Multi-layer structured coatings for cutting tools

Abstract

Coated cutting tool which features the following: a substrate; and a coating which has a multitude of alternating layers, comprising a first layer of Al2O3 and a second layer of MeAl2O3 / MeO2 composite material; where Me represents Ti, Zr, Hf or a combination thereof, and where intercrystalline MeO2 deposits are distributed along grain boundaries.

Description

AREA OF INVENTION

[0001] The present invention relates to coatings for cutting tools and in particular to coatings deposited by chemical vapor deposition (CVD). BACKGROUND

[0002] Cutting tools, including carbide cutting tools, are used in both coated and uncoated states for machining various metals and alloys. To increase the wear resistance, performance, and service life of cutting tools, one or more layers of refractory material have been deposited onto their surfaces. For example, TiC, TiCN, TiN, and / or Al₂O₃ have been deposited onto carbide substrates by CVD and physical vapor deposition (PVD). While refractory coatings based on single- or multi-layer structures of these materials are effective in a wide variety of applications for wear reduction and tool life extension, they naturally have performance limitations, necessitating the development of new coatings with improved properties.

[0003] DE 38 52 321 T2 and DE 38 53 545 T3 each relate to a hard ceramic or sintered carbide substrate body with a completely dense, adhesive, wear-resistant, multilayer oxide layer with a thickness of 0.3 to 20 µm, which is deposited on the substrate. The layer has at least three superimposed, adhesive oxide layers, each approximately 0.1 to 3 µm thick, and consisting of materials independently selected from the oxides of aluminum, zirconium, and yttrium. Each layer consists predominantly of a different material than the adjacent layers, with at least one layer containing discrete particles of at least one material that predominates in an adjacent layer. Furthermore, a coating scheme with alternating Al₂O₃ / ZrO₂ layers is described.

[0004] US Patent 7,531,213 B2 discloses a coating scheme that includes an Al₂O₃ layer or an (Al₂O₃ + ZrO₂) multilayer layer. However, Example 1 shows only a simple alpha-aluminum oxide layer. The structure of the (Al₂O₃ + ZrO₂) multilayer layer is not explained in detail.

[0005] German patent applications DE 27 18 647 A1 and DE 27 36 982 A1 describe mixed layers of aluminum oxide and titanium oxide, and aluminum oxide and zirconium oxide, respectively. WO 2014 / 153 469 A1 relates to a coating scheme with a ZrAl₂O₃ layer exhibiting a zirconium gradient within the grains. Due to a certain degree of segregation of zirconium atoms into the grain boundary regions, improved bonding between the grains is expected. SUMMARY

[0006] From one perspective, the cutting tools are described as having coatings adhered to them, which in some embodiments can exhibit desirable wear resistance and increased cutting tool life. A cutting tool described here has a substrate and a coating comprising a plurality of alternating layers with a first layer of Al₂O₃ and a second layer of MeAl₂O₃ / MeO₂ composite material, where Me represents Zr, Hf, or Ti, or a combination thereof, and wherein intergranular MeO₂ deposits are distributed along grain boundaries.

[0007] A method for producing a coated cutting tool as described herein comprises providing a cutting tool substrate and depositing a coating onto a surface of the cutting tool substrate by CVD, wherein the coating has a plurality of alternating layers with a first layer of Al₂O₃ and a second layer of MeAl₂O₃ / MeO₂ composite material, where Me represents Zr, Hf, or Ti, or a combination thereof. The plurality of alternating layers can begin with the first or second layer closest to the substrate.

