Surface-coated cutting tool

Abstract

To provide a surface-coated cutting tool that is able to sufficiently improve the sharpness (the cutting quality) of a cutting edge and is able to further reduce cutting resistance, by reducing a film thickness to reduce surface roughness to small roughness, while maintaining the wear resistance of the tool in cutting work using CFRP as a workpiece.SOLUTION: A surface-coated cutting tool includes a tool base material and an amorphous carbon film 2 coating at least a cutting edge of a surface of the tool base material; the amorphous carbon film 2 contains 0.1% or more and 14% or less of Ta in atomic %; and when a cross-sectional image of the amorphous carbon film 2 is observed, an average grain size of TaC micro-crystals 3 present in a matrix of the amorphous carbon film 2 is 7nm or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a surface-coated cutting tool. [Background technology]

[0002] CFRP (Carbon Fiber Reinforced Plastics) is known for its excellent specific strength and is used in aircraft materials (aircraft parts). CFRP requires a large amount of drilling because it is frequently joined using bolts and rivets. Cutting tools such as drills are used for drilling, but when machining CFRP, the tools wear out quickly, making them prone to losing their sharpness, and causing delamination and burrs in the workpiece, making it difficult to process.

[0003] Furthermore, workpieces such as aircraft parts have large external dimensions, which can make machining inside a machine tool difficult, so cutting tools are often held by robotic arms, etc. Since it is more difficult to ensure the rigidity of robotic arms, etc. compared to machine tools, there is a need to further reduce cutting resistance during cutting in order to achieve high-precision machining.

[0004] Generally, drills coated with CVD diamond film, which has excellent wear resistance, are often used for drilling CFRP. However, CVD diamond film has a high surface roughness, and it is difficult to make it thin (it is generally more than a few micrometers thick), so it cannot be said that the cutting edge is sufficiently sharp. As a result, problems such as increased cutting resistance and reduced hole quality can occur.

[0005] Therefore, in order to reduce cutting resistance and improve hole quality, attention has been focused on DLC (Diamond-like Carbon) coating as a coating film to replace CVD diamond film. 3 Bonds and sp 2 It is an amorphous carbon that has both sp bonds. 3DLC (ta-C), which has a bond ratio of approximately 80%, is second only to diamond in hardness, can be formed into a uniformly thin film, and is thought to be able to achieve both low cutting resistance and high wear resistance.

[0006] Under harsh conditions where a large impact is applied, such as during cutting, residual compressive stress in the DLC film can cause chipping, and so DLC films with added elements are sometimes used primarily to mitigate this (for example, Patent Document 1).The cutting tool in Patent Document 1 is described as having improved wear resistance when cutting cast iron or other ferrous materials as the workpiece. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-94914 Summary of the Invention [Problem to be solved by the invention]

[0008] With conventional surface-coated cutting tools, there was room for improvement in reducing cutting resistance while maintaining the tool's wear resistance when cutting CFRP, a workpiece that is often processed dry without using cutting oil.

[0009] The present invention aims to provide a surface-coated cutting tool that can sufficiently increase the sharpness (cutting performance) of the cutting edge and further reduce cutting resistance by minimizing surface roughness and thinning the surface while maintaining the wear resistance of the tool when cutting CFRP workpieces. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides the following means.

[0011] [Aspect 1 of the present invention] 1. A surface-coated cutting tool comprising: a tool substrate; and an amorphous carbon coating covering at least a cutting edge of a surface of the tool substrate, wherein the amorphous carbon coating contains, in atomic percent, 0.1% to 14% Ta, and when a cross-sectional image of the amorphous carbon coating is observed, TaC microcrystals present in a matrix of the amorphous carbon coating have an average grain size of 7 nm or less.

[0012] In the surface-coated cutting tool of the present invention, an amorphous carbon coating such as a DLC film is provided on at least the cutting edge of the surface of the tool substrate. The amorphous carbon coating can minimize surface roughness and is easily thinned, thereby minimizing cutting resistance and sufficiently enhancing the sharpness of the cutting edge after coating.

[0013] Specifically, while conventional CVD diamond films have a surface roughness Ra of several hundred nanometers, the amorphous carbon coating of the present invention reduces the surface roughness Ra to several tens of nanometers. Therefore, according to the present invention, a tool with low cutting resistance can be obtained when cutting CFRP by dry processing without using cutting oil. Furthermore, while conventional CVD diamond films have a film thickness of several micrometers or more, the amorphous carbon coating of the present invention reduces the film thickness to less than 1 micrometer. Therefore, according to the present invention, the cutting edge shape of the cutting edge can be maintained sharp after film formation, and sharpness can be sufficiently improved.

