Coated cutting tool

Abstract

Provided is a coated cutting tool having a hard coating on a base material. The hard coating is composed of a nitride or a carbonitride containing 50-70 at% of Al, 20-50 at% of Cr, and 4-15 at% of Si with respect to the total amount of metals including semimetals. In the hard coating, the atomic ratio (atom %) A of metal elements including semimetals and the atomic ratio (atom %) B of nitrogen satisfy the relationship 1.07<B / A<1.30. The hard coating has a maximum peak intensity originating from (200) or (111) plane of a cubic crystal in an intensity profile obtained from an X-ray diffraction pattern or a limited visual field diffraction pattern of a transmission electron microscope, and does not have a peak mainly originating from a hexagonal crystal in an intensity profile obtained from a limited visual field diffraction pattern.

Description

Coated Cutting Tools

[0001] This application claims priority to Japanese Patent Application No. 2023-103045, filed on June 23, 2023, the contents of which are incorporated herein by reference.

[0002] AlCrSi nitride is a film type with excellent heat resistance and wear resistance, and is used in coated cutting tools. The applicant of the present application has proposed further increasing the nitrogen content of AlCrSi nitride hard coatings with a high Si content and a refined structure (Patent Document 1). The hard coating described in Patent Document 1 has excellent wear resistance and can improve the durability of coated cutting tools when milling high-hardness steel. Patent Document 1 also indicates that if the nitrogen content of a hard coating is too high, the residual compressive stress of the hard coating increases excessively, making the hard coating more susceptible to self-destruction and reducing tool durability. For this reason, Patent Document 1 sets the upper limit of B / A, the ratio of the atomic ratio A of metal elements to the atomic ratio B of nitrogen, at 1.07.

[0003] International Publication No. 2015 / 141743

[0004] The inventors' studies have confirmed that, depending on the coating device, it is difficult to control the nitrogen content of the hard coating, and that the nitrogen content may be even higher than the upper limit of B / A specified in Patent Document 1. If a coated cutting tool with excellent durability can be obtained with a nitrogen content range higher than that of Patent Document 1, the range of application will expand and productivity will increase. An object of the present invention is to provide a coated cutting tool with excellent durability, even when the nitrogen content is high, using AlCrSi nitride with a high Si content and a fine structure.

[0005] (1) One aspect of the present invention is a coated cutting tool having a substrate and a hard coating on the substrate, wherein the hard coating is made of a nitride or carbonitride containing 50 atomic % or more and 70 atomic % or less of aluminum (Al), 20 atomic % or more and 50 atomic % or less of chromium (Cr), and 4 atomic % or more and 15 atomic % or less of silicon (Si) relative to the total amount of metals including metalloids, and wherein the atomic ratio (atomic %) A of the metal elements including metalloids and the atomic ratio (atomic %) B of nitrogen, when the total of the metal elements including metalloids and non-metallic elements is taken as 100 atomic %, satisfies the relationship 1.07 < B / A < 1.30, and in an intensity profile obtained from an X-ray diffraction pattern or a selected-area diffraction pattern obtained with a transmission electron microscope, the peak intensity due to the (200) plane or the (111) plane of a cubic crystal exhibits the maximum intensity, and the intensity profile obtained from the selected-area diffraction pattern does not have a peak mainly due to hexagonal crystals.

[0006] (2) In (1), it is preferable that 1.1<B / A<1.25. (3) In (1) or (2), it is preferable that, when observing the surface or cross section of the hard coating, there are 5 or fewer droplets with an equivalent circle diameter of 3 μm or more within an area of ​​50 μm × 40 μm. (4) In any one of (1) to (3), it is preferable that the compressive residual stress of the hard coating is 1.0 GPa or more and 4.0 GPa or less. (5) In any one of (1) to (4), an intermediate coating may be provided between the hard coating and the substrate. (6) In any one of (1) to (5), an upper layer may be provided on the hard coating. (7) In (6), it is preferable that the upper layer is a nitride or a carbonitride. (8) In (7), the upper layer is preferably a nitride or carbonitride containing 60 atomic % or more and 95 atomic % or less of titanium (Ti) and 5 atomic % or more and 40 atomic % or less of silicon (Si) relative to the total amount of metals including metalloids.