[0008] These and other embodiments are described in more detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 represents a coated cutting tool according to an embodiment described herein. Fig.Figure 2 is a scanning electron microscope (SEM) cross-sectional image of a coated cutting insert according to an embodiment described herein. Fig. Figure 3 is an enlarged radiotransmission electron microscope (RTEM) brightfield (HF) image of a coated cutting insert according to an embodiment described herein. Fig. Figure 4 is the enlarged RTEM-HF cross-sectional image of a coated cutting insert according to an embodiment described herein. Fig. 3. Fig. Figure 5 is an enlarged RTEM high-angle annular dark-field (HAADF) cross-sectional image of a coated cutting insert according to an embodiment described herein. Fig. Figure 6 is an enlarged RTEM-HAADF cross-sectional image of a coated cutting tool treated with a focused ion beam according to an embodiment described herein. Fig.Figure 7 is a schematic representation of various doping processes according to the embodiments described here. DETAILED DESCRIPTION

[0009] The embodiments described herein are more easily understood with reference to the following detailed description and examples, and their preceding and subsequent descriptions. However, the elements, devices, and methods described herein are not limited to the specific embodiments presented in the detailed description and examples. It is understood that these embodiments merely illustrate the principles of the present invention. Numerous modifications and adaptations are readily apparent to those skilled in the art without departing from the spirit and scope of the invention. I. Coated cutting tools

[0010] In one aspect, cutting tools are described as having coatings which, in some embodiments, offer desirable wear resistance and an increased cutting service life. With regard to Fig. 1. A coated cutting tool 10 described herein can have a cutting edge 12, a rake face 14, a clearance face 16, and a mounting hole 18. The insert 10 can have a variety of geometries and configurations, e.g., with or without a chip breaker, mounting hole, or positive or negative rake angle.

[0011] With reference to Fig.Figure 2 provides for an embodiment described herein comprising a cutting insert 20. The cutting insert 20 has a substrate 22 and a coating adhering to the substrate 22; the coating has a multilayer structure comprising an optional inner layer 24 and an optional bonding layer between the inner layer 24, a superlattice-like coating 26, and the outermost coating layer 28. The superlattice-like coating has repeating coating layers designated A and B, where A and B denote a periodicity of sequences of dopant-containing Al₂O₃ (B) and undoped Al₂O₃ (A). Alternatively, the periodicity can include dopant-containing Al₂O₃ (B) and lightly doped Al₂O₃ (A). Dopants can include Ti, Zr, Hf, or a combination thereof.The alternating doped and undoped layers, or layers with different doping levels, can cause the formation of superlattice-like coating structures.

[0012] In one embodiment of this invention, the cutting insert 20 comprises a substrate 22. Substrates of the coated cutting tools can comprise any material that does not contradict the objectives of the present invention. In some embodiments, a substrate comprises cemented carbide, PCD, PCB, ceramic, cermet, or steel.

[0013] A cemented carbide substrate may contain tungsten carbide (WC). WC may be present in a substrate at a proportion of at least approximately 70 wt.%. In some embodiments, WC is present in a substrate at a proportion of at least approximately 80 wt.% or at least approximately 85 wt.%. Furthermore, a cemented carbide substrate may contain cobalt or a cobalt alloy as a metallic binder. Cobalt, for example, may be present in a cemented carbide substrate at a proportion of approximately 3 wt.% to approximately 15 wt.%. In some embodiments, cobalt is present in a cemented carbide substrate at a proportion of approximately 5–12 wt.% to approximately 6–10 wt.%. A cemented carbide substrate may also have a binder enrichment zone that begins at the substrate surface and extends inwards.

[0014] Hard metal substrates may also contain one or more additives, such as one or more of the following elements and / or their compounds: titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium. In some embodiments, titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium form solid solution carbides with the WC in the substrate. In some embodiments, the substrate may contain one or more solid solution carbides in a proportion of approximately 0.1 wt.% to approximately 5 wt.%. Furthermore, a hard metal substrate may contain nitrogen.

[0015] In some embodiments, the substrate of a coated cutting tool described herein has one or more cutting edges formed at the interface between the rake face and the clearance faces of the substrate. In some embodiments, the substrate of a coated cutting tool is a drill, a milling cutter, a saw blade, or another cutting device.

