A coated cutting tool

Abstract

The present invention relates to a cutting tool comprising a substrate at least partially coated with a coating, said coating comprises an α-Al2O3 layer and at least one inner Ti(C,N) layer, said inner Ti(C,N) layer is located between a surface of the substrate and the α-Al2O3 layer. The coating further comprises at least one outer Ti(C,N) layer located between the α-Al2O3 layer and an outermost surface of the coating. There is a reaction layer between the α-Al2O3 layer and the outer Ti(C,N) layer, and said reaction layer has an average thickness of 20-70 nm.

Description

[0001] A COATED CUTTING TOOL

[0002] TECHNICAL FIELD

[0003] The present invention relates to the technical field of coated cutting tools for metal cutting. The cutting tool of the present invention is coated with a coating comprising an inner Ti(C,N) layer, an a-ALOs-layer and an outer Ti(C,N) layer.

[0004] BACKGROUND

[0005] Coated cutting tools are well known in the metal cutting industry. Advantages with a coating deposited on the cutting tool are that it gives the cutting tool an increased resistance to chemical and abrasive wear which are important to achieve long tool life of the cutting tool. Coatings comprising an inner layer of Ti(C,N) and an outer layer of alumina are known to perform well in for example turning or milling of steel.

[0006] EP3607110B1 discloses a coated cutting tool provided with a coating comprising a layer of a-ALOs and a Ti(C,N) layer deposited on the a-ALOs layer. The Ti(C,N) layer exhibits a texture coefficient TC(111 ) of >3.

[0007] There is a continuous need of improving the wear resistance of coated cutting tools to provide an increased tool life. For example, coating adhesion is important for the wear resistance of the cutting tool. It is an object of the present invention to provide a cutting tool with an increased lifetime in metal cutting. It is also an object of the present invention to provide a cutting tool with high resistance to flaking of the coating during metal cutting in steel.

[0008] DESCRIPTION OF THE INVENTION

[0009] At least one of the above-mentioned objects is achieved by a cutting tool according to claim 1. Preferred embodiments are disclosed in the dependent claims.

[0010] The present invention relates to a cutting tool comprising a substrate at least partially coated with a coating, said coating comprises an a-ALOs layer and at least one inner Ti(C,N) layer, said inner Ti(C,N) layer is located between a surface of the substrate and the a-ALOs layer, the coating further comprises at least one outer Ti(C,N) layer located between the a-ALOs layer and an outermost surface of the coating, wherein there is a reaction layer located between the a-Al2O3 layer and the outer Ti(C,N) layer, said reaction layer has an average thickness of 20-70 nm, preferably 20-50 nm, more preferably 20-30 nm.

[0011] It has recently been found that a coating comprising an inner Ti(C,N) layer, an intermediate a-Al2O3 layer and an outer wear layer of Ti(C,N) as an outer or outermost layer on a coated cutting tool is advantageous in wear resistance when turning in steel, such as medium carbon steel. It was unexpectedly found that by introducing a reaction layer between the a-Al2O3 layer and the outer Ti(C,N) layer in the coating of the cutting tool, the wear resistance of the cutting tool was improved, especially the wear resistance in turning in medium carbon steel was improved. The coated cutting tool of the present invention shows high resistance to flaking of the coating during metal cutting in steel.

[0012] Since the outermost portion of the a-Al2O3 is transformed into the reaction layer a strong adhesion to the a-Al2O3 layer is achieved. It seems as if Al atoms are replaced by Ti atoms during the reaction layer formation, that the growth-mechanism includes diffusion trough this reaction layer and that the growth of the reaction layer slows down with time and reaches an equilibrium thickness.

[0013] The term “cutting tool” is herein intended to denote cutting tools suitable for metal cutting applications such as inserts. The application areas can for example be turning, milling or drilling in metals such as steel.

