Coated cutting tool

Abstract

In the coated cutting tool, the surface of a base material is coated with a hard coating film. The hard coating film includes an A layer having a face-centered cubic lattice structure and a B layer having a face-centered cubic lattice structure, the A layer being disposed on the surface of the base material, the A layer containing at most W among metal elements including semimetals and then at most Ti, the total content ratio of W and Ti being 70 at% or more, the non-metal elements containing at most carbon, and the B layer containing at most Ti among metal elements including semimetals. The first layer has a high nitrogen content, the second layer has a high nitrogen content, the ratio NA / CA of the nitrogen content NA to the carbon content CA is 0.40 or more when the total content ratio of carbon, nitrogen, and oxygen is taken as 100 at%, the film thickness of the A layer is 1-20 nm, and the B layer is arranged on the A layer and is composed of a nitride or carbonitride.

Description

Technical Field

[0001] This invention relates to encased cutting tools such as end mills.

[0002] This application claims priority based on Japanese Patent Application No. 2023-120108, filed on July 24, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] AlCrSi nitrides or carbonitrides are a type of film with excellent heat resistance and wear resistance, suitable for coating cutting tools. As a tool applicable to milling high-hardness steel, the inventors have proposed the following coated cutting tool (Patent Document 1): This coated cutting tool has an intermediate film containing W and Ti with a face-centered cubic lattice structure formed directly above the substrate by bombardment with Ti, and an AlCrSi nitride or carbonitride is disposed directly above it to increase the Si content and refine the film structure.

[0004] Patent Document 1: International Publication No. 2021 / 131232

[0005] The coated cutting tool described in Patent Document 1 exhibits excellent durability in the machining of high-hardness steel. On the other hand, the inventors have confirmed that the intermediate film formed using Ti bombardment has room for improvement in terms of adhesion. Summary of the Invention

[0006] According to one aspect of the present invention, a coated cutting tool is provided, wherein the surface of a substrate is coated with a hard film, the hard film comprising a face-centered cubic (FCC) lattice layer A and a face-centered cubic (FCC) lattice layer B, the A layer being disposed on the surface of the substrate, wherein W is the most abundant metallic element, including half-metals, followed by Ti, and the combined content ratio of W and Ti is 70 atomic% or more; and carbon is the most abundant non-metallic element, followed by nitrogen, wherein when the combined content ratio of metallic elements, including half-metals, and carbon, nitrogen, and oxygen is set to 100 atomic%, the nitrogen content ratio N is [missing information]. A The ratio of carbon to C A The ratio of N A / C A The thickness of layer A is greater than or equal to 0.40, the thickness of layer A is greater than or equal to 1 nm and less than 20 nm, and layer B is disposed on layer A and is composed of nitride or carbonitride.

[0007] Preferably, in layer A, when the total content ratio of metallic elements, including half-metals, and carbon, nitrogen, and oxygen is set to 100 atomic%, the nitrogen content ratio N A The total content ratio M of metallic elements, including half-metals A The ratio of N A / MA It is above 0.6.

[0008] The B layer can be a nitride or carbonitride containing Al, Cr, and Si, in which the content of Al is 50 atomic% to 65 atomic% or more, the content of Cr is 20 atomic% to 40 atomic% or more, the combined content of Al and Cr is 85 atomic% to 96 atomic% or more, and the content of Si is 4 atomic% to 15 atomic% or more. In this case, in the B layer, when the total content of metal elements and non-metal elements is set to 100%, the atomic ratio M of the metal elements, including the half-metal, is... B The atomic ratio of nitrogen (N) B Satisfying 1.07 < N B / ME B The relationship is <1.30.

[0009] A C layer may be further provided on the B layer, the C layer being composed of nitrides or carbonitrides of metallic elements, including half-metals.