[0016] A coating adhering to the substrate can have a bonding layer between the inner layer 24 and the superlattice-like layer 26. This bonding layer contains TiCN and TiAlOC. In some embodiments, the bonding layer also contains TiOCN. TiCN, TiAlOC, and TiOCN can be provided as sublayers of the bonding layer. Furthermore, a bonding layer of a structural unit typically has a thickness of less than 5 µm. In some embodiments, the bonding layer has a thickness that is taken from Table I. Table I - Thickness of the bonding layer Bonding layer thickness (nm) 10-950 5-500 5-200 10-100

[0017] When one or more sublayers of TiCN, TiAlOC, and / or TiOCN form a bonding layer, each sublayer can have a thickness of 5–500 nm. In some other embodiments, a diffusion barrier layer comprising nitrite, TiN, ZrN, and HfN, and / or a combination thereof, can adhere directly to the substrate. The thickness of the diffusion barrier can be less than 2 µm.

[0018] Furthermore, a coating described herein can have one or more outer layers over the structural units. In some embodiments, an outer layer comprises 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, one or more outer layers deposited over the structural units comprise a nitride, carbonitride, 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, one or more outer layers are selected from the group consisting of TiN, TiCN, and TiOCN.The outer layers of the coatings described herein can have any thickness that does not contradict the objectives of the present invention. In some embodiments, an outer layer of a coating can have a thickness in the range of 0.5 µm to 5 µm. Taking all components into account, a coating described herein can have a thickness of up to 25 µm. For example, a coating can have a total thickness of 2–15 µm or 5–20 µm.

[0019] Fig.Figure 3 is an RTEM-HF image of a cross-section of a coating 30 according to an embodiment of this invention. The alternating A / B layers 32, 34 are clearly visible in the image. An A layer 32 with darker contrast in the image represents a doped layer, while a B layer 34 with lighter contrast in the image represents a layer with less or no doping. Alternating dark areas 36 and light areas 38 are visible at grain boundaries. The dark areas 36 indicate intergranular ZrO2 deposits. Numerous ZrO2 deposits distributed along the grain boundaries are visible in the image, although in Fig. 3 only the dark area 36 is specifically designated.

[0020] Fig.Figure 4 is also an RTEM-HF (bright-field) image of a cross-section of a coating 40 according to an embodiment of this invention. The alternating A / B layers 42, 44 are clearly visible in the image. An A layer 42 represents a layer with less or no doping, while a B layer represents a doped layer. Alternating dark areas 46 and light areas 48 are visible at grain boundaries. The dark areas 46 indicate intergranular ZrO2 deposits.

[0021] Fig. Figure 5 is an RTEM HAADF (High Angle Annular Dark Field) image of a cross-section of a coating 50. Dark layers 52 in the HAADF image indicate a lack of doping. Lighter layers 54 indicate higher doping levels. The light areas 56 indicate intercrystalline ZrO2 deposits. Fig. Figures 3-5 show a distinct angular stripe pattern that is present within the individual coating grain size.

[0022] In one embodiment, the present invention comprises a coating scheme with alternating doped and undoped aluminum oxide layers, or with different doping levels of high and low levels, or with differently doped layers exhibiting multiple periodicities. It is obvious to those skilled in the art that the periodicity relates to high and low doping levels with Zr, Hf, or Ti, and that the layers with the lower doping level may contain a smaller amount of dopant than the higher-level doping levels, or even no dopant at all. The terms "low-doped layer" and "high-doped layer" used herein refer to the alternating aluminum oxide-containing layers, in which the high-doped layer contains more dopant than the low-doped layer, and in which the low-doped layer contains less dopant than the high-doped layer, or even no dopant at all.The coating scheme features CVD coating layers with alternating highly doped and low-doped layers of predetermined thickness and / or grain size. The alternating highly and low-doped layers, combined with nanoscale layer thicknesses, give rise to superlattice-like structures. The layer thickness and / or grain size of the multilayer coating scheme can be adjusted in the range of 0.5–20 µm by modifying the process duration and source conditions for the dopants and aluminum oxides for the different coating layers. The individual thicknesses of the highly and low-doped layers can each be in the range of 0.05–0.2 µm. Different phases of alpha and kappa aluminum oxides can be introduced into the coating scheme via alternating bonding and interlayer structures.The coating procedure offers a good opportunity to control the doping stage through well-designed dopant introduction. The aluminum oxide dopants can be ZrCl4, HfCl4, or TiCl4, generated by the reaction of HCl gas with metal species of Ti, Zr, or Hf mixtures at 360–450 °C. These innovative coating procedures also provide a good opportunity to modify the coating structure. The doped particle size can be controlled, particularly with zirconium-doped aluminum oxide (ZrAl2O3) with ZrO2 formation in the coating system. This is due to the competition and selectivity between Al2O3, ZrO2, doped aluminum oxide (ZrAl2O3), and the ZrO2 formation of the second phase.

