Hard coating and element covered with hard coating

Abstract

A hard coating (30; 40; 50; 60; 70; 80) that is to be applied to a surface of a substrate (12) in such a way that it covers the surface of the substrate (12), wherein the hard coating (30; 40; 50; 60; 70; 80) has a total thickness (Ttotal) in the range of 0.5 - 20 µm and comprises three types of layers (32, 34, 36; 32, 52, 54) that are stacked alternately on top of each other, wherein the three types of layers (32, 34, 36; 32, 52, 54) consist of two types of single-composition layers (32, 34; 32, 52) and one nanolayer alternating layer (36; 54), wherein the two types of single-composition layers (32, 34; 32, 52) are formed by two of each of an A composition, a B composition and a C composition, wherein the nanolayer interlayer (36; 54) contains two types of nanolayers (32n, 34n; 32n, 52n) which are formed by two of each of the A composition, the B composition and the C composition and which are stacked alternately on top of each other;the A composition is a nitride represented by the composition formula AlaCrb′, where the atomic ratios a, b, c satisfy 0.30 ≤ a ≤ 0.85, 0.15 ≤ b ≤ 0.70, 0 ≤ c ≤ 0.10 and a + b + c = 1, and where the optional additional component ′ at least one type of element is selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; the B composition is a nitride represented by the composition formula AldCreSif&bgr; wherein the atomic ratios d, e, f, g satisfy 0.20 ≤ d ≤ 0.85, 0.10 ≤ e ≤ 0.50, 0.03 ≤ f ≤ 0.45, 0 ≤ g ≤ 0.10 and d + e + f + g = 1 and wherein the optional additional component &bgr; at least one type of element is selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; the C composition is a nitride defined by the composition formula AlhCri(SiC)j&ggr;is represented, wherein the atomic ratios h, i, j, k satisfy 0.20 ≤ h ≤ 0.85, 0.10 ≤ i ≤ 0.50, 0.03 ≤ j ≤ 0.45, 0 ≤ k ≤ 0.10 and h + i + j + k = 1 and wherein the optional additional component �ggr; is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; each of the two types of single composition layers (32, 34; 32, 52) has a thickness (T1, T2) in a range of 0.5 - 1000 nm; and each of the two types of nanolayers (32n, 34n; 32n, 52n) has a thickness in the range of 0.5 - 500 nm and the nanolayer interlayer (36; 54) has a thickness (T3) in the range of 1 - 1000 nm.;

Description

Technical field The present invention relates to a hard coating and an element covered with a hard coating, and in particular to such a hard coating which has excellent wear resistance and weld resistance. State of the art A hard coating is used on various elements, such as different machining tools and friction parts that require wear resistance, to cover the surface of a substrate made of cemented carbide, high-speed tool steel, or the like. The various machining tools include cutting tools such as end mills, milling cutters, drills, lathe end mills, and cutting tips, as well as non-cutting tools such as thread formers and rotary tools. For example, JP 2012-35378A proposes a hard coating with a multilayer structure of an AlCrN / AlTiSiN system. JP 2014-79834A proposes a hard coating with a multilayer structure of an AlCrN / CrN system. JP 2008-534297A proposes a hard coating with a multilayer structure of an AlCr / TiSi system. The CN 1 06 835 014 A, the WO 2018 / 078 731 A1, the WO 2010 / 150 411 A1, the DE 10 2011 086 901 A1, the US 2006 / 0 222 893 A1, the DE 11 2009 005 368 T5 and the JP 2002 - 337 007 A reveal further hard coatings. Disclosure of the invention Problem to be solved by the invention However, depending on factors such as machining and operating conditions, including workpiece materials and cutting speeds, conventional hard coatings may not provide sufficiently satisfactory wear and weld resistance, leaving room for improvement. For example, adequate wear resistance may not be achieved when a cutting tool coated with a multilayer AlCrN / CrN system is used for cutting carbon steel, cast iron, or similar materials. The present invention was developed in light of the prior art discussed above. It is therefore an object of the invention to provide a hard coating and a tool covered with a hard coating, which have a novel structure offering excellent wear resistance and weld resistance. Means of solving the problem Various experiments and studies carried out in the situation described above by the inventors of the present invention and their collaborators have revealed that excellent wear resistance and weld resistance can be achieved when an A-composition, a B-composition, and a C-composition are used and layered, for example, with certain thicknesses, wherein the A-composition is a nitride of AlCrα, wherein the optional additional component α is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W; the B-composition is a nitride of AlCrSiβ, wherein the optional additional component β is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W; and the C-composition is a nitride of AlCr(SiC)γ, wherein the optional additional component γ is at least one type of element.which is selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W. The present invention is based on the discovered fact. The above problem is solved by a hard coating according to claim 1 and by an element covered with a hard coating according to claim 6. It should be noted that the (SiC) in the C composition of claim 1 means that the (SiC) is present in the form of silicon carbide as a compound. Furthermore, it is difficult to precisely control the thickness of each layer across the entire range. Each of the thicknesses described in this description is an average thickness value, and the actual thickness may deviate from a corresponding value within the ranges described above, as long as the average thickness falls within the corresponding ranges described in claim 1. Subclaims 2 to 5 relate to further developments of the hard coating according to claim 1 and subclaim 7 to a further development of the element covered with a hard coating according to claim 6. It is pointed out that, as long as a rounded value of an actual value lies within a corresponding numerical range defined in the inventions described above, such an actual value is to be interpreted as lying within the corresponding numerical range. Effects of the invention In the hard coating of the present invention described above, the single-composition layer formed by composition A exhibits high hardness and excellent wear resistance, and the single-composition layer formed by composition B exhibits high hardness, excellent wear resistance, and oxidation resistance. Furthermore, the single-composition layer formed by composition C exhibits low affinity for oxygen, since Si in composition C is present in the form of SiC (silicon carbide) as a compound, and a high degree of hardness. The reduction in mechanical strength is minimal even at temperatures of 1000°C or higher because the SiC forms a covalent bond. Therefore, the single-composition layer formed by composition C exhibits excellent heat resistance, wear resistance, and oxidation resistance.Furthermore, the components α, β, and γ are optionally added to the respective