Cutting tool with textured alumina layer

Abstract

A coated cutting tool has a substrate of cemented carbide, cermet, ceramics, steel or cubic boron nitride and a multi-layered wear resistant coating deposited thereon has a total thickness from 4 to 25 μm. The multi-layered wear resistant coating includes a TiAlCN layer (a) represented by the formula Ti1-xAlxCyNz with 0.2≤x≤0.97, 0≤y≤0.25 and 0.7≤z≤1.15 deposited by CVD, and a κ-Al.sub.2O.sub.3 layer (b) of kappa aluminium oxide deposited by CVD immediately on top of the TiAlCN layer (a). The Ti1-AlxCyNz layer (a) has an overall fiber texture with the {111} plane growing parallel to the substrate surface and a {111} pole figure, measured over an angle range of 0°≤α≤80° and the κ-Al2O3 layer (b) has an overall fiber texture with the {002} plane growing parallel to the substrate surface and a {002} pole figure, over an angle range of 0°≤α≤80°.

Claims

1. A coated cutting tool comprising: a substrate of cemented carbide, cermet, ceramics, steel or cubic boron nitride, the substrate having a surface; and a multi-layered wear resistant coating deposited by chemical vapour deposition (CVD) and having a total thickness from 4 to 25 μm, the multi-layered wear resistant coating comprising a TiAlCN layer (a) represented by the formula Ti.sub.1-xAl.sub.xC.sub.yN.sub.z with 0.2≤x≤0.97, 0≤y≤0.25 and 0.7≤z≤1.15 deposited by CVD, and a κ-Al.sub.2O.sub.3 layer (b) of kappa aluminium oxide deposited by CVD immediately on top of the TiAlCN layer (a), and wherein the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a) has an overall fiber texture with a {111} plane growing parallel to the substrate surface, the fiber texture in a {111} pole figure of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a), measured by X-ray diffraction or electron backscatter diffraction over an angle range of 0°≤α≤80°, having an intensity maximum within ≤10° tilt angle from a sample normal, and having ≥50% of a relative intensity measured over an angle range of 0°≤α≤60° within ≤20° tilt angle from the sample normal, and wherein the κ-Al.sub.2O.sub.3 layer (b) has an overall fiber texture with a {002} plane growing parallel to the substrate surface, the fiber texture in a {002} pole figure of the κ-Al.sub.2O.sub.3 layer (b), measured by X-ray diffraction or electron backscatter diffraction over an angle range of 0°≤α≤80°, having an intensity maximum within ≤10° tilt angle from the sample normal, and having ≥50% of the relative intensity measured over an angle range of 0°≤α≤80° within ≤20° tilt angle from the sample normal.

2. The coated cutting tool of claim 1, wherein the fiber texture of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a) with the {111} pole figure of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a), measured by X-ray diffraction or electron backscatter diffraction, having an intensity maximum within ≤5° tilt angle from the sample normal.

3. The coated cutting tool of claim 1, wherein the fiber texture of the κ-Al.sub.2O.sub.3 layer (b) with the {002} pole figure of the κ-Al.sub.2O.sub.3 layer (b), measured by X-ray diffraction or electron backscatter diffraction, having an intensity maximum within ≤5° tilt angle from the sample normal.

4. The coated cutting tool of claim 1, wherein, within a distance of 30 nm from an interface of the TiAlCN layer (a) and the κ-Al.sub.2O.sub.3 layer (b), the TiAlCN layer (a) has a chemical composition Ti.sub.1-uAl.sub.uC.sub.vN.sub.w with a higher Ti content than an average composition of the TiAlCN layer (a), as represented by Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, the difference (x−u) being greater than or equal to 0.04, with 0.16≤u≤0.93, 0≤v≤0.25 and 0.7≤w≤1.15.

5. The coated cutting tool of claim 1, wherein the surface of the TiAlCN layer (a) forming the interface to the κ-Al.sub.2O.sub.3 layer (b) is terminated by facets of {100} crystallographic planes.

