Coated cutting tools

Abstract

To improve durability of a coated cutting tool.SOLUTION: A coated cutting tool includes a base material, and a hard film. The hard film has a laminated film in which a b1 layer of a nitride or a carbonitride containing 55 atom% or more of Al and 20 atom% or more of Cr with respect to the total amount of a metal (including semimetal) element, and a b2 layer of a nitride or a carbonitride containing 55 atom% or more of Al and 20 atom% or more of Ti with respect to the total amount of a metal (including semimetal) element are alternately laminated with each film thickness of 100 nm or less. The laminated film satisfies a relation of Ih×100 / (Ih+If)≤15, and has an Al inclusion ratio in the surface layer side region of the laminated film larger than that in the base material side region thereof.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a coated cutting tool with excellent durability to which an Al-rich laminated film in which AlCr nitride and AlTi nitride in which AlN having a hexagonal close-packed structure (hcp structure) is reduced at the micro level are alternately laminated at the nano level is applied.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a result of the study by the present inventor, it was confirmed that there is room for improvement in durability with respect to the conventionally proposed coated cutting tools.

Means for Solving the Problems

[0005] One aspect of the present invention comprises a substrate and a hard film formed on the substrate, wherein the hard film consists of a b1 layer of nitride or carbonitride containing 55 atomic% or more of aluminum (Al) and 20 atomic% or more of chromium (Cr) relative to the total amount of metallic (including metalloid) elements, and a b2 layer of nitride or carbonitride containing 55 atomic% or more of aluminum (Al) and 20 atomic% or more of titanium (Ti) relative to the total amount of metallic (including metalloid) elements, each alternately laminated with a film thickness of 100 nm or less. The laminated coating has a laminated film, and in the intensity profile obtained from the limited field diffraction pattern of a transmission electron microscope, if Ih is the maximum peak intensity due to AlN in the hexagonal close-packed structure and If is the sum of the peak intensities due to the (111), (200), and (220) planes of the face-centered cubic lattice structure, then the relationship Ih × 100 / (Ih + If) ≤ 15 is satisfied, and the aluminum (Al) content ratio is greater in the surface region of the laminated coating than in the substrate region.

[0006] Furthermore, it is preferable that the film thickness of the b1 and b2 layers in the substrate-side region of the laminated film is greater than the film thickness of the b1 and b2 layers in the surface-side region. Furthermore, it is preferable that the columnar particles in the surface region of the laminated film are finer than those in the substrate region. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a coated cutting tool with excellent durability. [Modes for carrying out the invention]

[0008] The coated cutting tool of this embodiment comprises a base material and a hard coating formed on the base material. The hard coating comprises, in order from the base material side, an intermediate coating which may be provided as needed, a laminated coating, and a protective coating which may be provided as needed. Each layer will be described in detail below.

[0009] ≪Base material≫ In the coated cutting tool of this embodiment, the base material is not particularly limited, but it is preferable to use a WC-Co-based cemented carbide, which has excellent strength and toughness, as the base material.

[0010] <Laminated coating> The laminated film according to this embodiment is an Al-rich laminated film in which an AlCr-based b1 layer and an AlTi-based b2 layer are alternately laminated with a film thickness of 100 nm or less. Specifically, the laminated film is a laminated film in which a b1 layer of nitride or carbonitride containing 55 atomic percent or more of aluminum (Al) and 20 atomic percent or more of chromium (Cr) relative to the total amount of metal elements, and a b2 layer of nitride or carbonitride containing 55 atomic percent or more of aluminum (Al) and 20 atomic percent or more of titanium (Ti) relative to the total amount of metal parts are alternately laminated with a film thickness of 100 nm or less. By alternately laminating Al-rich AlCrN-based hard films and Al-rich AlTiN-based hard films with different compositional systems at the nanoscale, the progression of film fracture is more easily suppressed. In addition, it becomes difficult to include AlN in a hexagonal close-packed structure (hcp structure), which increases the overall heat resistance of the hard film and improves the durability of coated cutting tools. The individual film thicknesses of layers b1 and b2 are preferably 50 nm or less. The individual film thicknesses of layers b1 and b2 are preferably 2 nm or more. Furthermore, the individual film thicknesses of layers b1 and b2 are preferably 5 nm or more. The total film thickness of the laminated film is preferably 1 μm or more and 10 μm or less. Even if an intermediate film or protective film is provided as needed, it is preferable that the laminated film has the thickest film thickness among the multiple films constituting the hard film.