A, B, and C compositions in a ratio of 10 at% (atomic percent) or less. This allows for the micronization of the coating's crystal particles and the control of particle size by adjusting the addition quantity, thereby tailoring the coating's hardness, toughness, and lubricity. Thanks to the structure, in which the two types of single-composition layers and the nanolayer layer with the properties described above are stacked alternately at predetermined thicknesses, it has become possible to achieve a hard coating with excellent wear resistance, toughness, lubricity, and weld resistance.Thanks to these features, it has become possible, for example in the case of a cutting tool, to increase the tool's service life during a cutting process with different workpiece materials such as carbon steel, cast iron, alloy steel and stainless steel, or under harsh machining conditions such as high-speed machining and dry machining. Since, in the second invention, the ratio T1 / T2 of the thickness T1 of one of the two types of single composition layers to the thickness T3 of the nanolayer alternating layer and the ratio T2 / T3 of the thickness T2 of the other of the two types of single composition layers to the thickness T3 of the nanolayer alternating layer are both in a range of 0.2 - 10, the two types of single composition layers and the nanolayer alternating layer are provided with corresponding thicknesses that ensure certain properties, making it possible to achieve corresponding performance characteristics such as wear resistance and weld resistance. In the third invention, the lowest layer of the three types of layers, consisting of the two types of single-composition layers and the nanolayer alternating layer, which are stacked alternately on top of each other, is arranged directly on a surface of the substrate, so that the coating formation costs can be reduced compared to an arrangement in which an interface layer or the like is provided in a boundary adjacent to the substrate. In the fourth invention, the interface layer is provided in the boundary adjacent to the substrate, which is formed by the predetermined composition or compositions and which has the predetermined thickness, so that it is possible to increase the adhesion strength of the hard coating to the substrate. In the fifth invention, the outermost layer of the hard coating is the surface layer, which is formed by the predetermined composition or compositions and has the predetermined thickness, so that it is possible to improve certain coating performances such as wear resistance and weld resistance by appropriately determining the composition or compositions and the thickness of the surface layer. In the case of the sixth invention, which relates to the element covered with a hard coating, it is possible, since the hard coating is provided by each of the first to fifth inventions, to achieve essentially the same effects as the corresponding invention. In the seventh invention, the element covered with a hard coating is an intermittent cutting tool, such as an end mill or a cutter, such that the element covered with the hard coating is repeatedly subjected to an impact load and is slightly heated when a cutting process occurs intermittently through the cutting edges. Therefore, the hard coating of the present invention, which is capable of achieving high wear resistance, toughness, and weld resistance, is advantageously used for such an intermittently cutting tool. Brief description of the drawings Fig. 1 is a front view showing an exemplary ball end mill in which the present invention is used. Fig. 2 is an enlarged bottom view from the side of a far end of the ball end mill of Fig. 1. Fig. 3 is a schematic view illustrating a coating structure of a hard coating provided on the ball end mill of Fig. 1. Fig. 4 is a schematic view illustrating another example of the coating structure of the hard coating provided on the ball end mill of Fig. 1. Fig. 5 is a schematic view illustrating yet another example of the coating structure of the hard coating provided on the ball end mill of Fig. 1. Fig. 6 is a schematic view illustrating yet another example of the coating structure of the hard coating provided on the ball end mill of Fig. 1.Figure 7 is a schematic view illustrating yet another example of the coating structure of the hard coating provided on the ball end mill of Figure 1. Figure 8 is a schematic view illustrating yet another example of the coating structure of the hard coating provided on the ball end mill of Figure 1. Figure 9 is a schematic view illustrating an arc ion plating device as an example of a physical vapor deposition device for forming the hard coating of each of Figures 3-8 on a tool substrate. Types of embodiments of the invention The present invention is advantageously used for a hard coating applied to the surface of one of several machining tools, including rotating cutting tools such as end mills, milling cutters, taps, and drills; non-rotating cutting tools such as lathe cutters; and non-cutting tools such as thread formers, rotary tools, and press tools. However, the present invention can also be used for a hard coating that serves as a surface protection coating for a bearing element, a semiconductor device, or the like, specifically as a hard coating applied to an element other than the machining tools and which must possess wear resistance and oxidation resistance.Furthermore, the present invention is also applicable to a cutting tip that can be attached to one of several machining tools. Advantageously, cemented carbide, high-speed tool steel, cermet, ceramic, polycrystalline diamond (PCD), monocrystalline diamond, polycrystalline CBN, or monocrystalline CBN are used as the tool substrate of a tool covered with a hard coating, although other tool materials can also be used. Advantageously, a PVD (physical vapor deposition) process such as arc ion plating, sputtering, and PLD (laser beam evaporation) is used as a method for forming the hard coating. The hard coating contains three types of layers, stacked alternately. These three types of layers consist of two types of single-composition layers and one nanolayer layer. The two types of single-composition layers are each formed by two of an A composition, a B composition, and a C composition. The nanolayer layer contains two types of nanolayers, each formed by two of an A composition, a B composition, and a C composition, stacked alternately. Therefore, if, for example, the two types of single-composition layers are each formed by an A composition and a B composition, and the two types of nanolayers contained in the nanolayer layer are each formed by an A composition and a B composition, the C composition is not required.Thus, the hard coating can only be formed from two compositions: A composition, B composition, and C composition. Furthermore, the two types of single-composition layers and the nanolayer layer can be stacked in a predetermined sequence. It is preferable that the three types of layers, consisting of the two types of single-composition layers and the nanolayer layer, be stacked in the predetermined sequence for at least one