[0014] The coated cutting tool disclosed herein can be an insert comprising a rake face, a flank face and a cutting edge therebetween. The substrate, the coating and the layers thereof each have an outer surface. With surface normal or normal to the outer surface is intended a direction perpendicular to a surface plane of the outer surface, i.e. a direction in the preferential growth direction of the coating.

[0015] Cemented carbide materials are useful in high demanding applications due to their high hardness and high wear resistance in combination with high toughness. Cemented carbides are produced by powder metallurgical methods, wherein the starting powders are mixed, milled and formed into a green body, pre-sintered and sintered. Cemented carbide materials generally consist of hard constituents of WC and optional carbides and / or nitrides such as TiC, NbC and TiN in a metallic binder of for example Co. The metallic binder content in the cemented carbide is typically 5-10 wt%.

[0016] In one embodiment of the present invention the reaction layer is a layer comprising titanium (Ti) and oxygen (0) such that an atomic ratio of Ti / O is between 0.3 and 0.6.

[0017] In one embodiment of the present invention the reaction layer is a titanium oxide layer.

[0018] In one embodiment of the present invention the reaction layer is in direct contact with the outer Ti(C,N) layer and with the a-Al2O3 layer.

[0019] In one embodiment of the present invention the average grain size of the Ti(C,N) grains in the outer Ti(C,N) layer is 0.30-0.60 pm, preferably 0.35-0.45 pm, as measured with EBSD on a cross section of said outer Ti(C,N) layer, wherein a surface normal of the outer Ti(C,N) layer is parallel to the surface normal of the substrate surface. The small grains of the outer Ti(C,N) of the invention contributes to hardness and wear resistance of the layer.

[0020] In one embodiment of the present invention the outer Ti(C,N) layer exhibits an orientation wherein >60%, preferably >70%, of the analysed area has a <111 > direction within 15 degrees from the surface normal of the outer Ti(C,N) layer as measured with EBSD on an analysed area of a cross section of the outer Ti(C,N) layer, wherein a surface normal of outer Ti(C,N) layer is parallel to the surface normal of the substrate surface, said cross section is parallel to the surface normal of the outer Ti(C,N) layer.

[0021] In one embodiment of the present invention the average thickness of the outer Ti(C,N) layer is > 2 pm, preferably 3-10 pm, more preferably 4-7 pm.

[0022] In one embodiment of the present invention the average thickness of the a-Al2O3 layer is > 2 pm, preferably 3-10 pm, more preferably 4-7 pm. In one embodiment of the present invention the average thickness of the inner Ti(C,N) layer is > 2 pm, preferably 3-10 pm, more preferably 4-7 pm

[0023] In one embodiment of the present invention the a-Al2O3 layer exhibits an orientation wherein > 70 %, of the analysed area has a <001 > direction within 15 degrees from the surface normal of the a-Al2O3 layer as measured with EBSD on an analysed area of a cross section of said a-Al2O3 layer, wherein a surface normal of the a-Al2O3 layer is parallel to the surface normal of the substrate surface, said cross section is parallel to the surface normal of the a-Al2O3 layer.

[0024] In one embodiment of the present invention the inner Ti(C,N) layer exhibits an orientation wherein > 60 % of the analysed area has a <211 > direction within 15 degrees from the surface normal of the inner Ti(C,N) layer as measured with EBSD on an analysed area of a cross section of the inner Ti(C,N) layer, wherein a surface normal of inner Ti(C,N) layer is parallel to the surface normal of the substrate surface, said cross section is parallel to the surface normal of the inner Ti(C,N) layer.

[0025] In one embodiment of the present invention the substrate is of cemented carbide.

[0026] In one embodiment of the present invention an average thickness of the coating is 9-30 pm, preferably 10-20 pm.

[0027] In one embodiment of the present invention the coating comprises an inner Ti(C,N) layer with an average thickness of 3-10 pm, an a-Al2O3 layer with an average thickness of 3-10 pm and an outer Ti(C,N) layer with an average thickness of 3-10 pm.

[0028] Still other objects and features of the present invention will become apparent from the following definitions and examples considered in conjunction with the accompanying drawings.