[0011] The b1 layer is a nitride or carbonitride containing 55 atomic percent or more of aluminum (Al) and 20 atomic percent or more of chromium (Cr) relative to the total amount of metallic elements. Al and Cr-based nitrides or carbonitrides are film types with excellent heat resistance. In particular, as the Al content increases, the heat resistance of the hard coating tends to improve, and the durability of coated cutting tools is improved. The b1 layer is preferably a nitride with excellent heat resistance and wear resistance. To impart high heat resistance to the hard coating, the Al content of the b1 layer should be 55 atomic% or more. Furthermore, it is preferable that the Al content of the b1 layer be 60 atomic% or more. To reduce the brittle hcp structure AlN contained in the microstructure, it is preferable that the Al content of the b1 layer be 75 atomic% or less. Furthermore, it is preferable that the Al content of the b1 layer be 70 atomic% or less.

[0012] To impart high wear resistance to the hard coating, the b1 layer has a Cr content ratio of 20 atomic% or more relative to the total amount of metal elements. The b1 layer contains a large amount of Cr after Al, as it is an AlCr-based nitride or carbonitride. To further enhance the heat resistance of the hard coating, it is preferable that the Cr content ratio of the b1 layer be 40 atomic% or less. Furthermore, it is preferable that the Cr content ratio of the b1 layer be 35 atomic% or less.

[0013] In order to achieve a high level of both heat resistance and wear resistance in the laminated film, it is preferable that the total content ratio of Al and Cr relative to the total amount of metal elements in the b1 layer be 85 atomic percent or more.

[0014] Because layers b1 and b2 are alternately stacked at the nanoscale, their compositions can diffuse. Therefore, layer b1 may contain Ti, which is essential for layer b2. However, in order to stack an Al-rich AlCrN-based hard film and an Al-rich AlTiN-based hard film with different compositions, the Ti content ratio of layer b1 is lower than that of layer b2.

[0015] The b1 layer may contain metallic elements other than Al and Cr. For example, the b1 layer may contain one or more elements selected from groups 4a, 5a, and 6a of the periodic table and Si, B, Y, and Cu, for the purpose of improving the wear resistance, heat resistance, and lubricity of the hard coating. These elements are commonly added to AlTiN-based and AlCrN-based hard coatings to improve the properties of the hard coating, and will not significantly reduce the durability of the coated cutting tool unless the content ratio is excessive. Preferably, the total amount of metallic elements other than Al and Cr in the b1 layer is 25 atomic% or less. Furthermore, preferably, the total amount of metallic elements other than Al and Cr in the b1 layer is 20 atomic% or less. Furthermore, preferably, the total amount of metallic elements other than Al and Cr in the b1 layer is 15 atomic% or less.

[0016] Al and Cr nitrides or carbonitrides are preferable because the inclusion of Si (silicon) element results in a finer film structure, further improving wear resistance and heat resistance. Therefore, it is preferable for the b1 layer to contain Si, as this enhances the overall wear resistance and heat resistance of the laminated film. The b1 layer preferably contains Si at a concentration of 1 atomic percent or more. However, if the Si content becomes too high, the amount of AlN and amorphous phases in the hcp structure within the microstructure increases. For this reason, it is preferable that the Si content of the b1 layer be 8 atomic percent or less.

[0017] The b2 layer is a nitride or carbonitride containing 55 atomic percent or more of aluminum (Al) and 20 atomic percent or more of titanium (Ti) relative to the total amount of metallic elements. Nitrides or carbonitrides mainly composed of Al and Ti are film types with excellent wear resistance and heat resistance. In particular, as the Al content increases, the heat resistance of the hard film tends to improve, improving the durability of coated cutting tools. Furthermore, it is preferable that the nitride has excellent heat resistance and wear resistance. To impart high heat resistance to the hard film, the b2 layer should contain 55 atomic percent or more of Al. Furthermore, it is preferable that the Al content of the b2 layer be 60 atomic percent or more. To reduce the brittle hcp structure of AlN contained in the microstructure, it is preferable that the Al content of the b2 layer be 75 atomic percent or less. Furthermore, it is preferable that the Al content of the b2 layer be 70 atomic percent or less.