[0014] The amorphous carbon coating contains Ta. By preferentially oxidizing Ta, destruction of the graphite structure on the outermost surface of the coating is suppressed, and the friction-reducing effect of the graphite structure is well maintained. Specifically, Ta, unlike other elements, has a strong bond with oxygen and is easily oxidized. This makes it possible to suppress destruction of the amorphous carbon coating due to oxidation, and to sustainably maintain the low-friction structure on the outermost surface of the coating.

[0015] Specifically, when the Ta content of the amorphous carbon coating is 0.1 atomic % or more, the Ta effect of inhibiting oxidation of the graphite structure is stably achieved, whereas when the Ta content of the amorphous carbon coating is less than 0.1 atomic %, a sufficient oxidation inhibition effect cannot be achieved.

[0016] Furthermore, by keeping the Ta content of the amorphous carbon coating at 14 atomic % or less, the decrease in hardness of the amorphous carbon coating is suppressed, and good wear resistance is maintained. On the other hand, if the Ta content of the amorphous carbon coating exceeds 14 atomic %, the hardness of the coating decreases and the coating becomes more susceptible to wear (i.e., good wear resistance cannot be maintained). In this case, the friction resistance between TaC and CFRP is not low.

[0017] Furthermore, by setting the average particle size of the TaC microcrystals present in the matrix of the amorphous carbon coating to 7 nm or less, damage to the coating initiated by the TaC is stably suppressed. On the other hand, if the average particle size of the TaC microcrystals present in the matrix of the amorphous carbon coating exceeds 7 nm, TaC is softer than the amorphous carbon coating, and there is a risk of damage to the coating initiated by the TaC. In this case, the friction between TaC and CFRP does not become low resistance.

[0018] The "average particle size" of the TaC microcrystals can be determined, for example, as follows: A predetermined square area (predetermined field of view) with sides measuring several tens to several hundreds of nanometers is determined in the cross-sectional image of the amorphous carbon coating, and the total area and number of TaC microcrystals within this predetermined area are determined by binarizing the image, etc. Then, the value obtained by dividing the total area of ​​the TaC microcrystals by the number (the area of ​​each TaC microcrystal) is converted into particle size, assuming that each microcrystal is circular. This allows the average particle size of the TaC microcrystals to be determined.

[0019] In particular, Ta has a larger atomic size than other elements such as Cr, and tends to reduce the hardness of the amorphous carbon coating. For this reason, it is difficult to add Ta while maintaining wear resistance using conventional techniques, and control of the Ta existence form, as in the present invention, is important.

[0020] As described above, according to the present invention, in cutting processes using CFRP as the workpiece, the sharpness (cutting performance) of the cutting edge can be sufficiently increased by minimizing surface roughness and thinning the tool while maintaining the wear resistance of the tool, thereby enabling further reduction in cutting resistance.

[0021] [Aspect 2 of the present invention] 2. The surface-coated cutting tool according to claim 1, wherein, when a cross-sectional image of the amorphous carbon coating is observed, the TaC crystallites present in the matrix of the amorphous carbon coating have an average grain size of 0.5 nm or more.

[0022] The amorphous carbon film around Ta is sp 2 Therefore, if the TaC crystallites are too small, Ta will be too dispersed, resulting in sp 2 Therefore, it is preferable that the average particle size of the TaC microcrystals present in the matrix of the amorphous carbon coating is 0.5 nm or more, which prevents the TaC microcrystals from being excessively dispersed in the amorphous carbon coating.

[0023] [Embodiment 3 of the present invention] 3. The surface-coated cutting tool according to claim 1, wherein the TaC microcrystals include particles extending in a film thickness direction, the particles having an aspect ratio in which a dimension in the film thickness direction is larger than a dimension in a direction perpendicular to the film thickness direction, and when a cross-sectional image of the amorphous carbon coating is observed, the proportion of the number of the particles to the total number of the TaC microcrystals is 80% or more.

[0024] In this case, the TaC microcrystals contain a large number (80% or more) of elongated particles extending in the film thickness direction. For example, compared to when the TaC microcrystals are simply spherical, the TaC microcrystals have a larger surface area in this configuration. This makes the TaC microcrystals more susceptible to oxidation, while stably suppressing oxidation of the graphite structure, thereby maintaining the friction-reducing function of the amorphous carbon coating.

[0025] Furthermore, compared to when the TaC microcrystals contain many elongated particles extending perpendicular to the film thickness direction, the above configuration can stably prevent the TaC microcrystals from becoming the starting point of film fracture. Therefore, low resistivity can be further improved while maintaining wear resistance. Specifically, when the TaC microcrystals contain many elongated particles, the TaC particles, which have low hardness, are easily sheared and can become the starting point of fracture, which may result in poor wear resistance.

