Electrode for discharge surface treatment and method of manufacturing the same

Abstract

This electrode (15) comprises a sintered body composed of a powder having any of a Co-based alloy, an Ni-based alloy, and an Fe-based alloy as a component. The sintered body includes a fine-grained powder that has a median diameter of 3.0 μm or less and is formed into scales. The specific surface area of the sintered body has a value within the range from 0.8 m2 / g to 10 m2 / g. The electrical resistivity of the sintered body has a value within the range from 3 mΩ∙cm to 30 mΩ∙cm.

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 coating on a workpiece by discharging an electric discharge using an electrode containing a material such as metal or ceramic. In electrical discharge surface treatment, a voltage is applied between the electrode and the workpiece, and pulsed electric discharges are repeatedly generated between the electrode and the workpiece. This discharge causes the electrode material to move toward the workpiece in a molten or semi-molten state, forming a coating made of the electrode material or a reaction product of the electrode material on the surface of the workpiece. The coating formed by electrical discharge surface treatment is stable and has excellent durability and wear resistance (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-140461 Summary of the Invention [Problem to be solved by the invention]

[0004] Electrodes for electrical discharge surface treatment are produced by compressing raw material powders, such as Co-based alloys, to form a green compact, which is then fired in a vacuum, inert gas, or reducing gas atmosphere. The raw material powder contains metal powder that has been refined by pulverization using a jet mill or other suitable means before compression molding, so that the molten or semi-molten electrode material can be easily transferred to the workpiece during electrical discharge. However, the shape and particle size distribution of the refined raw material powder are easily affected by environmental changes and slight variations in composition during the manufacturing process, which includes the pulverization and classification steps. These changes affect the stable generation of electrical discharges and hinder the smooth progress of coating formation.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an electrode for electrical discharge surface treatment that can stably generate an electrical discharge during film formation, and a method for manufacturing the same. [Means for solving the problem]

[0006] The electrode according to a first aspect of the present disclosure is an electrode for electrical discharge surface treatment that generates an electrical discharge between the electrode and a workpiece to form a coating made of an electrode material or a reactive substance of the electrode material on the surface of the workpiece, and includes a sintered body as the electrode made of powder made from any one of a Co-based alloy, a Ni-based alloy, and an Fe-based alloy, the sintered body including fine powder of the raw material formed into a scale shape, the median diameter of the fine powder being 3.0 μm or less, and the specific surface area of ​​the sintered body being 1.3 m 2 / g 8.0 m 2 / g, and the electrical resistivity of the sintered body is 1 It has a value ranging from mΩ·cm to 30 mΩ·cm.

[0007] In the first embodiment, the sintered body may further contain a coarse-grain powder as a raw material. The coarse-grain powder may have a larger particle size than the fine-grain powder and may contain particles with a maximum particle size of 53 μm. The proportion of the coarse-grain powder in the mixed powder of the fine-grain powder and the coarse-grain powder may be 70 wt % or less. The density of the sintered body may be 3.0 g / cm 3 to 5.0 g / cm 3 It may have a value ranging from

[0008] A method according to a second aspect of the present disclosure is a manufacturing method of an electrode for electrical discharge surface treatment, which generates an electrical discharge between an electrode and a workpiece, and forms a coating made of an electrode material or a reactive substance of the electrode material on the surface of the workpiece, the method comprising: granulating a powder made of any one of a Co-based alloy, a Ni-based alloy, and an Fe-based alloy as a raw material to produce a granulated powder; compressing the granulated powder to form a green compact; and firing the green compact to form a sintered body as the electrode, the powder including a fine powder formed in a scale shape with a median diameter of 3.0 μm or less; and adjusting the pressure during compression molding and the firing temperature during firing so that the specific surface area of ​​the sintered body is 1.3 m 2 / g 8.0 m 2 / g, and the electrical resistivity of the sintered body is 1 The pressure during compression molding is set to a value ranging from 50 MPa to 300 MPa, and the firing temperature is set to a value ranging from 450°C to 950°C.

[0009] In a second embodiment, the powder may further include a coarse-grained powder as a raw material. The coarse-grained powder may have a larger particle size than the fine-grained powder and may include particles with a maximum particle size of 53 μm. The proportion of the coarse-grained powder in the mixed powder of the fine-grained powder and the coarse-grained powder may be 70 wt % or less.

