Cutting tool

Abstract

A cutting tool, wherein the cutting tool comprises a substrate and a coating disposed on the substrate, the coating comprising a hard carbon film on its outermost surface, the hard carbon film comprising a first region, the first region being a region sandwiched between the surface of the hard carbon film and an imaginary plane P at a distance of 40 nm from the surface toward the substrate side, wherein in the first region, the sp2 component C2 and the sp3 component C3 exhibit the relationship of Equation 1 below, {C2 / (C2+C3)}×100≤2.0 Equation 1.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a cutting tool. BACKGROUND

[0002] Hard carbon films such as amorphous carbon, diamond-like carbon (DLC) are used as coating materials for cutting tools, molds, and mechanical parts because of their excellent wear resistance and lubricity.

[0003] Japanese Patent Application Publication No. 2003-62706 (Patent Literature 1) discloses an amorphous carbon-coated tool having a substrate composed of WC and an amorphous carbon film coating the substrate.

[0004] International Publication No. 2016 / 190443 (Patent Literature 2) discloses a cutting tool having a substrate and a DLC layer containing diamond-like carbon on the surface of the substrate.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2003-62706

[0008] Patent Literature 2: International Publication No. 2016 / 190443 SUMMARY

[0009] The cutting tool of the present disclosure has a substrate and a coating film disposed on the substrate,

[0010] the coating film includes a hard carbon film at its surface,

[0011] the hard carbon film includes a first region,

[0012] the first region is a region sandwiched between a surface of the hard carbon film and an imaginary plane P at a distance of 40 nm from the surface toward the substrate side,

[0013] in the first region, the sp2 component amount C2 and the sp3 component amount C3 show the following relation of Expression 1,

[0014] {C2 / (C2+C3)} x 100 ≤ 2.0 Expression 1. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a cross-sectional view of one example of a cutting tool according to one embodiment of the present disclosure.

[0016] Figure 2 is a cross-sectional view of another example of a cutting tool according to one embodiment of the present disclosure.

[0017] Figure 3 FIG. 1 is a graph showing an example of an XANES spectrum of a first region of a hard carbon film of a cutting tool according to an embodiment of the present disclosure.

[0018] Figure 4 FIG. 2 is a photographic substitute of an example of a dark field image obtained by observing a cross section of a cutting tool according to an embodiment of the present disclosure using a high-angle scattering annular dark field scanning transmission electron microscope.

[0019] Figure 5 FIG. 3 is a schematic view showing an example of a film forming apparatus used in the manufacture of a cutting tool according to an embodiment of the present disclosure.

[0020] Figure 6 FIG. 4 is a graph showing an example of a target used in the manufacture of a cutting tool according to an embodiment of the present disclosure.

[0021] Figure 7 FIG. 5 is a photographic substitute of a dark field image obtained by observing a cross section of a hard carbon film of a conventional cutting tool using a high-angle scattering annular dark field scanning transmission electron microscope. DETAILED DESCRIPTION

[0022] [PROBLEMS TO BE SOLVED BY THE PRESENT DISCLOSURE]

[0023] In recent years, with the diversification of materials to be cut, machining of soft metals such as aluminum alloys, non-ferrous metals such as titanium, magnesium, and copper, materials containing hard particles such as organic materials and graphite, and carbon fiber reinforced plastics (CFRP) and the like has been performed.

[0024] In the case where the above-described materials are cut using a cutting tool having a hard carbon film, there is a tendency that the cutting resistance increases due to the adhesion of the material to be cut to the cutting edge portion of the tool, or the tool life is reduced due to the tip wear. This is particularly likely to occur in the dry machining and MQL machining of soft metals. Therefore, a cutting tool capable of having a long tool life even in the case of cutting of soft metals is required.

[0025] Therefore, an object of the present disclosure is to provide a cutting tool capable of having a long tool life even in the case of cutting of soft metals.

[0026] [EFFECTS OF THE PRESENT DISCLOSURE]

[0027] According to the present disclosure, it is possible to provide a cutting tool capable of having a long tool life even in the case of cutting of soft metals.

[0028] Explanation of Embodiments of the Present Disclosure

[0029] First, an embodiment of the present disclosure is explained.

[0030] (1) The cutting tool of the present disclosure is provided with a base material and a coating film arranged on the base material,

[0031] The coating film contains a hard carbon film at its surface,

[0032] The hard carbon film contains a first region,

[0033] The first region is a region sandwiched between a surface of the hard carbon film and an imaginary plane P at a distance of 40 nm from the surface toward the base material side,

[0034] In the first region, the sp2 component amount C2 and the sp3 component amount C3 show the following relation of Formula 1,

[0035] {C2 / (C2+C3)} x 100 ≤ 2.0 Formula 1.

[0036] The cutting tool of the present disclosure can also have a longer tool life, especially in the case of cutting of soft metals.

[0037] (2) Preferably, in the hard carbon film, the area percentage of a black region having an equivalent circle diameter of 10 nm or more is 0.7% or less,

[0038] The area percentage of the black region is measured in a high-angle annular dark-field scanning transmission electron microscope image of a cross section of the hard carbon film.

[0039] Thus, the amount of defects in the hard carbon film is reduced, and therefore, damage starting from defects is less likely to occur. Therefore, the tool life of the cutting tool is further improved.

[0040] (3) Preferably, the thickness of the portion of the hard carbon film involved in cutting is 0.1 μm or more and 3.0 μm or less. Thus, peeling and damage of the hard carbon film can be suppressed.

[0041] (4) Preferably, the hydrogen content of the hard carbon film is 5 atomic% or less. Thus, the proportion of sp3 hybrid bonds in the hard carbon film becomes higher, and the hardness becomes higher. In addition, the oxidation resistance of the hard carbon film is also improved. Therefore, the tool life of the cutting tool is further improved.

[0042] (5) Preferably, the cutting tool is provided with an interface layer arranged between the base material and the hard carbon film,

[0043] The interface layer contains at least one selected from the group consisting of a single element, an alloy or a first compound, and a solid solution derived from the first compound, the single element being one element selected from a first group consisting of a Group 4 element, a Group 5 element, a Group 6 element, a Group 13 element, and a Group 14 element other than carbon, the alloy or the first compound containing at least one element selected from the first group, or,

[0044] The interface layer contains one or both of a second compound and a solid solution derived from the second compound, the second compound being composed of at least one element selected from the first group and carbon,

[0045] The thickness of the interface layer is 0.5 nm or more and less than 10 nm.

[0046] Thus, the substrate and the hard carbon film are firmly adhered via the interface layer, thereby suppressing adhesive wear in which the coating is peeled off at the time of spalling, and the interface layer functions to balance the difference in hardness between the substrate and the hard carbon film, i.e., functions in a cushioning manner, so that the impact resistance is also improved.

[0047] (6) Preferably, the substrate is composed of a WC-based cemented carbide or a cermet. Thus, the cutting tool is suitable for cutting of non-ferrous alloys, particularly aluminum alloys, copper alloys, magnesium alloys, and the like.

[0048] (7) Preferably, the substrate is composed of cubic boron nitride. Thus, the cutting tool is suitable for cutting of non-ferrous alloys, particularly aluminum alloys, copper alloys, magnesium alloys, and the like.

[0049] [Details of Embodiments of the Present Disclosure]

[0050] Hereinafter, specific examples of the cutting tool of the present disclosure will be described with reference to the accompanying drawings. In the drawings of the present disclosure, the same reference numerals denote the same parts or equivalent parts. In addition, the dimensional relationships of length, width, thickness, depth, and the like are appropriately changed for the sake of the clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0051] In the present specification, the expression in the form of "A to B" means the upper limit and the lower limit of the range (i.e., A or more and B or less), and in the case where the unit is not described in A and the unit is described only in B, the unit of A is the same as the unit of B.

