Coated cutting tool

Abstract

Provided is a coated cutting tool in which the surface of a base material is coated with a hard coating film. The hard coating film includes an A layer which has a face-centered cubic lattice structure and is disposed on the surface of the base material, and a B layer which has a face-centered cubic lattice structure, is disposed on the A layer, and comprises a nitride or a carbonitride, wherein: among metal elements including metalloids, the A layer contains W most abundantly followed by Ti, the total content ratio of W and Ti being at least equal to 70 atomic%; among non-metal elements, the A layer contains carbon most abundantly followed by nitrogen; if the total content ratio of metal elements including metalloids, and carbon, nitrogen and oxygen is 100 atomic%, the ratio NA / CA of the nitrogen content ratio NA to the carbon content ratio CA is 0.40 or more; and the film thickness of the A layer is 1 to 20 nm inclusive.

Description

Coated Cutting Tools

[0001] The present invention relates to a coated cutting tool such as an end mill. This application claims priority to Japanese Patent Application No. 2023-120108, filed on July 24, 2023, the contents of which are incorporated herein by reference.

[0002] AlCrSi nitrides or carbonitrides are films with excellent heat resistance and wear resistance, and are used in coated cutting tools. The present inventors have proposed a coated cutting tool applicable to the milling of high-hardness steel, in which an intermediate film containing W and Ti with a face-centered cubic lattice structure is formed directly on a substrate by Ti bombardment, and an AlCrSi nitride or carbonitride film with a refined film structure due to an increased Si content is provided directly on the intermediate film (Patent Document 1).

[0003] International Publication No. 2021 / 131232

[0004] The coated cutting tool described in Patent Document 1 has excellent durability when cutting high-hardness steel. However, the present inventors have confirmed that there is room for improvement in the adhesion of the intermediate coating formed by Ti bombardment.

[0005] According to one aspect of the present invention, there is provided a coated cutting tool in which the surface of a substrate is coated with a hard coating, the hard coating being disposed on the surface of the substrate, the hard coating containing W in the largest amount among metal elements including semi-metals, followed by Ti in the second largest amount, the total content ratio of W and Ti being 70 atomic % or more, the hard coating containing carbon in the largest amount among non-metal elements, followed by nitrogen in the second largest amount, and the total content ratio of metal elements including semi-metals, carbon, nitrogen and oxygen being taken as 100 atomic %, the nitrogen content ratio N Ａ and carbon content ratio C Ａ Ratio to N Ａ / C Ａ and a layer A having a face-centered cubic lattice structure, with a refractive index of 0.40 or more and a film thickness of 1 nm to 20 nm, and a layer B having a face-centered cubic lattice structure and made of a nitride or a carbonitride, which is disposed on the layer A.

[0006] The A layer has a nitrogen content ratio N Ａ and the total content ratio M of metal elements including metalloidsＡ Ratio to N Ａ / M Ａ The B layer may be a nitride or carbonitride containing Al, Cr, and Si, in which the content ratio of Al among the metal elements including semi-metals is 50 atomic % or more and 65 atomic % or less, the content ratio of Cr is 20 atomic % or more and 40 atomic % or less, the total content ratio of Al and Cr is 85 atomic % or more and 96 atomic % or less, and the content ratio of Si is 4 atomic % or more and 15 atomic % or less. In this case, the B layer may be a nitride or carbonitride containing Al, Cr, and Si, in which the atomic ratio M of the metal elements including semi-metals when the total of the metal elements and non-metal elements is 100%. Ｂ and the atomic ratio of nitrogen N Ｂ and 1.07<N Ｂ / ME Ｂ <1.30. A C layer made of a nitride or carbonitride of a metal element including a metalloid may be further provided on the B layer. The C layer may be a nitride or carbonitride in which the content of Ti among the metal elements including a metalloid is 60 atomic % or more and 95 atomic % or less, and the content of Si is 5 atomic % or more and 40 atomic % or less.

[0007] According to one aspect of the present invention, a coated cutting tool having excellent durability is provided.

[0008] 1 is a transmission electron microscope photograph of the cutting edge of the tool of Example 1. In the figure, the point indicated by 1 is the substrate, the point indicated by 2 is layer A, and the point indicated by 3 is layer B.

[0009] The present inventors have confirmed that when the nitrogen content of the intermediate coating formed by Ti bombardment is set to a certain level or more, the adhesion between the substrate and the hard coating improves, and the durability of the coated cutting tool tends to increase.

