Surface coated cutting tool

Abstract

In one aspect, cutting tools are described herein that include a wear resistant coating employing one or more polycrystalline alpha-Al2O3 refractory layers. In short, a coated cutting tool described herein includes a substrate, and a coating adhered to the substrate, the coating including a polycrystalline alpha-Al2O3 layer deposited by chemical vapor deposition (CVD), the polycrystalline alpha-Al2O3 layer having a length of sigma3 type grain boundaries as measured using electron backscatter diffraction (EBSD), the length is greater than 0% but less than 10% of the total length of all grain boundaries and has a texture coefficient (TC) greater than 6 for the (006) growth direction and a texture coefficient (TC) greater than 5 for the (012) growth direction.

Description

Technical Field

[0001] This invention relates to refractory coatings, and more particularly to refractory coatings deposited by chemical vapor deposition (CVD) for use in cutting tools and / or metal removal applications. Background Technology

[0002] Cutting tools, including cemented carbide cutting tools, have been used to machine various metals and alloys under both coated and uncoated conditions. To improve the wear resistance, performance, and lifespan of cutting tools, one or more layers of refractory materials have been applied to the tool surface. For example, TiC, TiCN, TiN, and / or Al2O3 have been applied to cemented carbide substrates via CVD and physical vapor deposition (PVD). While these methods effectively suppress wear and extend tool life in various applications, single-layer or multi-layer refractory coatings based on the aforementioned refractory materials are increasingly approaching their performance limits, necessitating the development of new coating structures for cutting tools. Summary of the Invention

[0003] In one aspect, this document describes a cutting tool comprising a wear-resistant coating using one or more polycrystalline α-Al₂O₃ refractory layers. Briefly, the coated cutting tool described herein comprises a substrate and a coating adhered to the substrate, the coating comprising at least one polycrystalline α-Al₂O₃ layer deposited by chemical vapor deposition (CVD), the polycrystalline α-Al₂O₃ layer having a length of Σ₃ type grain boundaries as measured using electron backscatter diffraction (EBSD), the length being greater than 0% but less than 10% of the total length of all grain boundaries, and having a texture factor (TC) greater than 6 for the (006) growth direction and a texture factor (TC) greater than 5 for the (0 0 12) growth direction, the texture factor being defined as:

[0004]

[0005] in

[0006] I(hkl) = (hkl) Measured intensity of reflection

[0007] I o (hkl) = Standard intensity of reflection as described in International Data Center for Diffraction (ICDD) Card 43-1484.

[0008] The number of reflections used in the n=TC calculation

[0009] The (hkl) reflection used in TC calculations is:

[0010] (012), (104), (110), (006), (113), (202), (024), and (116) for calculating TC(006); or

[0011] (012), (104), (110), (113), (116), (300), and (0 0 12) for calculating TC(0012).

[0012] In some embodiments, the polycrystalline α-Al₂O₃ layer comprises columnar grains exhibiting an average grain width less than 5 μm. In some embodiments, the average grain width is less than 3 μm, such as from 0.5 μm to 2.5 μm. Additionally, in some embodiments, at least 5% of all grain boundaries in the polycrystalline α-Al₂O₃ layer have a misorientation angle less than 15 degrees as determined using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector. In some embodiments, the misorientation angle is less than 10 degrees or less than 5 degrees. Furthermore, in some embodiments, 5% to 20% 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 greater than 5 degrees and less than or equal to 15 degrees. In some embodiments, for example, 16% - 20% of all grain boundaries in the polycrystalline α-Al₂O₃ layer have a misorientation of 2 - 5 degrees.

[0013] In another aspect, methods of making a coated cutting tool are described herein, the coated cutting tool comprising one or more refractory layers employing polycrystalline α-Al₂O₃. In some embodiments, a method includes depositing a polycrystalline α-Al₂O₃ layer from a gaseous reaction mixture comprising H₂, CO, CO₂, H₂S, HCl, AlCl₃, wherein the volume ratio of CO₂ to H₂S in the CVD reaction chamber is in the range of 5 < CO₂ / H₂S < 10, and the deposited polycrystalline α-Al₂O₃ layer has a length of Σ3 type grain boundaries as measured using EBSD that is greater than 0% but less than 10% of the total length of all grain boundaries, and a texture coefficient (TC) greater than 6 for the (006) growth direction and a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, as described above.

