Cutting tool with multi-layer coating

Abstract

In one aspect, described herein is a cutting tool comprising a wear resistant coating that employs a multi-layer structure in combination with a highly textured aluminum oxide layer for resisting various degradation mechanisms, including cracking and / or spalling.

Description

Cutting tools with multi-layer coating Technical Field

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

[0002] Cutting tools, including cemented carbide cutting tools, have been used to machine a wide variety of metals and alloys, both coated and uncoated. To increase 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 effectively suppressing wear and extending tool life in various applications, single-layer or multi-layer refractory coatings based on the aforementioned refractory materials are increasingly reaching 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, the wear-resistant coating employing a multilayer structure combined with a highly textured alumina layer. In some embodiments, the coated cutting tool comprises a substrate and a coating deposited on the substrate by chemical vapor deposition (CVD), the coating comprising an α-Al₂O₃ layer terminating above the α-Al₂O₃ layer in a multilayer structure comprising a base of a metal nitride, a metal carbonitride, a metal oxycarbonitride, or a combination thereof. An outer layer of metal oxide or metal oxynitride is positioned above the base, wherein the base has a thickness of 0.1 μm or less, and the α-Al₂O₃ layer has a texture coefficient of at least 7.0 with respect to the (006) growth direction, the texture coefficient being defined as:

[0004]

[0005] in

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

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

[0008] The number of reflections used in the n=TC calculation (8)

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

[0010] (012), (104), (110), (006), (113), (202), (024) and (116).

[0011] In some embodiments, the outer layer has a thickness of 0.2 μm to 3 μm. Furthermore, the metal oxide or metal oxynitride of the outer layer may comprise one or more metals selected from the group consisting of aluminum and elements in Groups IV-VI of the periodic table. In some embodiments, the substrate comprises titanium nitride, titanium carbonitride, titanium oxycarbonitride, or a combination thereof.

[0012] These and other embodiments are further described in the following detailed description. Attached Figure Description

[0013] Figure 1 shows a schematic cross-section of a coated cutting tool according to some embodiments described herein. Detailed Implementation

[0014] The embodiments described herein can be more readily understood by referring to the following detailed description and examples, as well as the descriptions preceding and following them. 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 adaptations will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

[0015] In one aspect, this document describes a cutting tool incorporating a wear-resistant coating, which employs a multilayer structure combined with a highly textured alumina layer to resist various degradation mechanisms, including cracking and / or flaking. Therefore, cutting tools with such refractory coatings are suitable for high-wear and / or abrasion applications, such as metal cutting operations. Figure 1 shows a schematic cross-section of a coated cutting tool according to some embodiments described herein. As shown in Figure 1, the coated cutting tool includes a substrate 10 and a CVD coating 14 adhered to the substrate 10. The coating 15 includes an α-Al₂O₃ layer 12 terminating in a multilayer structure 13 above the α-Al₂O₃ layer 12. The multilayer structure 13 includes a substrate 13b of a metal nitride, metal carbonitride, metal oxycarbonitride, or a combination thereof. An outer layer 13a of a metal oxide or metal oxynitride is located above the substrate layer, wherein the substrate has a thickness of 0.1 μm or less. An intermediate layer 11, as described herein, is located between the α-Al₂O₃ layer 12 and the substrate 10. In some embodiments, the outermost layer (not shown) may be deposited on the outer layer 13a.

[0016] Turning now to specific components, the coated article includes a substrate. The coated article may include any substrate not consistent with the purposes of this invention. For example, the substrate may be a cutting tool or tool for abrasive applications. Cutting tools include, but are not limited to, cutting inserts (indexable and non-indexable), end mills, drills, and other circular tools. Indexable cutting inserts may have any desired ANSI standard geometry for milling or turning applications. The substrate of the coated article described herein may be formed of 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 substrate in an amount of at least about 80% by weight or at least about 85% by weight. Additionally, the cemented carbide metal binder may comprise 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 may be present in the cemented carbide substrate in an amount ranging from 5-12% by weight or 6-10% by weight. Furthermore, the cemented carbide substrate may exhibit a binder-rich region that begins at and extends inward from the substrate surface.

