Composite materials, electrodes for electrical discharge machining, methods for manufacturing composite materials

Abstract

The present invention provides a composite material with excellent conductivity and mechanical strength, an electrode for electrical discharge machining, and a method for manufacturing the composite material. [Solution] A composite material 1 comprising a matrix 2 made of tungsten and two or more particles 3 made of a good electrical conductive material present within the matrix 2, wherein the particles 3 are spaced apart from each other.

Description

Technical Field

[0001] The present invention relates to a composite material, an electrode for electrical discharge machining, and a method for manufacturing the composite material.

Background Art

[0002] As metal processing, there is cutting using a lathe, a turning machine, a milling machine, etc. Further, as metal processing, there is electrical discharge machining. Electrical discharge machining is a machining method in which metal is melted by heat generated by arc discharge toward a workpiece, and profiling, cutting, and small-diameter hole drilling are performed. Electrical discharge machining can be performed on difficult-to-machine materials such as high-hardness materials and sticky materials without using different jigs (electrodes).

[0003] For an electrode for electrical discharge machining (hereinafter referred to as "electrode for electrical discharge machining"), it is required that the consumption amount is small, it has weld resistance, the contact resistance is low, and it is an electrical conductor. As an electrode for electrical discharge machining, for example, an electrode made of a copper-tungsten alloy or an electrode made of a silver-tungsten alloy is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a method for manufacturing an electrode for electrical discharge machining, an impregnation method is known in which a porous green compact made of tungsten powder is produced, and then molten copper is impregnated into the pores of the green compact. However, when manufacturing an electrode for electrical discharge machining by this impregnation method, in order to maintain the shape of the green compact, tungsten of 70% or more by mass ratio is required. Further, tungsten is a rare metal, and reduction of the usage amount is an issue.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a composite material with excellent conductivity and mechanical strength, an electrode for electrical discharge machining, and a method for manufacturing the composite material. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] comprising a matrix made of tungsten and two or more particles made of a good electrical conductive material present within the matrix, A composite material in which the particles are spaced apart from each other, and if the diameter of the particles is D, the distance between the particles is greater than D and less than 3D. [2] The composite material according to [1], wherein the good electrical conductivity material is at least one selected from copper, aluminum, silver, gold, and platinum. [3] The composite material according to [1] or [2], wherein the ratio of the good electrical conductive material to the tungsten (good electrical conductive material / tungsten) is 3 / 7 or more and 6 / 4 or less by mass ratio. An electrode for electrical discharge machining, comprising any of the composite materials described in [4][1] to [3]. [5] The process includes a step of sintering a group of coated particles, A method for producing a composite material according to any one of [1] to [3], wherein the coated particles include core particles made of a good electrical conductive material and a coating made of tungsten that covers the core particles. [6] A method for producing a composite material according to [5], further comprising the steps of mixing particles made of a good electrical conductive material and tungsten powder by mechanical milling, agglomerating the tungsten powder on the surface of the particles, and coating the surface of the particles with the tungsten powder to produce coated particles. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a composite material with excellent conductivity and mechanical strength, an electrode for electrical discharge machining, and a method for manufacturing the composite material. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing a composite material relating to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing a cross-section of the coated particles in the present invention. [Figure 3] This is a scanning electron microscope image showing the appearance of the coated particles in Example 1. [Figure 4] This is a backscattered electron image showing a cross-section of the coated particles in Example 1. [Figure 5] In Example 1, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 6] In Example 1, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 7] This is a backscattered electron image showing a cross-section of the composite material in Example 2. [Figure 8] In Example 2, the results of the analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 9] In Example 2, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 10] In the comparative example, this is a backscattered electron image showing a cross-section of the composite material. [Figure 11] In the comparative example, the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 12] In the comparative example, the results of cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 13] This figure shows the Vickers hardness of the composite material, copper sintered body, and tungsten sintered body in Example 3. [Figure 14] This figure shows the conductivity of the composite material, copper sintered body, and tungsten sintered body in Example 4. [Figure 15] A diagram showing the relationship between the measurement results of the Vickers hardness of the composite material, copper sintered body, and tungsten sintered body obtained in Example 3 and the measurement results of the conductivity of the composite material, copper sintered body, and tungsten sintered body obtained in Example 4. [Figure 16] A diagram showing the Vickers hardness of the composite material and tungsten sintered body in Example 6. [Figure 17] A diagram showing the conductivity of the composite material and tungsten sintered body obtained in Example 7. [Figure 18] A diagram showing the relationship between the measurement results of the Vickers hardness of the composite material and tungsten sintered body obtained in Example 6 and the measurement results of the conductivity of the composite material and tungsten sintered body obtained in Example 7. [Figure 19] A diagram showing the relationship between the copper content in the composite material, copper sintered body, and tungsten sintered body obtained in Example 9 and the density of the composite material, copper sintered body, and tungsten sintered body obtained in Example 9. [Figure 20] In Example 10, it is a backscattered electron image showing the cross-section of the coated particles. [Figure 21] In Example 10, it shows the analysis results of the cross-section of the coated particles by energy dispersive X-ray spectroscopy (EDS) and shows the analysis results of copper. [Figure 22] In Example 10, it shows the analysis results of the cross-section of the coated particles by energy dispersive X-ray spectroscopy (EDS) and shows the analysis results of tungsten. [Figure 23] In Example 10, it is a backscattered electron image showing the cross-section of the coated particles. [Figure 24] In Example 10, it shows the analysis results of the cross-section of the coated particles by energy dispersive X-ray spectroscopy (EDS) and shows the analysis results of copper. [Figure 25] In Example 10, it shows the analysis results of the cross-section of the coated particles by energy dispersive X-ray spectroscopy (EDS) and shows the analysis results of tungsten. [Figure 26] In Example 10, it is a backscattered electron image showing the cross-section of the coated particles. [Figure 27] In Example 10, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 28] In Example 10, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 29] This is a backscattered electron image showing a cross-section of the coated particles in Example 11. [Figure 30] In Example 11, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 31] In Example 11, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 32] This is a backscattered electron image showing a cross-section of the coated particles in Example 11. [Figure 33] In Example 11, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 34] In Example 11, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 35] This is a backscattered electron image showing a cross-section of the coated particles in Example 11. [Figure 36] In Example 11, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 37] In Example 11, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 38] This is a backscattered electron image showing a cross-section of the coated particles in Example 11. [Figure 39]In Example 11, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 40] In Example 11, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 41] This is a backscattered electron image showing a cross-section of the composite material in Example 12. [Figure 42] In Example 12, the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 43] In Example 12, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 44] This is a backscattered electron image showing a cross-section of the composite material in Example 12. [Figure 45] In Example 12, the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 46] In Example 12, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 47] This is a backscattered electron image showing a cross-section of the composite material in Example 12. [Figure 48] In Example 12, the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 49] In Example 12, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 50] This is a backscattered electron image showing a cross-section of the composite material in Example 13. [Figure 51] In Example 13, the results of the analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 52] In Example 13, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 53] This is a backscattered electron image showing a cross-section of the composite material in Example 13. [Figure 54] In Example 13, the results of the analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 55] In Example 13, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 56] This is a backscattered electron image showing a cross-section of the composite material in Example 13. [Figure 57] In Example 13, the results of the analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 58] In Example 13, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 59] This is a backscattered electron image showing a cross-section of the composite material in Example 13. [Figure 60] In Example 13, the results of the analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 61] In Example 13, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 62] This is a backscattered electron image showing a cross-section of the coated particles in Example 14. [Figure 63] In Example 14, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 64]In Example 14, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 65] This is a backscattered electron image showing a cross-section of the composite material in Example 15. [Figure 66] In Example 15, the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 67] In Example 15, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 68] This is a backscattered electron image showing a cross-section of the coated particles in Example 16. [Figure 69] In Example 16, the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 70] In Example 16, the results of the cross-sectional analysis of the coated particles by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the tungsten analysis. [Figure 71] This is a backscattered electron image showing a cross-section of the composite material in Example 17. [Figure 72] In Example 17, the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the results of the copper analysis. [Figure 73] In Example 17, the results of the cross-sectional analysis of the composite material by energy-dispersive X-ray spectroscopy (EDS) are shown, and the figure shows the analysis results for tungsten. [Figure 74] This figure shows the Vickers hardness of the composite material, copper sintered body, and tungsten sintered body in Example 18. [Figure 75] This figure shows the conductivity of the composite material, copper sintered body, and tungsten sintered body obtained in Example 18 in Example 19. [Figure 76]This figure shows the relationship between the Vickers hardness measurement results of the composite material, copper sintered body, and tungsten sintered body obtained in Example 18 and the conductivity measurement results of the composite material, copper sintered body, and tungsten sintered body obtained in Example 19 in Example 20. [Modes for carrying out the invention]