[0014] These and other embodiments are further described in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Shows measurement of the average α-Al₂O₃ grain width according to the method described herein. DETAILED DESCRIPTION

[0016] The embodiments described herein can be more readily understood by referring to the following detailed description and examples, as well as their preceding and following descriptions. However, the elements, apparatus, 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 invention. Many modifications and changes will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

[0017] In one aspect, this document describes cutting tools comprising a refractory coating with one or more polycrystalline α-Al₂O₃ layers having a grain boundary structure that is advantageous in resisting various degradation mechanisms, including cracking and / or spalling. Therefore, in some embodiments, cutting tools with such refractory coatings are suitable for high-wear and / or abrasive applications, such as metal cutting operations. Turning now to specific components, coated articles comprise a substrate. Coated articles can include any substrate inconsistent with the purposes of this invention. For example, the substrate can be a cutting tool or process equipment for abrasive applications. Cutting tools include, but are not limited to, cutting inserts (indexable and non-indexable), end mills, or drills. Indexable cutting inserts can have any desired ANSI standard geometry for milling or turning applications. The substrate of the coated articles described herein can be formed from cemented carbide, carbide, ceramic, cermet, steel, or other alloys. In some embodiments, the cemented carbide substrate comprises tungsten carbide (WC). WC may be present in the cutting tool matrix in an amount of at least about 80% by weight or in an amount of at least about 85% by weight. Additionally, the metal binder of the cemented carbide may contain cobalt or a cobalt alloy. For example, cobalt may be present in the cemented carbide substrate in an amount ranging from 1% to 15% by weight. In some embodiments, cobalt is present in the cemented carbide matrix in an amount ranging from 5-12% by weight or 6-10% by weight. Furthermore, the cemented carbide substrate may have a binder-rich region that begins at the substrate surface and extends inward from the substrate surface.

[0018] The cemented carbide substrate may also contain one or more additives, such as one or more of the following elements and / or compounds: titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium. In some embodiments, titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium form a solid solution carbide together with the WC of the substrate. In such embodiments, the matrix may include one or more solid solution carbides in an amount ranging from 0.1 to 5% by weight. Furthermore, the cemented carbide matrix may include nitrogen.

[0019] As described above, the coating adhered to the substrate comprises a polycrystalline α-Al₂O₃ layer deposited by CVD, the polycrystalline α-Al₂O₃ layer having a length of Σ₃ type grain boundaries as measured using EBSD, the length being greater than 0% but less than 10% of the total length of all grain boundaries, and having a texture factor (TC) greater than 6 for the (006) growth direction and a texture factor (TC) greater than 5 for the (0 0 12) growth direction, the texture factor being defined as:

[0020]

[0021] in

[0022] I(hkl) = (hkl) Measured intensity of reflection

[0023] I o (hkl) = Standard intensity of reflection as described in International Data Center for Diffraction (ICDD) Card 43-1484.

[0024] The number of reflections used in the n=TC calculation

[0025] The (hkl) reflection used in TC calculations is:

[0026] (012), (104), (110), (006), (113), (202), (024), and (116) are used to calculate TC(006); or

[0027] (012), (104), (110), (113), (116), (300), and (0 0 12) are used to calculate TC(0012).

[0028] XRD peak data for calculating TC(006) and TC(0 0 12) were measured on a Bragg focusing diffractometer.

[0029] The entrance optics comprise:

[0030] A long, narrow focal X-ray tube operating at 45 kV and 40 mA.

[0031] The variable diverging optics operate in automatic mode to ensure a constant volume of irradiated sample throughout the analysis.

[0032] Fixed anti-scattering slit

[0033] The receiving optics comprise :

[0034] Variable anti-scattering slits that operate in automatic mode to match the automatic divergence slits

[0035] A multi-state solid-state detector operating in scan mode.

[0036] Select scan parameters (speed and counting time) to ensure a minimum of ten data steps across the peak full width at half maximum (FWHM) and approximately 10,000 total counts at the strongest peak. The collected data is first converted from a variable mode to a fixed mode suitable for analysis. This conversion is performed using the following formula:

[0037]

[0038] Where a = divergence angle, and L = irradiation length on the sample.

[0039] Peak intensity correction was applied using peak finding software to identify the peak locations of all peaks in the collected data. The peaks were then refined using a profile function to precisely identify their locations and heights. This peak data was used for alumina texture coefficient analysis. Due to the complexity of the CVD coating structure, thickness correction was not applied to the peak intensity.

