Discharge surface treatment electrode and its manufacturing method

Abstract

According to the present invention, a discharge surface treatment is carried out by means of an electrode which comprises a sintered body that is produced by: forming an electrode powder which is composed of a small-diameter metal powder having a median diameter of 3 µm or less and a large-diameter metal powder having a median diameter of more than 3 µm but not more than 10 µm, the small-diameter metal powder and the large-diameter metal powder containing Cr and oxygen; mixing and granulating the small-diameter metal powder and the large-diameter metal powder; compression molding the granulated powder at a pressure of 20 MPa to 300 MPa; and sintering the thus-obtained powder compact at a temperature of 450°C to 950°C. With respect to this electrode, the sintered body is formed by sintering the small-diameter metal powder having a median diameter of 3 µm or less and the large-diameter metal powder having a median diameter of more than 3 µm but not more than 10 µm with each other; the small-diameter metal powder and the large-diameter metal powder contain Cr and oxygen; and the oxygen content ratio of the sintered body is 1.5% by mass to 4.0% by mass.

Description

[Technical Field]

[0001] The present disclosure relates to an electrode for electrical discharge surface treatment and a method for manufacturing the same. [Background technology]

[0002] Electrical discharge surface treatment is a technology for forming a functional film on a workpiece by electrical discharge using an electrical discharge surface treatment electrode made of metal, ceramics, or the like. In electrical discharge surface treatment, a voltage is applied between the electrical discharge surface treatment electrode and the workpiece, and pulsed electrical discharges are repeatedly generated between the electrical discharge surface treatment electrode and the workpiece. This electrical discharge causes the electrode material to move toward the workpiece in a molten or semi-molten state, and an electrical discharge surface treatment film made of the electrode material or a reaction product of the electrode material is formed on the surface of the workpiece (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2010 / 119865 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] Electrodes for electrical discharge surface treatment are typically formed by sintering fine metal powder of 3 μm or less containing chromium (Cr) and oxygen. Therefore, electrical discharge surface treatment films contain Cr. Because electrical discharge surface treatment films contain Cr, the Cr is oxidized to form chromium oxide (Cr2O3) during exposure to heat, primarily in jet engine parts and other applications. This chromium oxide functions as a protective oxide film and a high-temperature solid lubricant.

[0005] Here, the fine metal powder constituting the discharge surface treatment electrode contains oxygen, so the discharge surface treatment electrode also contains oxygen. If the oxygen content of the discharge surface treatment electrode is high, the proportion of Cr contained in the electrode material that melts or semi-melts during the discharge surface treatment is oxidized and consumed by the oxygen contained in the discharge surface treatment electrode increases. As a result, the Cr content of the discharge surface treatment film decreases, which may reduce the oxidation resistance and wear resistance of the discharge surface treatment film.

[0006] Therefore, an object of the present disclosure is to provide an electrode for electrical discharge surface treatment that can further reduce the oxygen content in the electrode, and a method for manufacturing the same. [Means for solving the problem]

[0007] The electrode for electrical discharge surface treatment according to the present disclosure includes a sintered body formed by sintering a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less, the small-diameter metal powder and the large-diameter metal powder containing Cr and oxygen, and the oxygen content of the sintered body is 1.5 mass% or more and 4.0 mass% or less. The large diameter metal powder has a median diameter of 8.5 μm or more and 10 μm or less.

[0009] In the electrode for electrical discharge surface treatment according to the present disclosure, the large-diameter metal powder may have a 10% cumulative particle size of 3 μm or more and 5 μm or less, and a 90% cumulative particle size of 12 μm or more and 15 μm or less in a cumulative particle size distribution.

[0010] In the electrode for electrical-discharge surface treatment according to the present disclosure, the oxygen content of the sintered body may be 2.0 mass % or more and 3.8 mass % or less.

[0011] In the electrode for electrical-discharge surface treatment according to the present disclosure, the electrical resistivity of the sintered body may be 3 mΩ·cm or more and 30 mΩ·cm or less.

[0012] In the electrode for electrical discharge surface treatment according to the present disclosure, the density of the sintered body is 3 g / cm 3 More than 5g / cm 3 It may be the following:

[0013] In the electrode for electrical discharge surface treatment according to the present disclosure, the content of the large-diameter metal powder may be greater than 0 mass% and not more than 70 mass%, when the total of the small-diameter metal powder and the large-diameter metal powder is 100 mass%.

[0014] In the electrode for electrical discharge surface treatment according to the present disclosure, the small-diameter metal powder and the large-diameter metal powder are formed of a metal material having the same alloy composition, and the metal material may be a Cr-containing Co alloy, a Cr-containing Ni alloy, or a Cr-containing Fe alloy.

[0015] The method for manufacturing an electrode for electrical discharge surface treatment according to the present disclosure includes an electrode powder forming step in which the small-diameter metal powder and the large-diameter metal powder have a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less, and the small-diameter metal powder and the large-diameter metal powder form an electrode powder containing Cr and oxygen; a granulation step in which the small-diameter metal powder and the large-diameter metal powder are mixed and granulated to form a granulated powder; a compression molding step in which the granulated powder is compressed at a pressure of 20 MPa to 300 MPa to form a green compact; and a sintering step in which the green compact is fired at 450°C to 950°C to form a sintered body. The large-diameter metal powder has a median diameter of 8.5 μm or more and 10 μm or less.

[0017] In the method for manufacturing an electrode for electrical-discharge surface treatment according to the present disclosure, the large-diameter metal powder may have a 10% cumulative particle size of 3 μm or more and 5 μm or less, and a 90% cumulative particle size of 12 μm or more and 15 μm or less in a cumulative particle size distribution.

[0018] In the manufacturing method of the electrode for electrical-discharge surface treatment according to the present disclosure, in the granulation step, the mixing ratio of the large-diameter metal powder may be greater than 0 mass% and not more than 70 mass%, when the total of the small-diameter metal powder and the large-diameter metal powder is 100 mass%.

[0019] In the method for producing an electrode for electrical discharge surface treatment according to the present disclosure, in the compression molding step, the green compact may be finally pressed by cold isostatic pressing at a pressure that decreases as the mixing ratio of the large-diameter metal powder increases.