[0052] The inventors of this invention investigated the reasons for adhesion that occurs when cutting soft metals using existing cutting tools with hard carbon films. Adhesion is particularly prone to occur in the early stages of cutting, therefore the inventors of this invention focused on the properties near the surface of the hard carbon film. As a result, it was newly discovered that in existing hard carbon films, the sp2 content in the near-surface region is greater than the sp2 content in deeper regions in the thickness direction (regions closer to the substrate than the near-surface region). In this specification, the sp2 content corresponds to the sp2 hybrid bonds in the hard carbon film. Here, the sp2 hybrid bond corresponds to the double bond (C=C) originating from the graphite component. The sp2 content corresponds to the number of carbon atoms constituting the sp2 hybrid bond. Therefore, in existing cutting tools with hard carbon films, the amount of graphite content near the surface is high, making adhesion particularly prone to occur in the early stages of cutting. As a result of in-depth research based on the above-mentioned new insights, the inventors of this invention have obtained a cutting tool that can have a long tool life even when cutting soft metals. The cutting tool of this disclosure will be described below.

[0053] [Implementation Method 1: Cutting Tool]

[0054] use Figure 1 as well as Figure 2 A cutting tool according to one embodiment of this disclosure (hereinafter also referred to as "this embodiment") will be described. Figure 1 This is a cross-sectional view of an example of a cutting tool involved in this embodiment. Figure 2 This is a cross-sectional view of another example of a cutting tool involved in this embodiment.

[0055] like Figure 1 As shown, the cutting tool 30 of this embodiment includes a substrate 5 and a coating 22 disposed on the substrate 5.

[0056] The coating 22 comprises a hard carbon film 20 on its outermost surface.

[0057] The hard carbon film 20 includes a first region A1.

[0058] The first region A1 is the region sandwiched between the surface S1 of the hard carbon film 20 and an imaginary surface P located 40 nm away from the surface S1 toward the substrate 5.

[0059] In this first region A1, the sp2 component C2 and the sp3 component C3 are related as shown in Equation 1 below.

[0060] {C2 / (C2+C3)}×100≤2.0 Equation 1.

[0061] The cutting tool of this embodiment exhibits a long tool life even when cutting soft metals. This is presumably because the cutting tool of this embodiment has a low sp2 component (graphite component) ratio near the surface of the hard carbon film, making adhesion less likely. Furthermore, it is presumably that the reduced adhesion lowers cutting resistance and improves the wear resistance of the cutting tool.

[0062] <Substrate>

[0063] As substrate 5, metallic or ceramic substrates can be used. Specifically, examples include iron, heat-treated steel, WC-based cemented carbide (e.g., WC-Co cemented carbide, which may contain carbonitrides such as Ti, Ta, and Nb), cermet (cermet with TiC, TiN, TiCN, etc. as the main components), stainless steel, nickel, copper, aluminum alloy, titanium alloy, alumina, cubic boron nitride, and silicon carbide substrates.

[0064] Among these various substrates, those made of WC-based cemented carbide, cermets (especially TiCN-based cermets), or cubic boron nitride are preferred. These substrates exhibit excellent balance between hardness and strength at high temperatures, making them superior substrates for cutting tools used in the aforementioned applications. When using WC-based cemented carbide as the substrate, its microstructure may include free carbon and anomalous layers known as the η-phase or ε-phase.

[0065] Furthermore, the surface of the substrate can be modified. For example, in the case of cemented carbide, a de-β layer can be formed on its surface, and in the case of cermet, a surface-hardened layer can be formed. The substrate exhibits the desired effect even when its surface is modified.

[0066] <Lamination>

[0067] The coating comprises a hard carbon film on its outermost surface. Figure 1 In this embodiment, the coating 22 is composed solely of a hard carbon film 20, and the substrate 5 is in contact with the hard carbon film 20. However, the cutting tool in this embodiment is not limited to this. For example, such as Figure 2 As shown, in the cutting tool 31 of this embodiment, the coating 32, in addition to having a hard carbon film 20, may also have an interface layer 21 disposed between the substrate 5 and the hard carbon film 20.

[0068] In addition to the hard carbon film and the interface layer, the coating may also include a mixed composition layer (not shown) formed by mixing the components of these coatings, or a gradient composition layer (not shown) with continuously varying compositions, between the substrate and the interface layer. Furthermore, in addition to the hard carbon film and the interface layer, the coating may also include a base layer (not shown) between the substrate and the interface layer to improve the adhesion between them.

[0069] The coating can be configured to cover the entire surface of the substrate or to cover only a portion of the surface of the substrate. When the coating is configured to cover only a portion of the substrate, it is preferable to cover at least the portion of the substrate involved in cutting. In this specification, the portion of the substrate involved in cutting refers to the area within the substrate surrounded by an imaginary surface 2 mm away from the cutting edge and a perpendicular line drawn from the cutting edge towards the substrate side along the tangent of the cutting edge.

[0070] The overall thickness of the coating is preferably 0.1 μm or more and 3 μm or less. When the overall thickness of the coating is 0.1 μm or more, the wear resistance is improved. When the overall thickness of the coating is 3 μm or less, the increase of internal stress accumulated inside the coating can be suppressed, and the peeling and defects of the coating can be suppressed.

[0071] The lower limit of the coating thickness is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 1.0 μm or more. The upper limit of the coating thickness is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.5 μm or less. The coating thickness is preferably 0.1 μm or more and 3.0 μm or less, more preferably 0.3 μm or more and 2.0 μm or less, and even more preferably 1.0 μm or more and 1.5 μm or less.

[0072] In this specification, "thickness" is measured by observing a cross-section along the normal to the surface of the coating using a SEM (scanning electron microscope, measuring device: JSM-6610 series manufactured by Nippon Egis Corporation, trademark). Specifically, the magnification of the cross-sectional sample is set to 15,000x, and a rectangular field of view (30 μm in the direction parallel to the substrate surface) × (the distance including the entire thickness of the coating) is set in the electron microscope image. Within this field of view, the thickness amplitude at three locations is measured, and the average value is taken as the "thickness". The thickness (average thickness) of each layer described below is also measured and calculated in the same way.

[0073] It should be noted that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the selected measurement field of view is changed and multiple measurements are performed, the measurement results will have almost no deviation. Even if the measurement field of view is arbitrarily set, the results will not change arbitrarily.

[0074] Hard carbon film

[0075] (composition)

[0076] In this specification, hard carbon film refers to films commonly known as diamond-like carbon (DLC), amorphous carbon, diamond-like carbon, etc. Hard carbon films contain carbon as the main component. Structurally, they are not crystalline and are classified as amorphous. They are considered to contain a mixture of single bonds (CC) visible in diamond crystals and double bonds (C=C) visible in graphite crystals. Depending on the manufacturing method, they may sometimes contain hydrogen, like CH.

[0077] A hard carbon film containing carbon as its main component means that the carbon content of the hard carbon film is 95 atomic% or higher. The carbon content in a hard carbon film can be determined using an energy-dispersive X-ray analyzer (EDS analyzer: BRUKER "Xflash 6-30" (trademark)). Specifically, an electron beam is irradiated onto the outermost surface of the hard carbon film, and the characteristic X-rays generated by the electron beam irradiation are detected. The energy is then used for spectral dispersion, thereby performing elemental and compositional analysis. The accelerating voltage of the electron beam is set to 15 kV. Elemental analysis based on the obtained spectra and the calculation of the carbon content are performed using the software "QUANTAX ESPRIT" (trademark) attached to the aforementioned analyzer.

[0078] It was confirmed that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the selected location of the measurement area is changed and the carbon content measurement results are calculated multiple times, the measurement results will have almost no deviation. Even if the measurement area is set arbitrarily, the results will not change arbitrarily.

[0079] The amorphous nature of hard carbon films can be confirmed, for example, by X-ray diffraction. The specific confirmation method is explained below.

[0080] (A1) For a hard carbon film formed on a substrate, X-ray diffraction was performed under the following conditions (measuring device: "SmartLab" manufactured by Rigaku Corporation (trademark)) to obtain an X-ray diffraction pattern.