[0010] Embodiments of the composite material, the electrode for electrical discharge machining, and the method for manufacturing the composite material of the present invention will be described. This embodiment is provided to give a better understanding of the spirit of the invention and does not limit the present invention unless otherwise specified.

[0011] [Composite materials] A composite material according to one embodiment of the present invention will be described with reference to Figure 1. Figure 1 is a cross-sectional view showing the composite material of this embodiment. As shown in Figure 1, the composite material 1 of this embodiment includes a matrix (base material) 2 and two or more particles 3. The two or more particles 3 are located within the matrix 2. Within the matrix 2, the two or more particles 3 are spaced apart from each other. If the diameter of a particle is D, the distance d between two adjacent particles 3 is greater than D and less than 3D. The matrix 2 is made of tungsten. The particles 3 are electrically conductive particles made of a highly electrically conductive material. In other words, composite material 1 has a sea (=tungsten) island (=particle) structure that includes tungsten and two or more good electrically conductive particles scattered within the tungsten.

[0012] The distance d between two adjacent particles 3, in other words, the width d of the matrix 2 between two adjacent particles 3, is not particularly limited, but is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 40 μm or less, and even more preferably 15 μm or more and 30 μm or less. The distance d is the average value measured by electron microscopy observation.

[0013] A good electrically conductive material is a material whose electrical resistivity is lower than that of aluminum.

[0014] The electrical resistivity (at 20°C) of a good electrically conductive material is 2.9 × 10⁻⁶ in volume resistivity. -8 It is preferable that the value is Ω·m or less.

[0015] The method for measuring the volume resistivity of a good electrically conductive material involves using, for example, the RM3545 manufactured by HIOKI E.E. CORPORATION. The test specimen is a cylindrical shape with a diameter of 15 mm, both sides are wet-polished with abrasive cloth up to #2000, and the measurement is performed 12 times using the 4-terminal method (evaluated at 10 points excluding the maximum and minimum values).

[0016] The melting point of a good electrically conductive material is preferably 800°C or higher.

[0017] The melting point of a good electrically conductive material can be measured using a differential scanning calorimetry (DSC) or similar device.