[0010] An electrode according to a third aspect of the present disclosure is an electrode for electrical discharge surface treatment that generates an electrical discharge between the electrode and a workpiece to form a coating made of an electrode material or a reactive substance of the electrode material on the surface of the workpiece, and includes a sintered body as the electrode made of a powder containing any one of Co, Ni, and Fe as a single raw material, the median diameter of the powder being 4 μm or less, and the specific surface area of ​​the sintered body being 0.8 m 2 / g to 1.2m 2 / g, and the electrical resistivity of the sintered body ranges from 3 mΩ·cm to 30 mΩ·cm.

[0011] In a third embodiment, the density of the sintered body is 2.4 g / cm 3 to 3.0 g / cm 3 It may have a value ranging from

[0012] A method according to a fourth aspect of the present disclosure is a manufacturing method of an electrode for electrical discharge surface treatment, which generates an electrical discharge between an electrode and a workpiece, and forms a coating made of an electrode material or a reactive substance of the electrode material on the surface of the workpiece, the method comprising: granulating a powder containing any one of Co, Ni, and Fe as a single raw material to produce a granulated powder; compressing the granulated powder to form a green compact; and firing the green compact to form a sintered body as the electrode, the powder including a fine powder having a median diameter of 4.0 μm or less; and adjusting the pressure during compression molding and the firing temperature during firing to a value that satisfies the conditions for the specific surface area of ​​the sintered body to 0.8 m.2 / g to 1.2m 2 / g, and the electrical resistivity of the sintered body is set to a value ranging from 3 mΩ·cm to 30 mΩ·cm, the pressure during compression molding is set to a value ranging from 10 MPa to 30 MPa, and the firing temperature is set to a value ranging from 450°C to 600°C. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an electrode for electrical discharge surface treatment that can stably generate electrical discharge during film formation, and a method for manufacturing the same. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of an electrical discharge surface treatment apparatus according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a flowchart showing a method for manufacturing an electrode for electrical discharge surface treatment according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram illustrating an example of the configuration of a grinding system according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram illustrating a compression molding method according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a diagram illustrating a method for firing a powder compact according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is an electron microscope photograph (SEM image) showing an example of a cross section of an electrode formed by the manufacturing method according to this embodiment. [Figure 7] 7A and 7B are electron microscope photographs (SEM images) showing an example of a cross section of an electrode formed by the manufacturing method according to this embodiment, where FIG. 7A is a low-magnification observation image and FIG. 7B is a high-magnification observation image. [Figure 8] FIG. 8 is an electron microscope photograph (SEM image) showing an example of a cross section of an electrode formed by the manufacturing method according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Several embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0016] (overview) An electric discharge surface treatment apparatus 10 equipped with an electrode 15 according to each embodiment will now be described. FIG. 1 is a schematic diagram showing an example of the configuration of an electric discharge surface treatment apparatus 10 that performs electric discharge surface treatment. The electric discharge surface treatment apparatus 10 is equipped with a bed 11, and a table 12 is provided on this bed 11. A liquid tank 13 is provided on the table 12. The liquid tank 13 stores an electrically insulating liquid L such as insulating oil. A work holder 14 is provided in the liquid tank 13. The work holder 14 holds a workpiece S made of a metal material or the like.

[0017] An electrode holder 16 is provided above the table 12. The electrode holder 16 is provided so as to be movable in the X-axis direction, the Y-axis direction, and the Z-axis direction, and holds an electrode 15 for electrical discharge surface treatment. The electrode holder 16 is also configured so as to be rotatable about the Z-axis as a rotation axis (center of rotation). By moving the electrode holder 16 while it is holding the electrode 15, the electrode 15 is positioned relative to the workpiece S.

[0018] The discharge power supply 17 includes a discharge circuit including a power supply, a capacitor, a switching element, a resistor, and the like, and a control circuit for controlling the operation of the discharge circuit. The discharge power supply 17 can use a known circuit configuration, such as that shown in Japanese Patent Application Laid-Open No. 2005-213554. The output of the discharge power supply 17 is electrically connected to the work holder 14 and the electrode holder 16, and repeatedly applies a pulsed voltage to generate a discharge between the electrode 15 and the workpiece S. The pulse width of the current during discharge is set to a value ranging from 2 μs to 30 μs, for example. The current waveform during discharge changes, for example, stepwise. In this case, the current value immediately after the start of discharge is set to 30 A or 40 A, and the subsequent current value is set to a value ranging from 1 A to 25 A. The interval time (rest time) between discharges is, for example, 60 μs to 70 μs. Note that the current value, pulse width, and interval time are not limited to the above values, and the current waveform is not limited to the above waveform. These are appropriately adjusted depending on the configuration of the electrode 15 and the workpiece S, the composition of the coating to be formed, the coating formation rate, etc.