cycle, and that for a complete cycle or cycles, the three types of layers are stacked such that the number of each of the three types of layers is equal.However, the layering of the three types of layers can be terminated without a top layer completing a corresponding cycle, for example, by having the top layer be of the same type as a bottom layer. This also applies to the alternating nanolayer layer, which has the two types of nanolayers stacked alternately. If the hard coating contains an interface layer and / or a surface layer, the total thickness of the hard coating includes the thickness of the interface layer and / or the thickness of the surface layer. It is preferable that the ratio T1 / T3 of the thickness T1 of one of the two types of single-composition layers to the thickness T3 of the nanolayer layer, and the ratio T2 / T3 of the thickness T2 of the other of the two types of single-composition layers to the thickness T3 of the nanolayer layer, both lie within the range of 0.2 to 10. However, each of the thicknesses T1, T2, and T3 can be set to a value that causes the corresponding ratio to deviate from the corresponding numerical range. The hard coating can, if required, include an interface layer to be placed adjacent to the substrate.It is preferable that the interface layer be formed by a single-composition layer consisting of one of the A, B, and C components, or by an alternating nanolayer layer containing two types of nanolayers, each consisting of two of the A, B, and C components, respectively, stacked alternately. However, the interface layer may be a layer of metal nitride, metal carbonitride, or metal carbide composed of at least one type of element consisting of B, Al, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, and W, or a layer composed of another composition or compositions. The interface layer has a thickness preferably in the range of 10–1000 nm. However, the thickness of the interface layer may be outside the numerical range of 10–1000 nm. The hard coating may, if required, have a surface layer. It is preferable that the surface layer be formed by a single-composition layer consisting of one of the A, one of the B, and one of the C components, or by an alternating nanolayer layer containing two types of nanolayers, each consisting of two of the A, B, and C components, respectively, stacked alternately. However, the surface layer may be a layer consisting of a different composition or compositions. The surface layer has a thickness preferably in the range of 5–1000 nm. However, the thickness of the surface layer may be outside this range. According to the findings of the inventors of the present invention and their collaborators, the hard coating of the present invention, thanks to the alternating layering of the three types of layers—consisting of two types of single-composition layers and the nanolayer alternating layer—provides higher oxidation resistance, hardness, wear resistance, and shear strength than a multilayer AlCrN-based coating. Furthermore, high hardness can be achieved thanks to the inhibition of lattice dislocations, which is effected by an interface between each pair of adjacent layers exhibiting different elastic properties (modulus of elasticity and hardness). This interface not only contributes to increased coating hardness but also improves toughness by inhibiting energy dissipation and crack propagation.Since the interface strongly influences the properties of the multilayer coating, the provision of the nanolayer layering, in which a layering cycle of the nanolayers lies in the nanometer range, makes it possible to achieve the effects of an improvement in the mechanical properties and the tribology of the hard coating when the sizes of the crystal particles and the coating density are adjusted accordingly by controlling the thickness of each nanolayer of the nanolayer layering. Example of implementation In the following, an embodiment of the invention is described in detail with reference to the drawings. Fig. 1 is a front view showing a ball end mill 10, which is an example of a hard-coated element in which the present invention is used. Fig. 2 is an enlarged bottom view seen from the side of a far end of the ball end mill 10. The ball end mill 10 has a tool substrate 12 (see Figs. 3-8) formed by a hard metal, and the tool substrate 12 has a shank section 14 and a cutting edge section 16 forming a unit. The cutting edge section 16 is provided with a pair of cutting edges that are symmetrical with respect to an axis of the ball end mill 10, each of the cutting edges having a peripheral cutting edge 18 and a ball end cutting edge 20.When the ball end mill 10 is rotated about the axis, it performs an intermittent cutting operation through the peripheral cutting edge 18 and the ball end cutting edge 20 of each cutting edge. The peripheral cutting edge 18 and the ball end cutting edge 20 are seamlessly connected, so that they merge into one another. On opposite sides of each cutting edge, comprising the peripheral cutting edge 18 and the ball end cutting edge 20, a rake face 22 and a flank face (clearance face) 24 are defined. In other words, the peripheral cutting edge 18 and the ball end cutting edge 20 are arranged on a ridge line, which is the intersection line of the rake face 22 and the flank face 24. The ball end mill 10 is a hard-coated tool and corresponds to an intermittent cutting tool. A hard coating 30, shown in Fig. 3, is provided such that it covers a surface of the blade section 16, which is a section of the tool substrate 12. Fig. 3 is a schematic view, enlarged to show a cross-section of a neighborhood of the surface of the blade section 16 covered by the hard coating 30. The area of ​​the surface covered by the hard coating 30 is represented by a hatched area in Fig. 1. It is also possible to provide the hard coating 30 such that the entire ball end mill 10, including the shank section 14, is covered with the hard coating 30. The hard coating 30 has a multilayer structure and comprises an A-layer 32, a B-layer 34, and a nanolayer alternating layer 36, arranged in that order in one direction from an outer surface of the hard coating 30 to the tool substrate 12. The A-layer 32, the B-layer 34, and the nanolayer alternating layer 36 are stacked on top of each other for at least one cycle. The hard coating 30 also includes an interface layer 38, which is located in its boundary section adjacent to the tool substrate 12. This means that the interface layer 38 is first arranged on a surface of the tool substrate 12, and then the nanolayer alternating layer 36, the B-layer 34, and the A-layer 32 are arranged on the interface layer 38.The nanolayer layer 36, the B-layer 34, and the A-layer 32 are repeatedly stacked on top of each other in the order described, such that the A-layer 32 provides the uppermost section of the hard coating 30. The hard coating 30 with the interface layer 38 has a total thickness Ttotal, which is set to a value in the range of 0.5–20 µm. The A-layer 32 has a thickness T1, which is set to a value in the range of 0.5–1000 nm. The B-layer 34 has a thickness T2, which is set to a value in the