[0020] In the method for producing an electrode for electrical-discharge surface treatment according to the present disclosure, in the firing step, the green compact may be fired at a higher temperature as the mixing ratio of the large-diameter metal powder increases.

[0021] In the method for manufacturing an electrode for electrical discharge surface treatment according to the present disclosure, the small-diameter metal powder and the large-diameter metal powder are formed of a metal material having the same alloy composition, and the metal material may be a Cr-containing Co alloy, a Cr-containing Ni alloy, or a Cr-containing Fe alloy. [Effects of the Invention]

[0022] According to the above configuration, the oxygen content in the discharge surface treatment electrode can be further reduced. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram schematically illustrating the microstructure of an electrode for electrical discharge surface treatment. [Figure 2] FIG. 2 is a flowchart outlining the procedure for manufacturing an electrode for electrical-discharge surface treatment. [Figure 3] FIG. 3 is an elevation view that schematically shows an electric discharge machining apparatus used for electric discharge surface treatment. [Figure 4A] FIG. 4A is a metallurgical microscope image of the electrode for electrical discharge surface treatment, relating to Example 1. [Figure 4B] FIG. 4B is a metallurgical microscope image of the electrode for electrical discharge surface treatment, relating to Example 2. [Figure 4C] FIG. 4C is a metallurgical microscope image of the electrode for electrical discharge surface treatment, relating to Comparative Example 1. [Figure 5A] FIG. 5A is a cross-sectional metallographic microscope image of the coating formed by electrical discharge surface treatment, relating to Example 1. [Figure 5B] FIG. 5B is a cross-sectional metallographic microscope image of the coating formed by electrical discharge surface treatment, relating to Comparative Example 1. [Figure 6A] FIG. 6A is a cross-sectional metallurgical microscope image of the discharge surface-treated specimen after the continuous joining test, relating to Example 1. [Figure 6B] FIG. 6B is a cross-sectional metallurgical microscope image of the discharge surface-treated specimen after the continuous joining test, relating to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of an electrode 10 for electrical discharge surface treatment. The electrode 10 for electrical discharge surface treatment includes a sintered body 12 formed by sintering a small-diameter metal powder and a large-diameter metal powder.

[0025] The sintered body 12 is formed by sintering a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less. The small-diameter metal powder and the large-diameter metal powder contain Cr (chromium) and oxygen. The median diameter is the particle size at which the cumulative value becomes 50% when the particle size distribution of particles measured by, for example, a laser diffraction / scattering method is accumulated from the smallest particle size. In other words, the median diameter is the 50% cumulative particle size (D 50 )

[0026] By including large-diameter metal powder in the sintered body 12, the oxygen content of the sintered body 12 can be reduced compared to when the sintered body 12 is formed only from small-diameter metal powder. Oxygen is adsorbed on the surfaces of the small-diameter metal powder and the large-diameter metal powder. Since the small-diameter metal powder and the large-diameter metal powder contain oxygen, the sintered body 12 also contains oxygen. The surface area per unit volume of the large-diameter metal powder and the small-diameter metal powder is smaller than that of the small-diameter metal powder. Therefore, by including large-diameter metal powder in the sintered body 12, the oxygen content of the sintered body 12 can be reduced.

[0027] By including small-diameter metal powder in the sintered body 12, the density of the sintered body 12 can be adjusted appropriately so as not to be excessively high compared to when the sintered body 12 is formed only from large-diameter metal powder. This is because the density of the sintered body 12 can be adjusted appropriately by interposing small-diameter metal powder between large-diameter metal powders. This makes it possible to keep the thermal conductivity of the discharge surface treatment electrode 10 low. As a result, the heat of the discharge plasma is less likely to escape from the tip of the discharge surface treatment electrode 10 during discharge surface treatment, which increases the temperature of the tip of the discharge surface treatment electrode 10 and makes it easier for the electrode material to melt or semi-melt.

[0028] The small-diameter metal powder and the large-diameter metal powder contain chromium (Cr) and oxygen. As a result, the sintered body 12 contains chromium and oxygen. The discharge surface treatment electrode 10, which is made up of the sintered body 12, contains Cr, so the discharge surface treatment film can contain Cr. When the discharge surface treatment film contains Cr, when the discharge surface treatment film is exposed to a high-temperature oxidizing atmosphere, the Cr contained in the discharge surface treatment film is selectively oxidized to form an oxide film containing chromium oxide (Cr2O3). This oxide film functions as a protective oxide film with excellent oxidation resistance. Furthermore, chromium oxide functions as a high-temperature solid lubricant, improving wear resistance.

[0029] The small-diameter metal powder and the large-diameter metal powder may be made of metal materials having the same alloy composition, or may be made of metal materials having different alloy compositions. The small-diameter metal powder and the large-diameter metal powder are preferably made of metal materials having the same alloy composition. The small-diameter metal powder and the large-diameter metal powder may be made of a heat-resistant metal such as a Cr-containing Co (cobalt) alloy, a Cr-containing Ni (nickel) alloy, or a Cr-containing Fe (iron) alloy.

[0030] The Cr-containing Co alloy preferably contains 8.5 to 32.5 mass % Cr to improve heat resistance, oxidation resistance, and wear resistance. Examples of such Cr-containing Co alloys include alloys commercially available under the names Stellite and Tribaloy (Kennametal Corporation).

[0031] Stellite alloys are Cr-containing Co alloys containing Cr, Si, W, C, etc., with the remainder being Co and unavoidable impurities. Stellite alloys, for example, contain Co as the main component, 20% by mass or more and 32.5% by mass or less of Cr, and 2.0% by mass or less of Si, and have excellent heat resistance and oxidation resistance. Stellite alloys are hard and have excellent wear resistance because fine carbides such as WC are dispersed in them. Examples of Stellite alloys that can be used include Stellite 31 alloy.

