Coated cutting tool

Abstract

A coated cutting tool has a base material and a hard coating film on the base material. The hard coating film is a nitride or carbonitride, and the nitride or carbonitride contains titanium (Ti) in an amount of 60-95 at% and silicon (Si) in an amount of 5-40 at% with respect to the total amount of the metal including the semimetal. The hard coating film satisfies the relationship 1.1 < B / A, where A represents the atomic ratio (at%) of the metal elements including the semimetal and B represents the atomic ratio (at%) of nitrogen, when the total of the metal elements including the semimetal and the non-metal elements is 100 at%. The crystal structure of the hard coating film is a cubic crystal, and the half-peak width of the (200) plane of the cubic crystal in X-ray diffraction is from 0.75 DEG to 1.10 DEG (inclusive).

Description

TECHNICAL FIELD

[0001] The present application relates to a coated cutting tool.

[0002] This application is based on patent application No. 2023-103054 filed in Japan on June 23, 2023, and the content thereof is hereby incorporated by reference. BACKGROUND

[0003] TiSi nitride is a film type excellent in wear resistance, and is suitable for a coated cutting tool (see, for example, Patent Documents 1 and 2).

[0004] Patent Document 1: Japanese Patent Publication No. 2000-334606

[0005] Patent Document 2: International Publication No. 2014 / 156699

[0006] As a result of the present inventor's research, it was confirmed that the durability of TiSi nitride coated using a conventional arc ion plating method still has room for improvement. SUMMARY

[0007] One aspect of the present application is a coated cutting tool having a substrate and a hard coating film on the substrate, the hard coating film being a nitride or a carbonitride, containing 60 atomic % or more and 95 atomic % or less of titanium (Ti), 5 atomic % or more and 40 atomic % or less of silicon (Si), with respect to the total amount of metals including a semimetal, and when the total of metal elements including a semimetal and nonmetal elements is taken as 100 atomic %, the atomic ratio (atomic %) A of the metal elements including a semimetal and the atomic ratio (atomic %) B of nitrogen satisfy the relationship of 1.1 < B / A, the crystal structure of the hard coating film is cubic crystal, and the half-value width of the (200) plane of the cubic crystal in X-ray diffraction is 0.75° or more and 1.10° or less.

[0008] It is preferable that, in the surface or cross-sectional observation of the hard coating film, the number of molten droplets (droplet) having a circular equivalent diameter of 3 μm or more be 5 or less within a range of 50 μm x 40 μm.

[0009] An intermediate coating film can be provided between the hard coating film and the substrate.

[0010] According to the present application, a coated cutting tool excellent in durability can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is an example of a surface observation photograph (x 2000) of the hard coating film involved in the present embodiment.

[0012] Figure 2This is one example of a surface observation photograph (×2000x) of the hard membrane involved in the existing examples. Detailed Implementation

[0013] The inventors discovered that by controlling the full width at half maximum (FWHM) of the (200) plane of a cubic crystal within a certain range using nitrogen-rich TiSi nitrides, excellent durability can be achieved, and thus the present invention was completed. The following is a detailed description of this embodiment.

[0014] The embodiments of the present invention will now be described in detail.

[0015] The coated cutting tool of this embodiment is a coated cutting tool having a hard film composed of TiSi nitrides or carbonitrides on the surface of the tool substrate.

[0016] The composition, structure, properties, and manufacturing method of the hard coating that constitutes the cutting tool of this embodiment are described in detail.

[0017] In the coated cutting tool of this embodiment, the substrate is not particularly limited, but WC-Co based cemented carbide with excellent strength and toughness is preferred as the substrate.

[0018] <Composition: Titanium (Ti), Silicon (Si)>

[0019] The hard coating involved in this embodiment is composed of nitride or carbonitride, wherein the nitride or carbonitride contains 60 atomic% or more and 95 atomic% or less titanium (Ti) and 5 atomic% or more and 40 atomic% or less silicon (Si) relative to the total amount of metal elements including half-metals.

[0020] TiSi nitrides or carbonitrides are types of films with excellent wear resistance. Regarding the hard film involved in this embodiment, titanium (Ti) is set to 60 atomic% or more and 95 atomic% or less to ensure wear resistance and heat resistance. Preferably, titanium (Ti) is 65 atomic% or more and 90 atomic% or less.

