Surface coated cutting tools

Abstract

A surface-coated cutting tool comprising a substrate and a hard coating formed on the surface of the substrate, wherein the hard coating has a lower layer formed on the substrate, an intermediate layer formed on the lower layer and consisting of alternating A and B layer laminates, and an upper layer formed on the intermediate layer, the lower layer being made of an AlCrXZ film, the A layer of the intermediate layer being made of an AlCrX'Z film, the B layer of the intermediate layer being made of an AlCrBWX''Z film, and the upper layer being made of a TiSiX'''Z film, the intermediate layer having a crystalline structure preferentially oriented to the (111) plane of a face-centered cubic structure, and the upper layer having a crystalline structure preferentially oriented to the (200) plane of a face-centered cubic structure.

Description

[Technical Field]

[0001] This application asserts the interests of Japanese Patent Application No. 2023-065856, filed in Japan on April 13, 2023, the entire contents of which are expressly incorporated herein by reference.

[0002] This invention relates to a surface-coated cutting tool.

[0003] prior art Conventionally, alternating laminated films of AlCrN and AlCrBN, and alternating laminated films of AlCrBWN and AlCrN have been known as hard coatings for cutting tools, as described, for example, in WO2016 / 102170A1 and WO2008 / 037556A1. However, it has been observed that when conventional hard coatings are applied to small-diameter tools, for example, with a diameter of 3 mm or less, surface smoothing by post-treatment is difficult, and sufficient tool life cannot be obtained. .

[0004] Purpose of the invention Therefore, an object of the present invention is to alleviate or overcome one or more difficulties associated with the prior art. In particular, an object of the present invention is to provide a surface-coated cutting tool that is easy to post-process and has sufficient durability even when cutting small diameter workpieces.

[0005] Description of the Invention According to this disclosure, a surface-coated cutting tool comprises a substrate and a hard coating formed on the surface of the substrate, wherein the hard coating has a lower layer formed on the substrate, an intermediate layer formed on the lower layer and consisting of an alternating laminate of layers A and B, and an upper layer formed on the intermediate layer, the lower layer having a composition formula: (Al 1-a-b Cr a X b When expressed as )Z(X is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, and CNO), it has an average composition that satisfies 0.30 ≤ a ≤ 0.50 and 0 ≤ b ≤ 0.05, and the intermediate layer A has the composition formula: (Al1-c-d Cr c X' d )Z (X' is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is any one of N, C, CN, NO, CO, CNO), when expressed as having an average composition satisfying 0.30 ≤ c ≤ 0.50 and 0 ≤ d ≤ 0.05, the B layer of the intermediate layer has a composition formula: (Al 1-e-f-g-h Cr e B f W g X'' h )Z (X'' is one or more elements selected from Mo, Ta, Zr, and Nb, and Z is any one of N, C, CN, NO, CO, CNO), when expressed as having an average composition satisfying 0.30 ≤ e ≤ 0.50, 0.01 ≤ f ≤ 0.15, 0.01 ≤ g ≤ 0.15, and 0 ≤ h ≤ 0.05, the upper layer has a composition formula: (Ti 1-i-j Si i X''' j )Z (X''' is one or more elements selected from Al, Cr, Zr, B, and W, and Z is any one of N, C, CN, NO, CO, CNO), when expressed as having an average composition satisfying 0.15 ≤ i ≤ 0.35 and 0 ≤ j ≤ 0.05, the lower layer and the intermediate layer have a crystal structure preferentially oriented on the (111) plane of the face-centered cubic structure, and the upper layer has a crystal structure preferentially oriented on the (200) plane of the face-centered cubic structure, a surface-coated cutting tool is provided.

[0006] The value of the ratio I(200) / I(111) of the X-ray diffraction peak intensities of the (200) plane and the (111) plane of the upper layer is 10 or more and 200 or less, and the value of the ratio I(200) / I(111) of the X-ray diffraction peak intensities of the (200) plane and the (111) plane of the lower layer and the intermediate layer combined is 0.01 or more and 0.50 or less, which may also be a configuration.

[0007] Furthermore, the lower layer may have a thickness of 0.1 μm or more and 6.0 μm or less, the intermediate layer A may have a thickness of 3 nm or more and 100 nm or less, the intermediate layer B may have a thickness of 3 nm or more and 100 nm or less, the overall thickness of the intermediate layer may be 0.5 μm or more and 16.0 μm or less, the upper layer may have a thickness of 0.1 μm or more and 6.0 μm or less, and the overall thickness of the hard coating may be 0.5 μm or more and 20.0 μm or less.