6. The coated cutting tool of claim 1, wherein >90% of the TiAlCN layer (a) has face centered cubic (fcc) crystal structure.

7. The coated cutting tool of claim 1, wherein the TiAlCN layer (a) has a lamellar structure of alternating TiAlCN sub-layers of different Ti and Al stoichiometric contents, and wherein each of the TiAlCN sub-layers have a thickness of 150 nm or less.

8. The coated cutting tool of claim 1, wherein between grains of the TiAlCN layer (a) having a face centered cubic (fcc) crystal structure and being represented by the formula Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, there are grain boundary precipitates having a chemical composition Ti.sub.1-oAl.sub.oC.sub.pN.sub.q with a higher Al content than the average composition of the TiAlCN layer (a), as represented by Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, characterized by a difference (o−x)≥0.05, with 0.25≤o≤1.05, 0≤p≤0.25 and 0.7≤q≤1.15.

9. The coated cutting tool of claim 1, wherein the thickness of the TiAlCN layer (a) is from 2 μm to 14 μm.

10. The coated cutting tool of claim 1, wherein the thickness of the κ-Al.sub.2O.sub.3 layer (b) is from 1 μm to 9 μm.

11. The coated cutting tool of claim 1, wherein the multi-layered wear resistant coating includes, in addition to the TiAlCN layer (a) and the κ-Al.sub.2O.sub.3 layer (b), between the substrate surface and the TiAlCN layer (a) and/or above the κ-Al.sub.2O.sub.3 layer (b), one or more refractory layer(s) selected from oxide, carbide, nitride, oxycarbide, oxynitride, carbonitride, oxycarbonitride or borocarbonitride of one or more of the elements of groups 4A, 5A or 6A of the periodic table or Al or Si, or combinations thereof, being deposited by chemical vapour deposition (CVD), and each refractory layer having a thickness of from 0.5 to 6 μm.

12. The coated cutting tool of claim 1, wherein the multi-layered wear resistant coating includes an outermost top coating having a thickness between 0.1 to 3 μm, selected from TiN, TiC, TiCN, ZrN, ZrCN, HfN, HfCN, VC, TiAlN, TiAlCN, AN and combinations or multilayers thereof.

13. The coated cutting tool of claim 1, wherein a first refractory layer immediately on top and in contact with the substrate surface is selected from Ti(C,N), TiN, TiC, Ti(B,C,N), HfN, Zr(C,N) and combinations thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a SEM image of a cross section of the coating of Example 1 (Invention), prepared as described below.

(2) FIG. 2 (a) shows the {111} pole figure of the TiAlN layer of the coating of Example 1 (Invention) measured by X-ray diffraction over an angle range of 0°≤α≤80° (increment 50) and 0°≤β≤360° (increment 50); measured intensities are represented by isolines; the dotted circles represent the radial angles from 10 to 70 degrees, the dashed circle represents the radial angle of 80 degrees, and the unbroken circle represents the radial angle of 90 degrees;

(3) FIG. 2 (b) shows a cross section through the pole figure of FIG. 2 (a) over the range of the alpha-angle from 0 to 90 degrees at a fixed beta angle of 0°; the abscissa shows the angle range from 0 to 90 degrees, and the ordinate shows the measured relative intensities;

(4) FIG. 3 (a) shows the {002} pole figure of the κ-Al.sub.2O.sub.3 layer of the coating of Example 1 (Invention) measured by X-ray diffraction over an angle range of 0°≤α≤80° (increment 50) and 0°≤β≤360° (increment 50); measured intensities are represented by isolines; the dotted circles represent the radial angles from 10 to 70 degrees, the dashed circle represents the radial angle of 80 degrees, and the unbroken circle represents the radial angle of 90 degrees;

(5) FIG. 3 (b) shows a cross section through the pole figure of FIG. 3 (a) over the range of the alpha-angle from 0 to 90 degrees at a fixed beta angle of 0°; the abscissa shows the angle range from 0 to 90 degrees, and the ordinate shows the measured relative intensities;

(6) FIG. 4 shows a SEM image of a cross section of the coating of Example 2 (Comparative Example), prepared as described below.