range of 0.5–1000 nm. The nanolayer layer 36 has a thickness T3, which is set to a value in the range of 1–1000 nm. Furthermore, the thicknesses T1 - T3 are set to the respective values ​​such that the ratio T1 / T3 of thickness T1 to thickness T3 and the ratio T2 / T3 of thickness T2 to thickness T3 both lie in a range of 0.2 - 10.The A-layer 32 is a single-composition layer formed solely by an A-composition. The A-composition is a nitride represented by the formula AlaCrbα, where the atomic ratios a, b, c satisfy 0.30 ≤ a ≤ 0.85, 0.15 ≤ b ≤ 0.70, 0 ≤ c ≤ 0.10, and a + b + c = 1, and where the optional additional component α is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W. Table 1 shows the types of constituent elements and their proportions in an A-composition forming the hard coating of each of test samples 1–50 used in a cutting test.Table 1 shows examples of the content (at%) of each element in the A composition, where each blank space indicates that the content (at%) of the corresponding element is 0, and each gray area (each column with scatter dots) indicates that the atomic ratio corresponding to the content of the respective element deviates from the corresponding numerical range of the composition formula described above. This means that test samples 7-50 meet the requirements of the A composition. The A-layer 32 with such a composition is characterized by high hardness and excellent wear resistance. Furthermore, by adding the optional additional component α in a ratio of no more than 10 at%, it is possible to micronize the crystal particles and control the particle size by adjusting the addition quantity, thereby adjusting the hardness, toughness, and lubricity of the coating. The B-position 34 is a single-composition position formed solely by a B-composition. The B-composition is a nitride represented by the formula AldCreSifβ, where the atomic ratios d, e, f, g satisfy 0.20 ≤ d ≤ 0.85, 0.10 ≤ e ≤ 0.50, 0.03 ≤ f ≤ 0.45, 0 ≤ g ≤ 0.10 and d + e + f + g = 1, and where the optional additional component β is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W. Table 2 shows the types of constituent elements and their proportions in a B composition that forms the hard coating of each test sample 1 - 50.Table 2 shows examples of the content (at%) of each element in the B composition, where each blank space indicates that the content (at%) of the corresponding element is 0, and each gray area (each column with scatter dots) indicates that the atomic ratio corresponding to the content of the respective element deviates from the corresponding numerical range of the composition formula described above. This means that test samples 7-50 meet the requirements of the B composition. B-layer 34 with such a composition is characterized by high hardness and excellent wear and oxidation resistance. Like the optional additional component α described above, the optional additional component β is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W.By adding the optional additional component β in a ratio of no more than 10 at%, it is possible to micronize crystal particles and control the particle sizes by controlling the amount added, thereby adjusting the hardness, toughness and lubricity of the coating. The nanolayer interlayer 36 has a multilayer structure comprising an A-nanolayer 32n and a B-nanolayer 34n, which are alternately stacked on top of each other for at least one cycle, wherein the A-nanolayer 32n is formed by the A-composition, like the A-layer 32, and the B-nanolayer 34n is formed by the B-layer 34, like the B-layer 34. In this embodiment, a bottommost section of the nanolayer interlayer 36, adjacent to the A-layer 32, is provided by the A-nanolayer 32n, while a topmost section of the nanolayer interlayer 36, adjacent to the B-layer 34, is provided by the B-nanolayer 34n. However, the bottom section and the top section of the nanolayer interlayer 36 can each be provided by the B nanolayer 34n and the A nanolayer 32n, respectively.The A-nanolayer 32n and the B-nanolayer 34n each have thicknesses specifically set within a range of 0.5–500 nm. The 36n nanolayer layer is characterized by high hardness and excellent wear resistance, toughness, and oxidation resistance. The interface between the 32n and 34n nanolayers contributes to increased coating hardness and, thanks to its ability to inhibit energy dissipation and crack propagation, also to improved toughness. Since the deposition cycle of the 32n and 34n nanolayers is on the nanometer scale, it is also possible to achieve improvements in the mechanical properties and tribology of the hard coating by adjusting the crystal particle size and coating density through precise control of the thickness of each of the 32n and 34n nanolayers. The interface layer 38 is a single-composition layer, which, like the A-layer 32, is formed solely by the A-composition. The interface layer 38 has a thickness that is accordingly set to a value in the range of 10–1000 nm. Since the interface layer 38 is provided at a boundary adjacent to the tool substrate 12, the adhesion strength of the hard coating 30 to the tool substrate 12 can be increased. Figures 4-8 are views illustrating further examples of the hard coatings, each of which is to be applied to the surface of the blade section 16 of the ball end mill 10. Each of Figures 4-8 is a schematic sectional view corresponding to the view in Figure 3, and the total thickness Ttotal of each hard coating is in the range of 0.5-20 µm. The hard coating 40 of Figure 4 has the layering sequence of the A-layer 32 and the B-layer 34 reversed compared to the hard coating 30 described above. In the hard coating 40 of Figure 4, the A-layer 32 is arranged between the B-layer 34 and the nanolayer alternating layer 36, with the B-layer 34 forming the uppermost or outermost layer. Furthermore, instead of the interface layer 38 of the A-composition, an interface layer 32 of a C-composition is provided.The carbon composition is a nitride represented by the formula AlhCri(SiC)jγ, where the atomic ratios h, i, j, k satisfy 0.20 ≤ h ≤ 0.85, 0.10 ≤ i ≤ 0.50, 0.03 ≤ j ≤ 0.45, 0 ≤ k ≤ 0.10 and h + i + j + k = 1, and where the optional additional component γ is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W. Table 3 shows the types of constituent elements and their proportions in a carbon composition forming the hard coating of each test sample 1–50. Specifically, Table 3 shows examples of the content (at%) of each element in the C composition, where each blank space means that the content (at%) of the corresponding element is 0, and each grey part (each column with scatter dots) means that the atomic ratio corresponding to the content of the corresponding element differs from the corresponding numerical range of the composition formula described above.This means that test samples 7-50 meet the requirements of the C composition. The interface layer 42 is a single-composition layer formed solely by the C composition and has a thickness appropriately adjusted to a value in the range of 10-1000 nm. If the interface layer 42 is provided at a boundary adjacent to the tool substrate 12, the adhesion