[0010] The C layer can be a nitride or carbonitride in which the content of Ti in the metal elements, including half-metals, is more than 60 atomic% and less than 95 atomic% and the content of Si is more than 5 atomic% and less than 40 atomic%

[0011] According to one aspect of the present invention, a coated cutting tool with excellent durability is provided. Attached Figure Description

[0012] Figure 1 This is a transmission electron microscope image of the tool tip from Example 1. Point "1" in the image represents the substrate, point "2" represents layer A, and point "3" represents layer B. Detailed Implementation

[0013] The inventors have confirmed that by setting the nitrogen content of the intermediate film formed by Ti bombardment to a certain level or above, the adhesion between the substrate and the hard film is improved, thereby increasing the durability of the coated cutting tool. Hereinafter, embodiments of the present invention will be described in detail.

[0014] The coated cutting tool of this embodiment includes a substrate, an A layer disposed on the surface of the substrate, and a B layer disposed on the A layer. In the coated cutting tool of this embodiment, the B layer is a hard coating that imparts durability to the tool. The A layer is an intermediate coating that improves the adhesion between the B layer and the substrate.

[0015] As the base material, WC-based cemented carbide base materials used in cutting tools can be used. The base material can be an integral tool with the tool head and tool holder as one piece, the tool head of an interchangeable-head tool, or a cutting insert mounted on a tool holder.

[0016] First, layer A, which serves as the intermediate membrane in this embodiment, will be described.

[0017] Layer A is a Ti-bombarded layer with a face-centered cubic (fcc) lattice structure disposed between the substrate and layer B, which is composed of a nitride or carbonitride structure (described later). By setting layer A on the surface of the substrate to a face-centered cubic lattice structure (fcc structure), layer B located on layer A easily maintains a face-centered cubic lattice structure (fcc structure), thereby improving the crystal continuity of the substrate, layer A, and layer B and enhancing adhesion. Furthermore, it can be considered that the crystallinity of layer B near its boundary with layer A is further enhanced, thereby further improving the adhesion between the substrate and layer B.

[0018] Layer A is a Ti-bombarded layer disposed on the surface of the substrate. Among the metallic elements (hereinafter referred to as metallic elements), including half-metals, W is the most abundant, followed by Ti, with a combined W and Ti content of 70 atomic percent or more (hereinafter simply referred to as "%)". Regarding layer A, by ensuring a combined W and Ti content of 70% or more among the metallic elements, the crystal structure is stabilized. Preferably, the combined W and Ti content of layer A is 75% or more.

[0019] Among the non-metallic elements in layer A, carbon is the most abundant, followed by nitrogen. Layer A may include oxygen and argon as non-metallic elements other than carbon and nitrogen. In layer A, when the combined content ratio of metallic elements, carbon, nitrogen, and oxygen is set to 100%, the nitrogen content ratio N is... A The ratio of carbon to C A The ratio of N A / C A The nitrogen content is 0.40 or higher. By containing nitrogen in layer A at a certain ratio relative to carbon, the adhesion between layer A and layer B is improved, thereby enhancing the durability of the coated cutting tool. In other words, the coated cutting tool of this embodiment improves the adhesion between layer B and the substrate by forming layer A between the substrate and layer B, which has a face-centered cubic lattice structure (fcc structure) dominated by W and Ti and has an increased nitrogen content. A / C A Preferably, it is 0.45 or higher. Furthermore, to stabilize the crystal structure of layer A, N... A / C A Preferably, it is below 0.7. Further, N A / C A Preferably, it is below 0.6.

[0020] Preferably, in layer A, when the total content ratio of metal elements, carbon, nitrogen, and oxygen is set to 100%, the nitrogen content ratio N A The total content ratio M of metal elements A The ratio of N A / M A The value is 0.6 or higher. Preferably, layer A contains nitrogen in a certain proportion relative to the metal element, thereby improving the adhesion between layer A and layer B. N A / M A Preferably, it is 0.7 or higher. To ensure the stability of the crystal structure of layer A, N... A / M A Preferably, N is below 1.0. Furthermore, N... A / M A Preferably, it is below 0.9.