[0081] X-ray source: Cu-kα rays

[0082] X-ray output: 45kV, 200mA

[0083] Detector: One-dimensional semiconductor detector

[0084] The range for measuring the diffraction angle 2θ is 15–140°.

[0085] Scanning speed: 0.2° / min

[0086] (A2) In the obtained diffraction pattern, apart from the peaks originating from the substrate, there are no peaks originating from graphite or diamond. If a relatively broad peak is confirmed, it is determined that the hard carbon film is an amorphous phase.

[0087] (The amount of sp2 component C2 and the amount of sp3 component C3)

[0088] In this embodiment, the hard carbon film 20 includes a first region A1, which is the region sandwiched between the surface S1 of the hard carbon film 20 and an imaginary surface P at a distance of 40 nm from the surface S1 toward the substrate 5. In the first region A1, the sp2 component C2 and the sp3 component C3 show the relationship of Equation 1 below.

[0089] {C2 / (C2+C3)}×100≤2.0 Equation 1

[0090] In this specification, the sp2 content C2 corresponds to the number of carbon atoms constituting the sp2 hybrid bond. Here, the sp2 hybrid bond corresponds to the double bond (C=C) originating from the graphite component in the hard carbon film. In this specification, the sp3 content C3 corresponds to the number of carbon atoms constituting the sp3 hybrid bond. Here, the sp3 hybrid bond corresponds to the C-C bond (single bond) or CH bond (single bond) originating from the diamond component in the hard carbon film. Therefore, when the hard carbon film satisfies the above formula 1, the graphite content ratio decreases in the first region near the surface of the hard carbon film. Therefore, the cutting tool equipped with this hard carbon film is less prone to initial adhesion even when cutting soft metals, and can have a longer tool life. Furthermore, since adhesion is less likely to occur, cutting resistance is reduced, and the wear resistance of the cutting tool is also improved.

[0091] The lower limit of the percentage of sp2 component C2 in the first region relative to the total percentage of sp2 component C2 and sp3 component C3, {C2 / (C2+C3)}×100 (hereinafter also referred to as "sp2 content"), is not particularly limited, and can be set to 0.5 or more. In the first region of the hard carbon film, C2 and C3 preferably show the relationship of Equation 2 below.

[0092] 0.5≤{C2 / (C2+C3)}×100≤2.0 (Equation 2)

[0093] In the first region of the hard carbon film, C2 and C3 preferably exhibit the relationship described in Formula 3 below, and more preferably the relationship described in Formula 4 below.

[0094] 0.5≤{C2 / (C2+C3)}×100≤1.5 (Equation 3)

[0095] 0.5≤{C2 / (C2+C3)}×100≤1.0 (Equation 4)

[0096] The percentage of the sp2 component C2 in the first region of the hard carbon film relative to the total of the sp2 component C2 and the sp3 component C3 ({C2 / (C2+C3)}×100) was determined using X-ray Absorption Near Edge Structure (XANES). The specific measurement method is described below.

[0097] (B1) X-ray absorption near-edge structure (XANES) spectra of carbon can be measured in radiation optics facilities. As an example, the BL17 Sumitomo Electric beamline at the Kyushu Synchrotron Light Research Center can be used. It should be noted that measurements can also be performed using other radiation optics facilities and beamlines. An example is shown of measuring the K-end XANES spectrum of carbon based on the electron yield method on the surface of a hard carbon film on a cutting tool using the BL17 Sumitomo Electric beamline at the Kyushu Synchrotron Light Research Center. The measurement conditions are described below.

[0098] <Measurement Conditions>

[0099] Diffraction grating: 400 lines / mm

[0100] Incident X-ray energy: 250–400 eV

[0101] Energy step sizes for measurement: Δ0.5 eV (250–280 eV, 320–400 eV), Δ0.1 eV (280–296 eV), Δ0.2 eV (296–320 eV)

[0102] Cumulative time: 1 second / step

[0103] Measurement method: Electronic output method

[0104] Detection method: I0: M3 mirror current at the downstream end of the beamline, I1: sample current. Both were measured using a Keithley 6485 picoammeter.

[0105] Sample fixation: The sample and sample holder are fixed in place using carbon tape. The carbon tape is not exposed to X-rays.

[0106] Sample surface treatment: Not performed (only alcohol cleaning was performed before the test).

[0107] Measurement chamber vacuum level: below 7E-8 Pa

[0108] The XANES spectrum obtained under the above measurement conditions is equivalent to the XANES spectrum of the first region surrounded by the surface of the hard carbon film and an imaginary surface P at a distance of 40 nm from the surface toward the substrate.

[0109] (B2) The bonding state of C can be investigated by X-ray absorption spectroscopy (XAS). Specifically, the XAS spectrum (hereinafter also referred to as XANES spectrum) near the K absorption end of C is measured. An example of the XANES spectrum of the K absorption end of C in the first region of the hard carbon film of this embodiment is shown below. Figure 3 The solid line. Figure 3 In the diagram, the horizontal axis represents the X-ray energy (hereinafter also denoted as X-ray energy) (eV), and the vertical axis represents the normalized X-ray absorption (au). The horizontal axis is corrected to 285.5 eV for the π* peak observed in highly oriented pyrolytic graphite (HOPG). To normalize the X-ray absorption on the vertical axis, the sample current intensity for each X-ray energy obtained from the sample was plotted using software capable of analyzing XANES spectra. The range of X-ray energies between any two points with 258 eV to 278 eV was subtracted as the background region, and the range of X-ray energies between any two points with 340 eV to 400 eV was set as the normalized region. Furthermore, the minimum distance between the two points defining the background region was at least 10 eV, and the minimum distance between the two points defining the normalized region was at least 20 eV.

[0110] For the analysis, software specialized for XANES spectral analysis, such as REX2000 (manufactured by Rigaku Corporation) and the free and publicly available Athena & Artemis software [IFEFFIT package] (http: / / cars9.uchicago.edu / ifeffit / Downloads), can be used. Using these analytical software programs, the vertical axis intensity is normalized to 1 based on the analytical steps described above. Furthermore, peak fitting of the XANES spectrum is performed, and the percentage of the sp2 component C2 relative to the total of the sp2 and sp3 components C3 is calculated ({C2 / (C2+C3)}×100). The peak fitting range is from 270 eV to 346 eV. A Gaussian function is used for the peak function, and an arctangent function is used for the step function. Highly-Oriented Pyrolytic Graphite (HOPG) is used as the standard sample. Furthermore, by using any software capable of performing the same analyses as REX2000 and Athena described above, the percentage of sp2 component C2 relative to the total of sp2 component C2 and sp3 component C3 can also be determined based on the above analytical steps. The peak height h2 of the peak originating from the sp2 hybrid bond and the peak height h3 of the peak originating from the sp3 hybrid bond are measured, and the value of {h2 / (h2+h3)×100} is calculated. This value corresponds to the percentage of sp2 component C2 relative to the total of sp2 component C2 and sp3 component C3.

[0111] An example of the XANES spectrum of the first region of the hard carbon film of this embodiment is shown below. Figure 3 .exist Figure 3 In the diagram, the solid line represents the XANES spectrum of the first region of the hard carbon film in this embodiment. Figure 3 In the diagram, the dashed lines represent hard carbon films formed under the same film-forming conditions as the hard carbon film of this embodiment, but without surface grinding. Figure 3 The XANES spectrum of the first region (represented as a reference example) is shown below. Figure 3 As shown, in the XANES spectrum of the first region of the hard carbon film in this embodiment, a peak originating from sp2 hybridization, indicated by arrow P2 at X-ray energy 285 eV, and a peak originating from sp3 hybridization, indicated by arrow P3 at X-ray energy 289 eV, were identified.

[0112] It should be noted that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the selected measurement area is changed and multiple measurements are performed, the measurement results will have almost no deviation. Even if the measurement area is set arbitrarily, the results will not change arbitrarily.