[0040] As described herein, the polycrystalline α-Al₂O₃ layer has Σ₃ grain boundary lengths as measured using EBSD, said lengths being greater than 0% but less than 10% of the total length of all grain boundaries. In some embodiments, the lengths of the Σ₃ grain boundaries are 1% to 8%, 2% to 6%, or 2% to 5% of the total length of all grain boundaries. For EBSD measurements / analysis, the cross-sectional area of ​​the coated tool was polished to a mirror finish. In this case, colloidal silica was used, but diamond paste, ion polishing, and other methods are also acceptable. The prepared surface was observed using a field emission scanning electron microscope (FESEM) and an EBSD detector. Using FESEM, the polished surface, tilted 70° relative to the incident electron beam, was irradiated with an electron beam at an accelerating voltage of 25 kV to measure the orientation angles of the hexagonal alumina grains based on the collected Kikuchi diffraction pattern. Data was collected from a region of approximately 20 μm × 80 μm in steps of 0.1 μm. Data processing was performed using commercially available software to determine co-located lattice (CSL) grain boundaries, including Σ₃ grain boundaries.

[0041] In some embodiments, the grains of the polycrystalline α-Al₂O₃ layer may exhibit a columnar morphology with their long axes perpendicular to or substantially perpendicular to the substrate. In some embodiments, the columnar grains may exhibit an average grain width of less than 5 μm. In some embodiments, the average grain width is less than 3 μm, such as 0.5 μm to 2.5 μm. In some embodiments, the average grain width is 0.5–4.5 μm or 1–3 μm. The average grain width is the average of the widths of 25 consecutive grains of the polycrystalline α-Al₂O₃ layer measured using contrast-enhanced EBSD imaging on a polished cross-section of the polycrystalline α-Al₂O₃ layer. Figure 1The method described herein is used to measure the average α-Al₂O₃ grain width. The alumina grain width was determined using the caliper function on an EBSD band contrast map in the data collection software. Approximately 20 adjacent grains from the center of the coating were measured. The caliper measurements were based on the SEM magnification and internal calibration in the software.

[0042] Additionally, in some embodiments, 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 electron backscatter diffraction (EBSD) detector. In some embodiments, the misorientation angle is less than 10 degrees or less than 5 degrees. Furthermore, in some embodiments, 5% to 20% of all grain boundaries in the polycrystalline α-Al₂O₃ layer have a misorientation angle 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 angle greater than 5 degrees and less than or equal to 15 degrees. In some embodiments, for example, 16% to 20% of all grain boundaries in the polycrystalline α-Al₂O₃ layer have a misorientation angle of 2-5 degrees.

[0043] In some embodiments, the grain boundaries of the polycrystalline α-Al₂O₃ layer are tilted or twisted boundaries. In some embodiments, the grain boundaries are a mixture of tilted and twisted boundaries. In some embodiments, when a mixture is present, most grain boundaries are tilted boundaries.

[0044] Grain boundaries are characterized by five rotation parameters and three translation parameters. All of these parameters affect the properties of the boundary. The three translation parameters describe the atomic displacements that may occur at the grain boundary. The rotation parameters are three parameters describing the orientation of dislocations between crystals and two parameters describing the grain boundary normal. Dislocation orientation itself is a rotation consisting of a rotation axis (two parameters) and a rotation angle (one parameter). Typically, when the rotation angle is small (approximately <15°), the grain boundary consists of a single dislocation, and the boundary is called a small-angle / low-angle grain boundary. When the angle is large, the boundary structure is less distinct and is called a large-angle grain boundary.

[0045] For example, grain boundaries and their characteristic rotational parameters can be observed using 2D and 3D EBSD or TEM. Atomic parameters can only be observed using TEM at atomic resolution.

[0046] 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 lattice, as defined by the basis of the unit cell. Similarly, misorientation is the transformation necessary to move from one local crystal framework to some other crystal framework. That is, it is the distance in orientation space between two different orientations. If orientation is defined according to the matrices of direction cosines gA and gB, then the misorientation operator ΔgAB from A to B can be defined as follows:

[0047] g B =Δg AB g A

[0048]

[0049] The term g -1 A is the inverse operation of gA, i.e., the transformation from crystal framework A back to sample framework. This provides an alternative description of misorientation as a successive operation of transforming from the first crystal framework (A) back to the sample framework and then to the new crystal framework (B).

