Coated cutting tool

Abstract

To prolong the service life of a hard film cutting tool.SOLUTION: The coated cutting tool includes a hard coating 2 in which the surface of a base material 1 is coated with a first nitride layer 3 and the surface of the first nitride layer 3 is coated with a second nitride layer 4. The first nitride layer 3 is a nitride layer which is inferior in wear resistance to the second nitride layer 4 but superior in oxidation resistance to the second nitride layer 4, and in which the crystal orientation during non-heating is substantially the same as the crystal orientation in the second temperature range. As a result, a hard coating having both the advantages of the first nitride layer 3 and the second nitride layer 4 and having a crystal structure that is hardly affected by the heating temperature is realized.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a cutting tool provided with a hard coating. [Background technology]

[0002] As cutting processes become faster and dryer and workpieces become harder, various improvements have been made to the hard coatings used in cutting tools. For example, the applicant of the present application proposed a cutting tool of this type in Patent Document 1, which has a multilayer structure on a substrate, comprising a first layer formed by laminating thin TiSiN and TiAlCrN layers, and one of the TiSiN and TiAlCrN layers on the surface of the first layer as a second layer. This cutting tool is characterized by having finer crystals in the Si-containing coating, thereby improving hardness and durability, and also improving the sharpness of the cutting edge.

[0003] Patent Document 2 discloses a hard-coated tool having a substrate surface on which a lower coating layer, an intermediate coating layer, an upper coating layer, and a surface coating layer are formed in this order. Patent Document 3 also discloses a cutting tool having a multilayer wear-protective coating deposited on the substrate of the cutting tool. This cutting tool has a multilayer wear-protective coating comprising a first coating deposited on the substrate, a second coating deposited on the first coating, and a harder coating on the second coating. The first coating has a composition of TiaAl(1-a)N (where 0.4≦a≦0.6) and a thickness of 0.5 μm to 4 μm. The second coating is a coat consisting of a sequence of 10 to 80 first and second layers arranged alternately, each with a thickness of 5 nm to 100 nm. Furthermore, Patent Documents 4, 5 and 6 disclose cutting tools in which the layer covering the outermost surface of the substrate, that is, the first layer, is a multi-layered layer containing AlCrSi-containing nitride or AlCrSiW-containing nitride. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-70075 [Patent Document 2] Japanese Patent Publication No. 2020-20030 [Patent Document 3] Special Publication No. 2018-521862 [Patent Document 4] International Publication No. 2019 / 239654 [Patent Document 5] Japanese Patent Publication No. 2021-000668 [Patent Document 6] Japanese Patent Application Laid-Open No. 2008-173754 Summary of the Invention [Problem to be solved by the invention]

[0005] The cutting tools described in Patent Documents 1 to 6 are each said to be able to increase the hardness of the hard coating covering the substrate and improve the durability of the cutting tool. However, in reality, changes in the physical properties of the hard coating due to the cutting environment of the workpiece, particularly changes in physical properties due to frictional heat generated during cutting and the crystalline structure of the hard coating, cause serious problems with the tool life of the cutting tool. However, Patent Documents 1 to 6 do not specifically point out such problems or provide solutions.

[0006] For example, when cutting difficult-to-cut materials such as cemented carbide, hard coatings in contact with such materials rapidly wear and are prone to peeling or slipping off the substrate. This exposes the cutting edge of the cutting tool, partially destroying its shape, increasing cutting resistance and further increasing the coating temperature. Specifically, the coating temperature can exceed several hundred degrees Celsius in a short period of time. In this case, atmospheric oxygen accelerates the oxidation reaction of the hard coating, weakening the inter-element bonding strength, resulting in a synergistic and accelerated decrease in coating hardness and wear. As a result, not only does the hard coating wear, but it also becomes prone to peeling or slipping off the substrate. When the hard coating is removed from the substrate, cutting resistance increases further and the substrate itself wears more rapidly, significantly shortening the tool life beyond its designed (expected) value.

[0007] The present invention was devised in view of the above-mentioned problems, and its main object is to provide a cutting tool having a hard coating that is less susceptible to heat-generating factors such as frictional heat and changes in physical properties due to crystalline structure. [Means for solving the problem]

[0008] One aspect of the present invention is a coated cutting tool having a first nitride layer covering the surface of a substrate and having an oxidation resistance temperature in a first temperature range, and a second nitride layer covering the surface of the first nitride layer and having an oxidation resistance temperature in a second temperature range lower than the first temperature range, wherein the second nitride layer has a higher hardness than the first nitride layer up to the second temperature range, and the first nitride layer has a crystal orientation in the unheated state that is substantially the same as that in the first temperature range. Crystal orientation refers to the statistical properties of the crystal axis orientation as a texture in a polycrystalline thin film. [Effects of the Invention]

[0009] The coated cutting tool according to the present disclosure is coated with a hard coating that combines the advantages of the high oxidation resistance and highly stable crystal orientation of the first nitride layer and the high wear resistance of the second nitride layer, and therefore reduces the reduction in tool life caused by frictional heat during cutting compared to when the hard coating is not of this type. [Brief explanation of the drawings]

[0010] [Figure 1] Illustrative diagrams of the component ratio, O / N ratio, hardness, and XRD of six prototypes. [Figure 2] FIG. 2 is an explanatory diagram of the diffraction profile in XRD of FIG. 1. [Figure 3] This is an explanatory diagram of the diffraction profiles extracted from the XRD diffraction profiles in Figure 2 when not heated and when heated at 800°C for 10 minutes. [Figure 4] FIG. 1 shows comparative examples of physical properties resulting from changes in the component ratios of two representative prototypes. [Figure 5] Enlarged photographs of the cutting edge of a cutting tool show (a) the state before use and (b) the state at the end of its life. [Figure 6] 1 is a schematic cross-sectional view showing an example of the structure of a hard coating having a surface-modified region. [Figure 7] FIG. 4 is a schematic cross-sectional view showing another example of a two-layer hard coating structure. [Figure 8] FIG. 4 is a schematic cross-sectional view showing another example of a two-layer hard coating structure. [Figure 9] FIG. 4 is a schematic cross-sectional view showing another example of a two-layer hard coating structure. [Figure 10] FIG. 4 is a schematic cross-sectional view showing an example of the structure of a coated cutting tool according to a second embodiment. [Figure 11] 10(a) to 10(c) are diagrams showing variations of the three-layer structure in the second embodiment. [Figure 12] An enlarged photograph showing that multiple laminated layers are formed even in thin films. [Figure 13] FIG. 10 is a schematic cross-sectional view showing an example of the structure of a coated cutting tool according to a third embodiment. [Figure 14] FIG. 10 is a schematic cross-sectional view showing an example of the structure of a coated cutting tool according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings, in which a cutting tool having a hard coating is applied. The cutting tool is, for example, an end mill having a cutting edge, the surface of which is coated with a hard coating. The cutting edge is formed at the tip and the outer periphery near the tip of a base material having a predetermined shape, for example, a substantially cylindrical shape, and a predetermined cutting diameter. In the following description, for convenience, an example using a ball end mill will be described.

[0012] [Base material] The substrate may be, for example, cemented carbide, cBN, cermet, or high-speed steel. Cemented carbide comes in various types, such as P, M, K, N, S, and H, depending on the added components, and any type may be used. One preferred example is tungsten carbide (WC) and cobalt (Co) powder sintered at high temperature under pressure. cBN is a sintered body of cubic boron nitride (B). Cermets are titanium compounds, such as titanium carbide (TiC) and titanium carbonitride (TiCN), bonded with nickel (Ni) or cobalt (Co).

[0013] [Hard coating] The hard coating is a nitride containing multiple elements and can be formed on a substrate using physical vapor deposition (PVD) or other methods. For example, a rotatable table is installed in a vacuum deposition furnace equipped with an arc discharge device. The substrate is held by a jig attached to the table, and a target (coating material, hereinafter the same) selected according to the physical properties of the coating is placed at a separate position in the vacuum deposition furnace. The table is rotated to bring the substrate closer to the target. The vacuum deposition furnace is evacuated, and the substrate is heated to a suitable temperature using a heater for heating the substrate. A bias voltage is applied to the substrate, and the necessary reactive gases are introduced into the vacuum deposition furnace, generating an arc discharge. This allows a film corresponding to the target to be formed on the substrate.