[0017] 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 with the WC of the substrate. In such embodiments, the substrate may contain one or more solid solution carbides in an amount ranging from 0.1 to 7 weight percent. Additionally, the cemented carbide substrate may contain nitrogen.

[0018] As described above, the CVD coating adhered to the substrate comprises an α-Al₂O₃ layer, which terminates in a multilayer structure above the α-Al₂O₃ layer. The α-Al₂O₃ layer has a texture factor of at least 7.0 for the (006) growth direction, where the texture factor is defined as:

[0019]

[0020] in

[0021] I(hkl) = (hkl) (Measured intensity of reflection)

[0022] I o (hkl) = Standard intensity of (hkl) reflection according to International Data Center for Diffraction (ICDD) Card 43-1484.

[0023] The number of reflections used in the n=TC calculation (8)

[0024] The (hkl) reflection used in TC calculations is:

[0025] (012), (104), (110), (006), (113), (202), (024) and (116).

[0026] In some embodiments, the texture coefficient of the α-Al2O3 layer for the (006) growth direction is 7.5-7.9 or 7.6-7.9.

[0027] The XRD peak data used to calculate the texture coefficient (TC) of the α-Al2O3 layer were measured on the top rake face of such a coated cutting tool (e.g., a cutting insert) using a Bragg focusing diffractometer.

[0028] Incident optical devices include:

[0029] The long fine-focusing X-ray tube operates at 45 kV and 40 MA.

[0030] The variable divergence optics operate in automatic mode to ensure a constant sample volume of illumination throughout the analysis.

[0031] Fixed anti-scattering slit

[0032] The receiving optical components include:

[0033] The variable anti-scattering slit operates in automatic mode to match the automatic diverging slit.

[0034] Multiple solid-state detectors operating in scanning mode.

[0035] Choose scan parameters (speed and counting time) to ensure a minimum of 10 data steps across the full width at half maximum (FWHM) and approximately 10,000 total counts on the strongest peak. First, convert the collected data from a variable mode to a fixed mode suitable for analysis. This conversion is performed using the following formula:

[0036]

[0037] Where a = divergence angle, L = irradiation length on the sample.

[0038] Peak intensity correction was analyzed using peak discovery software to identify the peak positions of all peaks in the collected data. The peaks were then refined using a profile function to accurately identify peak positions 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.

[0039] In some embodiments, the grains of the polycrystalline α-Al₂O₃ layer may exhibit a columnar morphology, with their long axis normal to or substantially normal 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 20 consecutive grains of the polycrystalline α-Al₂O₃ layer measured using band contrast EBSD imaging on a polished cross-section of the polycrystalline α-Al₂O₃ layer. The alumina grain width is determined by using the caliper function on the EBSD band contrast map in the data acquisition software. Measurements are taken from approximately 20 adjacent grains at the center of the coating. The measurements from the caliper function are based on the SEM magnification and internal calibration in the software.

[0040] The α-Al₂O₃ layer may have any desired thickness consistent with the technical objectives described herein. In some embodiments, the α-Al₂O₃ layer has a thickness of 2 μm to 20 μm, 2 μm to 6 μm, or 4 μm to 10 μm.

[0041] Furthermore, the α-Al₂O₃ layer 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 α-Al₂O₃ layer can be measured using Chi tilt Sin. 2 The ψ method is determined by reflection (116). For alumina phase analysis, Poisson's ratio ( The modulus of elasticity (E in GPa) was set to 0.19, and the elastic modulus was determined to be 415 by analyzing the nanoindentation hardness of the single-phase α-alumina coating.

[0042] The α-Al₂O₃ layer can be deposited directly on the substrate surface. Alternatively, the coating described herein may further comprise one or more inner layers between the 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 from groups IVB, VB, and VIB of the periodic table, and one or more nonmetallic elements selected from 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, oxycarbonitrides, oxides, or borides of one or more metallic elements selected from the group consisting of aluminum and metals from groups IVB, VB, and VIB of the periodic table.