[0019] The electrode 15 is a sintered body of powder (raw material powder) made from the metal components of the coating formed by electrical discharge surface treatment. The sintered body is porous and its density is lower than the true density of the raw material powder. The configuration and manufacturing method of the electrode 15 will be described later.

[0020] During discharge surface treatment, the electrode 15 is immersed in an electrically insulating liquid L and moves back and forth along the Z axis together with the electrode holder 16 (see Figure 1). While the electrode 15 moves back and forth, the discharge power supply 17 repeatedly generates pulsed discharges between the electrode 15 and the workpiece S. When a discharge occurs between the electrode 15 and the workpiece S, a portion of the material of the electrode 15 (hereinafter referred to as the electrode material) separates from the electrode 15 due to blast and electrostatic forces. The electrode material separated from the electrode 15 temporarily and locally becomes molten or semi-molten due to the heat of the discharge plasma generated between the electrode 15 and the workpiece S. The temperature of the discharge plasma exceeds 3000°C. The molten or semi-molten electrode material moves toward the workpiece S, reaches the surface of the workpiece S, and resolidifies. As pulsed discharges are continuously generated, the electrode material moves successively from the tip of the electrode 15 to the surface of the workpiece S, where it resolidifies and deposits on the workpiece S. In other words, a coating made of the electrode material is formed on the surface of the workpiece S. After melting, the electrode material dropped from the electrode 15 may react with components in the electrically insulating liquid L and deposit as a reactant on the surface of the workpiece S, eventually forming a coating. In the above configuration, the discharge surface treatment is performed in the electrically insulating liquid L. However, the discharge surface treatment according to the present disclosure may also be performed in a gas.

[0021] In order to stably deposit the electrode material or the reactants of the electrode material on the surface of the workpiece S (i.e., the surface of the substrate), the powder of the electrode material must be in a molten or semi-molten state. To achieve this state, it is important to keep the plasma around the electrode 15 warm, and the thermal conductivity of the electrode 15 must be reduced. Thermal conductivity and electrical resistivity are negatively correlated. That is, low thermal conductivity results in low electrical conductivity; in other words, high electrical resistivity. In this embodiment, the electrical resistivity of the electrode is set within the following range. If the electrical resistivity is within this range, it can adequately follow the pulse discharge period and thermal conductivity can be appropriately suppressed. This makes it difficult for the heat of the discharge plasma to escape from the tip of the electrode, allowing the temperature of the tip of the electrode to be maintained at a high temperature.

[0022] In this embodiment, focusing on the specific surface area, which is correlated with the electrical resistivity, the specific surface area of ​​electrode 15 is set to a predetermined range, thereby setting the electrical resistivity to a value in the range of 1 mΩ cm to 30 mΩ cm, where stable discharge can be obtained. Note that the setting range of the specific surface area varies depending on the components of electrode 15.

[0023] By setting the specific surface area to obtain the above-mentioned electrical resistivity, it is possible to synchronize the discharge with the pulse voltage period while also appropriately suppressing the thermal conduction in the electrode 15. In other words, it is possible to stably generate the discharge during the film formation. The specific surface area was measured using the well-known Brunauer-Emmett-Teller method (BET method), and the electrical resistivity was measured using the four-terminal method. The measurement using the BET method complies with Japanese Industrial Standard JIS Z 8830.

[0024] Next, the electrode 15 and a method for manufacturing the electrode 15 according to an embodiment of the present disclosure will be described.

[0025] (First embodiment: electrode) The electrode 15 according to the first embodiment is a sintered body made of powder (hereinafter referred to as raw material powder) containing any of a Co-based alloy, a Ni-based alloy, and an Fe-based alloy as a raw material. Examples of the Co-based alloy include Stellite® 31 (25 wt% Cr, 10 wt% Ni, 7 wt% W, balance Co), Tribaloy® T-800 (28 wt% Mo, 3.4 wt% Si, 18 wt% Cr, balance Co), a CoCrAlY alloy, or a CoNiCrAlY alloy. Examples of the Ni-based alloy include Inconel® 718, a NiCrAlY alloy, or a NiCoCrAlY alloy. Examples of the Fe-based alloy include austenitic stainless steels such as SUS304 (JIS) and SUS316 (JIS). However, the raw material components are not limited to the above examples, and may be Co-based, Ni-based, or Fe-based alloys with other component ratios.