[0032] Triballoy alloys are Cr-containing Co alloys containing Cr, Si, Mo, etc., with the remainder being Co and unavoidable impurities. Triballoy alloys, for example, contain Co as the main component, 8.5% by mass to 18% by mass of Cr, and 1.3% by mass to 3.7% by mass of Si, and have excellent heat resistance and oxidation resistance. Triballoy alloys have fine intermetallic compounds of Mo and Si dispersed therein, making them hard and highly wear-resistant. Triballoy alloys that can be used include Triballoy T-400 alloy, T-800 alloy, etc.

[0033] Examples of Cr-containing Ni alloys that can be used include alloys available under the name Inconel 718 (Special Metals Co., Ltd.), NiCrAlY alloys, NiCoCrAlY alloys, etc. Examples of Cr-containing Fe alloys that can be used include austenitic stainless steels such as JIS standard SUS304 and SUS316.

[0034] The small diameter metal powder has a median diameter of 3 μm or less. The reason why the median diameter of the small diameter metal powder is 3 μm or less is that if the median diameter of the small diameter metal powder is greater than 3 μm, the density of the sintered body 12 is likely to become excessively large. The median diameter of the small diameter metal powder may be 1 μm or less. The shape of the small diameter metal powder may be, for example, flaky.

[0035] The large-diameter metal powder has a median diameter of more than 3 μm and not more than 10 μm. If the median diameter of the large-diameter metal powder is 3 μm or less, the oxygen content of the sintered body 12 will be high. If the median diameter of the large-diameter metal powder is greater than 10 μm, it will be difficult to perform compression molding in the compression molding step (S14) described below. The shape of the large-diameter metal powder can be, for example, spherical or polygonal.

[0036] The large-diameter metal powder can be configured with a median diameter of 8.5 μm or more and 10 μm or less. The large-diameter metal powder can be configured with a 50% cumulative particle diameter (D 50 ) with a median diameter of 8.5 μm or more and 10 μm or less, and a 10% cumulative particle size (D 10 ) is 3 μm or more and 5 μm or less, and 90% cumulative particle size (D 90 ) may be 12 μm or more and 15 μm or less. This reduces the surface area per unit volume of the large-diameter metal powder, allowing the oxygen content of the sintered body 12 to be further reduced.

[0037] The large-diameter metal powder can be configured with a median diameter of 8.9 μm or more and 10 μm or less. The large-diameter metal powder can be configured with a 50% cumulative particle diameter (D 50 ) with a median diameter of 8.9 μm or more and 10 μm or less, and a 10% cumulative particle size (D 10 ) is 3 μm or more and 5 μm or less, and 90% cumulative particle size (D 90 ) may be 12 μm or more and 15 μm or less. This further reduces the surface area per unit volume of the large-diameter metal powder, allowing the oxygen content of the sintered body 12 to be further reduced.

[0038] In addition to the above particle sizes, the large-diameter metal powder may have a maximum particle size of 53 μm or less. The large-diameter metal powder may have a median diameter of more than 3 μm and not more than 10 μm, and a maximum particle size of 53 μm or less. The large-diameter metal powder may have a median diameter of 8.5 μm or more and not more than 10 μm, and a maximum particle size of 53 μm or less. The large-diameter metal powder may have a median diameter of 8.9 μm or more and not more than 10 μm, and a maximum particle size of 53 μm or less.

[0039] In addition to the above particle sizes, the large-diameter metal powder may have a maximum particle size of 22 μm or less. The large-diameter metal powder may have a median diameter of more than 3 μm and not more than 10 μm, and a maximum particle size of 22 μm or less. The large-diameter metal powder may have a median diameter of 8.5 μm or more and not more than 10 μm, and a maximum particle size of 22 μm or less. The large-diameter metal powder may have a median diameter of 8.9 μm or more and not more than 10 μm, and a maximum particle size of 22 μm or less.

[0040] The content of the large-diameter metal powder can be greater than 0% by mass and not greater than 70% by mass, when the total of the small-diameter metal powder and the large-diameter metal powder is taken as 100% by mass. If the content of the large-diameter metal powder is greater than 70% by mass, the density of the sintered body 12 may become excessively high.

[0041] The content of the large-diameter metal powder may be 50% by mass or more and 70% by mass or less, when the total of the small-diameter metal powder and the large-diameter metal powder is 100% by mass. By making the content of the large-diameter metal powder 50% by mass or more, it is possible to further reduce the oxygen content of the sintered body 12.

[0042] The content of the large-diameter metal powder may be 60% by mass or more and 70% by mass or less, when the total of the small-diameter metal powder and the large-diameter metal powder is 100% by mass. By making the content of the large-diameter metal powder 60% by mass or more, it is possible to further reduce the oxygen content of the sintered body 12.

[0043] The oxygen content of the sintered body 12 can be set to 1.5% by mass or more and 4.0% by mass or less. When the oxygen content of the sintered body 12 is within this range, the proportion of Cr contained in the molten or semi-molten electrode material that is oxidized and consumed by oxygen contained in the discharge surface treatment electrode 10 during the discharge surface treatment is reduced. As a result, a decrease in the Cr content in the discharge surface treatment film is suppressed, and the oxidation resistance and wear resistance of the discharge surface treatment film are improved.

[0044] If the oxygen content of the sintered body 12 is less than 1.5% by mass, the content of small-diameter metal powder contained in the sintered body 12 will be smaller, which may result in an excessively high density of the sintered body 12. If the oxygen content of the sintered body 12 is more than 4.0% by mass, a large proportion of Cr contained in the electrode material that is melted or semi-melted during the discharge surface treatment will be oxidized by the oxygen contained in the discharge surface treatment electrode 10 and consumed. The oxygen content of the sintered body 12 can be measured by a common infrared absorption method or the like.

[0045] The oxygen content of the sintered body 12 may be 1.5% by mass or more and 3.8% by mass or less, or 1.5% by mass or more and 2.5% by mass or less. This further reduces the rate at which Cr contained in the electrode material that is melted or semi-melted during the electrical discharge surface treatment is oxidized and consumed by oxygen contained in the electrical discharge surface treatment electrode 10. As a result, the decrease in the Cr content in the electrical discharge surface treatment film is further suppressed, and the oxidation resistance and wear resistance of the electrical discharge surface treatment film are further improved.