[0014] In this embodiment, we propose a hard coating that can suppress wear caused by frictional heat during cutting and fluctuations in crystal orientation caused by frictional heat, thereby extending the life of tools coated with it. To this end, the inventors first prototyped the following nitride layers, i.e., layers composed of nitrogen atoms (N) combined with other elements, using the PVD method, which were expected to have sufficient oxidation resistance and wear resistance for cutting difficult-to-cut materials such as cemented carbide steel, and analyzed the physical properties of each prototype. Among the film types listed below, "Ti" stands for titanium, "Si" for silicon, "Cr" for chromium, "Al" for aluminum, and "W" for tungsten.

[0015] <Prototype> <Film type> Prototype #1 TiSiN layer Prototype #2 TiAlCrN layer Prototype example #3 TiAlCrN-TiSiN multilayer Prototype #4 AlCrN layer Prototype #5 AlCrSiN layer Prototype #6 AlCrSiWN layer

[0016] In this embodiment, the substrate used to coat the prototypes is a cemented carbide alloy with a blade diameter of 2 mm, made by sintering tungsten carbide (WC) and cobalt (Co) powders at high temperature under pressure. The shape, size, and material of the substrate are the same for all prototypes, and the film thickness (3±0.5 μm) is also the same for each prototype. If the coating thickness is too thin, the desired performance cannot be achieved, while if it is too thick, the coating on the cutting edge will chip, immediately reducing the tool life and the quality of the machined surface, and deteriorating the dimensional accuracy of the tool. For this reason, the relationship between the type of cutting tool, cutting edge diameter, and hard coating thickness was established as above based on statistical data measured using actual measurements. When the cutting edge diameter is changed, the coating thickness will also be changed according to the above relationship.

[0017] Prototype #3 corresponds to the first layer of the two-layer hard coating described in Patent Document 1 disclosed by the applicant of the present application, and is a layer in which a first film made of thin TiSiN with an average thickness of about 10 nm to 60 nm and a second film made of thin TiAlCrN are alternately laminated.

[0018] Examples of the analysis results for Prototype Examples #1 to #6 are shown in Figure 1. Figure 1 shows an example of the component ratio, O / N ratio, hardness (Hv), and XRD (diffraction profile) for each prototype. Note that the analysis results in Figure 1 show representative examples of multiple prototypes of the same film type. Since not all targets are deposited on the substrate surface, there is some variation among the prototypes. However, the tendency of physical properties is the same for each prototype, regardless of the layer thickness (film thickness).

[0019] In Figure 1, the "component ratio" is the result of analyzing the composition of the coating excluding the nitrogen content using energy dispersive X-ray spectroscopy (EDS analysis), and is shown in atomic composition percentage (at%) excluding the nitrogen content. The measuring instrument used for the analysis was a JEOL JCM6000 electron microscope, and the analysis range was a 2000x field of view of the coating. The analysis conditions were an accelerating voltage of 15 kV and a probe current of 1.0 nA.

[0020] The "O / N ratio" is the ratio of O (oxygen) to N (nitrogen) detected on the coating surface by EDS analysis. The O / N ratio is one of the important factors for evaluating oxidation resistance, as it takes on a large value depending on the degree of progress of the oxidation reaction on the coating surface due to heating in air. The amount of nitrogen without heating is the amount of nitrogen in the coating itself as a nitride. All temperatures shown in FIG. 1 are in degrees Celsius (°C), and for ease of measurement, the temperature ranges that continue for a predetermined time are classified in increments of 100°C, for example. In this embodiment, the predetermined time is set to 10 minutes, but this is for convenience and may be 1 minute or more but less than 10 minutes, or 10 minutes or more. "Without heating" refers to the initial temperature, i.e., room temperature. For example, "heated to 600°C for 10 minutes" means that a temperature range of approximately 600°C continued for 10 minutes. The same applies to other temperature ranges. The measuring device used was a JEOL JCM6000 electron microscope (with EDS), and each coating was analyzed at a magnification of 2,000. The analysis conditions were an acceleration voltage of 15 kV and a probe current of 1.0 nA.

[0021] Referring to FIG. 1, the O / N ratio of prototype #1 was 0.08 without heating, 0.42 when heated at 600°C for 10 minutes (heating refers to heating in air; the same applies below), 1.01 when heated at 700°C for 10 minutes, and 1.83 when heated at 800°C for 10 minutes. The oxidation-resistant temperature is the temperature at which an O / N ratio of less than 1.0 can be maintained for a predetermined time (10 minutes in this example), which is 600°C for prototype #1. The O / N ratios for the other prototypes #2 to #6 are similarly described. The oxidation-resistant temperatures for the six prototypes are as follows. Note that prototypes #3 and #4 had O / N ratios less than 1.0 but close to 1.0 when heated at 1000°C for 10 minutes. Taking into account the above-mentioned variations during film formation, the former was classified as 700°C and the latter as 900°C.

[0022] <Prototype> <Oxidation resistance temperature> Prototype #1 600℃ Prototype #2 700℃ Prototype #3 700℃ Prototype #4 800℃ Prototype #5 900℃ Prototype #6 900℃

[0023] Note that O / N ratios at temperatures not shown in Figure 1 are omitted (denoted as "-") because, for example, the O / N ratio of prototype #1 after 10 minutes of heating at 900°C was already above 1.0 at temperatures prior to that. Conversely, prototypes #4, #5, and #6 had O / N ratios in the 0.1 range even after 10 minutes of heating at 800°C, meaning that their O / N ratios were smaller even at temperatures prior to that.

[0024] "Hardness" refers to the Vickers hardness (Hv: hereafter simply referred to as "hardness") of the coating surface, which changes as oxidation of the coating progresses due to heating. The hardness of the coating decreases as oxidation progresses, so it is used as one of the factors for evaluating oxidation resistance. The measuring device used was an Elionix ENT-1100a ultra-microindentation hardness tester, and the analysis conditions were a test load of 10 mN and a test load holding time of 1,000 msec.

[0025] Referring to Figure 1, the hardness of Prototype #1 was 3288 Hv without heating (initial temperature; same below), the highest among all the prototypes. However, after 10 minutes of heating at 700°C, it dropped to 2140 Hv, making it unsuitable for processing at temperatures higher than this. This fact corresponds to the oxidation-resistant temperature of 600°C. Similarly, the hardness of Prototype #2 was 3075 Hv without heating (initial temperature), 2974 Hv after 10 minutes of heating at 700°C, and dropped to 1974 Hv after 10 minutes of heating at 800°C. The hardness of Prototype #3 was 3176 Hv without heating, 3078 Hv after 10 minutes of heating at 700°C, and dropped to 2233 Hv after 10 minutes of heating at 800°C.

[0026] The hardness of prototype #4 was 3004 Hv without heating, and 2772 Hv after heating at 800°C for 10 minutes, and the degree of change in hardness decrease was smaller than that of prototype #3. This is because AlCrN has a lower hardness than TiSiN without heating, but its oxidation resistance temperature is higher than that of TiSiN. However, the hardness of prototype #4 decreased to 1875 Hv after heating at 900°C for 10 minutes, and the hardness change rate from heating at 800°C for 10 minutes was 32%.

[0027] In contrast, although the unheated hardness of prototypes #5 and #6 was in the 2800 Hv range, lower than that of prototypes #1 to #4, it maintained a hardness of the 2800 Hv range even after 10 minutes of heating at 800°C, and even after 100°C higher heating at 900°C, it maintained a hardness of the 2700 Hv range. In other words, the change in hardness from unheated to 10 minutes of heating at 800°C was 0.2% for prototype #5 and 2% for prototype #6. Furthermore, the change in hardness from 10 minutes of heating at 800°C to 10 minutes of heating at 900°C was 4.2% for prototype #5 and 0.1% for prototype #6. These prototypes #5 and #6 demonstrated significant suppression of the oxidation reaction.