[0021] Regarding the rigid film involved in this embodiment, in order to ensure toughness while miniaturizing the structure, the silicon (Si) content is set to 5 atomic percent or more and 40 atomic percent or less. Preferably, the silicon (Si) content is 10 atomic percent or more and 35 atomic percent or less.

[0022] <Atomic ratio A of metallic elements and atomic ratio B of nitrogen>

[0023] Regarding the hard coating involved in this embodiment, when the total of the metallic elements including the half-metal and the non-metallic elements is set to 100 atomic percent, the atomic ratio A of the metallic elements including the half-metal and the atomic ratio B of nitrogen satisfy the relationship 1.1 < B / A. In addition to nitrogen, the non-metallic elements may also include carbon and oxygen. A B / A value greater than 1.1 indicates sufficient potential for forming a complete nitride at the microscopic level. B / A is preferably greater than 1.15. On the other hand, if the B / A value is too large, it can easily cause coating damage. Preferably, B / A < 1.3, more preferably B / A < 1.25. More preferably, B / A is 1.15.

[0024] The composition of the hard coating involved in this embodiment can be determined by measuring the mirror-finished hard coating using an electron probe microanalysis (EPMA) apparatus. In this case, for example, after mirror finishing of the hard coating surface, five points within an analytical range of approximately 1 μm in diameter can be analyzed and the composition determined based on their average value.

[0025] <Crystal Structure>

[0026] The hard coating involved in this embodiment has a cubic crystal structure. The half-width at half-maximum (WHM) of the X-ray diffraction peak of the (200) plane of the cubic crystal in the hard coating involved in this embodiment is 0.75° or more and 1.10° or less. For nitrogen-rich TiSi nitrides, nitrides with a WHM of 0.75° or more and 1.10° or less on the (200) plane of the cubic crystal tend to have excellent durability. The WHM of the (200) plane of the hard coating involved in this embodiment is preferably 0.8° or more. The WHM of the (200) plane of the hard coating involved in this embodiment is preferably 1.0° or less.

[0027] Within the scope of satisfying the above requirements, the hard coating according to this embodiment may contain one or more metallic elements and half-metallic elements selected from those other than Ti and Si. For example, to improve the wear resistance, heat resistance, lubricity, etc., of the hard coating, it may contain one or more elements selected from Groups 4a, 5a, and 6a of the periodic table, and B, Y, and Cu. These elements are commonly added to improve the properties of the hard coating, and if their content ratio is not excessive, they will not significantly reduce the durability of the coated cutting tool. When the hard coating according to this embodiment contains one or more metallic elements and half-metallic elements selected from those other than Ti and Si, the total content ratio is preferably 20 atomic% or less. The above-mentioned total content ratio is more preferably 10 atomic% or less.

[0028] ​Preferably, in the surface or cross-sectional observation of the hard film according to this embodiment, the number of molten droplets with a circular equivalent diameter of 3 μm or more is 5 or less within the range of 50 μm × 40 μm. More preferably, it is 2 or less. The molten droplets in this invention refer to the deposits on the hard film caused by molten particles of about 1 μm to tens of μm that fly out from the cathode during arc ion plating. Since fewer large molten droplets are contained in the hard film, the durability of the tool is improved. Further, preferably, in the surface or cross-sectional observation of the hard film according to this embodiment, the number of molten droplets with a circular equivalent diameter of 5 μm or more is 1 or less within the range of 50 μm × 40 μm. Since fewer larger molten droplets are present, the durability of the tool is improved.

[0029] Regarding the molten droplets of hard films, observation was performed using an electron microscope at a magnification of 2000x, observing more than 5 fields of view within a range of 50μm×40μm, and the average value was used to determine the result.

[0030] The thickness of the rigid film involved in this embodiment is preferably 0.3 μm or more and 5 μm or less.