[0007] According to the present invention, it is possible to provide a coated cutting tool having excellent durability.

[0008] 1 is a diagram showing a selected-area diffraction pattern of the hard coating according to the present embodiment; FIG. 2 is a diagram showing an intensity profile determined from the selected-area diffraction pattern of FIG. 1; FIG. 3 is an example of a surface observation photograph (×2,000 magnification) of the hard coating according to the present embodiment; and FIG. 4 is an example of a surface observation photograph (×2,000 magnification) of a hard coating according to a conventional example.

[0009] The present inventors have arrived at the present invention by discovering that AlCrSi nitrides with a high Si content exhibit excellent durability by further reducing the amount of hexagonal AlN contained at the microscopic level, even when the nitrogen content is high. The details of this embodiment will be described below.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A coated cutting tool according to the present invention has a hard coating made of nitride or carbonitride of AlCrSi on the surface of the tool.

[0011] The component composition, structure, properties, and manufacturing method of the hard coating that constitutes the coated cutting tool of this embodiment will be described in detail below.

[0012] <Composition: Aluminum (Al), Chromium (Cr), Silicon (Si)> The hard coating according to this embodiment is composed of a nitride or carbonitride containing 50 atomic % or more and 70 atomic % or less of aluminum (Al), 20 atomic % or more and 50 atomic % or less of chromium (Cr), and 4 atomic % or more and 15 atomic % or less of silicon (Si) relative to the total amount of metal elements, including semimetals (hereinafter referred to as metal elements). AlCrSi nitrides or carbonitrides are film species with excellent wear resistance and heat resistance. Al is an element that imparts heat resistance to hard coatings. The inclusion of a certain amount of Al in a hard coating enhances heat resistance. Furthermore, the formation of an oxidation protective coating on the tool surface facilitates the suppression of tool damage. Furthermore, the coating structure becomes finer, which facilitates the suppression of wear of the hard coating due to welding. Furthermore, cutting resistance tends to decrease. To fully utilize the effects of adding Al, the hard coating according to this embodiment contains 50 atomic % or more of Al. Preferably, the Al content is 55 atomic % or more. On the other hand, if the amount of Al is too much, the amount of hexagonal AlN increases, making the hard coating brittle. Therefore, the hard coating according to this embodiment has an Al content of 70 atomic % or less, and more preferably, 68 atomic % or less.

[0013] Cr is an element that imparts wear resistance to a hard coating. When a hard coating contains a certain amount of Cr, its wear resistance is enhanced. The hard coating according to this embodiment contains 30 atomic % or more of Cr. It is more preferable that the Cr content be 35 atomic % or more. On the other hand, if the Cr content is too high, the heat resistance of the hard coating decreases. Therefore, the hard coating according to this embodiment contains 50 atomic % or less of Cr. It is more preferable that the Cr content be 45 atomic % or less. It is more preferable that the total of Al and Cr in the hard coating according to this embodiment is 85 atomic % or more. It is more preferable that the total of Al and Cr is 90 atomic % or more.

[0014] Si is an element that refines the structure of the hard coating. Refining the coating structure improves wear resistance and heat resistance. The hard coating according to this embodiment contains 4 atomic % or more of Si. Preferably, the Si content is 5 atomic % or more. On the other hand, if the Si content is too high, the amount of hexagonal AlN increases, reducing the durability of the coated cutting tool. Therefore, the hard coating according to this embodiment contains 15 atomic % or less of Si. Preferably, the Si content is 12 atomic % or less.

[0015] The content ratio of the metal element in the hard coating according to this embodiment can be measured by measuring the mirror-finished hard coating using an electron probe microanalyzer (EPMA). 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 content ratio can be determined by averaging the three points excluding the maximum and minimum values.