[0028] XRD is an X-ray diffraction technique that can reveal various information about polycrystalline materials. In this embodiment, XRD is used to examine the diffraction profile of a coated cutting tool, which shows changes in the diffracted X-ray intensity caused by heating. This profile, including the position, intensity, width, shape, and shift of peaks where the diffracted X-ray intensity significantly increases relative to the angles (2θ: degrees) before and after the peak, is used to examine the crystal orientation. The examination is performed using the well-known "θ-2θ measurement." In the figure, the vertical axis represents the diffracted X-ray intensity (I), and the horizontal axis represents the diffraction angle, i.e., the angle (2θ) between the incident X-ray direction and the diffracted X-ray direction. The peak position (2θ) is related to the crystal lattice constant. The peak intensity indicates how strongly a particular crystal plane diffracts. The higher the peak intensity, the more pronounced the orientation of the crystal structure of each prototype. However, peak intensity is affected by the film thickness. The peak width is related to the crystal size, distortion, and elemental microstructure. The peak shape tends to become more asymmetric as the crystal structure becomes more heterogeneous. A shift in peak position (change in 2θ) can indicate chemical changes or stress within the crystal.

[0029] In the example in Figure 1, diffraction profiles corresponding to the temperature ranges at which hardness was measured are shown for each of prototypes #1 to #6. The bottom diffraction profile is that without heating, and the temperature ranges increase as you move up the profile. As oxidation of the coating progresses due to heating, the crystal orientation changes due to the oxides formed, which in turn changes the physical properties, and this is therefore one of the factors used to evaluate oxidation resistance. The measuring device used was a Rigaku XRD SmartLab, and the analytical method was the oblique incidence method. The analytical conditions were an X-ray output of 45 kV and 200 mA, a scan speed of 3.0 deg. / min, and a scan range of 30 to 70 deg.

[0030] For the "XRD" in Figure 1, to facilitate comparison of crystal orientation, the diffraction profile in Figure 2 shows the variation in diffracted X-ray intensity I, with the base axis common to each temperature range. In Figure 2, (0) represents the diffraction profile without heating, (7) represents the diffraction profile after heating at 700°C for 10 minutes, and (9) represents the diffraction profile after heating at 900°C for 10 minutes. Also, Figure 3 shows the diffraction profiles extracted from Figure 2 without heating and after heating at 800°C for 10 minutes.

[0031] In Figure 3, (8) represents the diffraction profile after heating at 800°C for 10 minutes. In Figures 1 to 3, there are peaks of diffracted X-ray intensity near 36° and 49° on the horizontal axis (2θ), which do not change position regardless of the heating temperature. These are information about the substrate that is commonly obtained across all prototypes. The diffraction profile from near 36° to 49° reflects the variation in crystal orientation caused by the progression of oxidation on the coating surface in each temperature range. Typical peaks of diffracted X-ray intensity for this type of hard coating are near 37° and 43° on the horizontal axis, which correspond to the (111) and (200) planes, respectively, of the crystal structure that follows the well-known "hkl" law.

[0032] Comparing the diffraction profiles in Figures 1 to 3, prototype #1 has a crystal structure strongly oriented to the (200) plane, and the position of the diffracted X-ray intensity peak shifts depending on the temperature range, with large intensity fluctuations. Prototypes #2 and #4 have crystal structures strongly oriented to the (111) and (200) planes, respectively, and the position of the diffracted X-ray intensity peak shifts depending on the temperature range, with large intensity fluctuations. Prototype #3 has a crystal structure strongly oriented to the (200) plane, and the position of the diffracted X-ray intensity peak shifts depending on the temperature range, although not as much as prototypes #2 and #4, and the intensity fluctuations are also large.

[0033] Although the crystal structure of Samples #5 and #6 exhibits peaks in the diffracted X-ray intensity on the (111) and (200) planes, the peaks are smaller than those of Samples #1 to #4 at any temperature range, with small variations in intensity and small shifts in the peak positions. Furthermore, the half-widths of Samples #5 and #6 near the (200) plane are approximately 2° when unheated, heated at 800°C for 10 minutes, and heated at 900°C for 10 minutes, which are significantly larger than those of Samples #1 to #4. In particular, as shown in Figure 3, Samples #5 and #6 exhibit crystal orientations that are approximately, or essentially, identical to those when unheated and in the temperature range near the oxidation-resistant temperature (heated at 800°C for 10 minutes).

[0034] "Substantially the same" means that the crystal orientations are similar enough to be considered identical. Whether or not they are considered identical can be determined by whether the ratio of changes in at least two of the peak position, shape, shift amount, half-width, and crystal plane spacing in each temperature range is less than a predetermined value compared to when not heated. In one embodiment, if the ratio of the above changes is less than 1.18 (equivalent to a film thickness of 3 μm) compared to when not heated, the two samples exhibit similar physical properties and can be considered to be substantially identical. In addition, whether or not the positions and dominance of the oriented crystal planes (the (111) plane and the (200) plane in the example of Figure 2) are the same can also be included as one of the criteria for whether or not they are "substantially the same."

[0035] For the (200) plane of Sample #6, the unheated X-ray diffraction intensity peak height was 334 counts and the half-width was 2.06 degrees, whereas after heating at 800°C for 10 minutes the X-ray diffraction intensity peak height was 300 counts and the half-width was 2.00 degrees. These variations can be taken as an example of the above-mentioned predetermined value. This fact indicates that the unheated crystal structure is maintained without distortion up to the oxidation-resistant temperature, i.e., a highly stable crystal orientation is maintained.

[0036] Thus, compared to prototypes #1 to #4, prototypes #5 and #6 showed almost no distortion in crystal orientation even when the heating temperature due to friction increased. In other words, prototypes #5 and #6 had stable crystal orientation at most temperatures that affect tool life compared to prototypes #1 to #4. It is believed that the reason the above-mentioned change in hardness due to temperature change is suppressed is due to this stable crystal orientation.

[0037] [Comparison of physical properties of prototype examples] From the above test results, it was found that each prototype had the following physical properties. Prototype #1: High hardness without heating and excellent wear resistance, but insufficient oxidation resistance. Prototype #2: Compared to prototype #1, it has lower hardness but higher oxidation resistance temperature. However, both the hardness and oxidation resistance temperature are lower than those of prototype #3. Prototype #3: Compared to prototype #2, both hardness and oxidation resistance temperature are higher. Prototype #4: Hardness is lower than prototypes #1 to #3, but because it does not contain Ti, High oxidation resistance temperature. The change in hardness between heating at 800°C and heating at 900°C is 32%. Prototype #5: Compared to prototype #4, it has lower hardness but higher oxidation resistance temperature. The crystal orientation is also stable. The change in hardness between heating at 800°C and heating at 900°C is 4.2%. Prototype #6: Hardness and oxidation temperature resistance are equivalent to those of prototype #5. The crystal orientation is also stable. The change in hardness between heating at 800°C and heating at 900°C is 1%.

[0038] [Comparison of physical properties using representative prototypes] Both Prototype Example #5 and Prototype Example #6 showed physical properties with stable crystal orientation within the layer. However, it was considered that in Prototype Example #5, the Si concentration in the nitride layer mainly had an impact, while in Prototype Example #6, the W concentration in the nitride layer mainly had an impact. Therefore, the hardness and oxidation resistance temperature (°C) without heating were measured when the component ratios in these film types were changed. The measurement results for representative composition concentrations are shown in Figure 4.

[0039] The upper part of Figure 4 shows an example of Prototype Example #6. Here, when the total of the element group excluding N was set to 100 at% (=1), the ratio of Si was 8 ± 1 at%, and examples of the component ratios of each element (analysis results after film formation), hardness (hardness according to individual component ratios), and oxidation resistance temperature when the W concentration was changed are shown. In actual film formation, not all of the target is formed on the substrate surface, so there is some variation depending on the prototype example. However, as described above, the tendency of the physical properties is the same in this prototype example regardless of the layer thickness (film thickness).

