Hard coating film and tool coated with hard coating film

Abstract

Provided are a hard coating film which has a new composition and has excellent wear resistance and anti‑adhesion properties to a wide range of workpieces, and a tool coated with the hard coating film. A hard coating film according to the present invention has features such as improved wear resistance, high hardness, and excellent lubricity, owing to not only refinement of crystal particles in a composition A and a composition B but also to the fact that the crystal structures thereof have a cubic rock salt type structure. In addition, the hard coating film includes interfaces AB at which layers composed of the composition A and layers composed of the composition B are in contact with each other. Since each of the layers composed of the composition A is adjacent to the corresponding layer composed of the composition B, AlCrN particles having a cubic rock salt type crystal structure are surrounded by a thin BNx structure phase, whereby the hardness of an AlCrN layer that is a characteristic of the composition B can be increased while reducing the compressive residual stress of an AlCrBN layer that is a characteristic of the composition A. Therefore, the relationship between the hardness and the toughness of the coating film can be controlled, and the wear resistance can be further improved.

Description

Hard coatings and hard coating-coated tools

[0001] The present invention relates to hard coatings and hard coating-coated tools, and more particularly to hard coatings having excellent wear resistance and welding resistance.

[0002] In various types of machining tools, such as cutting tools like end mills, milling cutters, drills, cutting tools, and inserts, as well as non-cutting tools like tamping taps and rolling tools, and various components such as friction parts requiring wear resistance, hard coatings are applied to the surface of base materials such as cemented carbide and high-speed tool steel. For example, Non-Patent Documents 1 and 2 describe examples of end mills coated with AlCrB-based or AlCrB-based / TiAl-based nanolayer coatings. Patent Document 1 also describes tools coated with AlCrN-based and AlCrNB-based multilayer structures.

[0003] Patent No. 6249452

[0004] C Tritremmel et al., Microstructure and mechanical properties of nanocrystalline Al-Cr-BN thin films, Surface & Coating Technology, 213 (2012) 1-7C. Tritremmel et al., Mechanical and tribological properties of Al-Ti-N / Al-Cr-BN multilayer films synthesized by cathodic arc evaporation, Surface & Coating Technology, 246 (2014) 57-63

[0005] However, even with tools coated with such hard coatings, satisfactory performance could not always be obtained depending on the type of workpiece, cutting speed, and other processing and usage conditions, leaving room for improvement. For example, when the tools described in Non-Patent Documents 1 and 2 were used for cutting carbon steel or cast iron, the wear resistance was sometimes insufficient, or when the tools described in Patent Document 1 were used for cutting alloy steel or stainless steel, the resistance to welding was sometimes insufficient, resulting in insufficient performance as tools.

[0006] The present invention was made against the above circumstances, and its objective is to provide a hard coating and a hard coating-coated tool with a new structure that has excellent wear resistance and welding resistance for a wide range of workpiece materials.

[0007] Based on the above circumstances, the inventors conducted various experiments and studies and discovered that by using composition A, consisting of AlCrBα (where α is an optional additive, one or more elements selected from Ti, Si, V, Y, Zr, Nb, and Mo) nitride or carbonitride, and composition B, consisting of AlCrBβ (where β is an optional additive, one or more elements selected from C, V, Y, Zr, Nb, and Mo) nitride, to construct a first and second layer with different thicknesses, and by stacking these first and second layers to form a first layer group and a second layer group, respectively, and by arranging the layer consisting of composition A and the layer consisting of composition B adjacent to each other, a hard coating with superior abrasion resistance and welding resistance can be obtained. The present invention is based on this finding.

[0008] The first invention is (a) a hard coating attached to the surface of a base material so as to cover the surface of the base material, (b) the hard coating comprising a first layer group and a second layer group alternately at least once each, (c) the first layer group comprising at least one of a first layer composed of composition A and a first layer composed of composition B, (d) the second layer group comprising at least one of a second layer composed of composition A and a second layer composed of composition B, and (e) composition A is (Al ａ Cr ｂ B ｃ α ｄC ｘ N １－ｘ However, a, b, c, and d are atomic ratios, where 0.29 ≤ a ≤ 0.85, 0.14 ≤ b ≤ 0.70, 0 < c ≤ 0.15, 0 ≤ d ≤ 0.1, 0 ≤ x ≤ 0.3, and a + b + c + d = 1. α is one or more elements selected from the group consisting of Ti, Si, V, Y, Zr, Nb, and Mo, and is contained at 10 at% or less in atomic ratio. (f) The B composition is (Al ｅ Cr ｆ B ｇ β ｈ N, where e, f, g, and h are atomic ratios, respectively, 0.35 ≤ e ≤ 0.85, 0.1 ≤ f ≤ 0.50, 0 < g ≤ 0.30, 0 ≤ h ≤ 0.10, and e + f + g + h = 1. β is one or more elements selected from the group consisting of C, V, Y, Zr, Nb, and Mo, and is contained at 10 at% or less in atomic ratio. (g) In the first layer group, the thickness of the first layer composed of the A composition and the first layer composed of the B composition is each 0.5 nm or more and 500 nm or less, and the thickness of the first layer group is 1 nm or more and 1,500 nm or less. (h) In the second layer group, the thickness of the second layer composed of the A composition and the second layer composed of the B composition is each 0.5 nm or more and 500 nm or less, and the thickness of the second layer group is 1 nm or more and 1,500 nm or less. (i) The hard film further has at least one AB interface where any layer composed of the A composition and any layer composed of the B composition are in contact within the first layer group, within the second layer group, or at the interface between the first layer group and the second layer group.

[0009] The second invention is the hard film of the first invention, where (j) the first layer group includes at least one of the first layer composed of the A composition, the first layer composed of the B composition, and the first layer composed of the C composition. (k) The second layer group includes at least one of the second layer composed of the A composition, the second layer composed of the B composition, and the second layer composed of the C composition. (l) The thickness of the second layer composed of the C composition is 0.5 nm or more and 500 nm or less. (m) The C composition is (Cr ｉ C ｊ γｋ ) O ｙ N １－ｙ The compound is characterized by the following conditions: (where i, j, and k are in atomic ratios such that 0 < i ≤ 1, 0 ≤ j ≤ 0.35, 0 ≤ k ≤ 0.1, 0 ≤ y ≤ 0.3, and i + j + k = 1), and γ is one or more elements selected from the group consisting of B, Ti, Si, V, Y, Zr, and Mo, and is present in an atomic ratio of 20 at% or less.