[0113] (Percentage of area in black)

[0114] Regarding the hard carbon film 20, when observing its cross-section using HADDF-STEM, the area percentage (hereinafter also referred to as "area percentage of black region") of the equivalent circle diameter of 10 nm or more is preferably 0.7% or less.

[0115] It is believed that black regions with an equivalent circle diameter greater than 10 nm in hard carbon films originate from defects in the film, such as macroscopic particles, voids, and abnormal growth portions. Therefore, it is believed that if the area percentage of black regions in hard carbon films is less than 0.7%, the amount of defects in the hard carbon film is reduced.

[0116] When machining soft metals such as aluminum alloys using a coated cutting tool, the workpiece is repeatedly deposited and detached from the coated surface. It is believed that when the deposited workpiece detaches from the coating, stress is applied to the coating in the direction that peels it off, and stress is also applied in a shear direction approximately parallel to the coating surface. It is believed that if defects exist in the coating at this time, damage to the coating will originate from those defects, exacerbating the damage to the coating.

[0117] If the area percentage of the black region is less than 0.7%, the amount of defects in the hard carbon film is reduced, thus making it less prone to damage starting from defects. Consequently, cutting tools, especially when cutting soft metals, can also have a longer tool life.

[0118] The upper limit of the area percentage of the black region is preferably 0.7% or less, more preferably 0.5% or less, even more preferably 0.3% or less, and even more preferably 0.2% or less. The lower limit of the area percentage of the black region is preferably 0% or more. From a manufacturing point of view, the lower limit of the area percentage of the black region can be set to 0.05% or more. The area percentage of the black region is preferably 0% or more and 0.7% or less, more preferably 0% or more and 0.5% or less, more preferably 0% or more and 0.3% or less, and even more preferably 0% or more and 0.2% or less.

[0119] The area percentage of the black region in the hard carbon film was determined by observation using a high-angle scattering annular dark-field scanning transmission electron microscope (HADDF-STEM). The specific measurement method is described below.

[0120] (C1) A sample containing a hard carbon film is prepared by cutting along the normal direction of the surface using a cutting tool. Ten samples are prepared by setting ten arbitrary positions at the cutting points, including the portion involving the cutting tool. The cutting is performed using a focused ion beam device, a cross-sectional polishing machine, etc.

[0121] (C2) The cross-sections of each sample were observed using HADDF-STEM at a magnification of 200,000 times, and high-angle scattering annular dark-field scanning transmission electron microscope images (hereinafter also referred to as "dark-field images") were obtained.

[0122] (C3) The hard carbon film was identified in the obtained dark field image. By using energy-dispersive X-ray analysis (EDX) attached to the HAADF-STEM for cross-sectional mapping analysis, the interface layer, substrate, and carbon-based hard carbon film were identified.

[0123] (C4) A rectangular measurement field of view is defined within the hard carbon film region in the dark field image. One pair of opposite sides of this rectangle is parallel to the interface on the hard carbon film side of the substrate, and has a length of 800 nm. The distance between the substrate-side edge of this opposite side and the interface on the hard carbon film side of the substrate is 30 nm. The distance between the surface-side edge of this opposite side of the hard carbon film and the surface of the hard carbon film is 30 nm.

[0124] use Figure 4 The above-mentioned measurement of the field of view will be explained in detail. Figure 4 The dark-field image is obtained by observing the cross-section of the cutting tool of this embodiment using HADDF-STEM at a magnification of 200,000x. In this dark-field image, the area enclosed by line segments a, b, c, and d corresponds to a rectangular measurement field of view. A pair of opposite sides of this rectangle (line segments a and b) are parallel to the interface S2 on the hard carbon film side of the substrate 5, with a length of 800 nm. The distance between the substrate-side edge of this opposite side (line segment b) and the interface S2 on the hard carbon film 20 side of the substrate 5 is 30 nm. The distance between the surface S1 side of this opposite side of the hard carbon film 20 (line segment a) and the surface S1 of the hard carbon film 20 is 30 nm.

[0125] When the interface S2 on the hard carbon film side of the substrate 5 has unevenness, the interface S2 on the hard carbon film side of the substrate is set as follows: In the measurement field, determine the part of the substrate that extends the most towards the hard carbon film side. Draw a line parallel to the average line of the unevenness of the main surface of the substrate, passing through this part. This line is taken as the interface S2 on the hard carbon film side of the substrate.

[0126] When the surface of the hard carbon film 20 has unevenness, the surface S1 of the hard carbon film is set as follows: In the measurement field, the portion of the surface of the hard carbon film with the largest depression is determined. A line parallel to the average line of the unevenness of the hard carbon film surface is drawn through this portion. This line is taken as the surface S1 of the hard carbon film.

[0127] The reason for excluding the area within 30 nm of the hard carbon film at the interface S2 on the substrate side and the area within 30 nm of the hard carbon film at the surface S1 in the setting of the measurement field of view is to eliminate the influence of sample adjustment and the influence of the interface layer.

[0128] (C5) The dark-field image was processed using image analysis software (WinROOF, a trademark of Mitani Corporation) and converted into a 256-grayscale monochrome image. Adjustments were then made to the converted monochrome image to avoid contrast differences in the white areas within the measurement field of view.

[0129] (C6) Calculate the average concentration within the measured field of view in the monochrome image above. Use this average concentration as a threshold to binarize the monochrome image.

[0130] (C7) Perform particle analysis on the binarized image to determine the area of ​​the black region with an equivalent circle diameter greater than 10 nm. Calculate the percentage of the black region with an equivalent circle diameter greater than 10 nm relative to the total area of ​​the measured field of view.

[0131] (C8) The area percentage of the black region was measured for each of the 10 samples. The average of the area percentages of the black region measured in the 10 samples was taken as the "area percentage of the black region of the hard carbon film". Specifically, when the average area percentage of the black region measured in the 10 samples was less than 0.7%, it was confirmed that the "area percentage of the black region of the hard carbon film was less than 0.7%".

[0132] In Figure 4 The cutting tool of this embodiment, as photographed, has almost no black areas, therefore... Figure 4 In dark-field images, almost no black areas were detected. As a reference example where the existence of black areas could be confirmed, in... Figure 7 The image shows a dark-field image obtained by observing a cross-section of a hard carbon film on an existing cutting tool using a high-angle scattering annular dark-field scanning transmission electron microscope. Figure 7 In the attached figure, the black part indicated by reference numeral B corresponds to the black area.

[0133] It was confirmed that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the selected location of the cut surface or the selected location of the measurement field of view is changed, the measurement results will have almost no deviation. Even if the measurement field of view is set arbitrarily, the results will not change arbitrarily.

[0134] (thickness)

[0135] The thickness of the portion of the hard carbon film 20 involved in cutting (hereinafter also referred to as "thickness of the hard carbon film") is preferably 0.1 μm or more and 3.0 μm or less. In this specification, the portion of the hard carbon film involved in cutting refers to the area within the hard carbon film enclosed by an imaginary surface 2 mm away from the cutting tool's tip edge and a perpendicular line drawn from that tip edge towards the cutting tool side along the tangent to that tip edge. The thickness of the portion of the hard carbon film involved in cutting refers to the thickness of the hard carbon film in the area involved in cutting, in the direction from its surface along the normal to that surface.

[0136] When the thickness of the hard carbon film is greater than 0.1 μm, the wear resistance is improved. When the thickness of the hard carbon film is less than 3 μm, it can suppress the increase of internal stress accumulated inside the hard carbon film and suppress the peeling and defects of the hard carbon film.

[0137] The lower limit of the thickness of the hard carbon film is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. The upper limit of the thickness of the hard carbon film is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less. The thickness of the hard carbon film is preferably 0.1 μm or more and 3.0 μm or less, more preferably 0.5 μm or more and 2 μm or less, and even more preferably 1 μm or more and 1.5 μm or less.