[0040] According to the results in the upper part of Figure 4, when the component ratios of Al, Cr, Si, and W are expressed by the composition formula AlaCrbSicWd, it was found that the oxidation resistance temperature described above can be maintained by satisfying the following relationships for a, b, c, and d indicating the component ratios of the elements excluding N. 0.5 ≤ a ≤ 0.6 0.2 ≤ b ≤ 0.4 0.08 ≤ c ≤ 0.09 0.01 ≤ d ≤ 0.06, especially 0.01 ≤ d ≤ 0.03 a + b + c + d = 1 (= 100 at%)

[0041] Also, the lower part of Figure 4 shows an example of Prototype Example #5. When Al, Cr, and Si are expressed by the composition formula AlaCrbSic, it was found that it is preferable that a, b, and c indicating the component ratios of the elements satisfy the following relationships. 0.5 ≤ a ≤ 0.6 0.3 ≤ b ≤ 0.4 0.05 < c ≤ 0.11, especially 0.08 < c ≤ 0.1 a + b + c = 1 (= 100 at%)

[0042] [Tool life of prototype example] As far as oxidation resistance (high oxidation resistance temperature) is concerned, prototypes #1 and #2 are not necessarily sufficient. Therefore, prototypes #3 to #6, which can be evaluated as having excellent oxidation resistance, were measured to see what kind of performance they actually exhibited from the perspective of tool life. The measurement conditions were as follows: Cutting tool: 2-flute ball end mill with a blade diameter of φ2 mm and made of cemented carbide substrate (Standard product manufactured by NS TOOL Co., Ltd.) Total thickness of hard coating on cutting edge: approx. 3 μm (average 2.95 μm) Work material:STAVAX(52HRC) Cutting speed Vc:94.2m / min, Rotation speed n: 25000 min -1 , Feed rate Vf: 2500 mm / min, 1 tooth feed fz: 0.05mm / tooth Axial cutting depth x radial cutting depth: 0.2 mm x 0.5 mm Tool life criteria: The wear width of the cutting edge exceeds 20% of the flank (second face), And / or, the cutting edge has been deformed to the extent that it is impossible to measure the wear width.

[0043] An example of the criteria for tool life is shown in Figure 5. Figure 5 is an enlarged photograph of the cutting edge of a cutting tool, where (a) shows the state before use and (b) shows the state at the end of the tool's life. The substrate in the tool's life state is considered to be before it reaches a critical value that reduces the yield of the workpiece. The time from the start of cutting until the tool is judged to have reached its end of life is as follows, and for prototypes #4 to #6, all of these were shorter than prototype #3 (single layer) disclosed in Patent Document 1.

[0044] <Prototype example> <Tool life> Prototype #3 9 hours 20 minutes Prototype #4 4 hours 40 minutes Prototype #5 6 hours 20 minutes Prototype #6 7 hours

[0045] Based on the physical properties and performance tests of the above prototypes #1 to #6, the inventors further prototyped two-layer hard coatings that were expected to mutually complement each other in terms of oxidation resistance, wear resistance, and highly stable crystal orientation, and verified the tool life of each. Specifically, the hard coating disclosed in Patent Document 1 (a hard coating in which the above-mentioned prototype #3 was used as the first nitride layer and the above-mentioned prototype #1 (TiSiN layer), which had the highest coating hardness without heating, was used as the second nitride layer) was designated as the "Reference Example." This Reference Example and the hard coatings of the following prototypes #7 to #12 were then formed on the surface of the above-mentioned substrates, and their physical properties and performance were compared. The component ratios of the film species in each layer were the same as those in the "Component Ratio" in Figure 1, and the film thicknesses of the first nitride layer and the second nitride layer were set to about half (about 1.5 μm) of those of prototypes #1 to #6, respectively, resulting in a total film thickness equivalent to that of each of the above-mentioned prototypes.

[0046] Reference example: TiAlCrN-TiSiN multilayer layer + TiSiN layer Prototype #7: AlCrSiWN layer + AlCrN layer Prototype #8: AlCrSiWN layer + TiAlCrN layer Prototype #9: AlCrSiWN layer + TiSiN layer Prototype #10: AlCrSiN layer + AlCrN layer Prototype #11: AlCrSiN layer + TiAlCrN layer Prototype #12: AlCrSiN layer + TiSiN layer

[0047] In prototypes #7 to #12, the first target contained elements with the composition ratio of the first nitride layer, and the second target contained elements with the composition ratio of the second nitride layer. Nitrogen gas was introduced into a vacuum deposition furnace as a reactive gas, and an arc discharge was generated with the first or second target, which was the evaporation source, as the cathode to ionize the evaporated elements, which were then deposited as nitrides containing the ionized elements on the surface of a substrate to which a bias voltage was applied.

[0048] [Comparison of physical properties] The O / N ratio, Young's modulus (GPa), and hardness (Hv) without heating in the reference example and prototype examples #7 to #12 were as follows. In prototype examples #9 and #12, the Young's modulus is relatively small with respect to the hardness (Hv), so the amount of deformation that elastically responds to the stress (external force) from the workpiece is reduced.

[0049] <Film type> <O / N ratio> <Young's modulus> <Hardness (Hv)> Reference example 0.06 480 3288 Prototype example #7 0.04 346 2988 Prototype example #8 0.05 411 3145 Prototype example #9 0.00 360 3284 Prototype example #10 0.03 340 2995 Prototype example #11 0.06 414 3155 Prototype example #12 0.01 356 3292

[0050] [Performance comparison] The performance actually exhibited by prototype examples #7 to #12 was measured from the perspective of the tool life length. The measurement conditions were the same as above. The measurement results were as follows. The tool lives of prototype examples #7, #8, #10, and #11 were all shorter than that of the reference example, but the tool life of prototype example #9 was 1.62 times that of the reference example, and the tool life of prototype example #12 was 1.58 times that of the reference example.

[0051] <Film type> <Tool life> Reference example 9 hours 20 minutes Prototype example #7 5 hours 50 minutes Prototype example #8 7 hours Prototype example #9 15 hours 10 minutes Prototype example #10 5 hours 30 minutes Prototype example #11 6 hours 20 minutes Prototype example #12 14 hours 30 minutes

[0052] The tool life of prototypes #9 and #12 was longer than that of the reference sample. This is thought to be because both samples combined the advantages of the first nitride layer's high oxidation resistance and highly stable crystal orientation with the second nitride layer's high wear resistance, thereby suppressing wear of the hard coating, which is accelerated by frictional heat during cutting. In fact, the second nitride layer exhibited wear resistance almost equivalent to that of the reference sample until the oxidation resistance temperature was reached. Then, once the oxidation resistance temperature was exceeded and the second nitride layer wore down, the hardness of the first nitride layer became relatively high and was able to maintain its high oxidation resistance for a longer period, thereby extending tool life.

[0053] [Comparison between prototype #9 and prototype #12] Both Samples #9 and #12 showed improved tool life compared to the Reference Sample, but Sample #9 had a longer tool life than Sample #12. Sample #9 differs from Sample #12 in that the first nitride layer is the same as Sample #6, and the composition of Sample #5 is increased by increasing the Al content, decreased by decreasing the Cr and Si content, and a small amount of W is added. This difference, which resulted in Sample #9 having a longer tool life than Sample #12, is likely due not only to the differences in the types of elements and their composition ratios, but also to the presence of a surface-modified region on the outermost surface of the substrate in Sample #9. This is explained with reference to Figure 6.

[0054] Fig. 6 is a schematic cross-sectional view showing an example of the structure of the hard coating of Prototype #9. Referring to Fig. 6, Prototype #9 has a hard coating 2 with a total thickness of TAB, in which an AlCrSiWN layer (Prototype #6 with a thickness of 1 / 2) is coated on the surface of a substrate 1 as a first nitride layer 3 with a thickness of TA, and a TiSiN layer (Prototype #1 with a thickness of 1 / 2) is coated on the surface of the first nitride layer 3 as a second nitride layer 4 with a thickness of TB. The TA and TB are about 1.5 μm, and the TAB is 3 μm. This two-layer structure itself is the same for prototypes #7, #8, #10, #11, and #12. However, in the case of prototype #9, a surface-modified region 11 with a thickness T11 exists on the outermost surface of the substrate 1. T11 is approximately 10 nm to approximately 30 nm.