[0010] The coated cutting tool of this embodiment includes a substrate, a layer A disposed on the surface of the substrate, and a layer B disposed on the layer A. In the coated cutting tool of this embodiment, the layer B is a hard coating that imparts durability to the tool. The layer A is an intermediate coating that improves adhesion between the layer B and the substrate. A WC-based cemented carbide substrate for cutting tools is used as the substrate. The substrate may be a solid tool in which the head and shank are integrated, the head of a tool with an exchangeable head, or a cutting insert attached to a holder.

[0011] First, the A layer, which is the intermediate coating of this embodiment, will be described. The A layer is a Ti bombarded layer with a face-centered cubic lattice structure provided between the substrate and the B layer, which has a face-centered cubic lattice structure and is made of a nitride or carbonitride, as described below. By making the A layer disposed on the surface of the substrate have a face-centered cubic lattice structure (fcc structure), the B layer above the A layer is more likely to maintain its face-centered cubic lattice structure (fcc structure), resulting in continuous crystals between the substrate, the A layer, and the B layer, improving adhesion. It is also believed that the crystallinity of the B layer near the boundary with the A layer is enhanced, further improving adhesion between the substrate and the B layer. The A layer is a Ti bombarded layer disposed on the surface of the substrate. Among metal elements (hereinafter referred to as metal elements), including semimetals, the A layer contains W most abundantly, followed by Ti, with the total content of W and Ti being 70 atomic % or more (hereinafter simply referred to as %). The A layer's crystal structure is stabilized by having a total content of W and Ti of 70% or more among the metal elements. In the A layer, the total content ratio of W and Ti is preferably 75% or more.

[0012] Layer A contains carbon in the largest amount among non-metallic elements, followed by nitrogen. Layer A may contain oxygen and argon as non-metallic elements other than carbon and nitrogen. When the total content ratio of metal elements, carbon, nitrogen, and oxygen in layer A is 100%, the nitrogen content ratio N Ａ and carbon content ratio C Ａ Ratio to N Ａ / C Ａis 0.40 or more. When Layer A contains nitrogen at a certain ratio or more relative to carbon, adhesion to Layer B is enhanced, and the durability of the coated cutting tool is improved. In other words, the coated cutting tool of this embodiment improves 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) mainly composed of W and Ti and has an increased nitrogen content. N Ａ / C Ａ is preferably 0.45 or more. In addition, in order to stabilize the crystal structure of the A layer, N Ａ / C Ａ is preferably 0.7 or less. Ａ / C Ａ is preferably 0.6 or less.

[0013] The A layer has a nitrogen content ratio N when the total content ratio of metal elements, carbon, nitrogen and oxygen is 100%. Ａ and the total content ratio of metal elements M Ａ Ratio to N Ａ / M Ａ It is preferable that the ratio of nitrogen to metal elements in the A layer is at least 0.6. The A layer preferably contains nitrogen at a certain ratio or more relative to the metal elements, because this increases the adhesion to the B layer. Ａ / M Ａ is preferably 0.7 or more. In order to stabilize the crystal structure of the A layer, N Ａ / M Ａ is preferably 1.0 or less. Ａ / M Ａ is preferably 0.9 or less.

[0014] The A layer may contain hard coating components and substrate components in addition to W and Ti. However, to stabilize the composition and crystalline structure of the A layer, the total content ratio of Al and Si among the metal elements in the A layer is preferably 15% or less. Reducing the Al and Si content in the A layer makes the composition and crystalline structure of the A layer more stable. The A layer is preferably a metal element having a total content ratio of Al and Si of 10% or less. The A layer is likely to contain Co and Cr contained in the binder phase of the substrate. Even when the A layer contains Co and Cr, the total content ratio of Co and Cr among the metal elements is preferably 15% or less. The A layer is preferably a metal element having a total content ratio of Co and Cr of 10% or less. The A layer's film thickness, composition, and crystalline structure can be confirmed by cross-sectional observation using a transmission electron microscope, composition analysis, and nanobeam diffraction pattern.

[0015] If the thickness of the A layer is too thin, the adhesion to the substrate decreases. Also, if the thickness of the A layer is too large, the adhesion to the substrate tends to decrease. Therefore, the thickness of the A layer is set to 1 nm or more and 20 nm or less. The thickness of the A layer is preferably set to 2 nm or more and 15 nm or less.