(7) FIG. 5 (a) shows the {111} pole figure of the TiAlN layer of the coating of Example 2 (Comparative Example) measured by X-ray diffraction over an angle range of 0°≤α≤80° (increment 50) and 0°≤β≤360° (increment 50); measured intensities are represented by isolines; the dashed circle represents the radial angle of 80 degrees, and the unbroken circle represents the radial angle of 90 degrees (this representation does not comprise dotted circles representing the radial angles from 10 to 70 degrees);

(8) FIG. 5 (b) shows a cross section through the pole figure of FIG. 5 (a) over the range of the alpha-angle from 0 to 90 degrees at a fixed beta angle of 0°; the abscissa shows the angle range from 0 to 90 degrees, and the ordinate shows the measured relative intensities;

(9) FIG. 6 (a) shows the {002} pole figure of the κ-Al.sub.2O.sub.3 layer of the coating of Example 2 (Comparative Example) measured by X-ray diffraction over an angle range of 0°≤α≤80° (increment 50) and 0°≤β≤360° (increment 50); measured intensities are represented by isolines; the dotted circles represent the radial angles from 10 to 70 degrees, the dashed circle represents the radial angle of 80 degrees, and the unbroken circle represents the radial angle of 90 degrees;

(10) FIG. 6 (b) shows a cross section through the pole figure of FIG. 6 (a) over the range of the alpha-angle from 0 to 90 degrees at a fixed beta angle of 0°; the abscissa shows the the angle range from 0 to 90 degrees, and the ordinate shows the measured relative intensities;

DEFINITIONS AND METHODS

(11) Fiber Texture

(12) The term “fiber texture” or “texture”, respectively, as used herein and as it is generally used in connection with thin films produced by vapor deposition, distinguishes the orientation of the grown grains from random orientation. Three types of textures are usually distinguished in thin films and coatings: (i) random texture, when grains have no preferred orientation; (ii) fiber texture, where the grains in the coating are oriented such that one set of geometrically equivalent crystallographic planes {hkl}, defined by the Miller indices, h, k and l, is found to be preferentially oriented parallel to the substrate surface plane, while there is a rotational degree of freedom of the grains around the fiber axis which is perpendicular to this plane, and (iii) epitaxial alignment (or in-plane texture) on single-crystal substrates, where an in-plane alignment fixes all three axes of the grain with respect to the substrate. In the context of the present application, the term “texture” is used synonymously for “fiber texture”.

(13) X-Ray Diffraction (XRD) Measurements

(14) X-ray diffraction measurements were done on a XRD3003 PTS diffractometer of GE Sensing and Inspection Technologies using CuKα-radiation. The X-ray tube was run in point focus at 40 kV and 40 mA. A parallel beam optic using a polycapillary collimating lens with a measuring aperture of fixed size was used on the primary side whereby the irradiated area of the sample was defined in such manner that a spill over of the X-ray beam over the coated face of the sample is avoided. On the secondary side a Soller slit with a divergence of 0.4° and a 25 μm thick Ni K.sub.β filter were used.

(15) Pole Figures

(16) Pole figures of a particular {hkl} reflection of the analysed layer were measured using XRD, as described herein, over an angle range of 0°≤α≤80° (increment 50) and 0°≤β≤360° (increment 50) with a circular arrangement of the measurement points. For background correction of the measured intensities the background intensity was measured for each increment of a at a fixed 2θ angle which does not overlap with diffraction peaks of any of the other coating layers or the substrate. No defocusing correction was applied. If the intensity distribution of all measured and back-calculated pole figures was approximately rotationally symmetrical, the investigated layer exhibited fibre texture.

