures 2d and 2e, which can be seen when observed with an SEM. The area of ​​the newly formed surface can be calculated using image analysis software. In the present invention, the area ratio of the cutting marks calculated by formula (2) is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more. When the area ratio of the cutting marks is within the above range, a surface with more uniform roughness is formed over a wide area. [Example]

[0043] The present invention will be specifically described below with reference to examples of the present invention, but the present invention is not construed as being limited to these examples. In the following examples and comparative examples, the state of the ceramic spray coating formed on the substrate (A5052: aluminum alloy) before treatment is as follows: Thermal spray coating material: Y2O3 Sprayed film thickness: approx. 0.2 mm Arithmetic mean roughness of the thermal spray coating surface Ra: 3.59 μm Skewness Rsk of thermal spray coating surface: 0.15

[0044] The above ceramic spray coating was subjected to a surface treatment using polyhedral media of the present invention (Example), a wet blasting treatment using spherical media (Comparative Example 1), and a surface treatment by dry blasting (Comparative Example 2). The powder media used in the examples were alumina polyhedrons with a particle size of 21.5 μm in median diameter D50 (Wanami Co., Ltd., trade name: White Alundum #600 (mixture of tetrahedrons to decahedrons, angle between faces: 10 to 135 degrees)). The powder media used in Comparative Example 1 were alumina spheres with a particle size of 22.1 μm in median diameter D50 (Denka Co., Ltd., DAW-20), and the powder media used in Comparative Example 2 were alumina spheres with a particle size of 71.5 μm in median diameter D50 (Denka Co., Ltd., DAW-70).

[0045] The conditions for the surface treatment of each example and comparative example are shown in Table 1 below. The film reduction amount in Table 1 refers to the amount of reduction in the thickness of the thermal spray coating determined by measuring the thickness of the test piece with a micrometer before and after the surface treatment. The injection pressure values ​​are gauge pressure values. .

[0046] [Table 1]

[0047] To compare the surface texture, roughness, and amount of brittle layer of the thermal spray coatings after each of the above surface treatments, the arithmetic mean roughness Ra and skewness Rsk of the surfaces of the thermal spray coatings that had been subjected to the surface treatments were measured using a stylus roughness meter. The results are shown in Table 2 below. After surface treatment, the test pieces used in this test were ultrasonically cleaned in pure water and dried in a thermostatic chamber maintained at 60°C before analysis.

[0048] [Table 2]

[0049] As can be seen from Table 2 above, after the surface treatment of the thermal spray coating, the arithmetic roughness Ra and skewness Rsk were smaller in all of the examples, comparative examples 1 and 2 than before the surface treatment, indicating that the surface was smoothed.

[0050] Meanwhile, the surface of the thermal spray coating that had undergone the above surface treatment was observed using a scanning electron microscope (JEOL 6060LA). Figures 2a, 2b, and 2c show surface SEM images of the Example, Figure 2d shows Comparative Example 1, and Figure 2e shows Comparative Example 2, respectively. An example of a newly formed surface resulting from the detachment of the sprayed particles is shown as region b in Figures 2d and 2e. Table 3 below shows the area ratio of the newly formed, uncut surface resulting from the detachment of the sprayed particles in Figure 2a (Example), Figure 2d (Comparative Example 1), and Figure 2e (Comparative Example 2). The area ratio (%) of the newly formed surface was determined by identifying the area of ​​the newly formed surface in the 1,000x magnification image and calculating the proportion (%) of the newly formed surface in the 1,000x magnification image according to the above formula (1).

[0051] As can be seen in Figures 2d and 2e, in Comparative Examples 1 and 2, the film thickness was reduced by about 60 μm. Despite the high speed, the smooth, flat, splat-like sprayed particle surface seen on the surface of the thermal spray coating before treatment (see Figure 1) is occasionally exposed as new surfaces are found due to particle peeling. On the other hand, as can be seen in Figure 2a, in the example, the smoothing treatment was able to be performed while suppressing the peeling of the sprayed particles, and the area ratio of the new surface was significantly smaller at less than 1%.

[0052] In Figure 2c, an example of a cutting mark caused by the collision of the polyhedral media in the example is shown as region a. The cutting mark in region a is approximately 2 μm long and 0.8 μm wide, but as shown in Figures 2a and 2b, countless cutting marks of various sizes can be seen on most of the treated surface. Table 3 below shows the area coverage of the cutting marks in the areas where cutting marks are formed in Figure 2b (Example), Figure 2d (Comparative Example 1), and Figure 2e (Comparative Example 2). The area coverage rate (%) of cutting marks was determined by identifying the area of ​​the region in the 1,000x magnification image that had five or more cutting marks within a 10 μm x 10 μm range (area of ​​the cutting mark region), the area of ​​the voids in the cutting mark region, and the area of ​​the newly formed surface in the cutting mark region, according to the above formula (2), determining the area obtained by subtracting (i.e., subtracting) the area of ​​the voids and the area of ​​the newly formed surface from the total area of ​​the cutting mark region, and calculating the percentage (%) of this area in the 1,000x magnification image.