[0055] The surface-modified region 11 is a region in which one or more elements commonly contained in the substrate 1 and the first nitride layer 3, i.e., elements including tungsten (W), are irregularly mixed from the first nitride layer 3 toward the interior (e.g., the central axis) of the substrate 1. When these elements are randomly irradiated toward the outermost surface of the substrate 1, the outermost surface of the substrate 1 becomes uneven, and further, the inter-element bonding strength between the W of the substrate 1 and the W that constitutes part of the first nitride layer 3 is strengthened, or multiple W elements are integrated within the surface-modified region 11. This prevents the first nitride layer 3 from peeling off or sliding off from the substrate 1.

[0056] The above explanation is based on the assumption that the substrate 1 is made by sintering tungsten carbide (WC) and cobalt (Co) powders under pressure at high temperature. If the elements constituting the substrate 1 are other types of elements, a similar surface modified region 11 can be formed by incorporating such elements into the first nitride layer 3.

[0057] As described above, the AlCrSi-containing nitride and AlCrSiW-containing nitride cannot utilize their high oxidation resistance by themselves. However, by laminating a high-hardness TiSi-containing nitride on top of the AlCrSi-containing nitride to form a two-layer structure, and mutually complementing each other's advantages, it has become possible to realize a hard coating that combines the advantages of the high oxidation resistance and highly stable crystal orientation of the first nitride layer and the high wear resistance of the second nitride layer.

[0058] [Modification of the first embodiment] One of the points of focus of the inventors in the first embodiment is that, in the example of FIG. 6 , the substrate 1 has a first nitride layer 3 covering the surface thereof and a second nitride layer 4 covering the surface thereof, the first nitride layer 3 having an oxidation resistance temperature in a first temperature range (e.g., 800°C for 10 minutes), the second nitride layer 4 having an oxidation resistance temperature in a second temperature range (e.g., 600°C for 10 minutes) lower than the first temperature range, the second nitride layer 4 having a higher hardness than the first nitride layer 3 up to the second temperature range, and the first nitride layer 3 having a crystal orientation in the first temperature range that is substantially the same as that in the unheated state. Therefore, in addition to the above-described embodiment, various modifications can be implemented. Further prototype examples according to the modifications will be described below with reference to FIGS. 7 to 9. For convenience, the substrate 1, the first nitride layer 3, the second nitride layer 4, and the thicknesses of the layers shown in FIG. 6 will be described using the same reference numerals as in FIG. 6.

[0059] <Prototype #13> FIG. 7 is a schematic cross-sectional view showing an example of the structure of the hard coating of prototype #13. In prototype #13, the first nitride layer 21 is the thin film of prototype #6, the second nitride layer 22 is the thin film of prototype #1, and the hard coating is composed of only a multilayered layer 20 formed by alternately stacking these layers. The outermost surface is preferably the film of prototype #1. The average film thicknesses of the first nitride layer 21 and the second nitride layer 22 are both 10 nm to 60 nm, and the total film thickness TAB of the multilayered layer 20 is approximately 3 μm.

[0060] By forming the first nitride layer 21 and the second nitride layer 22 into thin films and stacking them alternately to form a multilayered layer 20, as shown in Patent Document 1, the crystal grains of each layer 21, 22 can be refined, resulting in even higher strength. When manufacturing prototype #13 using the PVD method, for example, the first target is AlCrSiW, the second target is TiSi, nitrogen gas is introduced as the reactive gas into a vacuum deposition furnace, and an arc discharge is generated with the first or second target (the evaporation source) as the cathode, ionizing the evaporated elements, which can then be deposited in the form of nitrides on the surface of the substrate to which a bias voltage is applied. The tool life of prototype #13 was 14 hours and 30 minutes, approximately 1.55 times that of the reference example (9 hours and 20 minutes).

[0061] <Prototype #14> FIG. 8 is a schematic cross-sectional view showing an example of the structure of the hard coating of Prototype #14. In Prototype #14, the layer corresponding to the first nitride layer is the multilayer layer 30 of Prototype #13, and the second nitride layer 4 is Prototype #1. The thickness TA of the multilayer layer 30 is half the thickness TAB of the multilayer layer 20 of Prototype #13. The thickness TB of Prototype #1 is approximately 1.5 μm, and the total thickness TAB is approximately 3 μm. The layer of the multilayer layer 30 in contact with the outermost surface of the substrate 1 is preferably the film of Prototype #6. While Prototype #1 inherently has high hardness, as shown in Patent Document 1, epitaxial growth is promoted during film formation in imitation of the multilayer layer 30 with its refined grain size, resulting in finer grain size and even higher hardness. The tool life of prototype #14 was 14 hours and 20 minutes, which was approximately 1.54 times longer than the tool life of the reference example (9 hours and 20 minutes).

[0062] <Prototype #15> Figure 9 is a schematic cross-sectional view showing an example of the structure of the hard coating of prototype #15. In prototype #15, the first nitride layer 3 is the same as in prototype #5, and the layer corresponding to the second nitride layer is the multilayered layer 40 of prototype #13, with the multilayered layer 40 being half the thickness of prototype #13. The average thickness of each layer in the multilayered layer 40 is 10-60 nm, with a total thickness TB of approximately 1.5 μm. In prototype #5, the thickness TB is approximately 1.5 μm, and the total thickness TAB is approximately 3 μm. The tool life of prototype #15 was 14 hours and 40 minutes, which was approximately 1.57 times longer than that of the reference example (life of 9 hours and 20 minutes).

[0063] <Prototype #16> Prototype #16 has the same structure as the schematic cross-sectional view of Figure 7. For convenience, the same reference numerals as in Figure 7 are used. Prototype #16 is constructed solely of a multilayered layer 20, in which the first nitride layer 21 is the thin film of Prototype #5 and the second nitride layer 22 is the thin film of Prototype #1, alternately stacked multiple times. The average film thickness is, for example, 10 nm to 60 nm, with a total film thickness of approximately 3 µm. By alternately stacking the first nitride layer 21 and the second nitride layer 22 as thin films, the crystal grains can be refined, which further increases the strength of the multilayered layer 20. The tool life of Prototype #16 was 13 hours and 50 minutes, approximately 1.48 times that of the Reference Example (9 hours and 20 minutes).

[0064] <Prototype #17> Prototype sample #17 has the same structure as the schematic cross-sectional view of Figure 8. For convenience, the same reference numerals as in Figure 8 are used to describe the structure. In prototype sample #17, the first nitride layer was made of the multilayered layer 30 of prototype sample #16, and the second nitride layer 4 was made of prototype sample #1. The average thickness of the multilayered layer 30 is, for example, 10 nm to 60 nm, and the total thickness TAB is about 3 μm. The tool life of prototype #17 was 14 hours and 20 minutes, which was approximately 1.54 times longer than the tool life of the reference example (9 hours and 20 minutes).

[0065] <Prototype #18> Sample #18 has the same structure as the schematic cross-sectional view of Figure 9. For convenience, the same reference numerals as in Figure 9 are used to describe Sample #18. The first nitride layer 3 of Sample #18 is made of Sample #5, and the second nitride layer is made of the multilayered layer 40 of Sample #16. The average thickness of the multilayered layer 40 is, for example, 10 nm to 60 nm, and the total thickness TAB is about 3 μm. The tool life of prototype #17 was 14 hours and 10 minutes, which was approximately 1.52 times longer than the tool life of the reference example (9 hours and 20 minutes).

[0066] In this way, in prototypes #13 to #18, by providing a hard coating that combines a nitride layer that has excellent oxidation resistance and stable crystal orientation even when the temperature changes, with a nitride layer that has excellent wear resistance, it is possible to realize a cutting tool with a longer tool life than the reference example (a cutting tool with a hard coating shown in Patent Document 1).

[0067] In addition, in the case where Prototype Example #1 is used for the second nitride layer in the two-layer hard coating, when the composition of elements other than nitrogen in TiSiN is expressed as TixSi1-x, it is desirable that x, which indicates the composition ratio of each element, satisfy the following relational expression: 0.6≦x≦0.9

[0068] In the first embodiment, it is assumed that the substrate 1 is a cemented carbide alloy obtained by sintering tungsten carbide (WC) and cobalt (Co) powders at high temperature while applying pressure, but the present invention can also be applied to cases where cBN, cermet, or high-speed steel is used as the substrate. In the first embodiment, the cutting tool is described as a two-flute ball end mill with a cutting edge diameter of 2 mm, but the diameter size and cutting edge shape may be other. Furthermore, the present invention is applicable not only to ball end mills, but also to square end mills, roughing end mills, radius end mills, tapered end mills, and other end mills or drills.