[0018] In order to impart high wear resistance to the hard film, the b2 layer contains 20 atomic % or more of Ti. Since the b2 layer is an AlTi-based nitride or carbonitride, it contains a large amount of Ti following Al. In order to further increase the heat resistance of the hard film, the Ti content ratio of the b2 layer is preferably 40 atomic % or less. Further, the Ti content ratio of the b2 layer is preferably 35 atomic % or less.

[0019] In order to make the heat resistance and wear resistance of the laminated film compatible at a high level, the total content ratio of Al and Ti in the b2 layer is preferably 80 atomic % or more.

[0020] Since the b1 layer and the b2 layer are alternately laminated at the nano level, their compositions can diffuse into each other. Therefore, the b2 layer may contain Cr which is essentially contained in the b1 layer. However, in order to laminate an Al-rich AlCrN-based hard film and an Al-rich AlTiN-based hard film having different composition systems, the Cr content ratio of the b2 layer is made lower than the Cr content ratio of the b1 layer.

[0021] The b2 layer can contain metal elements other than Al and Ti. For example, the b2 layer can contain one or more elements selected from the elements of Group 4a, Group 5a, Group 6a of the periodic table and Si, B, Y, Cu for the purpose of improving the wear resistance, heat resistance, lubricity, etc. of the hard film. These elements are generally added to AlTiN-based or AlCrN-based hard films to improve the properties of the hard film, and if the content ratio does not become excessive, it will not significantly reduce the durability of the coated cutting tool. The total of the metal elements other than Al and Ti in the b2 layer is preferably 25 atomic % or less. Further, the total of the metal elements other than Al and Ti in the b2 layer is preferably 20 atomic % or less. Further, the total of the metal elements other than Al and Ti in the b2 layer is preferably 15 atomic % or less.

[0022] In order to quantitatively determine AlN with a hcp structure present in the microstructure of the hard film, for the processed cross-section of the hard film, a selected area diffraction pattern is obtained using a transmission electron microscope, and the intensity profile obtained from the selected area diffraction pattern is used. Specifically, in the intensity profile of the selected area diffraction pattern of the transmission electron microscope, the relationship of Ih×100 / (Ih + If) is evaluated. Ih and If are defined as follows.

[0023] Ih: The maximum peak intensity due to AlN with a hexagonal close-packed structure (hcp structure). If: The sum of the peak intensities due to the (111), (200), and (220) planes of the face-centered cubic lattice structure (fcc structure).

[0024] By evaluating the relationship between Ih and If, in a hard film where the peak intensity due to AlN with a hcp structure is not confirmed by X-ray diffraction, the AlN with a hcp structure contained in the microstructure can be quantitatively evaluated. A smaller value of Ih×100 / (Ih + If) means that there is less fragile AlN with a hcp structure present in the microstructure of the multilayer film. The inventor has confirmed that when the value of Ih×100 / (Ih + If) in the multilayer film is greater than 15, the durability of the coated cutting tool tends to decrease under a harsh usage environment. In the present embodiment, by configuring the multilayer film to satisfy Ih×100 / (Ih + If) ≤ 15, a coated cutting tool with good durability is realized. Furthermore, it is preferable that the multilayer film satisfies Ih×100 / (Ih + If) ≤ 10. Furthermore, it is preferable that the multilayer film satisfies Ih×100 / (Ih + If) ≤ 5. Furthermore, it is preferable that the peak intensity due to AlN with a hcp structure is not confirmed in the multilayer film, that is, the multilayer film satisfies Ih×100 / (Ih + If) = 0.