[0008] Furthermore, the hard coating may be configured such that its arithmetic mean surface roughness Ra is 0.1 μm or less.

[0009] According to one aspect of the present invention, a surface-coated cutting tool is provided that can achieve excellent tool life even with small-diameter tools. Detailed explanation [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram showing the cross-sectional structure of a surface-coated cutting tool according to an embodiment of the present invention. [Figure 2] Figure 2 shows an example of the X-ray diffraction profile of a surface-coated cutting tool according to the embodiment shown in Figure 1.

[0011] The surface-coated cutting tool according to an embodiment of the present invention will be described in detail below. In this specification and the claims, when a numerical range is expressed as "L~M" (where L and M are both numerical values), the range includes an upper limit (M) and a lower limit (L), and the units of the upper limit (M) and the lower limit (L) are the same.

[0012] Figure 1 is a schematic diagram showing the cross-sectional structure of a surface-coated cutting tool according to an embodiment. The surface-coated cutting tool 1 of this embodiment has a substrate 10 and a hard coating 20 formed on the surface of the substrate 10. The hard coating 20 consists of a lower layer 21 formed on the substrate 10, which is made of an (AlCrX)Z film (where X is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, and CNO), and an A layer formed on the lower layer 21, which is made of an (AlCrX')Z film (where X' is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, and CNO), and an (AlCrB The film comprises an intermediate layer 22 made of alternating layers with a B layer made of a WX'')Z(X'' is one or more elements selected from Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, and CNO) film, and an upper layer 23 formed on the intermediate layer 22 and made of a (TiSiX''')Z(X''' is one or more elements selected from Al, Cr, Zr, B, and W, and Z is one of N, C, CN, NO, CO, and CNO) film. Furthermore, the element Z included in the composition of each layer can be arbitrarily placed as element Z in each layer, with one of N, C, CN, NO, CO, or CNO being selected. Therefore, the elements selected as element Z in each layer may be different from each other. For example, the lower layer 21 may consist of an AlCrN film and the upper layer 23 may consist of a TiSiCNO film.

[0013] The base body 10 can be any of the conventionally known tool bases. For example, cemented carbide (WC-based cemented carbide, including those containing WC and Co, and further including those with carbonitrides such as Ti, Ta, and Nb added), cermet (mainly composed of TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cBN sintered bodies, etc. can be used.

[0014] The hard film 20 may include layers other than the lower layer 21, the intermediate layer 22, and the upper layer 23. For example, a layer for improving the adhesion between the lower layer 21 and the substrate 10 may be formed between the lower layer 21 and the substrate 10. Also, for example, a layer made of another nitride or carbonitride may be formed on the upper layer 23.

[0015] The total film thickness of the hard film 20 is preferably 0.5 μm or more and 20.0 μm or less. If the total film thickness of the hard film 20 is less than 0.5 μm, it is difficult to obtain sufficient wear resistance over a long period. If the total film thickness of the hard film 20 exceeds 20.0 μm, abnormal damages such as chipping and peeling are likely to occur. The total film thickness of the hard film 20 is preferably 0.7 μm or more, or 0.9 μm or more. The total film thickness of the intermediate layer 22 is preferably 15.0 μm or less, 10.0 μm or less, or 5.0 μm or less.

[0016] The lower layer 21 of the hard film 20 has an average composition satisfying 0.30 ≦ a ≦ 0.50 and 0 ≦ b ≦ 0.05 when represented by the compositional formula: (Al 1-a-b Cr a X b )Z (X is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is any one of N, C, CN, NO, CO, and CNO), and is a composite compound layer of Al, Cr, and X. The lower layer 21 is preferably a composite nitride layer of Al and Cr. Al improves the high-temperature hardness and heat resistance, Cr improves the high-temperature strength, and Cr and Al coexist to improve the high-temperature oxidation resistance. When the a value (atomic ratio) indicating the content ratio of Cr is less than 0.30, hexagonal crystal grains appear due to the relative increase in the Al content ratio, resulting in a decrease in hardness and wear resistance. On the other hand, when the a value (atomic ratio) exceeds 0.50, sufficient high-temperature hardness and heat resistance cannot be ensured due to the relative decrease in the Al content ratio, and the wear resistance decreases. The a value is preferably 0.33 or more, or 0.35 or more. The a value is preferably 0.47 or less, or 0.45 or less. The lower layer 21 may contain element X. X is one or more elements selected from W, Mo, Ta, Zr, and Nb. The range of the content ratio (b value) of X is 0 or more and 0.05 or less in atomic ratio. By adding element X, the hardness and oxidation resistance (oxidation start temperature) of the film are improved. Element X can be added within a range that does not adversely affect the properties of the hard film. The b value is preferably 0.02 or more. The b value is preferably 0.04 or less.