[0138] (Hydrogen content)

[0139] The rigid carbon film 20 is basically composed of carbon and unavoidable impurities, but sometimes contains hydrogen. It is believed that the hydrogen originates from residual hydrogen in the film-forming device and from moisture entering the rigid carbon film during film formation.

[0140] The hydrogen content of the hard carbon film 20 is preferably 5 atomic% or less. This increases the proportion of sp3 hybrid bonds in the hard carbon film, resulting in higher hardness. Furthermore, the oxidation resistance of the hard carbon film is also improved. The upper limit of the hydrogen content of the hard carbon film is more preferably 4 atomic% or less, and even more preferably 2 atomic% or less. The lower limit of the hydrogen content of the hard carbon film is preferably 0 atomic%, but from a manufacturing point of view, it can also be 0 atomic% or more, 1 atomic% or more, or 2 atomic% or more. The hydrogen content of the hard carbon film is preferably 0 atomic% or more and 5 atomic% or less, more preferably 0 atomic% or more and 4 atomic% or less, and even more preferably 0 atomic% or more and 2 atomic% or less. Additionally, the hydrogen content of the hard carbon film can be set to 1 atomic% or more and 5 atomic% or less, 1 atomic% or more and 4 atomic% or less, 1 atomic% or more and 2 atomic% or less, 2 atomic% or more and 5 atomic% or less, or 2 atomic% or more and 4 atomic% or less.

[0141] The hydrogen content of a hard carbon film can be determined using ERDA (Elastic Recoil Detection Analysis, measuring device: Kobe Steel's "HRBS500"). This method involves recoiling hydrogen (H) ions that collide with helium (He) ions incident at a low angle of incidence forward and analyzing the energy of the recoiling hydrogen particles to determine the hydrogen content.

[0142] It was confirmed that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the measurement site is changed and multiple calculations are performed, the measurement results will have almost no deviation. Even if the measurement site is set arbitrarily, the results will not change arbitrarily.

[0143] (hardness)

[0144] The hard carbon film 20 preferably has a hardness of 35 GPa or higher and 75 GPa or lower. When the hard carbon film has a hardness of 35 GPa or higher, its wear resistance is improved. When the hard carbon film has a hardness of 75 GPa or lower, its chip resistance is improved. The lower limit of the hard carbon film's hardness is preferably 35 GPa or higher, more preferably 45 GPa or higher, and even more preferably 55 GPa or higher. The upper limit of the hard carbon film's hardness is preferably 75 GPa or lower, and even more preferably 73 GPa or lower.

[0145] The hardness of hard carbon films can be measured using nanoindentation (measuring device: "Nano IndenterXP" (trademark) manufactured by MTS). Specifically, the hardness is measured at three points on the surface of the hard carbon film, and the average value is taken as the "hardness".

[0146] It was confirmed that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the measurement site is changed and multiple calculations are performed, the measurement results will have almost no deviation. Even if the measurement site is set arbitrarily, the results will not change arbitrarily.

[0147] <Interface Layer>

[0148] like Figure 2 As shown, the cutting tool 31 of this embodiment may have an interface layer 21 disposed between the substrate 5 and the hard carbon film 20. Thus, the substrate and the hard carbon film are firmly bonded together via the interface layer.

[0149] (composition)

[0150] The interface layer 21 may be composed as described below (K1) or (K2).

[0151] (K1) comprises at least one element selected from the group consisting of an elemental substance, an alloy or a first compound, and a solid solution derived from the first compound, wherein the elemental substance is an element selected from the first group consisting of elements from Group 4, Group 5, Group 6, Group 13 and Group 14 of the periodic table, and the alloy or the first compound comprises at least one element selected from the first group.

[0152] (K2) comprises a second compound consisting of at least one element selected from the first group above and carbon, and one or both of a solid solution derived from the second compound.

[0153] That is, the interface layer can be any of the following (k1) to (k4) forms.

[0154] (k1) is composed of at least one of the following groups: an element selected from the first group, an alloy containing at least one element selected from the first group, a first compound, and a solid solution derived from the first compound.

[0155] (k2) comprises at least one of the following groups: an element selected from the first group, an alloy comprising at least one element selected from the first group, a first compound, and a solid solution derived from the first compound.

[0156] (k3) consists of one or both of the second compound and a solid solution derived from the second compound, wherein the second compound consists of at least one element selected from the first group and carbon.

[0157] (k4) comprises one or both of a second compound and a solid solution derived from the second compound, the second compound being composed of at least one element selected from the first group and carbon.

[0158] Here, Group 4 elements of the periodic table include, for example, titanium (Ti), zirconium (Zr), and hafnium (Hf). Group 5 elements include, for example, vanadium (V), niobium (Nb), and tantalum (Ta). Group 6 elements include, for example, chromium (Cr), molybdenum (Mo), and tungsten (W). Group 13 elements include, for example, boron (B), aluminum (Al), gallium (Ga), and indium (In). Group 14 elements, excluding carbon, include, for example, silicon (Si), germanium (Ge), and tin (Sn). Hereinafter, elements contained in Group 4, Group 5, Group 6, Group 13, and Group 14 elements (excluding carbon) will also be referred to as "Element 1".

[0159] Alloys containing the first element include, for example, Ti-Zr, Ti-Hf, Ti-V, Ti-Nb, Ti-Ta, Ti-Cr, and Ti-Mo. Intermetallic compounds containing the first element include, for example, TiCr2 and Ti3Al.

[0160] Examples of first compounds containing the first element include titanium boride (TiB2), zirconium boride (ZrB2), hafnium boride (HfB2), vanadium boride (VB2), niobium boride (NbB2), tantalum boride (TaB2), chromium boride (CrB), molybdenum boride (MoB), tungsten boride (WB), and aluminum boride (AlB2).

[0161] The aforementioned solid solutions derived from the first compound refer to the state in which two or more of these first compounds are dissolved in each other's crystal structures, and include interstitial solid solutions and substitutional solid solutions.

[0162] Examples of second compounds consisting of a first element and carbon include titanium carbide (TiC), zirconium carbide (ZrC), hafnium carbide (HfC), vanadium carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr3C2), molybdenum carbide (MoC), tungsten carbide (WC), and silicon carbide (SiC).

[0163] The aforementioned solid solutions derived from the second compound refer to the state in which two or more of these second compounds are dissolved in each other's crystal structures, and include interstitial solid solutions and substitutional solid solutions.

[0164] The total content (hereinafter also referred to as "content of the first compound, etc.") of the element selected from the first group, the alloy containing at least one element selected from the first group, the first compound, and the solid solution derived from the first compound in the interface layer is preferably 70% by volume or more and 100% by volume or less, more preferably 80% by volume or more and 100% by volume or less, further preferably 90% by volume or more and 100% by volume or less, and most preferably 100% by volume.

[0165] The total content of the second compound in the interface layer and the solid solution derived from the second compound (hereinafter also referred to as "content of the second compound, etc.") is preferably 70% by volume or more and 100% by volume or less, more preferably 80% by volume or more and 100% by volume or less, further preferably 90% by volume or more and 100% by volume or less, and most preferably 100% by volume.

[0166] The composition of the interface layer, the content of the first compound, and the content of the second compound can be determined using transmission electron microscopy-energy dispersive X-ray spectrometry (TEM-EDX). Specifically, the interface layer is exposed by cutting with a cutting tool using a FIB (focused ion beam) device. The cross-section is observed using TEM, and the composition of the elements constituting the interface layer, the content of the first compound, and the content of the second compound are determined simultaneously.

[0167] It was confirmed that as long as the measurement is within the scope of the applicant's measurement and is performed on the same sample, even if the selected location of the measurement field is changed and the measurement results are calculated multiple times, the measurement results will have almost no deviation. Even if the measurement field is set arbitrarily, the results will not change arbitrarily.