[0050] This transformation operation can be represented using various methods, such as Euler angles, Rodrigues vectors, axis / angle (where the axis is specified as the crystallographic direction), or unit quaternions. EBSD is well-suited for extracting this type of information because it provides statistical and spatial information about grain boundaries. The pattern consists of straight bright bands, known as Kikuchi bands, which are directly related to the lattice planes of the diffracting crystal: the center line of each band directly corresponds to the sundial projection of the lattice plane. The width of the Kikuchi band is approximately proportional to the Bragg angle of electron diffraction on the associated lattice plane. The band intensity distribution corresponds to the dynamic electron diffraction intensity obtained in a rocking experiment on the associated lattice plane.

[0051] Based on the geometry of the Kikuchi bands in the pattern, the crystalline phase and orientation can be determined. The band profile contains information about the local defect density (especially about dislocation density). This information can be obtained in a highly automated manner using computer software, and then the basis for so-called EBSD-based orientation microscopy (ORM) can be displayed.

[0052] Grain boundary misorientations in polycrystalline α-Al₂O₃ can be determined using the following scheme. The cross-sectional area of ​​the coated tool is polished to a mirror finish. Colloidal silica is a suitable polishing agent, but diamond paste, ion polishing, and other methods are also acceptable. The prepared surface is observed using a field emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector. Using FESEM, the polished surface, tilted 70° relative to the incident electron beam, is irradiated with an electron beam at an accelerating voltage of 25 kV to measure the orientation angles of hexagonal alumina grains based on the collected Kikuchi diffraction patterns. Data is collected from a region 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 apparatus to determine the misorientation angles. Misorientation angles <2° are considered as possible strain within a single grain, while grain boundaries are identified by misorientation angles >2°. The average of more than three EBSD patterns is taken to obtain the misorientation value.

[0053] Furthermore, the alumina phase can exhibit low residual tensile stress in the deposited state. In some embodiments, the alumina phase has a residual tensile stress of 100-500 MPa or 20-400 MPa in the deposited state. The residual stress of the alumina phase can be measured using the Chitilt Sin (116) reflection. 2 The ψ method was used to determine the composition. For alumina phase analysis, Poisson's ratio (υ) was set to 0.19, and the elastic modulus (E, in GPa) was determined to be 415 by analysis of the single-phase α-alumina coating using nanoindentation hardness. Furthermore, the polycrystalline α-Al₂O₃ layer can have any desired thickness. In some embodiments, the polycrystalline α-Al₂O₃ layer has a thickness of 1-20 μm or 5-15 μm.

[0054] The polycrystalline α-Al₂O₃ layer can be deposited directly on the substrate surface. Alternatively, the coating described herein may also include one or more inner layers between the polycrystalline α-Al₂O₃ layer and the substrate. In some embodiments, the inner layer comprises one or more metallic elements selected from the group consisting of aluminum and metals of Groups IVB, VB, and VIB of the periodic table, and one or more nonmetallic elements selected from the group consisting of nonmetallic elements of Groups IIIA, IVA, VA, and VIA of the periodic table. In some embodiments, one or more inner layers between the substrate and the multiphase refractory layer comprise carbides, nitrides, carbonitrides, carbonitrides, oxides, or borides of one or more metallic elements selected from the group consisting of aluminum and metals of Groups IVB, VB, and VIB of the periodic table.

[0055] For example, one or more inner layers are selected from the group consisting of: titanium nitride, titanium carbonitride, titanium carbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, hafnium nitride, hafnium carbonitride, TiAl x Si y C v N and aluminum oxynitride. Furthermore, the titanium carbonitride layer can be used as an adhesive layer between the refractory layer and the inner layers of the coating. The inner layers of the coating can have any thickness inconsistent with the purpose of this 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.

[0056] The polycrystalline α-Al₂O₃ layer may be the outermost layer of the coating. Alternatively, the coating described herein may include one or more outer layers on the polycrystalline α-Al₂O₃ layer. The outer layers may comprise one or more metallic elements selected from the group consisting of aluminum and metals of Groups IVB, VB, and VIB of the periodic table, and one or more nonmetallic elements selected from the group consisting of nonmetals of Groups IIIA, IVA, VA, and VIA of the periodic table. The outer layers on the polycrystalline α-Al₂O₃ layer may comprise carbides, nitrides, carbonitrides, carbonitride oxides, oxides, or borides of one or more metallic elements selected from the group consisting of aluminum and metals of Groups IVB, VB, and VIB of the periodic table. For example, one or more outer layers may be selected from the group consisting of: titanium nitride, titanium carbonitride, titanium carbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, hafnium nitride, hafnium carbonitride, aluminum oxide, TiAl x Si y C v N, aluminum oxynitride and their combinations.