[0018] Examples of good electrical conductive materials that constitute particle 3 include copper, aluminum, silver, gold, and platinum. In other words, particle 3 can be copper particles, aluminum particles, silver particles, gold particles, or platinum particles. Particle 3 may be used individually or in combination of two or more types.

[0019] The particle size of group 3 is not particularly limited, but is preferably 40 μm to 350 μm, more preferably 40 μm to 200 μm, even more preferably 40 μm to 100 μm, and most preferably 40 μm to 60 μm.

[0020] The particle size of group 3 can be measured using a laser diffraction particle size distribution analyzer or the like.

[0021] The ratio of good electrical conductivity material to tungsten (good electrical conductivity material / tungsten) is preferably 3 / 7 or more and 5 / 5 or less by mass ratio, more preferably 3.5 / 6.5 or more and 4.5 / 5.5 or less, and even more preferably 3.9 / 6.1 or more and 4.1 / 5.9 or less. When the above ratio is within the above range, composite material 1 can achieve both conductivity and hardness compared to conventional materials, and its performance is improved.

[0022] In the composite material 1 of this embodiment, tungsten is bonded in a network-like manner to form a matrix 2. Therefore, particles 3 of the good electrical conductivity material can be individually dispersed within the matrix 2, and the forces acting on the composite material 1 can be distributed and received by the entire tungsten matrix 2. Thus, even if the tungsten content is lower (for example, 60% by mass or more) than in conventional composite materials containing tungsten and copper produced by the fusion method, deformation due to forces acting on the composite material is suppressed throughout the matrix 2, and the composite material 1 of this embodiment has higher hardness. Furthermore, the conductivity can be increased by increasing the content of particles 3 of the good electrical conductivity material compared to composite materials produced by the conventional fusion method.

[0023] Because the composite material 1 of this embodiment has excellent conductivity and mechanical strength, it can be suitably used for electrical discharge machining electrodes, heat dissipation substrate materials, heat sinks, and the like.

[0024] [Method for manufacturing composite materials] The present invention relates to a method for manufacturing a composite material (hereinafter sometimes simply referred to as the "manufacturing method"), which comprises a step of sintering a group of coated particles. The coated particles consist of core particles made of a highly electrically conductive material and a coating made of tungsten that covers the core particles. The manufacturing method of the present invention will be described below with reference to one embodiment. The manufacturing method of this embodiment comprises the steps of: mixing particles made of a good electrical conductive material and tungsten powder by mechanical milling, agglomerating the tungsten powder onto the surface of the particles, and coating the surface of the particles with the tungsten powder to produce coated particles (hereinafter referred to as the "first step"), and sintering the group of coated particles (hereinafter referred to as the "second step").

[0025] "First step" In the first step, particles made of the above-mentioned good electrical conductivity material and tungsten powder are mixed by mechanical milling.

[0026] The particle size of the particles made of a good electrical conductive material is the same as the particle size of particle 3 described above.

[0027] The particle size of the tungsten powder is not particularly limited, but is preferably between 0.1 μm and 8.0 μm, more preferably between 0.1 μm and 6.0 μm, and even more preferably between 0.1 μm and 1.5 μm. If the particle size is below the lower limit, it will disperse into the air and become difficult to handle. Furthermore, if humans inhale particles dispersed in the air, there is a concern about health damage.

[0028] The method for measuring the particle size of the tungsten powder group is the same as the method for measuring particle 3 described above.

[0029] The mixing ratio of particles made of a good electrically conductive material to tungsten powder (particles made of a good electrically conductive material / tungsten powder) is preferably 3 / 7 or more and 5 / 5 or less by mass ratio, more preferably 3.5 / 6.5 or more and 4.5 / 5.5 or less, and even more preferably 3.9 / 6.1 or more and 4.1 / 5.9 or less. When the above ratio is within the above range, the composite material 1 can achieve both conductivity and hardness compared to conventional materials, and its performance is improved.

[0030] In the mixing method using mechanical milling, for example, cemented carbide balls made of stainless steel or the like with a diameter of 3.0 mm to 7.0 mm are used, the rotation speed is 80 rpm to 120 rpm, and the mixing time is 1 hour to 24 hours.

[0031] In the first step, tungsten powder aggregates on the surface of particles made of a good electrical conductive material, forming coated particles in which the surface of the particles made of the good electrical conductive material is coated with tungsten powder.

[0032] Figure 2 is a schematic diagram showing a cross-section of the coated particles in the present invention. As shown in Figure 2, the coated particles 10 have a core particle 11 made of a good electrical conductive material and a coating 12 made of tungsten that covers the core particle 11. The thickness t of the tungsten coating 12 on the coated particles 10 is not particularly limited, but is preferably 5 μm or more and 30 μm or less, more preferably 10 μm or more and 25 μm or less, and even more preferably 15 μm or more and 20 μm or less. If the thickness t of the coating 12 is less than the lower limit, the core particles 11 may bond together during sintering, and a composite harmonious structure may not be formed. In the manufacturing method of the composite material of this embodiment, the distance d between two adjacent particles 3 (the width d of the matrix 2 between the two adjacent particles 3) can be adjusted by adjusting the thickness t of the coating.

[0033] The thickness of the coating can be measured by electron microscopy.

[0034] "The second step" In the second step, the coated particles obtained in the first step are sintered.

[0035] The sintering method for the coated particles is not particularly limited, but for example, atmospheric pressure sintering, pressure sintering methods such as hot press sintering and hot isostatic sintering, discharge sintering methods such as discharge plasma sintering, liquid phase sintering, atomization sintering, etc. can be used.