[0026] The sintered body of the electrode 15 according to the first embodiment contains, as its constituent powder, fine powder of the above-mentioned raw material (sintered particles of the fine powder). Alternatively, the sintered body of the electrode 15 contains, as its constituent powder, a mixed powder of the above-mentioned fine powder and the above-mentioned coarse powder of the raw material (sintered particles of the mixed powder). The coarse powder has the same components as the fine powder, but contains particles with larger particle sizes than the fine powder. The proportion of the coarse powder in the mixed powder of the fine powder and the coarse powder is 70 wt% or less.

[0027] The median diameter (D50) of the fine powder is 3.0 μm or less, for example, 1.5 μm. On the other hand, the coarse powder is, for example, a powder under 53 μm or under 22 μm (i.e., a powder with a maximum particle size of 53 μm or 22 μm). These are available as raw material powders. Alternatively, powders with a maximum particle size of approximately 22 to 53 μm may be used. This powder can be obtained, for example, by using a 280 mesh (53 μm opening) sieve and a 600 mesh (22 μm opening) sieve in combination during classification.

[0028] The specific surface area of ​​the electrode 15 according to the first embodiment is 1.3 m 2 / g to 8.0m 2 / g, and the electrical resistivity is in the range of 1 mΩ·cm to 30 mΩ·cm. The specific surface area and electrical resistivity are kept within the above ranges by adjusting the content of the fine powder, the pressure set during compression molding, and the firing temperature during firing of the green compact. The specific surface area and electrical resistivity tend to increase as the content of the fine powder increases. The density of the electrode 15 according to the first embodiment is 3.0 g / cm 3 to 5.0 g / cm 3 It has values ​​ranging from

[0029] By having the specific surface area and electrical resistivity of the above values, the density of the electrode does not become excessively large, and heat conduction in the electrode 15 is also suppressed. Furthermore, by keeping the high-temperature region (plasma) at the tip of the electrode generated by the discharge warm, the temperature at the tip of the electrode 15 increases, making it easier for the electrode material to melt or semi-melt. Therefore, it becomes possible to stably generate discharge during film formation.

[0030] (First embodiment: electrode manufacturing method) Next, a method for manufacturing the electrode 15 according to the first embodiment will be described. The electrode 15 according to the first embodiment is formed by sintering a powder in which coarse powder is added to fine powder obtained by pulverizing raw material powder at a ratio of 0 to 70 wt % relative to the total amount of powder.

[0031] 2 is a flowchart showing a method for manufacturing the electrode 15. As shown in this figure, the manufacturing method according to the first embodiment includes a pulverization step S11, a granulation step S12, a compression molding step S13, and a firing step S14.

[0032] First, the pulverization system 20 used in the pulverization step S11 will be described. Fig. 3 is a diagram showing an example of the configuration of the pulverization system 20. The pulverization system 20 includes a jet mill 21 that pulverizes the raw material powder described above, a compressor 22 that supplies compressed air to the jet mill 21, a cyclone 23 that classifies the powder pulverized by the jet mill 21, and a bag filter 24 that collects the powder that has passed through the cyclone 23. Note that a ball mill or a bead mill may be used instead of the jet mill 21.

[0033] The jet mill 21 includes a supply section 25 and a grinding chamber 26. The jet mill 21 uses compressed air supplied from a compressor 22 to form a high-speed swirling flow in the grinding chamber 26. When raw material powder is supplied from the supply section 25 to the grinding chamber 26, the raw material powder particles collide with each other due to the swirling flow and are ground. The ground raw material powder is discharged from the grinding chamber 26 and supplied to a cyclone 23. The cyclone 23 uses the swirling flow to collect powder with a relatively large particle size. The powder collected by the cyclone 23 is returned to the supply section 25 and is ground again in the grinding chamber 26. On the other hand, powder with a relatively small particle size passes through the cyclone 23 and is collected by a bag filter 24.

[0034] The raw material powder of the electrode 15 may be formed, for example, by an atomization method and classified into powders with a predetermined maximum particle size. For example, the raw material powder may be powder under 53 μm or under 22 μm (i.e., powder with a maximum particle size of 53 μm or powder with a maximum particle size of 22 μm).

[0035] Next, each step will be described in detail. The pulverization step S11 is a step of forming a fine powder to be used for granulation in the granulation step S12 from a raw material powder that is the material of the electrode 15 (hereinafter referred to as the electrode material). In the pulverization step S11, the raw material powder is pulverized using a pulverizer such as a jet mill 21. The compressor pressure during pulverization is, for example, 1.2 MPa.