[0021] In addition to W and Ti, the A layer may also contain hard coating components and substrate components. However, to stabilize the composition and crystal structure of the A layer, it is preferable that the combined content of Al and Si in the metal elements of the A layer is 15% or less. By reducing the amount of Al and Si included in the A layer, the composition and crystal structure of the A layer are more easily stabilized. It is preferable that the combined content of Al and Si in the metal elements of the A layer is 10% or less.

[0022] In layer A, Co and Cr, which are included in the binding phase of the substrate, are readily present. Even when layer A contains Co and Cr, it is preferable that the total content of Co and Cr in the metallic elements is 15% or less. Preferably, the total content of Co and Cr in the metallic elements of layer A is 10% or less.

[0023] The thickness, composition, and crystal structure of layer A can be confirmed through cross-sectional observation, compositional analysis, and nanobeam diffraction patterns based on transmission electron microscopy.

[0024] If the thickness of layer A is too thin, the adhesion to the substrate will decrease. Furthermore, even if the thickness of layer A is too thick, there is a tendency for the adhesion to the substrate to decrease. Therefore, the thickness of layer A is 1 nm or more and 20 nm or less. Preferably, the thickness of layer A is 2 nm or more and 15 nm or less.

[0025] Next, layer B, which is the rigid film of the present invention, will be described.

[0026] Layer B is a hard film with a face-centered cubic lattice structure composed of nitrides or carbonitrides, disposed on layer A. Hard films with a face-centered cubic lattice structure composed of nitrides or carbonitrides are widely used for coating cutting tools with excellent wear resistance and heat resistance. Nitrides or carbonitrides mainly composed of Al, Cr, and Ti are suitable for coating cutting tools, and layer B preferably contains at least 80% of one or more of Al, Cr, and Ti nitrides or carbonitrides. Nitrides with excellent heat resistance are more preferred materials for layer B. Layer B can be a single layer or a laminated film with multiple layers having different compositions.

[0027] In the coated cutting tool of this embodiment, it is important that layer B has a face-centered cubic (fcc) lattice structure. In this embodiment, a face-centered cubic (fcc) lattice structure refers to a structure whose diffraction intensity exhibits maximum intensity in X-ray diffraction. Since a hard film exhibiting maximum diffraction intensity due to a hexagonal close-packed (hcp) structure is fragile, it lacks durability as a coated cutting tool. In particular, there is a tendency for durability to decrease during wet machining.

[0028] Regarding layer B, it is preferable that no diffraction intensity caused by the hexagonal close-packed structure (hcp structure) is detected in X-ray diffraction. However, if the diffraction intensity caused by the face-centered cubic lattice structure (fcc structure) shows the maximum intensity, then layer B may partially contain the hexagonal close-packed structure (hcp structure) and an amorphous phase.

[0029] When the area of ​​the membrane being examined is small, or when other membranes (described later) are covering layer B, it is sometimes difficult to determine the face-centered cubic (fcc) lattice structure using the aforementioned X-ray diffraction. Even in such cases, the crystal structure can be determined using limited-field diffraction by transmission electron microscopy (TEM). Preferably, layer B does not have peaks predominantly hexagonal in the intensity distribution obtained from the limited-field diffraction pattern.

[0030] Layer B is preferably a film type with excellent heat resistance and wear resistance, namely AlCrSi nitride or carbonitride. Among them, AlCrSi nitride or carbonitride films with a high Si content have a fine film structure, and the adhesion can be easily improved by setting a Ti bombardment layer. Therefore, layer B is preferably a nitride or carbonitride containing Al, Cr, and Si, with an Al content of 50% to 65% or less, a Cr content of 20% to 40% or less, a combined Al and Cr content of 85% to 96% or less, and a Si content of 4% to 15%.