[0016] <Atomic Ratio A of Metal Elements and Atomic Ratio B of Nitrogen> In the hard coating according to this embodiment, the atomic ratio A of metal elements including metalloids and the atomic ratio B of nitrogen satisfy the relationship 1.07<B / A<1.30, where the total of metal elements including metalloids and non-metallic elements is 100 atomic %. The values ​​of atomic ratios A and B are measured by EPMA using the measurement method described above. In addition to nitrogen, non-metallic elements may include carbon and oxygen. Ar may also be included. When the value of B / A is greater than 1.07, complete nitrides are sufficiently formed at the microscopic level. On the other hand, when the value of B / A is greater than 1.30, film breakdown is likely to occur even when the amount of hexagonal AlN is reduced at the microscopic level. B / A is preferably greater than 1.10, and more preferably greater than 1.15. B / A is preferably less than 1.25, and more preferably less than 1.23. B / A is preferably 1.10<B / A<1.25. Further, it is more preferable that B / A satisfies the condition 1.15<B / A<1.23.

[0017] <Crystal Structure> In the intensity profile obtained from an X-ray diffraction pattern or a selected-area diffraction pattern obtained by a transmission electron microscope, the hard coating according to this embodiment exhibits the maximum peak intensity attributable to the (200) or (111) plane of the cubic crystal. Furthermore, the intensity profile obtained from the selected-area diffraction pattern does not have a peak mainly composed of hexagonal crystals. This significantly reduces the amount of brittle hexagonal AlN contained in the hard coating, and it is estimated that even if the nitrogen content of the hard coating increases to such an extent that the B / A ratio exceeds 1.07, the coated cutting tool will have excellent durability. The intensity profile obtained from the selected-area diffraction pattern is an intensity profile in which the horizontal axis represents the distance (radius r) from the center of the (000) plane spot and the vertical axis represents the integrated intensity (arbitrary units) for one circumference at each radius r. In the intensity profile obtained from the selected-area diffraction pattern, a peak mainly composed of hexagonal crystals appears within a distance range of 3 to 4 nm from the center of the (000) spot. In this embodiment, "having no peaks mainly composed of hexagonal crystals" means that there are no peaks with higher intensity in the range of 3 to 4 nm from the spot center than before or after. In this embodiment, the intensity profile obtained from the selected area diffraction pattern is evaluated after removing the background. Even if a diffraction pattern of hexagonal AlN is confirmed in the selected area diffraction pattern, if the amount is very small, no peak (apex) will appear in the intensity profile, and it will only bulge slightly.

[0018] As long as the above requirements are met, the hard coating according to this embodiment may contain metal elements other than Al, Cr, and Si. For example, to improve the wear resistance, heat resistance, lubricity, and other properties of the hard coating, the hard coating may contain one or more elements selected from elements of Groups 4a, 5a, and 6a of the periodic table, as well as B, Y, and Cu. These elements are commonly added to AlTiN-based and AlCrN-based hard coatings to improve the properties of the hard coating, and as long as the content is not excessive, the durability of the coated cutting tool will not be significantly reduced. If the hard coating according to this embodiment contains metal elements other than Al, Cr, and Si, the total content of these elements is preferably 10 atomic % or less, and more preferably 5 atomic % or less.

[0019] In the hard coating according to this embodiment, when observed on the surface or cross section, it is preferable that there are five or fewer droplets with an equivalent circle diameter of 3 μm or more within a 50 μm × 40 μm area. Two or fewer droplets are even more preferable. In the present invention, droplets refer to deposits on the hard coating that result from molten particles of 1 to several tens of μm in size that fly out from the cathode during arc ion plating. Tool durability is enhanced by having fewer coarse droplets in the hard coating. Furthermore, in the hard coating according to this embodiment, when observed on the surface or cross section, it is preferable that there is one or fewer droplets with an equivalent circle diameter of 5 μm or more within a 50 μm × 40 μm area. Tool durability is enhanced by having fewer coarse droplets. The number of droplets in the hard coating can be determined by observing five or more fields of view in a 50 μm × 40 μm area using an electron microscope at 2000x magnification and averaging the results.

[0020] The hard coating according to this embodiment preferably has a residual compressive stress of 1.0 GPa or more and 4.0 GPa or less. A residual compressive stress of 1.0 GPa or more and 4.0 GPa or less is preferred because peeling of the coating is less likely to occur.