[0031] The coating cutting tool of this embodiment can, as needed, have an intermediate film between the substrate and the hard film. For example, an AlTi-based or AlCr-based nitride or carbonitride can be used as the intermediate film. The intermediate film is preferably a nitride or carbonitride containing 40 atomic% or more and 70 atomic% or less Al, 30 atomic% or more and 60 atomic% or less Ti, and Cr. Multiple intermediate films can also be used. The intermediate film can also be a laminated film. Alternatively, a modified layer can be formed on the substrate surface by metal bombardment.

[0032] The coated cutting tool of this embodiment can have an upper layer formed on a hard film as needed. For example, an AlTi-based or AlCr-based nitride or carbonitride can be formed as the upper layer. Substances other than nitrides or carbonitrides can also be formed.

[0033] The hard film in this embodiment is a physical vapor deposition film. Preferably, the hard film involved in this embodiment is a hard film formed by arc ion plating, which also exhibits excellent adhesion among physical vapor deposition films. The coating cutting tool involved in this embodiment is preferably coated using a film-forming apparatus equipped with a cathode. A permanent magnet is provided on the back side and outer periphery of the target, and a magnetic field generating coil for generating a magnetic field to propel plasma forward is further provided in front of the target. Furthermore, the distance from the target surface to the substrate is preferably 250 mm or more. By increasing the distance from the target surface to the substrate, there is a tendency to reduce the number of large droplets reaching the substrate.

[0034] The coating temperature is preferably 450℃~550℃. The bias voltage of the negative voltage applied to the substrate is preferably -30~-90V. The furnace pressure is preferably 2~8Pa. The current supplied to the target is preferably 100~200A. The current supplied to the magnetic field generating coil is preferably 3~10A.

[0035] Example

[0036] <Substrate>

[0037] Regarding the substrate, a double-edged ball end mill made of cemented carbide with the composition of WC (balance)-Co (8% by mass)-Cr (0.5% by mass)-VC (0.3% by mass), an average WC particle size of 0.6 μm, and a hardness of 93.9 HRA was prepared.

[0038] <Manufacturing Method>

[0039] The film-forming apparatus uses an arc ion plating method. This apparatus includes multiple cathodes (arc evaporation sources), a vacuum container, and a substrate rotation mechanism.

[0040] The apparatus used in this embodiment and comparative example includes a cathode, on which permanent magnets are provided on the back side and outer periphery of the target. Furthermore, a magnetic field generating coil is provided in front of the target to generate a magnetic field for propelling plasma forward. Additionally, the cathode includes a filtering mechanism capable of reducing molten droplets through a magnetic field. The distance from the target surface to the substrate is 400 mm.

[0041] The interior of the vacuum container is vented by a vacuum pump, and gas is introduced through the supply port. A bias power supply is connected to the substrate placed inside the vacuum container, and a negative bias voltage is independently applied to the substrate.

[0042] The substrate rotation mechanism is equipped with a worktable, a plate-shaped clamp on the worktable, and a tubular clamp on the plate-shaped clamp. The worktable rotates at a speed of 3 revolutions per minute, and the plate-shaped clamp and the tubular clamp revolve on their own orbits.

[0043] <Heating and Vacuum Exhaust Process>

[0044] The substrates are fixed onto the tubular clamps inside the vacuum container, and the pre-film deposition process is performed as follows. First, the vacuum inside the vacuum container is evacuated to 5×10⁻⁶. -3 Below Pa. Then, the substrate temperature is heated to 500°C by a heater installed inside the vacuum container, and vacuum degassing is performed. Thus, the substrate temperature is set to 500°C, and the pressure inside the vacuum container is set to 5 × 10⁻⁶. -3 Below Pa.

[0045] <Ar bombardment process>

[0046] Then, Ar gas was introduced into the vacuum container, and the pressure inside the container was set to 0.50 Pa. Then, a current of 20 A was supplied to the filament electrode, and a negative bias voltage of -150 V was applied to the substrate to perform Ar bombardment for 60 minutes.

[0047] <Film Forming Process>

[0048] After Ar bombardment, the gas in the vacuum container is replaced with nitrogen, and the pressure inside the vacuum container is set to 4 Pa. A current of 100 A is supplied to the AlCr target, a power of 5 A is supplied to the magnetic field generating coil, a bias voltage of -150 V is applied to the substrate, and an intermediate film of approximately 2 μm of AlCr nitride is formed.