[0046] The oxygen content of the sintered body 12 may be 2.0% by mass or more and 3.8% by mass or less, or 2.0% by mass or more and 2.5% by mass or less, which allows a good balance between preventing an excessive increase in the density of the sintered body 12 and reducing the oxygen content of the sintered body 12.

[0047] Furthermore, even when the small-diameter metal powder and the large-diameter metal powder contain Al or Si, which form a good protective oxide film, in addition to Cr, so long as the oxygen content of the sintered body 12 is within the above range, the rate at which Al or Si contained in the molten or semi-molten electrode material is oxidized and consumed by oxygen contained in the discharge surface treatment electrode 10 during the discharge surface treatment is reduced. As a result, the decrease in the Al content or Si content in the discharge surface treatment film is suppressed, and the oxidation resistance of the discharge surface treatment film is improved.

[0048] The electrical resistivity of the sintered body 12 can be set to 3 mΩ·cm or more and 30 mΩ·cm or less. The electrical resistivity of the sintered body 12 can be measured using a common four-terminal method, etc. Thermal conductivity and electrical resistivity are negatively correlated; low thermal conductivity results in low electrical conductivity, and therefore high electrical resistivity. If the electrical resistivity of the sintered body 12 is within this range, it can adequately follow the pulse discharge cycle and also appropriately suppress thermal conductivity. This makes it difficult for the heat of the discharge plasma to escape from the tip of the discharge surface treatment electrode 10, allowing the temperature of the tip of the discharge surface treatment electrode 10 to be maintained at a high temperature.

[0049] The density of the sintered body 12 is 3 g / cm 3 More than 5g / cm 3 The density of the sintered body 12 can be measured by a general density measurement method such as the Archimedes method. The density of the sintered body 12 is closely related to the electrical resistivity of the sintered body 12. When the density of the sintered body 12 is 3 g / cm or less, 3 More than 5g / cm 3 If the temperature is equal to or lower than this, the electrical resistivity of the sintered body 12 can be set to 3 mΩ·cm or more and 30 mΩ·cm or less.

[0050] Next, a description will be given of a method for manufacturing the discharge surface treatment electrode 10. Fig. 2 is a flowchart showing the configuration of the method for manufacturing the discharge surface treatment electrode 10. The method for manufacturing the discharge surface treatment electrode 10 includes an electrode powder formation step (S10), a granulation step (S12), a compression molding step (S14), and a firing step (S16).

[0051] The electrode powder forming process (S10) is a process in which an electrode powder is formed from a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less, and the small-diameter metal powder and the large-diameter metal powder contain Cr and oxygen.

[0052] The raw material powder can be a metal powder such as a Cr-containing Co alloy powder, a Cr-containing Ni alloy powder, or a Cr-containing Fe alloy powder. An alloy powder containing Cr is used as the raw material powder. This allows the small-diameter metal powder and the large-diameter metal powder to form an electrode powder containing Cr. Furthermore, oxygen is adsorbed on the surface of the raw material powder. This allows the small-diameter metal powder and the large-diameter metal powder to form an electrode powder containing oxygen.

[0053] The raw material powder can be an alloy powder formed by an atomization method or the like. The atomization method can be a water atomization method, a gas atomization method or the like. The raw material powder can be, for example, an alloy powder with a maximum particle size of 22 μm or less, or an alloy powder with a maximum particle size of 53 μm or less. The raw material powder can be a commercially available product or the like.

[0054] The small-diameter metal powder having a median diameter of 3 μm or less and the large-diameter metal powder having a median diameter of more than 3 μm and not more than 10 μm can be produced, for example, by pulverizing the raw material powder using a jet mill or the like. The jet mill may be a swirl-type jet mill or the like. The pulverization pressure should be 0.4 MPa or more and 2.6 MPa or less.

[0055] The large-diameter metal powder is classified using a cyclone or the like and recovered. The small-diameter metal powder is collected using a bag filter or the like and recovered. The large-diameter metal powder can be formed into, for example, a spherical or polygonal shape. The small-diameter metal powder can be formed into, for example, a scale shape.

[0056] The large-diameter metal powder may be further classified using a sieve or the like to have a predetermined particle size. By classifying the large-diameter metal powder using a sieve or the like, the particle size of the large-diameter metal powder can be adjusted to, for example, the 50% cumulative particle size (D 50) with a median diameter of 8.5 μm or more and 10 μm or less, and a 10% cumulative particle size (D 10 ) is 3 μm or more and 5 μm or less, and 90% cumulative particle size (D 90 ) can be adjusted to 12 μm or more and 15 μm or less.

[0057] The granulation step (S12) is a step of mixing and granulating a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less to form a granulated powder.

[0058] First, a slurry is prepared by mixing a small-diameter metal powder and a large-diameter metal powder. The mixing ratio of the large-diameter metal powder can be greater than 0% by mass and less than 70% by mass, when the total of the small-diameter metal powder and the large-diameter metal powder is taken as 100% by mass. The mixing ratio of the large-diameter metal powder can be greater than 50% by mass and less than 70% by mass, or can be greater than 60% by mass and less than 70% by mass, when the total of the small-diameter metal powder and the large-diameter metal powder is taken as 100% by mass.

[0059] The slurry is produced by adding small-diameter metal powder, large-diameter metal powder, a binder, and a lubricant to a solvent stored in a storage tank and stirring and mixing them with a stirrer or the like. An organic solvent or the like can be used as the solvent. The solvent is preferably added in an amount of 200% by mass when the total of the small-diameter metal powder and the large-diameter metal powder is taken as 100% by mass.

[0060] Examples of binders that can be used include thermoplastic resins such as polypropylene (PP), polyethylene (PE), polymethyl methacrylate (PMMA), and polyvinyl alcohol (PVA), and polysaccharides such as agar. The binder is preferably added in an amount of 2 to 3% by mass when the total of the small-diameter metal powder and the large-diameter metal powder is taken as 100% by mass.

[0061] The lubricant may be stearic acid, paraffin wax, zinc stearate, etc. The lubricant may be added in an amount of 1 to 10% by mass, assuming that the total of the small-diameter metal powder and the large-diameter metal powder is 100% by mass.