[0069] The surface-modified region 11 shown in FIG. 6 can be formed on the outermost layer of the substrate 1 in a manner different from that described above. For example, prior to the film-forming process on the substrate 1, compressed air at a discharge pressure of about 0.5 MPa can be irradiated at high speed to roughen the surface of the substrate 1, and then the first nitride layer 3 can be formed. Alternatively, together with or instead of compressed air, an element different from the elements constituting the substrate 1 can be irradiated toward the interior of the substrate 1 at high speed or high pressure to form irregularities on the outermost surface of the substrate 1, and then the first nitride layer 3 can be formed. In this way, a surface-modified region can be formed that is not limited by the type of substrate 1.

[0070] Second Embodiment In the first embodiment, an example of a hard coating with a two-layer structure was described. However, as a result of further investigation by the inventors, it was found that a hard coating with a structure of two or more layers can provide a significant effect of extending the tool life of a single hard-coated tool, not only in rough machining but also in finish machining. Therefore, in the second embodiment, an example of a hard coating with a three-layer structure will be described first. Items in this embodiment that are not particularly different, such as the substrate 1 and its size, hard coating prototypes #5 and #6, and the modifications in Figures 7 to 9, are the same as those in the first embodiment.

[0071] 10 is a schematic cross-sectional view showing an example of the structure of a coated cutting tool according to the second embodiment. This coated cutting tool has a hard coating 2 that coats the surface of a substrate 1. The hard coating 2 coats the surface of the substrate 1 with a layer thickness T A the first nitride layer 3 and the layer thickness T B the second nitride layer 4 and the layer thickness T C and a third nitride layer 5. In one example, the first nitride layer 3 and the third nitride layer are AlCrSiWN layers similar to those of prototype #6, the composition of which is illustrated in FIG. 4, and the second nitride layer 4 is a TiSiN layer illustrated by reference numeral 4 in FIG.

[0072] When the composition ratio of Al, Cr, Si, and W (excluding N) in the first nitride layer 3 and the third nitride layer 5, an AlCrSiWN layer, is expressed as the composition formula AlaCrbSicWd, a, b, c, and d are expressed by the following conditions. The right-hand side of each shows the ratio that was frequently obtained. 0.50≦a<0.61, especially 0.50≦a<0.55 0.28≦b<0.38, especially 0.33≦b<0.36 0.06≦c<0.10, especially 0.07≦c<0.09 0.01≦d<0.07, especially 0.02≦d<0.07 a+b+c+d=1(=100at%) In applications where hardness is important, the Si content (condition c) of the first nitride layer 3 may be 7 at % or more and less than 11 at %. Of course, the Si content of the third nitride layer 5 as well as the first nitride layer 3 may also satisfy such a condition.

[0073] Hard coating 2 overall thickness T ABC is 3 μm, the same as the hard coating 2 of the first embodiment, but the thickness relationships among the nitride layers 3, 4, and 5 are as follows: T B >T A >T C For example, T ABC If we set it to 100%, T A 40% and T B 45% and T C However, when the film formation accuracy is taken into consideration, T A 30-50% in T B 35-55% and T C A variation of 10 to 20% is allowed.

[0074] When the physical properties of each layer were analyzed using the same procedure as described in the first embodiment, the O / N ratio (an index for evaluating oxidation resistance temperature), hardness (Hv), and XRD (diffraction profile) trend (an index for evaluating crystal orientation) of the first nitride layer 3 to the third nitride layer 5 were found to maintain nearly the same trends as those in the structure of the first embodiment (FIG. 1), even though the thickness of each layer was physically reduced. For example, the hardness (Hv) and oxidation resistance temperature of the first nitride layer 3 to the third nitride layer 5 were as follows: <Structure> <Hardness (Hv)> <Oxidation resistance temperature> First nitride layer 3,200 900℃ Second nitride layer 3,600 600℃ Third nitride layer 3,200 900℃

[0075] The hardness (Hv) of the first nitride layer 3 to the third nitride layer 5 is slightly different from that of prototypes #1 (TiSiN layer), #5 (AlCrSiN layer), and #6 (AlCrSiNW layer) of the first embodiment, but this is because the composition ratios of metal elements other than nitrogen (N) were kept the same while the film formation conditions (bias voltage, etc.) were finely adjusted. The hardness (Hv) of the second nitride layer 4 is higher than that of the first nitride layer 3 up to the oxidation resistance temperature of 600°C, and the crystal orientation of the first nitride layer 3 and the third nitride layer 5 when not heated is substantially the same as that at the oxidation resistance temperature of 900°C, as in the first embodiment.

[0076] According to this three-layer structure, the substrate 1 is coated with the hard coating 2 which combines the advantages of the high oxidation resistance and highly stable crystal orientation of the first nitride layer 3 and the third nitride layer 5, and the high wear resistance of the second nitride layer 4. This suppresses wear of the third nitride layer 5 which comes into contact with the workpiece due to frictional heat during cutting, thereby further suppressing the decrease in overall tool life compared to the first embodiment, and a single coated cutting tool can be used for rough machining through to finish machining.

[0077] <Examples of variations in three-layer structure> FIG. 11 shows a variation of the three-layer structure of the second embodiment. In FIG. 11(a), the first nitride layer 3 is a multilayer structure as shown in FIG. 8 and designated by reference numeral 30, the second nitride layer 4 is a TiSiN layer as shown in FIG. 8 and designated by reference numeral 4, and the third nitride layer 5 is an AlCrSiWN layer similar to that of prototype #6, the composition of which is shown in FIG. 4. In FIG. 11(b), the first nitride layer 3 is an AlCrSiWN layer similar to that of FIG. 11(a), the second nitride layer 4 is a TiSiN layer similar to that of FIG. 11(a), and the third nitride layer 5 is a multilayer structure similar to that of FIG. 11(a). In FIG. 11(c), the first nitride layer 3 and the third nitride layer 5 are AlCrSiWN layers similar to those of FIG. 11(a), and the second nitride layer 4 is a TiSiN layer similar to that of FIG. 11(a). The physical properties of each layer are as described in the first embodiment. Because of the three-layer structure, the thickness of each of the multilayered layers is smaller (thinner) than that of the two-layered structure example given in the first embodiment, but by adjusting the discharge timing of two cathodes each equipped with two types of targets, it is possible to easily form a multilayered layer, as shown in the enlarged photograph of Figure 12, for example.

[0078] In addition, even if at least one of the first nitride layer 3 and the third nitride layer 5, which is the AlCrSiWN layer, is replaced with the AlCrSiN layer of prototype #5 shown in the first embodiment, or if the multi-layered AlCrSiWN film is replaced with the AlCrSiN film of prototype #5, a hard coating 2 can obtain substantially the same effect as above. In this case, when the composition ratio of Al, Cr, and Si (excluding N) in the AlCrSiN layer and the AlCrSiN film in the multilayered layer is expressed by the composition formula AlaCrbSic, a, b, c, and d are expressed by the following conditions. The right-hand side of each shows the ratio obtained most frequently. 0.49≦a<0.61, especially 0.50≦a<0.55 0.30≦b<0.44, especially 0.36≦b<0.41 0.06≦c<0.11, especially 0.06≦c<0.10 a+b+c=1(=100at%)

[0079] <Third embodiment> In the third embodiment, an example of a four-layer hard coating will be described. The substrate 1 and its size, hard coating prototypes #5 and #6, and other aspects of this embodiment that are not specifically described as different are the same as those of the first embodiment. 13 is a schematic cross-sectional view showing an example of the structure of a coated cutting tool according to the third embodiment. The hard coating 2 of this coated cutting tool covers the surface of the substrate 1 and has a layer thickness T A and a layer having a thickness T B the second nitride layer 4 and the layer thickness T C and a layer having a thickness T D and a fourth nitride layer 6.