[0023] Fig.Figure 6 is a cross-section of a coating example 60 according to an embodiment of this invention. The sample was prepared by treatment with a focused ion beam. Positions 62, 64, and 66 were analyzed using energy-dispersive X-ray spectroscopy (EDS) in an RTEM. Table II contains the quantitative data obtained from the EDS spectra for each of positions 62, 64, and 66. Table II Quantitative EDS of a coating sample 60 position element % by weight At.-% 62 O 39,92 58,67 Al 42,1 36,69 Zr 17,96 4,63 64 O 39,76 52,98 Al 59,19 46,76 Zr 1,03 0,24 66 O 46,24 59,20 Al 53,75 40,79 Zr 0,00 0,00

[0024] Position 62 is a composite section of the coating that exhibits high Zr content (17.96 wt%) due to the formation of a ZrO₂ intragrain. Position 64 is located within a doped layer of coating pattern 60. Position 64 contains 1.03 wt% Zr and 59.19 wt% Al. Position 66 is located within an undoped layer of coating pattern 60. Position 66 contains no Zr and 53.75 wt% Al.

[0025] A thin top TiCN / TiN layer can be deposited as a wear indicator and for aesthetic purposes. This top TiCN / TiN layer can also act as a sacrificial layer for wet or dry blasting after coating, thus altering the stress distribution within the coating layers. Other outer layer systems, such as ZrCN, HfCN, and TiOCN, can also be used in the coating scheme.

[0026] The layer thickness of the coating scheme can be adjusted in the range of 0.05-20 µm by adjusting the process duration provided for the different coating layers and the dopant and aluminium oxide source conditions accordingly.

[0027] The coatings of the cutting tools described herein can be subjected to post-treatment. For example, coatings can be blasted with various wet and / or dry particle compositions. Post-treatment blasting can be performed in any desired manner. In some embodiments, the blasting treatment includes shot peening or pressure blasting. Pressure blasting can be performed in a variety of ways, including compressed air blasting, wet compressed air blasting, hydraulic jet blasting, wet blasting, hydraulic jet blasting, and steam blasting. Wet blasting, for example, is performed using a slurry of inorganic and / or ceramic particles, such as alumina and water. The slurry containing aluminum oxide particles can be pneumatically applied to a surface of the body of the coated cutting tool to impact the coating surface.The alumina particles can generally range in size from about 20 µm to about 100 µm.

[0028] Blasting parameters include pressure, impact angle, distance to the surface, and duration. In some embodiments, the impact angle can range from approximately 5° to approximately 90°, meaning the particles strike the coating surface at an angle within this range. Suitable pressures can range from 0.21 to 0.38 megapascals (MPa) (30 to 55 pounds per square inch (psi)) at a distance of 2.5 to 15 centimeters (1 to 6 inches) from the coated surface. Furthermore, the blasting duration can generally range from 1 to 10 seconds or longer. Blasting can generally be performed over the surface area of ​​the coating or can be targeted at selected locations, such as a workpiece contact area of ​​the cutting tool. A workpiece contact area could be a honed area of ​​the cutting tool.

[0029] In other embodiments, a coating is subjected to a subsequent polishing treatment. Polishing can be performed with a paste of suitable diamond or ceramic abrasive grain size. The grain size of the paste is in the range of 1 µm to 10 µm in some embodiments. In one embodiment, a diamond abrasive grain paste of 5-10 µm is used for polishing the coating. Furthermore, the polishing paste can be applied to the CVD coating by means of any device that does not contradict the objectives of this invention, such as by brushing. In one embodiment, for example, a flat brush is used to apply polishing paste to the CVD coating in a workpiece contact area of ​​the cutting tool.