[0062] After preparing the slurry, a granulated powder is formed using a spray dryer or the like. When granulating with a spray dryer, the slurry is sprayed from the nozzle of the spray dryer into a high-temperature nitrogen gas atmosphere inside the spray dryer. This dries and removes the solvent contained in the slurry, forming a granulated powder.

[0063] The compression molding step (S14) is a step in which the granulated powder is compression molded at a pressure of 20 MPa to 300 MPa to form a green compact. The granulated powder is filled into a mold and pressed with a press device. This causes the granulated powder to be compression molded into a green compact. The pressure of the mold press may be, for example, 20 MPa to 300 MPa.

[0064] After die pressing, the green compact may be finally pressed by CIP (cold isostatic pressing). CIP allows the green compact to be isotropically pressed, which makes the density distribution of the green compact more uniform. The CIP pressure can be changed based on the mixing ratio of the small-diameter metal powder to the large-diameter metal powder. The CIP pressure should be lower as the mixing ratio of the large-diameter metal powder increases, and higher as the mixing ratio of the large-diameter metal powder decreases.

[0065] When the total of the small-diameter metal powder and the large-diameter metal powder is 100% by mass, if the large-diameter metal powder is greater than 0% by mass and 70% by mass or less, the CIP pressure should be 20 MPa to 300 MPa. When the total of the small-diameter metal powder and the large-diameter metal powder is 100% by mass, if the large-diameter metal powder is 50% by mass or more and 70% by mass or less, the CIP pressure should be 20 MPa to 120 MPa. When the total of the small-diameter metal powder and the large-diameter metal powder is 100% by mass, if the large-diameter metal powder is 60% by mass or more and 70% by mass or less, the CIP pressure should be 20 MPa to 60 MPa.

[0066] The firing step (S16) is a step of firing the powder compact at 450°C to 950°C to form a sintered body 12. The powder compact is fired using a heating furnace such as a vacuum heating furnace or an atmospheric furnace. The powder compact is sintered by being heated using a heater or the like in a vacuum, an inert atmosphere, or a reducing atmosphere. The firing should be performed to a degree that allows the electrode powder to maintain its shape and to form a moderately strong bond at the contact points between the powder particles. The holding time at the firing temperature can be 5 hours to 15 hours.

[0067] If the firing temperature is lower than 450°C, the bond between the powder particles at their contact points may be weak. If the firing temperature is higher than 950°C, the bond between the powder particles at their contact points may be excessively strong. It is recommended that the firing temperature be between 700°C and 800°C. This will ensure that the bond between the powder particles at their contact points is appropriately strong.

[0068] In the firing step (S16), the green compact should be fired at a higher temperature the greater the mixing ratio of large-diameter metal powder, and at a lower temperature the smaller the mixing ratio of large-diameter metal powder. This allows the bonding at the contact points between powder particles to be suitably strong, even when large-diameter metal powder is contained in the electrode powder.

[0069] The green compact is preferably sintered by firing in a vacuum or a reducing atmosphere, which facilitates the removal of oxygen contained in the small-diameter metal powder and the large-diameter metal powder that make up the green compact, thereby further reducing the oxygen content of the sintered body 12.

[0070] The sintered body 12 thus produced has an oxygen content of 1.5% by mass or more and 4.0% by mass or less. The sintered body 12 also has an electrical resistivity of 3 mΩ·cm or more and 30 mΩ·cm or less, and a density of 3 g / cm 3 More than 5g / cm 3 It is preferable that the electrode be made of the following materials: In this way, the electrode for electrical discharge surface treatment 10 made of the sintered body 12 is manufactured.

[0071] Next, an explanation will be given of electrical discharge surface treatment using the electrical discharge surface treatment electrode 10. First, an electrical discharge machining apparatus used for electrical discharge surface treatment will be explained. Fig. 3 is a schematic diagram showing the configuration of an electrical discharge machining apparatus 20.

[0072] The electric discharge machining apparatus 20 includes a bed 22. A table 24 is provided on the bed 22. The table 24 is provided with a liquid tank 26 that stores an electrically insulating liquid L such as insulating oil. The liquid tank 26 is provided with a jig 28 on which a part P made of a Ni alloy or the like can be set.

[0073] An electrode holder 32 for holding the discharge surface treatment electrode 10 is provided above the table 24 so as to be movable in the X-axis, Y-axis, and Z-axis directions. The electrode holder 32 is configured to be rotatable about the Z-axis. A discharge power supply 34 is electrically connected to the jig 28 and the electrode holder 32. A known discharge power supply can be used as the discharge power supply 34.

[0074] Next, the discharge surface treatment method will be described. The component P is set in a jig 28. The electrode holder 32 holding the discharge surface treatment electrode 10 is moved in the X-axis and Y-axis directions to position the discharge surface treatment electrode 10 relative to the component P. Next, while the electrode holder 32 is moved back and forth in the Z-axis direction, a pulsed discharge D is generated between the discharge surface treatment electrode 10 and the component P by a discharge power supply device 34 in an electrically insulating liquid L. The energy of this discharge D causes the electrode material or a reactant of the electrode material to adhere to the surface of the component P, forming a discharge surface treatment film.

[0075] Specifically, when a discharge D occurs between the discharge surface treatment electrode 10 and the component P, a portion of the electrode material is detached from the discharge surface treatment electrode 10 by the blast wave and electrostatic force caused by the discharge D and becomes molten or semi-molten due to the heat of the discharge plasma. The detached portion of the electrode material moves in a molten or semi-molten state toward the component P, reaches the surface of the component P, and resolidifies into metal particles. By continuously generating a pulsed discharge, the electrode material at the electrode tip moves successively to the surface of the component P, where it resolidifies and accumulates. As a result, metal particles are layered on the surface of the component P, forming a discharge surface treatment film. Note that although the above configuration describes discharge surface treatment in an electrically insulating liquid L, discharge surface treatment may also be performed in the atmosphere, etc.

