Surface-coated cutting tools

Abstract

In one embodiment, a cutting tool is described herein that includes a wear-resistant coating that uses one or more refractory layers of polycrystalline α-Al2O3. Briefly, the coated cutting tool described herein comprises a substrate and a coating bonded to the substrate, the coating including a layer of polycrystalline α-Al2O3 deposited by chemical vapor deposition (CVD), and at least 5% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation angle of less than 15 degrees as determined using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority under Article 8 of the Patent Cooperation Treaty to U.S. Patent Application No. 63 / 238,551, filed August 30, 2021, which is incorporated by reference in its entirety.

[0002] The present invention relates to refractory coatings, and in particular to refractory coatings deposited by chemical vapor deposition (CVD) for cutting tools and / or metal removal applications. [Background technology]

[0003] Cutting tools, including cemented carbide cutting tools, have been used in both coated and uncoated conditions to machine a variety of metals and alloys. To enhance the wear resistance, performance, and life of cutting tools, one or more layers of refractory materials have been applied to the cutting tool surface. For example, TiC, TiCN, TiN, and / or Al2O3 have been applied to cemented carbide substrates by CVD and physical vapor deposition (PVD). Refractory coatings based on single or multi-layered structures of the aforementioned refractory materials, while effective in reducing wear and extending tool life in various applications, are increasingly reaching their performance limits, thereby calling for the development of new coating architectures for cutting tools. Summary of the Invention

[0004] In one embodiment, a cutting tool is described herein that includes a wear-resistant coating that uses one or more refractory layers of polycrystalline α-Al2O3. Briefly, the coated cutting tool described herein comprises a substrate and a coating adhered to the substrate, the coating including a layer of polycrystalline α-Al2O3 deposited by chemical vapor deposition (CVD), and at least 5% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation angle of less than 15 degrees as determined using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector.

[0005] In some embodiments, the misorientation angle is less than 10 degrees or less than 5 degrees.

[0006] In some embodiments, 5% to 15% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of 2 to 5 degrees, and at least 5% or at least 6% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of more than 5 degrees to a maximum of 15 degrees. In some embodiments, for example, 7 to 10% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of 2 to 5 degrees, and 6.5 to 10% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of more than 5 degrees to a maximum of 15 degrees. Furthermore, the ratio of grain boundaries in the polycrystalline α-Al2O3 layer having a misorientation of 2 to 5 degrees to grain boundaries having a misorientation of more than 5 degrees to a maximum of 15 degrees is a value of 0.7 to 1.8.

[0007] Furthermore, in addition to the low angle grain boundaries mentioned above, in some embodiments, the layer of polycrystalline α-AlO may also exhibit a texture coefficient (TC) greater than 6 for the (006) growth direction, where the texture coefficient is defined as follows:

number

[0008] In a further embodiment, the layer of polycrystalline α-Al2O3 may exhibit a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, where the texture coefficient is defined as:

number

[0009] These and other embodiments are further described in the Detailed Description below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiments described herein can be more easily understood by referring to the following detailed description and examples, as well as the preceding and following descriptions thereof. However, the elements, devices, and methods described herein are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention.

[0011] In one aspect, described herein is a cutting tool comprising a refractory coating that utilizes one or more polycrystalline α-Al2O3 layers with favorable grain boundary structure to resist various degradation mechanisms, including cracking and / or spalling. Thus, in some embodiments, cutting tools with such refractory coatings are suitable for high wear and / or abrasion applications, such as metal cutting operations. Referring now to specific components, the coated article comprises a substrate. The coated article can include any substrate not inconsistent with the objectives of the present invention. For example, the substrate can be a cutting tool or tooling used in abrasive applications. Cutting tools include, but are not limited to, cutting inserts (indexable and non-indexable), end mills or drills. The indexable cutting inserts can have any desired ANSI standard shape for milling or turning applications. The substrate of the coated articles described herein can be formed of cemented carbide, carbide, ceramic, ceramic, cermet, steel, or other alloys. In some embodiments, the cemented carbide substrate comprises tungsten carbide (WC). The WC can be present in the cutting tool substrate in an amount of at least about 80 weight percent or at least about 85 weight percent. Additionally, the metal binder of the cemented carbide can include cobalt or a cobalt alloy. The cobalt can be present in the cemented carbide substrate in an amount ranging from 1 weight percent to 15 weight percent, for example. In some embodiments, the cobalt is present in the cemented carbide substrate in an amount ranging from 5 to 12 weight percent or from 6 to 10 weight percent. Additionally, the cemented carbide substrate can exhibit a binder enriched zone beginning at and extending inwardly from the surface of the substrate.