[0010] The third invention is characterized in that, in the hard coating of the first or second invention, the total thickness of the hard coating is 0.5 to 15 μm.

[0011] The fourth invention is characterized in that, in the hard coating of the first or second invention, a base layer is provided between the hard coating and the base material, and the hard coating has the AB interface in place of, or in addition to, the interface between the surface layer and the surface layer or the second layer adjacent to the surface layer, within the first layer group, within the second layer group, or at the interface between the first layer group and the second layer group.

[0012] The fifth invention is characterized in that the hard coating of the first or second invention has a surface layer on its outermost surface.

[0013] The sixth invention is characterized by (a) a hard-coated tool in which part or all of the tool base material is covered with a hard coating, and (b) the hard coating is the hard coating described in any one of claims 1 to 3.

[0014] According to the first invention, in a hard coating, the compound of composition A has a cubic rock salt type structure, exhibiting high hardness, wear resistance, lubricity, and oxidation resistance, and improving high-temperature strength and high-temperature toughness. Furthermore, by adding element α to composition A, the crystal grains in the coating are refined, further improving high-temperature strength. The compound of composition B has a cubic crystal layer structure. Furthermore, since the layer composed of composition A and the layer composed of composition B are adjacent to each other at the AB interface, AlCrN particles having a nanometer-sized face-centered cubic (FCC) lattice structure are surrounded by a thin BNx microstructure phase, thereby reducing the compressive residual stress of the AlCrBN layer, which is a characteristic of composition A, while increasing the hardness of the AlCrN layer, which is a characteristic of composition B. Furthermore, by adding element β to composition B, the crystal grains are refined, improving hardness and wear resistance, resulting in a coating with high hardness and excellent lubricity. Therefore, the relationship between the hardness and toughness of the coating can be controlled, and further improvement in wear resistance can be obtained.

[0015] According to the second invention, the hard coating improves the lubricity of the coating of the first invention by forming a Cr-based coating in the C composition. Furthermore, the addition of element γ in the C composition refines the crystal grains, improving hardness and toughness, as well as making the surface smoother and improving wear resistance. In addition, the compressive residual stress increases, improving the mechanical strength of the coating. Moreover, even at high temperatures of 1000°C or higher, there is little decrease in mechanical strength and hardness, maintaining excellent wear resistance. Furthermore, the lubricating film CrCN formed on the surface of the layer composed of the C composition suppresses the progression of wear inward, thus improving the friction and wear characteristics of the entire coating. Furthermore, due to the heat generated during cutting, oxides are formed, exhibiting a self-lubricating effect, which improves tribological properties, allows for higher hardness, and provides excellent wear resistance and oxidation resistance.

[0016] According to the third invention, the thickness of the hard coating of the first or second invention can be appropriately determined, so that the desired wear resistance and welding resistance can be achieved.

[0017] According to the fourth invention, there is a surface layer between the hard coating and the base material. Since the hard coating has the AB interface at the interface between the surface layer and the first layer group or the second layer group adjacent to the surface layer, instead of or in addition to, within the first layer group or within the second layer group, the hard coating is more suitably provided on the base material by the surface layer, and the degree of freedom in the position where the AB interface is provided increases.

[0018] According to the fifth invention, since a surface layer is provided on the outermost surface of the hard coating, the wear resistance and lubricity of the hard coating are improved.

[0019] According to the sixth invention, since the hard coating-coated tool is partially or entirely coated with the hard coating of the first to third inventions, it is excellent in wear resistance and oxidation resistance, and high wear resistance, toughness, lubricity, and weld resistance can be obtained even during processing of carbon steel, stainless steel, nickel alloy, etc. In addition, long life in dry and wet processing can be achieved.

[0020] This is a front view showing an example of an end mill to which the present invention is applied. This is an enlarged bottom view of the end mill in Figure 1, viewed from the tip side. This is a schematic diagram illustrating the coating structure of the hard coating provided on the end mill in Figure 1. This is a schematic diagram illustrating another example of the coating structure of the hard coating provided on the end mill in Figure 1. This is a schematic diagram illustrating yet another example of the coating structure of the hard coating provided on the end mill in Figure 1. This is a schematic diagram illustrating yet another example of the coating structure of the hard coating provided on the end mill in Figure 1. This is a schematic diagram illustrating an arc ion plating apparatus, which is an example of a physical deposition apparatus for forming the hard coatings of Figures 3 to 6 on the tool base material. This is a diagram showing the types and content ratios of constituent elements of composition A that make up the hard coatings of test samples 01 to 06 and development samples 01 to 44 used in cutting tests. This is a diagram showing the types and content ratios of constituent elements of composition B that make up the hard coatings of test samples 01 to 06 and development samples 01 to 44. This figure shows the types and content ratios of constituent elements of the C composition that make up the hard coating of test samples 01 to 06 and development samples 01 to 44. This figure shows the coating hardness of test samples 01 to 06 and development samples 01 to 44, the cutting distance measured by cutting tests, and the judgment results. This figure shows the results of cutting tests for the test samples and development samples in comparison. This figure shows the results of friction and wear tests for the test samples and development samples in comparison. This figure shows the results of analysis by X-ray diffraction (XRD) for the test samples and development samples in comparison. This figure shows the evaluation of the results by X-ray analysis method shown in Figure 14 for the test samples and development samples in comparison.

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front view for explaining an end mill 10 which is an example of a hard film-coated tool to which the present invention is applied, and FIG. 2 is an enlarged bottom view seen from the tip side. This end mill 10 is mainly composed of a tool base material 12 (see FIGS. 3 to 6) of cemented carbide. A shank 14 and a cutting edge portion 16 are integrally provided on the tool base material 12. On the cutting edge portion 16, a cutting edge composed of an outer peripheral edge 18 and a bottom edge 20 is provided around the axis, and intermittent cutting is performed by being rotationally driven around the axis. The end mill 10 of the present embodiment is a ball end mill in which the bottom edge 20 is provided with a roundness. The end mill 10 is a hard film-coated tool and corresponds to an intermittent cutting tool.

[0022] On the surface of the tool base material 12 in the cutting edge portion 16 of FIG. 1, as shown in FIG. 3, a hard film 30 is coated. FIG. 3 is a schematic view showing an enlarged cross section near the surface of the cutting edge portion 16 coated with the hard film 30, and the shaded portion in FIG. 1 represents the region coated with the hard film 30. It is also possible to coat the entire end mill 10 including the shank 14 with the hard film 30. Note that the explanations in FIG. 3 and FIGS. 4 to 6 in the embodiments described later are diagrams for understanding the structure of the film, and do not necessarily accurately represent the thickness of each film.