strength of the hard coating 40 to the tool substrate 12 can be increased. In a hard coating 50 of Fig. 5, a C-layer 52, formed solely by the C composition, is provided instead of the B-layer 34 described above, and a nanolayer 54 is provided instead of the nanolayer 56 described above. The nanolayer 54 comprises an A-nanolayer 32n, formed by the A composition, and a C-nanolayer 52n, formed by the C composition, such that the A-nanolayer 32n and the C-nanolayer 52n are alternately layered on top of each other for at least one cycle.The C-layer 52 and the C-nanolayer 52n each exhibit low affinity for oxygen because the carbon composition contains silicon carbide (SiC) as a compound. They also possess high hardness, with minimal reduction in mechanical strength even at temperatures of 1000°C or higher due to the covalent bond between the SiC and the nanolayer 52n. Consequently, the C-layer 52 and the C-nanolayer 52n are characterized by excellent heat resistance, wear resistance, and oxidation resistance. Similar to the optional additional component α described above, the optional additional component γ is at least one element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta, and W.By adding the optional additional component γ in a ratio of no more than 10 at%, it is possible to micronize crystal particles and control their size by adjusting the addition quantity, thereby adjusting the coating's hardness, toughness, and lubricity. The C-layer 52 is a single-composition layer consisting solely of the carbon composition. The thickness of the C-layer 52 is adjusted to a value within the range of 0.5–1000 nm such that the ratio of its thickness to the thickness of the nanolayer interlayer 54 is within the range of 0.2–10. In this embodiment, a bottom section of the nanolayer interlayer 54, adjacent to the C-layer 52, is provided by the C-nanolayer 52n, while a top section of the nanolayer interlayer 54, adjacent to the A-layer 32, is provided by the A-nanolayer 32n.However, the bottom and top sections of the nanolayer interlayer 54 can each be provided by the A nanolayer 32n and the C nanolayer 52n, respectively. The nanolayer interlayer 54 has a thickness that is adjusted to a value in the range of 1–1000 nm. Like the nanolayer interlayer 36 described above, the nanolayer interlayer 54 is characterized by high hardness and excellent wear resistance, toughness, and oxidation resistance. Furthermore, the hard coating 50 contains an interface layer 56, which is a single-composition layer formed solely by the B composition described above. A hard coating 60 of Fig. 6 differs from the hard coating 30 of Fig. 3 described above with respect to the layering sequence of the A-layer 32, B-layer 34, and nanolayer alternating layer 36. In the hard coating 60 of Fig. 6, the nanolayer alternating layer 36, A-layer 32, and B-layer 34 are layered one on top of the other in the direction from the outer surface of the hard coating 30 to the tool substrate 12, in the order described. Furthermore, the hard coating 60 includes an interface layer 62 located between the lowest B-layer 34 and the tool substrate 12. The interface layer 62 is a nanolayer alternating layer containing two types of A-nanolayer 32n, B-nanolayer 34n, and C-nanolayer 52n, and the two types of nanolayers are layered alternately.The interface layer 62 has a thickness that is set accordingly to a value in the range of 1 - 1000 nm, and each of the two types of nanolayers has a thickness that is set accordingly to a value in the range of 0.5 - 500 nm. A hard coating 70 of Fig. 7 differs from the hard coating 30 of Fig. 3 described above in that the interface layer 38 is missing. A hard coating 80 of Fig. 8 differs from the hard coating 30 of Fig. 3 described above in that a surface layer 82 provides an outermost surface of the hard coating 80, and an interface layer 84 is formed by a composition or compositions that are different from the A, B, and C compositions. For example, the surface layer 82 is an alternating nanolayer layer which, like the alternating nanolayer layer 36, contains the A nanolayer 32n and B nanolayer 34n, which are stacked alternately. The surface layer 82 has a thickness that is appropriately set to a value in the range of 5–1000 nm, and each of the A nanolayer 32n and B nanolayer 34n has a thickness that is appropriately set to a value in the range of 0.5–500 nm. The interfacial layer 84 is formed by a metal nitride, metal carbonitride or metal carbide formed by at least one type of element selected from B, Al, Ti, Y, Zr, Hf, V, Nb, Ta, Cr and W, and it has a thickness appropriately set to a value in the range of 10 - 1000 nm. Furthermore, the hard coating can be structured in other ways, even if this is not shown in the drawings. For example, the nanolayer layer 36 of the hard coating 30 described above contains the A nanolayer 32n and B nanolayer 34n, which are layered alternately. However, the nanolayer layer 36 can also be structured to contain the C nanolayer 52n. If the individual composition layers are formed by the A layer 32 and B layer 34, this means that the nanolayer layer 36 can be formed by the nanolayer layer 36 containing the A nanolayer 32n and C nanolayer 52n, which are layered alternately, or by the nanolayer layer 36 containing the B nanolayer 34n and C nanolayer 52n, which are layered alternately. Furthermore, the individual composition layers in the hard coating 30 are formed by the A-layer 32 and B-layer 34, and the individual composition layers in the hard coating 50 are formed by the A-layer 32 and C-layer 52. However, the two types of individual composition layers can also be formed by the B-layer 34 and C-layer 52. Furthermore, surface layer 82 of the hard coating 80 is the nanolayer alternating layer containing the A nanolayer 32n and B nanolayer 34n, which are layered alternately on top of each other. However, surface layer 82 can also be a nanolayer alternating layer containing the C nanolayer 52n. Additionally, surface layer 82 can be a single-composition layer formed by the A composition, B composition, or C composition. Furthermore, in each of the hard coatings 30, 40, 50, 60, 70, 80, the three types of layers, consisting of two layers of single-composition layers (each consisting of two of A-layer 32, B-layer 34, and C-layer 52) and one of the nanolayer alternating layers 36, 54, are stacked alternately in a predetermined sequence for one or more complete cycles, such that the number of each of the three types of layers is equal. However, the stacking of the three types of layers can be terminated without either the top or bottom layer completing a corresponding cycle, for example, by omitting A-layer 32, which forms the top layer of the hard coating 30.In other words, in each of the hard coatings 30, 40, 50, 60, 70, in which the surface layer is not specified, the outermost layer can be considered a surface layer that is different from the three types of layers that are alternately stacked. Similarly, with regard to each of the nanolayer alternating layers 36, 54, which contains the two types of nanolayers (each consisting of two of the A-nanolayer 32a, B-nanolayer 34n, and