[0043] For example, one or more inner layers are selected from titanium nitride, titanium carbonitride, titanium carbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, hafnium nitride, hafnium carbonitride, TiAl x Si y C v The group consists of nitrogen and aluminum oxynitride. Furthermore, a titanium carbonitride layer can be used as a bonding layer between the α-Al₂O₃ layer and the inner layers of the coating. One or more inner layers of the coating can have any thickness that is not inconsistent with the purpose of the invention. In some embodiments, a single inner layer may have a thickness of at least 1.5 μm. Alternatively, multiple inner layers may collectively achieve a thickness of at least 1.5 μm.

[0044] The α-Al₂O₃ layer terminates in a multilayer structure comprising a substrate of metal nitride, metal carbonitride, metal oxycarbonitride, or a combination thereof, and an outer layer of metal oxide or metal oxynitride over the substrate, wherein the substrate has a thickness of 0.1 μm or less. In some embodiments, the substrate has a thickness selected from those in Table 1.

[0045] Table 1 – Substrate Thickness (μm)

[0046]

[0047] In alternative embodiments, the substrate may have a thickness greater than 0.1 μm, including 0.2 μm to 2 μm.

[0048] The nitride, carbonitride, and / or oxycarbonitride of the substrate may comprise one or more metals selected from Groups IV-VI of the periodic table. For example, in some embodiments, the substrate layer is titanium nitride, titanium carbonitride, or titanium oxycarbonitride. In other embodiments, the substrate may comprise zirconium or chromium nitride, carbonitride, and / or oxycarbonitride. The substrate may be a single layer having the thickness described herein, or the substrate may be multiple layers. In some embodiments, the multiple layers may have different compositions. When multiple layers are present, the thickness of each layer is such that the sum of the thicknesses of the multiple layers produces the thickness value of the substrate described herein, such as the values ​​listed in Table 1.

[0049] The multilayer structure terminating the grain growth of the α-Al₂O₃ layer also includes an outer layer of metal oxide or metal oxynitride on a substrate layer. In some embodiments, the metal oxide or metal oxynitride comprises one or more metals selected from the group consisting of aluminum and elements from Groups IV-VI of the periodic table. For example, the metal may be aluminum used to produce alumina, AlON, or mixtures thereof in the outer layer. In some embodiments, where Al₂O₃ is present in the outer layer, the Al₂O₃ may be α-Al₂O₃, κ-Al₂O₃, or mixtures thereof. In other embodiments, the outer layer may comprise zirconium oxide (ZrO₂). Additionally, in some embodiments, the metal oxide and / or metal oxynitride of the outer layer is doped with a metal selected from Groups IV-VI of the periodic table. For example, the outer layer of the multilayer structure may comprise alumina doped with zirconium. In some embodiments, the metal dopant may be dispersed throughout the oxide or oxide-oxygen layer. Alternatively, the metal dopant may be located at grain boundaries within the oxide or oxide-oxygen layer. In another embodiment, the outer metal oxide or metal oxynitride layer may comprise a dispersed metal oxide phase comprising one or more metals selected from Groups IV-VI of the periodic table. The outer layer of metal oxide or metal oxynitride may have any desired thickness consistent with the technical objectives described herein. In some embodiments, the outer layer has a thickness of 0.05 μm to 3 μm.

[0050] In some embodiments, the coating described herein further comprises an outermost layer disposed on the outer layer of a multilayer structure. The outermost layer may comprise a nitride, carbonitride, and / or oxynitride of one or more metals selected from Groups IV-VI of the periodic table. The outermost layer may be a single layer or multiple layers. In some embodiments, for example, the outermost layer comprises one or more of TiN, TiCN, TiOCN, or ZrCN. In some embodiments, the outermost layer may have a thickness of 0.2 μm to 3 μm.

[0051] The coatings described herein can be post-coated. For example, the coating can be sandblasted 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 blasting or pressure blasting. Pressure blasting can be applied in various forms, including compressed air blasting, wet compressed air blasting, pressurized liquid blasting, wet blasting, and steam blasting. For example, wet blasting can be performed using a slurry of inorganic and / or ceramic particles (e.g., 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 size of the inorganic and / or ceramic particles is typically in the range of about 20 μm to about 100 μm.