[0023] The hard film 30 has a surface layer 40 on the surface side, and further has a multilayer structure in which a second layer group 36 and a first layer group 34 are laminated at least one cycle or more. In the example of FIG. 3, the hard film 30 has the second layer group 36 and the first layer group 34 laminated. Further, a base layer 32 is provided at the boundary portion with the tool base material 12. That is, first, the base layer 32 is provided on the surface of the tool base material 12, and on the base layer 32, the first layer group 34 and the second layer group 36 are repeatedly laminated in that order, and the surface layer 40 is provided at the uppermost portion. The total film thickness Ttotal of the hard film 30 including the base layer 32 is appropriately determined within the range of 0.5 to 15 μm.

[0024] The first layer group 34 is composed of either a first layer 34a composed of composition A and a first layer 34b composed of composition B, or it is formed by laminating a first layer 34a composed of composition A and a first layer 34b composed of composition B. In the example in Figure 3, the first layer group 34 is composed of a first layer 34a composed of composition A.

[0025] In the example shown in Figure 3, the second layer group 36 is constructed by laminating a second layer 36a composed of composition A and a second layer 36b composed of composition B. The film thickness Tl2 of the second layer 36a composed of composition A and the second layer 36b composed of composition B are set to be between 0.5 nm and 500 nm, respectively. The total film thickness Tlg2 of the second layer group 36 is set to be between 1 nm and 1,500 nm.

[0026] The aforementioned composition A has the composition formula (Al ａ Cr ｂ B ｃ α ｄ ) C ｘ N １－ｘ (where a, b, c, and d are atomic ratios, with 0.29 ≤ a ≤ 0.85, 0.14 ≤ b ≤ 0.70, 0 < c ≤ 0.15, 0 ≤ d ≤ 0.1, 0 ≤ x ≤ 0.3, and a + b + c + d = 1). That is, (Al ａ Cr ｂ B ｃ α ｄ ) is a nitride or carbonitride. α is one or more elements selected from the group consisting of Ti, Si, V, Y, Zr, Nb, and Mo, and is present in an atomic ratio of 10 at% or less. Figure 8 shows specific examples of the content (at%) of each element in composition A, where a blank space means the content (at%) = 0. That is, products labeled as "development products" meet the requirements of composition A, and products labeled as "test products" do not meet the requirements of composition A. Development products 01 to 04 and development products 08 to 09 do not include the second layer 36c, which is composed of composition C, in the second layer group 36, and correspond to the second layer group 36 in Figure 3. The others correspond to other examples described later.

[0027] The first layer 34a or the second layer 36a, composed of such A composition, contains one or more elements selected from the group consisting of Ti, Si, V, Y, Zr, Nb, and Mo as additives in a proportion of 10 at% or less in the AlCrB nitride or carbonitride. This allows for the refinement of the crystalline particles of the coating, and the particle size of the coating can be controlled simply by changing the amount of additive. All of these compounds have a cubic rock salt type structure as a crystalline system and exhibit high hardness and excellent wear resistance. Furthermore, by including at least one of the aforementioned elements as an additive, they exhibit excellent lubricity and oxidation resistance, resulting in improved high-temperature strength and toughness due to heat generated during cutting, and are effective in reducing oxidative wear caused by heat generated during high-speed machining. Therefore, the coating 30 having A composition has a good balance of wear resistance and welding resistance, and can extend the tool life in high-speed machining regardless of whether it is dry or wet machining. Note that the same A composition is used in the first layer group 34 and the second layer group 36.

[0028] The aforementioned composition B has the composition formula (Al ｅ Cr ｆ B ｇ β ｈ )N, (where e, f, g, and h are atomic ratios, with 0.35 ≤ e ≤ 0.85, 0.1 ≤ f ≤ 0.50, 0 < g ≤ 0.30, 0 ≤ h ≤ 0.10, and e + f + g + h = 1). That is, (Al ｅ Cr ｆ B ｇ β ｈ It is a nitride of ). β is one or more elements selected from the group consisting of C, V, Y, Zr, Nb, and Mo, and is present in an atomic ratio of 10 at% or less. Figure 9 shows specific examples of the content (at%) of each element in composition B, where a blank space means the content (at%) = 0. Products labeled as "development product" meet the requirements of composition B, while products labeled as "test product" do not meet the requirements of composition B.

[0029] The second layer 36b, composed of such a B composition, contains one or more elements selected from the group consisting of C, V, Y, Zr, Nb, and Mo as additives in a proportion of 10 at% or less within the AlCrB nitride, resulting in a coating with high hardness and excellent lubricity, thereby improving wear resistance. Specifically, the coating composed of the B composition has a cubic crystal layer structure, and the crystal grains are refined, resulting in improved hardness and wear resistance. Furthermore, the crystal structure of the coating composed of the B composition is characterized by preferential orientation of the (111) plane over the (200) plane, with the integrated intensity of the diffraction lines of the (111) plane being 1.5 times or more than the integrated intensity of the diffraction lines of the (200) plane. Among the above additives, C, V, Y, Zr, Nb, and Mo, etc., form oxides due to the heat generated during cutting, exhibiting a self-lubricating effect, thus improving tribological properties. Therefore, heat resistance and wear resistance are obtained, contributing to the extension of tool life.

[0030] Furthermore, in the hard coating 30 of this embodiment, the second layer group 36 is constructed by alternately laminating a second layer 36a composed of composition A and a second layer 36b composed of composition B. Of these, at least one of the outermost surface side or the side closest to the tool base material 12 in the second layer group 36 is a second layer 36b composed of composition B. In this way, the second layer 36b composed of composition B in the second layer group 36 and the first layer 34a composed of composition A, which is the first layer group 34, have an interface, that is, an AB interface 51 in the present invention where a layer composed of composition B and a layer composed of composition A are in contact. Note that the number of layers and the lamination order of each second layer group 36 in the hard coating 30 of this embodiment are common.

