Machining tool and method for manufacturing machining tool

Abstract

This machining tool has a metal bond layer that holds abrasive grains, wherein: the metal bond layer contains Cu and Mg, and further contains at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W; and the content of Cu is the highest among the respective elements constituting the metal bond layer.

Description

Machining tool and manufacturing method of machining tool

[0001] TECHNICAL FIELD The present disclosure relates to machining tools and methods for manufacturing machining tools.

[0002] 2. Description of the Related Art Known processing tools used for cutting and grinding high-hardness, brittle materials include, for example, metal-bonded wheels in which diamond or cBN (cubic boron nitride) abrasive grains are bonded with a metal bond.

[0003] For example, Patent Document 1 discloses a metal bonded grinding wheel in which abrasive grains are bonded with a metal bond, the metal bond having an intermetallic compound of a silver-tin alloy, and the silver-tin alloy having a composition of 20 to 30 mass % tin and 70 to 80 mass % silver.

[0004] Patent No. 5358968

[0005] When using a Ni-Cr-based metal bond, which is commonly used in known grinding wheels, heat treatment at high temperatures (e.g., above 1000°C) is required. This can lead to thermal denaturation of the abrasive grains (e.g., graphitization in the case of diamond) and a decrease in the reliability of the abrasive grains due to residual stress caused by the difference in thermal expansion coefficient between the metal bond and the abrasive grains (e.g., cleavage in diamond and cBN), resulting in problems such as a decrease in machinability and grindability (hereinafter, to avoid complexity, simply referred to as machinability). Furthermore, when using an Ag-based metal bond, as in Patent Document 1, the metal bond layer has a low Young's modulus, which may prevent the tool from improving its machinability. Furthermore, the use of expensive Ag may increase costs.

[0006] An object of the present disclosure is to provide a machining tool that can be expected to have high cutting performance.

[0007] According to one aspect of the present disclosure, there is provided a machining tool having a metal bond layer that holds abrasive grains, the metal bond layer containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, and the Cu content being the highest among the elements constituting the metal bond layer.

[0008] According to another aspect of the present disclosure, there is provided a method for manufacturing a machining tool, comprising the steps of: preparing a brazing filler metal containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, with Cu being the highest content of the contained elements; disposing the brazing filler metal on a metal substrate; disposing abrasive grains on the brazing filler metal; and heating and maintaining the metal substrate with the brazing filler metal and the abrasive grains disposed thereon at a temperature equal to or higher than the melting point of the brazing filler metal and equal to or lower than 800°C.

[0009] According to the present disclosure, it is possible to provide a machining tool that can be expected to have high cutting performance.

[0010] FIG. 1 is a partial cross-sectional schematic diagram of a processing tool 100 according to one embodiment of the present disclosure. FIG. 2 is a schematic diagram illustrating a method for manufacturing the processing tool 100 according to one embodiment of the present disclosure. FIG. 3 is a schematic diagram illustrating a method for manufacturing the processing tool 100 according to one embodiment of the present disclosure. FIG. 4 is a cross-sectional SEM photograph of Sample 2 according to an example of the present disclosure. FIG. 5 is an enlarged cross-sectional SEM photograph (left side of the figure) of Sample 2 according to an example of the present disclosure, and the results of EDX analysis (right side of the figure).

[0011] <One Aspect of the Present Disclosure> One aspect of the present disclosure will be described below with reference to the above-mentioned drawings. Note that all drawings used in the following description are schematic. The dimensions and proportions of each element shown in the drawings do not necessarily correspond to the actual dimensions. Furthermore, the dimensions and proportions of each element do not necessarily correspond between drawings. Note that in this specification, "A to B" means a numerical range of "greater than or equal to A and less than or equal to B."

[0012] (1) Configuration of the Machining Tool Fig. 1 is a partial cross-sectional schematic diagram of a machining tool 100 according to one embodiment of the present disclosure. As shown in Fig. 1, the machining tool 100 includes a substrate 10, a metal bond layer 20 formed on the substrate 10, and abrasive grains 30 held by the metal bond layer 20.

[0013] The substrate 10 is, for example, a metal member corresponding to the tool body, and is preferably made of stainless steel (SUS), carbon steel, molybdenum steel, or the like.