[0168] (thickness)

[0169] The thickness of the interface layer 21 is preferably 0.1 nm or more and less than 10 nm. When the thickness of the interface layer is within this range, the effect of improving the adhesion between the substrate and the hard carbon film is enhanced. More preferably, the thickness of the interface layer is 0.6 nm or more and less than 8 nm, and even more preferably, it is 1 nm or more and less than 5 nm.

[0170] <Other Layers>

[0171] The cutting tool in this embodiment preferably has a mixed composition layer formed by mixing the compositions of these coatings or a gradient composition layer with continuously varying compositions between the interface layer and the hard carbon film. This further improves the adhesion between the substrate and the hard carbon film.

[0172] The hybrid layer and the gradient composition layer may not be clearly distinguishable. When switching the fabrication conditions from interfacial layer deposition to hard carbon film deposition, the compositions of the interfacial layer and the hard carbon film usually mix slightly, forming a hybrid composition layer or a gradient composition layer. This is difficult to confirm directly, but its existence can be reasonably inferred based on results from XPS (X-ray Photo-electronic Spectroscopy), AES (Auger Electron Spectroscopy), etc.

[0173] <Applications of Cutting Tools>

[0174] The cutting tool of this embodiment exhibits excellent wear resistance and adhesion resistance, making it particularly suitable for machining aluminum and its alloys. It is also suitable for machining non-ferrous materials such as titanium, magnesium, and copper. Furthermore, it is suitable for cutting materials containing hard particles, such as graphite, organic materials, printing circuit board machining, and co-machining of ferrous materials and aluminum. In addition, the hard carbon film of the cutting tool of this embodiment has very high hardness, thus enabling its use not only for non-ferrous materials but also for machining steel such as stainless steel and castings.

[0175] Types of cutting tools

[0176] The cutting tools in this embodiment can be, for example, drill bits, end mills, indexable inserts for end mill machining, indexable inserts for milling, indexable inserts for turning, metalworking saws, gear cutting tools, reamers, and taps.

[0177] [Implementation Method 2: Method for Manufacturing a Cutting Tool]

[0178] The cutting tool disclosed herein can, for example, be used by... Figure 5 The film-forming apparatus 1 shown is used to form a coating containing a hard carbon film on a substrate. Hereinafter, an example of a method for manufacturing the cutting tool of this disclosure will be described.

[0179] (Preparation of substrate)

[0180] Prepare substrate 5. The type of substrate can be any of the substrates described in Embodiment 1. For example, the substrate is preferably made of WC-based cemented carbide, cermet, or cubic boron nitride.

[0181] The substrate 5 is assembled into the substrate holder 4 within the film forming apparatus 1. The substrate holder 4 rotates between the targets with the center point of the targets 2 and 3 as the center.

[0182] While heating the substrate 5 to 200°C using the substrate heater 6, the vacuum level inside the film forming apparatus 1 is set to 5 × 10⁻⁶. -4 An atmosphere of Pa was introduced. Next, the set temperature of the substrate heater 6 was lowered to 100°C, and then argon gas was introduced and maintained at 2 × 10⁻⁶ Pa. -1 Under a Pa atmosphere, an argon plasma cleaning of the substrate surface is performed by applying a voltage of -1000V to the substrate holder 4 through a film-forming bias power supply 9. Afterwards, the argon gas is discharged. In the film-forming apparatus 1, gas is supplied through a gas supply port 10, and gas is discharged through an exhaust port 11.

[0183] Next, a target 2 composed of elements from Group 4, Group 5 or Group 6 of the periodic table is placed in the film-forming apparatus 1.

[0184] While the target 2 is evaporated and ionized, a -600V voltage is applied to the substrate holder 4 using a bias power supply 9 to perform metal ion bombardment treatment. As a result, the surface of the substrate is etched, and the adhesion of the subsequently formed interface layer and hard carbon film is improved.

[0185] It should be noted that the formation of the interface layer and the hard carbon film described later can also be carried out without subjecting the substrate to metal ion bombardment treatment.

[0186] (Formation of the interface layer)

[0187] Next, a target 2 is placed inside the film-forming apparatus 1. The target 2 is composed of one element selected from the group consisting of elements from Group 4, Group 5, Group 6, Group 13, and Group 14 (excluding carbon) of the periodic table. While introducing or not introducing hydrocarbon gas, the target 2 is evaporated and ionized by vacuum arc discharge. A voltage of -100V to -800V is applied to the substrate holder 4 using a bias power supply 9, forming an interface layer on the substrate. Afterward, the hydrocarbon gas is discharged.

[0188] It should be noted that the hard carbon film described later can also be formed without forming an interface layer on the substrate.

[0189] (Formation of hard carbon film)

[0190] Next, a target 3 made of glassy carbon is placed inside the film-forming apparatus 1. While argon gas is introduced at a flow rate of 5–25 cc / min, the target 3 is evaporated and ionized by vacuum arc discharge (cathode current 100–120 A). A voltage of -50–150 V is applied to the substrate holder 4 using a bias power supply 9, forming a hard carbon film on the interface layer to obtain a cutting tool. Alternatively, hydrocarbon gas can be introduced along with argon gas. The temperature of the substrate heater 6 during the film-forming process is set to 180°C.

[0191] Glassy carbon can be commercially available. As a high-purity carbon material, glassy carbon does not contain contamination caused by metallic elements, unlike existing sintered carbon materials used in cathodes (such as sintered graphite). In particular, glassy carbon manufactured by Hitachi Chemical does not contain aluminum (Al), making it especially suitable for machining aluminum alloys. Furthermore, using glassy carbon can suppress the formation of macroscopic particles in the hard carbon film, resulting in a smooth hard carbon film and improved cutting performance.

[0192] Regarding the target shape, cylindrical, disc-shaped, or rectangular targets are generally used. However, the inventors of this invention, through in-depth research, have discovered a new preferred shape from the viewpoint of improving the film quality of hard carbon films. Figure 6The target is shown as a triangular prism shape. A high current needs to flow through the target, but by using a V-shaped electrode, the sides of the target are in close contact with the electrode, enabling a stable power supply to the target. Furthermore, the close contact between the target and the electrode also improves cooling. Efficient cooling of the target reduces resistance, making it easier for the arc point to move. As a result, the formation of defects in the hard carbon film is suppressed, and the film quality of the hard carbon film is improved.

[0193] From the viewpoint of improving the purity of hard carbon films, it is preferable to form films in a vacuum without introducing Ar gas. However, the inventors of this invention have conducted in-depth research and have discovered that, compared to a vacuum, arc discharge is more stable and film quality is improved when Ar gas is flowed at a flow rate of 15 cc / min.

[0194] (Grinding of hard carbon film)

[0195] Next, the surface of the hard carbon film formed above is ground. The region near the surface of the hard carbon film obtained above has a higher sp2 content than the region deeper in the thickness direction. Therefore, by removing the region near the surface through grinding, the region with a low sp2 content can be exposed to the outermost surface. In the hard carbon film after surface grinding, the sp2 content C2 and sp3 content C3 in the first region show the relationship of Equation 1 below.

[0196] {C2 / (C2+C3)}×100≤2.0 Equation 1

[0197] The preferred grinding method is mechanical grinding using a wet media. The preferred grinding amount is 40 nm or more. The hard carbon film obtained by the above-described method for forming a hard carbon film has a smooth surface. Therefore, by using the above-described grinding method and grinding amount, areas with high sp2 content can be removed, and the removed surface becomes smooth, improving adhesion resistance.

[0198] It should be noted that existing hard carbon films have a high sp2 content overall. Therefore, even if the surface of an existing hard carbon film is polished, the sp2 content C2 and sp3 content C3 in the area near the newly exposed surface do not satisfy the relationship in Equation 1 above.

[0199] Compared to the hard carbon film obtained by the hard carbon film formation method of this embodiment described above, existing hard carbon films have more black areas (droplets, etc.). Therefore, even if the surface of the existing hard carbon film is polished, adhesion is easily generated due to the influence of the black areas.