C-nanolayer 52n) that are alternately stacked, the number of stacked nanolayers can also be an odd number, for example, such that the nanolayer alternating layer 36 begins with the A-nanolayer 32n and ends with the A-nanolayer 32n. Table 4 shows a detailed view of the coating structure of the hard coating of each of the test samples 1–50 on end mills. In the column "Single Composition Layer," "A-Layer," "B-Layer," and "C-Layer" correspond to the A-Layer 32, B-Layer 34, and C-Layer 52 described above, respectively. Similarly, in the column "Nanolayer Interchangeable Layer," "A-Layer," "B-Layer," and "C-Layer" correspond to the A-Nanolayer 32n, B-Nanolayer 34n, and C-Nanolayer 52n described above, respectively. “BORDER SITE LOCATION” corresponds to the boundary surface locations 38, 42, 56, 62, 84 described above. Each space in the column “SINGLE COMPOSITION LOCATION” for “A-LOCATION”, “B-LOCATION” and “C-LOCATION”, in the column “NANO-LOCATION-CHANGING LOCATION” for “A-LAYER”, “B-LAYER” and “C-LAYER” for “NANO-LAYER-CHANGING LOCATION” and in “BORDER SITE LOCATION” means that the corresponding location or layer is not provided.In test sample 27 without the interface layer, for example, the individual composition layers are the A layer and the C layer, and the nanolayer alternating layer contains the A nanolayer and the C nanolayer, which are stacked alternately on top of each other, so that the components of the B composition described in Table 2 are essentially not present in test sample 27. Furthermore, in test sample 45 without the interface layer, the individual composition layers are the B layer and the C layer, and the nanolayer alternating layer contains the B nanolayer and the C nanolayer, which are stacked alternately on top of each other, so that the components of the A composition described in Table 1 are essentially not present in test sample 45. Similarly, not all components of the A composition, B composition, and C composition shown in the figures are necessarily present in each of the other test samples.The components described in sections 10-12 are included, provided the hard coating is formed by at least two of the A, B, and C compositions. Furthermore, none of the test samples 1-50 shown in Table 4 are provided with the surface layer. In Table 4, each gray section (each column with scatter dots) indicates that a corresponding thickness requirement of the embodiment (of claim 1 of the invention) is not met, and test samples 1-6 are comparison products, while test samples 7-50 are products of the present invention. Fig. 9 is a schematic design view (schematic view) illustrating an arc ion plating device 100 used to form the hard coatings 30, 40, 50, 60, 70, 80 described above, or the hard coatings of the test samples 1-50 described in Fig. 13 (hereinafter simply referred to as "hard coating 30 or the like" when not distinguished from one another), on the tool substrate 12. The arc ion plating device 100 is configured to form the hard coating 30 or the like on the surface of the tool substrate 12 by arc ion plating as a type of PVD process, and it is capable of continuously forming a variety of types of layers, differing in composition, with predetermined thicknesses by changing an evaporation source (target) and a reaction gas.For example, if the hard coating 30 is to be formed, the nanolayer alternating layer 36, B-layer 34 and A-layer 32 are stacked alternately on top of each other after the interface layer 38 has been formed on the surface of the tool substrate 12. Fig. 9 corresponds to a top view of the arc ion plating device 100 as seen from a top side of the arc ion plating device 100. The arc ion plating device 100 comprises the following: a rotary table 154, which is to be driven to rotate about a rotational axis S extending essentially in a vertical direction, and which is intended to hold a variety of workpieces, i.e.The system comprises a multitude of tool substrates 12, each on which the hard coating 30 or the like is to be formed; a preload current source 156 for applying a negative preload to the tool substrates 12; a process vessel in the form of a chamber 158, which houses the tool substrates 12; a reaction gas supply device 160 for supplying a reaction gas into the chamber 158; a gas discharge device 162 for removing a gas from the interior of the chamber 158, for example by means of a vacuum pump, in order to reduce the pressure inside the chamber 158; a first arc current source 164; a second arc current source 166; a third arc current source 168; and a fourth arc current source 170. The rotary table 154 is a disk-shaped table whose center corresponds to the axis of rotation S described above.The multitude of tool substrates 12 are arranged in an outer circumferential section of the rotary table 154 such that each tool substrate 12 assumes a position that makes each substrate 12 substantially parallel to the axis of rotation S. While the tool substrates 12 are rotated about the axis of rotation S by the rotary table 154, each tool substrate 12 can be rotated about its own axis. When the nitride of A-layer 32, B-layer 34, C-layer 52, or the like is to be formed, the reaction gas supply device 160 introduces nitrogen gas into the chamber 158. The interior of the chamber 158 is, for example, brought into a vacuum state of about 2–10 Pa by the gas discharge device 162 and heated to a vapor deposition temperature of, for example, about 300–600°C by a heater or the like, which is not shown in the drawings. Each of the first arc current source 164, second arc current source 166, third arc current source 168 and fourth arc current source 170 is configured to generate an arc current between a corresponding anode 174, 178, 182, 186 and a corresponding cathode in the form of a first evaporation source 172, second evaporation source 176, third evaporation source 180 and fourth evaporation source 184, which consist of vapor deposition material, in order to bring about an arc discharge, thereby selectively causing evaporation material to evaporate from the corresponding one of the first evaporation source 172, second evaporation source 176, third evaporation source 180 and fourth evaporation source 184. After it has evaporated, the evaporation material becomes positive ions, which are deposited in such a way that they cover each of the tool substrates 12 on which a negative (-) bias is applied.This means that each of the evaporation sources 172, 176, 180, 184 is formed by an alloy of composition A, B, and C, respectively, so that one of the evaporation sources can serve as an extra source, formed, for example, by the alloy of composition A, B, and C, which must be formed with a relatively large thickness to enable efficient coating formation. The number of evaporation sources can be three to correspond to the number of compositions that form the hard coating 30 or the like.In a case where the hard coating 30 or the like is formed by only two compositions of the A composition, B composition and C composition, the four evaporation sources 172, 176, 180, 184 can also be grouped into two groups such that two of the evaporation sources 172, 176, 180, 184 belonging to