(17) For the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layers, pole figures may alternatively be generated from EBSD maps of the specimens with the layer being polished parallel to the substrate surface to approximately 20-80% remaining layer thickness and adequate smoothness, typically using grid sizes≤0.075 μm, map sizes≥25 μm×25 μm. When orientation maps with sufficient quality of diffraction patterns and indexing are obtained, the texture of fcc-Ti.sub.1-xAl.sub.xC.sub.yN.sub.z within the layer may be calculated and pole figures may be plotted using commercially available software (e.g. EDAX OIM Analysis). For κ-Al.sub.2O.sub.3 layers, acquisition and correct indexing of Kikuchi diffraction patterns is often hindered by the high density of twins or other stacking faults within the grains of the polycrystalline layer. Therefore, XRD measurements are recommended for a safe determination of texture in this case. A detailed procedure of EBSD sample preparation, measurement and processing for the determination of the minimum content of fcc-phase in the TiAlCN layer is given below, and from the data sets acquired according to this procedure the texture may be determined as well. Generally, it is within the purview of the person skilled in the art to perform specimen preparation, EBSD measurement and data processing in an appropriate manner.

(18) For checking and confirming the preferential crystallographic orientation of a {hkl} crystal plane, additional pole figures were measured from at least two further reflections for cubic crystal systems or from at least three further reflections for other (non-cubic) crystal systems, respectively. From the data of a sufficient number of XRD pole figure measurements the orientation density distribution function (ODF) was calculated using the software LaboTex3.0 from LaboSoft, Poland, and the preferential crystallographic orientation could be represented by an inverse pole figure. The presentation of the ODF as an inverse pole figure is suitable to demonstrate the crystallographic orientation and sharpness of a fiber texture present in the sample. In EBSD (electron backscatter diffraction) measurements, the ODF may be calculated from a statistically relevant number of individual local orientation measurements using commercially available EBSD data processing software, e.g. EDAX OIM Analysis. [L. Spieß et al., Moderne Röntgenbeugung, 2.sup.nd edition, Vieweg & Teubner, 2009].

(19) Transmission Electron Microscopy (TEM) EDS Analysis

(20) Transmission electron microscopic (TEM) analyses were performed in a FEI Titan 80-300 microscope with field emission cathode at an acceleration voltage of 300 kV. For EDS analyses an Oxford Inca EDS system was used. The preparation of samples for TEM was made by the in-situ lift-out technique using a combined FIB/SEM equipment to cut a thin cross sectional piece out of the surface and thin the sample down to sufficient electron transparency.

(21) Electron Backscatter Diffraction (EBSD)

(22) EBSD analysis was performed in a Zeiss SUPRA40VP scanning electron microscope (SEM) with a field emission cathode using a 60 μm aperture and 15 kV acceleration voltage working in high current mode with a 70° incident angle of the electron beam to the polished samples surface at about 12 mm working distance. The EBSD system was EDAX (Digiview camera), and the TSL OIM Data Collection 7 and TSL OIM Analysis 7 software packages were used for data collection and analysis, respectively.

(23) Crystal Structure Determination by Electron Backscatter Diffraction (EBSD)

(24) The percentage of face-centered cubic (fcc) crystal structure of the Ti.sub.1-xAl.sub.xC.sub.yN of layer (b) was determined by EBSD analysis on polished cross-sections of the samples. The polishing was done according to the following procedure: 6 min grinding using a grinding disc Struers Piano 220 and water; 3 min polishing using Struers 9 μm MD-Largo diamond suspension; 3:40 min polishing using Struers 3 μm MD-dac diamond suspension; 2 min polishing using Struers 1 μm MD-Nap diamond suspension; at least 12 min chemical polishing using Struers OP-S colloidal silica suspension with 0.04 μm average particle size. Prior to SEM/EBSD analysis the specimens were ultrasonically cleaned in ethanol and demagnetized. Inspection of the accordingly prepared specimens in the FE-SEM (typically using an Everhart-Thornley secondary electron detector at 2.5 kV acceleration voltage and working distances of 3-10 mm) showed that grains of face centered cubic Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layers are polished to a flat surface, showing a pronounced orientation contrast, whereas layers of h-AlN or h-AlN precipitated at grain boundaries of fcc-Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layers are etched considerably stronger than fcc-phase grains, and therefore the surface of these proportions of the coating is lower than the fcc phase, and does not have a flat surface. Due to this topography, proportions in the coating which consist of h-AlN will give poor EBSD patterns in the EBSD analysis described below.