[0200] Existing hard carbon films have a large surface roughness. Therefore, when the surface is smoothed by grinding to improve adhesion resistance, the amount of grinding increases, and the coating at the cutting edge tends to crack and break, thus shortening the tool life.

[0201] As described above, even if the surface of an existing hard carbon film is polished, it is impossible to obtain a hard carbon film in the first region where the sp2 content C2 and sp3 content C3 show the relationship of Equation 1 above.

[0202] [Postscript 1]

[0203] In the cutting tool of this embodiment, the substrate and the hard carbon film can be in contact.

[0204] [Postscript 2]

[0205] Preferably, the cutting tool of this embodiment includes an interface layer disposed between the substrate and the hard carbon film.

[0206] The interface layer comprises at least one element selected from the group consisting of an elemental substance, an alloy or a first compound, and a solid solution derived from the first compound. The elemental substance is an element selected from the first group consisting of Group 4, Group 5, Group 6, Group 13 elements, and Group 14 elements excluding carbon. The alloy or the first compound comprises at least one element selected from the first group.

[0207] The interface layer comprises a second compound and one or both of a solid solution derived from the second compound, wherein the second compound is composed of at least one element selected from the first group and carbon.

[0208] The thickness of the interface layer is greater than 0.5 nm and less than 10 nm.

[0209] Example

[0210] The present embodiment will be further described in detail through examples. However, the present embodiment is not limited to these examples.

[0211] [Making Cutting Tools]

[0212] <<Sample 1 to Sample 3, Sample 8 to Sample 23, Sample 1-1, Sample 1-3>>

[0213] In samples 1 to 3, 8 to 23, 1-1, and 1-3, glassy carbon was used as the raw material, and a hard carbon film was formed on the substrate using the cathode arc ion plating method (referred to as "arc method" in Table 1) to make cutting tools.

[0214] (Preparation of substrate)

[0215] As a base material, prepare WC (grain size: 1μm) based cemented carbide drill bit (model: MDW0600NHGS5). The base material contains 8% by mass Co as a bonding material.

[0216] Assemble the substrate Figure 5 In the film-forming apparatus 1 shown, the substrate is heated to 200°C using the substrate heater 6, while the vacuum level within the film-forming apparatus 1 is set to 5 × 10⁻⁶. -4 An atmosphere of Pa was then introduced. Next, the set temperature of the substrate heater 6 was lowered to 100°C, and then argon gas was introduced while maintaining the temperature at 2 × 10⁻⁶ Pa. -1 Under a Pa atmosphere, an argon plasma cleaning of the substrate surface is performed by applying a voltage of -1000V to the substrate holder 4 using a film-forming bias power supply 9. Afterward, the argon gas is discharged.

[0217] (Formation of hard carbon film)

[0218] Next, while introducing argon gas into the film-forming apparatus 1 at the flow rate recorded in the "Argon Flow Rate" column of Table 1, a triangular prism-shaped target made of glassy carbon ("glassy carbon" manufactured by Hitachi Chemical Co., Ltd.) is evaporated and ionized by vacuum arc discharge (the cathode current is recorded in the "Cathode Current (A)" column of Table 1). The voltage recorded in the "Bias Voltage (V)" column of "Film Formation Conditions for Hard Carbon Films" in Table 1 is applied to the substrate holder 4 using the bias power supply 9, thereby forming a hard carbon film on the substrate. The set temperature of the substrate heater 6 during the film formation process of the hard carbon film is set to 180°C.

[0219] (Grinding of hard carbon film)

[0220] Next, the surface of the hard carbon film formed above was ground to obtain a cutting tool. The grinding method was mechanical grinding based on a wet medium. The grinding amount is recorded in the "Grinding Amount" column of Table 1. The thickness of the part of the hard carbon film that participates in cutting of each sample after grinding is shown in the "Thickness (μm)" column of "Hard Carbon Film" in Table 2.

[0221] <<Sample 4 to Sample 7>>

[0222] In samples 4 to 7, a cutting tool was fabricated by sequentially forming an interface layer and a hard carbon film on a substrate using cathodic arc ion plating.

[0223] <Sample 4>

[0224] (Preparation of substrate)

[0225] The substrate was prepared using the same method as that used for sample 1.

[0226] (Formation of the interface layer)

[0227] Next, while introducing hydrocarbon gas into the film-forming apparatus 1 at a flow rate of 15 cc / min, a triangular prism-shaped target made of chromium (Cr) is evaporated and ionized by vacuum arc discharge (cathode current 80A). A voltage of -100V is applied to the substrate holder 4 using a bias power supply 9, forming an interface layer with a thickness of 5 nm made of chromium carbide (CrC) on the substrate. Afterward, the hydrocarbon gas is discharged.

[0228] (Formation of hard carbon film)

[0229] Next, a hard carbon film is formed on the interface layer. The film formation conditions for the hard carbon film are shown in Table 1. The set temperature of the substrate heater 6 during the film formation process of the hard carbon film is set to 180°C.

[0230] (Grinding of hard carbon film)

[0231] Next, the surface of the hard carbon film formed above was ground using the same method as for sample 1 to obtain a cutting tool. The thickness of the part of the hard carbon film involved in cutting after grinding is shown in the "Thickness (μm)" column of "Hard Carbon Film" in Table 2.

[0232] <Sample 5>

[0233] (Preparation of substrate)

[0234] The substrate was prepared using the same method as that used for sample 1.

[0235] (Formation of the interface layer)

[0236] Next, without introducing gas into the film-forming apparatus 1, the target composed of chromium (Cr) is evaporated and ionized by vacuum arc discharge (cathode current 80A), and a voltage of -800V is applied to the substrate holding member 4 using the bias power supply 9 to form an interface layer of chromium (Cr) with a thickness of 5nm on the substrate.

[0237] (Formation of hard carbon film)

[0238] Next, a hard carbon film is formed on the interface layer. The film formation conditions for the hard carbon film are shown in Table 1. The set temperature of the substrate heater 6 during the film formation process of the hard carbon film is set to 180°C.

[0239] (Grinding of hard carbon film)

[0240] Next, the surface of the hard carbon film formed above was ground using the same method as for sample 1 to obtain a cutting tool. The thickness of the part of the hard carbon film involved in cutting after grinding is shown in the "Thickness (μm)" column of "Hard Carbon Film" in Table 2.

[0241] <Sample 6>

[0242] (Preparation of substrate)

[0243] The substrate was prepared using the same method as that used for sample 1.

[0244] (Formation of the interface layer)

[0245] Next, while introducing hydrocarbon gas into the film-forming apparatus 1 at a flow rate of 15 cc / min, a triangular prism-shaped target made of titanium (Ti) is evaporated and ionized by vacuum arc discharge (cathode current 80A). A voltage of -100V is applied to the substrate holder 4 using a bias power supply 9, forming an interface layer with a thickness of 5 nm made of titanium carbide (TiC) on the substrate. Afterward, the hydrocarbon gas is discharged.

[0246] (Formation of hard carbon film)

[0247] Next, a hard carbon film is formed on the interface layer. The film formation conditions for the hard carbon film are shown in Table 1. The set temperature of the substrate heater 6 during the film formation process of the hard carbon film is set to 180°C.

[0248] (Grinding of hard carbon film)

[0249] Next, the surface of the hard carbon film formed above was ground using the same method as for sample 1 to obtain a cutting tool. The thickness of the part of the hard carbon film involved in cutting after grinding is shown in the "Thickness (μm)" column of "Hard Carbon Film" in Table 2.

[0250] <Sample 7>

[0251] (Preparation of substrate)

[0252] The substrate was prepared using the same method as that used for sample 1.

[0253] (Formation of the interface layer)

[0254] Next, without introducing gas into the film-forming apparatus 1, the target made of titanium (Ti) is evaporated and ionized by vacuum arc discharge (cathode current 80A). A voltage of -100V is applied to the substrate holder 4 using the bias power supply 9, and an interface layer with a thickness of 5nm made of titanium (Ti) is formed on the substrate.