[0036] According to the manufacturing method of the composite material of this embodiment, since the composite material is produced by sintering the coated particles, it is possible to produce a composite material in which tungsten is bonded in a network-like manner to form a matrix 2, and in which particles of good electrical conductivity material are spaced apart from each other within the matrix. Furthermore, it is possible to produce a composite material with a lower tungsten content (for example, 60% by mass or more) and a higher content of particles of good electrical conductivity material compared to composite materials containing tungsten and copper produced by conventional immersion methods.

[0037] Although the above-described embodiment includes a first step, the manufacturing method of the present invention may also involve purchasing the above-mentioned coated particles and using those coated particles to manufacture the composite material.

[0038] [Electrode for electrical discharge machining] An electrode for electrical discharge machining according to one embodiment of the present invention includes the composite material of the above embodiment. The electrodes for electrical discharge machining in this embodiment include cylindrical or rectangular prism-shaped electrodes, and electrodes with shapes that match the shape of the workpiece. Cylindrical or rectangular prism-shaped electrodes allow for non-contact electrical discharge machining, enabling the creation of fine or deep holes that are difficult to achieve with drills. Electrodes with shapes that match the shape of the workpiece enable the creation of special shapes (fine grooves or complex uneven shapes). The electrical discharge machining electrode of this embodiment contains the composite material of the above-described embodiment, and therefore exhibits excellent conductivity, thereby improving energy efficiency in electrical discharge machining. Furthermore, the electrical discharge machining electrode of this embodiment has excellent mechanical strength, allowing for stable use over a long period of time. [Examples]

[0039] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0040] [Example 1] Copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8, 3 / 7, 4 / 6, and 5 / 5 by mass. Of the obtained coated particles, those with the above ratio of 4 / 6 were subjected to microstructural observation. A Schottky field emission scanning electron microscope JSM-7200 manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 3 to 6. Figure 3 is a scanning electron microscope image showing the appearance of the coated particles. Figure 4 is a backscattered electron image showing the cross-section of the coated particles. Figure 5 shows the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 6 shows the results of analysis of the cross-section of the coated particles by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 4 to 6, the thickness of the coating on the coated particles is approximately 15 μm. The results shown in Figures 4 to 6 confirm that tungsten powder is attached to the copper particles.

[0041] [Example 2] Of the coated particles obtained in Example 1, those with the above ratio of 4 / 6 were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The obtained composite materials were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the composite materials. The results of the microstructural observation of the composite materials are shown in Figures 7 to 9. Figure 7 is a backscattered electron image showing a cross-section of the composite material. Figure 8 shows the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 9 shows the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 7 to 9 confirm that copper particles are present within a tungsten matrix, and that these copper particles are spaced apart from each other.

[0042] [Comparative Example] A composite material containing tungsten and copper was obtained by immersion using the method described in Non-Patent Literature 1 (Akira Okada, Shingo Ogami, Yoshiyuki Uno, Takayuki Shoji, Takahiro Fukushima, Osamu Terada. Development of high-performance copper-tungsten electrodes for electrical discharge machining. Journal of the Japan Society for Electrical Engineering, 2007, Vol. 41, No. 97, pp. 69-76). In the obtained composite material, the ratio of copper particles to tungsten powder (copper particles / tungsten powder) was 3 / 7 by mass. Microstructure observation was performed on the obtained composite materials. A Schottky field emission scanning electron microscope JSM-7200 manufactured by JEOL Ltd. was used for microstructure observation of the composite materials. The results of the microstructure observation of the composite materials are shown in Figures 10 to 12. Figure 10 is a backscattered electron image showing the cross-section of the composite material. Figure 11 shows the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 12 shows the results of analysis of the cross-section of the composite material by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 10 to 12 confirm that although copper is present within the tungsten matrix, the copper is connected in a linear fashion, and as shown in Example 2, the copper is not separated from each other.

[0043] [Example 3] The coated particles obtained in Example 1, with the above ratios of 2 / 8, 3 / 7, 4 / 6, and 5 / 5, were sintered in the same manner as in Example 2 to obtain a composite material. The copper particles used in Example 1 were sintered in the same manner as in Example 2 to obtain a copper sintered body. The tungsten powder used in Example 1 was sintered in the same manner as in Example 2 to obtain a tungsten sintered body. The Vickers hardness of the obtained composite material, copper sintered body, and tungsten sintered body was measured. For comparison, the Vickers hardness of the composite material obtained in the comparative example was also measured. For the Vickers hardness test, we used the FV-100e manufactured by Futuretech Co., Ltd. In the Vickers hardness test, a load of 30 kgf (294.2 N) was applied, the holding time was 15 seconds, and the number of measurements was 12 (evaluated using 10 points excluding the maximum and minimum values). The results are shown in Figure 13. In Figure 13, the HS material is the composite material of the example, the Cu IP sintered body is a copper sintered body, the W IP sintered body is a tungsten sintered body, and the fusion method Cu-W is the composite material of the comparative example. As shown in Figure 13, the Vickers hardness of the composite material in the example was close to the upper limit of the composite rule, confirming that it exhibited superior hardness compared to the composite material in the comparative example.