[0014] The metal bond layer 20 is a metal layer that holds the abrasive grains 30 and contains, for example, copper (Cu) and magnesium (Mg), and further contains at least one active metal element selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), and tungsten (W). The metal bond layer 20 may further contain at least one element selected from tin (Sn), antimony (Sb), and bismuth (Bi). The metal bond layer 20 may further contain at least one element selected from silver (Ag), indium (In), and manganese (Mn). In this embodiment, Ti is used as the active metal element, and the metal bond layer 20 contains Cu, Mg, Sn (Sb, Bi), and Ti.

[0015] As described below, the metal bond layer 20 is formed by heat treating a brazing filler metal 50 containing Cu, Mg, Sn (Sb, Bi), and the aforementioned active metal element Ti in predetermined proportions. The brazing filler metal 50 used in this embodiment is a Cu-Mg brazing filler metal that does not contain Ag as a main component, and the Cu content (at %) is the highest among the elements constituting the brazing filler metal 50 (here, the Cu, Mg, and active metal content elements). Therefore, the Cu content (at %) is the highest among the elements constituting the metal bond layer 20. The brazing filler metal 50 contains, for example, 40 to 85 at % Cu, 1 to 25 at % Mg, 1 to 25 at % total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at % total of the active metal element (Ti in this embodiment). By using such a brazing filler metal 50, the heat treatment temperature during formation of the metal bond layer 20 can be lowered (e.g., 800°C or lower), thereby suppressing thermal denaturation and reliability degradation of the abrasive grains 30 and improving the cutting performance of the machining tool 100. The brazing filler metal 50 used in this embodiment may further contain at least one element selected from Ag, In, and Mn in order to further lower the melting point. However, a high Young's modulus for the metal bond layer 20 is preferable to improve the cutting performance of the tool. Therefore, the total content of at least one element selected from Ag, In, and Mn is preferably 0 to 35 at%. Even when at least one element selected from Ag, In, and Mn is contained in the brazing filler metal 50, it is preferable that the brazing filler metal 50 contains at least one element selected from Ag, In, and Mn, and that the Cu content be the highest among the elements constituting the brazing filler metal 50.

[0016] The abrasive grains 30 are hard particles for cutting and grinding, and preferably contain at least one of diamond and cBN. As described above, in this embodiment, the heat treatment temperature when forming the metal bond layer 20 can be lowered, so the abrasive grains 30 are held in the metal bond layer 20 in an unaltered state (e.g., in a state where they are not graphitized when the abrasive grains 30 are diamond) and in a highly reliable state (e.g., in a state where they are not cleaved). This allows the cutting performance of the machining tool 100 to be improved.

[0017] 1, it is preferable that an interface reaction layer 21 containing an active metal element exists between the abrasive grains 30 and the metal bond layer 20. The interface reaction layer 21 is a layer formed by a reaction between a part of the abrasive grains 30 and a part of the active metal element contained in the brazing material 50. In this embodiment in which the brazing material 50 contains Ti as the active metal element, when the abrasive grains 30 are diamond, the interface reaction layer 21 contains TiC, and when the abrasive grains 30 are cBN, the interface reaction layer 21 contains TiN, TiB, TiB ２ The interfacial reaction layer 21 contains at least one of the following active metal elements: a carbide of the active metal element if the abrasive grains 30 are diamond; and a nitride or boron compound of the active metal element if the abrasive grains 30 are cBN. The other active metal element may be at least one of the active metal carbides, nitrides, or borides, which have a low standard free energy of formation and easily react with the abrasive grains 30. In addition to Ti, at least one element selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, and W may be used. The interfacial reaction layer 21 thus formed by the reaction of a portion of the abrasive grains 30 with a portion of the active metal element improves the wettability of the metal bond layer 20 to the abrasive grains 30, thereby improving the retention of the abrasive grains 30.

[0018] 1, it is preferable that there are abrasive grains 30, some of which are held within the metal bond layer 20 and other parts of which are exposed outside the metal bond layer 20. It is also preferable that the interfacial reaction layer 21 is not formed on the part of the abrasive grains 30 exposed outside the metal bond layer 20, and that the abrasive grains 30 themselves are exposed. This makes it possible to improve the retention force of the abrasive grains 30 while achieving high cutting performance.

[0019] As shown in FIG. 1, the metal bond layer 20 is composed of a solid solution phase 22 formed by dissolving other metal elements in Cu, and a Cu ４ and a compound phase 23 having at least one intermetallic compound selected from MgSn, CuMgSb, and CuMgBi.