[0016] Next, the hard coating layer B of the present invention will be described. The layer B is a hard coating having a face-centered cubic lattice structure made of a nitride or carbonitride and provided on the above-described layer A. Hard coatings having a face-centered cubic lattice structure made of nitrides or carbonitrides have excellent wear resistance and heat resistance and are widely used in coated cutting tools. Among these, nitrides or carbonitrides mainly composed of Al, Cr, and Ti are used in coated cutting tools, and nitrides or carbonitrides containing at least 80% of Al, Cr, and Ti in total are preferred for the layer B. A nitride, which has excellent heat resistance, is more preferred for the layer B. The layer B may be a single-layer film or a laminated film consisting of multiple layers with different compositions. In the coated cutting tool of this embodiment, it is important that the layer B has a face-centered cubic lattice structure (fcc structure). In this embodiment, the face-centered cubic lattice structure (fcc structure) refers to a film in which the diffraction intensity due to the face-centered cubic lattice structure (fcc structure) exhibits maximum intensity in X-ray diffraction. The hard coating that the diffraction intensity that is caused by hexagonal close-packed structure (hcp structure) shows maximum intensity is fragile, so that it has poor durability as a coated cutting tool.In particular, in wet processing, durability tends to decrease.Preferably, the diffraction intensity that is caused by hexagonal close-packed structure (hcp structure) is not confirmed in X-ray diffraction for B layer.But, if the diffraction intensity that is caused by face-centered cubic lattice structure (fcc structure) shows maximum intensity, B layer can partially contain hexagonal close-packed structure (hcp structure) and amorphous phase.

[0017] When the test area of ​​the coating is small or when another coating described later is coated on the B layer, it may be difficult to identify the face-centered cubic lattice structure (fcc structure) by the X-ray diffraction. Even in such cases, the crystal structure can be identified by selected area diffraction using a transmission electron microscope (TEM). It is preferable that the B layer does not have a peak mainly composed of hexagonal crystals in the intensity profile obtained from the selected area diffraction pattern.

[0018] The B layer is preferably an AlCrSi nitride or carbonitride, which is a film type with excellent heat resistance and wear resistance. Among these, AlCrSi nitrides or carbonitrides with a high Si content have a fine coating structure, and the provision of a Ti bombarded layer is likely to improve adhesion. Therefore, the B layer is preferably a nitride or carbonitride containing Al, Cr, and Si, in which the Al content of the metal elements is 50% to 65%, the Cr content is 20% to 40%, the total content of Al and Cr is 85% to 96%, and the Si content is 4% to 15%.

[0019] When the B layer is a nitride or carbonitride of AlCrSi with a high Si content, the atomic ratio M of metal elements including semimetals when the total of metal elements and nonmetal elements in the B layer is 100%. Ｂ and the atomic ratio of nitrogen N Ｂ and 1.07<N Ｂ / M Ｂ It is preferable that the relationship of <1.30 is satisfied. By applying the layer A according to the present invention to the layer B having a high nitrogen content, the effect of improving adhesion can be easily obtained.

[0020] The composition of Layer B can be measured by using an electron probe microanalyzer (EPMA) on a mirror-finished hard coating. In this case, for example, after mirror-finishing the hard coating surface, five analysis points with a diameter of about 1 μm are analyzed, and the composition can be determined by averaging the three values ​​excluding the maximum and minimum values.

[0021] If the thickness of Layer B is too thin, excellent durability may not be fully exhibited. Furthermore, if the thickness is too thick, peeling of the coating may occur. The thickness of Layer B may be selected from the range of, for example, 0.5 μm or more and 10 μm or less. The thickness of Layer B is more preferably 1 μm or more. Furthermore, the thickness of Layer B is more preferably 5 μm or less.

[0022] In this embodiment, the effects of this embodiment can be achieved even if another layer is coated on the B layer. Therefore, the coating structure consisting of the A layer and the B layer in this embodiment may have another layer coated thereon in addition to the B layer being the outermost surface of the tool. In this case, the B layer is preferably coated with a C layer made of a nitride or carbonitride having excellent heat resistance and wear resistance as a protective coating. The C layer is more preferably made of a nitride. The C layer is preferably a hard coating having excellent thermal shock resistance and residual compressive stress. The composition of the C layer may be selected appropriately depending on the workpiece material and processing conditions. In particular, in wet processing, hard coatings are prone to peeling due to heating and cooling cycles, so it is preferable to provide a hard coating having high residual compressive stress as a protective coating. As the C layer, a nitride or carbonitride having a Ti content of 60% to 95% and a Si content of 5% to 40% is preferred, as it is a coating type with high residual compressive stress.