[0017] The film thickness of the lower layer 21 is preferably 0.1 μm or more and 6.0 μm or less. If the film thickness of the lower layer 21 is less than 0.1 μm, it becomes difficult to obtain sufficient wear resistance over a long period. If the film thickness of the lower layer 21 exceeds 6.0 μm, abnormal damages such as chipping and peeling are likely to occur. The film thickness of the lower layer 21 is preferably 0.15 μm or more, or 0.2 μm or more. The film thickness of the lower layer 21 is preferably 4.0 μm or less, 2.0 μm or less, or 1.0 μm or less.

[0018] The A layer of the intermediate layer 22 has an average composition represented by the compositional formula: (Al 1-c-d [[ID=I0]]Cr c X' d )Z (X' is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is any one of N, C, CN, NO, CO, and CNO), and is a composite compound layer of Al, Cr, and X' having an average composition that satisfies 0.30 ≦ c ≦ 0.50 and 0 ≦ d ≦ 0.05. The reason for setting the c value within the above range is the same as the reason for setting the above a value. The c value is preferably 0.33 or more, or 0.35 or more. The c value is preferably 0.47 or less, or 0.45 or less. The A layer is preferably a composite nitride layer containing Al and Cr. The A layer may contain element X'. X' is one or more elements selected from W, Mo, Ta, Zr, and Nb. The range of the content ratio (d value) of X' is 0 or more and 0.05 or less in atomic ratio. By adding element X', the hardness and oxidation resistance (oxidation start temperature) of the film are improved. Element X' can be added within a range that does not adversely affect the properties of the hard film. The d value is preferably 0.02 or more. The d value is preferably 0.04 or less.

[0019] The B layer of the intermediate layer 22 is (Al 1-e-f-g-h Cr e B f W g X'' h When expressed as )Z(X'' is one or more elements selected from Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, CNO), it has an average composition that satisfies 0.30≦e≦0.50, 0.01≦f≦0.15, 0.01≦g≦0.15, and 0≦h≦0.05. Layer B is a layer mainly composed of a composite compound of Al and Cr, with B (boron) and W added. The reason for setting the e and f values ​​within the above ranges is the same as the reason for setting the a value above. The e value is preferably 0.33 or higher, or 0.35 or higher. The e value is preferably 0.47 or lower, or 0.45 or lower. The f value is preferably 0.03 or higher, or 0.05 or higher. The f value is preferably 0.12 or lower, or 0.10 or lower. The g value is preferably 0.03 or higher, or 0.05 or higher. The g-value is preferably 0.12 or less, or 0.10 or less. The B layer is preferably a composite nitride layer containing Al, Cr, B, and W.

[0020] By setting the total content of B (boron) within the above range, the hardness of the B layer can be increased. By setting the total content of W (boron) within the above range, the crystallinity of the B layer can be improved. The total content of B (boron) is preferably 0.03 or more and 0.05 or more in terms of atomic ratio. The total content of B (boron) is preferably 0.12 or less and 0.10 or less in terms of atomic ratio. The total content of W (boron) is preferably 0.03 or more and 0.05 or more in terms of atomic ratio. The total content of W (boron) is preferably 0.12 or less and 0.10 or less in terms of atomic ratio.

[0021] The intermediate layer 22 is an alternating laminated film in which layers A, made of AlCrX'Z film, and layers B, made of AlCrBWX''Z film, are alternately stacked. The thickness of each layer of layer A is preferably 3 nm to 100 nm. The thickness of each layer of layer B is preferably 3 nm to 100 nm. By setting the thickness within this range, the lattice mismatch between layers A and B can be mitigated, improving the toughness of the entire alternating laminated film and making it easier to suppress crack propagation. The film thickness per layer of layer A is preferably 60 nm or less, 30 nm or less, or 10 nm or less. The film thickness per layer of layer B is preferably 60 nm or less, 30 nm or less, or 10 nm or less.