[0044] [Example 4] The coated particles obtained in Example 1, with the above ratios of 2 / 8, 3 / 7, 4 / 6, and 5 / 5, were sintered in the same manner as in Example 2 to obtain a composite material. The copper particles used in Example 1 were sintered in the same manner as in Example 2 to obtain a copper sintered body. The tungsten powder used in Example 1 was sintered in the same manner as in Example 2 to obtain a tungsten sintered body. The conductivity of the obtained composite material, copper sintered body, and tungsten sintered body was measured. For comparison, the conductivity of the composite material obtained in the comparative example was also measured. For measuring conductivity, we used the RM3545 manufactured by HIOKI E.E. CORPORATION. For conductivity measurements, the test specimen was a cylindrical shape with a diameter of 15 mm, both sides were wet-polished with abrasive cloth up to #2000 grit, the measurement method was the 4-terminal method, and measurements were taken 12 times (evaluated at 10 points excluding the maximum and minimum values), and the conductivity (%IACS) was converted from the volume resistivity. The results are shown in Figure 14. In Figure 14, the HS material is the composite material of the example, the Cu IP sintered body is a copper sintered body, the W IP sintered body is a tungsten sintered body, and the fusion method Cu-W is the composite material of the comparative example. As shown in Figure 14, when comparing the composite material of the example with the comparative example, where the ratio of copper to tungsten is the same, it was confirmed that the conductivity of the composite material of the example was lower than that of the composite material of the comparative example. This is thought to be because the composite material of the example has a structure in which copper particles are coated with tungsten, which has low conductivity.

[0045] [Example 5] Figure 15 shows the relationship between the Vickers hardness measurement results of the composite material, copper sintered body, and tungsten sintered body obtained in Example 3 and the conductivity measurement results of the composite material, copper sintered body, and tungsten sintered body obtained in Example 4. In Figure 15, HS material is the composite material of the example, Cu IP sintered body is the copper sintered body, W IP sintered body is the tungsten sintered body, and fusion method Cu-W is the composite material of the comparative example. As shown in Figure 15, the composite material of the example with a ratio of 4 / 6 showed a 28% improvement in Vickers hardness and an 11% improvement in electrical conductivity compared to the composite material of the comparative example.

[0046] [Example 6] Copper particles with a particle size of 212 μm to 300 μm (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) or copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were mixed with tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. When copper particles with a particle size of 106 μm or less were used, the ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 3 / 7, 4 / 6, and 5 / 5 by mass. The obtained coated particles were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The Vickers hardness of the obtained composite material, the tungsten sintered body, and the composite material obtained in the comparative example was measured. The Vickers hardness test was performed in the same manner as in Example 3. The results are shown in Figure 16. In Figure 16, the HS material using 212-300 μm Cu powder is a composite material containing copper particles with a particle size of 212 μm to 300 μm, the HS material using -106 μm Cu powder is the composite material of Example 6 containing copper particles with a particle size of 106 μm or less, the W IP sintered body is a tungsten sintered body, and the fusion method Cu-W is the composite material of the comparative example. As shown in Figure 16, the composite material of the example was found to have a higher Vickers hardness compared to the composite material containing copper particles with the same copper content but particle sizes of 212 μm to 300 μm, and the composite material of the comparative example. This is thought to be due to the fact that the copper particles are spaced apart from each other within the tungsten matrix.

[0047] [Example 7] The conductivity of the composite material obtained in Example 6, the tungsten sintered body, and the composite material obtained in the comparative example was measured. The conductivity was measured in the same manner as in Example 4. The results are shown in Figure 17. In Figure 17, the HS material using 212-300 μm Cu powder is a composite material containing copper particles with a particle size of 212 μm to 300 μm, the HS material using -106 μm Cu powder is the composite material of Example 6 containing copper particles with a particle size of 106 μm or less, the W IP sintered body is a tungsten sintered body, and the fusion method Cu-W is the composite material of the comparative example. As shown in Figure 17, the conductivity of the composite material in the example was found to be lower than that of the composite material containing copper particles with the same copper content but particle sizes of 212 μm to 300 μm, and the composite material in the comparative example. This is thought to be because the composite material in the example has a structure in which the copper particles are coated with tungsten, which has low conductivity.

[0048] [Example 8] Figure 18 shows the relationship between the Vickers hardness measurement results for the composite material obtained in Example 6, the HS material using 212-300 μm Cu powder (a composite material containing copper particles with a particle size of 212 μm to 300 μm), the tungsten sintered body, and the composite material of the comparative example, and the conductivity measurement results for the composite material obtained in Example 7, the HS material using 212-300 μm Cu powder (a composite material containing copper particles with a particle size of 212 μm to 300 μm), the tungsten sintered body, and the composite material of the comparative example. In Figure 18, the HS material using 212-300 μm Cu powder is a composite material containing copper particles with a particle size of 212 μm to 300 μm, the HS material using -106 μm Cu powder is the composite material of the example containing copper particles with a particle size of 106 μm or less, the W IP sintered body is the tungsten sintered body, and the fusion method Cu-W is the composite material of the comparative example. As shown in Figure 18, the composite material of the example with a ratio of 4 / 6 showed improved Vickers hardness and conductivity compared to the composite material ratio containing copper particles with particle sizes of 212 μm to 300 μm and the comparative composite material.