[0057] The outer coating described herein may have any thickness that is inconsistent with the purpose of this invention. In some embodiments, the outer coating may have a thickness ranging from 0.2 μm to 5 μm.

[0058] The coatings described herein may undergo post-coating treatments. The coatings can be treated, for example, by sandblasting with various wet and / or dry particle compositions. Post-coating sandblasting can be applied in any desired manner. In some embodiments, post-coating sandblasting includes shot peening or pressurized sandblasting. Pressurized sandblasting can be applied in various forms, including compressed air sandblasting, wet compressed air sandblasting, pressurized liquid sandblasting, wet sandblasting, and steam sandblasting. For example, wet sandblasting is achieved using a slurry of inorganic and / or ceramic particles, such as alumina, and water. The particle slurry can be pneumatically atomized onto the surface of the coated cutting tool body to impact the coating surface. The size of the inorganic and / or ceramic particles is generally in the range of about 20 μm to about 100 μm.

[0059] Sandblasting parameters include pressure, impact angle, distance from the part surface, and duration. In some implementations, the impact angle can range from about 10 degrees to about 90 degrees, meaning the particles impact the coated surface at an angle ranging from about 10 degrees to about 90 degrees. Suitable pressures range from 30 to 55 pounds per square inch (psi) at a distance of 1–6 inches from the coated surface. Furthermore, the duration of sandblasting is typically from 1 to 10 seconds or longer. Sandblasting can be applied generally to the surface area of ​​the coating or to selected locations, such as the workpiece contact area of ​​a cutting tool. The workpiece contact area can be the honed area of ​​the cutting tool.

[0060] In other embodiments, the coating undergoes a post-coating polishing process. Polishing can be performed using a paste with a suitable rhomboid or ceramic coarse-grained size. In some embodiments, the coarse-grained size of the paste is in the range of 1 μm to 10 μm. In one embodiment, a rhomboid coarse-grained paste of 5-10 μm was used to polish the coating. Furthermore, the coarse-grained paste can be applied to the CVD coating using any device that does not contradict the purpose of the invention, such as a brush. For example, in one embodiment, a flat brush is used to apply the coarse-grained paste to the CVD coating in the workpiece contact area of ​​the cutting tool.

[0061] The coating described in this article can be sandblasted or polished for a period of time sufficient to achieve the desired surface roughness (R). a ) and / or other parameters, such as reducing residual tensile stress in the coating. In some embodiments, the coating subjected to post-coating treatment has a surface roughness (R) selected from Table I. a ).

[0062] Table I - Surface Roughness After Coating (R) a )

[0063] coating surface roughness (R a - nm ≤500 ≤250 <200 10-250 50-175 25-150

[0064] The surface roughness of the coating can be measured using optical profilometry, and is available from Veeco Instruments, Inc. of Plainview, New York. The surface roughness of the coating can be measured using an NT series optical profilometer. Optical metrology can be used to measure the surface roughness using instruments commercially available from Bruker Alicona of Itasca, IL.

[0065] Furthermore, in some embodiments, the post-coating process does not remove one or more outer layers of the coating. For example, in some embodiments, the post-coating process does not remove the outer layers of TiN, TiCN, and / or TiOCN. Alternatively, the post-coating process may remove or partially remove one or more outer layers, such as TiN, TiCN, and TiOCN, to expose the underlying polycrystalline α-Al2O3 layer.

[0066] In another aspect, methods of making coated cutting tools are described herein, the coated cutting tools including one or more refractory layers employing polycrystalline α-Al2O3. In some embodiments, a method includes depositing a polycrystalline α-Al2O3 layer from a gaseous reaction mixture comprising H2, CO, CO2, H2S, HCl, AlCl3, wherein the volume ratio of CO2 to H2S in a CVD reaction chamber is in the range of 5 < CO2 / H2S < 10, and the deposited polycrystalline α-Al2O3 layer has a length of Σ3-type grain boundaries as measured using EBSD, the length being greater than 0% but less than 10% of the total length of all grain boundaries, and having a texture coefficient (TC) greater than 6 for the (006) growth direction and a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, as described above. In some embodiments, the deposited polycrystalline α-Al2O3 layer may have any of the properties described above. In some embodiments, in the methods described herein, the CO / H2S ratio > 2.