[0030] A coating described herein can be blasted or polished for a period of time sufficient to achieve a desired surface roughness (Ra) and / or other parameters, such as the removal of residual tensile stress in the coating. In some embodiments, a coating that undergoes subsequent treatment exhibits a surface roughness (R) selected from Table III. a ) on. Table III - Surface roughness (R a ) after treatment Surface roughness (R a ) - nm ≤500 ≤250 <200 10-250 50-175 25-150

[0031] The surface roughness of the coating can be determined via optical profilometry using the WYKO® NT-Series Optical Profilers, commercially available from Veeco Instruments, Inc. of Plainview, New York.

[0032] Furthermore, in some embodiments, a coating post-treatment does not remove one or more outer layers of the coating. For example, in some embodiments, a coating post-treatment does not remove an outer layer of TiN, TiCN, and / or TiOCN. Alternatively, a post-treatment may remove or partially remove one or more outer layers, such as TiN, TiCN, and TiOCN. II. Method for manufacturing coated cutting tools

[0033] Methods for manufacturing coated cutting tools are also provided. One method described here for manufacturing a coated cutting tool involves providing a cutting tool substrate and depositing a CVD coating on a surface of the cutting tool substrate.

[0034] Now, with reference to specific steps, a method described herein includes the provision of a substrate. A substrate can be any substrate listed in the preceding Section I. In some embodiments, for example, a substrate is a hard metal, such as a sintered tungsten carbide listed in the preceding Section I. Furthermore, coatings deposited according to the methods described herein can have any designs and / or properties described in Section I.

[0035] In some embodiments, one or more base layers of the coating are located between the substrate and the aluminum oxide-containing layers. A base layer can comprise 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 of groups IIIA, IVA, VA, and VIA of the periodic table. For example, a base layer can be selected from the group consisting of titanium nitride (TiN), titanium carbonitride (TiCN), and titanium oxycarbonitride (TiOCN). In some embodiments, a multilayer arrangement comprising TiN and TiCN is used. General CVD deposition parameters for various base layers are given in Table IV. Table IV - CVD parameters for base layer deposition Composition of the base layer Gas mixture Temperature (°C) Pressure kPa (Torr) Duration (minutes) TiN H2, N2, TiCl4 800-900 8-40 (60-300) 20-120 TiCN(MT) H2, N2, TiCl4, CH3CN 750-900 4-40 (30-300) 60-300 TiCN(HT)TiOCN H2, N2, TiCl4, CH4H2, N2, TiCl4, CH4, CO 900-1050 4-40 (30-300) 30-200 900-1050 8-67 (60-500) 30-300

[0036] Furthermore, the processes described herein may also include the deposition of one or more outer layers on the aluminum oxide-containing layer. In some embodiments, an outer layer may comprise 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 the group consisting of non-metallic elements of groups IIIA, IVA, VA, and VIA of the periodic table. In one embodiment, for example, an outer layer of TiCN and / or TiOCN is deposited with reference to the CVD parameters given in Table IV. Coatings deposited according to the processes described herein may have an architecture as shown in Table IV above.

[0037] The aluminum oxide-containing layers can be formed under the following exemplary conditions: Temp.: 800–1500 °C; Pressure: 4–67 kPa (30–500 Torr); Gas mixture of AlCl3 + H2 + CO2 + H2S (optional) + HCl (optional) for 3–600 minutes. The doped aluminum oxides can be formed under the following exemplary conditions: Temp.: 800–1500 °C; Pressure: 4–67 kPa (30–500 Torr); Gas mixture of AlCl3 + (TiCl4 or ZrCl4 or HfCl4 or a combination thereof) + H2 + CO2 + H2S (optional) + HCl (optional) for 1–600 minutes and with varying levels of dopant introduction. CVD parameters relating to the aluminum oxide-containing layers are given in Table V. Table V - CVD parameters for base layer deposition Composition of the base layer Gas mixture Temperature (°C) Pressure kPa (Torr) Duration (minutes) Al2O3 AlCl3 + H2 + CO2 + H2S(optional) + HCl (optional) 800-1500 4-67 (30-500) 3-600 MeAl2O3 / MeO2 [(AlCl3 + TiCl4 or ZrCl4 or 800-1500 4-67 (30-500) 1-600 HfCl4) or (combination from this)] + H2 + CO2 + H2S (optional) + HCl (optional)