[0049] [Example 9] Copper particles with a particle size of 53 μm or less (manufactured by Sanyo Special Steel Co., Ltd.) or copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were mixed with tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. When copper particles with a particle size of 53 μm or less were used, the ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8, 3 / 7, 4 / 6, 5 / 5, and 6 / 4 by mass. When copper particles with a particle size of 106 μm or less were used, the ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8, 3 / 7, 4 / 6, and 5 / 5 by mass ratio. The obtained coated particles were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The densities of the obtained composite material, the tungsten sintered body, and the composite material obtained in the comparative example were measured. Density was measured using the AUX220 specific gravity measuring device manufactured by Shimadzu Corporation, employing Archimedes' principle. The results are shown in Figure 19. In Figure 19, the -53μmCu powder-based HS material is a composite material containing copper particles with a particle size of 53μm or less, the -106μmCu powder-based HS material is a composite material containing copper particles with a particle size of 106μm or less, the Cu IP sintered body is a copper sintered body, the W IP sintered body is a tungsten sintered body, and the fusion-method Cu-W is a composite material of the comparative example. The results shown in Figure 19 confirm that the density of the composite material decreases as the copper content increases.

[0050] [Example 10] Copper particles with a particle size of 212-300 μm (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) or copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were mixed with tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 3 / 7 and 5 / 5 by mass. The obtained coated particles were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 20 to 28. Figure 20 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 1") containing copper particles and tungsten powder with particle diameters of 212-300 μm in a mass ratio of 3 / 7. Figure 21 shows the analysis results of the cross-section of coated particles 1 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 22 shows the analysis results of the cross-section of coated particles 1 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 20 to 22, the thickness of the coating on the coated particles is 18 μm. The results shown in Figures 20 to 22 confirm that in coated particle 1, tungsten powder is attached to the copper particles with a nearly uniform thickness. Figure 23 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 2") containing copper particles with a particle diameter of 106 μm or less and tungsten powder in a mass ratio of 3 / 7. Figure 24 shows the analysis results of the cross-section of coated particles 2 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 25 shows the analysis results of the cross-section of coated particles 2 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 23 to 25, the thickness of the coating on the coated particles is 15 μm. The results shown in Figures 23 to 25 confirm that in coated particle 2, tungsten powder is attached to the copper particles with a nearly uniform thickness. Figure 26 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 3") containing copper particles with a particle diameter of 106 μm or less and tungsten powder in a mass ratio of 5 / 5. Figure 27 shows the analysis results of the cross-section of coated particles 3 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 28 shows the analysis results of the cross-section of coated particles 3 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 26 to 28, the thickness of the coating on the coated particles ranges from 3 μm to 20 μm. The results shown in Figures 26 to 28 confirm that in coated particle 3, tungsten powder is attached to the copper particles with an uneven thickness.

[0051] [Example 11] Copper particles with a particle size of 53 μm or less (manufactured by Sanyo Special Steel Industry Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8, 3 / 7, 4 / 6, and 6 / 4 by mass. The obtained coated particles were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 29 to 40. Figure 29 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 4") containing copper particles with a particle diameter of 53 μm or less and tungsten powder in a mass ratio of 2 / 8. Figure 30 shows the analysis results of the cross-section of coated particles 4 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 31 shows the analysis results of the cross-section of coated particles 4 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 29 to 31, the thickness of the coating on the coated particles ranges from 3 μm to 16 μm. The results shown in Figures 29 to 31 confirm that in coated particle 4, tungsten powder is attached to the copper particles with an uneven thickness. Figure 32 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 5") containing copper particles with a particle diameter of 53 μm or less and tungsten powder in a mass ratio of 3 / 7. Figure 33 shows the analysis results of the cross-section of coated particles 5 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 34 shows the analysis results of the cross-section of coated particles 5 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 32 to 34, the thickness of the coating on the coated particles ranges from 6 μm to 20 μm. The results shown in Figures 32 to 34 confirm that in coated particle 5, tungsten powder is attached to the copper particles with an uneven thickness. Figure 35 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 6") containing copper particles with a particle diameter of 53 μm or less and tungsten powder in a mass ratio of 4 / 6. Figure 36 shows the analysis results of the cross-section of coated particles 6 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 37 shows the analysis results of the cross-section of coated particles 6 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 35 to 37, the thickness of the coating on the coated particles is 3 μm to 9 μm. The results shown in Figures 35 to 37 confirm that in coated particle 6, tungsten powder is attached to the copper particles with an uneven thickness. Figure 38 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 7") containing copper particles with a particle diameter of 53 μm or less and tungsten powder in a mass ratio of 6 / 4. Figure 39 shows the analysis results of the cross-section of coated particles 7 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 40 shows the analysis results of the cross-section of coated particles 7 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 38 to 40, the thickness of the coating on the coated particles is 2 μm to 8 μm. The results shown in Figures 38 to 40 confirm that in coated particle 7, tungsten powder is attached to the copper particles with an uneven thickness.

[0052] [Example 12] Copper particles with a particle size of 212-300 μm (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) or copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were mixed with tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 3 / 7 and 5 / 5 by mass. The obtained coated particles were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The obtained coated particles were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 41 to 49. Figure 41 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 1") containing copper particles with a particle size of 212-300 μm and tungsten powder in a mass ratio of 3 / 7. Figure 42 shows the results of analysis of the cross-section of composite material 1 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 43 shows the results of analysis of the cross-section of composite material 1 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 41 to 43 confirm that in composite material 1, copper particles are present within a tungsten matrix, and that the copper particles are spaced apart from each other. Figure 44 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 2") containing copper particles with a particle size of 10⁶ μm or less and tungsten powder in a mass ratio of 3 / 7. Figure 45 shows the analysis results of the cross-section of composite material 2 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 46 shows the analysis results of the cross-section of composite material 2 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 44 to 46 confirm that in composite material 2, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other. Figure 47 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 3") containing copper particles with a particle size of 106 μm or less and tungsten powder in a mass ratio of 5 / 5. Figure 48 shows the analysis results of the cross-section of composite material 3 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 49 shows the analysis results of the cross-section of composite material 3 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 47 to 49 confirm that copper particles are present within a tungsten matrix, and that these copper particles are spaced apart from each other.