[0021] The coated cutting tool of this embodiment may optionally have an intermediate coating between the substrate and the hard coating. For example, a nitride, carbonitride, or carbide containing one or more elements selected from titanium (Ti), aluminum (Al), and chromium (Cr) may be provided. A modified layer formed by metal bombardment may also be provided. Furthermore, an upper layer may be provided on the hard coating to enhance the durability of the coated cutting tool. The upper layer is preferably a nitride or carbonitride. The upper layer is preferably a nitride or carbonitride containing 60 atomic % to 95 atomic % of titanium (Ti) and 5 atomic % to 40 atomic % of silicon (Si).

[0022] The hard coating of this embodiment is a physical vapor deposition coating. The hard coating of this embodiment is preferably a hard coating formed by arc ion plating, which has excellent adhesion among physical vapor deposition coatings. Hard coatings with a high Al content tend to generate a large number of droplets. Although the hard coating formed by arc ion plating has a high Al content, the reduced coarse droplets contribute to the stable tool performance of the coated cutting tool. The coated cutting tool of this embodiment is preferably formed using a film-forming apparatus equipped with permanent magnets on the back and outer periphery of the target and a cathode equipped with a magnetic field generating coil in front of the target that generates a magnetic field to push the plasma forward. Furthermore, the distance from the target surface to the substrate is preferably 250 mm or more. Increasing the distance from the target surface to the substrate tends to reduce the number of coarse droplets that reach the substrate. The coating temperature is preferably 450°C to 550°C. The negative pressure bias voltage applied to the substrate is preferably -180 to -120 V. The furnace pressure is preferably 2 to 8 Pa. The current applied to the target is preferably 100 to 200 A. The current applied to the magnetic field generating coil is preferably 3 to 10 A.

[0023] <Substrate> A two-flute ball end mill made of cemented carbide having a composition of WC (bal.)-Co (8% by mass)-Cr (0.5% by mass)-VC (0.3% by mass), an average WC grain size of 0.6 μm, and a hardness of 93.9 HRA was prepared as the substrate. Additionally, a test piece made of cemented carbide was prepared for measuring residual stress.

[0024] <Manufacturing Method> An arc ion plating type film formation device was used for film formation. This device includes multiple cathodes (arc evaporation sources), a vacuum chamber, and a substrate rotation mechanism. The coating device used in this example is equipped with permanent magnets on the back and outer periphery of the target, and a cathode equipped with a magnetic field generating coil in front of the target to generate a magnetic field for pushing plasma forward. The distance from the target surface to the substrate is 400 mm. The vacuum chamber is evacuated by a vacuum pump, and gas is introduced through a supply port. A bias power supply is connected to the substrate placed in the vacuum chamber, and a negative bias voltage is applied to the substrate independently. The substrate rotation mechanism is equipped with a work table, a plate-shaped jig on the work table, and a pipe-shaped jig on the plate-shaped jig. The work table rotates at a speed of 3 revolutions per minute, and the plate-shaped jig and pipe-shaped jig each rotate and revolve.

[0025] <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.

[0026] <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 20 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.

[0027] <Film formation process> After Ar bombardment, the gas in the vacuum chamber was replaced with nitrogen, and the pressure in 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 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 bias voltage of -50 V was applied to the substrate, resulting in a nitride upper layer with a thickness of approximately 1 μm.

[0028] In the conventional coating, a deposition apparatus equipped with a cathode with permanent magnets arranged on the back and outer periphery of the target was used. The distance from the target surface to the substrate was 170 mm. The deposition conditions were the same as those for the coating of this example, except that no current was applied to the magnetic field generating coil. The hard coating of the conventional example corresponds to that disclosed in Japanese Patent No. 6410797.

[0029] <Composition Analysis> The film composition was measured using a wavelength dispersive electron probe microanalyzer (WDS-EPMA) attached to an electron probe microanalyzer (JXA-8500F manufactured by JEOL Ltd.). A ball end mill for evaluating physical properties was mirror-finished, and the film composition was measured at an acceleration voltage of 10 kV and a probe current of 5 × 10 －８ The B / A ratio was calculated by measuring five points in an analysis area of ​​approximately 1 μm in diameter over a 10-second acquisition time. The average composition of the hard coatings in this example and the conventional example was (Al56Cr33Si11)N. The B / A ratio in this example was 1.20.