[0022] The overall thickness of the intermediate layer 22 is preferably 0.5 μm or more and 16.0 μm or less. If the overall thickness of the intermediate layer 22 is less than 0.5 μm, it becomes difficult to obtain sufficient wear resistance over a long period of time. If the overall thickness of the intermediate layer 22 exceeds 16.0 μm, abnormal damage such as chipping and peeling is more likely to occur. The overall thickness of the intermediate layer 22 is preferably 0.8 μm or more, or 1.0 μm or more. The overall thickness of the intermediate layer 22 is preferably 10.0 μm or less, 5.0 μm or less, or 3.0 μm or less.

[0023] Layer B may contain element X''. X'' is one or more elements selected from Mo, Ta, Zr, and Nb. The range of the X'' content ratio (h value) is 0 to 0.05 in atomic ratio. Adding element X'' improves the hardness and oxidation resistance (oxidation onset temperature) of the film. Element X'' can be added within a range that does not adversely affect the properties of the hard film. An h value of 0.02 or higher is preferred. An h value of 0.04 or lower is preferred.

[0024] The upper layer 23 has the following compositional formula: (Ti 1-i-j Si i X''' jThe composite compound layer of Ti, Si, and X''' has an average composition that satisfies 0.15 ≤ i ≤ 0.35 and 0 ≤ j ≤ 0.05 when represented as Z(X''' is one or more elements selected from Al, Cr, Zr, B, and W, and Z is one of N, C, CN, NO, CO, and CNO). By forming an upper layer 23 made of a composite compound containing Ti, Si, and X''', the chipping resistance of the hard coating is improved. If the i value is less than 0.15, the improvement in chipping resistance is small. If the i value exceeds 0.35, the lattice strain increases and the upper layer 23 becomes more prone to peeling. It is preferable that the i value be 0.18 or higher, or 0.20 or higher. It is preferable that the i value be 0.32 or lower, or 0.30 or lower. It is preferable that the upper layer 23 is a composite nitride layer containing Ti and Si.

[0025] The upper layer 23 may contain element X'''. X''' is one or more elements selected from Al, Cr, Zr, B, and W. The range of the X''' content ratio (j value) is 0 to 0.05 in atomic ratio. Adding element X''' improves the hardness and oxidation resistance (oxidation onset temperature) of the film. Element X''' can be added within a range that does not adversely affect the properties of the hard film. A j value of 0.02 or higher is preferred. A j value of 0.04 or lower is preferred.

[0026] The thickness of the upper layer 23 is preferably 0.1 μm or more and 6.0 μm or less. If the thickness of the upper layer 23 is less than 0.1 μm, it becomes difficult to obtain sufficient wear resistance over a long period of time. If the thickness of the upper layer 23 exceeds 6.0 μm, abnormal damage such as chipping and peeling is more likely to occur. The thickness of the upper layer 23 is preferably 0.15 μm or more, or 0.2 μm or more. The thickness of the upper layer 23 is preferably 4.0 μm or less, 2.0 μm or less, or 1.0 μm or less.

[0027] In the hard coating 20, the lower layer 21 and the intermediate layer 22 have a face-centered cubic structure as identified by X-ray diffraction, with crystals preferentially oriented to the (111) plane. The upper layer 23 also has a face-centered cubic structure as identified by X-ray diffraction, with crystals preferentially oriented to the (200) plane. Normally, when a TiSiX'''Z film is formed on an intermediate layer 22 preferentially oriented to the (111) plane, the TiSiX'''Z film preferentially oriented to the (111) plane. In this invention, by controlling the film deposition apparatus and deposition conditions when depositing the upper layer 23 made of the TiSiX'''Z film, an upper layer 23 preferentially oriented to the (200) plane is formed on an intermediate layer 22 preferentially oriented to the (111) plane. As a result, the upper layer 23 can be composed of a TiSiX'''Z film with excellent hardness and thermal conductivity, and a surface-coated cutting tool with excellent chipping resistance and wear resistance can be obtained.