[0031] In the hard coating 30, at least one of the first layer 34a and the second layer 36a, both composed of composition A, is adjacent to at least one of the second layer 36b, which is composed of composition B, and has the AB interface 51. With this configuration, composition B has a higher boron content than composition A, resulting in finer grain structure. This difference in crystalline structure causes strain at the interface, strengthening the coating. Furthermore, the AlCrN particles having nano-sized rock salt-type crystals contain a nanocomposite structure of AlCrBN coating surrounded by a thin BNx microstructure phase, significantly increasing the hardness of the AlCrN coating while reducing compressive residual stress. This allows for good control of the relationship between the hardness and toughness of the coating. In addition, the wear resistance effect on the rake face and the suppression of wear on the outer flank face of the end mill 10 provided with the hard coating 30 can be further improved.

[0032] As described above, the hard coating 30 can take various forms, but in all cases, it is constructed by alternately stacking a first layer group 34 and a second layer group 36. In the second layer group 36, at least two second layers 36a, 36b, and 36c, which are composed of different compositions, are alternately stacked, and the second layers 36a, 36b, and 36c have a thickness on the order of nanometers. By controlling the stacking period, the hard coating 30 has finer crystalline particles in the first layer group 34 or the second layer group 36, increasing the hardness of the coating and resulting in a coating with a smooth surface that is excellent in terms of high hardness and high toughness. Furthermore, the stacking of layers of different compositions within the first layer group 34, within the second layer group 36, or at the boundary between the first layer group 34 and the second layer group 36 affects the hardness of the multilayer coating. Here, in these layers of different compositions aligned in the growth direction of the coating, particle growth stops at the interface, recrystallization nucleation occurs, and then the crystals and structure grow again. Thus, the increase in hardness of the hard coating 30 is related to the effect of reducing particle size. Due to slight differences in the lattice constants of the FCC phases of composition A and composition B, coherence strain occurs at the AB interface 51 between the layers composed of composition A and composition B, improving the hardness of the coating 30. More specifically, crystal growth is affected by the AB interface 51, and subsequent competitive growth conditions are controlled. As a result, particle growth in the coating layer stops at the AB interface 51, recrystallization nucleation occurs, and then the crystals and structure grow again. Therefore, the increase in hardness is related to the effect of reducing particle size according to the Hall-Petch relationship, as crystal growth is inhibited throughout the AB interface 51.

[0033] On the other hand, the elastic properties are affected by the presence of the AB interface 51, and because the rigidity of the multilayer coating 30 is high, the Young's modulus becomes high, and the tensile stress increases in the hard coating 30 of this embodiment. This is thought to be due to the following combined effects: the stress levels of the individual layers constituting the first layer group 34 and the second layer group 36, the thickness of the layers, and the configuration of the AB interface 51. The increase in tensile stress between the layer composed of composition A and the layer composed of composition B is determined by the boron (B) content. As the boron (B) content increases, the orientation (111) seen in the AlCrBN film increases compared to the layer composed of composition A and the layer composed of composition B, as the boron content is lower, and the AlCrBN crystal grains become finer. Therefore, composition A (Al ａ Cr ｂ B ｃ α ｄ ) C ｘ N １－ｘ ) and B composition (Al ｅ Cr ｆ B ｇ β ｈ Because defects and dislocations effectively disappear within the multilayer structure of the material, tensile stress increases.

[0034] The surface layer 40 is the surface of the hard coating 30, that is, the outermost layer of the laminated hard coating 30. The surface layer 40 is composed of, for example, one of the compositions that make up the first layer group 34 or the second layer group 36 described above. In the example in Figure 3, the surface layer 40 may be composed of composition A or composition B. In Figure 3 and the example in Figure 4 described later, an example is shown in which the surface layer 40 is composed of composition B.

[0035] The base layer 32 is a layer that constitutes the hard coating 30 and is provided at the boundary with the tool base material 12. That is, the base layer 32 is first provided on the surface of the tool base material 12, and the first layer group 34, the second layer group 36, and the surface layer 40 are provided on top of the base layer 32. The base layer 32 is composed of, for example, one of the compositions that make up the first layer group 34 or the second layer group 36. In the example of the hard coating 50 in Figure 4, the surface layer 40 can be composed of composition A, composition B, or composition C. In the example in Figure 3, an example is shown in which the base layer 32 is composed of composition B, and in the example in Figure 4, which will be described later, an example is shown in which the base layer 32 is composed of composition C. The total film thickness T of the hard coating 30 including the base layer 32 and the surface layer 40 is set within the range of 0.5 to 15 μm. When the surface layer 40 is composed of composition B, and a first layer 34a composed of composition A is provided below the surface layer 40 as the first layer group 34, the AB interface 51 will occur as the interface between the surface layer 40 and the first layer 34a composed of composition A as the first layer group 34. That is, the AB interface 51 is not limited to the interface that occurs between the first layer 34a or second layer 36a composed of composition A and the first layer 34b or second layer 34b composed of composition B, as described above. In addition to the above-described embodiments, or in place of these, the AB interface 51 may also occur between the first layer group 34 or second layer group 36 and the surface layer 40.

[0036] Figures 4 to 6 illustrate another embodiment of this model. In the example in Figure 4, the first layer group 34 of the hard coating 50 includes a first layer 34a composed of composition A and a first layer 34b composed of composition B, and the second layer group 36 is constructed by laminating a second layer 36b composed of composition B and a second layer 36c composed of composition C, which differs from the example in Figure 3. Furthermore, in the examples in Figures 4 and 6, the base layer 32 is composed of composition C, and in the example in Figure 5, the base layer 32 is constructed by alternately laminating compositions A and B, which also differs from the example in Figure 3.

[0037] The above C composition is (Cr ｉ Cｊ γ ｋ ) O ｙ N １－ｙ , (where i, j, and k are atomic ratios, and 0 < i ≤ 1, 0 ≤ j ≤ 0.35, 0 ≤ k ≤ 0.1, 0 ≤ y ≤ 0.3, and i + j + k = 1). That is, Cr ｉ C ｊ γ ｋ It is a nitride or oxynitride. The additive γ is one or more elements selected from the group consisting of B, Ti, Si, V, Y, Zr, and Mo, and is present in an atomic ratio of 20 at% or less. Figure 10 shows specific examples of the content (at%) of each element in the C composition, with blank spaces indicating a content (at%) of 0. Products labeled as "development product" meet the requirements for the C composition, while products labeled as "test product" do not meet the requirements for the C composition.

[0038] In the hard coating 50 shown in Figure 4, the thicknesses of the second layer 36b, which is composed of composition B, and the second layer 36c, which is composed of composition C, which constitute the second layer group 36, are set to 0.5 nm or more and 500 nm or less, respectively.