[0067] These and other embodiments are further illustrated in the following non-limiting examples.

[0068] Example 1 - Coated Cutting Tool

[0069] A sintered carbide cutting insert of ANSI geometry CNMG433RP is provided, having the composition of Table II.

[0070] Table II - Sintered Carbide Substrate Composition

[0071] Component Weight percent Cobalt 6.5-7.5 Group IV-VI carbide 5-7 WC Balance

[0072] The sintered carbide cutting insert is provided with a base CVD layer having the composition and structure provided in Table III.

[0073] Table III - CVD Coating Structure

[0074] Layer Thickness (pm) TiN 0.2-0.75 MT-TiCN 6-10 TiO x C y N z ]]> 0.5-1

[0075] * Base layer adjacent to the substrate

[0076] The base layer is deposited in a Sucotec CVD furnace commercially available from Oerlikon Balzers. TiN, MT-TiCN, and TiO are deposited according to the parameters in Tables IV and V. x C y N z layers.

[0077] Table II - CVD Deposition of Coatings

[0078]

[0079] Table V - CVD Deposition Steps

[0080]

[0081] According to Table VI, the α-Al2O3 layer of the sample was deposited in two steps at 1000 °C.

[0082] Table VI - CVD Deposition of α-Al2O3 Layer

[0083]

[0084] For samples A - C of the present invention, for the second step, the volume ratio of CO2 to H2S in the CVD reaction chamber is within the range of 5 < CO2 / H2S < 10. The CO2 / H2S of comparative sample A exceeds this range. The deposition time of each sample was adjusted to obtain an α-Al2O3 layer thickness of approximately 8 μm. The properties of the polycrystalline α-Al2O3 layers of samples A - C of the present invention and comparative sample A are provided in Table VII.

[0085] Table VII - Properties of α-Al2O3 Layer

[0086]

[0087] Subsequently, metal cutting tests were carried out on the coated cutting tools (samples A - C of the present invention and comparative sample A). The metal cutting test conditions and results are provided below.

[0088] Metal Cutting Test Conditions and Results

[0089] 1) Flank Wear Resistance after Turning 4340 Steel

[0090] Cutting Parameters - 700 sfm / 0.012 ipr / 0.1 doc / Flood

[0091] Tool description Tool life (repeat 1) Tool life (repeat 2) Inventive sample A 13.5 NW 13.0 NW Inventive sample B 13.5 MW 13.9 NW Inventive sample C 16.4 MW 16.1 NW Comparative sample A 7.0 NW 6.0 NW

[0092] 2) Pit Wear Resistance after Turning 1045 Steel

[0093] Cutting Parameters - 1200 sfm / 0.013 ipr / 0.08 doc / Flood

[0094] Tool description Tool life (repeat 1) Tool life (repeat 2) Inventive sample A 29 NW 27.6 NW Inventive sample B 32.9 NW 41.3 MW Inventive sample C 27.0 NW 30.7 NW Comparative sample A 13.4 NW 12.8 NW

[0095] 3) Resistance to Chipping during Interrupted Cutting of 4140 Steel

[0096] Cutting Parameters - 500 sfm / 0.010 ipr / 0.100 doc / Flood

[0097] Tool description Tool life (repeat 1) Tool life (repeat 2) Inventive sample A 21.9 MW 26.8 MW Inventive sample B 21.3 MW 28.4 MW Inventive sample C 22.7 NW 18.6 MW Comparative sample A 4.4 NW 8.7 MW

[0098] 4) Test for coating peeling during cyclic intermittent cutting of ductile iron end face

[0099] Cutting parameters—895sfm / 0.012ipr / 0.08doc / overflow

[0100]

[0101] As shown in the metal cutting test, the present invention sample AC significantly outperforms the comparative sample A in a variety of workpieces and cutting applications (including turning and interrupted cutting).