[0031] When the B layer is a Si nitride or carbonitride containing a high proportion of AlCrSi, it is preferable that, when the total of the metal and non-metal elements in the B layer is set to 100%, the atomic ratio M of the metal elements, including half-metals, is [missing information]. B The atomic ratio of nitrogen (N) B Satisfying 1.07 < N B / M B The relationship is <1.30. By applying the A layer involved in this invention to the B layer, which has a high nitrogen content, it is easy to obtain an effect that improves the adhesion.

[0032] The composition of layer B can be determined using an electron probe microanalysis (EPMA) device on a mirror-finished hard film. In this case, for example, five points can be analyzed within an analytical range of approximately 1 μm in diameter after mirror finishing of the hard film surface, and the composition can be determined based on the average of the three points excluding the maximum and minimum values.

[0033] If the B layer is too thin, its excellent durability may not be fully realized. Conversely, if the film is too thick, film peeling may occur. Regarding the thickness of the B layer, an appropriate value can be selected from, for example, a range of 0.5 μm or more and 10 μm or less. A thickness of 1 μm or more is more preferred. Furthermore, a thickness of 5 μm or less is more preferable.

[0034] In this embodiment, the effects of this embodiment can be achieved even if other layers are further coated on layer B. Therefore, regarding the film structure composed of layers A and B in this embodiment, in addition to using layer B as the outermost surface of the tool, a structure covered with other layers can also be adopted. Moreover, in this case, it is preferable to coat layer B with a layer C composed of nitride or carbonitride, which serves as a protective film and has excellent heat resistance and wear resistance. Layer C is more preferably a layer composed of nitride. Layer C is preferably a hard film with excellent thermal shock resistance and residual compressive stress. The composition of layer C can be appropriately selected according to the workpiece or processing conditions. In particular, since hard films are easily peeled off due to heating and cooling cycles during wet processing, it is preferable to provide a hard film with high residual compressive stress as a protective film.

[0035] As the C layer, especially from the viewpoint of film types with high residual compressive stress, nitrides or carbonitrides with a Ti content of 60% or more and 95% or less and a Si content of 5% or more and 40% or less are preferred.

[0036] To form the A layer of this embodiment on the substrate, the substrate is bombarded with Ti. The film-forming apparatus for Ti bombardment preferably has a cathode with a magnetic field structure, in which a coil magnet is provided around the outer periphery of the target to confine the arc spot inside the target. By using such a cathode and bombarding with Ti, an element that readily forms carbides, oxides on the substrate surface are removed, thereby achieving cleaning. Furthermore, in addition to this cleaning, the bombarded Ti ions diffuse into the WC on the substrate surface, facilitating the formation of a layer comprising W and Ti.

[0037] In this embodiment, by forming an A layer comprising W and Ti on the cutting tip, which is a functional part, the adhesion between the substrate on the cutting tip and the hard coating is improved, thereby enhancing the durability of the coated cutting tool.

[0038] When the absolute value of the bias voltage applied to the substrate during Ti bombardment is small, and the current flowing to the target is low, it is difficult to form a layer including W and Ti on the substrate surface. Therefore, the bias voltage applied to the substrate is preferably -1000V or higher and -700V or lower. Furthermore, the current flowing to the target is preferably 80A or higher and 150A or lower. The furnace temperature is preferably 400°C or higher and 800°C or lower. Ti bombardment is preferably carried out by introducing nitrogen gas into the vacuum chamber at a rate of 5 to 50 sccm.

[0039] Furthermore, according to the inventors' research, it has been confirmed that the thickness of the A layer formed at the tool tip is affected by shape differences such as tool diameter and tip shape.

[0040] Example

[0041] <Substrate>

[0042] 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.

[0043] <Manufacturing Method>

[0044] The film formation device uses an arc ion plating method. The device includes multiple cathodes (arc evaporation sources), a vacuum container, and a substrate rotation mechanism.