[0039] The second layer 36c, composed of such a C composition, contains 20 at% or less of one or more elements selected from the group consisting of B, Ti, Si, V, Y, Zr, and Mo as additives in the CrC nitride or oxynitride. This results in refinement of the crystal grain of the coating within the second layer 36c composed of the C composition, improving hardness and wear resistance. The inclusion of the aforementioned additive γ provides improved hardness and toughness. The CrC nitride or oxynitride with the C composition, when additive γ is added, has finer columnar crystals than that of the CrN coating, and the compressive residual stress also increases, thus increasing the hardness of the coating. It exhibits less reduction in mechanical strength even at temperatures above 1000°C, has excellent wear resistance, and the smooth surface of the coating results in a coating with high hardness and excellent low friction properties, thus improving wear resistance. The CrCN lubricating film formed on the surface of the second layer 36c, which is composed of C, suppresses wear progression into the interior of the second layer 36c, improving wear resistance and low friction characteristics. Furthermore, the heat generated during cutting forms oxides, exhibiting a self-lubricating effect, thereby improving tribological properties, enabling high hardness, and providing excellent wear resistance and oxidation resistance. Therefore, an end mill 10 coated with a hard coating 50 including the second layer 36c composed of C can achieve extended tool life in high-speed dry and wet machining of general-purpose materials and heat-resistant alloys such as carbon steel, stainless steel, and nickel alloys.

[0040] Furthermore, in the hard coating 50 shown in Figure 4, the first layer group 34 is constructed by alternately stacking a first layer 34a composed of composition A and a first layer 34b composed of composition B. Of these, at least one of the outermost surface side or the side closest to the tool base material 12 in the first layer group 34 is a first layer 34a composed of composition A. In the second layer group 36, a second layer 36b composed of composition B and a second layer 36c composed of composition C are alternately stacked. In this case, an AB interface 51 may be formed when the first layer 34a composed of composition A at the end face of the first layer group 34 and the adjacent second layer 36b composed of composition B in the second layer group 36 are in contact. In this way, an AB interface 51 is present at the interface where the second layer 36b composed of composition B in the second layer group 36 and the first layer 34a composed of composition A in the first layer group 34 are in contact. An AB interface 51 is also present within the first layer group 34. In this embodiment, the number of layers and the layering order of each first layer group 34 and each second layer group 36 in the hard coating 30 are common to all.

[0041] In the example shown in Figure 5, the first layer group 34 of the hard coating 60 includes a first layer 34b composed of composition B and a first layer 34c composed of composition C. The second layer group 36 is constructed by laminating a second layer 36a composed of composition A, a second layer 36b composed of composition B, and a second layer 36c composed of composition C. The base layer 32 is constructed by laminating a base layer 32a composed of composition A and a base layer 32b composed of composition B. In Figure 5, since the first layer group 34 is laminated in the order of first layer 34c and first layer 34b from the base material side, composition B appears on the surface side of the first layer group 34. In this case, in the second layer group 36, the second layer 36a composed of composition A is positioned closest to the base material 12, so that the first layer 34b composed of composition B in the first layer group 34 and the second layer 36a composed of composition A in the second layer group 36 are in contact. Alternatively, or in addition to the above, the second layer group 36 may be laminated such that a second layer 36a composed of composition A and a second layer 36b composed of composition B are in contact with each other. The surface layer 40 is composed of multiple layers of surface layer 40b composed of composition B.

[0042] In the example shown in Figure 6, the first layer group 34 of the hard coating 70 is constructed by laminating a first layer 34a composed of composition A, a first layer 34b composed of composition B, and a first layer 34c composed of composition C. The second layer group 36 is constructed by laminating a second layer 36a composed of composition A, a second layer 36b composed of composition B, and a second layer 36c composed of composition C. The base layer 32 is composed of composition C. In this case, within the first layer group 34, the first layer 34a composed of composition A and the first layer 34b composed of composition B can be arranged to be in contact. Similarly, within the second layer group 36, the second layer 36a composed of composition A and the second layer 36b composed of composition B can be arranged to be in contact. That is, the AB interface 51 is formed inside the first layer group 34 and inside the second layer group 36, respectively. The effects of the present invention can be achieved by applying at least one of these. In the example shown in Figure 6, the surface layer 40 is not provided. Furthermore, in the example shown in Figure 6, the second layer 36a, which is composed of composition A and is closest to the base material 12 in the second layer group 36, and the first layer 34b, which is composed of composition B and is adjacent to the tool base material side of the first layer group 34, can be arranged in contact with each other. In this case, an AB interface 51 is also provided by the second layer 36a, which is composed of composition A, and the first layer 34b, which is composed of composition B.

[0043] Figure 7 is a schematic diagram illustrating the configuration of an arc ion plating apparatus 100 used when coating a tool base material 12 with the hard coatings 30, 50, 60, 70, or the hard coating of the developed product described in Figure 11 (hereinafter, unless otherwise specified, simply referred to as hard coating 30, etc.). This apparatus coats the surface of the tool base material 12 with the hard coating 30, etc. by the arc ion plating method, which is a type of PVD method. By switching the evaporation source (target) and reaction gas, multiple types of layers with different compositions can be continuously formed with predetermined film thicknesses. For example, in the case of the hard coating 30 shown in Figure 3, after providing a base layer 32 on the surface of the tool base material 12, a first layer 34a composed of composition A and a second layer group 36 are repeatedly and alternately laminated as the first layer group 34, and finally a surface layer 40 is provided. When laminating the second layer group 36, the second layer 36a composed of composition A and the second layer 36b composed of composition B are laminated to a predetermined thickness and number of repetitions. Figure 7 is a plan view of the arc ion plating apparatus 100, seen from above.