[0036] The pulverized raw material powder is classified by particle size by a cyclone 23, and powder with a larger particle size is recovered and returned to the jet mill 21. Powder with a smaller particle size than the powder recovered by the cyclone 23 passes through the cyclone 23 and is collected by a bag filter 24.

[0037] During pulverization by the jet mill 21, the surfaces of the raw material powder particles are gradually worn away by collisions between the particles. As a result, the powder becomes a fine powder (i.e., a scaly powder) having a median diameter of 3.0 μm or less and containing particles that have been deformed into a roughly flaky shape, and is collected by the bag filter 24.

[0038] The particles of scaly powder have a flat shape that unfolds in a plane, and have a larger specific surface area than clumped particles. Therefore, the specific surface area of ​​the electrode can be increased compared to when only clumped powder is used to form the electrode. For example, the specific surface area of ​​spherical powder with a particle size of 1 μm is 0.75 m. 2 / g, whereas the specific surface area of ​​the fine powder of this embodiment is larger, 1.3 to 8.0 m 2 That is, in the granulation step S12 described below, the desired specific surface area can be easily obtained by adjusting the amount of the scaly powder.

[0039] The median diameter (D50) of the fine powder obtained by the pulverization step S11 is 3.0 μm or less, for example, 1.5 μm. The particle size distribution of the particles can be evaluated by a well-known measurement method using, for example, a laser diffraction / scattering method.

[0040] The granulation process S12 is a process for producing granulated powder 36 (see Figure 4), which is the material for the green compact, from fine powder or a mixture of fine and coarse powders. In the granulation process S12, a slurry containing fine powder or a mixture of fine and coarse powders is first prepared. As mentioned above, coarse powder has the same components as fine powder but has a larger particle size. Coarse powder can be raw powder whose maximum particle size has been determined by classification, or powder recovered by the cyclone 23 during the pulverization process S11. When coarse powder is included in the slurry, it is mixed with the fine powder at a ratio of 70 wt% or less of the total powder. The higher the content of fine powder, the better the smoothness and adhesion rate of the coating. On the other hand, the higher the content of coarse powder, the shorter the time required for pulverization and classification, thereby reducing production costs. The term "fine particle powder only" is not limited to a strict meaning, but also includes the case where a small amount of coarse particle powder is mixed in, to the extent that it does not affect the performance of the electrode 15 formed from the fine particle powder.

[0041] In the following description of the granulation step S12, for convenience of explanation, the fine powder as a single component that is the raw material of the slurry, or the mixed powder of the fine powder and the coarse powder, will be referred to as intermediate powder.

[0042] The specific surface area of ​​the intermediate powder according to the first embodiment is 1.8 m 2 / g to 12.0m 2 / g. The specific surface area varies depending on the content of coarse powder in the intermediate powder, and the higher the content, the larger the specific surface area. For example, when the raw powder is Stellite (registered trademark) 31, and the fine powder is 30 wt% and the coarse powder is 70 wt%, the specific surface area of ​​the intermediate powder is 1.8 to 3.6 m 2 / g, and when the fine powder is 50 wt% and the coarse powder is 50 wt%, the specific surface area of ​​the intermediate powder is 3.0 to 5.0 m 2 / g, and when the fine powder is 100 wt%, the specific surface area of ​​the intermediate powder is 6.0 to 12.0 m 2 / g. The change in the range of specific surface area relative to the content is similar for other raw materials. For example, even when the raw material powder is Inconel (registered trademark) 718, when the fine powder is 80 wt% and the coarse powder is 20 wt%, the specific surface area of ​​the intermediate powder is 4.8 to 9.5 m 2 / g. Thus, the specific surface area of ​​the intermediate powder is slightly higher than that of the sintered body at the same weight ratio, and decreases as a result of sintering.

[0043] The slurry is prepared by mixing the intermediate powder and 2-3 wt% of a binder in, for example, 200 wt% of an organic solvent, assuming the total amount of the intermediate powder to be 100 wt%, and stirring the mixture. The binder is, for example, a mixture of a thermoplastic resin and wax. However, the binder may also be a thermoplastic resin alone. If the binder is water-soluble, the intermediate powder and binder are mixed in water instead of an organic solvent.

