Coated cutting tool

Abstract

The present invention relates to a coated cutting tool comprising a substrate at least partially coated with a coating comprising a Ti (C, N) layer, an alpha-Al2O3 layer, and a bond layer therebetween. The Ti (C, N) layer has a thickness of 3-20 [mu] m, and the Ti (C, N) layer comprises an inner Ti (C, N) portion T1 and a subsequent outer Ti (C, N) portion T2 when viewed from the substrate towards the outer surface of the tool. The thickness of the inner part T1 is 2.5-15 [mu] m, and the thickness of the outer part T2 is 0.5-5 [mu] m. The average grain width of Ti (C, N) grains in T1 and T2 is less than 300 nm. The atomic ratio C / N in the inner Ti (C, N) portion T1 is from 1.50 to 1.60, and the atomic ratio C / N in the outer Ti (C, N) portion T2 is from 1.25 to 1.40.

Description

Technical Field

[0001] The invention relates to a coated cutting tool comprising a substrate and a coating, wherein the coating is deposited by chemical vapor deposition (CVD) and comprises a Ti(C,N) layer and an α-Al2O3 layer. Background Art

[0002] Coated cutting tools are well known in the metal cutting industry. CVD coated cutting tools and PVD coated cutting tools are the two most dominant types of coated cutting tools. The advantage of these coatings is the high resistance to chemical and abrasive wear, which is important for achieving a long tool life of the coated cutting tools. CVD coatings comprising a Ti(C,N) layer as well as an aluminum oxide layer are known to perform well in, for example, turning or milling of steel.

[0003] Recent studies have shown that the combination of a very fine-grained Ti(C,N) layer and an Al2O3 layer sometimes results in poor adhesion between the Ti(C,N) and the Al2O3. There is interest in solving this problem because very fine-grained Ti(C,N) has shown promising properties for cutting tools.

[0004] One object of the present invention is to provide a coated cutting tool for metal cutting having high adhesion between the Ti(C,N) and Al2O3 layers of the coating. Another object is to provide a coated cutting tool having high wear resistance, especially high resistance to spalling during metal cutting. Another object of the present invention is to provide a cutting tool having high resistance to crater wear in metal cutting in steel. Summary of the invention

[0005] At least one of the above objects is achieved by a coated cutting tool according to item 1. Preferred embodiments are disclosed in the dependent items.

[0006] The present invention relates to a coated cutting tool, comprising a substrate at least partially coated with a coating, wherein the coating comprises a Ti(C,N) layer, an α-Al2O3 layer and a bonding layer therebetween. The Ti(C,N) layer having a thickness of 3-20 μm, preferably 5-15 μm, most preferably 6-10 μm, consists of columnar grains, wherein the Ti(C,N) layer comprises an inner Ti(C,N) portion T1 and a subsequent outer Ti(C,N) portion T2 when viewed in a direction from the substrate towards the outer surface of the tool. The inner portion T1 has a thickness of 2.5-15 μm, preferably 3-10 μm, and the outer portion T2 has a thickness of 0.5-5 μm, preferably 0.5-3 μm, more preferably 0.5-2 μm. The grain width of the Ti(C,N) grains in the inner Ti(C,N) portion T1 is less than 300 nm, preferably less than 200 nm, more preferably less than 100 nm, and the grain width of the Ti(C,N) grains in the outer Ti(C,N) portion T2 is less than 300 nm, preferably less than 200 nm. The atomic ratio C / N in the inner Ti(C,N) portion T1 is 1.50-1.60, and the atomic ratio C / N in the outer Ti(C,N) portion T2 is 1.25-1.40, preferably 1.27-1.36.

[0007] The Ti(C,N) portions T1 and T2 are defined by their atomic C / N ratios. Line scans in electron probe microanalysis (EPMA) are used to identify the thickness of these portions based on their C / N ratios. The atomic C / N ratios are preferably approximately constant within the respective portions, i.e., the ratios may vary by about ±2%.

[0008] It was surprisingly found that coated cutting tools containing a Ti(C,N) layer comprising two parts of columnar fine grains, the inner part having a slightly higher carbon content than the outer part, showed increased resistance to crater wear and also increased resistance against coating delamination.

[0009] In one embodiment of the present invention, the average grain width of the Ti(C,N) grains in the inner Ti(C,N) portion T1 is smaller than the average grain width of the Ti(C,N) in the outer Ti(C,N) portion T2. ​​An outer portion having a larger grain width than the inner portion is advantageous because it facilitates adhesion of a subsequent bonding layer.