[0045] The cathode comprises: one cathode (hereinafter referred to as "C1") equipped with a coil magnet on the outer periphery of the target; and two cathodes (hereinafter referred to as "C2" and "C3") equipped with permanent magnets on the back and outer periphery of the target and disposed in front of the target to generate a magnetic field for propelling the plasma forward. The distance from the target surface to the substrate is 400 mm.

[0046] The interior of the vacuum chamber is evacuated by a vacuum pump, and gas is introduced through the supply port. A bias power supply is connected to the substrate disposed within the vacuum chamber, and a negative bias voltage is independently applied to the substrate.

[0047] The substrate rotation mechanism is equipped with a workbench, a plate-shaped fixture on the workbench, and a tubular fixture on the plate-shaped fixture. The workbench rotates at a speed of 3 revolutions per minute, and the plate-shaped fixture and the tubular fixture rotate independently about their own axes. A metal Ti target is provided at C1, an AlCrSi alloy target is provided at C2, and a TiSi alloy target is provided at C3.

[0048] <Heating and Vacuum Exhaust Process>

[0049] The substrate is fixed to the tubular fixture within the vacuum chamber, and the pre-film formation process is carried out as follows. First, the interior of the vacuum chamber is evacuated to 5×10 -3 Pa or less. Then, it is heated to a substrate temperature of 500 °C by a heater provided within the vacuum chamber, and vacuum exhaust is carried out. Thus, the substrate temperature is set to 500 °C and the pressure within the vacuum chamber is set to 5×10 - 3 Pa or less.

[0050] <Ar Bombardment Process>

[0051] Then, Ar gas is introduced into the vacuum chamber, and the internal pressure of the chamber is set to 0.50 Pa. Then, a current of 30 A is supplied to the filament electrode, and a negative bias voltage of -150 V is applied to the substrate, and Ar bombardment is carried out for 60 minutes.

[0052] <Ti Bombardment Process>

[0053] Then, nitrogen gas is introduced into the vacuum chamber at 30 sccm, and the internal pressure of the chamber is set to 0.3 Pa. Then, a current of 90 A is supplied to the metal Ti target, and a negative bias voltage of -800 V is applied to the substrate, and Ti bombardment is carried out for 15 minutes.

[0054] <Film Formation Process>

[0055] After Ti bombardment, nitrogen gas is introduced into the vacuum chamber, and the pressure within the vacuum chamber is set to 4 Pa. A current of 100 A is supplied to the Al60Cr30Si10 target (the values are atomic ratios. The same applies hereinafter), a current of 5 A is supplied to the magnetic field generating coil, and a negative bias voltage of -150 V is applied to the substrate to coat a hard film of nitride with a thickness of about 2 μm. Next, a current of 150 A is supplied to the Ti75Si25 target, a current of 5 A is supplied to the magnetic field generating coil, and a negative bias voltage of -50 V is applied to the substrate to coat an upper layer of nitride with a thickness of about 1 μm.

[0056] In the existing coating example, Ar gas is introduced into a vacuum container at 30 sccm during Ti bombardment, and the pressure inside the container is set to 0.3 Pa. Then, a current of 90 A is supplied to the Ti target, and a bias voltage of -800 V is applied to the substrate, and Ti bombardment is carried out for 15 minutes. The film formation conditions of the hard film are the same as those in this embodiment.

[0057] To confirm the film structure of layer A, a cross-sectional observation of the tip of the ball end mill was performed using a field emission transmission electron microscope (JEM-2010F, manufactured by NEC Corporation). The sample was cut and bonded to a dummy substrate with epoxy resin. Then, cutting, bonding of a Mo reinforcing ring, grinding, indentation, and Ar ion milling were performed to prepare the sample for measurement. Carbon vapor deposition was performed prior to measurement. Observation, compositional analysis, and nanobeam diffraction were performed at an accelerating voltage of 200 kV.