[0012] The cemented carbide substrate may also include one or more additives, such as one or more of the elements titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium and / or compounds thereof. In some embodiments, the titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium form solid solution carbides with the WC of the substrate. In such embodiments, the substrate may include one or more solid solution carbides in an amount ranging from 0.1 to 5 weight percent. Additionally, the cemented carbide substrate may include nitrogen.

[0013] As described above, the coating adhered to the substrate includes a layer of polycrystalline α-Al2O3 deposited by CVD, and at least 5% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation angle of less than 15 degrees as determined using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector. Such low angle grain boundaries can enhance the strength and performance of the alumina layer for cutting applications. In some embodiments, at least 10% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation angle of less than 15 degrees. For example, 10-50% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation angle of less than 15 degrees. Furthermore, in some embodiments, the aforementioned percentage of grain boundaries in the polycrystalline α-Al2O3 layer can exhibit a misorientation angle of less than 10 degrees (e.g., 2-5 degrees). It is contemplated herein that deposition conditions of the polycrystalline α-Al2O3 layer can be selected to tailor the misorientation angle of the grain boundaries and / or the percentage of grain boundaries that exhibit a misorientation angle, in some embodiments, for example, more than 50% of all grain boundaries in the polycrystalline α-Al2O3 layer exhibit a misorientation angle of less than 15 degrees, or less than 10 degrees.

[0014] In some embodiments, 5%-15% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of 2-5 degrees, and at least 5% or at least 6% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of more than 5 degrees up to 15 degrees. In some embodiments, for example, 7-10% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of 2-5 degrees, and 6.5-10% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of more than 5 degrees up to 15 degrees. Furthermore, the ratio of grain boundaries in the polycrystalline α-Al2O3 layer having a misorientation of 2-5 degrees to grain boundaries having a misorientation of more than 5 degrees up to 15 degrees is a value between 0.7 and 1.8. Table I provides additional values ​​for the ratio of grain boundaries in the polycrystalline α-Al2O3 layer having a misorientation of 2-5 degrees to grain boundaries having a misorientation of more than 5 degrees up to 15 degrees. [Table 1]

[0015] The aforementioned misorientation ratios indicate a wider spread of aligned alumina grains, which can enhance cutting performance and coating life. Previous α-Al2O3 layers may exhibit 10-15% of all grain boundaries with misorientation of less than 5 degrees. However, above 5 degrees, the alumina grains become highly disordered. This abrupt drop between ordered and disordered grains compromises the integrity of the α-Al2O3 layer, thereby making the layer more susceptible to one or more degradation mechanisms during cutting and / or other wear operations.

[0016] In some embodiments, the grain boundaries of the polycrystalline α-AlO layer are tilt or twist boundaries. In some embodiments, the grain boundaries are a mixture of tilt and twist boundaries. When a mixture is present, in some embodiments, the majority of the grain boundaries are tilt boundaries.

[0017] Grain boundaries are characterized by five rotational parameters and three translational parameters. All these parameters affect the properties of the boundary. The three translational parameters describe the atomic shifts that can occur at the grain boundary. The rotational parameters are three parameters that describe the misorientation between the crystals and two parameters that describe the grain boundary normal. The misorientation itself is a rotation consisting of the axis of rotation (two parameters) and the angle of rotation (one parameter). Usually, when the rotation angle is small (less than about 15 degrees), the grain boundary consists of individual dislocations and the boundary is called a low-angle grain boundary. When the angle is larger, the boundary structure is less clearly defined and is called a high-angle grain boundary.

[0018] Grain boundaries and their characteristic rotational parameters can be observed, for example, by EBSD in 2D and 3D or by TEM. Atomic parameters can only be observed by atomic resolution TEM.