[0023] To form the A layer of this embodiment on a substrate, Ti bombardment is performed on the substrate. The film-forming apparatus used for Ti bombardment preferably includes a cathode with a magnetic field configuration in which a coil magnet is arranged around the outer periphery of the target to confine the arc spot within the target. Using such a cathode, bombardment with Ti, an element species that easily forms carbides, removes oxides from the substrate surface and cleans it. In addition to this cleaning, the bombarded Ti ions diffuse into the WC on the substrate surface, facilitating the formation of a layer containing W and Ti. In this embodiment, the A layer containing W and Ti is formed on the cutting edge, which is the functional part, thereby improving adhesion between the substrate and the hard coating at the cutting edge and enhancing the durability of the coated cutting tool. If the absolute value of the negative pressure bias voltage applied to the substrate during Ti bombardment is small and the current input to the target is low, it is difficult to form a layer containing W and Ti on the substrate surface. Therefore, the negative pressure bias voltage applied to the substrate is preferably between -1000 V and -700 V. The current applied to the target is preferably 80 A or more and 150 A or less. The temperature inside the furnace is preferably 400°C or more and 800°C or less. Ti bombardment is preferably carried out by introducing nitrogen gas into the vacuum chamber at 5 to 50 sccm. The inventors' studies have confirmed that the thickness of Layer A formed on the tool cutting edge is affected by differences in the tool diameter, cutting edge shape, etc.

[0024] <Substrate> As the substrate, a two-blade ball end mill made of cemented carbide having a composition of WC (bal.)-Co (8 mass%)-Cr (0.5 mass%)-VC (0.3 mass%), an average WC particle size of 0.6 μm, and a hardness of 93.9 HRA was prepared.

[0025] <Manufacturing Method> An arc ion plating deposition system was used for deposition. This system included multiple cathodes (arc evaporation sources), a vacuum chamber, and a substrate rotation mechanism. The cathodes included one cathode (hereinafter referred to as "C1") with a coil magnet attached to the outer periphery of the target, and two cathodes (hereinafter referred to as "C2" and "C3") with permanent magnets attached to the back and outer periphery of the target and magnetic field-generating coils in front of the target to generate a magnetic field for pushing plasma forward. The distance from the target surface to the substrate was 400 mm. The vacuum chamber was evacuated using a vacuum pump, and gas was introduced through a supply port. A bias power supply was connected to the substrate placed inside the vacuum chamber, independently applying a negative bias voltage to the substrate. The substrate rotation mechanism included a worktable, a plate-shaped jig on the worktable, and a pipe-shaped jig attached to the plate-shaped jig. The worktable rotated at a speed of three revolutions per minute, while the plate-shaped jig and the pipe-shaped jig each rotated on their own axis. A metal Ti target was placed in C1, an AlCrSi alloy target in C2, and a TiSi alloy target in C3.

[0026] <Heating and Vacuum Evacuation Step> Each substrate was fixed to a pipe-shaped jig in a vacuum chamber, and a pre-film formation process was carried out as follows. First, the vacuum chamber was heated to 5×10 －３ The vacuum chamber was then evacuated to a pressure of 500°C or less. Thereafter, the substrate was heated to a temperature of 500°C by a heater installed in the vacuum chamber, and the vacuum chamber was then evacuated. －３ Pa or less.

[0027] <Ar bombardment step> Then, Ar gas was introduced into the vacuum chamber, and the pressure inside the chamber was set to 0.50 Pa. Then, a current of 30 A was supplied to the filament electrode, and a negative bias voltage of −150 V was applied to the substrate, and Ar bombardment was carried out for 60 minutes.

[0028] <Ti bombardment step> Nitrogen gas was then introduced into the vacuum chamber at 30 sccm, and the pressure inside the chamber was set to 0.3 Pa. Thereafter, a current of 90 A was supplied to the metal Ti target, and a negative bias voltage of −800 V was applied to the substrate, thereby carrying out Ti bombardment for 15 minutes.

[0029] <Film formation process> After Ti bombardment, nitrogen gas was introduced into the vacuum chamber, and the pressure inside the vacuum chamber was set to 4 Pa. A current of 100 A was supplied to the Al60Cr30Si10 target (numerical values ​​are atomic ratios; the same applies below), a current of 5 A was supplied to the magnetic field generating coil, and a negative bias voltage of -150 V was applied to the substrate, resulting in a hard nitride coating with a thickness of approximately 2 μm. Subsequently, a current of 150 A was supplied to the Ti75Si25 target, a current of 5 A was supplied to the magnetic field generating coil, and a negative bias voltage of -50 V was applied to the substrate, resulting in a nitride upper layer with a thickness of approximately 1 μm.

[0030] In the conventional coating, Ar gas was introduced into the vacuum chamber at 30 sccm during Ti bombardment, and the pressure inside the chamber was set to 0.3 Pa. Then, a current of 90 A was supplied to the Ti target, and a negative bias voltage of -800 V was applied to the substrate, and Ti bombardment was carried out for 15 minutes. The conditions for forming the hard coating were the same as those for the coating of this example.