[0076] The electrode 10 for electrical discharge surface treatment is configured such that the oxygen content of the sintered body 12 is 1.5 mass % or more and 4.0 mass % or less. This suppresses the consumption of Cr contained in the molten or semi-molten electrode material due to oxidation during electrical discharge surface treatment. As a result, it is possible to suppress the reduction in the Cr content of the electrical discharge surface treatment film. The electrode 10 for electrical discharge surface treatment is configured such that the electrical resistivity of the sintered body 12 is 3 mΩ·cm or more and 30 mΩ·cm or less, and the density of the sintered body 12 is 3 g / cm 3 More than 5g / cm 3 It is preferable that the discharge surface treatment be configured as follows: This allows the discharge surface treatment to be performed more stably.

[0077] The part P may be a gas turbine part or the like. Gas turbine parts are parts that are exposed to high-temperature environments exceeding 1000°C, such as jet engine parts for aircraft and industrial gas turbine parts. An example of a jet engine part for aircraft is a turbine blade with an integrated shroud.

[0078] The part P may be a sliding part. The sliding surface of the sliding part is subject to, for example, fretting wear, which is caused by repeated small sliding movements due to a surface pressure load, and impact wear, which is caused by repeated cyclic pressure and sliding movements. For example, by coating the sliding surface of the part P with an electrical discharge surface treatment film made of a Cr-containing Co alloy or the like, it is possible to maintain wear resistance even in high-temperature environments exceeding 1000°C.

[0079] According to the above configuration, the electrode for electrical discharge surface treatment is formed by sintering a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and not more than 10 μm, and comprises a sintered body having an oxygen content of 1.5% by mass to 4.0% by mass. The small-diameter metal powder and the large-diameter metal powder contain Cr and oxygen. In this way, the electrode for electrical discharge surface treatment having the above configuration has a reduced oxygen content. This suppresses the consumption of Cr contained in the molten or semi-molten electrode material due to oxidation during electrical discharge surface treatment. As a result, the reduction of Cr contained in the electrical discharge surface treatment film can be suppressed.

[0080] Example After forming the electrode for discharge surface treatment, discharge surface treatment was carried out, and the characteristics of the electrode for discharge surface treatment were evaluated.

[0081] (Formation of electrodes for electrical discharge surface treatment) First, a method for forming electrodes for electrical discharge surface treatment will be described. Three types of electrodes for electrical discharge surface treatment were produced: electrodes of Examples 1 and 2, and an electrode of Comparative Example 1. These electrodes differ in the ratio of small-diameter metal powder to large-diameter metal powder, the CIP (cold isostatic pressing) pressure, and the firing temperature, as described below, but the other configurations were the same. Next, a method for forming each electrode will be described in detail.

[0082] The raw material powder used was Stellite 31 alloy powder, a Cr-containing Co alloy powder. The alloy composition of Stellite 31 alloy is, by mass, 9.5% to 11.5% Ni, 2.0% or less Fe, 0.45% to 0.55% C, 24.5% to 26.5% Cr, 1.0% Mn, 1.0% Si, and 7.5% W, with the remainder being Co and unavoidable impurities. The raw material powder used had a maximum particle size of 53 μm or less. Atomized powder was used as the raw material powder.

[0083] The raw material powder was pulverized using a swirling jet mill at a compressor pressure of 1.2 MPa. The large-diameter metal powder was collected using a cyclone and then classified using a sieve. The small-diameter metal powder was collected using a bag filter. The large-diameter metal powder was spherical in shape. The small-diameter metal powder was flaky in shape.

[0084] The particle size distributions of the small-diameter metal powder and the large-diameter metal powder were measured by a laser diffraction / scattering method. The small-diameter metal powder had a median diameter of 3 μm or less. The large-diameter metal powder had a median diameter of more than 3 μm and 10 μm or less. More specifically, the large-diameter metal powder had a median diameter of 50% of the cumulative particle size distribution (D 50 ) the median diameter is 8.9 μm, and the 10% cumulative particle size (D 10 ) is 4.0 μm, and the 90% cumulative particle size (D 90 ) was 13.8 μm.

[0085] The oxygen concentration of the small-diameter metal powder and the large-diameter metal powder was measured by infrared absorption. Oxygen was detected in both the small-diameter metal powder and the large-diameter metal powder. The oxygen concentration of the small-diameter metal powder was higher than that of the large-diameter metal powder.

[0086] Small-diameter metal powder and large-diameter metal powder were mixed and granulated to form granulated powder. The small-diameter metal powder, large-diameter metal powder, binder, lubricant, and solvent were mixed and stirred in a stirrer to produce a slurry. An acrylic resin-based binder was used as the binder. Stearic acid was used as the lubricant. Isopropyl alcohol (IPA) was used as the solvent.

[0087] In the electrode of Example 1, when the total of the small-diameter metal powder and the large-diameter metal powder was 100 mass%, the small-diameter metal powder was 30 mass% and the large-diameter metal powder was 70 mass%. In the electrode of Example 2, when the total of the small-diameter metal powder and the large-diameter metal powder was 100 mass%, the small-diameter metal powder was 50 mass% and the large-diameter metal powder was 50 mass%. In the electrode of Comparative Example 1, the small-diameter metal powder was 100 mass%, and only the small-diameter metal powder was used.

[0088] A mixture of small-diameter metal powder and large-diameter metal powder was mixed with 2% by mass of binder, and then 200% by mass of isopropyl alcohol (IPA) was added and stirred to prepare a slurry. After preparing the slurry, the solvent was dried using a spray dryer to form a granulated powder.

[0089] Next, this granulated powder was compressed to form a green compact. The granulated powder was filled into a mold and pressed using a press. The pressing pressure was 20 MPa to 300 MPa. The green compact was rectangular, measuring 14 mm long, 110 mm wide, and 7 mm high.

[0090] After die pressing, the green compact was finally pressed by CIP (cold isostatic pressing). The CIP pressure was set to be lower as the mixing ratio of large-diameter metal powder increased. For the electrode of Example 1, the CIP pressure was set to 40 MPa. For the electrode of Example 2, the CIP pressure was set to 80 MPa. For the electrode of Comparative Example 1, the CIP pressure was set to 250 MPa.