[0026] [Aspect 4 of the present invention] 4. The surface-coated cutting tool of any one of Aspects 1 to 3, wherein the amorphous carbon coating includes a first layer having a thickness direction dimension of 10 nm to 100 nm, and a second layer having a thickness direction dimension of 10 nm to 100 nm, the second layer having a different amount of dispersion of the TaC microcrystals from the first layer, wherein, when a cross-sectional image of the amorphous carbon coating is observed, the number of TaC microcrystals straddling a 10 nm line in the first layer is 0.04 or more per nm, and when a cross-sectional image of the amorphous carbon coating is observed, the number of TaC microcrystals straddling the 10 nm line in the second layer is less than 0.04 per nm, and the first layer and the second layer are alternately stacked in the thickness direction.

[0027] In this case, the amorphous carbon coating has a first layer with a large amount of dispersed TaC microcrystals and a second layer with a small amount of dispersed TaC microcrystals. By alternately stacking the first and second layers with different amounts of dispersed TaC microcrystals in the film thickness direction, the following effects can be obtained.

[0028] For example, if TaC microcrystals are uniformly distributed within the coating, Ta may accumulate on the outermost surface of the coating, increasing the frictional resistance with the CFRP. On the other hand, the above-described configuration of the present invention suppresses such a problem.

[0029] Furthermore, in the above-described configuration of the present invention, the first layer and the second layer, which have different hardnesses, are repeatedly (periodically) laminated, which makes it easier to obtain the effect of suppressing the progression of wear of the coating when cutting CFRP, and thus maintains low friction resistance and good wear resistance. [Effects of the Invention]

[0030] According to the above aspect of the present invention, in cutting processes using CFRP as a workpiece, a surface-coated cutting tool is provided that can sufficiently increase the sharpness (cutting performance) of the cutting edge by reducing the surface roughness and thinning the film while maintaining the wear resistance of the tool, thereby further reducing cutting resistance. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a part of a tool substrate and an amorphous carbon coating of a surface-coated cutting tool according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional image showing a portion of an amorphous carbon coating. [Figure 3] FIG. 3(a) shows a cross-sectional image of an amorphous carbon coating when the Ta content is 1.1 at %, and FIG. 3(b) is an enlarged cross-sectional image of a portion of FIG. 3(a). [Figure 4] FIG. 4 is a plan view schematically showing a film-forming apparatus for manufacturing the surface-coated cutting tool of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0032] A surface-coated cutting tool 10 according to one embodiment of the present invention will be described with reference to the drawings. The surface-coated cutting tool 10 of this embodiment is, for example, a drill. As shown in Fig. 1, the surface-coated cutting tool 10 includes a generally columnar tool substrate 1 extending axially around a central axis (rotation axis), and an amorphous carbon coating 2 covering at least the cutting edge of the surface of the tool substrate 1.

[0033] The tool substrate 1 is made of cemented carbide or tool steel, etc. The amorphous carbon coating 2 is made of a DLC film. Specifically, this DLC film is, for example, sp 3 The coating is tetrahedral amorphous carbon (ta-C), which has a bonding ratio of about 80%. In the following description, the surface-coated cutting tool 10 may be simply referred to as a tool, and the amorphous carbon coating 2 may be simply referred to as a coating.

[0034] The amorphous carbon coating 2 contains Ta in an atomic percentage ranging from 0.1% to 14%. The Ta content in the amorphous carbon coating 2 is calculated, for example, by performing XPS analysis on the coating surface. The XPS analysis is performed under conditions such as AlKα X-rays, an acceleration voltage of 15 kV, and a beam diameter of 100 μm. The amorphous carbon coating 2 has a plurality of TaC microcrystals 3 dispersed within the coating. For example, as shown in Figures 3(a) and 3(b), when observing the cross-sectional image of the amorphous carbon coating 2, the average grain size of the TaC microcrystals 3 present in the matrix of the amorphous carbon coating 2 is 0.5 nm or more and 7 nm or less.

[0035] The "average particle size" of the TaC microcrystals 3 can be determined, for example, as follows. A predetermined square area (predetermined field of view) with sides measuring several tens to several hundreds of nanometers is defined in the cross-sectional image of the amorphous carbon coating 2, and the total area and number of TaC microcrystals 3 within this predetermined area are determined by binarizing the image, etc. Then, the value obtained by dividing the total area of ​​the TaC microcrystals 3 by the number (the area of ​​each TaC microcrystal 3) is converted into particle size, assuming that each microcrystal is circular. This allows the average particle size of the TaC microcrystals 3 to be determined.