[0080] In one example, the first nitride layer 30 and the third nitride layer 50 are multi-layered layers as illustrated by the reference numeral 30 in FIG. 8, the second nitride layer 4 is a TiSiN layer similar to that shown in FIG. 11(a), and the fourth nitride layer 6 is an AlCrSiWN layer as described in the second embodiment. As explained in the first and second embodiments, the TiSiN layer has a higher hardness (Hv) than the AlCrSiWN layer up to around 600°C, and the AlCrSiWN layer has substantially the same crystal orientation in the temperature range around the oxidation resistance temperature as that in the unheated state. A-D is 3 μm, the same as the hard coating 2 of the first embodiment, but the relationship in thickness between the nitride layers 30, 4, 50, and 6 is as follows: T B >T A >T D >T C

[0081] The first nitride layer (multilayered layer) 30 may be the single-layered first nitride layer 3 described in the second embodiment, such as an AlCrSiWN layer or an AlCrSiN layer, and the fourth nitride layer 6 may also be the AlCrSiWN layer or an AlCrSiN layer. The first nitride layer 30 and the third nitride layer 50, which are multilayered layers, may also be alternately laminated films of AlCrSiN films and TiSiN films described in the second embodiment.

[0082] <Fourth embodiment> In the fourth embodiment, an example of a hard coating having a five-layer structure will be described. The substrate 1 and its size, hard coating prototypes #5 and #6, and other items in this embodiment that are not specifically described as different are the same as those in the first embodiment. 14 is a schematic cross-sectional view showing an example of the structure of a coated cutting tool according to the fourth embodiment. The hard coating 2 of this coated cutting tool covers the surface of the substrate 1 and has a layer thickness T A the first nitride layer 3 and the layer thickness T B The second nitride layer (multi-layered layer) 40 and the layer thickness T C and a layer having a thickness T DThe fourth nitride layer (multilayer laminated layer) 60 and the layer having a thickness T E The fifth nitride layer 7 is formed of the above.

[0083] In one example, the second nitride layer 40 and the fourth nitride layer 60 are the multilayered layers 30, 50 described in the third embodiment, i.e., alternately laminated films of AlCrSiNW films and TiSiN films, although they are thinner, the third nitride layer 5 is a TiSiN layer similar to that shown in FIG. 11(a), and the fifth nitride layer 7 is an AlCrSiWN layer or an AlCrSiN layer described in the third embodiment. The second nitride layer 40 and the fourth nitride layer 60 may be alternately laminated films of AlCrSiN films and TiSiN films. As explained in the first to third embodiments, the TiSiN layer (or film) has a higher hardness (Hv) than the AlCrSiWN layer (or film) and the AlCrSiN layer (or film) up to around 600°C, the crystal orientation of the AlCrSiWN layer or AlCrSiN layer when not heated is substantially the same as the crystal orientation in the temperature range around the oxidation resistance temperature, and the multilayered layer also has such physical properties. Hard coating 2 overall thickness T A-D is 3 μm, the same as the hard coating 2 of the first embodiment, but the thickness relationships among the nitride layers 3, 40, 5, 60, and 7 are as follows: T C >T A ≧T E >T B ≧T D

[0084] [Disclosure of the present specification] This specification discloses the following aspects of the invention. A first aspect is a coated cutting tool having a first nitride layer that coats the surface of a substrate and has an oxidation resistance temperature in a first temperature range, and a second nitride layer that coats the surface of the first nitride layer and has an oxidation resistance temperature in a second temperature range that is lower than the first temperature range, wherein the second nitride layer has a higher hardness than the first nitride layer up to the second temperature range, and the first nitride layer has a crystal orientation in the first temperature range that is substantially the same as that when unheated. In this embodiment, the substrate is coated with a hard coating that combines the advantages of the high oxidation resistance and highly stable crystal orientation of the first nitride layer and the high wear resistance of the second nitride layer, and therefore, the reduction in tool life caused by frictional heat during cutting is suppressed compared to cutting tools coated with films that are not such hard coatings.

[0085] The second aspect is a coated cutting tool according to the first aspect, wherein the first nitride layer has a change rate of less than 3% between its hardness when unheated and its hardness after maintaining the first temperature range for a predetermined period of time. This makes it possible to realize a first nitride layer with a crystal structure that is less susceptible to the effects of heating temperature.

[0086] A third aspect is a coated cutting tool according to the first aspect, wherein the first nitride layer has a hardness that changes less than 3% between its unheated hardness and its hardness after maintaining the first temperature range for a predetermined time, and further has a hardness that changes less than 5% between its hardness after maintaining the first temperature range for a predetermined time and its hardness after maintaining a temperature range 100 degrees Celsius higher than the first temperature range for a predetermined time. This makes it possible to realize a first nitride layer with a crystal structure that is less susceptible to the effects of heating temperature.

[0087] A fourth aspect is a coated cutting tool according to the first aspect, wherein the first nitride layer has an O / N ratio of less than 0.2 when maintained in the first temperature range for a predetermined time, and an O / N ratio of less than 0.35 when maintained in a temperature range 100 degrees Celsius higher than the first temperature range for a predetermined time. Such a first nitride layer can suppress the progress of oxidation reaction of the hard coating caused by frictional heat with the work material during high-speed machining, for example.

[0088] A fifth aspect is a coated cutting tool according to any one of the first to fourth aspects, wherein the first nitride layer is an AlCrSiW-containing nitride containing Al, Cr, Si, and W as metal elements, with the proportion of W in these metal elements being 1 at % or more but less than 5 at %, and the second nitride layer is a TiSi-containing nitride. This embodiment makes it possible to realize a hard coating that combines the advantages of the first nitride layer, which has high oxidation resistance and highly stable crystal orientation, and the advantages of the second nitride layer, which has high wear resistance.

[0089] A sixth aspect is a coated cutting tool according to the fifth aspect, in which a surface-modified region is present on the surface of the substrate in contact with the first nitride layer, in which elements commonly contained in the substrate and the first nitride layer are irregularly mixed toward the interior of the substrate. By forming the surface-modified region in this manner, the outermost surface of the substrate is no longer smooth, and further, the interatomic bonding strength between the substrate and the elements that constitute part of the first nitride layer is increased, or multiple elements are integrated within the surface-modified region, thereby suppressing peeling or sliding off of the first nitride layer from the substrate.

[0090] A seventh aspect is the coated cutting tool of any one of the first to fourth aspects, wherein the first nitride layer is an AlCrSi-containing nitride containing Al, Cr, and Si as metal elements, with the Si content in these metal elements being 8 at % or more and less than 11 at %, and the second nitride layer is a TiSi-containing nitride. This embodiment makes it possible to realize a hard coating that combines the advantages of the first nitride layer, which has high oxidation resistance and little variation in crystal orientation, and the advantages of the second nitride layer, which has high wear resistance.

[0091] An eighth embodiment is the coated cutting tool of the seventh embodiment, wherein the first nitride layer and the second nitride layer are alternately stacked in a multi-layer structure. This embodiment combines the advantages of the first nitride layer, which has high oxidation resistance and little variation in crystal orientation, with the advantages of the second nitride layer, which has high wear resistance, and because the crystal size of each layer is refined, a hard coating with even greater hardness can be achieved.

[0092] A ninth aspect is any of the first to fourth aspects, wherein the first nitride layer is a multilayer layer in which films of an AlCrSi-containing nitride containing Al, Cr, and Si as metal elements, with the proportion of Si in these metal elements being 8 at% or more and less than 11 at%, or an AlCrSiW-containing nitride containing Al, Cr, Si, and W as metal elements, with the proportion of W in these metal elements being 1 at% or more and less than 5 at%, and a TiSi-containing nitride are alternately stacked, and the second nitride layer is a TiSi-containing nitride. By forming the first nitride layer from multiple laminated layers, the crystal structure can be made finer and the hardness can be increased, resulting in a longer tool life than when the first nitride layer is not provided with multiple laminated layers.

[0093] A tenth aspect is the coated cutting tool of any one of the first to fourth aspects, wherein the first nitride layer is an AlCrSi-containing nitride containing Al, Cr, and Si as metallic elements, with the Si content in these metallic elements being 8 at% or more and less than 11 at%, or an AlCrSiW-containing nitride containing Al, Cr, Si, and W as metallic elements, with the W content in these metallic elements being 1 at% or more and less than 5 at%, and the second nitride layer is a multilaminate layer in which first films of the AlCrSi-containing nitride or the AlCrSiW-containing nitride and second films of TiSi-containing nitride are alternately laminated, with the second films being the outermost surface. The second nitride layer also has oxidation resistance, wear resistance and highly stable crystal orientation, which can extend the tool life.