[0019] In crystalline materials, the orientation of a crystallite is defined by a transformation from the sample reference frame (i.e., defined by the direction of the rolling or extrusion process and two orthogonal directions) to the local reference frame of the crystal lattice, as defined by the basis of the unit cell. Similarly, misorientation is the transformation required to move from one local crystal frame to some other crystal frame; that is, the distance in orientation space between two distinct orientations. If the orientations are specified in the form of matrices of direction cosines gA and gB, the misorientation operator ΔgAB going from A to B can be defined as follows:

number

[0020] Various methods can be used to represent this conversion operation, e.g. Euler angles, Rodrigues vectors, axes / angles (when axes are specified as crystallographic directions), or unit quaternions. EBSD is well suited to extract this type of information, since it gives both statistical and spatial information about grain boundaries. The pattern consists of straight bright bands, called Kikuchi bands, which are directly related to the lattice planes of the diffracting crystal, and the center line of each of the bands corresponds directly to the gnomon projection of the lattice planes. The width of the Kikuchi bands is approximately proportional to the Bragg angle of electron diffraction on the associated lattice plane. The band intensity profile corresponds to the dynamic electron diffraction intensity obtained in a rocking experiment across the associated lattice plane.

[0021] From the geometry of the Kikuchi bands in the pattern, the crystal phase and orientation can be determined. The band profile contains information about the local defect density (especially the dislocation density). This information can be obtained in a highly automated manner by computer software, which represents the basis of the so-called EBSD-based orientation microscopy (ORM).

[0022] The misorientation of grain boundaries in polycrystalline α-Al2O3 can be determined according to the following protocol: The cross-section of the coated tool is polished to a mirror finish. Colloidal silica is the preferred abrasive, but diamond paste, ion milling, and other methods are acceptable. The prepared surface is observed using a field emission scanning electron microscope (FESEM) and an electron backscattered diffraction (EBSD) detector. With the FESEM, an electron beam of 25 kV accelerating voltage irradiates the polished surface, which is inclined at 70 degrees to the incident electron beam, and the orientation angle of the hexagonal alumina grains is measured based on the collected Kikuchi diffraction patterns. Data are collected from an area of ​​approximately 20 μm × 80 μm with a step size of 0.1 μm. Data processing is performed using commercially available software for the FESEM / EBSD instrument to determine the misorientation angle. Misorientation angles less than 2 degrees are discarded due to possible distortion within individual grains, while grain boundaries are identified by misorientation angles greater than 2 degrees. The misorientation value is obtained by averaging over the three EBSD maps.

[0023] In addition to the low angle grain boundaries mentioned above, in some embodiments, the layer of polycrystalline α-Al2O3 may also exhibit a texture coefficient (TC) greater than 6 relative to the (006) growth direction, where the texture coefficient is defined as:

number

[0024] In a further embodiment, the layer of polycrystalline α-Al2O3 may exhibit a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, where the texture coefficient is defined as:

number

[0025] The XRD peak data for the calculation of TC(006) and TC(0 0 12) are measured on a Bragg focusing diffractometer.

[0026] <Input optics include:> High precision long focal length X-ray tube operating at 45KV and 40MA. Variable divergence optics operated in automatic mode to ensure a constant illuminated sample volume throughout the analysis.

[0027] Fixed anti-scatter slit <Receiving optics included:> Variable anti-scatter slits operated in automatic mode to match the automatic divergence slits A multi-strip solid-state detector operated in scan mode.

[0028] Scan parameters (speed and count time) are selected to ensure a minimum of 10 data steps for the most intense peak, covering the full width at half maximum (FWHM) of the peak, and a total of approximately 10,000 counts. The collected data is first converted from variable mode to fixed mode usable for analysis. This conversion is completed using the following equation:

number

[0029] In some embodiments, the grains of the polycrystalline α-Al2O3 layer can exhibit a columnar morphology with their long axes perpendicular or substantially perpendicular to the substrate. Additionally, the alumina phase can exhibit low residual tensile stress in the as-deposited state. In some embodiments, the alumina phase has a residual tensile stress in the as-deposited state of 100-500 MPa or 20-400 MPa. The residual stress of the alumina phase can be measured by the χ tilt Sin 2 For alumina phase analysis, the Poisson's ratio can be determined from the analysis of a single-phase α-alumina coating by nanoindentation hardness.