[0031] To confirm the film structure of Layer A, a cross-section of the cutting edge of a ball end mill was observed using a field emission transmission electron microscope (JEM-2010F, manufactured by JEOL Ltd.). The sample was cut and bonded to a dummy substrate using epoxy resin. The measurement sample was then prepared by cutting, attaching a Mo reinforcing ring, polishing, dimpling, and Ar ion milling. Carbon deposition was performed prior to measurement. Observation, composition analysis, and nanobeam diffraction were performed at an acceleration voltage of 200 kV. The composition of Layer A was determined using energy dispersive X-ray spectroscopy (EDS). Nanobeam diffraction was performed using a camera length of 50 cm and a beam diameter of approximately 0.2 nm, analyzing the center of the film thickness. The analysis results are shown in Table 1.

[0032]

[0033] The composition of layer B was measured using a wavelength dispersive electron probe microanalysis (WDS-EPMA) attached to an electron probe microanalyzer (JXA-8500F manufactured by JEOL Ltd.). The mirror-finished sample was subjected to irradiation with a 10 kV accelerating voltage and a 5 × 10 －８The average composition of layer A was (Al56Cr33Si11)N, and the average composition of layer B was (Al56Cr33Si11)N. Ｂ / M Ｂ The refractive index was 1.20. It was also confirmed that the intensity profile obtained from the selected area diffraction pattern did not have a peak mainly due to hexagonal crystals.

[0034] (Conditions) Dry machining Tool: 2-blade carbide ball end mill Model number: EPDBE2010-6, ball radius 0.5 mm Cutting method: Bottom cutting Workpiece: STAVAX (52HRC) (manufactured by Böhler-Uddeholm Co., Ltd.) Depth of cut: Axial direction 0.04 mm, radial direction 0.04 mm Cutting speed: 75.4 m / min Feed per blade: 0.0179 mm / blade Cutting distance: 15 m Evaluation method: After cutting, the workpiece was observed at a magnification of 1000 times using a scanning electron microscope, and the width of the abrasion between the tool and workpiece on the tool flank was measured, and the part with the largest abrasion width was defined as the maximum abrasion width on the flank.

[0035]

[0036] In Example 1, the layer A had a high nitrogen content and exhibited excellent adhesion. In the above-described examples, the layer B was made of AlCrSi nitride, which has a high Si content and tends to have a fine coating structure and poor adhesion, but even if the layer B has a different composition, the effect of improving adhesion can be achieved.

Claims

1. A coated cutting tool having a substrate surface coated with a hard coating, the hard coating being disposed on the substrate surface, containing W in the largest amount among metal elements including metalloids, followed by Ti in the second largest amount, the total content ratio of W and Ti being 70 atomic % or more, containing carbon in the largest amount among non-metal elements, followed by nitrogen in the second largest amount, and the nitrogen content ratio N being 100 atomic % when the total content ratio of metal elements including metalloids, carbon, nitrogen and oxygen is 100 atomic %. Ａ and carbon content ratio C Ａ Ratio to N Ａ / C Ａ 1. A coated cutting tool comprising: a layer A having a face-centered cubic lattice structure, having a refractive index of 0.40 or more and a film thickness of 1 nm to 20 nm; and a layer B having a face-centered cubic lattice structure and made of a nitride or a carbonitride, disposed on the layer A.

2. The A layer has a nitrogen content ratio N of 100 atomic % when the total content ratio of metal elements including metalloids, carbon, nitrogen and oxygen is 100 atomic %. Ａ and the total content ratio M of metal elements including metalloids Ａ Ratio to N Ａ / M Ａ 2. The coated cutting tool according to claim 1, wherein the coefficient of friction is 0.6 or more.

3. The coated cutting tool according to claim 1 or 2, characterized in that layer B is a nitride or carbonitride containing Al, Cr and Si, in which, among metal elements including semi-metals, the Al content is from 50 atomic % to 65 atomic %, the Cr content is from 20 atomic % to 40 atomic %, the combined Al and Cr content is from 85 atomic % to 96 atomic %, and the Si content is from 4 atomic % to 15 atomic %.

4. The B layer has an atomic ratio M of metal elements including metalloids when the total of metal elements and nonmetallic elements is 100%. Ｂ and the atomic ratio of nitrogen N Ｂ and 1.07<N Ｂ / M Ｂ The coated cutting tool according to claim 3 , which satisfies the relationship:

5. The coated cutting tool according to claim 1, further comprising a C layer on said B layer, said C layer being made of a nitride or carbonitride of a metallic element including a metalloid.

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

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