[0029] METHODS

[0030] Coating deposition

[0031] The coatings in the examples below were deposited partly in a radial lonbond Bernex TM type CVD equipment 530L size capable of housing 10000 half-inch size cutting inserts and partly in a radial lonbond Bernex TM type CVD equipment 530S size capable of housing 7000 half-inch size cutting inserts. thickness

[0032] Scanning Electron Microscopy (SEM) investigations of polished cross sections of the coatings were carried out in a Carl Zeiss AG- Supra 40 type operated at 3kV acceleration voltage using a 30 pm aperture size. The images were acquired using a secondary electron detector. The layer thicknesses were measured in the SEM images of the cross sections.

[0033] Since the reaction layer is very thin its thickness is herein measured in transmission electron microscope (TEM) using Scanning Transmission Electron Microscopy (STEM) High Angle Annular Dark Field (HAADF) imaging. The samples for characterization of the reaction layer by TEM was produced by manufacturing a thin foil specimen of the sample by the well known FIB in-situ lift out technique. A Helios Nanolab 650 using a Ga+ ion source was used for the sample preparation. The specimens were mounted on Omniprobe™ 5-post Cu grids. The target thickness for the thin foils was approximately 100 nm. In order to minimize the ion beam-induced damage, low accelerating voltages of 5 kV and 2 kV, with respective ion currents of 49 pA and 24 pA, were used in the final thinning process. A CS- and Probe- corrected FEI Titan transmission electron microscope equipped with a Schottky FEG operated in scanning mode (STEM) at an accelerating voltage of 300 kV.

[0034] The composition of the “reaction layer” was analyzed using energy dispersive X-ray spectroscopy (EDS) in the TEM. The measurement area(s) were specifically selected to ensure they were entirely within the interaction layer between the a- AI2O3 and the outer Ti(C,N) layer, with total area covering at least 1000 nm2.

[0035] A Broker Super X EDS detector was used for the EDS measurements and quantifications were done in Esprit software using Series deconvolution method. Orientation and grain size of layers

[0036] The orientation of the layers and the grain size of the Ti(C,N) grains of the outer Ti(C,N) layer were measured using electron backscatter diffraction (EBSD), wherein the width of the analysed area was at least 80 pm in parallel with the substrate surface, the height of the analysed area was selected to include the whole layer thickness of the layer that was studied, and a step size of 50 nm was used.

[0037] More specifically, the analysis was performed on the coatings cross-section using a Zeiss Supra 55 equipped with Oxford Instruments Symmetry EBSD detector. The coating cross-sections were prepared for CNMG120408-PM inserts which were baked in a black conductive phenolic resin from AKASEL, ground down about 1 mm and polished in two steps: rough polishing (9 pm) and fine polishing (1 pm) using a diamond slurry solution followed by a final polishing using colloidal silica solution. After the final polishing step, the polished inserts were cleaned in ethanol, nitrogen blow dried and mounted on a 70°pre-tilted holder for EBSD analysis. The microscope was operated at an acceleration voltage of 20 kV, and 13 nA beam current (120 pm aperture) and a working distance of 9-15 mm.

[0038] Regions which included only the sub layer in focus, i.e. the inner Ti(C,N), AI2O3 or the outer Ti(C,N) layer, with a width of at least 80 pm were analyzed with a step size of 50nm. Speed 1 binning mode was used (622x512 pix). One auto-clean up step was applied to the data. The Aztec Crystal software (v 3.1 , build 3.1 .390) was used for the determination of the grain size and orientation.

[0039] The Alumina (Alpha), Acta Crystallogr, Sec B [ACBCAR], (1993) vol 49B pp 973- 980, reference pattern was used for the AI2O3 measurements, 89 reflectors were used for the measurements.

[0040] The Ti(C,N), J.EIectrochem. Soc. [JESOAN], (1950), vol 97, pp 299-304, reference pattern was used for the Ti(C,N) measurements, 89 reflectors were used for the measurements.