[0044] Binders are added to improve the compressibility of the intermediate powder and to help the green compact retain its shape. Examples of binders include thermoplastic resins such as polypropylene (PP), polyethylene (PE), polymethyl methacrylate (PMMA), and polyvinyl alcohol (PVA), as well as polysaccharides such as agar. It is preferable to use general-purpose polymeric materials that are highly volatile and leave relatively few residual components.

[0045] Wax is added to improve the fluidity of the intermediate powder and improve the transmission of pressure during compression molding. Examples of wax that can be used include stearic acid, acrylic resin, and paraffin wax.

[0046] After preparing the slurry, it is granulated using a spray dryer or the like to form a granulated powder. When granulation is performed using a spray dryer, the slurry is sprayed from the nozzle of the spray dryer into a spray dryer container. The container is filled with high-temperature nitrogen gas or the like, and the solvent contained in the slurry is dried and removed by spraying the slurry into this atmosphere, forming a granulated powder.

[0047] The compression molding step S13 is a step of compressing and molding the granulated powder 36 to form a green compact. FIG. 4 shows an example of a mold 30 used for compression molding. As shown in FIG. 4, the mold 30 includes a main mold 31, an upper punch 32, and a lower punch 33. The main mold 31 is formed in a hollow cylindrical shape having the same cross-sectional shape as the cross-sectional shape of the electrode 15. The main mold 31 is filled with the granulated powder 36. The upper punch 32 is provided above the main mold 31 so as to be movable in the vertical direction. The upper punch 32 presses the granulated powder 36 in the main mold 31 downward by an upper ram (not shown) of a press device. The lower punch 33 is provided below the main mold 31 so as to be movable in the vertical direction. The lower punch 33 presses the granulated powder 36 in the main mold 31 upward by a lower ram (not shown) of the press device. In other words, the granulated powder 36 in the main mold 31 is pressurized from above and below. This causes the granulated powder 36 in the main mold 31 to be compressed and molded into a green compact. The set pressure (surface pressure) during compression molding is roughly constant, 50 to 300 MPa (for example, 50 MPa), regardless of the mixing ratio of the fine powder and the coarse powder.

[0048] After compression molding using the mold 30, the green compact 40 may be further compressed by cold isostatic pressing (hereinafter referred to as CIP). In this case, the pressure setting using the mold 30 is set to a lower value than the pressure setting using CIP. By using CIP, the green compact can be isotropically pressed. The CIP setting is set in the range of 50 to 300 MPa depending on the mixture ratio of fine powder and coarse powder. This setting varies depending on the content of coarse powder in the intermediate powder, and the higher the content, the higher the setting value. For example, in the case of Stellite (registered trademark) 31 as the raw powder, when the fine powder is 30 wt% and the coarse powder is 70 wt%, the setting value is 50 to 100 MPa; when the fine powder is 50 wt% and the coarse powder is 50 wt%, the setting value is 80 to 120 MPa; and when the fine powder is 100 wt%, the setting value is 150 to 300 MPa. The change in the set pressure range relative to the content is similar for other raw materials. For example, even when the raw material powder is Inconel (registered trademark) 718, when the fine powder is 80 wt% and the coarse powder is 20 wt%, the set value is 100 to 150 MPa.

[0049] The firing step S14 is a step of firing the powder compact to form a sintered body. FIG. 5 shows a method for firing the powder compact 40. The powder compact 40 is fired using a heating furnace 41 such as a vacuum heating furnace or an atmospheric furnace. First, the powder compact 40 is placed in the heating furnace 41. The powder compact 40 is subjected to a heat treatment using a heater 42 in a vacuum, an inert atmosphere (e.g., Ar gas), or a reducing atmosphere (e.g., a mixed gas of 95 wt % Ar and 5 wt % H2) to form a sintered body.

[0050] The firing temperature of the powder compact 40 is set according to the composition of the raw material powder. In this embodiment, the raw material powder is a powder containing one of a Co-based alloy, a Ni-based alloy, and an Fe-based alloy. In this case, the firing temperature of the powder compact 40 is set to a value ranging from 600°C to 950°C. The holding time at the firing temperature is 5 to 15 hours. To determine the specific time, several samples of the powder compact 40 obtained in the compression molding step S13 are fired as samples, and the time at which the electrical resistivity becomes 1 to 30 mΩ·cm is adopted. This allows the binder and wax contained in the powder compact 40 to be removed and allows the bonds between the powder particles in the powder compact 40 to have an appropriate strength.