[0010] In one embodiment of the present invention, the Ti(C,N) layer includes an outer portion T2 adjacent to the bonding layer, wherein the Ti(C,N) grains in the uppermost region of T2 have an average grain width of 90-250nm, preferably 100-200nm. The T2 portion may contribute to increased adhesion of the bonding layer and the subsequent α-Al2O3 layer. If the average grain width in the uppermost region of T2 is too large, the adhesion is still high, but it is found that the TC(0012) of the subsequently deposited α-Al2O3 layer is reduced. If the average grain width in the uppermost region of T2 is too low, the coating adhesion of subsequent layers may be reduced. The uppermost region of T2 is the region of T2 closest to the bonding layer. The average grain width of the Ti(C,N) grains adjacent to the bonding layer refers herein to the average grain width of the Ti(C,N) grains measured along a line approximately 300nm away from the bonding layer.

[0011] In one embodiment of the present invention, the average grain width of the Ti(C,N) grains in the inner Ti(C,N) portion T1 is <100 nm. Fine-grained Ti(C,N) can advantageously act as a wear-resistant layer, which can be attributed to its large number of grain boundaries or to the smoother or uniform thickness of the layer. Therefore, the fine-grained portion of the TiCN layer should be relatively thick.

[0012] In one embodiment of the present invention, the average grain size D of the inner Ti(C,N) portion T1 of the Ti(C,N) layer is 200 Å when measured by X-ray diffraction using CuKα radiation. 422 The grain size D is 25-50nm. 422 The full width at half maximum (FWHM) of the (422) peak was calculated according to the Scherrer equation:

[0013]

[0014] Where D 422 is the average grain size of Ti(C,N), K is the shape factor set here to 0.9, λ is the wavelength of the CuKα radiation set here to 1.5405 Å, B 422 is the FWHM value of the (422) reflection, and θ is the Bragg angle.

[0015] It is difficult to study the average grain width of very fine-grained Ti(C,N) because the orientation contrast differences of the grains and the identification of grain boundaries in polished cross-sections studied, for example, using SEM and EBSD can be very low. Those skilled in the art recognize that when the amount of signal in the analysis becomes too low, the results can no longer be trusted. In order to study even finer-grained Ti(C,N), for example when the average grain width is less than 75nm, XRD and the Scherrer equation are used herein.

[0016] In one embodiment of the present invention, the thickness of the α-Al 2 O 3 layer is 1-15 μm, preferably 3-9 μm.

[0017] A coated cutting tool according to item 1, wherein the α-Al 2 O 3 layer exhibits a texture coefficient TC (hkl) defined according to the Harris formula when measured by X-ray diffraction using CuKα radiation and θ-2θ scanning.

[0018]

[0019] Where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to PDF card number 00-010-0173 of ICDD, n = number of reflections, the reflections used are: (1 0 4), (1 1 0), (1 1 3), (0 24), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), where TC (0 0 12) is the maximum texture coefficient. High TC (0 012) has been shown to contribute to high crater wear resistance in steel metal cutting.

[0020] In one embodiment of the present invention, the TC(0012) of the α-Al2O3 layer is >7.7, preferably >7.8.

[0021] In one embodiment of the present invention, the α-Al2O3 layer comprises a portion A1 extending 1 μm from the bonding layer, wherein the portion A1 is measured by electron backscatter diffraction (EBSD) on a cross section of the α-Al2O3 layer, wherein the surface normal of the α-Al2O3 layer is parallel to the surface normal of the substrate surface, and the portion A1 exhibits an orientation in which ≥70%, preferably ≥80%, more preferably ≥90%, and most preferably ≥95% of the analyzed area has a surface normal within 15 degrees from the surface normal of the α-Al2O3 layer. <001> direction.

[0022] In one embodiment of the present invention, the Ti(C,N) layer including the T1 portion and the T2 portion exhibits a texture coefficient TC(hkl) defined according to Harris equation (2) when measured by X-ray diffraction using CuKα radiation and θ-2θ scanning,

[0023] where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to PDF card number 42-1489 of the ICDD, n is the number of reflections, and the reflections used in the calculations are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 2 0), and (4 2 2), where TC(422)>3.

[0024] In one embodiment of the present invention, the TC(422)+TC(311) of the Ti(C,N) layer is 5-6.

[0025] In one embodiment of the invention, the bonding layer comprises at least one compound selected from the group consisting of titanium oxycarbide, titanium oxynitride and titanium oxycarbonitride. A bonding layer comprising titanium oxycarbide, titanium oxynitride or titanium oxycarbonitride is advantageous because it can provide an epitaxial relationship between the Ti(C,N) layer and the α-Al2O3 layer. The lowermost portion of the bonding layer is preferably a very nitrogen-rich Ti(C,N) layer preferably deposited at about 1000°C. Preferably, the total thickness of the bonding layer is 0.5-2 μm.

[0026] In one embodiment of the invention, the coating comprises an innermost layer of TiN, preferably with a thickness of 0.1-0.5 μm.

[0027] In one embodiment of the present invention, the substrate of the coated cutting tool is selected from the group of cemented carbide and cermet.

[0028] definition

[0029] The term "cutting tool" is intended herein to mean a cutting tool, such as a blade, suitable for metal cutting applications. The field of application may be, for example, turning, milling or drilling in metals, such as steel.