[0052] In some embodiments, a post-coating process can be used to remove the multilayer structure and any outermost layer to expose the underlying α-Al₂O₃ layer. The removal of the multilayer structure and any outermost layer can be performed on either the rake face or the flank face of the cutting tool. In some embodiments, this removal is performed on both the rake face and the flank face. Removal of the multilayer structure can impart compressive residual stress conditions to the underlying α-Al₂O₃ layer. In some embodiments, the multilayer structure is removed on the rake face of the cutting tool to impart compressive residual stress conditions to the underlying α-Al₂O₃ layer. In some embodiments, the compressive stress conditions can range from -100 MPa to -500 MPa. The multilayer structure is not removed from adjacent rake faces, thereby causing the underlying α-Al₂O₃ layer to exhibit a tensile residual stress state, as described above.

[0053] These and other embodiments are further illustrated in the following non-limiting examples.

[0054] Example 1 – Coated Cutting Tools

[0055] Sintered carbide cutting inserts of CNMG432RN with the geometry having the composition shown in Table 2 are provided.

[0056] Table 2 - Composition of Sintered Hard Alloy Substrates

[0057]

[0058] The sintered carbide cutting insert is provided with a multilayer CVD coating having the composition and structure provided in Table 3.

[0059] Table 3 – CVD Coating Structure

[0060]

[0061] Layers adjacent to the substrate

[0062] The coating was deposited in a Bernex CVD furnace, commercially available from Ionbond IHI Group. The coating was deposited according to the parameters in Tables 4 and 5.

[0063] Table 4 – Deposition of intermediate layer and highly textured α-Al2O3

[0064]

[0065] Table 5 - Deposition of multilayer structures

[0066]

[0067] Two of the coated inserts of the present invention were subjected to metal cutting tests relative to a KCP25C comparison insert of the same geometry, which is commercially available from Kennametal Inc. Both coated inserts of the present invention exhibited a texture factor exceeding 7.5 in the (006) growth direction of the α-Al2O3 layer.

[0068] The parameters used for the turning test of flank wear are:

[0069] Workpiece: 4340 steel

[0070] Speed: 675 sfm

[0071] Feed rate: 0.12 ipr

[0072] Depth of cut: 0.1 doc

[0073] Coolant: Overflow

[0074] The parameters for the turning test of pitted wear are:

[0075] Workpiece: 1045 steel

[0076] Speed: 1200 sfm

[0077] Feed rate: 0.12 ipr

[0078] Depth of cut: 0.08 doc

[0079] Coolant: Overflow

[0080] Table 6 provides the results of the continuous turning test.

[0081] Table 6 – Metal Cutting Results

[0082]

[0083] As shown in Table 6, the cutting inserts containing the coating of the present invention described herein exhibit significantly longer tool life compared to Comparative Example KCP25C.

[0084] Example 2 – Coated Cutting Tools

[0085] A multilayer CVD coating with the composition and structure provided in Table 7 is applied to the sintered carbide cutting insert of Example 1.

[0086] Table 7 – CVD Coating Structure

[0087]

[0088] Layers adjacent to the substrate

[0089] Deposit coatings in a Bernex CVD furnace according to the parameters in Table 4 of Example 1 and Table 8 below.

[0090] Table 8 - Deposition of multilayer structures

[0091]

[0092] Two of the coated patches of the present invention were subjected to metal-cutting tests relative to a KCP25C comparison patch of the same geometry, which is commercially available from Kennametal Inc. Both coated patches of the present invention exhibited a texture factor exceeding 7.5 for the (006) growth direction of the α-Al2O3 layer. The parameters for the metal-cutting tests were the same as in Example 1.

[0093] Table 9 provides the results of the continuous turning test.

[0094] Table 9 – Metal Cutting Results

[0095]

[0096] As shown in Table 9, the cutting inserts containing the coating of the present invention described herein exhibit significantly longer tool life compared to Comparative Example KCP25C.

[0097] Example 3 – Coated Cutting Tools

[0098] A multilayer CVD coating with the composition and structure provided in Table 10 is applied to the sintered carbide cutting insert of Example 1.