one of the two groups are formed by the alloy of one of the two compositions of the A composition, B composition and C composition, while the other two of the evaporation sources 172, 176, 180, 184 belonging to the other of the two groups are formed by the alloy of the other of the two compositions of the A composition, B composition and C composition. The arc current sources 164, 166, 168, 170 described above are changed as needed in order to successively form the layers of predetermined compositions, whereby the hard coating 30 or the like with a predetermined coating structure can be achieved. The thickness of each layer can be adjusted by setting the rotational speed of the rotary table 154 and the switching time of a corresponding arc current source or sources 164, 166, 168, 170. A boundary section located between a multitude of layers with different compositions can be provided with a mixed layer formed by a mixture of two types of composition. The results of a performance test of the hard coatings are now described. This test was carried out by producing test samples 1-50, in which the hard coatings with the respective coating structures shown in Figures 10-13 were arranged as described above on a two-tooth ball end mill with a carbide tool substrate 12 and a diameter of 6 mm (nose radius R = 3 mm). Table 5 shows the coating hardness of the hard coating of each test sample 1-50, as well as a wear width, a cutting length, and an evaluation result measured or achieved during the cutting test. Specifically, "COATING HARDNESS" represents an HV value (Vickers hardness) of each hard coating, determined in accordance with the Vickers hardness test method according to the Japanese Industrial Standard JIS Z 2244:2009.Vickers hardness test – test procedure performed under a condition specified by the hardness symbol HV0.025. Additionally, a cutting operation was carried out by using each of the test specimens 1–50 in accordance with a cutting test condition described below, and the cutting distance and wear width of the clearance face (flank face) adjacent to the ball-head cutting edge 20 were measured, and coating performance (wear resistance) was assessed. The assessment of coating performance was carried out by interrupting the cutting operation at a suitable stage where the cutting distance reached 500 m or more, and then measuring the cutting distance and wear width of the clearance face.In one instance where the clearance width was increased (to 0.3 mm or more), the cutting process was interrupted even when the cutting distance was no longer than 500 m, and the cutting distance and clearance width were measured at each interruption. The clearance width is a maximum width value and was measured by interrupting the cutting process each time the cutting distance reached a predetermined value, using a microscope (MM-400 / LM) manufactured by Nikon Corporation. - Cutting test condition - Workpiece material: S50C (carbon steel for mechanical engineering defined by the Japanese industrial standard JIS G 4404: 2015) Cutting speed: 254 m / min Rotational speed: 13500 min-1 Feed rate: f = 0.12 mm / t, F = 3240 mm / min Depth of cut: ap (axial direction) = 0.3 mm, ae (radial direction) = 0.6 mm As can be seen from Table 5, each of the test samples 7-50, as products of the present invention, exhibited a high surface hardness (HV0.025) of 3000 or higher, indicating high wear resistance. In contrast, test samples 1-6, as the comparison products, showed a hardness of approximately 2000-2700. Regarding the wear width of the clearance face and the cutting distance, each of the test samples 7-50, as products of the present invention, was able to perform the cutting process for 500 m or more before the wear width of the clearance face reached 0.2 mm, and accordingly exhibited excellent wear and weld resistance. However, in each of the test samples 1-6, as comparison products, the wear width of the clearance face exceeded 0.3 mm before the cutting process was completed over 500 m.In the assessment, "O" was assigned to a case where the cutting process continued for 500 m or more before the clearance face wear width reached 0.2 mm, while "×" was assigned to a case where the clearance face wear width exceeded 0.2 mm before the cutting distance reached 500 mm, meaning that insufficient tool life was achieved. In each of the test samples 7-50, which are the products of the present invention, the assessment result was "O", and excellent tool life was achieved. Regarding wear width and cutting distance, each gray area (each column with scatter dots) indicates that the clearance face wear width exceeded 0.2 mm before the cutting distance reached 500 mm. As described above, with the hard coating 30 or the like of the ball end mill 10 according to the exemplary embodiment, in which two types of single-composition layers, each formed by two of the A composition, B composition and C composition (i.e. two each of A-layer 32, B-layer 34 and C-layer 52), and one type of nanolayer alternating layer (nanolayer alternating layer 36, 54 or the like), which contains the two types of nanolayers formed by two each of the A composition, B composition and C composition (i.e. two each of A-nanolayer 32n, B-nanolayer 34n and C-nanolayer 52n) and are alternately layered on top of each other with predetermined thicknesses, it is possible to achieve excellent wear resistance, toughness, lubricity and weld resistance.Thanks to these features, it has become possible to increase the tool's service life during cutting operations with various workpiece materials such as carbon steel, cast iron, alloy steel and stainless steel, or under harsh machining conditions such as high-speed machining and dry machining. Since the ratio T1 / T2 of the thickness T1 of one of the two types of single-composition layers to the thickness T3 of the nanolayer interchangeable layer and the ratio T2 / T3 of the thickness T2 of the other of the two types of single-composition layers to the thickness T3 of the nanolayer interchangeable layer are both in a range of 0.2 - 10, the two types of single-composition layers and the one type of nanolayer interchangeable layer are also provided with corresponding thicknesses that ensure certain properties, making it possible to achieve corresponding performance characteristics such as wear resistance and weld resistance. Furthermore, the hard coating 70 of Fig. 7 and the test samples 27, 45, which are not provided with the interface layer, can each be produced at reduced coating costs, and the ball end mill 10 with the hard coating 70 or the like can be manufactured cost-effectively. On the other hand, with the hard coatings 30, 40, 50, 60, 80 and the test samples 7-26, 28-44 and 46-50, which are provided with the interface layer 38 or the like, having the predetermined composition(s) and the predetermined thickness, it is each possible to increase the adhesion strength of the hard coating 30 or the like to the tool substrate 12. Furthermore, with the hard coating 80 of Fig. 8, which is provided with the surface layer 82 having the predetermined composition or compositions and the predetermined thickness, it is