[0041] The orientations of the layers were determined as the amount in (%) of an analyzed area that is within a certain angular deviation from a set fiber axis. The samples were analyzed so that the surface of the specimen was parallel to the substrate surface, thus ensuring that the coating out of plane orientation was parallel to the sample normal.

[0042] For the AI2O3 the <001 > direction was chosen as the direction parallel to the surface normal. The texture component was calculated as the amount of analyzed area that was <15°deviation from the <001 > AI2O3 direction.

[0043] For the outer Ti(C,N) the <111 > direction was chosen as the direction parallel to the surface normal. The texture component was calculated as the amount of analyzed area that was <15°deviation from the <111 > Ti(C,N) direction.

[0044] For the inner Ti(C,N) the <211 > direction was chosen as the direction parallel to the surface normal. The texture component was calculated as the amount of analyzed area that was <15°deviation from the <211 > Ti(C,N) direction.

[0045] The grain size of the layers was analyzed using the same EBSD data as the orientation analysis. The “fitted ellipse minor diameter” parameter and 10° misorientation threshold were used for grain size determination, where grain size was determined by the arithmetic mean value of the analyzed layer. The measurement was done on grains whose entire area fell within the boundaries of the measured area.

[0046] BRIEF DESCRIPTION OF DRAWINGS

[0047] In the following examples embodiments of the invention will be described with reference to the accompanying drawings.

[0048] Figure 1 shows a Scanning Electron Microscope (SEM) image of a cross section of the CVD coating (2) of Sample 1 , with substrate (1 ), inner Ti(C,N) (4), AI2O3 layer (3), reaction layer (6) and the outer Ti(C,N) layer (5) indicated.

[0049] Figure 2 shows a STEM HAADF image of the Al2O3 / Ti(C,N) interface of Reference 1 with no surface treatment.

[0050] Figure 3 shows a STEM HAADF image of the Al2O3 / Ti(C,N) interface of Reference with 5 minutes flushing treatment. Figure 4 shows a STEM HAADF image of the Al2O3 / Ti(C,N) interface of Sample 1 with 10 minutes flushing treatment.

[0051] Figure 5 shows a STEM HAADF image of Sample 5 with a reaction layer made with 60 minutes flushing treatment. No outer Ti(C,N) layer was deposited on this sample.

[0052] EXAMPLES

[0053] Exemplifying embodiments of the present invention will be disclosed in more detail and compared to reference embodiments. The examples are to be considered as illustrative and not limiting embodiments. In the following examples coated cutting tools (inserts) were manufactured, analyzed and evaluated in cutting tests.

[0054] Substrates

[0055] Cemented carbide substrates were manufactured utilizing conventional processes including milling, mixing, spray drying, pressing and sintering. The ISO-type geometry of the cemented carbide substrates (inserts) was CNMG-120408-PM. The composition of the cemented carbide was 7.2 wt% Co, 2.9 wt% TaC, 0.5 wt% NbC, 1 .9 wt% TiC, 0.4 wt% TiN and the rest WC.

[0056] Before the coating depositions the substrates were exposed to a mild blasting treatment to remove any residuals on the substrate surfaces from the sintering process.

[0057] The sintered and blasted substrates were CVD coated in a radial CVD reactor of Bernex Type size 530L capable of housing 10.000 half inch size cutting inserts. The samples to be tested and analysed further were selected from the middle of the chamber and at a position along half the radius of the plate between the center and the periphery of the plate. Mass flow controllers are to be chosen so that the flow rate of for example CH3CN is selected to allow the flow rates in the CVD recipe.

[0058] A first innermost layer of about 0.3 pm TiN was deposited on all substrates using a deposition temperature of 885 °C and a pressure of 400 mbar and a deposition time of 40 minutes. Thereafter a Ti(C,N) layer was deposited by employing the well- known MTCVD technique using TiCk, CH3CN, N2, HCI and H2 at 885 °C and 55 mbar. Two steps were used, the first one for 10 minutes and the second step was adjusted to give a coating thickness of about 5 pm. The details of the TiN and the inner Ti(C,N) deposition are shown in Table 1 .