[0038] In one embodiment of this invention, the doping level is varied by controlling the Al / Me ratio via the HCl gas stream introduced into the metal chloride generators. In another embodiment of this invention, the dopant introduction time is varied during coating deposition. It is also possible to generate a multi-periodic sequence of dopant-containing and undoped aluminum oxide, or of sequences with different doping levels and varying layer thickness ratios. The dopant introduction can be abrupt, intermittent, variable, constant, high, or low. Several embodiments of doping variations are described in Fig. 7 reproduced.

[0039] Furthermore, the deposited coatings can be subjected to post-treatment processes such as subsequent blasting or polishing, as described in Section I above. In some embodiments, subsequent blasting can change a moderate tensile stress of the coating to a moderate compressive stress or increase the compressive stress of the originally deposited coating.

[0040] These and other embodiments are illustrated in the following non-restrictive examples. III. Examples - Coated cutting tool

[0041] A coated cutting tool described here was produced by placing a substrate of a sintered tungsten carbide (WC-Co) cutting insert [ANSI standard geometry CNMG432RN] into an axial-flow hot-wall CVD reactor. The cutting insert contained approximately 6 wt% cobalt binder, with the remaining WC grains ranging in size from 1 µm to 5 µm. A coating with an architecture specified in Table VI was deposited onto the sintered WC cutting insert according to the CVD process parameters given in Tables IV-V. Al₂O₃-ZrAl₂O₃ / ZrO₂ denotes a two-layer system with α-Al₂O₃ and ZrAl₂O₃ / ZrO₂.

[0042] Samples AD featured the two-layer system with α-Al₂O₃ and ZrAl₂O₃-ZrO₂. Sample E was used as a comparison example and had only an outermost layer of α-Al₂O₃. All samples were initially coated with outermost TiCN / TiN layers. These layers were subsequently treated by intensive wet blasting with a slurry containing aluminum oxide particles to remove the TiCN / TiN layers. Table VI - CVD coating architecture Pattern substrate CVD coating architecture n A WC-Co TiN*-TiCN(MT)-TiCN / TiOCN / [Al2O3 / ZrAl2O3-ZrO2] n 1 B WC-Co TiN*-TiCN(MT)-TiCN / TiOCN / [Al2O3 / ZrAl2O3-ZrO2] n 26 C WC-Co TiN*-TiCN(MT)-TiCN / TiOCN / [Al2O3 / ZrAl2O3-ZrO2] n 40 D WC-Co TiN - -TiCN(MT)-TicN / TiOCN / [Al2O3 / ZrAl2O3-Zr02] n 40 E WC-Co TiN*-TiCN(MT)-TiCN(MT)-OCN / Al2O3 - * Innermost layer adjacent to the substrate acts as a diffusion barrier.

[0043] The resulting multilayer coating exhibited the properties specified in Table VII.

[0044] The deposition times were modified to create the different layer thicknesses in AD. Table VII - Properties of CVD coatings A B C D E EXAMPLE (1X) (26X) (40X) (40X) (- ) TiN 0,4 0,4 0,5 0,3 0,5 MT-TiCN 7,9 6,8 8,8 10,0 9,5 HT-TiCN / TiOCN 1,0 0,9 1,0 1,1 0,9 [Al2O3 / ZrAl2O3-ZrO2] n 7,2 8,8 8,1 10,9 7,7 In total 16,2 16,9 18,3 22,3 18,5 Zr / Al ratio* 0,625 0,442 0,625 0,442 - ZrAl2O3 (µm) 7,2 0,17 0,08 0,10 - IV. Metal cutting test