[0036] The TaC microcrystals 3 include elongated particles extending in the thickness direction of the coating. The elongated particles have an aspect ratio in which the dimension in the thickness direction is larger than the dimension in the direction perpendicular to the thickness direction. When a cross-sectional image of the amorphous carbon coating 2 is observed, the proportion of the number of elongated particles to the total number of TaC microcrystals 3 is 80% or more. The ratio of the number of elongated particles to the total number of TaC microcrystals 3 is calculated, for example, as follows: A predetermined range is defined in the cross-sectional image of the amorphous carbon coating 2, and TaC microcrystals 3 are extracted from this predetermined range using binarization or the like to determine the number (total number) of TaC microcrystals 3. Next, the aspect ratio of each extracted TaC microcrystal 3 is measured to determine the number of elongated particles extending in the film thickness direction. Then, the ratio (number of elongated particles / total number of TaC microcrystals 3) is calculated.

[0037] Specifically, the term "cross-sectional image" in this embodiment refers to a cross-sectional image based on the following observation conditions, for example: a transmission electron microscope (TEM) is used, the acceleration voltage is 200 kV, the cross-section of the coating is observed at a position about 250 nm from the surface of the tool substrate 1 in the normal direction (corresponding to the film thickness direction), and the magnification (observation field) is 100,000 times (see FIG. 2), 500,000 times (see FIG. 3(a)), 2,000,000 times (see FIG. 3(b)), etc. Furthermore, it is preferable that the numerical values ​​of the cross-sectional images described in this embodiment are determined by measuring multiple fields of view and averaging them.

[0038] 2, the amorphous carbon coating 2 includes a first layer 11 having a thickness direction dimension of 10 to 100 nm, and a second layer 12 having a thickness direction dimension of 10 to 100 nm, and a different amount of dispersed TaC microcrystals 3 from that of the first layer 11. When a cross-sectional image of the amorphous carbon coating 2 is observed, the number of TaC microcrystals 3 straddling a 10-nm line in the first layer 11 is 0.04 or more per nm, and when a cross-sectional image of the amorphous carbon coating 2 is observed, the number of TaC microcrystals 3 straddling a 10-nm line in the second layer 12 is less than 0.04 per nm. The first layer 11 and the second layer 12 are alternately stacked in the thickness direction.

[0039] The dimensions (layer thickness) of the first layer 11 and the second layer 12 in the film thickness direction are calculated, for example, as follows: In a cross-sectional image of the amorphous carbon coating 2, the number of TaC microcrystals 3 straddling a 10-nm-wide line is measured at 1-nm intervals in the normal direction (film thickness direction). A location where the number of particles straddling the line is 0.04 particles / nm or more for 3 nm or more consecutively in the normal direction is considered to be the first layer 11. A location where the number of particles straddling the line is less than 0.04 particles / nm for 3 nm or more consecutively in the normal direction is considered to be the second layer 12. When determining the thickness of each of the first layer 11 and the second layer 12 and the period appearing in the film thickness direction, any portions not considered to be layers 11 and 12 are treated as not existing.

[0040] 4 is a plan view schematically showing a film-forming apparatus 50 for manufacturing the surface-coated cutting tool 10 of this embodiment. The film-forming apparatus 50 is a sputtering apparatus configured by combining a T-FAD (T-shape filtered arc disposition system) and a UBMS (registered trademark).

[0041] In the film-forming apparatus 50, a substrate 52 with a plurality of tool substrates 1 attached thereto is placed in a furnace 51, and while the substrate 52 is being rotated, a carbon solid target 53 is ionized by T-FAD and introduced into the furnace 51. At the same time, a Ta target 54 is sputtered by UBMS (registered trademark) from the direction opposite to the introduction direction, thereby forming a Ta-containing DLC ​​film on each tool substrate 1.

[0042] T-FAD performs ion beam deposition using FCVA (Filtered Cathodic Vacuum Arc) film formation technology. In T-FAD, a 99.99% pure carbon solid target 53 used as a cathode is ionized by arc discharge, and the direction of travel is bent 90 degrees by a magnetic field to remove droplets before being introduced into a furnace 51. The droplet collection unit is indicated by reference numeral 56 in Figure 4. The furnace 51 is also equipped with an ion bombardment device 55.

[0043] Here, a specific example will be given to explain the film formation method of the surface-coated cutting tool 10 using the film formation apparatus 50. The film formation method of the surface-coated cutting tool 10 of the present embodiment includes a bombardment treatment step of the tool substrate 1, a film formation step of the Ta intermediate layer, and a film formation step of the amorphous carbon film 2. The Ta intermediate layer is a layer provided to suppress peeling and chipping of the amorphous carbon film 2 having a large compressive residual stress, but it may not be provided. That is, the film formation step of the Ta intermediate layer may not be provided.