[0030] The cutting tool disclosed herein comprises a substrate and a coating. The coated cutting tool can be a blade comprising a rake face, a flank face and a cutting edge therebetween. The substrate, the coating and its layers each have an outer surface. The surface normal or perpendicular to the outer surface refers to the direction perpendicular to the surface plane of the outer surface, i.e. in the preferred growth direction of the coating.

[0031] method

[0032] Coating deposition

[0033] The coatings in the following examples were deposited in a radial Ionbond Bernex™ model CVD apparatus 530 size capable of accommodating 10,000 half-inch size cutting inserts.

[0034] C / N Measurement Using Electron Probe Microanalysis (EPMA)

[0035] In order to determine the atomic C / N ratio of the Ti(C,N) layer portions T1 and T2, elemental analysis of the coating was performed by electron microprobe analysis using a JEOL electron microprobe JXA-8530F equipped with a wavelength dispersive spectrometer (WDS). A Ti(C,N) reference sample was used for calibration, and its composition was 10.22 wt% C, 10.68 wt% N, 78.86 wt% Ti and 0.24 wt% O. The analysis of each Ti(C,N) layer portion was performed on a polished cross section of the coating on the front face of the cutting tool. Mapping of titanium, carbon and nitrogen was performed over the entire layer thickness of the Ti(C,N) layer using 10 kV and 40 nA. The Ti, C and N contents of portions T1 and T2 of the Ti(C,N) layer were measured in the middle of the portions at at least 5 different positions separated by at least 5 μm. The thickness of each portion T1 and T2 was identified by line scanning. The atomic C / N ratio is preferably approximately constant within the respective portion, ie the ratio may vary, for example, by about ±2% within a portion.

[0036] Grain size of Ti(C,N) using XRD and Scherrer

[0037] In order to study the average grain size of Ti(C,N) grains with an average grain size less than about 75 nm (as can be found in the lower portion T1 of the Ti(C,N) layer in an embodiment of the present invention), X-ray diffraction (XRD) was performed on the back face using a PANalytical CubiX3 diffractometer equipped with a PIXcel detector. Since the layers above the Ti(C,N) layer will affect the intensity of X-rays entering the Ti(C,N) layer and leaving the entire coating, these need to be corrected by taking into account the linear absorption coefficients of the corresponding compounds in the layer. Alternatively, the above-mentioned layers, such as the Ti(C,N) portion T2, can be removed by methods that do not substantially affect the XRD measurement results (such as grinding or laser ablation).

[0038] The coated cutting tool was mounted in the sample holder, ensuring that the flank face of the sample was parallel to the reference surface of the sample holder and also ensuring that the flank face was at the proper height. Cu-Kα radiation was used for the measurements, using a voltage of 45 kV and a current of 40 mA. Anti-scatter slits and The diffraction intensity from the coated cutting tool was measured in the 2θ range of 20° to 140°, i.e., in the range of incident angle θ of 10 to 70°. Data analysis was performed using PANalytical's X'Pert HighScore Plus software, including background fitting, Cu-Kα2 stripping, and profile fitting of the data.

[0039] The grain size of the layer was calculated according to the Scherrer equation (Eq1) (Birkholz, 2006) using the full width at half maximum of the integrated peak of the profile fitting curve obtained from PANalytical's X'Pert High Score Plus software.

[0040] The average grain size D was then calculated from the full width at half maximum (FWHM) of the (422) peak according to the Scherrer equation: 422 :

[0041]

[0042] Where D 422 is the average grain size of Ti(C,N), K is the shape factor set here to 0.9, λ is the wavelength of the CuKα1 radiation set here to 1.5405 Å, B 422 is the FWHM value of (422) reflection, and θ is the Bragg angle, i.e. the angle of incidence.

[0043] The FWHM obtained from the measurement contains both the broadening from the instrument and the broadening caused by the small grain size. To compensate for this, the Gaussian approximation is used (Birkholz, 2006). 422 is the line width (in radians) at FWHM after subtracting the instrumental broadening (0.00174533 radians) and is defined in equation (3):

[0044]

[0045] Among them B 422 is the width (in radians) used for grain size calculation, FWHM obs is the measured width (in radians), FWHM ins is the instrument width in radians.

[0046] Grain Width Measurement Using Electron Backscatter Diffraction (EBSD)

[0047] The average grain width of Ti(C,N) grains in the uppermost region of Ti(C,N) T2, about 300 nm from the bonding layer, was determined in this paper by the average grain intercept (AGI) method, which is a technique to quantify the grain width by drawing a line on a micrograph, counting the number of times the line intersects the grain boundary, and finding the ratio of the intercept to the line length.

[0048] AGI = (number of intercepts) / (line length).