[0053] [Example 13] Copper particles with a particle size of 53 μm or less (manufactured by Sanyo Special Steel Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8, 3 / 7, 4 / 6, and 6 / 4 by mass. The obtained coated particles were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The obtained coated particles were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 50 to 61. Figure 50 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 4") containing copper particles with a particle size of 53 μm or less and tungsten powder in a mass ratio of 2 / 8. Figure 51 shows the analysis results of the cross-section of composite material 4 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 52 shows the analysis results of the cross-section of composite material 4 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 50 to 52 confirm that in composite material 4, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other. Figure 53 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 5") containing copper particles with a particle size of 53 μm or less and tungsten powder in a mass ratio of 3 / 7. Figure 54 shows the results of analysis of the cross-section of composite material 5 by energy-dispersive X-ray spectroscopy (EDS), specifically the results for copper. Figure 55 shows the results of analysis of the cross-section of composite material 5 by energy-dispersive X-ray spectroscopy (EDS), specifically the results for tungsten. The results shown in Figures 53 to 55 confirm that in composite material 5, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other. Figure 56 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 6") containing copper particles with a particle size of 53 μm or less and tungsten powder in a mass ratio of 4 / 6. Figure 57 shows the analysis results of the cross-section of composite material 6 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 58 shows the analysis results of the cross-section of composite material 6 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 56 to 58 confirm that in composite material 6, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other. Figure 59 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 7") containing copper particles with a particle size of 53 μm or less and tungsten powder in a mass ratio of 6 / 4. Figure 60 shows the results of analysis of the cross-section of composite material 7 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 61 shows the results of analysis of the cross-section of composite material 7 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 59 to 61 confirm that in composite material 7, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other.

[0054] [Example 14] Copper particles with a particle size of 53 μm or less (manufactured by Sanyo Special Steel Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 5 / 5 by mass. The obtained coated particles were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 62 to 64. Figure 62 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 8") containing copper particles with a particle diameter of 53 μm or less and tungsten powder in a mass ratio of 5 / 5. Figure 63 shows the analysis results of the cross-section of coated particles 8 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 64 shows the analysis results of the cross-section of coated particles 8 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 62 to 64, the thickness of the coating on the coated particles is 5 μm to 10 μm. The results shown in Figures 62 to 64 confirm that in coated particle 8, tungsten powder is attached to the copper particles with an uneven thickness.

[0055] [Example 15] Copper particles with a particle size of 53 μm or less (manufactured by Sanyo Special Steel Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 5 / 5 by mass. The obtained coated particles were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The resulting composite material was subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the composite material. The results of the microstructural observation of the composite material are shown in Figures 65 to 67. Figure 65 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 8") containing copper particles with a particle size of 53 μm or less and tungsten powder in a mass ratio of 5 / 5. Figure 66 shows the analysis results of the cross-section of composite material 8 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 67 shows the analysis results of the cross-section of composite material 8 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 65 to 67 confirm that in composite material 8, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other.

[0056] [Example 16] Copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8 by mass. The obtained coated particles were subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the coated particles. The results of the microstructural observation of the coated particles are shown in Figures 68 to 70. Figure 68 is a backscattered electron image showing a cross-section of coated particles (hereinafter referred to as "coated particles 9") containing copper particles with a particle diameter of 106 μm or less and tungsten powder in a mass ratio of 2 / 8. Figure 69 shows the analysis results of the cross-section of coated particles 9 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 70 shows the analysis results of the cross-section of coated particles 9 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. In Figures 68 to 70, the thickness of the coating on the coated particles ranges from 5 μm to 18 μm. The results shown in Figures 68 to 70 confirm that in coated particle 9, tungsten powder is attached to the copper particles with an uneven thickness.

[0057] [Example 17] Copper particles with a particle size of 106 μm or less (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) and tungsten powder with a particle size of 0.5 μm (manufactured by Nippon Shinkinzoku Co., Ltd.) were mixed by mechanical milling to obtain coated particles in which the surface of the copper particles was coated with tungsten powder. In the mechanical milling process, a FRITSCH P-5 planetary ball mill and tungsten carbide balls with a diameter of 5 mm were used to mix the copper particles and tungsten powder at a rotation speed of 100 rpm for 10 hours. The ratio of copper particles to tungsten powder (copper particles / tungsten powder) was set to 2 / 8 by mass. The obtained coated particles were placed in a mold made of graphite and sintered by discharge plasma sintering to obtain a composite material. In the discharge plasma sintering process, the pressure was set to 100 MPa, the temperature was raised to 1273 K in 45 minutes, and then maintained at 1273 K for 60 minutes. The resulting composite material was subjected to microstructural observation. A Schottky field emission scanning electron microscope (JSM-7200) manufactured by JEOL Ltd. was used for microstructural observation of the composite material. The results of the microstructural observation of the composite material are shown in Figures 71 to 73. Figure 71 is a backscattered electron image showing a cross-section of a composite material (hereinafter referred to as "composite material 9") containing copper particles with a particle size of 106 μm or less and tungsten powder in a mass ratio of 2 / 8. Figure 72 shows the analysis results of the cross-section of composite material 8 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for copper. Figure 73 shows the analysis results of the cross-section of composite material 9 by energy-dispersive X-ray spectroscopy (EDS), specifically the analysis results for tungsten. The results shown in Figures 71 to 73 confirm that in composite material 9, copper particles are present within a tungsten matrix, and these copper particles are spaced apart from each other.