[0030] <TEM analysis> Microanalysis was performed using a field discharge transmission electron microscope (JEM-2100F manufactured by JEOL Ltd.). The selected area diffraction pattern of the hard coating was obtained using an accelerating voltage of 200 kV, a selected area diameter of 500 nm, a camera length of 100 cm, and an incident electron dose of 5.0 pA / cm. ２ The analysis was performed under the conditions of (on a fluorescent screen). The central portion of the AlCrSi nitride hard coating in the film thickness growth direction was analyzed. The brightness of the obtained selected area diffraction pattern was converted to obtain an intensity profile.

[0031] Residual stress: Residual stress and crystal structure were measured using an X-ray diffraction device. ２ The compressive residual stress measured by the ψ method was about 3 GPa in the present example and the comparative example.

[0032] (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.

[0033]

[0034] The maximum wear width of this example was smaller than that of the conventional example. Figure 1 shows the selected area diffraction pattern of the hard coating of this example. Figure 2 shows the intensity profile of the selected area diffraction pattern obtained from Figure 1. Peak "2" in Figure 2 is the peak intensity corresponding to the (111) plane of the cubic crystal, peak "3" is the peak intensity corresponding to the (200) plane of the cubic crystal, and peak "4" is the peak intensity corresponding to the (220) plane of the cubic crystal. Peak "1" has a slight bulge, but does not have a sharp peak like peaks "2" to "4". In other words, the hard coating of this example does not have a peak mainly composed of hexagonal crystals. It is confirmed that this example contains little hexagonal AlN. Since this example contains very little hexagonal AlN at the microscopic level, it is estimated that the durability of this example is superior to that of the conventional example, even though the nitrogen content of the hard coating is high.

[0035] Figure 3 shows an example of a surface observation photograph of the coated cutting tool of this example. Figure 4 shows an example of a surface observation photograph of a conventional coated cutting tool. It can be seen that this example has fewer coarse droplets than the conventional example. Depending on the tool shape and processing conditions, droplets can have a significant impact on tool performance. The coated cutting tool of this example is suitable for smaller diameter tools. By applying the hard coating of this example to small diameter tools that are more susceptible to droplets, it is expected that durability will be even better than that of the conventional example.

Claims

1. A coated cutting tool having a substrate and a hard coating on the substrate, wherein the hard coating is made of a nitride or carbonitride containing 50 atomic % or more and 70 atomic % or less of aluminum (Al), 20 atomic % or more and 50 atomic % or less of chromium (Cr), and 4 atomic % or more and 15 atomic % or less of silicon (Si) relative to a total amount of metals including metalloids, and wherein the atomic ratio (atomic %) A of the metal elements including metalloids and the atomic ratio (atomic %) B of nitrogen when the sum of the metal elements including metalloids and non-metallic elements is taken as 100 atomic %, satisfies the relationship of 1.07 < B / A < 1.30, and in an intensity profile obtained from an X-ray diffraction pattern or a selected-area diffraction pattern of a transmission electron microscope, the peak intensity due to the (200) plane or the (111) plane of a cubic crystal shows the maximum intensity, and in an intensity profile obtained from a selected-area diffraction pattern of a transmission electron microscope, there is no peak mainly due to a hexagonal crystal.

2. A coated cutting tool according to claim 1, characterized in that 1.1<B / A<1.

25.

3. A coated cutting tool according to claim 1 or 2, in which observation of the surface or cross section of the hard coating reveals that there are 5 or less droplets with an equivalent circle diameter of 3 μm or more within an area of ​​50 μm×40 μm.

4. The coated cutting tool according to claim 1, characterized in that the hard coating has a compressive residual stress of 1.0 GPa or more and 5.0 GPa or less.

5. The coated cutting tool according to claim 1, further comprising an intermediate coating provided between the hard coating and the substrate.

6. The coated cutting tool according to claim 1, further comprising an upper layer provided on said hard coating.

7. The coated cutting tool according to claim 6, wherein the upper layer is a nitride or a carbonitride.

8. The coated cutting tool according to claim 7, wherein the upper layer is a nitride or carbonitride containing 60 atomic % or more and 95 atomic % or less of titanium (Ti) and 5 atomic % or more and 40 atomic % or less of silicon (Si) based on the total amount of metals including metalloids.

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