[0049] In order to clearly determine the grain boundaries of the T2 section, electron backscatter diffraction (EBSD) was performed on the coating cross section using a Zeiss Supra55 equipped with an Oxford Instruments Symmetry EBSD detector. The coating cross section was prepared for a CNMG120408-PM blade, which was baked in a black conductive phenolic resin from AKASEL, ground about 1 mm and polished in two steps: coarse polishing (9 μm) and fine polishing (1 μm) using a diamond slurry solution, followed by final polishing using a colloidal silica solution. After the final polishing step, the blade was removed from the conductive resin, cleaned in ethanol, dried with nitrogen and mounted on a 70° pre-tilted holder for EBSD analysis. The microscope was operated at an accelerating voltage of 15 kV, a beam current of 1.6 nA and a working distance of 13-15 mm. For data acquisition, a detector was used in a merged mode of 622x512 pixels for an area of ​​at least 12 μm in width and 2 μm in height, and analyzed with a step size of 15 nm. In this area, a line was placed about 300nm from the bonding layer, which was 12μm long. Three separate measurements were made in different analysis areas of the sample to obtain the average value of the grain width, Ti2CN (J Electrochem. Soc [JESOAN], (1950), Vol. 97, pp. 299-304) crystallographic structure data was used as a reference for the Ti (C, N) phase, and 44 reflectors were used for measurement. Aztec software version 3.0 was used to analyze the average grain width of the Ti (C, N) grains at the area closest to the bonding layer of part T2 by defining the grain boundary misorientation as 10° and counting the number of intercepts between the boundaries of the drawn lines defined along the EBSD (with contrast) map.

[0050] Orientation of the lowermost Al2O3 part A1

[0051] The portion of the Al2O3 layer close to the bonding layer has a very high orientation in the present invention. In order to analyze this area, a cross section of the coating was prepared, and the Al2O3 grains in the portion A1 extending 1 μm in height from the bonding layer were studied in detail by EBSD. The preparation of the polished cross section was carried out in the following manner: Each of the CNMG120408-PM blades was mounted in a black conductive phenolic resin from AKASEL, which was then ground for about 1 mm and then polished in two steps: coarse polishing (9 μm) and fine polishing (1 μm) using a diamond slurry solution. A final polish using a colloidal silica solution was applied.

[0052] The orientation of the lowermost portion of Al2O3 is determined as the fraction (in %) of the analyzed area that is within a certain angular deviation from a set axis. For portion A1, select <001> The Al2O3 direction is taken as the direction parallel to the surface normal. The orientation is calculated as the deviation from the set <001> The amount of the analyzed area with Al2O3 orientation ≤15°.

[0053] Areas of at least 80 μm width were analyzed with a step size of 50 nm, using speed 1 merge mode (622x512 pixels). To analyze the orientation of A1, four rectangular sections of A1 were randomly selected along the interface with dimensions of 10 μm wide and 1 μm high. The orientation was calculated as the average of the four rectangular sections. An automatic cleaning step and a zero solution removal using 5 nearest neighbor levels were applied to the data. Aztec Crystal software (v2.0) was used to determine the orientation.

[0054] The orientation of section A1 was analyzed using a Zeiss Supra55 and a Helios Nanolab 650, both equipped with Oxford-symmetry EBSD detectors. A 20 kV accelerating voltage and 13-26 nA beam current were used. The samples were mounted on a 70° pre-tilted sample holder to ensure maximum collection efficiency.

[0055] Alumina (α) (Acta Crystallogr, Sec B [ACBCAR], Vol. 49B, pp. 973-980) reference was used for Al2O3 measurements and 89 reflectors were used for the measurements.

[0056] SEM Research

[0057] SEM investigations of polished cross sections and upper surfaces of the samples were performed in a Carl Zeiss AG-Supra model 40, operated at 3 kV accelerating voltage with a 30 μm aperture size. Images were acquired using a secondary electron detector. Layer thicknesses were measured in SEM images of cross sections.

[0058] X-ray diffraction measurements of Ti(C,N) and Al2O3

[0059] To investigate the texture of the layers, X-ray diffraction was performed on the flank face of the cutting tool insert using a PANalytical CubiX3 diffractometer equipped with a PIXcel detector. The coated cutting tool insert was mounted in a sample holder ensuring that the flank face of the cutting tool insert was parallel to the reference surface of the sample holder and also ensuring that the flank face was at an appropriate height. Cu-Kα radiation was used for the measurements using a voltage of 45 kV and a current of 40 mA. Anti-scatter slits and The diffraction intensity from the coated cutting tool was measured in the 2θ range of 20° to 140°, i.e. in the range of incident angle θ of 10 to 70°.