[0044] The arc ion plating apparatus 100 includes a rotary table 154 that holds multiple workpieces, i.e., tool base materials 12 to be coated with a hard film 30, etc., and is driven to rotate around a substantially vertical rotation center S; a bias power supply 156 that applies a negative bias voltage to the tool base materials 12; a chamber 158 that serves as a processing container housing the tool base materials 12 inside; a reaction gas supply device 160 that supplies a predetermined reaction gas into the chamber 158; an exhaust device 162 that discharges the gas in the chamber 158 using a vacuum pump or the like to reduce the pressure; a first arc power supply 164; a second arc power supply 166; a third arc power supply 168; and the like. The rotary table 154 has a disc shape centered on the rotation center S, and multiple tool base materials 12 are arranged on the outer circumference of the rotary table 154 in a position substantially parallel to the rotation center S. The tool base materials 12 can also be rotated on their own axis while revolving around the rotation center S by the rotary table 154. The reaction gas supply device 160 supplies nitrogen gas into the chamber 158 when coating nitrides such as layers 32a and 34a composed of composition A, layers 32b and 34b composed of composition B, and layers 32c and 34c composed of composition C. The chamber 158 is kept under vacuum, for example, 2 to 10 Pa, by the exhaust device 162, and heated to a deposition processing temperature of, for example, 300 to 600°C by the heater 185 or the like.

[0045] The first arc power supply 164, the second arc power supply 166, and the third arc power supply 168 each use a first evaporation source 172, the second evaporation source 176, and the third evaporation source 180, all made of deposition material, as cathodes. By selectively applying a predetermined arc current between these cathodes and anodes 174, 178, and 186, they cause an arc discharge, selectively evaporating the evaporation material from these first evaporation sources 172, the second evaporation source 176, and the third evaporation source 180. The evaporated evaporation material becomes positive ions and is deposited onto the tool base material 12 to which a negative bias voltage is applied. That is, the evaporation sources 172, 176, and 180 are each composed of one of the alloys of composition A, composition B, and composition C. If a layer composed of another composition in addition to these compositions A, B, and C is to be constructed, this can be realized by using the alloy of the other composition as a fourth evaporation source and further providing corresponding arc power supplies and anodes.

[0046] Then, by appropriately switching the arc power supplies 164, 166, and 168 to sequentially coat layers of a predetermined composition, the hard coating 30 or the like with a predetermined coating structure can be obtained. The thickness of each layer can be adjusted by the rotation speed of the rotary table 154, the energizing time of the arc power supplies 164, 166, and 168, etc. A mixed layer of two different compositions may be formed at the boundary between multiple layers of different compositions.

[0047] Furthermore, although not shown in the illustrations, the hard coating can be constructed in yet another manner. For example, in the hard coating 30, a first layer 34a composed of composition A was used as the first layer group 34, but instead, a first layer 34b composed of composition B may be used. In the hard coating 50, a first layer 34a composed of composition A and a first layer 34b composed of composition B were laminated as the first layer group 34, but a first layer 34a composed of composition A may be used alone. In the hard coating 60, a first layer 34b composed of composition B and a first layer 34c composed of composition C were laminated as the first layer group 34, but at least one selected from the first layer 34a composed of composition A, the first layer 34b composed of composition B, and the first layer 34c composed of composition C may be used. The hard coating 70 is configured as a first layer group 34 in which a first layer 34a composed of composition A, a first layer 34b composed of composition B, and a first layer 34c composed of composition C are laminated together. However, at least one selected from the first layer 34a composed of composition A, the first layer 34b composed of composition B, and the first layer 34c composed of composition C may be used.

[0048] Similarly, in the hard coating 30, the second layer group 36 is configured with a second layer 36a composed of composition A and a second layer 36b composed of composition B, but instead, it may be configured with a second layer 36a composed of composition A, a second layer 36b composed of composition B, and a second layer 36c composed of composition C, all of which are laminated together. In the hard coating 50, the second layer group 36 is configured with a second layer 36b composed of composition B and a second layer 36c composed of composition C, but instead, it may be configured with a second layer 36a composed of composition A and a second layer 36c composed of composition C, or with a second layer 36a composed of composition A, a second layer 36b composed of composition B, and a second layer 36c composed of composition C, all of which are laminated together. Furthermore, in the hard coatings 60 and 70, the second layer group 36 is configured by laminating a second layer 36a composed of composition A, a second layer 36b composed of composition B, and a second layer 36c composed of composition C. However, instead, two of the second layers from the second layer 36a composed of composition A, the second layer 36b composed of composition B, and the second layer 36c composed of composition C may be combined.

[0049] In the hard coatings 30, 50, 60, and 70, a base layer 32 was provided in all of them, but the presence of the base layer 32 is optional, and the first layer group 34 or the second layer group 36 may be directly laminated onto the tool base material 12. Also, in the hard coatings 30, 50, and 60, a surface layer 40 was provided in all of them, but not in the hard coating 70, but the presence of the surface layer 40 is optional, and the surface layer 40 may not be provided in the hard coatings 30, 50, and 60, or the surface layer 40 may be provided in the hard coating 70.

[0050] Furthermore, in all of the hard coatings 30, 50, 60, and 70, the first layer group 34 and the second layer group 36 are stacked alternately in units of one cycle, but it is arbitrary whether the top layer of the hard coatings 30, 50, 60, and 70 is the first layer group 34 or the second layer group 36.

[0051] Next, we will explain the results of performance tests of the hard coatings on ball end mills similar to the end mill 10, which has a diameter of 6 mm and two blades, with a tool base material 12 made of ultrafine grain cemented carbide. Test specimens 01 to 06 and development specimens 01 to 44 were prepared, each fitted with a hard coating structure as shown in Figures 8 to 11. Figure 11 shows the test results, where the coating hardness is the value measured under conditions indicated by the hardness symbol HV0.025 according to the Vickers hardness test method (JIS G0202, Z2244). Furthermore, the wear width of the flank surface of the outer cutting edge 18 and the cutting distance were measured when cutting was performed using test specimens 01 to 06 and development specimens 01 to 44 according to the following cutting test conditions, and the coating performance (durability) was determined. Specifically, the cutting process was interrupted at various points to measure the flank wear width, and the cutting distance was measured when the flank wear width exceeded 0.2 mm. A cutting distance of 2000 m or more was marked as a pass ("○"), and a cutting distance of less than 2000 m was marked as a fail ("×"). The flank wear width was measured by visual observation using a measuring microscope (MM-400 / LM) manufactured by Nikon Corporation. <Cutting test conditions> ・Workpiece material: SUS304 ・Cutting fluid: Water-soluble ・Rotation speed n: 10610 min －１ - Feed rate: f = 0.12 mm / t, F = 2540 mm / min - Cutting method: Linear pick cutting - Axial depth of cut ap: 0.3 mm - Radial depth of cut pf: 0.6 mm As is clear from Figure 11, regarding the coating hardness (HV 0.025), all of the inventive products, development products 01 to 44, are in the range of 3020 to 3850 (HV), and excellent wear resistance and impact resistance (strength against cracking and peeling due to intermittent cutting) can be expected, whereas the comparative test products 01 to 06 were in the range of 2340 to 2980 (HV). Regarding the cutting distance, all of the inventive products, development products 01 to 44, were able to perform cutting operations of 2000 m or more, and excellent durability was obtained. In contrast, the comparative test products 01 to 06 all had cutting distances of less than 2000 m.