[0020] The solid solution phase 22 is mainly composed of, for example, a solid solution of Mg dissolved in Cu crystals, and may also contain other metal elements and active metal elements that were contained in the brazing filler metal 50. When other metal elements are dissolved in Cu, the strength of the solid solution phase 22 (the strength of the metal bond layer 20) can be improved by solid solution strengthening.

[0021] In the solid solution phase 22, the amount of each metal element dissolved in Cu is, for example, preferably 5 at% or less for Mg, 5 at% or less for Sn, 4 at% or less for Sb, and 1 at% or less for Bi. The amount of each metal element dissolved can be measured, for example, by energy dispersive X-ray analysis (EDX).

[0022] In the solid solution phase 22, when Mg and Sn are dissolved in Cu, the ratio A / B is preferably 0.1 or more and 2.0 or less, where A is the amount of dissolved Mg and B is the amount of dissolved Sn. When Mg and Sn are dissolved in Cu at such a ratio, the strength of the metal bond layer 20 can be further increased.

[0023] The compound phase 23 is, for example, Cu ４The compound phase 23 is formed by precipitation of at least one intermetallic compound selected from MgSn, CuMgSb, and CuMgBi. The compound phase 23 may also contain other intermetallic compounds formed from Cu, Mg, Sn, Sb, Bi, and active metal elements. The presence of a trace amount of the compound phase 23 in the metal bond layer 20 can improve the strength of the metal bond layer 20 through precipitation strengthening. From this viewpoint, it is preferable that the compound phase 23 is uniformly dispersed in the solid solution phase 22.

[0024] The average particle size d of the abrasive grains 30 is preferably larger than the film thickness a of the metal bond layer 20. This tends to result in a state in which, as shown in FIG. 1 , a portion of the abrasive grains 30 is retained within the metal bond layer 20, while the other portion is exposed outside the metal bond layer 20, thereby improving cutting performance. Furthermore, since the metal bond layer 20 has excellent retention of the abrasive grains 30 even when it is thin, it is advantageous in terms of cost when manufacturing the machining tool 100. Furthermore, from the viewpoint of maintaining the retention of the abrasive grains 30, the average particle size d of the abrasive grains 30 is preferably smaller than three times the film thickness a of the metal bond layer 20. Specifically, the average particle size d of the abrasive grains 30 is preferably 50 to 500 μm, for example, and the film thickness a of the metal bond layer 20 is preferably 20 to 400 μm, for example. The average particle size d is determined by SEM observation of the cross-sectional structure, randomly selecting 30 abrasive grains 30, and averaging the major axes of these grains.

[0025] The metal bond layer 20 is formed using the brazing filler metal 50 described above, thereby suppressing the occurrence of voids. When a brazing filler metal containing Mg is used, there is a concern that the evaporation of the Mg contained in the brazing filler metal may cause voids or pinholes (hereinafter, collectively referred to as voids) to occur in the metal bond layer. The presence of such voids can reduce the strength of the metal bond layer. In this regard, in the present embodiment, the brazing filler metal 50 contains at least one element selected from Sn, Sb, and Bi, which is an element that suppresses the evaporation of Mg, thereby suppressing the evaporation of Mg and the occurrence of voids in the metal bond layer 20.

[0026] Specifically, when the cross section of the metal bond layer 20 of this embodiment is observed, the thickness is approximately 10,000 μm.２ In other words, when observing the cross section of the metal bond layer 20, the number of voids having a circular equivalent diameter of 8 μm or more is 10,000 μm or less, and more preferably, no voids are observed in any field of view. ２ It is preferable that the number of voids having a circular equivalent diameter of 4 μm or more is one or less per 10,000 μm. ２ It is more preferable that the number of voids having a circular equivalent diameter of 1 μm or more is one or less per 10,000 μm. ２ It is more preferable that there is one or less per molecule.

[0027] By having these various features, this embodiment succeeds in improving the cutting performance of the machining tool 100. In addition, the retention force of the abrasive grains 30 can be increased, and the life of the machining tool 100 can be extended.

[0028] (2) Manufacturing Method of the Machining Tool Next, a manufacturing method of the above-described machining tool 100 will be described.