[0060] Data analysis was performed using PANalytical's X'Pert HighScore Plus software, including background subtraction, Cu-K α2 Stripping and profile fitting. A general description of the fitting is given below. The output from the program (the integrated peak area of ​​the profile fitting curve) is then used to calculate the texture coefficient of the layer (such as a layer of Ti(C,N) or α-Al2O3) by comparing the measured intensity data with the ratio of the standard intensity data according to the PDF card for the specific layer (such as a layer of Ti(C,N) or α-Al2O3) using the Harris formula (2) as described above. Since the layer is of finite thickness, the relative intensity of a pair of peaks at different 2θ angles is different from their relative intensity for the bulk sample due to the difference in path length through the layer. Therefore, when calculating the TC value, a thin film correction is applied to the integrated peak area intensity of the extracted profile fitting curve taking into account the linear absorption coefficient of the layer. Since possible additional layers above, for example, the α-Al2O3 layer will affect the X-ray intensity entering the α-Al2O3 layer and leaving the entire coating, it is also necessary to correct these taking into account the linear absorption coefficients of the corresponding compounds in the layer. If the Ti(C,N) layer is located below, for example, the α-Al2O3 layer, the same applies to X-ray diffraction measurements of the Ti(C,N) layer. Alternatively, other layers (eg, TiN) above the aluminum oxide layer may be removed by methods (eg, chemical etching) that do not substantially affect the XRD measurement results.

[0061] In order to study the texture of α-Al2O3 layer, CuK α The X-ray diffraction of the radiation is carried out, and the texture coefficient TC (hkl) of the columnar grains of the α-Al2O3 layer in different growth directions is calculated according to the Harris formula (2), where I (hkl) = the measured (integrated area) intensity of the (hkl) reflection, I0 (hkl) = the standard intensity according to the PDF card number 00-010-0173 of the ICDD, and n = the number of reflections to be used in the calculation. In this case, the (hkl) reflections used are: (1 0 4), (1 1 0), (1 13), (0 2 4), (1 1 6), (2 1 4), (3 0 0) and (0 0 12). Before calculating the ratio, the measured integrated peak area is corrected for thin films and for any additional layers above the α-Al2O3 layer (i.e., on top).

[0062] The texture coefficient TC(hkl) of the columnar grains of the Ti(C,N) layer in different growth directions was calculated according to the previously published Harris formula (2), where I(hkl) is the measured (integrated area) intensity of the (hkl) reflection, I0(hkl) is the standard intensity according to the PDF card number 42-1489 of the ICDD, and n is the number of reflections to be used in the calculation. In this case, the (hkl) reflections used are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 2 0), and (4 2 2).

[0063] It should be noted that peak overlap is a phenomenon that may occur in X-ray diffraction analysis of coatings containing, for example, multiple crystalline layers and / or deposited on substrates containing crystalline phases, and this must be considered and compensated for. Overlap of peaks from α-Al2O3 layers with peaks from Ti(C,N) layers may affect the measurement and need to be considered. It should also be noted that, for example, WC in the substrate may have diffraction peaks that are close to the relevant peaks of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Embodiments of the present invention will be described with reference to the accompanying drawings, in which:

[0065] Figure 1 A scanning electron microscope (SEM) image of a cross section of an example sample 090 of the coating of the present invention is shown, wherein portions T1 and T2 of the Ti(C,N) layer, a bonding layer (B), a substrate (S) and a portion A1 of the α-Al2O3 layer are indicated,

[0066] Figure 2 Shows Figure 1 Close-up image of the T2 section of the sample shown,

[0067] Figure 3 A scanning electron microscope (SEM) image of a cross section of an example sample 045 of a coating of the present invention is shown,

[0068] Figure 4 Shows Figure 3 Close-up image of the T2 section of the sample shown in,

[0069] Figure 5 A scanning electron microscope (SEM) image of a cross section of a reference sample Ref 0 is shown,

[0070] Figure 6 Shows Figure 5 Close-up image of the outer portion of the Ti(C,N) layer of the sample shown in

[0071] Figure 7 A scanning electron microscope (SEM) image of a cross section of a reference sample (sample Ref260) is shown,

[0072] Figure 8 Shows Figure 7 Close-up image of the outer portion of the Ti(C,N) layer of the sample shown in .

[0073] Fig. 9 A forward scattering image of a cross section of an example sample 130 of the coating of the present invention is shown, which is acquired from a central low forward scattering detector (FSD) on an EBSD camera, provides orientation contrast, and reveals the grain structure on the Ti(C,N) layer, where portions T1 and T2 of the Ti(C,N) layer, a bonding layer (B), a substrate (S), and a portion A1 of the α-Al2O3 layer are indicated,

[0074] Fig.10 An EBSD-band contrast image of sample 130 is shown revealing the grain structure, wherein dark areas correspond to low band contrast values ​​and light areas correspond to high band contrast values,

[0075] Fig.11 EPMA carbon map from sample 090 is shown, with portions T1 and T2 of the Ti(C,N) layer, the bonding layer (B), the substrate (S) and portion A1 of the α-Al2O3 layer indicated,

[0076] Fig.12 The EPMA nitrogen map from sample 090 is shown.