[0044] <Bombardment treatment step of the tool substrate 1> In the present embodiment, before forming a film on the tool substrate 1, the tool substrate 1 is bombarded by the ion bombardment apparatus 55. Specifically, for example, the following bombardment treatment is performed.

[0045] The inside of the film formation apparatus 50 is evacuated, and the pressure in the furnace 51 is set to 0.004 Pa or less. Then, Ar gas is introduced into the furnace 51 at 18 sccm, and the pressure in the furnace 51 is adjusted to 0.18 Pa. Using an ion gun, Ar ions are irradiated toward the tool substrate 1 (substrate 52) rotating at 4 rpm at the center in the furnace 51, and at the same time, a DC bias voltage of -100 V is applied to perform cleaning of the tool (bombardment treatment) by Ar ions.

[0046] <Film formation step of the Ta intermediate layer> When forming the Ta intermediate layer on the tool substrate 1, for example, the film formation is performed as follows. While rotating the tool substrate 1 (substrate 52) at 4 rpm, the flow rate of Ar gas is set to 25 sccm, and the pressure in the furnace 51 is adjusted to 0.22 Pa. A bias voltage of -100 V is applied to the substrate, and the Ta intermediate layer is formed by the UBMS (registered trademark) apparatus at a discharge current of 500 mA until the target film thickness is reached.

[0047] <Film formation step of the amorphous carbon film 2> To form the amorphous carbon film 2 on the tool substrate 1, for example, the film formation is performed as follows. While the tool substrate 1 (substrate 52) is being rotated at 4 rpm, the flow rate of Ar gas is set to 10 sccm, and the pressure inside the furnace 51 is adjusted to 0.12 Pa. Thereafter, the arc current is set to 50 A, the sputtering current to 0, 60, 100, and 300 mA, and the substrate bias is set to −100 V, and an amorphous carbon coating 2 is formed.

[0048] In the surface-coated cutting tool 10 of the present embodiment described above, an amorphous carbon coating 2 made of a DLC film is provided on at least the cutting edge of the surface of the tool substrate 1. The amorphous carbon coating 2 can minimize surface roughness and can be easily thinned, thereby minimizing cutting resistance and sufficiently enhancing the sharpness of the cutting edge after coating.

[0049] Specifically, while conventional CVD diamond films have a surface roughness Ra of several hundred nanometers, the amorphous carbon coating 2 of this embodiment has a surface roughness Ra of only several tens of nanometers. Therefore, this embodiment makes it possible to obtain a tool with low cutting resistance when cutting CFRP by dry machining without using cutting oil. Furthermore, while conventional CVD diamond films have a film thickness of several micrometers or more, the amorphous carbon coating 2 of this embodiment has a film thickness of less than 1 micrometer. Therefore, this embodiment makes it possible to maintain the sharpness of the cutting edge shape after film formation, and to sufficiently improve sharpness.

[0050] The amorphous carbon coating 2 contains Ta. By preferentially oxidizing Ta, destruction of the graphite structure on the outermost surface of the coating is suppressed, and the friction-reducing effect of the graphite structure is well maintained. Specifically, Ta, unlike other elements, has a strong bond with oxygen and is easily oxidized. This makes it possible to suppress destruction of the amorphous carbon coating 2 due to oxidation, and to sustainably maintain the low-friction structure on the outermost surface of the coating.

[0051] Specifically, when the Ta content of the amorphous carbon coating 2 is 0.1 atomic % or more, the Ta effect of inhibiting oxidation of the graphite structure is stably exerted. On the other hand, when the Ta content of the amorphous carbon coating 2 is less than 0.1 atomic %, a sufficient oxidation inhibition effect cannot be obtained.

[0052] Furthermore, by keeping the Ta content of the amorphous carbon coating 2 at 14 atomic % or less, a decrease in the hardness of the amorphous carbon coating 2 is suppressed, and good wear resistance is maintained. On the other hand, if the Ta content of the amorphous carbon coating 2 exceeds 14 atomic %, the hardness of the coating decreases and the coating becomes more susceptible to wear (i.e., good wear resistance cannot be maintained). In this case, the friction resistance between TaC and CFRP is not low.

[0053] Furthermore, by setting the average particle size of the TaC microcrystals 3 present in the matrix of the amorphous carbon coating 2 to 7 nm or less, damage to the coating initiated by the TaC is reliably suppressed. On the other hand, if the average particle size of the TaC microcrystals 3 present in the matrix of the amorphous carbon coating 2 exceeds 7 nm, there is a risk of damage to the coating initiated by the TaC because TaC is softer than the amorphous carbon coating 2. In this case, the friction between the TaC and the CFRP does not result in low resistance.