[0051] Through the above process, 1.3 to 8.0 m 2 The electrode 15 has a specific surface area of ​​1.0 to 30 mΩ·cm and a specific surface area of ​​3.0 to 5.0 g / cm. 3 The effect of the produced electrode 15 is as described above.

[0052] The particles of the fine powder and the coarse powder remain in the electrode 15 without melting, and can be observed using a microscope such as a scanning electron microscope (SEM). FIGS. 6 to 8 are electron microscope photographs (SEM images) showing the cross section of the electrode 15 formed by the manufacturing method according to this embodiment. FIG. 6 shows the cross section of the electrode 15 made from fine powder of Stellite 31. The median diameter (D50) of the fine powder used to manufacture the electrode 15 is 1.5 μm. As shown in FIG. 6, the fine powder is densely packed, and the scaly particles P1 remain without melting. Spaces are also observed between the particles, indicating that the electrode 15 is porous.

[0053] Figure 7 shows the cross section of an electrode 15 made from a mixture of fine-grained powder (30 wt%) and coarse-grained powder (70 wt%) of Stellite 31. Figure 7(a) is a low-magnification image, and Figure 7(b) is a high-magnification image. The median diameter (D50) of the fine-grained powder used to make the electrode 15 is 1.5 μm, and the maximum particle size of the coarse-grained powder is 22 μm. Figure 7(a) shows the coarse-grained powder aggregates P2 scattered among the fine-grained powder. The maximum particle size of the aggregated particles P2 is approximately 20 μm. Figure 7(b) shows that the gray area R shown in Figure 7(a) is occupied by scaly particles P1 of the fine-grained powder. However, as in Figure 6, the fine-grained powder shown in Figure 7(b) is densely packed with minute spaces between them. That is, in both examples, it is clear that the specific surface area of ​​the fine powder made of scaly particles contributes greatly to the specific surface area of ​​the electrode 15.

[0054] Figure 8 shows a cross section of electrode 15 made from a mixture of fine-grained Inconel 718 powder (80 wt%) and coarse-grained Inconel 718 powder (20 wt%). The median diameter (D50) of the fine-grained powder used to make electrode 15 is 1.5 μm, and the maximum particle size of the coarse-grained powder is 53 μm. As with the cross section shown in Figure 7(a), Figure 8 also shows the presence of coarse-grained powder agglomerates P2 scattered throughout the gray region R of fine powder. The dark circular regions are areas where agglomerated particles P2 fell off during observation.

[0055] (Second embodiment: electrode) Next, an electrode 15 according to a second embodiment of the present disclosure will be described. The electrode 15 according to the second embodiment is a sintered body made of a powder (hereinafter referred to as raw material powder) containing any one of Co (cobalt), Ni (nickel), and Fe (iron) as a single raw material. That is, the sintered body of the electrode 15 contains the raw material powder (sintered particles of the raw material powder) as its constituent powder. The raw material powder is produced by, for example, the carbonyl method, and the particles thereof are approximately spherical. As in the first embodiment, in the electrode 15 according to the second embodiment, the particles of the raw material powder remain in the electrode 15 without melting and can be observed using a microscope such as a scanning electron microscope (SEM).

[0056] The median diameter (D50) of the raw material powder is 4 μm or less. For example, Co powder with a median diameter of 3.3 μm can be used as the Co raw material powder. For example, Co powder manufactured by GTP (Global Tungsten & Powders Corporation) can be used as such a powder. The specific surface area of ​​this powder is 1.9 m 2 / g.

[0057] The specific surface area of ​​the electrode 15 according to the second embodiment is 0.8 m 2 / g to 1.2m 2 / g, and the electrical resistivity is in the range of 3 mΩ·cm to 30 mΩ·cm. The specific surface area and electrical resistivity are kept within the above ranges by adjusting the pressure set during compression molding and the firing temperature during firing of the green compact. The density of the electrode 15 according to the second embodiment is 2.4 g / cm 3 to 3.0 g / cm 3 It has values ​​ranging from

[0058] The electrode 15 according to the second embodiment also provides the same effects as the electrode 15 according to the first embodiment. That is, by having the specific surface area and electrical resistivity of the above values, the density of the electrode does not become excessively large, and excessive heat conduction in the electrode 15 is also suppressed. Furthermore, by keeping the high-temperature region (plasma) at the tip of the electrode generated by the discharge warm, the temperature of the tip of the electrode 15 increases, making it easier for the electrode material to melt or semi-melt. Therefore, it becomes possible to stably generate discharge during film formation.