[0077] Fig.13 The carbon map from EPMA of sample 130 is shown,

[0078] Fig.14 shows a nitrogen map of sample 130, and

[0079] Fig.15 A schematic diagram of one embodiment of a cutting tool (1) having a rake face (2) and a flank face (3) and a cutting edge therebetween is shown. DETAILED DESCRIPTION

[0080] Exemplary embodiments of the invention will now be disclosed in more detail and compared with reference embodiments. Coated cutting tools were manufactured and analyzed and tested in metal cutting tests.

[0081] Base

[0082] The cemented carbide substrate was manufactured using conventional methods including grinding, mixing, spray drying, pressing and sintering. The ISO type geometry of the cemented carbide substrate (insert) 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 balance WC.

[0083] Prior to coating deposition, the substrate was exposed to a light grit blasting treatment to remove any residues on the substrate surface from the sintering process.

[0084] CVD deposition

[0085] The sintered substrates were CVD coated in a radial CVD reactor of Bernex model size 530, which was capable of accommodating 10,000 half-inch size cutting inserts. The samples to be further tested and analyzed were selected from the middle of the chamber, at a position halfway along the plate radius between the center and the periphery of the plate. The mass flow controller was selected so that the flow rate of, for example, CH3CN was selected to match the flow rate in the CVD recipe.

[0086] A first innermost coating of about 0.3 μm TiN was deposited on all substrates using a deposition temperature of 885° C. and a pressure of 400 mbar. A gas mixture of 48.8 vol % H2, 48.8 vol % N2 and 2.4 vol % TiCl4 was used.

[0087] Ti(C,N) layer deposition was then performed and all samples were deposited with different Ti(C,N) recipes according to the following. Reference sample Ref260 was deposited with process step V followed by process step W as shown in Table 1. The Ti(C,N) layer of reference sample Ref0 was deposited with process step X as shown in Table 1. Ti(C,N) layers were deposited on samples 015, 020, 030, 045, 090, 130 using process step X followed by process step Z using the deposition times shown in Tables 1 and 2. Before the start of process step X for the relevant samples, a temperature adjustment from 885°C to 870°C was performed in 50 vol% H2 and 50 vol% N2 at 80 mbar. The layer thicknesses of the samples are shown in Table 4.

[0088]

[0089]

[0090] A 0.7-1.1 μm 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 HTCVD Ti(C,N) step with TiCl4, CH4, N2, HCl and H2 was performed at 400 mbar for 8 minutes, followed by a second step (Ti(C,N,O)-1) with TiCl4, CH3CN, CO, N2 and H2 at 70 mbar for 7 minutes, then a third step (Ti(C,N,O)-2) with TiCl4, CH3CN, CO, N2 and H2 at 70 mbar for 5 minutes, and finally a fourth step (TiN) with TiCl4, N2 and H2 at 70 mbar for 6 minutes. During the third deposition step, the CO gas flow was continuously and linearly increased from a starting value at the beginning of the process step to a stop value at the end of the process step, as shown in Table 3. All other gas flows were kept constant, but the concentrations of all gases were affected to some extent due to the increase in the total gas flow. Before the subsequent Al2O3 nucleation started, the bond coat was oxidized in a mixture of CO2, CO, N2 and H2 for 4 min.

[0091] Details of the tie layer deposition are shown in Table 3.

[0092]

[0093] An α-Al2O3 layer was deposited on top of the bonding layer. All α-Al2O3 layers were deposited in two steps at 1000°C and 55 mbar. The first step using 1.2% by volume AlCl3, 4.7% by volume CO2, 1.8% by volume HCl and balance H2 was performed for 30 minutes to obtain about 0.1 μm α-Al2O3. The treatment time of the second step was adjusted to obtain a total α-Al2O3 layer thickness of about 5 μm. The second step of depositing the α-Al2O3 layer was performed using 1.16% AlCl3, 4.65% CO2, 2.91% HCl, 0.58% H2S and balance H2.

[0094] Coating analysis results

[0095] The layer thickness was measured on the rake face of the cutting tool samples using a scanning electron microscope. The layer thickness of the samples is shown in Table 4.

[0096]

[0097] The thickness of the inner part T1 and the outer part T2 were measured in cross section by using line scanning and element mapping in EPMA and SEM. It can be noted that the bonding layer of the sample contains a HT-Ti(C,N) sublayer which is very common in the technical field of Ti(C,N) and α-Al2O3 coated cutting tools, and this HT-Ti(C,N) sublayer is very rich in nitrogen.

[0098] Average grain size measurements were performed with XRD on the Ref0 sample using the Scherrer equation, giving an average grain size of about 30 nm for T1 in all samples.

[0099] The average grain width of the Ti(C,N) grains in the portion T2 of the Ti(C,N) layer was measured using the method disclosed in the Methods section above. The results are shown in Table 5.

[0100] The C and N content measurements were performed according to the above methods. The atomic percentages of the elements were used in the ratio calculations.