number

[0030] The polycrystalline α-Al2O3 layer can be deposited directly on the substrate surface. Alternatively, the coatings described herein can further include one or more inner layers between the polycrystalline α-Al2O3 layer and the substrate. In some embodiments, the inner layer can include one or more metallic elements selected from the group consisting of aluminum and metallic elements of groups IVB, VB, and VIB of the periodic table, and one or more non-metallic elements selected from groups IIIA, IVA, VA, and VIA of the periodic table. In some embodiments, the one or more inner layers between the substrate and the multi-phase refractory layer include carbides, nitrides, carbonitrides, oxycarbonitrides, oxides, or borides of one or more metallic elements selected from the group consisting of aluminum and metallic elements of groups IVB, VB, and VIB of the periodic table.

[0031] For example, one or more of the inner layers may be titanium nitride, titanium carbonitride, titanium oxycarbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, hafnium nitride, hafnium carbonitride, TiAl x S y C v N, and aluminum oxynitride. Additionally, a layer of titanium oxycarbonitride can be used as a tie layer for the refractory layer and the inner layer of the coating. The inner layer of the coating can have any thickness consistent with the objectives of the present invention. In some embodiments, a single inner layer can have a thickness of at least 1.5 μm. Alternatively, multiple inner layers can collectively achieve a thickness of at least 1.5 μm.

[0032] The polycrystalline α-Al2O3 layer can be the outermost layer of the coating. Alternatively, the coatings described herein can include one or more outer layers on the polycrystalline α-Al2O3 layer. The outer layer can include one or more metallic elements selected from the group consisting of aluminum and metallic elements of groups IVB, VB, and VIB of the periodic table, and one or more non-metallic elements selected from groups IIIA, IVA, VA, and VIA of the periodic table. The outer layer on the polycrystalline α-Al2O3 layer can include a carbide, nitride, carbonitride, oxycarbonitride, oxide, or boride of one or more metallic elements selected from the group consisting of aluminum and metallic elements of groups IVB, VB, and VIB of the periodic table. For example, the one or more outer layers can include titanium nitride, titanium carbonitride, titanium oxycarbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, hafnium nitride, hafnium carbonitride, alumina, TiAl x S y C v N, aluminum oxynitride, and combinations thereof.

[0033] The outer layer of the coating described herein can have any thickness consistent with the objectives of the present invention. In some embodiments, the outer layer of the coating can have a thickness in the range of 0.2 μm to 5 μm.

[0034] The coatings described herein can be subjected to post-coating treatments. For example, the coatings can be blasted with various wet and / or dry particulate compositions. The post-coat blasting can be performed in any desired manner. In some embodiments, the post-coat blasting includes shot blasting or pressure blasting. Pressure blasting can be performed in various forms including compressed air blasting, wet compressed air blasting, pressurized liquid blasting, wet blasting, and vapor blasting. For example, wet blasting is accomplished using a slurry of inorganic and / or ceramic particles (such as alumina) and water. The particle slurry can be pneumatically projected onto the surface of the coated cutting tool body to impact the surface of the coating. The inorganic and / or ceramic particles can generally range in size from about 20 μm to about 100 μm.

[0035] Blasting parameters include pressure, impact angle, distance to the part surface, and duration. In some embodiments, the impact angle can range from about 10 degrees to about 90 degrees, i.e., the particles impact the coating surface at an angle ranging from about 10 degrees to about 90 degrees. Suitable pressures can range from 30 to 55 pounds per square inch (psi) at a distance to the coating surface of 1 to 6 inches. Furthermore, the duration of the blasting process can generally range from 1 to 10 seconds or more. The blasting process can generally be performed over the entire surface area of ​​the coating or can be applied to selected locations, such as the workpiece contact area of ​​the cutting tool. The workpiece contact area can be the honing area of ​​the cutting tool.