[0028] In the lower layer 21 and the intermediate layer 22, it is preferable that the ratio I(200) / I(111) of the X-ray diffraction peak intensity I(200) of the (200) plane encompassing the lower layer 21 and the intermediate layer 22 to the X-ray diffraction peak intensity I(111) of the (111) plane encompassing the lower layer 21 and the intermediate layer 22 is 0.01 or more and 0.50 or less. In the upper layer 23, it is preferable that the ratio I(200) / I(111) of the X-ray diffraction peak intensity I(200) of the (200) plane and the X-ray diffraction peak intensity I(111) of the (111) plane is between 10 and 200. The lower layer 21 and intermediate layer 22, which are preferentially oriented on the (111) plane, have excellent hardness. In particular, when used as a drill, the wear resistance of the margin is improved. The upper layer 23, which is preferentially oriented on the (200) plane, has excellent thermal conductivity. In particular, it can improve the heat resistance of the rake face of the tool.

[0029] The hard coating 20 of this embodiment has a very smooth surface. Specifically, in the surface-coated cutting tool of this embodiment, the arithmetic mean roughness Ra of the hard coating 20 surface is 0.1 μm or less. This reduces friction with the workpiece and improves the wear resistance of the hard coating 20.

[0030] The composition, film thickness, film thickness of each layer constituting the hard coating 20, the film thickness of each layer of the alternating laminated film, and the total film thickness can be measured by cross-sectional measurements of the hard coating perpendicular to the substrate surface using scanning electron microscopy (SEM), transmission electron microscope (TEM), and energy-dispersive X-ray spectroscopy (EDS). Here, the surface of the substrate is defined as the reference line for the interface roughness between the tool substrate and the hard coating layer in the cross-sectional observation image. When the tool substrate has a planar surface such as an insert, elemental mapping using EDS is performed in the longitudinal section. The interface between the lower layer 21 and the tool substrate is determined by performing known image processing on the obtained elemental map. The average line is arithmetically calculated for the roughness curve of the interface between the lower layer 21 and the tool substrate obtained in this way. The obtained average line is taken as the surface of the tool substrate. The direction perpendicular to this average line is taken as the direction perpendicular to the tool substrate. Furthermore, even if the tool substrate has a curved surface, such as a drill, if the tool diameter is sufficiently large relative to the thickness of the hard coating layer, the interface between the hard coating layer and the tool substrate in the measurement area will be substantially planar. Since the interface is substantially planar, the surface of the tool substrate can be determined by a similar method. That is, for example, in the case of a drill, elemental mapping using EDS is performed on the longitudinal cross-section of the hard coating layer with a cross-section perpendicular to the axial direction. The interface between the lower layer 21 and the tool substrate is determined by performing known image processing on the obtained elemental map. The average line of the roughness curve of the interface between the lower layer 21 and the tool substrate obtained in this way is arithmetically calculated and taken as the surface of the tool substrate. Then, the direction perpendicular to this average line is taken as the direction perpendicular to the tool substrate. Furthermore, the measurement area in the longitudinal section should be set to include the entire thickness of the hard coating layer. Considering the total thickness of the hard coating layer and the measurement accuracy of the layer thickness, it is preferable to perform observation and measurement using multiple fields of view (e.g., 3 fields of view) with a field of view of approximately 10 μm × 10 μm. Furthermore, layers A and B exhibit repeated changes in either the B or W concentration. Therefore, the B or W concentration in each layer is measured along multiple analysis lines (e.g., 5 lines) perpendicular to the surface of the tool substrate (in the layer thickness direction). The positions where the B or W concentration appears and reaches 1 atomic percent are defined as the interface with the adjacent layer, and the layer thickness is determined for each of the multiple lines. The calculated layer thicknesses are then averaged to obtain the average layer thickness. Since there is only one lower layer 21 and one upper layer 23, the average layer thickness is calculated by averaging the layer thicknesses measured by multiple analysis lines for these layers.

[0031] The crystalline structure of each layer constituting the hard coating 20 can be measured using X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The crystalline structure of each layer constituting the hard coating 20 is confirmed by electron diffraction using a transmission electron microscope (TEM). Specifically, the crystalline structures of the lower layer 21, the intermediate layer 22, and the upper layer 23 are identified and confirmed to be NaCl-type face-centered cubic structures. X-ray diffraction is performed using Cu-Kα rays and the 2θ / θ focusing method. Figure 2 shows an example of the X-ray diffraction profile of a surface-coated cutting tool according to the embodiment. The 111 diffraction line encompassing the lower layer 21 and intermediate layer 22 can be observed around 37.5 degrees, the 111 diffraction line of the upper layer 23 can be observed around 36.5 degrees, the 200 diffraction line encompassing the lower layer 21 and intermediate layer 22 can be observed around 43.5 degrees, and the 200 diffraction line of the upper layer 23 can be observed around 42 degrees. The peaks around 36 and 48 degrees are due to hexagonal WC. The arithmetic mean roughness Ra of the surface of the hard coating can be measured using a laser microscope (for example, a Keyens VK-X3000) in accordance with JIS B-0601 (2001). [Examples]