[0052] Figure 12 shows the results of measuring the wear width of the outer cutting edge 18 after a predetermined cutting distance has elapsed in each test, for test product 01, development products 15, 20, 26, and 29, which are ball end mills with a hard coating, as shown in Figures 8 to 11, and for each of them, the cutting test shown in Figure 11 was performed twice, and the wear width of the outer cutting edge 18 was measured after a predetermined cutting distance has elapsed in each test. In Figure 12, the cutting distance (m) is shown on the horizontal axis and the wear width of the outer cutting edge 18 (mm) is shown on the vertical axis. As can be seen from Figure 12, development products 15, 20, 26, and 29, which are embodiments of the present invention, all show a smaller wear width compared to test product 01, which is a comparative example. In other words, the ball end mills of this embodiment have improved wear resistance and, consequently, durability compared to the comparative example.

[0053] Figure 13 shows the results of friction and wear tests conducted on test specimen 01, development specimens 15, 20, 26, and 29, which are ball end mills coated with a hard coating, as shown in Figures 8 to 11, test specimens 01 to 06 and development specimens 01 to 44. In Figure 13, the horizontal axis shows the test time (seconds), and the vertical axis shows the measured friction coefficient μ value. The test conditions for the friction and wear test are as follows. 《Cutting Test Conditions》 ・Friction and wear testing machine: Pin-on-disk type ・Laying material: S45C ・Cooling conditions: Dry ・Load: 500 gf ・Linear speed: 450 mm / s ・Test time: 900 seconds ・Ambient temperature: 25°C ・Ambient humidity: 52% The friction and wear characteristics obtained under these conditions are shown in Figure 13. It can be seen that the developed products 15, 20, 26, and 29, which are embodiments of the present invention, all show a smaller increase in the coefficient of friction over time compared to the comparative example test product 01, and maintain low friction characteristics. In other words, it can be seen that the ball end mill of this embodiment is superior to the comparative example in terms of tribological characteristics.

[0054] Figure 14 shows the X-ray diffraction (XRD) patterns obtained using the powder method with CuKα rays for test sample 01, development samples 15, 26, and 29, which are among the hard coatings of test samples 01 to 06 and development samples 01 to 44 shown in Figures 8 to 11. In the XRD patterns shown in Figure 14, a peak corresponding to (111) in the crystal structure is observed around 2θ = 37.5°. Also, a peak corresponding to (200) in the crystal structure is observed around 2θ = 44°.

[0055] Here, the crystal structure corresponding to (200) does not affect the hardness of the film compared to the crystal structure corresponding to (111), but because the crystals are refined, the wear characteristics and lubricity are improved.

[0056] Figures 15(a) to 15(c) are diagrams for evaluating the XRD patterns of Figure 14. Figure 15(a) shows the ratio of the peak intensity (count) corresponding to (111) to the peak intensity (count) corresponding to (200) for each of test sample 01 and development samples 15, 26, and 29. Figure 15(b) shows the peak intensity (count) corresponding to (200) and the peak intensity (count) corresponding to (111) for each of test sample 01 and development samples 15, 26, and 29. Figure 15(c) shows the full width at half maximum (°) of the peak corresponding to (200) and the full width at half maximum (°) of the peak corresponding to (111) for each of test sample 01 and development samples 15, 26, and 29.

[0057] As shown in Figures 15(a) and (b), for all of the development samples 15, 26, and 29, the intensity (count) of the peak corresponding to (111) is greater than the intensity (count) of the peak corresponding to (200) compared to test sample 01. Therefore, the ratio of the intensity (count) of the peak corresponding to (111) to the intensity (count) of the peak corresponding to (200) is also a large value. This is thought to be because, in test sample 01, boron B is not included in any of the element γ added to compositions A, B, and C, while in development samples 15, 26, and 29, boron B is included in any of the element γ added to compositions A, B, and C.

[0058] Furthermore, the significant improvement in the mechanical properties of the Al-Cr-N film observed with the addition of boron B is thought to be due to a combined effect of solid solution hardening, grain refinement (Hall-Petch hardening), and the formation of the a-BN_x phase, as can be seen from Figure 15(c). When a microstructure containing Al-Cr-(B)-N microcrystals is formed, adding boron B beyond the solubility limit within the Al-Cr-N lattice increases hardness. This is related to the small crystal size and the presence of a-BN_x in the particles, as boron B and possibly the a-BN_x phase also affect local bonding at the particle boundaries, thereby increasing the strength of the grain boundaries. This allows for improvement of mechanical properties without increasing compressive stress.

[0059] In the hard coatings 30, 50, 60, and 70 of this embodiment, the addition of element α in composition A makes it possible to refine the crystal grains in the coating. Furthermore, the compound of composition A has a cubic rock salt type structure and is excellent in hardness, wear resistance, lubricity, and oxidation resistance, thus improving high-temperature strength and high-temperature toughness. In addition, the addition of element β in composition B makes the crystal grains smaller, improving hardness and wear resistance, and results in a coating that is both hard and has excellent lubricity. Furthermore, the hard coatings 30, 50, 60, and 70 of this embodiment have an AB interface 51 where the layer composed of composition A and the layer composed of composition B are in contact. Here, the compound of composition B has a cubic rock salt type crystal structure. Furthermore, since the layer composed of composition A and the layer composed of composition B are adjacent, the AlCrN particles having a nanometer-sized cubic rock salt-type crystalline structure are surrounded by a thin BNx microstructure. This reduces the compressive residual stress of the AlCrBN layer, which is a characteristic of composition A, while increasing the hardness of the AlCrN layer, which is a characteristic of composition B. As a result, the relationship between the hardness and toughness of the coating can be controlled, leading to further improvements in wear resistance.