[0101]

[0102] The texture coefficients of the Ti(C,N) and α-Al2O3 layers were analyzed using X-ray diffraction, and the results are shown in Table 6.

[0103] EBSD measurement of the inner aluminum oxide A1 was performed. The orientation of the α-Al2O3 grains in the inner portion A1 of the α-Al2O3 layer was analyzed. The results are shown in Table 6.

[0104]

[0105] Performance Testing

[0106] The cutting tool was first evaluated by exposure to abrasive wet blasting. The rake face of the cutting tool was blasted. The blasting slurry consisted of 20% by volume of aluminum oxide in water, and the angle between the rake face of the cutting blade and the direction of the blasting slurry was 90°. The distance between the gun nozzle and the surface of the blade was about 145 mm. For all samples, the slurry pressure on the gun was 1.8 bar, and the air pressure on the gun was 2.2 bar. The aluminum oxide grit was F230 mesh (FEPA 42-2:2006). The average time for blasting per unit area was 4.4 seconds. Sample Ref0 could not withstand wet blasting, and the coatings of samples 015 and 020 showed severe peeling. All other samples 030, 045, 090 and 130 and Ref260 withstood wet blasting without coating peeling.

[0107] The coated cutting tools were also tested in a face turning operation (from 180 mm diameter to 60 mm diameter) in workpiece material DIN C45E (a medium carbon alloy steel). The spindle speed was fixed at n = 120 rpm; therefore, the cutting speed was constantly varied from Vc, ~70 m / min (at 180 mm diameter) to Vc, ~20 m / min (at 60 mm diameter) along the face turning operation; the feed fn was constantly increased from 0.1 mm / rev (at 180 mm diameter) to 0.5 mm / rev (at 60 mm diameter) along the face turning operation; the cutting depth was 2 mm and no cutting fluid was used. Four samples of each variant were used in the test.

[0108] In order to measure the total area of ​​Ti(C,N) exposed on the rake face after the end turning operation, the insert was etched in an HCl (hydrochloric acid) solution for 15 minutes. In this sequence, a SEM study of the upper surface was performed using a Zeiss AG-Supra 40 model operating at an accelerating voltage of 10 kV using a 30 μm aperture size. Images were collected at 50X magnification using a backscattered electron detector. The images were then used to measure the area of ​​the peeled coating through image analysis software, where a larger measured area corresponds to more wear due to the smaller adhesion of the α-Al2O3 layer.

[0109] The coated cutting tools were further tested in longitudinal turning operations in workpiece material Ovako 825B (100CrMo7-3), a high alloy steel. The cutting speed Vc was 220 m / min, the feed fn was 0.3 mm / rev, the cutting depth was 2 mm, and a water miscible cutting fluid was used. Machining was continued for 14 minutes, and then the wear of the cutting tools was evaluated. One cutting edge per cutting tool was evaluated.

[0110] The wear of the cutting tool was evaluated after the longitudinal cutting test. In order to measure the total area of ​​Ti(C,N) exposed on the rake face, a SEM study of the upper surface was performed using a Zeiss AG-Supra40 model operated at 10 kV accelerating voltage using a 30 μm aperture size. Multiple images were collected at 250X magnification using a backscattered electron detector. The images were then used to measure the area of ​​exposed Ti(C,N) by image analysis software, where a larger measured area corresponds to more wear.

[0111] Wear after longitudinal turning operations was also studied by cross-sectioning of the crater area. A controlled cross section was produced on the rake face parallel to the chip flow direction using a FEI Helios FIB / SEM instrument. A cross section was produced at an exact location 550 μm from the main edge and 320 μm from the secondary edge with a length of 150 μm and a depth of about 18 μm, so that the entire coating and a portion of the substrate were visible. In order to protect the surface from ion beam damage, a thin Pt layer with a thickness of about 100 nm was first deposited onto the surface (150 μm long and 3.5 μm wide) using an electron beam, and then a thicker Pt layer (~3 μm) was deposited on top with the assistance of Ga ions. The cross section was produced in two steps, with coarse ion milling using a regular cross-section pattern with a 47 nA ion beam, followed by fine ion milling using a clean cross-section pattern at 9.2 nA. The cross section was then used to measure the area of ​​the Ti(C, N) layer using image analysis software, where a larger Ti(C, N) layer area means less wear.

[0112] The results of the cutting test are shown in Table 7.

[0113]

[0114] (na = not analyzed)

[0115] As can be seen from Table 7, all samples 030, 045, 090 and 130 show higher resistance to crater wear compared to the Ref260 reference sample.

[0116] While the present invention has been described in connection with various exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments; on the contrary, the invention is intended to cover various modifications and equivalent arrangements within the appended claims.