[0102] Various embodiments of the invention have been described to achieve the various objectives of the invention. It should be understood that these embodiments are merely illustrative of the principles of the invention. Many modifications and adaptations will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A coated cutting tool, the coated cutting tool comprising: Substrate, and A coating adhered to the substrate, the coating comprising a polycrystalline α-Al₂O₃ layer deposited by chemical vapor deposition (CVD), the polycrystalline α-Al₂O₃ layer having a length of Σ₃ type grain boundaries as measured using EBSD, the length being greater than 0% but less than 10% of the total length of all grain boundaries, and having a texture factor (TC) greater than 6 for the (006) growth direction and a texture factor (TC) greater than 5 for the (0 012) growth direction, the texture factor being defined as: in I(hkl) = (hkl) Measured intensity of reflection I o (hkl) = Standard intensity of reflection as described in International Data Center for Diffraction (ICDD) Card 43-1484. The number of reflections used in the n=TC calculation The (hkl) reflection used in TC calculations is: (012), (104), (110), (006), (113), (202), (024), and (116) are used to calculate TC(006); or (012), (104), (110), (113), (116), (300), and (0 0 12) are used to calculate TC(0012).

2. The coated cutting tool according to claim 1, wherein the length of the Σ3 type grain boundary is 1% to 8% of the total length of all grain boundaries.

3. The coated cutting tool according to claim 1, wherein the length of the Σ3 type grain boundary is 2% to 5% of the total length of all grain boundaries.

4. The coating cutting tool according to claim 1, wherein the TC is 6.5-7.8 for the (006) growth direction.

5. The coated cutting tool according to claim 4, wherein the TC is 5.5-6.5 for the (0 0 12) growth direction.

6. The coated cutting tool according to claim 1, wherein the polycrystalline α-Al2O3 layer comprises columnar grains.

7. The coated cutting tool according to claim 6, wherein the columnar grains have an average grain width of 0.1 μm to 3 μm.

8. The coated cutting tool according to claim 6, wherein the columnar grains have an average grain width of 0.5 μm to 4.5 μm.

9. The coated cutting tool according to claim 6, wherein the columnar grains have an average grain width of 1 μm to 2 μm.

10. The coated cutting tool according to claim 1, wherein at least 5% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation angle of less than 15 degrees.

11. The coated cutting tool according to claim 10, wherein 5% to 20% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of 2-5 degrees, and at least 5% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of greater than 5 degrees and less than or equal to 15 degrees.

12. The coated cutting tool according to claim 11, wherein 16%-20% of all grain boundaries in the polycrystalline α-Al2O3 layer have a misorientation of 2-5 degrees.

13. The coated cutting tool according to claim 1, wherein the polycrystalline α-Al2O3 layer has a thickness of 1-20 μm.

14. The coated cutting tool according to claim 1, wherein the polycrystalline α-Al2O3 layer has a residual stress of 20-400 MPa.

15. The coated cutting tool according to claim 1, wherein the coating further comprises one or more inner layers between the polycrystalline α-Al2O3 layer and the substrate.

16. The coated cutting tool according to claim 15, wherein the one or more inner layers comprise one or more metal elements selected from the group consisting of aluminum and metal elements of groups IVB, VB, and VIB in the periodic table, and one or more non-metal elements selected from the group consisting of non-metal elements of groups IIIA, IVA, VA, and VIA in the periodic table.

17. The coated cutting tool according to claim 1, wherein the substrate comprises cemented carbide, and the cemented carbide comprises 1-15 weight percent of a metal binder.

18. A method, the method comprising: Depositing a polycrystalline α-Al2O3 layer from a gaseous reaction mixture comprising H2, CO, CO2, H2S, HCl, AlCl3, wherein the volume ratio of CO2 to H2S in the CVD reaction chamber is in the range of 5 < CO2 / H2S < 10, and the deposited polycrystalline α-Al2O3 layer has a length of Σ3-type grain boundaries as measured by EBSD, the length being greater than 0% but less than 10% of the total length of all grain boundaries, and having a texture coefficient (TC) greater than 6 for the (006) growth direction and a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, the texture coefficient being defined as: Where I(hkl) = the measured intensity of the (hkl) reflection I o (hkl) = Standard intensity of reflection as described in International Data Center for Diffraction (ICDD) Card 43-1484. n = the number of reflections used in the TC calculation The (hkl) reflections used in the TC calculation are: (012), (104), (110), (006), (113), (202), (024), and (116) for calculating TC(006); or (012), (104), (110), (113), (116), (300), and (0 0 12) for calculating TC(0012).

19. The method according to claim 18, wherein the length of the Σ3-type grain boundaries is 1% to 8% of the total length of all grain boundaries.

20. The method according to claim 18, wherein the polycrystalline α-Al2O3 layer comprises columnar grains having an average width of 0.1 μm to 3 μm.

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