[0060] Furthermore, in the hard coatings 30, 50, 60, and 70 of this embodiment, the addition of element γ in the C composition refines the crystal grains, improving hardness and toughness. In addition, since there is little decrease in mechanical strength even at high temperatures of 1000°C or higher, it exhibits excellent wear resistance in tool usage environments, and the smooth surface of the coating results in a coating with excellent low friction properties. The lubricating film CrCN that forms on the surface of the layer composed of the C composition suppresses the progression of wear inward, thus improving the overall wear resistance and low friction properties of the coating structure for a long time. Moreover, the heat generated during cutting forms oxides, exhibiting a self-lubricating effect, which improves tribological properties, allows for high hardness, and provides excellent high-temperature mechanical properties.

[0061] Furthermore, since the thicknesses of the hard coatings 30, 50, 60, and 70 in this embodiment are appropriately determined, the desired wear resistance and welding resistance can be achieved.

[0062] Furthermore, the end mill 10 coated with the hard coatings 30, 50, 60, and 70 of this embodiment exhibits excellent wear resistance and oxidation resistance because part or all of it is covered with the hard coatings 30, 50, 60, and 70. High wear resistance, toughness, lubricity, and welding resistance can be obtained even when machining carbon steel, stainless steel, nickel alloys, etc. In addition, extended tool life can be achieved in both dry and wet machining.

[0063] Although embodiments of the present invention have been described in detail above with reference to the drawings, these are merely examples, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

[0064] For example, in the above-described embodiment, the tool coated with the hard coating 30 was an end mill 10, but it is not limited to this. For example, it is suitably applied to hard coatings provided on the surface of various processing tools, such as rotary cutting tools like milling cutters, taps, and drills, as well as non-rotary cutting tools like cutting tools, or non-cutting tools like build-up taps and rolling tools. It can also be applied to hard coatings provided on the surface of components other than processing tools that require wear resistance, lubricity, oxidation resistance, etc., such as press molds, bearing members, and surface protective films for semiconductor devices. It can also be applied to cutting edge tips used attached to various processing tools. As the tool base material for hard-coated tools, cemented carbide, high-speed tool steel, cermet, ceramics, polycrystalline diamond (PCD), single-crystal diamond, and CBN are suitably used, but other tool materials can also be used. As the means for forming the hard coating, PVD methods (physical vapor deposition) such as arc ion plating, sputtering, and PLD (Pulse Laser Deposition) are suitably used.

[0065] The hard coating of the present invention is suitably used in cutting tools for machining other workpiece materials such as carbon steel, stainless steel, cast iron, and alloy steel, but is also suitably used in cutting tools for machining titanium alloys, for example. It can also be used in cutting tools that perform machining under harsh machining conditions such as high-speed machining and dry machining.

[0066] It should be noted that the above-described embodiment is merely one example, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

[0067] 10: End mill 12: Tool base material 30, 50, 60, 70: Hard coating 32: Base layer 34: First layer group 34a: First layer composed of composition A 34b: First layer composed of composition B 36: Second layer group 36a: Second layer composed of composition A 36b: Second layer composed of composition B 36c: Second layer composed of composition C 40: Surface layer 51: AB interface 100: Arc ion plating apparatus

Claims

1. A hard film adhered to the surface so as to coat the surface of a base material, the hard film including at least once each of a first layer group and a second layer group alternately, the first layer group including at least one of a first layer composed of an A composition and a first layer composed of a B composition, the second layer group including at least one of a second layer composed of an A composition and a second layer composed of a B composition, the A composition being (Al ａ Cr ｂ B ｃ α ｄ )C ｘ N １－ｘ , (where a, b, c, d are atomic ratios respectively, 0.29 ≤ a ≤ 0.85, 0.14 ≤ b ≤ 0.70, 0 < c ≤ 0.15, 0 ≤ d ≤ 0.1, 0 ≤ x ≤ 0.3, and a + b + c + d = 1), α is one or more elements selected from the group consisting of Ti, Si, V, Y, Zr, Nb, and Mo, and is included at 10 at% or less in atomic ratio, the B composition being (Al ｅ Cr ｆ B ｇ β ｈ )N, (where e, f, g, h are atomic ratios respectively, 0.35 ≤ e ≤ 0.85, 0.1 ≤ f ≤ 0.50, 0 < g ≤ 0.30, 0 ≤ h ≤ 0.10, and e + f + g + h = 1), β is one or more elements selected from the group consisting of C, V, Y, Zr, Nb, and Mo, and is included at 10 at% or less in atomic ratio, in the first layer group, the thicknesses of the first layer composed of the A composition and the first layer composed of the B composition are each 0.5 nm or more and 500 nm or less, and the thickness of the first layer group is 1 nm or more and 1,500 nm or less, in the second layer group, the thicknesses of the second layer composed of the A composition and the second layer composed of the B composition are each 0.5 nm or more and 500 nm or less, and the thickness of the second layer group is 1 nm or more and 1,500 nm or less, the hard film further having at least one AB interface in the first layer group, in the second layer group, or at the interface between the first layer group and the second layer group where any layer composed of the A composition contacts any layer composed of the B composition, a hard film characterized by the above.

2. The single layer group includes at least one of a first layer composed of composition A, a first layer composed of composition B, and a first layer composed of composition C; the second layer group includes at least one of a second layer composed of composition A, a second layer composed of composition B, and a second layer composed of composition C; the thickness of the first layer composed of composition C and the second layer composed of composition C are, respectively, 0.5 nm or more and 500 nm or less; and composition C is (Cr ｉ C ｊ γ ｋ ) O ｙ N １－ｙ The hard coating according to claim 1, characterized in that (where i, j, and k are in atomic ratios such that 0 < i ≤ 1, 0 ≤ j ≤ 0.35, 0 ≤ k ≤ 0.1, 0 ≤ y ≤ 0.3, and i + j + k = 1), and γ is one or more elements selected from the group consisting of B, Ti, Si, V, Y, Zr, and Mo, and is contained in an atomic ratio of 20 at% or less.

3. The hard coating according to claim 1 or 2, characterized in that the total thickness of the hard coating is 0.5 to 15 μm.

4. The hard coating according to claim 1, characterized in that it has a base layer between itself and the base material.

5. The hard coating according to claim 1, characterized in that, having a surface layer on its outermost surface, the hard coating has the AB interface at the interface between the surface layer and the surface layer or the second layer adjacent to the surface layer, instead of, or in addition to, the interface within the first layer group, within the second layer group, or between the first layer group and the second layer group.

6. A hard-coated tool in which part or all of the tool base material is covered with a hard coating, wherein the hard coating is the hard coating described in any one of claims 1 to 3.

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