[0036] In other embodiments, the coating undergoes an abrasive post-coating treatment. Abrasion can be performed using a paste of appropriate diamond or ceramic grit size. In some embodiments, the grit size of the paste ranges from 1 μm to 10 μm. In one embodiment, a 5-10 μm diamond grit paste is used to abrade the coating. Furthermore, the grit paste can be applied to the CVD coating by any implement (such as a brush) not inconsistent with the objectives of the present invention. In one embodiment, the grit paste is applied to the CVD coating at the workpiece contact area of ​​the cutting tool using, for example, a flat brush.

[0037] The coatings described herein provide a desired surface roughness (R a ) and / or other parameters such as residual tensile stress in the coating. In some embodiments, the coating that undergoes the post-coating treatment has a surface roughness (R a ). [Table 2]

[0038] Coating surface roughness can be determined by optical profilometry using a WYKO® NT Series Optical Profiler available from Veeco Instruments, Inc. (Plainview, NY, USA). Coating surface roughness can be determined via optical metrology with instruments available from Bruker Alicona (Itasca, IL).

[0039] Further, in some embodiments, the post-coating treatment does not remove one or more outer layers of the coating. In some embodiments, for example, the post-coating treatment does not remove the TiN, TiCN, and / or TiOCN outer layers. Alternatively, the post-coating treatment can remove or partially remove one or more outer layers of TiN, TiCN, TiOCN, etc., to expose the underlying polycrystalline α-Al2O3 layer.

[0040] These and other embodiments are further illustrated in the following non-limiting examples. EXAMPLES

[0041] Example 1 - Coated Cutting Tool Sintered cemented carbide cutting inserts of ANSI geometry CNMG433RP having the composition of Table II were provided. [Table 3]

[0042] Sintered cemented carbide cutting inserts were provided with a CVD coating having the composition and structure provided in Table III. [Table 4]

[0043] The coatings were deposited in a Sucotec CVD furnace commercially available from Oerlikon Balzers. The coatings were deposited according to the parameters in Tables IV and V. A tie layer comprising HT-TiCN and TiOCN is adjacent to the Al2O3 layer to enhance adhesion. [Table 5] [Table 6]

[0044] The rake faces of the coated inserts were blasted with a slurry as described above to remove the outer TiCN / TiN layer and expose the underlying α-Al2O3 layer. Nine of the blasted inserts were selected for texture evaluation and characterization of the grain misorientation of the α-Al2O3 layer. The characterization results are provided in Tables VI and VII. [Table 7] [Table 8]

[0045] Two of the coated inserts were subjected to metal cutting tests against KCP25 inserts of the same geometry commercially available from Kennametal Inc. The parameters of the turning tests were as follows: Workpiece: 1045 steel Speed: 1200sfm Feed rate: 0.013ipr Cutting depth: 0.08mm Coolant:Flood The results of the continuous turning tests are shown in Table VIII. [Table 9]

[0046] As provided in Table VIII, cutting inserts including the inventive coatings described herein exhibit significantly longer tool life compared to comparable KCP25.

[0047] Additional metal cutting tests were performed as follows. Workpiece: 4340 steel Speed:700sfm Feed rate: 0.012ipr Cutting depth: 0.1mm Coolant:Flood The results of the continuous turning tests are shown in Table IX. [Table 10]

[0048] As provided in Table IX, cutting inserts including the inventive coatings described herein exhibit significantly longer tool life compared to comparable KCP25.

[0049] Various embodiments of the present invention have been described in fulfillment of various objectives of the present invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. 1. A coated cutting tool comprising: A substrate; a coating adhered to the substrate, the coating being polycrystalline α-Al deposited by chemical vapor deposition (CVD); ２ O ３ as determined using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector, ２ O ３ 5% to 15% of all grain boundaries in the layer have a misorientation of 2 to 5 degrees, and the polycrystalline α-Al ２ O ３ At least 5% of all grain boundaries in the layer have a misorientation of more than 5 degrees up to 15 degrees; The polycrystalline α-Al 2 O 3 layer has a texture coefficient (TC) greater than 6 for the (006) growth direction, the texture coefficient being defined as: [Equation 1] During the ceremony, I(hkl) = Intensity measurement of the (hkl) reflection I o (hkl) = standard intensity of the (hkl) reflection according to the International Center for Diffraction Data (ICDD) card 43-1484 n = number of reflections used in the TC calculation and a coating wherein the (hkl) reflections used in the TC calculation are (012), (104), (110), (006), (113), (202), (024), and (116).