possible to further improve certain coating performances such as wear resistance and weld resistance if the composition or compositions and the thickness of the surface layer 82 are determined accordingly. Furthermore, the ball end mill 10 is an intermittently cutting tool designed to perform an intermittent cutting operation via the peripheral cutting edge 18 and the ball end cutting edge 20. This results in repeated impact loading of the peripheral cutting edge 18 and the ball end cutting edge 20, causing them to heat up slightly during the cutting process. However, by applying a hard coating 30 or similar material with high wear resistance, toughness, and weld resistance, the tool's service life can be extended. Although the embodiment of the invention has been described in detail with reference to the accompanying drawings, it is understood that the described embodiment is merely one embodiment and that the present invention can be carried out with various modifications and improvements based on the knowledge of a person skilled in the art. Reference symbol list 10: Ball end mill (element covered with a hard coating, intermittent cutting tool), 12: Tool substrate (substrate), 14: Shank section, 16: Blade section, 18: Peripheral cutting edge (cutting edge), 20: Ball end cutting edge (cutting edge), 22: Rake face, 24: Flank face, 30, 40, 50, 60, 70, 80: Hard coating, 32: A layer (single composition layer), 32n: A nanolayer (nanolayer), 34: B layer (single composition layer), 34n: B nanolayer (nanolayer), 36, 54: Nanolayer alternating layer, 38, 42, 56, 62, 84: Interface layer, 52: C layer (single composition layer), 52n: C-nanolayer (nanolayer), 82: surface layer, 100: arc ion plating device, 154: rotary table, 156: bias current source, 158: chamber, 160: reaction gas supply device, 162: gas discharge device, 164, 166, 168, 170: arc current source, 172, 176, 180, 184: evaporation source (cathode), 174, 178, 182, 186: anode, S: axis of rotation, Ttotal: total thicknessT1: Thickness A-layer (thickness of single-composition layer), T2: Thickness B-layer (thickness of single-composition layer), T3: Thickness of nanolayer alternating layer,

Claims

A hard coating (30; 40; 50; 60; 70; 80) that is to be applied to a surface of a substrate (12) in such a way that it covers the surface of the substrate (12), wherein the hard coating (30; 40; 50; 60; 70; 80) has a total thickness (Ttotal) in the range of 0.5 - 20 µm and comprises three types of layers (32, 34, 36; 32, 52, 54) that are stacked alternately on top of each other, wherein the three types of layers (32, 34, 36; 32, 52, 54) consist of two types of single-composition layers (32, 34; 32, 52) and one nanolayer alternating layer (36; 54), wherein the two types of single-composition layers (32, 34; 32, 52) are formed by two of each of an A composition, a B composition and a C composition, wherein the nanolayer interlayer (36; 54) contains two types of nanolayers (32n, 34n; 32n, 52n) which are formed by two of each of the A composition, the B composition and the C composition and which are stacked alternately on top of each other;the A composition is a nitride represented by the formula AlaCrbA, where the atomic ratios a, b, c satisfy 0.30 ≤ a ≤ 0.85, 0.15 ≤ b ≤ 0.70, 0 ≤ c ≤ 0.10 and a + b + c = 1, and where the optional additional component α is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; the B composition is a nitride represented by the formula AldCreSifβ, where the atomic ratios d, e, f, g satisfy 0.20 ≤ d ≤ 0.85, 0.10 ≤ e ≤ 0.50, 0.03 ≤ f ≤ 0.45, 0 ≤ g ≤ 0.10 and d + e + f + g = 1 satisfy and where the optional additional component β is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W;the C composition is a nitride represented by the composition formula AlhCri(SiC)jγ, where the atomic ratios h, i, j, k satisfy 0.20 ≤ h ≤ 0.85, 0.10 ≤ i ≤ 0.50, 0.03 ≤ j ≤ 0.45, 0 ≤ k ≤ 0.10 and h + i + j + k = 1, and where the optional additional component γ is at least one type of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; each of the two types of single composition layers (32, 34; 32, 52) has a thickness (T1, T2) in a range of 0.5 - 1000 nm; and each of the two types of nanolayers (32n, 34n; 32n, 52n) has a thickness in the range of 0.5 - 500 nm and the nanolayer interlayer (36; 54) has a thickness (T3) in the range of 1 - 1000 nm.; Hard coating (30; 40; 50; 60; 70; 80) according to claim 1, wherein a ratio (T1 / T3) of the thickness (T1) of one of the two types of single composition layers (32, 34; 32, 52) to the thickness (T3) of the nanolayer alternating layer (36; 54) and a ratio (T2 / T3) of the thickness (T2) of the other of the two types of single composition layers (32, 34; 32, 52) to the thickness (T3) of the nanolayer alternating layer (36; 54) are both in a range of 0.2 - 10. Hard coating (70) according to claim 1 or 2, wherein a bottom layer of the two types of single composition layers (32, 34) and the nanolayer alternating layer (36), which are stacked alternately on top of each other, is to be arranged directly on a surface of the substrate (12). A hard coating (30; 40; 50; 60; 80) according to claim 1 or 2, wherein the hard coating (30; 40; 50; 60; 80) comprises an interface layer (38; 42; 56; 62; 84) which is to be arranged adjacent to the substrate (12); the interface layer (38; 42; 56; 62; 84) has a thickness in the range of 10–1000 nm and is provided by one of three types of layers, which are: a single-composition layer formed by one of the A composition, the B composition, and the C composition; a nanolayer alternating layer comprising two types of nanolayers, each formed by two of the A composition, the B composition, and the C composition, and which are alternately stacked such that each of the two types of nanolayers has a thickness in a has a range of 0.5 - 500 nm;and a layer of metal nitride, metal carbonitride or metal carbide formed by at least one type of element selected from B, Al, Ti, Y, Zr, Hf, V, Nb, Ta, Cr and W; A hard coating (80) according to claim 1, 2 or 4, wherein the hard coating (80) comprises a surface layer (82) providing an outermost surface of the hard coating (80); the surface layer (82) is provided by a single-composition layer formed by one of the A composition, the B composition and the C composition, or by an alternating nanolayer layer comprising two types of nanolayers, each formed by two of the A composition, the B composition and the C composition, and which are alternately stacked such that each of the two types of nanolayers has a thickness in the range of 0.5 - 500 nm; and the surface layer (82) has a thickness in the range of 5 - 1000 nm. An element (10) covered with a hard coating, comprising a substrate (12) whose surface is partially or completely covered with the hard coating (30; 40; 50; 60; 70; 80) according to one of claims 1 - 5. An element (10) covered with a hard coating according to claim 6, wherein the element (10) covered with a hard coating is an intermittently cutting tool (10) having cutting edges (18, 20) and which is to be rotated about an axis such that it performs an intermittent cutting operation through the cutting edges (18, 20).

Images