[0255] (Formation of hard carbon film)

[0256] Next, a hard carbon film is formed on the interface layer. The film formation conditions for the hard carbon film are shown in Table 1. The set temperature of the substrate heater 6 during the film formation process of the hard carbon film is set to 180°C.

[0257] (Grinding of hard carbon film)

[0258] Next, the surface of the hard carbon film formed above was ground using the same method as for sample 1 to obtain a cutting tool. The thickness of the part of the hard carbon film involved in cutting after grinding is shown in the "Thickness (μm)" column of "Hard Carbon Film" in Table 2.

[0259] <<Sample 1-2>>

[0260] In Sample 1-2, a hard carbon film with a thickness of 0.5 μm was formed on the same substrate as in Sample 1-1 using plasma CVD with methane gas as the raw material, thereby fabricating a cutting tool.

[0261] Table 1

[0262]

[0263] [evaluate]

[0264] (Confirmation of composition and crystallinity)

[0265] The carbon content in the hard carbon film of each sample was determined. The specific determination method is described in Example 1, and therefore will not be repeated.

[0266] In all samples, the carbon content in the hard carbon film was above 95 atomic%. Therefore, it was confirmed that the hard carbon film in all samples contained carbon as the main component.

[0267] The crystallinity of the hard carbon film on each sample was measured. The specific measurement method is described in Example 1, and therefore will not be repeated.

[0268] In all samples, the hard carbon film was confirmed to be amorphous.

[0269] (Determination of {C2 / (C2+C3))}×100)

[0270] For the hard carbon film of each sample, the percentage of sp2 component C2 relative to the total of sp2 component C2 and sp3 component C3 in the first region ({C2 / (C2+C3)}×100) was measured. The specific measurement method is described in Embodiment 1, so it will not be repeated here. The results are shown in the column “{C2 / (C2+C3)}×100(%)” in Table 2.

[0271] (Determination of the percentage of the black area)

[0272] For the hard carbon film of each sample, the percentage of the black area was measured. The specific measurement method is described in Example 1, so it will not be repeated here. The results are shown in the "Percentage of Black Area (%)" column of Table 2.

[0273] (Determination of hydrogen content)

[0274] The hydrogen content of the hard carbon film for each sample was determined. The specific determination method is described in Example 1, and therefore will not be repeated. The results are shown in the "Hydrogen Content (atomic %)" column of Table 2.

[0275] (Hardness Measurement)

[0276] The hardness of the hard carbon film on each sample was measured. The specific measurement method is described in Example 1, and therefore will not be repeated. The results are shown in the "Hardness (GPa)" column of Table 2.

[0277] (Cutting test)

[0278] Using the cutting tools for each specimen, hole drilling was performed under the following cutting conditions. The following cutting conditions are equivalent to MQL machining of soft metals.

[0279] Material being cut: ADC12 (Al-Si-Cu alloy)

[0280] Cutting speed: 200 m / min

[0281] Feed rate: 0.20 mm / rev

[0282] Hole depth: 12mm (blind hole)

[0283] Cutting fluid: Water MQL (UNICUT-JINEN MW-A)

[0284] The number of machined holes was measured from the point of drill tip wear and aluminum alloy adhesion until the defect (greater than 500 μm). A higher number of machined holes indicates better wear resistance and longer tool life. The results are shown in the "Number of Machined Holes" column of the "Cutting Test" section in Table 2.

[0285] Table 2

[0286]

[0287] <Inspection>

[0288] The cutting tools of specimens 1 to 23 correspond to the examples. The cutting tools of specimens 1-1 to 1-3 correspond to the comparative examples.

[0289] It was confirmed that samples 1 to 23 (Examples) had more machined holes and longer tool life compared to samples 1-1 to 1-3 (Comparative Examples).

[0290] It is speculated that the {C2 / (C2+C3)}×100 of samples 1 to 23 (Examples) is less than 2.0, making it less prone to adhesion during the initial cutting stage. Therefore, it is less likely to cause abnormal damage due to adhesive wear, resulting in low cutting resistance and a long tool life. In this embodiment, it was confirmed that even in MQL machining of soft metals where adhesion during machining is prone to occur, the cutting tool of this embodiment has a long tool life. Therefore, it is speculated that the cutting tool of this embodiment will have the same long tool life even in dry machining of soft metals.

[0291] It is speculated that the {C2 / (C2+C3)}×100 of the samples 1-1 to 1-3 (comparative examples) is greater than 2.5, which makes them prone to adhesion in the early stage of cutting and resulting in short tool life.

[0292] The embodiments and examples of this disclosure have been described above, but it is also intended from the outset that the above-described embodiments and examples may be appropriately combined or modified.

[0293] The embodiments and examples disclosed herein should be considered exemplary in all respects, and not restrictive. The scope of the invention is defined not by the foregoing embodiments and examples, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

[0294] Explanation of reference numerals in the attached figures

[0295] 1: Film forming apparatus; 2, 3: Target; 4: Substrate holder; 5: Substrate; 6: Substrate heater; 7, 8: Power supply; 9: Film forming bias power supply; 10: Gas supply port; 11: Exhaust port; 20: Hard carbon film; 21: Interface layer; 22, 32: Coating; 30, 31: Cutting tool; a, b, c, d: Line segments; P: Imaginary surface; S1: Surface of hard carbon film; S2: Interface on the hard carbon film side of the substrate; B: Black area.

Claims

1. A cutting tool, wherein, The cutting tool has a substrate and a coating disposed on the substrate. The coating comprises a hard carbon film on its outermost surface. The hard carbon film includes a first region. The first region is the area sandwiched between the surface of the hard carbon film and an imaginary surface P located 40 nm away from the surface toward the substrate. The hydrogen content of the hard carbon film is less than 5 atomic percent. In the first region, the sp2 component C2 and the sp3 component C3 exhibit the relationship shown in Equation 1 below. {C2 / (C2+C3)}×100≤2.0 Equation 1.

2. The cutting tool according to claim 1, wherein, In the first region, the sp2 component C2 and the sp3 component C3 exhibit the relationship shown in Equation 2 below. 0.5≤{C2 / (C2+C3)}×100≤2.0 Equation 2.

3. The cutting tool according to claim 1 or 2, wherein, In the hard carbon film, the area percentage of black regions with an equivalent circle diameter of 10 nm or more is less than 0.7%. The percentage of the black area was determined in a high-angle scattering annular dark-field scanning transmission electron microscope image of the profile of the hard carbon film.

4. The cutting tool according to claim 1 or 2, wherein, The thickness of the portion of the hard carbon film involved in cutting is greater than 0.1 μm and less than 3.0 μm.

5. The cutting tool according to claim 1 or 2, wherein, The hydrogen content of the hard carbon film is less than 4 atomic%.

6. The cutting tool according to claim 1 or 2, wherein, The cutting tool has an interface layer disposed between the substrate and the hard carbon film. The interface layer comprises at least one element selected from the group consisting of an elemental substance, an alloy or a first compound, and a solid solution derived from the first compound. The elemental substance is one element selected from the first group consisting of Group 4, Group 5, Group 6, Group 13 elements, and Group 14 elements excluding carbon. The alloy or the first compound comprises at least one element selected from the first group. The interface layer comprises one or both of a second compound and a solid solution derived from the second compound, wherein the second compound is composed of at least one element selected from the first group and carbon. The thickness of the interface layer is greater than 0.5 nm and less than 10 nm.

7. The cutting tool according to claim 1 or 2, wherein, The substrate is made of WC-based cemented carbide or cermet.

8. The cutting tool according to claim 1 or 2, wherein, The substrate is composed of cubic boron nitride.

9. The cutting tool according to claim 1, wherein, In the first region, the percentage of sp2 component C2 relative to the total of sp2 component C2 and sp3 component C3, {C2 / (C2+C3)}×100, is 0.4 or more.

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