2. The polycrystalline α-Al ２ O ３ 10. The coated cutting tool of claim 1, wherein at least 6% of all grain boundaries in the layer have a misorientation of more than 5 degrees up to 15 degrees.

3. Polycrystalline α-Al ２ O ３ 7-10% of all grain boundaries in the layer have a misorientation of 2-5 degrees, and polycrystalline α-Al ２ O ３ 10. The coated cutting tool of claim 1, wherein 6.5 to 10% of all grain boundaries in the layer have a misorientation of more than 5 degrees up to 15 degrees.

4. The polycrystalline α-Al ２ O ３ 2. The coated cutting tool of claim 1, wherein the ratio of grain boundaries in the layer that are misoriented between 2 and 5 degrees to grain boundaries that are misoriented from more than 5 degrees up to 15 degrees is a value between 0.7 and 1.

8.

5. The coated cutting tool of claim 4, wherein the ratio is between 0.9 and 1.

7.

6. The coated cutting tool of claim 4, wherein the ratio is between 1.3 and 1.

6.

7. The coated cutting tool of claim 4, wherein the ratio is between 1.4 and 1.

7.

8. The polycrystalline α-Al ２ O ３ The coated cutting tool of claim 1, wherein the layer has a thickness of 1 to 20 μm.

9. The polycrystalline α-Al ２ O ３ The coated cutting tool of claim 1 , wherein the layer has a columnar grain structure.

10. The coated cutting tool of claim 1 , wherein the TC(006) is greater than 7.

11. The polycrystalline α-Al ２ O ３ The layer has a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, the texture coefficient being defined as: [Equation 2] During the ceremony, I(hkl) = Intensity measurement of the (hkl) reflection I ｏ (hkl) = standard intensity of (hkl) reflections according to the International Center for Diffraction Data (ICDD) card 42-1468 n = number of reflections used in the TC calculation 2. The coated cutting tool of claim 1, wherein the (hkl) reflections used in the TC calculation are (012), (104), (110), (113), (116), (300), and (0 0 12).

12. The coated cutting tool of claim 11 , wherein the TC(0 0 12) is greater than 6.

13. 13. The coated cutting tool of claim 12, wherein the ratio of TC(006) to TC(0 0 12) is greater than 1 and up to 1.

2.

14. The coating is the polycrystalline α-Al ２ O ３ 10. The coated cutting tool of claim 1, further comprising one or more inner layers between the layer of and the substrate.

15. 15. The coated cutting tool of claim 14, wherein the one or more inner layers comprise one or more metallic elements selected from the group consisting of aluminum and metallic elements from Groups IVB, VB, and VIB of the periodic table, and one or more non-metallic elements selected from the group consisting of non-metallic elements from Groups IIIA, IVA, VA, and VIA of the periodic table.

16. 16. The coated cutting tool of claim 15, wherein the one or more inner layers comprises a TiCN layer.

17. The coated cutting tool of claim 1 , wherein the coating further comprises one or more outer layers over the multi-phase refractory layer.

18. The coated cutting tool of claim 1 , wherein the substrate comprises a cemented carbide with a metal bond in an amount of 1 to 15 weight percent.

19. The coated cutting tool of claim 1 , wherein the substrate comprises a cemented carbide with a metal binder in an amount of 5 to 12 weight percent.

20. 1. A coated cutting tool comprising: A substrate; a coating adhered to the substrate, the coating being polycrystalline α-Al deposited by chemical vapor deposition (CVD); ２ O ３ as determined using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector, ２ O ３ a coating in which the ratio of grain boundaries in the layer having a misorientation of 2 to 5 degrees to grain boundaries having a misorientation of more than 5 degrees up to 15 degrees has a value of 0.7 to 1.

8.

21. 21. The coated cutting tool of claim 20, wherein the ratio is between 0.9 and 1.

7.

22. 21. The coated cutting tool of claim 20, wherein the ratio is between 1.3 and 1.

6.

23. 21. The coated cutting tool of claim 20, wherein the ratio is between 1.4 and 1.7.

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