[0045] The coated cutting inserts (AD) and the reference coating insert (E) were subjected to a continuous turning test according to the parameters specified below. Two repetitions were performed to provide an average tool life. Workpiece - 1045 steel (C 45 DIN) Speed ​​- 1000 sfm Feed rate - 304.8 m / min Cutting depth - 0.08 mm Incline angle: -5°

[0046] The lifespan was determined by one or more failure modes of the following factors: Uniform wear (UW) of 0.03 cm (0.012") Maximum wear (MW) of 0.03 cm (0.012") Nose wear (NW) of 0.03 cm (0.012") Depth of cut notch wear (DOCN) of 0.03 cm (0.012") Trailing edge wear (TW) of 0.03 mm (0.012")

[0047] Three cutting inserts were tested for each coating architecture (1-4), providing data for replicates 1-3 and an average cutting life. The results of the continuous turning test are shown in Table VIII. Table VIII - Results of the continuous rotation test Coated cutting insert Repetition 1 Lifespan (minutes) Repetition 2 Lifespan (minutes) Average cutting life (minutes) A 5,6 8,5 7,1 B 14,7 15,0 14,9 C 14,0 13,7 13,9 D 13,2 13,8 13,5 E* 11,8 12,2 12,0 * Comparative use

[0048] According to the information in Table VIII, the coated cutting inserts BD with a multilayer structure with alternating doped and undoped layers outlasted the insert A with only one undoped and doped layer and the insert E with a continuous α-Al2O3 outer layer.

[0049] Various embodiments of the invention have been described, each fulfilling a different objective. It is understood that these embodiments merely illustrate the principles of the present invention. Numerous modifications and adaptations thereof are readily apparent to those skilled in the art, without deviating from the spirit and scope of the invention.

Claims

[1] Coated cutting tool comprising the following: a substrate; and a coating which has a multitude of alternating layers, comprising a first layer of Al2O3 and a second layer of MeAl2O3 / MeO2 composite material; where Me represents Ti, Zr, Hf or a combination thereof, and where intercrystalline MeO2 deposits are distributed along grain boundaries. [2] Coated cutting tool according to claim 1, wherein the first layer or the second layer is 0.05 to 0.5 µm thick. [3] Coated cutting tool according to claim 1 or 2, wherein the first layer and the second layer are each 0.05 to 0.5 µm thick. [4] Coated cutting tool according to claim 1 or 2, wherein the thickness of the first layer and the second layer is less than or equal to 0.015 µm. [5] Coated cutting tool according to any one of claims 1 to 4, wherein the first layer comprises α-Al2O3, K-Al2O3 or a combination thereof. [6] Coated cutting tool according to any one of claims 1 to 5, wherein the second layer is closer to the substrate than the first layer. [7] Coated cutting tool according to any one of claims 1 to 5, wherein the first layer is closer to the substrate than the second layer. [8] Coated cutting tool according to claim 3, wherein an intermediate layer between the substrate and the first layer comprises one or more metallic elements selected from the group consisting of aluminium and metallic elements of groups IVB, VB and VIB of the periodic table, and one or more non-metallic elements of groups IIIA, IVA, VA and VIA of the periodic table. [9] Coated cutting tool according to any one of claims 1 to 8, wherein the coating further comprises a base layer adjacent to the substrate surface, the base layer comprising one or more metallic elements selected from the group consisting of aluminium and metallic elements of groups IVB, VB and VIB of the periodic table, and one or more non-metallic elements of groups IIIA, IVA, VA and VIA of the periodic table. [10] Coated cutting tool according to any one of claims 1 to 7, wherein the alternating coating layers within a grain form an angled stripe pattern. [11] Coated cutting tool according to claim 9, wherein the base layer comprises at least TiN and / or MT-TiCN and / or TiOCN. [12] Coated cutting tool according to claim 9, wherein the coating further comprises an outer layer comprising one or more metallic elements selected from the group consisting of aluminium and metallic elements of groups IVB, VB and VIB of the periodic table, and one or more non-metallic elements of groups IIIA, IVA, VA and VIA of the periodic table. [13] Coated cutting tool according to any one of claims 1 to 12, wherein the Me is in wt.% and the wt.% proportion is different between two or more second layers.

Images