[0025] In this embodiment, the aluminum (Al) content is higher in the surface region of the laminated film than in the substrate region. This configuration suppresses the increase in AlN in the hcp structure contained in the microstructure of the entire laminated film while further improving the heat resistance of the surface region. It is preferable that the aluminum (Al) content in the surface region of the laminated film is higher than in the substrate region by 2 to 10 atomic percent. Furthermore, it is preferable that the aluminum (Al) content in the surface region of the laminated film is higher than in the substrate region by 2 to 5 atomic percent. In this embodiment, the substrate-side region is the area within 0.3 μm in the film thickness direction from the interface between the substrate and the hard film. In this embodiment, the surface-side region is the area within 0.3 μm in depth from the outermost surface of the laminated film. The composition of the laminated film can be confirmed by analyzing a mirror-finished cross-sectional sample using EPMA or similar methods. For both the surface and substrate regions of the laminated film, five analysis points with a diameter of 0.1 to 0.2 μm are performed, and the composition of the surface and substrate regions of the laminated film can be determined from the average of the obtained measurements.

[0026] In this embodiment, it is preferable that the film thickness of layers b1 and b2 in the substrate-side region of the laminated film is greater than the film thickness of layers b1 and b2 in the surface-side region. The relative sizes of the film thicknesses are determined by comparing the average film thicknesses of the b1 layers and the b2 layers. More specifically, the average film thickness of all b1 layers included in the substrate-side region is compared with the average film thickness of all b1 layers included in the surface-side region. Similarly, the average film thickness of all b2 layers included in the substrate-side region is compared with the average film thickness of all b2 layers included in the surface-side region. Layers b1 and b2 that straddle the surface-side boundary of the substrate-side region, and layers b1 and b2 that straddle the substrate-side boundary of the surface-side region, are excluded from the calculation of the average film thickness.

[0027] The adhesion between the substrate and the laminated film is enhanced when the film thickness of layers b1 and b2 in the substrate-side region is relatively large. The effects of both AlCr-based and AlTi-based hard coatings are more easily reproduced when the film thickness of layers b1 and b2 in the surface-side region is relatively small. It is preferable that the film thickness of layers b1 and b2 in the substrate-side region of the laminated film be between 2 and 10 times the film thickness of layers b1 and b2 in the surface-side region. Furthermore, it is preferable that the film thickness of layers b1 and b2 in the substrate-side region of the laminated film be between 3 and 6 times.

[0028] In this embodiment, the microstructure of the laminated film is composed of fine columnar particles. The columnar particles constituting the laminated film extend along the film thickness direction (lamination direction). The composition of the laminated film with fine columnar particles tends to increase its hardness and toughness. The average width of the columnar particles in the laminated film is preferably 10 nm to 100 nm. The columnar particles in the surface region of the laminated film are preferably finer than those in the substrate region. Relatively finer columnar particles in the surface region can further improve abrasion resistance. Also, relatively coarser columnar particles in the substrate region can further improve adhesion. The average width of the columnar particles in the laminated film is preferably 1.2 to 3 times greater in the substrate region than in the surface region. The width of the columnar particles can be confirmed by cross-sectional observation using a transmission electron microscope. The width of the columnar particles is the length of the columnar particles in a direction perpendicular to the direction in which the columnar particles extend (generally the film thickness direction). The average width of columnar particles is calculated using the width of columnar particles measured in the central part of the film thickness direction of the laminated film. The central part of the film thickness direction refers to the area within 10% on both sides of the center of the film thickness direction of the laminated film. The average width of columnar particles is calculated as the average value of the widths of 10 or more columnar particles confirmed by cross-sectional observation images.

[0029] In this embodiment, an intermediate film may be provided between the substrate and the laminated film, if necessary. For example, a metal, metal carbide, metal nitride, or metal carbonitride may be provided as the intermediate film. Alternatively, a metal bombarded layer may be formed by metal bombarding the surface of the substrate.

[0030] In this embodiment, a protective film may be provided on the upper layer of the laminated film, if necessary. For example, a nitride or carbonitride containing Ti and Si, which are film types with excellent wear resistance, may be provided as the protective film. Alternatively, an AlCr-based or AlTi-based nitride or carbonitride may be provided as the protective film. Furthermore, a metal nitride or metal carbonitride with a composition other than TiSi-based, AlCr-based, and AlTi-based may be provided as the protective film. In addition, a metal other than a metal nitride or metal carbonitride, such as a metal, metal carbide, or metal boride, may be provided as the protective film.