[0053] [Table 3]

[0054] As can be seen from Table 3, most of the surface of the Example is occupied by areas where cutting marks have been formed. On the other hand, no cutting marks are observed on the surfaces of Comparative Examples 1 and 2, and it can be seen that these surfaces are composed of the sprayed particle surface exposed by peeling of the sprayed particles and the fractured surface caused by impact with the media.

[0055] In addition, polyimide tape (Kapton double-sided adhesive tape 760H#25, manufactured by Teraoka Seisakusho Co., Ltd.) was applied to the surface of the thermal spray coating that had been subjected to the above surface treatment at a pressure of 0.3 MPa, and then peeled off.The adhesive surface of the tape was then observed with a scanning electron microscope (6060LA, manufactured by JEOL Ltd.) to evaluate the amount of brittle fracture layer on the coating surface that had been transferred to the tape. Figure 3a shows SEM images of the adhesive surface of the tape after the transfer test for Example, Figure 3b shows Comparative Example 1, and Figure 3c shows Comparative Example 2. The transfer rates of transferred coating fragments, indicated by white dots in Figures 3a, 3b, and 3c, are shown in Table 4.

[0056] The transfer rate of the film fragments was determined as follows: The observation area of ​​1200 μm × 700 μm of the SEM image was analyzed using image analysis software (Mitani Shoji Co., Ltd., WINROOF2018) to identify the area occupied by the transferred film fragments in the image, and the percentage of the observation area occupied by the film fragments was calculated. In Comparative Examples 1 and 2, the transfer rate was high, indicating that the surface had many fragile fractured layers. In the Example, the transfer rate was significantly lower, indicating that the smoothing treatment was successful while suppressing the formation of fragile fractured layers.

[0057] [Table 4]

[0058] In the above example, silicon carbide polyhedrons (manufactured by Fuji Manufacturing Co., Ltd., product name: Fuji Alundum C #400) were used as powder media instead of alumina polyhedrons (manufactured by Wanami Co., Ltd., product name: White Alundum #600), but it was found that almost the same results were obtained. [Industrial Applicability]

[0059] The surface-treated ceramic spray coating of the present invention has improved wear resistance due to reduced friction and adhesion and is therefore widely applicable to various sliding members such as bearings, pistons, cylinders, etc. Furthermore, since the surface-treated ceramic spray coating of the present invention has few brittle, fractured layers that are prone to falling off after smoothing treatment, it is useful for the inner wall members of plasma etching equipment used in semiconductor manufacturing, which requires high cleanliness. [Explanation of symbols]

[0060] a: Cutting marks b: New surface c: Void area

[0061] The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2022-059072, filed on March 31, 2022, are hereby incorporated by reference as the disclosure of the specification of the present invention.

Claims

1. A ceramic thermal spray coating that has been subjected to a smoothing surface treatment, The smoothed surface has an arithmetic mean roughness Ra of 3 μm or less and a skewness Rsk of 0 or less, and the smoothed surface has a new surface generated by the peeling of sprayed particles, and the occupied area ratio of the new surface calculated by the following formula (1) is 10% or less, Furthermore, the smoothed surface has a plurality of recessed cutting marks having a width of 0.01 to 5 μm, a length of 0.01 to 10 μm, and an aspect ratio of the short side to the long side of 1.5 or more, and the ceramic thermal spray coating is characterized in that the area occupied by the cutting marks is 50% or more as calculated by the following formula (2): Occupied area ratio (%) of new surface = (area of ​​new surface / area of ​​surface-treated surface) × 100: (1) Area ratio of cutting marks (%) = {(total area of ​​cutting marks - area of ​​voids - area of ​​newly formed surface) / area of ​​surface-treated surface} × 100: (2) (The total area of ​​cutting trace regions is the total area of ​​regions having five or more cutting traces within an area of ​​10 μm × 10 μm. The area of ​​voids is the area of ​​voids within the cutting trace regions that are formed when the thermal spray coating is produced and that remain after surface treatment. The area of ​​new surfaces is the area of ​​new surfaces generated by peeling off of thermal spray particles within the cutting trace regions.)

2. 2. The ceramic sprayed coating according to claim 1, which is a sprayed coating on an inner wall member of a plasma etching apparatus used in semiconductor manufacturing.

3. 2. The ceramic sprayed coating according to claim 1, which is a sprayed coating on a sliding member such as a bearing, a piston, or a cylinder.

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