[0032] As the base material, we prepared drill bases made of WC cemented carbide with tool diameters of φ0.8 mm and 2.0 mm. A hard coating with the configuration shown in Table 1 below was formed on the drill substrate described above.

[0033] In this embodiment, a sputtering apparatus capable of simultaneously sputtering three types of targets was used. Of these deposition sources, an AlCr alloy target, an AlCrBW alloy target, and a TiSi alloy target were installed in the apparatus as deposition sources. The drill substrate was fixed to a sample holder in the sputtering apparatus, and a bias power supply was connected to the drill substrate. The bias power supply was structured to apply a negative bias voltage to the substrate independently of the target. The drill substrate was attached to a fixture that could rotate three times around its own axis. Ar and N2 were used as the introduction gases and were introduced from a gas supply port provided in the sputtering apparatus.

[0034] <Bombard treatment> First, before coating the drill base with a hard coating, the tool was subjected to bombardment treatment using the following procedure. The furnace temperature was raised to 430°C by the heater in the sputtering apparatus and heated for 30 minutes. Afterward, the furnace of the sputtering apparatus was evacuated, and the furnace pressure was set to 5.0 × 10⁻⁶. -3 The pressure was kept below Pa. Then, Ar gas was introduced into the furnace of the sputtering apparatus, and the furnace pressure was adjusted to 0.7 Pa. A DC bias voltage of -200V was applied to the drill base to perform tool cleaning (bombardment) with Ar ions.

[0035] <Layer 21 deposition> Next, an AlCrN coating was applied to the tool using the following procedure. While maintaining the furnace temperature at 430°C, Ar gas was introduced into the sputtering apparatus at a rate of 360 sccm, followed by N2 gas at a rate of 330 sccm to set the furnace pressure to 0.75 Pa. A DC bias voltage of -40V was applied to the tool, and power was continuously applied to the alloy target containing Al and Cr, with a discharge time of 0.2 milliseconds per cycle of power applied to the target, thereby coating the surface of the tool with an intermediate film approximately 0.2 μm thick.

[0036] <Deposition of intermediate layer 22> Next, a hard coating was applied to the lower layer 21 using the following procedure. While maintaining the furnace temperature at 430°C, Ar gas was introduced into the sputtering apparatus at a rate of 360 sccm, followed by N2 gas at a rate of 380 sccm to set the furnace pressure to 0.70 Pa. A DC bias voltage of -50V was applied to the tool, and power was applied simultaneously to the AlCr alloy target and the AlCrBW alloy target, with a discharge time of 0.2 milliseconds per cycle for the power applied to the Al and Cr alloy target and the Al, Cr, B, and W alloy target, thereby coating the lower layer 21 with a hard film approximately 1.5 μm thick.

[0037] <Deposition of the upper layer 23> Next, a hard coating was applied to the intermediate layer 22 using the following procedure. While maintaining the furnace temperature at 430°C, Ar gas was introduced into the sputtering apparatus at a rate of 360 sccm, followed by N2 gas at a rate of 170 sccm to set the furnace pressure to 0.55 Pa. A DC bias voltage of -70V was applied to the tool, and the discharge time per cycle of the power applied to the alloy target containing Ti and Si was set to 4.5 milliseconds, thereby coating the intermediate layer 22 with a hard film approximately 0.2 μm thick.

[0038] (Comparative example) For comparative examples No. 5 to 10, the same apparatus, bombardment conditions, and film deposition conditions as for examples No. 1 to 4 were used, and the film deposition time was adjusted to achieve the film thickness shown in Table 1 below, thereby depositing a hard film on the surface of the drill substrate. Furthermore, for samples No. 11 to 13, the film was deposited under the same conditions as for samples No. 1 to 4, except that the composition of the alloy target was changed and the conditions were adjusted to achieve the film thickness shown in Table 1.