[0059] Table 1 TiN and the inner Ti(C,N) deposition

[0060] After the deposition of the inner Ti(C,N) layer the temperature was increased from 885°C to 1000°C in an N2 atmosphere.

[0061] A 0.7-1.1 pm thick bonding layer was deposited at 1000°C on top of the Ti(C,N) layer by a process consisting of four separate reaction steps. First a 8 minutes HTCVD Ti(C,N) step using TiCk, CH4, N2, HCI and H2 at 400 mbar, then a second step (Ti(C,N,O)-1 ) using TiCk, CH3CN, CO, N2 , HCI and H2 at 70 mbar for 7 minutes, then a third step (Ti(C,N,O)-2) using TiCk, CH3CN, CO, N2 and H2 at 70 mbar for 5 minutes and finally a fourth step (TiN) using TiCU, N2 and H2 at 70 mbar for 6 minutes. During the third deposition step the CO gas flow was continuously linearly increased from a start value at the beginning of the process step to a stop value at the end of the process step as shown in Table 2. All other gas flows were kept constant, but since the overall gas flow is increased, the concentration of all gases was somewhat influenced due to this. Prior to the start of the subsequent AI2O3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO2, CO, N2 and H2.

[0062] The details of the bonding layer deposition are shown in Table 2. Table 2 Bonding layer deposition

[0063] On top of the bonding layer a-Al2O3 was deposited. All the a-Al2O3 layers were deposited at 1000°C and 55 mbar in two steps. The first step using 1 .2 vol-% AlCh, 4.7 vol-% CO2, 1.8 vol-% HCI and balance H2 was run for 30 minutes giving about

[0064] 0.1 pm a-Al2O3. The process time of the second step was adjusted to give a total a- AI2O3 layer thickness of about 5 pm. The second step of the a-Al2O3 layer was deposited using 1.2 % AICI3, 4.7 % CO2, 2.9 % HCI, 0.58 % H2S and balance H2.

[0065] The outer surface of the a-Al2O3 layers were subjected to a gas flushing treatment using a Bernex 530S CVD reactor in a reactor temperature of 885°C and a pressure of 55 mbar and a gas mixture of 98.9 vol% H2 and 1.15 vol% TiCk This flushing treatment results in a reaction layer at the outer portion of the a-Al2O3 layer. The flushing treatment duration varied between samples, as presented in Table 3. The gas compositions are presented in Table 4.

[0066] Table 3 Flush treatment

[0067] On top of the reaction layer an outer Ti(C,N) layer was deposited. The outer Ti(C,N) layer was deposited at 885°C and at 55 mbar. The gas mixture was during the deposition composed of 38.10 vol% N2, 1.35 vol% TiCk, 0.68 vol% CH3CN and balance H2 and it was run for 165 minutes giving about 5 pm Ti(C,N). The process parameters for the outer Ti(C,N) layer is presented in Table 4.

[0068] Table 4 Outer Ti(C,N) deposition

[0069] Coating analyses The samples to be tested and analysed further were selected from the middle of the chamber and at a position along half the radius of the plate between the center and the periphery of the plate.

[0070] The layer thicknesses were measured on a cross section of the rake face of the cutting tool samples. The thicknesses of the Ti(C,N) layers and the a-Al2O3 layer were measured with SEM and the reaction layer with a TEM. The measured thicknesses of the layers of the samples are shown in Table 5. Table 5 Layer thicknesses n.a.= not analysed

[0071] The thickness values presented above of the inner Ti(C,N) layer do not include the approx. 0.3 pm thickness of the inner TiN and about 0.7 pm bonding layer between the inner Ti(C,N) and the a-ALOs layer.