[0054] In particular, Ta has a larger atomic size than other elements such as Cr, and tends to reduce the hardness of the amorphous carbon coating 2. For this reason, it is difficult to add Ta while maintaining wear resistance using conventional techniques, and it is therefore important to control the state of existence of Ta as in this embodiment.

[0055] As described above, according to this embodiment, in cutting processes using CFRP as the workpiece, the wear resistance of the tool is maintained while the surface roughness is kept small to achieve a thin film, thereby sufficiently increasing the sharpness (cutting performance) of the cutting edge and further reducing cutting resistance.

[0056] In this embodiment, when a cross-sectional image of the amorphous carbon coating 2 is observed, the TaC microcrystals 3 present in the matrix of the amorphous carbon coating 2 have an average grain size of 0.5 nm or more.

[0057] The amorphous carbon film 2 around Ta is sp 2 Therefore, if the TaC crystallites 3 are too small, Ta will be too dispersed, resulting in sp 2 Therefore, the TaC microcrystals 3 present in the matrix of the amorphous carbon coating 2 preferably have an average particle size of 0.5 nm or more, which prevents the TaC microcrystals 3 from being excessively dispersed in the amorphous carbon coating 2.

[0058] In this embodiment, the TaC microcrystals 3 include particles (vertically elongated particles) extending in the film thickness direction, and the particles have an aspect ratio in which the dimension in the film thickness direction is larger than the dimension in the direction perpendicular to the film thickness direction.When a cross-sectional image of the amorphous carbon coating 2 is observed, the proportion of the number of the particles to the total number of TaC microcrystals 3 is 80% or more.

[0059] In this case, the TaC microcrystals 3 contain a large number (80% or more) of elongated particles extending in the film thickness direction. For example, compared to when the TaC microcrystals 3 are simply spherical, the above configuration ensures a large surface area for the TaC microcrystals 3. This makes the TaC microcrystals 3 more susceptible to oxidation, while stably suppressing oxidation of the graphite structure, thereby maintaining the friction-reducing function of the amorphous carbon coating 2.

[0060] Furthermore, compared to when the TaC microcrystals 3 contain many elongated particles extending perpendicular to the film thickness direction, the above configuration can stably prevent the TaC microcrystals 3 from becoming the starting point of film fracture. This makes it possible to further improve low resistivity while maintaining wear resistance. Specifically, if the TaC microcrystals 3 contain many elongated particles, the TaC particles, which have low hardness, are more likely to shear and become the starting point of fracture, which may result in poor wear resistance.

[0061] In this embodiment, the amorphous carbon coating 2 has a first layer 11 whose dimension in the film thickness direction is 10 nm or more and 100 nm or less, and a second layer 12 whose dimension in the film thickness direction is 10 nm or more and 100 nm or less and which has a different amount of dispersion of TaC microcrystals 3 particles from that of the first layer 11. When observing a cross-sectional image of the amorphous carbon coating 2, the first layer 11 has TaC microcrystals 3 whose number of particles straddling a 10 nm line is 0.04 particles / nm or more, and when observing a cross-sectional image of the amorphous carbon coating 2, the second layer 12 has TaC microcrystals 3 whose number of particles straddling a 10 nm line is less than 0.04 particles / nm, and the first layer 11 and the second layer 12 are alternately stacked in the film thickness direction.

[0062] In this case, the amorphous carbon coating 2 has a first layer 11 having a large amount of dispersed TaC microcrystals 3 particles and a second layer 12 having a small amount of dispersed TaC microcrystals 3 particles. By alternately stacking the first layers 11 and the second layers 12 having different amounts of dispersed TaC microcrystals 3 in the film thickness direction, the following effects can be obtained.

[0063] For example, if the TaC microcrystals 3 are uniformly distributed in the coating, Ta may accumulate on the outermost surface of the coating, increasing the frictional resistance with the CFRP. On the other hand, the above-described configuration of this embodiment suppresses such a problem.

[0064] Furthermore, in the above-described configuration of this embodiment, the first layer 11 and the second layer 12, which have different hardnesses, are repeatedly (periodically) laminated, which makes it easier to obtain the effect of suppressing the progression of wear of the coating when cutting CFRP. Furthermore, low friction resistance is maintained, and good wear resistance is maintained.

[0065] The present invention is not limited to the above-described embodiment, and modifications to the configuration are possible within the scope of the invention, as described below.