[0099] Table 10 – CVD Coating Structure

[0100]

[0101] Layers adjacent to the substrate

[0102] Deposit coatings in a Bernex CVD furnace according to the parameters in Table 4 of Example 1 and Table 11 below.

[0103] Table 11 - Deposition of multilayer structures

[0104]

[0105] Metal cutting tests were performed on two of the coated patches, relative to KCP25C patches of the same geometry available commercially from Kennametal Inc. Both coated patches exhibited texture coefficients exceeding 7.5 for the (006) growth direction of the α-Al₂O₃ layer. The parameters for the metal cutting tests were the same as in Example 1.

[0106] Table 12 provides the results of the continuous turning test.

[0107] Table 12 – Metal Cutting Results

[0108]

[0109] As shown in Table 11, the cutting inserts containing the coating of the present invention described herein exhibit significantly longer tool life compared to Comparative Example KCP25C.

[0110] Various embodiments of the invention have been described to achieve its various objectives. 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 comprising: a substrate; and a coating deposited on the substrate by chemical vapor deposition (CVD), the coating comprising an α-Al₂O₃ layer terminating at a multilayer structure above the α-Al₂O₃ layer, the multilayer structure comprising a substrate of a metal nitride, a metal carbonitride, a metal oxycarbonitride, or a combination thereof, and an outer layer of a metal oxide or metal oxynitride on the substrate layer, wherein the substrate has a thickness of 0.1 μm or less, and the α-Al₂O₃ layer has a texture coefficient of at least 7.0 with respect to a (006) growth direction, the texture coefficient being defined as: Where I(hkl) = (hkl) is the measured intensity of the reflected light. o (hkl) = According to the International Data Center for Diffraction (ICDD) Card 43-1484, the standard intensity of (hkl) reflection n = the number of reflections used in the TC calculation (8) The (hkl) reflections used in the TC calculation are: (012), (104), (110), (006), (113), (202), (024) and (116).

2. The coated cutting tool according to claim 1, wherein the texture coefficient is 7.6 to 7.

9.

3. The coated cutting tool according to claim 1, wherein the outer layer has a thickness of 0.2 μm to 3 μm.

4. The coated cutting tool according to claim 1, wherein the metal oxide or metal oxynitride comprises one or more metals selected from the group consisting of aluminum and groups IV-VI of the periodic table.

5. The coated cutting tool according to claim 1, wherein the metal oxide or metal oxynitride is doped with a metal selected from Groups IV-VI of the periodic table.

6. The coated cutting tool according to claim 5, wherein the metal oxide is Al2O3.

7. The coated cutting tool according to claim 4, wherein the outer layer comprises Al2O3, AlON, or a mixture thereof.

8. The coated cutting tool according to claim 4, wherein the outer layer comprises ZrO2.

9. The coated cutting tool according to claim 1, wherein the substrate thickness is 0.005 μm to 0.05 μm.

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

11. The coated cutting tool according to claim 1, wherein the α-Al2O3 layer comprises columnar grains terminating in the substrate.

12. The coated cutting tool of claim 1, wherein the multilayer structure further comprises an outermost layer above the outer layer.

13. The coated cutting tool according to claim 12, wherein the outermost layer comprises at least one of a metal carbide, a metal nitride, a metal carbonitride, and a metal oxycarbonitride.

14. The coated cutting tool according to claim 13, wherein the metal of the outermost layer of metal carbide, metal nitride, metal carbonitride, or metal oxycarbonitride is selected from groups IV-VI of the periodic table.

15. The coated cutting tool according to claim 13, wherein the outermost layer comprises TiCN and TiN.

16. The coated cutting tool according to claim 14, wherein the outermost metal is chromium.

17. The coated cutting tool of claim 1, wherein the substrate comprises TiN, TiCN, TiOCN, or a combination thereof.

18. The coating cutting according to claim 6, wherein the metal dopant is zirconium.

19. The coated cutting tool according to claim 1, wherein the α-Al2O3 layer has a thickness of 2 μm to 20 μm.

20. The coated cutting tool of claim 1, wherein the substrate comprises cemented carbide.

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