[0029] First, a brazing filler metal 50 for forming the metal bond layer 20 is prepared. As described above, the brazing filler metal of this embodiment is a Cu-Mg brazing filler metal containing Cu as the main component (e.g., a Cu content of 40 at% or more, with Cu being the highest among the elements constituting the brazing filler metal). Specifically, the brazing filler metal 50 contains 40 to 85 at% Cu, 1 to 25 at% Mg, 1 to 25 at% Sn, Sb, and Bi in total, and 0.1 to 10 at% active metal elements (Ti in this embodiment). By using such a brazing filler metal 50, the heat treatment temperature during the formation of the metal bond layer 20 can be reduced (e.g., 800°C or less), thereby suppressing thermal denaturation and reliability degradation of the abrasive grains 30 and improving the cutting performance of the machining tool 100. The brazing filler metal 50 used in this embodiment may contain at least one element selected from Ag, In, and Mn in a total amount of 0 to 35 at % from the viewpoint of further lowering the melting point.

[0030] Cu is an element that forms a solid solution that mainly constitutes the metal bond layer 20 when the brazing filler metal 50 is heat treated. Cu also contributes to the ductility and malleability of the metal bond layer 20.

[0031] Mg acts to lower the melting point of Cu and to lower the heat treatment temperature of the brazing filler metal 50. Furthermore, Mg acts to increase the wettability of the brazing filler metal 50 with respect to the abrasive grains 30.

[0032] At least one element selected from Sn, Sb, and Bi is an element that easily reacts with Mg when the brazing filler metal 50 is heated, and forms a ternary intermetallic compound with, for example, Cu or Mg. Therefore, these elements act to suppress evaporation of Mg.

[0033] When the brazing filler metal 50 is heated, the active metal element reacts with a portion of the abrasive grains 30 to form a compound, which acts to increase the wettability of the metal bond layer 20 to the abrasive grains 30 and improve the retention of the abrasive grains 30. Therefore, the content of the active metal element may be changed depending on the amount of the abrasive grains 30, which will be described later. It is also preferable to change the content of the active metal element depending on the surface condition of the abrasive grains 30.

[0034] Each metal element constituting the brazing filler metal 50 may be in the form of a powder containing at least one of an element, a hydride, or an intermetallic compound with another metal element, and a mixture of these powders can be used as the brazing filler metal 50. The form after mixing may be any form, and details thereof will be described later.

[0035] In the brazing material 50 , the particle size of the powder containing each metal element can be changed as appropriate depending on the type of the substrate 10 and the thickness of the metal bond layer 20 .

[0036] The brazing filler metal 50 may be in the form of a powder, foil, or paste. When the brazing filler metal 50 is in the form of a paste, the main solvent may be an alcohol such as terpineol or butanediol, or a toluene, the binder may be polyvinyl alcohol, ethyl cellulose, polymethacrylic acid, polyacrylic, or the like, and the surfactant may be a cationic, anionic, or nonionic activator. A plasticizer or a dispersant may also be included. The method for preparing the brazing filler metal 50 is not particularly limited, and any known method may be used.

[0037] After the brazing filler metal 50 is prepared, it is placed on the substrate 10 as shown in Fig. 2. The brazing filler metal 50 can be placed by any known method such as screen printing, transfer, dispensing, inkjet printing, spray coating, sputtering, or vapor deposition.

[0038] 3, abrasive grains 30 (e.g., diamond or cBN) are arranged so as to be sprinkled on the brazing material 50. The abrasive grains 30 are preferably arranged so that a portion thereof is held (embedded) within the brazing material 50 and the other portion is exposed outside the brazing material 50. In other words, the abrasive grains 30 are preferably arranged so as to be sprinkled on top of the brazing material 50 after it has been placed, rather than being mixed in advance with the brazing material 50 paste. This makes it easier for a portion of the abrasive grains 30 to be exposed outside the metal bond layer 20, thereby improving cutting performance.

[0039] Here, in machining tools using diamond or cBN as abrasive grains, the abrasive grains may be coated with metals such as nickel (Ni), Cu, Ti, Zr, and Cr to improve the abrasive grain retention. In this case, not only is the cost of coating the abrasive grains increased, but the machinability of the abrasive grains also decreases. In order to prevent the machinability of the abrasive grains from decreasing, it is necessary to remove the coating from the exposed portion of the metal bond layer after forming the metal bond layer, which further increases costs. In contrast, in this embodiment, the formation of the interface reaction layer 21 improves the wettability of the metal bond layer 20 with the abrasive grains 30, thereby improving the abrasive grain 30 retention, and therefore there is no need to coat the abrasive grains 30 with a metal.