[0031] ≪Manufacturing method≫ The hard coating according to this embodiment is preferably coated by an arc ion plating method with a high target ionization rate. Alternatively, it may be coated by a high-power sputtering method with a high target ionization rate. For Al-rich laminated coatings, in order to enhance crystallinity and reduce the amount of AlN in the hcp structure contained in the microstructure, it is preferable to use a cathode with a magnetic flux density of 10 mT or more in the vertical direction near the center of the target.

[0032] For forming AlCr-based hard coatings, it is preferable to deposit the film at a cathode voltage in the range of 20V to 35V. If the cathode voltage is too low, the amount of AlN in the hcp structure of the laminated film increases, reducing durability. If the cathode voltage is too high, the film structure of the laminated film becomes too coarse, which tends to reduce durability.

[0033] For forming AlTi-based hard coatings, it is preferable to deposit the film at a cathode voltage in the range of 20V to 30V. If the cathode voltage is too low, the amount of AlN in the hcp structure increases, reducing durability. If the cathode voltage is too high, the film structure of the laminated film becomes too coarse, which tends to reduce durability. The cathode current is preferably between 120A and 200A for all cathodes.

[0034] It is preferable to select a film deposition apparatus in which the magnetic flux density and cathode voltage in the vertical direction near the center of the target are within the above range, and then increase the absolute value of the negative bias voltage applied to the substrate, thereby suppressing the formation of AlN in the hcp structure of the microstructure and making the value of Ih × 100 / (Ih + If) less than 15. The negative bias voltage applied to the substrate is preferably -200V or more and less than -100V. More preferably -120V or less. If the absolute value of the bias voltage is too high, film formation becomes unstable and it becomes difficult to adjust the film thickness. If the absolute value of the bias voltage is too low, the amount of AlN in the hcp structure increases and durability decreases. The coating temperature is preferably 400°C or more and 600°C or less. When coating with nitrides, nitrogen gas is introduced into the furnace during coating. The nitrogen gas pressure during coating is preferably 2.0 Pa or more and 8.0 Pa or less. When coating with carbonitrides, for example, a portion of the nitrogen gas can be replaced with methane gas.

[0035] To increase the aluminum (Al) content in the surface region of the laminated film compared to the substrate region, or to make columnar particles finer, it is preferable to increase the coil current applied to the target in the surface region compared to the substrate region. Targets with different compositions in the substrate region and the surface region may also be used. The individual film thicknesses of the laminated film can be controlled by adjusting the table rotation rate during coating and the arc current applied to the target.

Claims

1. The device comprises a base material and a hard coating formed on the base material. The hard coating has a laminated film in which a b1 layer of nitride or carbonitride containing 55 atomic percent or more of aluminum (Al) and 20 atomic percent or more of chromium (Cr) relative to the total amount of metallic (including metalloid) elements, and a b2 layer of nitride or carbonitride containing 55 atomic percent or more of aluminum (Al) and 20 atomic percent or more of titanium (Ti) relative to the total amount of metallic (including metalloid) elements, are alternately laminated with a film thickness of 100 nm or less. The aforementioned laminated film satisfies the relationship Ih × 100 / (Ih + If) ≤ 15 in the intensity profile obtained from the limited field diffraction pattern of a transmission electron microscope, where Ih is the maximum peak intensity due to the hexagonal close-packed AlN structure and If is the sum of the peak intensities due to the (111), (200), and (220) faces of the face-centered cubic lattice structure. A coated cutting tool characterized in that the surface region, which is the area within a depth of 0.3 μm from the outermost layer of the laminated film, has a higher aluminum (Al) content than the substrate region, which is the area within a depth of 0.3 μm from the interface between the substrate and the hard film in the film thickness direction.

2. The coated cutting tool according to claim 1, characterized in that the film thickness of the b1 and b2 layers in the substrate-side region of the laminated film is greater than the film thickness of the b1 and b2 layers in the surface-side region.

3. The coated cutting tool according to claim 1 or 2, characterized in that the columnar particles in the surface layer region of the laminated film are finer than those in the substrate region.