[0058] The composition of layer A was determined by energy-dispersive X-ray spectroscopy (EDS). For nanobeam diffraction, the area near the center of the film thickness was analyzed under conditions of a camera length of 50 cm and a beam diameter of approximately 0.2 nm. The analytical results are shown in Table 1.

[0059] [Table 1]

[0060]

[0061] The composition of layer B was determined using wavelength dispersive electron probe microanalysis (WDS-EPMA) on an electron probe microanalysis system (JXA-8500F, NEC Corporation). For the mirror-finished sample, the accelerating voltage was set to 10 kV and the irradiation current to 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.

[0062] The average composition of layer B is (Al56Cr33Si11)N, N B / M B The value is 1.20. Furthermore, the intensity distribution derived from the confined field-of-view diffraction pattern confirmed the absence of peaks dominated by hexagonal crystals.

[0063] (Conditions) Dry processing

[0064] Tools: Double-edged carbide ball end mill

[0065] Model: EPDBE2010-6, Ball head radius 0.5mm

[0066] Cutting method: Bottom surface cutting

[0067] Workpiece: STAVAX (52HRC) (manufactured by Böhler Uthem Co., Ltd.)

[0068] Depth of cut: 0.04 mm axially, 0.04 mm radially

[0069] Cutting speed: 75.4 m / min

[0070] Single-edge feed rate: 0.0179mm / edge

[0071] Cutting distance: 15m

[0072] 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.

[0073] [Table 2]

[0074]

[0075] In Example 1, layer A has a high nitrogen content and superior adhesion. In the above examples, layer B uses AlCrSi nitride with a high Si content, which has a fine membrane structure and tends to lack adhesion. However, even if layer B has other compositions, it can still improve adhesion.

Claims

1. A coated cutting tool, a surface of a substrate being coated with a hard coating film, characterized in that, the hard coating film includes an A layer of a face-centered cubic lattice structure and a B layer of a face-centered cubic lattice structure, Layer A is disposed on the surface of the substrate. Among the metallic elements, including half-metals, W is the most abundant, followed by Ti, with a combined W and Ti content of over 70 atomic percent. Among the non-metallic elements, carbon is the most abundant, followed by nitrogen. When the combined content of metallic elements, including half-metals, and carbon, nitrogen, and oxygen is set to 100 atomic percent, the nitrogen content is N. A The ratio of carbon to C A The ratio of N A / C A The value is 0.40 or higher, and the thickness of layer A is 1 nm or more and 20 nm or less. the B layer is disposed on the A layer and is composed of a nitride or a carbonitride.

2. The coated cutting tool according to claim 1, characterized in that, In the A layer, when the total content ratio of metal elements including semi-metals and carbon, nitrogen and oxygen is set to 100 atom%, the content ratio of nitrogen N A to the total content ratio M of metal elements including semi-metals A is 0.6 or more. A N A / M 3. The coated cutting tool according to claim 1 or 2, characterized in that, the B layer is a nitride or a carbonitride containing Al at a ratio of 50 atomic % or more and 65 atomic % or less, Cr at a ratio of 20 atomic % or more and 40 atomic % or less, and Al and Cr at a total ratio of 85 atomic % or more and 96 atomic % or less, and Si at a ratio of 4 atomic % or more and 15 atomic % or less, among metal elements including semi-metals.

4. The coated cutting tool according to claim 3, wherein, In the B layer, the atomic ratio M of metal elements including semimetals, when the total of the metal elements and nonmetal elements is taken as 100% B and the atomic ratio N of nitrogen B satisfies the relationship 1.07 < N B / M B < 1.

30.

5. The coated cutting tool according to claim 1, wherein, a C layer further has on the B layer, the C layer being composed of a nitride or a carbonitride of metal elements including semi-metals.

6. The coated cutting tool according to claim 5, wherein, the C layer is composed of a nitride or a carbonitride containing Ti at a ratio of 60 atomic % or more and 95 atomic % or less, and Si at a ratio of 5 atomic % or more and 40 atomic % or less, among metal elements including semi-metals.

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