[0040] After the abrasive grains 30 are placed, the substrate 10 and the brazing material 50 are heated and held in a predetermined atmosphere. The predetermined atmosphere may be any one of a vacuum atmosphere (reduced pressure atmosphere), an inert gas atmosphere, and a reducing atmosphere. ２ The oxygen concentration can be adjusted by introducing an inert gas such as toluene.

[0041] The heat treatment temperature is preferably set to, for example, the melting point of the brazing material 50 or higher and 800° C. or lower, thereby suppressing thermal denaturation and a decrease in reliability of the abrasive grains 30. Note that, as the heat treatment furnace used for bonding the substrate 10 and the metal bond layer 20, a known furnace such as a stationary batch furnace, a multi-chamber furnace, a belt conveyor furnace, or a roller hearth kiln can be used.

[0042] Other conditions for bonding are exemplified as follows: Oxygen concentration: 0.01 volume ppm or more and 1000 volume ppm or less Holding time: Not particularly limited, but for example, 30 minutes or more and 180 minutes or less

[0043] After the heat treatment, the temperature of the substrate 10 is lowered. Through the above steps, the machining tool 100 of this embodiment can be manufactured.

[0044] Other Aspects of the Present Disclosure The above describes specific aspects of the present disclosure. However, the present disclosure is not limited to the above aspects and can be modified in various ways without departing from the spirit and scope of the present disclosure.

[0045] (Preparation of Samples 1 to 9) A 6 mm x 6 mm x 5 mm SUS plate was prepared as the substrate 10. Diamond and cBN particles with the particle size ranges and average particle sizes shown in Table 1 were prepared as the abrasive grains 30. A paste was prepared as the brazing filler metal 50 by mixing the metal elements in the ratios shown in Table 1. Terpineol was used as the solvent and polyisobutyl methacrylate was used as the binder, with the total solvent and binder content in the paste being 17 mass%. This paste was applied to the substrate 10 using screen printing, and the abrasive grains 30 (diamond or cBN) were arranged so as to be sprinkled on the applied paste film. Samples 1 to 9 were then prepared by performing a 120-minute heat treatment at the predetermined heat treatment temperature and atmosphere shown in Table 1. The heat treatment temperature was higher than the melting point of each brazing filler metal 50. To determine the particle size range and average particle size of the abrasive grains 30 from each sample after heat treatment, the cross-sectional structure was observed using an SEM and 30 random abrasive grains 30 were selected. The particle size range was calculated from the minimum and maximum values ​​of their major diameters, and the average particle size was calculated from the average value of their major diameters.

[0046]

[0047] The cross-sectional structures of Samples 1 to 9 were observed using an SEM. A cross-sectional SEM photograph of Sample 2 is shown in FIG. 4. As shown in FIG. 4, it was confirmed that a metal bond layer 20 was formed on the substrate 10, and that the abrasive grains 30 were held by the metal bond layer 20. It was also confirmed that no noticeable voids with a circle equivalent diameter of 20 μm or more were generated in the metal bond layer 20. It was also confirmed that the abrasive grains 30 were free of cleavage. Furthermore, FIG. 5 shows an enlarged cross-sectional SEM photograph of Sample 2 (left side of the figure) and the results of EDX analysis (right side of the figure). As shown in FIG. 5, it was confirmed that an interfacial reaction layer 21 containing an active metal element (here, Ti) was present between the abrasive grains 30 and the metal bond layer 20. The same was true for Samples 1 and 3 to 9. Samples in which the metal bond layer 20 had no noticeable voids with a circle equivalent diameter of 20 μm or more, the abrasive grains 30 had no cleavage, and the interfacial reaction layer 21 was confirmed were marked with a "◯" in the cross-sectional structure column of Table 1.

[0048] For Samples 1 to 9, an X-ray diffractometer (XRD) was used to check whether or not the abrasive grains 30 had been altered. As a result, it was confirmed that the abrasive grains 30 of Samples 1 to 9 were not thermally altered. Samples in which the abrasive grains 30 were not thermally altered are indicated with an "X" in the column for alteration of abrasive grains in Table 1.

[0049] From the above, it has been confirmed that the use of the above-described brazing filler metal 50 can suppress thermal denaturation and a decrease in reliability of the abrasive grains 30, and can be expected to improve the cutting performance of the machining tool 100. In addition, it has been confirmed that the formation of the interface reaction layer 21 between the metal bond layer 20 and the abrasive grains 30 can be expected to improve the retention force of the abrasive grains 30.