Claims

1. A coated cutting tool, comprising a substrate at least partially coated with a coating, the coating comprising a Ti(C,N) layer, an α-Al2O3 layer and a bonding layer therebetween, wherein the Ti(C,N) layer having a thickness of 3-20 μm, preferably 5-15 μm, most preferably 6-10 μm consists of columnar grains, wherein, when viewed in a direction from the substrate towards an outer surface of the tool, the Ti(C,N) layer comprises an inner Ti(C,N) portion T1 and a subsequent outer Ti(C,N) portion T2, the inner portion T1 having a thickness of 2.5-15 μm, preferably 3-10 μm, the outer portion T2 The thickness is 0.5-5μm, preferably 0.5-3.5μm, wherein the average grain width of the Ti(C,N) grains in the inner Ti(C,N) portion T1 is less than 300nm, preferably <200nm, more preferably <100nm, and the average grain width of the Ti(C,N) grains in the outer Ti(C,N) portion T2 is less than 300nm, preferably <200nm, wherein the atomic ratio C / N in the inner Ti(C,N) portion T1 is 1.50-1.60, and wherein the atomic ratio C / N in the outer Ti(C,N) portion T2 is 1.25-1.40, preferably 1.27-1.

36.

2. The coated cutting tool according to claim 1, wherein an average grain width of Ti(C,N) grains in the inner Ti(C,N) portion T1 is smaller than an average grain width of Ti(C,N) in the outer Ti(C,N) portion T2.

3. A coated cutting tool according to any one of claims 1-2, wherein the Ti(C,N) layer comprises an outer portion T2 adjacent to the bonding layer, wherein the Ti(C,N) grains in the uppermost region of T2 have an average grain width of 90-250 nm, preferably 100-200 nm.

4. The coated cutting tool according to any of the preceding claims, wherein the average grain width of the Ti(C,N) grains in the inner Ti(C,N) portion T1 is <100 nm.

5. The coated cutting tool according to any one of the preceding claims, wherein the average grain size D of the inner Ti(C,N) portion T1 of the Ti(C,N) layer is 0.1447 W / cm2 when measured by X-ray diffraction using CuKα radiation. 422 The grain size D is 25-50nm. 422 The full width at half maximum (FWHM) of the (422) peak was calculated according to the Scherrer equation: Where D 422 is the average grain size of Ti(C,N), K is the shape factor set here to 0.9, λ is the wavelength of the CuKα radiation set here to 1.5405 Å, B 422 is the FWHM value of the (422) reflection, and θ is the Bragg angle.

6. The coated cutting tool according to any of the preceding claims, wherein the thickness of the α-Al2O3 layer is 1-15 μm, preferably 3-9 μm.

7. A coated cutting tool according to any one of the preceding claims, wherein the α-Al2O3 layer exhibits a texture coefficient TC(hkl) defined according to the Harris formula when measured by X-ray diffraction using CuKα radiation and θ-2θ scanning, where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to PDF card number 00-010-0173 of the ICDD, n = number of reflections, and the reflections used are: (1 0 4), (1 1 0), (1 1 3), (0 2 4), (11 6), (2 1 4), (3 0 0) and (0 0 12), where TC(0 0 12) is the maximum texture coefficient.

8. The coated cutting tool according to any of the preceding claims, wherein the TC(0012) of the α-Al2O3 layer is >7.7, preferably >7.

8.

9. The coated cutting tool according to any of the preceding claims, wherein the α-Al2O3 layer comprises a portion A1 extending 1 μm from the bonding layer, wherein the portion A1 is measured on a cross section of the α-Al2O3 layer using electron backscatter diffraction (EBSD), wherein the surface normal of the α-Al2O3 layer is parallel to the surface normal of the substrate surface, and the portion A1 exhibits an orientation wherein ≥70%, preferably ≥80%, more preferably ≥90%, most preferably ≥95% of the analyzed area has a surface normal within 15 degrees from the surface normal of the α-Al2O3 layer. <001> direction.

10. A coated cutting tool according to any one of the preceding claims, wherein the Ti(C,N) layer exhibits a texture coefficient TC(hkl) defined according to Harris formula (2) when measured by X-ray diffraction using CuKα radiation and θ-2θ scanning, wherein I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to PDF card number 42-1489 of the ICDD, n is the number of reflections, and the reflections used in the calculation are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 2 0) and (4 2 2), wherein TC(422)>3.

11. The coated cutting tool according to any one of the preceding claims, wherein the TC(422)+TC(311) of the Ti(C,N) layer is 5-6.

12. The coated cutting tool according to any one of the preceding claims, wherein the bonding layer comprises at least one compound selected from the group consisting of titanium oxycarbide, titanium oxynitride and titanium oxycarbonitride, preferably the bonding layer has a thickness of 0.5-2 μm.

13. A coated cutting tool according to any one of the preceding claims, wherein the coating comprises an innermost TiN layer, the TiN layer preferably having a thickness of 0.1 - 0.5 μm.

14. The coated cutting tool according to any one of the preceding claims, wherein the substrate of the coated cutting tool is selected from the group of cemented carbide and cermet.

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