[0039] [Table 1]

[0040] (evaluation) Drilling was performed using the surface-coated cutting tools of each fabricated sample under the conditions shown in Table 2 below. Table 3 shows the tool life of each sample, with the life of the control sample No. 5 surface-coated cutting tool set to 100. Compared to sample No. 5, which had the same shape as the drill base coated with a conventional coating (without an intermediate layer), the samples of the present invention (Nos. 1 to 4) all showed superior tool life. In particular, samples No. 1 and 4, which used a drill base with a tool diameter of φ0.8 mm, showed a life of more than 200% compared to the conventional tool (No. 5). Furthermore, when using a drill base with a tool diameter of φ2.0 mm, samples No. 3 and 4 also achieved a life of more than 200% compared to the conventional tool. On the other hand, samples No. 6 to 10, which omitted some layers, and samples No. 11 to 13, whose composition range was outside the scope of the present invention, all performed worse than sample No. 5.

[0041] [Table 2]

[0042] [Table 3] [Explanation of Symbols]

[0043] 1...Surface coated cutting tool, 10...Base, 20...Hard coating, 21...Lower layer, 22...Middle layer, 23...Upper layer

Claims

1. A surface-coated cutting tool comprising a substrate and a hard coating formed on the surface of the substrate, wherein the hard coating is The substrate comprises a lower layer formed on the substrate, an intermediate layer formed on the lower layer and consisting of an alternating laminated film of layers A and B, and an upper layer formed on the intermediate layer. The aforementioned lower layer has the following compositional formula: (Al １－ａ－ｂ Cr ａ X ｂ When expressed as Z (where X is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, and CNO), it has an average composition that satisfies 0.30 ≤ a ≤ 0.50 and 0 ≤ b ≤ 0.

05. The aforementioned intermediate layer A is (Al １－ｃ－ｄ Cr ｃ X' ｄ When expressed as Z (where X' is one or more elements selected from W, Mo, Ta, Zr, and Nb, and Z is one of N, C, CN, NO, CO, and CNO), it has an average composition that satisfies 0.30 ≤ c ≤ 0.50 and 0 ≤ d ≤ 0.

05. The B layer of the intermediate layer has an average composition satisfying 0.30 ≦ e ≦ 0.50, 0.01 ≦ f ≦ 0.15, 0.01 ≦ g ≦ 0.15, and 0 ≦ h ≦ 0.05 when represented by the compositional formula: (Al 1－ｅ－ｆ－ｇ－ｈ Cr ｅ B ｆ W ｇ X'')Z (X'' is one or more elements selected from Mo, Ta, Zr, and Nb, and Z is any one of N, C, CN, NO, CO, and CNO).​​ The aforementioned upper layer has the composition formula: (Ti １－ｉ－ｊ Si ｉ X'' ｊ When expressed in terms of Z (where X''' is one or more elements selected from Al, Cr, Zr, B, and W, and Z is one of N, C, CN, NO, CO, and CNO), it has an average composition that satisfies 0.15 ≤ i ≤ 0.35 and 0 ≤ j ≤ 0.

05. The lower layer and the intermediate layer have a crystalline structure preferentially oriented to the (111) plane of the face-centered cubic structure. The upper layer has a crystalline structure preferentially oriented to the (200) plane of a face-centered cubic structure. Surface coated cutting tools.

2. The ratio I(200) / I(111) of the X-ray diffraction peak intensities of the (200) plane and (111) plane of the upper layer is 10 or more and 200 or less. The ratio I(200) / I(111) of the X-ray diffraction peak intensities of the (200) plane and the (111) plane, which encompass the lower layer and the intermediate layer, is 0.01 or more and 0.50 or less. A surface-coated cutting tool according to claim 1.

3. The thickness of the lower layer is 0.1 μm or more and 6.0 μm or less. The thickness of the intermediate layer A is 3 nm or more and 100 nm or less. The thickness of the intermediate layer B is 3 nm or more and 100 nm or less. The total thickness of the intermediate layer is 0.5 μm or more and 16.0 μm or less. The thickness of the upper layer is 0.1 μm or more and 6.0 μm or less. The total thickness of the hard coating is 0.5 μm or more and 20.0 μm or less. A surface-coated cutting tool according to claim 1 or 2.

4. The arithmetic mean roughness Ra of the surface of the hard coating is 0.1 μm or less. A surface-coated cutting tool according to claim 1 or 2.

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