[0049] Next, a current of 150A is supplied to the TiSi target, a bias voltage of -50V is applied to the substrate, and the power and gas pressure supplied to the magnetic field generating coil are changed according to the sample to coat a hard film of Ti75Si25 (numerical ratio) nitride of about 1μm.

[0050] The apparatus used in the existing coating example includes a cathode, on which permanent magnets are disposed on the back side and outer periphery of a target. The distance from the target surface to the substrate is 170 mm. Regarding the film formation conditions, they are the same as those in the coating of Example 1 described above, except that no current is supplied to the coil generating the magnetic field.

[0051] Composition Analysis

[0052] The composition of the film was determined using wavelength dispersive electron probe microanalysis (WDS-EPMA) on an electron probe microanalysis system (JXA-8500F, Nippon Electronics Manufacturing Co., Ltd.). A ball end mill used for property evaluation was mirror-finished, with an accelerating voltage of 10 kV and an irradiation current of 5 × 10⁻⁶ kV. -8 A. The measurement time is 10 seconds. Five points are measured within an analysis area with a diameter of about 1 μm, and the average value is calculated.

[0053] The results were confirmed using an X-ray diffraction apparatus (EMPY REA, manufactured by Panalytical Co., Ltd.) under the following measurement conditions: tube voltage 45 kV, tube current 40 mA, X-ray source Cukα (λ = 0.15405 nm), and 2θ of 20–80 degrees.

[0054] (Conditions) Dry processing

[0055] Tools: Double-edged carbide ball end mill

[0056] Model: EPDBE2010-6, Ball head radius 0.5mm

[0057] Cutting method: Bottom surface cutting

[0058] Workpiece: STAVAX (52HRC) (manufactured by Böhler Uthem Co., Ltd.)

[0059] Depth of cut: 0.03mm axially, 0.03mm radially

[0060] Cutting speed: 67.8 m / min

[0061] Single-edge feed rate: 0.0135m / edge

[0062] Cutting distance: 5m

[0063] Evaluation method: After cutting, the tool is observed at 1000x magnification using a scanning electron microscope. The width of the friction between the tool and the workpiece on the tool's back face is measured, and the part with the largest friction width is the maximum wear width of the back face.

[0064] [Table 1]

[0065]

[0066] Compared with the comparative and existing examples, the maximum wear width is smaller in this embodiment. Regarding nitrogen-rich TiSi nitrides, nitrides with a full width at half maximum (FWHM) of the cubic (200) plane within a certain range exhibit excellent durability.

[0067] Figure 1 This is an example of a surface observation photograph of the covered cutting tool in this embodiment. Figure 2 This is an example of a surface observation photograph of a conventional coated cutting tool. It is confirmed that this embodiment has fewer large molten droplets compared to conventional examples. Depending on the tool shape and machining conditions, molten droplets have a significant impact on tool performance. The coated cutting tool of this embodiment is suitable for smaller diameter tools. By applying this embodiment to small-diameter tools that are greatly affected by molten droplets, further improvements in durability compared to conventional examples are expected.

Claims

1. A coated cutting tool having a substrate and a hard coating on the substrate, characterized in that, The hard coating is a nitride or carbonitride, wherein the nitride or carbonitride contains, relative to the total amount of metal including half-metals, 60 atomic% to 95 atomic% of titanium (Ti) and 5 atomic% to 40 atomic% of silicon (Si), and when the total amount of metal elements including half-metals and non-metal elements is set to 100 atomic%, the atomic ratio A of metal elements including half-metals and the atomic ratio B of nitrogen satisfy the relationship 1.1 < B / A. The crystal structure of the hard coating is cubic, and the full width at half maximum (FWHM) of the (200) plane of the cubic crystal in X-ray diffraction is 0.75° to 1.10° or more, wherein the unit of the atomic ratio is atoms.

2. The coated cutting tool according to claim 1, wherein, In observation of the surface or cross-section of the hard film, there are fewer than 5 droplets with a circular equivalent diameter of 3 μm or more within the range of 50 μm × 40 μm.

3. The coated cutting tool according to claim 1, characterized in that, An intermediate film is provided between the rigid film and the substrate.

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