[0091] The compact was heated and fired to form a sintered body. The firing was performed by flowing a mixed gas of argon gas and hydrogen gas and evacuating the chamber with a rotary pump. The mixed gas was 95% by mass Ar-5% by mass H2. The firing temperature was maintained in the range of 700°C to 800°C for 6 hours to adjust the electrical resistivity. The firing temperature was set higher as the mixing ratio of large-diameter metal powder increased. More specifically, the firing temperature was set to be the highest for the electrode of Example 1, the lowest for the electrode of Comparative Example 1, and an intermediate temperature for the electrode of Example 2. In this manner, an electrode for electrical discharge surface treatment was formed.

[0092] The electrical resistivity of the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1 was measured by the four-terminal method. The electrode of Example 1 had a resistivity of 15 mΩ·cm, the electrode of Example 2 had a resistivity of 18 mΩ·cm, and the electrode of Comparative Example 1 had a resistivity of 12 mΩ·cm.

[0093] The densities of the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1 were measured by the Archimedes method. The electrode of Example 1 had a density of 4.4 g / cm 3 The electrode of Example 2 had a density of 4.0 g / cm 3 The electrode of Comparative Example 1 had a capacitance of 3.6 g / cm 3 It was.

[0094] The oxygen content of the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1 was measured by infrared absorption. The electrode of Example 1 had an oxygen content of 2.1 mass %. The electrode of Example 2 had an oxygen content of 3.2 mass %. The electrode of Comparative Example 1 had an oxygen content of 6.0 mass %. The electrode of Example 1 had the smallest oxygen content. The electrode of Comparative Example 1 had the largest oxygen content.

[0095] Metallographic observation was performed with a scanning electron microscope (SEM) on the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1. Fig. 4 is a photograph showing the results of metallographic observation of the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1, Fig. 4A is a photograph of the electrode of Example 1, Fig. 4B is a photograph of the electrode of Example 2, and Fig. 4C is a photograph of the electrode of Comparative Example 1.

[0096] In the metallographic structure of the electrodes of Examples 1 and 2, as shown in Figures 4A and 4B, spherical large-diameter metal powder particles, indicated by white circles, and scaly small-diameter metal powder particles filling the gaps between the large-diameter metal powder particles were observed. The metallographic structure of the electrodes of Examples 1 and 2 was composed of dispersed large-diameter metal powder particles. On the other hand, the metallographic structure of the electrode of Comparative Example 1 was composed of a uniform metallographic structure consisting of scaly small-diameter metal powder particles, as shown in Figure 4C.

[0097] (Discharge surface treatment) Electrical discharge surface treatment was performed using the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1. Electrical discharge surface treatment was performed on a substrate in insulating oil using an electrical discharge machining device, forming an electrical discharge surface treatment film on the surface of the substrate. The substrate was formed of a Ni alloy. Regarding the discharge conditions, the peak current value Ip of the initial portion of the waveform of the discharge pulse current supplied between the electrode and the substrate was set to 30 A or 40 A, the peak current value Ie of the middle and subsequent portions was adjusted to 1 A to 25 A, and the pulse width te of the discharge pulse current was adjusted to 2 μs to 30 μs. The pause time was also set to 64 μs. The thickness of the electrical discharge surface treatment film was set to 300 μm to 400 μm. Both the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1 were capable of electrical discharge surface treatment.

[0098] The Cr concentration was measured for the discharge surface treatment films obtained by discharge surface treatment using the electrodes of Example 1 and Comparative Example 1. The Cr concentration was measured using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Figure 5 is a photograph showing the measurement points of the Cr concentration for the discharge surface treatment films obtained by discharge surface treatment using the electrodes of Example 1 and Comparative Example 1. Figure 5A is a photograph showing the measurement points of the Cr concentration for the discharge surface treatment film obtained by discharge surface treatment using the electrode of Example 1. Figure 5B is a photograph showing the measurement points of the Cr concentration for the discharge surface treatment film obtained by discharge surface treatment using the electrode of Comparative Example 1. In Figures 5A and 5B, the arrows indicate the measurement points of the Cr concentration.

[0099] The Cr concentration of the discharge surface treatment film obtained by discharge surface treatment using the electrode of Example 1 was 23.9 mass %. The Cr concentration of the discharge surface treatment film obtained by discharge surface treatment using the electrode of Comparative Example 1 was 17.5 mass %. The discharge surface treatment film obtained by discharge surface treatment using the electrode of Example 1 had a higher Cr concentration than the discharge surface treatment film obtained by discharge surface treatment using the electrode of Comparative Example 1.

[0100] The electrode of Comparative Example 1 had the highest oxygen content, which is thought to be due to the fact that the Cr contained in the electrode material, which was melted or semi-melted during the electrical discharge surface treatment, was oxidized and consumed at a high rate by the oxygen contained in the electrode, resulting in a decrease in the Cr content in the electrical discharge surface treatment film.

[0101] In contrast, the electrode of Example 1 had a lower oxygen content than the electrode of Comparative Example 1, which is thought to have reduced the rate at which Cr contained in the melted or semi-melted electrode material during the electrical discharge surface treatment was oxidized and consumed by oxygen contained in the electrode, thereby suppressing the reduction in the Cr content in the electrical discharge surface treatment film.

[0102] (Oxidation resistance test) An oxidation resistance test was conducted on specimens that had been discharge surface-treated using the electrodes of Examples 1 and 2 and the electrode of Comparative Example 1. The oxidation resistance test consisted of a continuous oxidation test in which the specimens that had been discharge surface-treated using each electrode were continuously exposed to heat in an air atmosphere at 1,080°C for 100 hours. The discharge surface treatment films after the continuous oxidation test were observed with a scanning electron microscope (SEM).