[0094] An eleventh aspect is a coated cutting tool having a first nitride layer coating the surface of a substrate and having an oxidation resistance temperature in a first temperature range; a second nitride layer coating the surface of the first nitride layer and having an oxidation resistance temperature in a second temperature range lower than the first temperature range; and a third nitride layer coating the surface of the second nitride layer and having an oxidation resistance temperature in the first temperature range, wherein the second nitride layer has a higher hardness than the first nitride layer up to the second temperature range, and the first nitride layer and the third nitride layer have crystal orientations in the first temperature range that are substantially identical to those in the unheated state. In this cutting tool, the substrate is coated with a hard coating that combines the advantages of the high oxidation resistance and highly stable crystal orientation of the first and third nitride layers and the high wear resistance of the second nitride layer, so that the third nitride layer, which comes into contact with the workpiece during rough machining, is suppressed from wear due to frictional heat during cutting. Furthermore, even if the third nitride layer wears, the second nitride layer can be used for finish machining, reducing the number of tool changes and improving machining efficiency.

[0095] A twelfth aspect is the coated cutting tool of the eleventh aspect, wherein the second nitride layer is a TiSi-containing nitride, and the first nitride layer and the third nitride layer are AlCrSi-containing nitride layers containing Al, Cr, and Si as metal elements, and the proportions of these metal elements satisfy the following condition 1: Condition 1) Al: 49 at% or more and less than 61 at% Cr: 30at% or more and less than 44at% Si: 6 at% or more and less than 11 at% Al+Cr+Si=100at% The cutting tool of this embodiment can exhibit high oxidation resistance and high wear resistance up to at least the first temperature range.

[0096] A thirteenth aspect is the coated cutting tool of the eleventh aspect, wherein the second nitride layer is a TiSi-containing nitride, and at least the first nitride layer of the first and third nitride layers contains Al, Cr, and Si as metal elements, and the coated cutting tool is a multilayer layer in which AlCrSi-containing nitride films and TiSi-containing nitride films are alternately laminated, the proportions of these metal elements satisfying the above-mentioned condition 1. The cutting tool of this embodiment can exhibit high oxidation resistance and high wear resistance up to at least the first temperature range.

[0097] A fourteenth aspect is the coated cutting tool of the eleventh aspect, wherein the second nitride layer is a TiSi-containing nitride, and the first nitride layer and the third nitride layer are AlCrSiW-containing nitride layers containing Al, Cr, Si, and W as metal elements, and the proportions of these metal elements satisfy the following condition 2: Condition 2) Al: 50 at% or more and less than 61 at% Cr: 28 at% or more and less than 38 at% Si: 6 at% or more and less than 10 at% W: 1 at% or more and less than 7 at% Al+Cr+Si+W=100at% The cutting tool of this embodiment can exhibit high oxidation resistance and high wear resistance up to at least the first temperature range.

[0098] A fifteenth aspect is the coated cutting tool of the eleventh aspect, wherein the second nitride layer is a TiSi-containing nitride, and at least the first nitride layer of the first nitride layer and the third nitride layer contains Al, Cr, Si, and W as metal elements, and the ratios of these metal elements satisfy the above-mentioned condition 2, and the coated cutting tool is a multilayer layer in which AlCrSiW-containing nitride films and TiSi-containing nitride films are alternately laminated. The cutting tool of this embodiment can exhibit high oxidation resistance and high wear resistance up to at least the first temperature range.

[0099] The 16th aspect is a coated cutting tool in any one of the 11th to 15th aspects, wherein the thicknesses of the first nitride layer, the second nitride layer, and the third nitride layer are greatest in the order of the second nitride layer, the first nitride layer, and the third nitride layer.

[0100] A seventeenth aspect of the present invention is a method for manufacturing a semiconductor device comprising: a first nitride layer covering a surface of a substrate and having an oxidation resistance temperature in a first temperature range; a second nitride layer covering the surface of the first nitride layer and having an oxidation resistance temperature in a second temperature range lower than the first temperature range; a third nitride layer covering the surface of the second nitride layer; and a fourth nitride layer covering the surface of the third nitride layer, wherein the first nitride layer is a layer having a crystal orientation in the unheated state and a crystal orientation in the first temperature range that is substantially the same, or a multi-layered layer in which a plurality of films having different compositions are alternately formed; and the second nitride layer is a layer having a crystal orientation in the first temperature range that is substantially the same as the crystal orientation in the unheated state, the third nitride layer is the multi-layered layer; the fourth nitride layer is a layer having an oxidation resistance temperature in the first temperature range in which its crystalline orientation in the unheated state is substantially the same as its crystalline orientation in the first temperature range; and the multi-layered layer is a layer formed from a first film whose crystalline orientation in the unheated state is substantially the same as its crystalline orientation in the first temperature range; and a second film whose hardness is highest up to the second temperature range. The cutting tool of this embodiment can exhibit high oxidation resistance and high wear resistance up to a higher temperature range.

[0101] An eighteenth aspect is a coated cutting tool comprising: a first nitride layer coating a surface of a substrate and having an oxidation resistance temperature in a first temperature range; a second nitride layer coating the surface of the first nitride layer; a third nitride layer coating the surface of the second nitride layer; a fourth nitride layer coating the surface of the third nitride layer; and a fifth nitride layer coating the surface of the fourth nitride layer, wherein the first nitride layer and the fifth nitride layer have crystal orientations in the first temperature range that are substantially identical to those in the unheated state; the second nitride layer and the fourth nitride particle layer are multilayer layers formed from a first film whose crystal orientation in the unheated state is substantially identical to those in the first temperature range; and a second film whose hardness is highest up to a second temperature range that is lower than the first temperature range; and the third nitride layer is thicker than the first nitride layer, the second nitride layer, the fourth nitride layer, and the fifth nitride layer and has the hardest hardness up to the second temperature range. The cutting tool of this embodiment can exhibit high oxidation resistance and high wear resistance up to an even higher temperature range. [Explanation of symbols]

[0102] 1...Base material, 2...hard coating, 3, 21, 31, 41...first nitride layer, 4, 22, 32, 40, 42...second nitride layer, 5, 50...Third nitride layer, 6, 60...fourth nitride layer, 7...Fifth nitride layer

Claims

1. A coated cutting tool in which the surface of a substrate is coated with a hard film, The hard film includes one or more multilayer laminated layers in which a first nitride film having an oxidation resistance temperature of a first temperature and a second nitride film having an oxidation resistance temperature of a second temperature lower than the first temperature are alternately laminated a plurality of times in a thickness direction; At least one of the first nitride layer and the second nitride layer is in contact with any of the multilayer stacked layers, the second nitride is a TiSi-containing nitride having a higher hardness than the first nitride up to the second temperature and a lower hardness than the first nitride when the temperature exceeds the second temperature; the first nitride is an AlCrSiW-containing nitride or an AlCrSi-containing nitride, the change rate between the hardness without heating and the hardness after maintaining the first temperature for 10 minutes being less than 3%; Coated cutting tools.

2. The first nitride has an O / N ratio of less than 0.35 after maintaining a temperature 100 degrees Celsius higher than the first temperature for 10 minutes. The coated cutting tool of claim 1 .

3. The AlCrSi-containing nitride has a ratio of Si in the metal elements Al, Cr, and Si of 8 at% or more and less than 11 at%. The coated cutting tool of claim 1 .

4. The AlCrSiW-containing nitride has a W ratio of 1 at% or more and less than 5 at% among the metal elements Al, Cr, Si, and W. The coated cutting tool of claim 1 .

5. When the multilayer laminate is coated on the surface of the substrate or the first nitride layer, the first formed film is the first nitride film. The coated cutting tool according to any one of claims 1 to 4.

6. When the multilayer laminate is coated on the surface of the second nitride layer, the last formed film is the second nitride film. The coated cutting tool according to any one of claims 1 to 4.

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