[0066] In the above-described embodiment, the surface-coated cutting tool 10 is a drill, but the present invention is not limited to this. The surface-coated cutting tool 10 may be any tool that cuts CFRP, such as an end mill or a reamer, other than a drill.

[0067] The present invention may be combined with the various configurations described in the above-described embodiments and modifications, and may also include additions, omissions, substitutions, and other modifications of the configurations, without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the above-described embodiments, but is limited only by the claims. [Example]

[0068] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0069] <Analysis and evaluation of amorphous carbon coating> The amorphous carbon coatings of the examples of the present invention and the conventional comparative examples were subjected to nanoindentation testing, Raman spectroscopic analysis, XPS analysis, and TEM (transmission electron microscope) to analyze the properties and microstructure of the coatings.

[0070] The indentation load in the nanoindentation test (hardness evaluation test) was 1 mN, and measurements were taken at 20 points for each sample, with the average value of the central 10 points being calculated.

[0071] Raman spectroscopy was performed using an Ar ion laser with a wavelength of 532 nm. After background subtraction of the obtained Raman spectrum, the Raman spectrum was obtained at 1331 cm -1 and 1580cm -1 Assuming that there are D and G peaks in the vicinity, peak fitting was performed using a Gaussian function. The intensities of the obtained peaks were designated ID and IG, respectively, and the intensity ratio ID / IG was calculated.

[0072] For XPS analysis, after argon ion etching to remove the outermost oxide layer, narrow peaks of C, O, and Ta were measured using AlKaα rays, an acceleration voltage of 15 kV, and a power of 25 W, and the Ta content was calculated from the area intensity ratio of each peak.

[0073] The following examples and comparative examples were prepared as coating samples to be analyzed. To facilitate measurements, the coatings were formed on test pieces made of cemented carbide instead of drills, and measurements were performed using these test pieces. ·Comparative example 1…DLC film (Ta content: 0) ·Example 1...Ta-containing DLC ​​film (Ta content: 1.1at%) ·Example 2...Ta-containing DLC ​​film (Ta content: 3.5at%) Example 3: Ta-containing DLC ​​film (Ta content: 8.0 at%) ·Example 4...Ta-containing DLC ​​film (Ta content: 8.2at%) Example 5: Ta-containing DLC ​​film (Ta content: 7.6 at%) The Ta contents are similar to each other in Examples 3 to 5. Specifically, Example 3 was formed by the <Step of forming amorphous carbon coating 2> described in the above embodiment, whereas Example 4 differs from Example 3 only in the rotation speed of the tool substrate 1 (substrate 52) (0.4 rpm), and Example 5 differs from Example 3 only in the substrate bias voltage (-200 V).

[0074] Furthermore, in Examples 1 to 4, when cross-sectional images of the amorphous carbon coating 2 were observed by TEM as described below, the average particle size of the TaC microcrystals 3 present in the matrix of the amorphous carbon coating 2 was 0.5 nm or more and 7 nm or less, whereas in Example 5, the average particle size of the TaC microcrystals 3 was less than 0.5 nm. Furthermore, in Examples 1 to 5, the dimensions (layer thickness) of the first layer 11 and the second layer 12 of the amorphous carbon coating 2 in the film thickness direction were 10 nm or more and 100 nm or less, whereas in Example 4, the dimensions (layer thickness) of the first layer 11 and the second layer 12 in the film thickness direction were less than 10 nm (approximately 5 nm). Table 1 below shows the Ta content, hardness, intensity ratio ID / IG, and the percentage of the number of elongated particles in the total number of TaC crystallites for each sample.

[0075] [Table 1]

[0076] From the results in Table 1, it was found that in Examples 1 to 5 of the present invention, the hardness of the coating was ensured to be 18 GPa or more, and the intensity ratio ID / IG was ensured to be 1.1 or less. 3 It was confirmed that a sufficient bonding ratio was ensured. In particular, it was found that in Examples 1 to 3, the hardness of the coating was ensured to be 20 GPa or more, and the intensity ratio ID / IG was ensured to be 0.75 or less.

[0077] The results of cross-sectional observation of the coating by TEM are shown in Figures 2 and 3. Figures 2, 3(a), and 3(b) show cross-sectional images of the amorphous carbon coating 2 of Example 1. Cross-sectional images of the amorphous carbon coatings 2 of Examples 2 to 5 are omitted from the drawings.

[0078] The high-resolution image of Example 1 confirmed that a fine crystalline phase was dispersed within the amorphous structure, and the average diameter (average particle size) of these microcrystals was 2 nm. Phase identification from the diffraction pattern revealed that these microcrystals were TaC crystals. Similarly, in Example 3, the presence of TaC microcrystals within the amorphous structure was confirmed, and the average diameter (average particle size) of these microcrystals was 3 nm. In Example 3, the TaC microcrystals were more densely packed than in Example 1.