[0050] <Preferred Aspects of the Present Disclosure> Preferred aspects of the present disclosure are described below. Note that any combination of the technical matters described in the following supplementary notes is possible and will bring about useful effects.

[0051] According to one aspect of the present disclosure, there is provided a machining tool having a metal bond layer that holds abrasive grains, the metal bond layer containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, and the Cu content being the highest among the elements constituting the metal bond layer.

[0052] Preferably, the abrasive grains include at least one of diamond and cBN.

[0053] Preferably, an interface reaction layer containing the active metal element exists between the abrasive grains and the metal bond layer.

[0054] Preferably, there are abrasive grains, a portion of which is held within the metal bond layer and another portion of which is exposed outside the metal bond layer (exposed from the surface of the metal bond layer).

[0055] Preferably, the metal bond layer further contains at least one element selected from the group consisting of Sn, Sb, and Bi.

[0056] Preferably, the metal bond layer further contains at least one element selected from the group consisting of Ag, In, and Mn.

[0057] Preferably, the metal bond layer comprises a solid solution phase in which another metal element is dissolved in Cu, and a solid solution phase in which Cu ４ and a compound phase having at least one intermetallic compound selected from MgSn, CuMgSb, and CuMgBi.

[0058] Preferably, the average particle size d of the abrasive grains is larger than the film thickness a of the metal bond layer.

[0059] Preferably, the average particle size d of the abrasive grains is smaller than three times the film thickness a of the metal bond layer.

[0060] According to another aspect of the present disclosure, there is provided a method for manufacturing a machining tool, comprising the steps of: preparing a brazing filler metal containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, with Cu being the highest content of the contained elements; disposing the brazing filler metal on a metal substrate; disposing abrasive grains on the brazing filler metal; and heating and maintaining the metal substrate with the brazing filler metal and the abrasive grains disposed thereon at a temperature equal to or higher than the melting point of the brazing filler metal and equal to or lower than 800°C.

[0061] Preferably, in the step of preparing the brazing filler metal, a brazing filler metal containing 40 to 85 at % Cu, 1 to 25 at % Mg, 1 to 25 at % in total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at % in total of the active metal elements is prepared.

[0062] Preferably, in the step of preparing the brazing filler metal, a brazing filler metal is prepared that further contains 35 at % or less in total of at least one element selected from Ag, In, and Mn.

[0063] REFERENCE SIGNS LIST 10 substrate 20 metal bond layer 21 interface reaction layer 22 solid solution phase 23 compound phase 30 abrasive grains 50 brazing material 100 machining tool

Claims

1. A machining tool having a metal bond layer that holds abrasive grains, the metal bond layer containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, and the Cu content being the highest among the elements constituting the metal bond layer.

2. The machining tool according to claim 1, wherein the abrasive grains include at least one of diamond and cBN.

3. The machining tool according to claim 1, wherein an interface reaction layer containing the active metal element exists between the abrasive grains and the metal bond layer.

4. The machining tool according to claim 1, wherein there are abrasive grains, some of which are held within said metal bond layer and other of which are exposed outside said metal bond layer.

5. The machining tool according to claim 1, wherein the metal bond layer further contains at least one element selected from the group consisting of Sn, Sb, and Bi.

6. The machining tool according to claim 5, wherein the metal bond layer further contains at least one element selected from the group consisting of Ag, In, and Mn.

7. The machining tool according to claim 1, wherein the average particle diameter d of the abrasive grains is larger than the film thickness a of the metal bond layer.

8. A method for manufacturing a machining tool, comprising the steps of: preparing a brazing filler metal containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, with Cu being the highest content of the contained elements; placing the brazing filler metal on a metal substrate; placing abrasive grains on the brazing filler metal; and heating and maintaining the metal substrate with the brazing filler metal and abrasive grains placed thereon at a temperature equal to or higher than the melting point of the brazing filler metal and equal to or lower than 800°C.

9. The method for manufacturing a machining tool according to claim 8, wherein in the step of preparing the brazing filler metal, a brazing filler metal containing 40 to 85 at% Cu, 1 to 25 at% Mg, 1 to 25 at% in total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at% in total of the active metal elements is prepared.

10. The method for manufacturing a machining tool according to claim 9, wherein in the step of preparing the brazing filler metal, a brazing filler metal is prepared which further contains 35 at% or less in total of at least one element selected from Ag, In, and Mn.

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