[0072] The orientation and the grain size in the Ti(C,N) layers and the a-ALOs layers were analysed with EBSD in accordance with the method described above. Table 6 provides detailed information on the measured texture components for each sample and the grain size of the Ti(C,N) grains in the outer Ti(C,N) layers. Table 6. Measured texture components and grain size

[0073] Composition

[0074] The reaction layer's composition was analyzed using energy-dispersive X-ray spectroscopy on samples subjected to surface treatment. To achieve a more precise analysis and quantification of the reaction layer while avoiding interference from the outer Ti(C,N) layer, an additional sample was prepared with only a 60- minute surface treatment of a-Al2O3, excluding the outer Ti(C,N) (Fig. 6). Analysis of this sample revealed that the reaction layer primarily consists of titanium and oxygen, with small amounts of aluminum and carbon. The aluminum signal likely originates from the a-Al2O3 layer, while the carbon is likely originating from the protective platinum layer applied during TEM lamella preparation. The result of the analyses of Sample 5 is presented in Table 7. It was concluded that the reaction layer is titanium oxide, with a Ti / O ratio of approximately 0.5.

[0075] Table 7. Composition of the reaction on layer sample 5 Blasting test The cutting tools were first evaluated by being exposed to an abrasive wet blasting. The blasting was performed on the rake faces of the cutting tools. The blaster slurry consisted of 20 vol-% alumina in water and an angle of 90° between the rake face of the cutting insert and the direction of the blaster slurry. The distance between the gun nozzle and the surface of the insert was about 145 mm. The pressure of the slurry to the gun was 1 .8 bar for all samples, while the pressure of air to the gun was 2.2 bar. The alumina grits were F230 mesh (FEPA 42-2:2006). The average time for blasting per area unit was 4.4 seconds. The reference samples Reference 1 and Reference 2 showed flaking. All the other samples, Samples 1 -4, did withstand the wet blasting with no flaking of the coatings, see table 8.

[0076] Table 8 Blasting test results

[0077] Cutting test

[0078] The as coated cutting tools were also tested in a face turning operation (from dia. 180 mm to dia. 60mm) in a work-piece material DIN C45E, a medium carbon steel.

[0079] The spindle speed was fixed in n = 120 rpm; thus, the cutting speed linearly varied from, Vc, ~70 m / min (at dia. 180 mm) to Vc, ~20 m / min ( at dia. 60 mm) along the face turning operation; the feed, fn, was linearly increased from 0.1 mm / revolution (at dia. 180 mm), to 0.5 mm / revolution (at dia. 60 mm) along the face turning operation; the depth of cut was 2 mm and no cutting fluid was used. The test was stopped when the cutting piece material reached the 60 mm in diameter. Four samples of each variant were used. Four parallel tests were made, the average is presented in table 8.

[0080] In order to measure the total area of the damaged coating on the rake face after the face turning operation, the inserts were etched for 15 min in a HCI (Hydrochloric acid) solution with concentration 37 wt%. In the sequence, SEM investigations of the top surface were carried out using a Zeiss AG- Supra 40 type operated at 10 kV acceleration voltage using a 30 pm aperture size. Images were acquired at 50X magnification using a backscatter electron detector. Images were used to measure the area of coating ripped out using an image analysis software, where a larger measured area from table 9 corresponds to more wear due to unsatisfying adhesion of the top Ti(C,N).

[0081] Table 9 Cutting test results

[0082] The cutting test revealed that the samples treated for a duration of 10 minutes to 60 minutes exhibited less coating damage compared to the reference samples Reference 1 and Reference 2 with no or too short surface treatment.

[0083] While the invention has been described in connection with various exemplary embodiments, it is to be understood that the invention is not to be limited to the disclosed exemplary embodiments; on the contrary, it is intended to cover various modifications and equivalent arrangements within the appended claims.