[0079] <Cutting evaluation> Using each of the drills according to the embodiment of the present invention and the conventional comparative example, drilling was carried out on a CFRP workpiece for aircraft under the following cutting conditions. (Cutting conditions) ·Cutting speed: 100m / min Feed: 0.1mm / rev -Drilled hole depth 10mm (through hole) Dry processing

[0080] Furthermore, as drills for the cutting test, examples and comparative examples in which the following coatings were formed on tool substrates were prepared. ·Comparative example 1…DLC film (Ta content: 0) ·Example 1...Ta-containing DLC ​​film (Ta content: 1.1at%) ·Example 2...Ta-containing DLC ​​film (Ta content: 3.5at%) Example 3: Ta-containing DLC ​​film (Ta content: 8.0 at%) ·Example 4...Ta-containing DLC ​​film (Ta content: 8.2at%) Example 5: Ta-containing DLC ​​film (Ta content: 7.6 at%) Comparative Example 2: No coating (uncoated drill) Comparative Example 3: CVD diamond film

[0081] The thickness of each coating, surface roughness Ra, and thrust force (cutting resistance) at the fifth hole are shown in Table 2. Note that the thrust force at the fifth hole represents the performance of each drill when Comparative Example 1 is used as the reference (100%).

[0082] [Table 2]

[0083] From the results in Table 2, it was confirmed that the thrust force (cutting resistance) was reduced in all of Examples 1 to 5 of the present invention compared to Comparative Example 1. Therefore, the machining accuracy of the machined holes was also good, with no delamination or burrs being observed. On the other hand, the thrust force increased with the non-coated drill (Comparative Example 2), and the thrust force became excessive with the CVD diamond film of Comparative Example 3, and in both cases the machining accuracy of the drilled hole decreased.

[0084] The present invention is intended solely to improve hole accuracy by reducing thrust force, and wear resistance can be considered good if it achieves, for example, about 90% or more of the performance of Comparative Example 1 (100%). The reason for this is that, particularly in aircraft parts made of CFRP, which tend to have large external dimensions, the cost disadvantage of discarding parts due to poor hole machining is significant, so improving hole quality is given priority over wear resistance (tool life). It was confirmed that all of the above Examples 1 to 5 ensured wear resistance (tool life) of about 90% or more compared to Comparative Example 1. In other words, it was found that the products of the present invention also maintained good wear resistance. [Industrial Applicability]

[0085] The drill of the present invention can maintain the wear resistance of the tool when cutting CFRP workpieces, by reducing the surface roughness and thinning the film, thereby sufficiently increasing the sharpness (cutting performance) of the cutting edge and further reducing the cutting resistance, and therefore has industrial applicability. [Explanation of symbols]

[0086] 1...Tool base material 2...Amorphous carbon coating 3...TaC microcrystal 10…Surface coated cutting tool 11…1st layer 12…Second layer

Claims

1. a tool substrate; an amorphous carbon coating covering at least the cutting edge of the surface of the tool substrate; the amorphous carbon coating contains Ta in an atomic percentage of 0.1% or more and 14% or less, When a cross-sectional image of the amorphous carbon coating is observed, the average grain size of TaC microcrystals present in the matrix of the amorphous carbon coating is 7 nm or less. Surface coated cutting tools.

2. When a cross-sectional image of the amorphous carbon coating is observed, the average grain size of TaC microcrystals present in the matrix of the amorphous carbon coating is 0.5 nm or more. The surface-coated cutting tool of claim 1 .

3. The TaC microcrystals include grains extending in the film thickness direction, the particles have an aspect ratio in which the dimension in the film thickness direction is larger than the dimension in the direction perpendicular to the film thickness direction, When a cross-sectional image of the amorphous carbon coating is observed, the ratio of the number of the particles to the total number of the TaC microcrystals is 80% or more. The surface-coated cutting tool according to claim 1 or 2.

4. The amorphous carbon coating is a first layer having a dimension in a thickness direction of 10 nm to 100 nm; a second layer having a different amount of dispersed TaC microcrystal particles from the first layer and a dimension in the film thickness direction of 10 nm to 100 nm, When a cross-sectional image of the amorphous carbon coating is observed, the first layer has a number of TaC microcrystals straddling a 10 nm line of 0.04 particles / nm or more; When a cross-sectional image of the amorphous carbon coating is observed, the number of TaC microcrystal particles straddling a 10 nm line is less than 0.04 particles / nm, The first layer and the second layer are alternately and repeatedly stacked in the film thickness direction. The surface-coated cutting tool according to claim 1 or 2.

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