[0059] (Second embodiment: electrode manufacturing method) Next, a method for manufacturing the electrode 15 according to the second embodiment will be described. The steps of the manufacturing method according to the second embodiment are the same as those of the manufacturing method according to the first embodiment, except that the pulverization step S11 is omitted. This is because powders with particle sizes that provide the specific surface area described above are readily available. Therefore, in the following explanation, explanations that overlap with those of the first embodiment will be omitted. However, since the metal powder to be processed is only the raw material powder and its components are different from those of the electrode 15 according to the first embodiment, the set values ​​for each step are changed. Furthermore, this embodiment does not exclude the pulverization step S11, and the raw material powder may be pulverized in the pulverization step S11 until the median diameter described above is obtained.

[0060] In the granulation step S12 according to the second embodiment, a slurry containing raw material powder is prepared to produce granulated powder 36, which is the material for the green compact. The total amount of raw material powder is 100 wt %, and the slurry is prepared by, for example, mixing the raw material powder and 2 to 3 wt % of a binder in 200 wt % of an organic solvent and stirring. The components of this binder are the same as those used in the first embodiment. Furthermore, as in the first embodiment, after the slurry is prepared, granulation is performed using a spray dryer or the like to form granulated powder 36 (see FIG. 4).

[0061] Next, a compression molding step S13 is carried out using the mold 30 shown in Fig. 4. As a result, the granulated powder 36 in the main mold 31 is compression molded to form a green compact. The set pressure (surface pressure) during compression molding is 10 to 30 MPa. Since the metal powder used in the second embodiment, such as the Co powder, is softer than the alloy powder used in the first embodiment, the set pressure in the second embodiment is set to a value lower than the set pressure in the first embodiment.

[0062] Next, as in the first embodiment, the powder compact 40 formed in the compression molding step S13 is subjected to the firing step S14. The firing temperature is set to a value in the range of 450°C to 600°C, and firing is carried out in a vacuum or an inert atmosphere (e.g., Ar gas). The holding time at the firing temperature is 4 to 15 hours. To determine the specific time, several samples of the powder compact 40 obtained in the compression molding step S13 are fired as samples, and the time at which the electrical resistivity becomes 3 to 30 mΩ·cm is adopted. This allows the binder and wax contained in the powder compact 40 to be removed and also makes it possible to ensure that the bonds between the powder particles in the powder compact 40 have an appropriate strength.

[0063] Through the above process, 0.8 to 1.2 m 2 The electrode 15 has a specific surface area of ​​2.4 to 3.0 g / cm. The specific surface area of ​​the electrode 15 has an electrical resistivity of 3 to 30 mΩ·cm and a specific surface area of ​​2.4 to 3.0 g / cm. 3 The manufacturing method according to the second embodiment also makes it possible to manufacture an electrode 15 that can provide the same effects as those of the first embodiment.

[0064] The present disclosure is not limited to the above-described embodiments, but is defined by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

Claims

1. An electrode for discharge surface treatment that generates a discharge between the electrode and a workpiece to form a coating made of an electrode material or a reactant of the electrode material on a surface of the workpiece, The electrode is a sintered body made of powder containing any one of Co, Ni, and Fe as a single raw material, The median diameter of the powder is 4 μm or less, The specific surface area of ​​the sintered body is 0.8 m ２ / g to 1.2m ２ / g, The sintered body has an electrical resistivity ranging from 3 mΩ·cm to 30 mΩ·cm. electrode.

2. The density of the sintered body is 2.4 g / cm ３ to 3.0 g / cm ３ has values ​​ranging from 10. The electrode of claim 1.

3. A method for manufacturing an electrode for electrical discharge surface treatment, which generates an electrical discharge between an electrode and a workpiece to form a coating made of an electrode material or a reactant of the electrode material on a surface of the workpiece, comprising: A powder containing any one of Co, Ni, and Fe as a single raw material is granulated to produce a granulated powder; The granulated powder is compressed to form a green compact; The powder compact is fired to form a sintered body as the electrode; The powder includes a fine powder having a median diameter of 4.0 μm or less, The pressure during the compression molding and the firing temperature during the firing are set so that the specific surface area of ​​the sintered body is 0.8 m ２ / g to 1.2m ２ / g, and the electrical resistivity of the sintered body is set to a value ranging from 3 mΩ cm to 30 mΩ cm; The pressure during the compression molding is set to a value in the range of 10 MPa to 30 MPa, The baking temperature is set to a value ranging from 450°C to 600°C. Electrode manufacturing method.

Images