[0103] In the specimens that were discharge surface-treated using the electrodes of Comparative Example 1, the discharge surface treatment film completely peeled off after the continuous oxidation test. In the specimens that were discharge surface-treated using the electrodes of Examples 1 and 2, no peeling of the discharge surface treatment film was observed even after the continuous oxidation test. FIG. 6 is a photograph showing the cross-sectional observation results of the specimens that were discharge surface-treated using the electrodes of Examples 1 and 2 after the continuous oxidation test. FIG. 6A is a photograph of the specimen that was discharge surface-treated using the electrode of Example 1, and FIG. 6B is a photograph of the specimen that was discharge surface-treated using the electrode of Example 2. The area indicated by the symbol M is the substrate, and the areas indicated by the symbols C1 and C2 are the discharge surface treatment films, respectively. In the specimens that were discharge surface-treated using the electrodes of Examples 1 and 2, the discharge surface treatment film remained even after the continuous oxidation test, and the substrate and the discharge surface treatment film were in close contact.

[0104] It is believed that the oxidation resistance of the discharge surface treatment film obtained by discharge surface treatment using the electrode of Comparative Example 1 was reduced due to a decrease in the Cr content in the discharge surface treatment film. In contrast, it is believed that the oxidation resistance of the discharge surface treatment film obtained by discharge surface treatment using the electrodes of Examples 1 and 2 was improved because the decrease in the Cr content in the discharge surface treatment film was suppressed.

[0105] Next, a cyclic oxidation test was conducted on the test specimens that had been subjected to the discharge surface treatment using the electrodes of Examples 1 and 2. The cyclic oxidation test involved 500 cycles of thermal exposure between 100°C and 1100°C. Some peeling of the discharge surface treatment film was observed on the test specimen that had been subjected to the discharge surface treatment using the electrode of Example 2. In contrast, no peeling of the discharge surface treatment film was observed on the test specimen that had been subjected to the discharge surface treatment using the electrode of Example 1.

[0106] These results show that the electrode of Example 1 can be coated with an electrical discharge surface treatment film with better oxidation resistance than the electrode of Example 2. The main reason for this is thought to be that the electrode of Example 1 has a lower oxygen content than the electrode of Example 2, and therefore the electrical discharge surface treatment film using the electrode of Example 1 shows less reduction in Cr content than the electrical discharge surface treatment film using the electrode of Example 2.

[0107] Although several embodiments have been described, modifications or variations of the embodiments can be made based on the above disclosure.

Claims

1. An electrode for electrical discharge surface treatment, The sintered body is formed by sintering a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less, the small-diameter metal powder and the large-diameter metal powder contain Cr and oxygen, In the electrode for electrical discharge surface treatment, the sintered body has an oxygen content of 1.5 mass % or more and 4.0 mass % or less, and the large-diameter metal powder has a median diameter of 8.5 μm or more and 10 μm or less.

2. The electrode for electrical discharge surface treatment according to claim 1, The large-diameter metal powder has a 10% cumulative particle size of 3 μm or more and 5 μm or less, and a 90% cumulative particle size of 12 μm or more and 15 μm or less in a cumulative particle size distribution.

3. The electrode for electrical discharge surface treatment according to any one of claims 1 and 2, The sintered body has an oxygen content of 2.0 mass % or more and 3.8 mass % or less.

4. The electrode for electrical discharge surface treatment according to any one of claims 1 and 2, The sintered body has an electrical resistivity of 3 mΩ·cm or more and 30 mΩ·cm or less.

5. The electrode for electrical discharge surface treatment according to any one of claims 1 and 2, The density of the sintered body is 3 g / cm ３ 5g / cm or more ３ The following is an electrode for discharge surface treatment.

6. The electrode for electrical discharge surface treatment according to any one of claims 1 and 2, The electrode for electrical discharge surface treatment, wherein the content of the large-diameter metal powder is greater than 0 mass % and not more than 70 mass % when the total of the small-diameter metal powder and the large-diameter metal powder is 100 mass %.

7. The electrode for electrical discharge surface treatment according to any one of claims 1 and 2, the small-diameter metal powder and the large-diameter metal powder are formed of metal materials having the same alloy composition, The electrode for electrical discharge surface treatment, wherein the metal material is a Cr-containing Co alloy, a Cr-containing Ni alloy, or a Cr-containing Fe alloy.

8. A method for manufacturing an electrode for electrical discharge surface treatment, comprising: an electrode powder forming step in which a small-diameter metal powder having a median diameter of 3 μm or less and a large-diameter metal powder having a median diameter of more than 3 μm and 10 μm or less is formed into an electrode powder containing Cr and oxygen by the small-diameter metal powder and the large-diameter metal powder; a granulation step of mixing and granulating the small-diameter metal powder and the large-diameter metal powder to form a granulated powder; a compression molding step of compressing the granulated powder at a pressure of 20 MPa to 300 MPa to form a green compact; and a firing step of firing the green compact at 450°C to 950°C to form a sintered body, wherein the large-diameter metal powder has a median diameter of 8.5 μm or more and 10 μm or less.

9. 9. A method for producing the electrode for electrical discharge surface treatment according to claim 8, The method for producing an electrode for electrical discharge surface treatment, wherein the large-diameter metal powder has a 10% cumulative particle size of 3 μm or more and 5 μm or less, and a 90% cumulative particle size of 12 μm or more and 15 μm or less in a cumulative particle size distribution.

10. 10. A method for manufacturing the electrode for electrical discharge surface treatment according to claim 8, In the granulation step, a mixing ratio of the large-diameter metal powder is greater than 0 mass% and not more than 70 mass%, when the total of the small-diameter metal powder and the large-diameter metal powder is 100 mass%.

11. 10. A method for manufacturing the electrode for electrical discharge surface treatment according to claim 8, In the compression molding step, the green compact is finally pressed by cold isostatic pressing with a pressure that decreases as the mixing ratio of the large-diameter metal powder increases.

12. 10. A method for manufacturing the electrode for electrical discharge surface treatment according to claim 8, In the firing step, the green compact is fired at a higher temperature as the mixing ratio of the large-diameter metal powder increases.

13. 10. A method for manufacturing the electrode for electrical discharge surface treatment according to claim 8, the small-diameter metal powder and the large-diameter metal powder are formed of metal materials having the same alloy composition, The method for producing an electrode for electrical discharge surface treatment, wherein the metal material is a Cr-containing Co alloy, a Cr-containing Ni alloy, or a Cr-containing Fe alloy.

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