Claims

CLAIMS1. A cutting tool comprising a substrate (1 ) at least partially coated with a coating (2), said coating comprises an a-ALOs layer (3) and at least one inner Ti(C,N) layer (4), said inner Ti(C,N) layer (4) is located between a surface of the substrate and the a-ALOs layer (3), the coating further comprises at least one outer Ti(C,N) layer (5) located between the a-ALOs layer (3) and an outermost surface of the coating (2), wherein there is a reaction layer (6) located between the a-ALOs layer (3) and the outer Ti(C,N) layer (5), wherein the average thickness of the outer Ti(C,N) layer is 3-10 pm, said reaction layer (6) has an average thickness of 20-70 nm, preferably 20-50 nm, more preferably 20-30 nm.

2. The cutting tool in accordance with claim 1 , wherein the reaction layer (6) is a layer comprising titanium (Ti) and oxygen (O) such that an atomic ratio of Ti / O is between 0.3 and 0.6.

3. The cutting tool in accordance with any of the preceding claims, wherein the reaction layer (6) is a titanium oxide layer.

4. The cutting tool in accordance with any of the preceding claims, wherein the reaction layer (6) is in direct contact with the outer Ti(C,N) layer (5) and with the a-ALOs layer (3).

5. The cutting tool in accordance with any of the preceding claims, wherein the average grain size of the Ti(C,N) grains in the outer Ti(C,N) layer (5) is 0.30-0.60 pm, preferably 0.35-0.45 pm, as measured with EBSD on a cross section of said outer Ti ( C , N) layer, wherein a surface normal of the outer Ti ( C , N) layer is parallel to the surface normal of the substrate surface.

6. The cutting tool in accordance with any of the preceding claims, wherein the outer Ti(C,N) layer exhibits an orientation wherein >60%, preferably >70%, of the analysed area has a <111 > direction within 15 degrees from the surface normal of the outer Ti(C,N) layer as measured with EBSD on an analysed area of a cross section of the outer Ti(C,N) layer, wherein a surface normal of outerTi(C,N) layer is parallel to the surface normal of the substrate surface, said cross section is parallel to the surface normal of the outer Ti(C,N) layer.

7. The cutting tool in accordance with any of the preceding claims, wherein the average thickness of the outer Ti(C,N) layer is 4-7 pm.

8. The cutting tool in accordance with any of the preceding claims, wherein the average thickness of the a-Al2O3 layer is > 2 pm, preferably 3-10 pm, more preferably 4-7 pm.

9. The cutting tool in accordance with any of the preceding claims, wherein the average thickness of the inner Ti(C,N) layer is > 2 pm, preferably 3-10 pm, more preferably 4-7 pm10. The cutting tool in accordance with any of the preceding claims, wherein the a- AI2O3 layer exhibits an orientation wherein > 70 %, of the analysed area has a <001 > direction within 15 degrees from the surface normal of the a-Al2O3 layer as measured with EBSD on an analysed area of a cross section of said a-Al2O3 layer, wherein a surface normal of the a-Al2O3 layer is parallel to the surface normal of the substrate surface, said cross section is parallel to the surface normal of the a-Al2O3 layer11. The cutting tool in accordance with any of the preceding claims, wherein the inner Ti(C,N) exhibits an orientation wherein > 60 % of the analysed area has a <211 > direction within 15 degrees from the surface normal of the inner Ti(C,N) layer as measured with EBSD on an analysed area of a cross section of the inner Ti(C,N) layer, wherein a surface normal of inner Ti(C,N) layer is parallel to the surface normal of the substrate surface, said cross section is parallel to the surface normal of the inner Ti(C,N) layer.

12. The cutting tool in accordance with any of the preceding claims, wherein the substrate is of cemented carbide.

13. The cutting tool in accordance with any of the preceding claims, wherein an average thickness of the coating is 9-30 pm, preferably 10-20 pm.1914. The cutting tool in accordance with any of the preceding claims, wherein the coating comprises an inner Ti(C,N) layer with an average thickness of 3-10 pm, an a-Al2O3 layer with an average thickness of 3-10 pm and an outer Ti(C, N) layer with an average thickness of 3-10 pm.

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