[0058] [Example 18] In the same manner as in Example 15, coated particles containing copper particles with a particle size of 53 μm or less, and with a copper particle / tungsten powder ratio of 2 / 8, 3 / 7, 4 / 6, and 5 / 5, were sintered to obtain composite materials. Also, in the same manner as in Example 17, coated particles containing copper particles with a particle size of 106 μm or less, and with a copper particle / tungsten powder ratio of 2 / 8, 3 / 7, 4 / 6, and 5 / 5, were sintered to obtain composite materials. The Vickers hardness of the obtained composite material was measured. For comparison, the Vickers hardness of the composite material obtained in the comparative example was also measured. For the Vickers hardness test, we used the FV-100e manufactured by Futuretech Co., Ltd. In the Vickers hardness test, a load of 30 kgf (294.2 N) was applied, the holding time was 15 seconds, and the number of measurements was 12 (evaluated using 10 points excluding the maximum and minimum values). The results are shown in Figure 74. In Figure 74, the -53μmCu powder-based HS material is a composite material containing copper particles with a particle size of 53μm or less, the -106μmCu powder-based HS material is a composite material containing copper particles with a particle size of 106μm or less, the Cu IP sintered body is a copper sintered body, the W IP sintered body is a tungsten sintered body, and the fusion-method Cu-W is a composite material of the comparative example. As shown in Figure 74, the Vickers hardness of the composite material in the example was close to the upper limit of the composite law, confirming superior hardness compared to the composite material in the comparative example. Furthermore, it was found that when the mixing ratio of copper and tungsten was the same, a smaller copper particle size resulted in a higher Vickers hardness. This is thought to be due to the refinement of the tungsten matrix that suppresses the deformation of the composite material.

[0059] [Example 19] The conductivity of the composite material obtained in Example 18 was measured. For comparison, the conductivity of the composite material obtained in the comparative example was also measured. For measuring conductivity, we used the RM3545 manufactured by HIOKI E.E. CORPORATION. For conductivity measurements, the test specimen was a cylindrical shape with a diameter of 15 mm, both sides were wet-polished with abrasive cloth up to #2000 grit, the measurement method was the 4-terminal method, and measurements were taken 12 times (evaluated at 10 points excluding the maximum and minimum values), and the conductivity (%IACS) was converted from the volume resistivity. The results are shown in Figure 75. In Figure 75, the -53μmCu powder-based HS material is a composite material containing copper particles with a particle size of 53μm or less, the -106μmCu powder-based HS material is a composite material containing copper particles with a particle size of 106μm or less, the Cu IP sintered body is a copper sintered body, the W IP sintered body is a tungsten sintered body, and the fusion-method Cu-W is a composite material of the comparative example. As shown in Figure 75, when comparing the composite material of the example with the comparative example, where the ratio of copper to tungsten was the same, it was confirmed that the conductivity of the composite material of the example was lower than that of the composite material of the comparative example. This is thought to be because the composite material of the example has a structure in which copper particles are coated with tungsten, which has low conductivity. Furthermore, it was found that there was no difference in the conductivity of the composite material due to differences in the copper particle size. In other words, it was found that the conductivity of the composite material depends on the mixing ratio of copper.

[0060] [Example 20] Figure 76 shows the relationship between the Vickers hardness measurement results of the composite material, copper sintered body, and tungsten sintered body obtained in Example 18 and the conductivity measurement results of the composite material, copper sintered body, and tungsten sintered body obtained in Example 19. In Figure 76, the -53μmCu powder-using HS material is a composite material containing copper particles with a particle size of 53μm or less, the -106μmCu powder-using HS material is a composite material containing copper particles with a particle size of 106μm or less, the Cu IP sintered body is a copper sintered body, the W IP sintered body is a tungsten sintered body, and the fusion method Cu-W is a composite material of the comparative example. As shown in Figure 76, the composite material of the example with a ratio of 4 / 6 showed a 44% improvement in Vickers hardness and an 11% improvement in electrical conductivity compared to the composite material of the comparative example. [Explanation of Symbols]

[0061] 1 Composite materials 2 Matrix 3 particles 10 Coated particles 11 core particles 12 Coating

Claims

1. It comprises a matrix made of tungsten and two or more particles made of a good electrical conductive material present within the matrix, A composite material in which the particles are spaced apart from each other, and if the diameter of the particles is D, the distance between the particles is less than 3D greater than D.

2. The composite material according to claim 1, wherein the good electrical conductivity material is at least one selected from copper, aluminum, silver, gold, and platinum.

3. The composite material according to claim 1, wherein the ratio of the good electrical conductive material to the tungsten (good electrical conductive material / tungsten) is 3 / 7 or more and 5 / 5 or less by mass ratio.

4. An electrode for electrical discharge machining comprising the composite material described in any one of claims 1 to 3.

5. The process includes a step of sintering a group of coated particles, The method for producing a composite material according to any one of claims 1 to 3, wherein the coated particles comprise core particles made of a good electrical conductive material and a coating made of tungsten that covers the core particles.

6. The method for producing a composite material according to claim 5, further comprising the steps of mixing particles made of a good electrical conductive material and tungsten powder by mechanical milling, agglomerating the tungsten powder on the surface of the particles, and coating the surface of the particles with the tungsten powder to produce the coated particles.

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