(25) Typical acquisition and processing parameters for the EBSD maps are as follows: The map size is at least 50×30 μm with 50.15 μm step size and a hexagonal grid of measurement points. A 4×4 or 8×8 binning and optionally a dynamic background subtraction is performed on the camera picture, using exposure times corresponding to 20 to 100 frames per second. However, as a rule, the preparation procedure described above yielded samples which gave diffraction patterns of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layers with sufficient quality without performing background subtraction procedures.

(26) Indexing of the diffraction pattern is done by Hough transformation. The data points thus recorded should ideally be indexed with an average confidence index (CI) of >0.2. The CI is calculated by the TSL OIM Analysis 7 software during automated indexing of the diffraction pattern. For a given diffraction pattern several possible orientations may be found which satisfy the diffraction bands detected by the image analysis routines. The software ranks these orientations (or solutions) using a voting scheme. The confidence index is based on the voting scheme and is given as CI=(V.sub.1−V.sub.2)/V.sub.IDEAL where V.sub.1 and V.sub.2 are the number of votes for the first and second solutions and V.sub.IDEAL is the total possible number of votes from the detected bands. The confidence index ranges from 0 to 1. Even though there are cases when a pattern may still be correctly indexed even at a confidence index of 0, the CI can be regarded as statistical a measure for the pattern quality.

(27) Samples with rough surfaces have to be polished to a roughness in order to get satisfactory pattern quality and indexing for EBSD. A CI value greater than 0.3 corresponds to 99% accuracy of the automated pattern indexing, and generally patterns indexed with a CI>0.1 are considered to be correct.

(28) In a first step, the EBSD map is cropped to get only the data points of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (b) to be analysed. In a second step, grain CI standardization is carried out applying a grain tolerance angle of 5° and a minimum grain size of 5 data points. In a third step, partitioning of the so generated data set is carried out applying the filter CI>0.1, i.e. all data points that, after grain CI standardization, have a lower confidence index are disregarded. The ratio (number of data points indexed as fcc phase after CI standardization and filtering/total number of data points in the cropped map) corresponds to an area ratio of fcc phase within the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer analysed (given in area-%). However, since pattern overlap and topography at grain boundaries lead to poor indexing of EBSD patterns obtained from fcc phase Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, the values thus obtained represent a minimum fraction of fcc phase in the layer, the actual fraction being higher. Typically in Ti.sub.1-xAl.sub.xC.sub.yN.sub.z coatings where XRD and SEM gives no indication of h-AlN, and which therefore consist practically of about 100% fcc phase, the EBSD measurement and processing method described above yields>95 area-% of the EBSD map indexed as fcc phase.

EXAMPLES

(29) Sample Preparation

(30) For the preparation of cutting tools according to the present invention and of comparative examples cemented carbide cutting tool substrate bodies (composition: 90.5 wt-% WC, 1.5 wt-% TaC+NbC and 8.0 wt-% Co; geometry: SEHW1204AFN) were coated in a cylindrical CVD reactor, type Bernex BPX 325S, having a height of 1250 mm and a diameter of 325 mm.

(31) The gas flow over the substrate bodies was conducted radially from a central gas distribution tube, using a first and second precursor gas streams, PG1 and PG2. The first and second precursor gas streams, PG1 and PG2, were introduced into the reactor separately and combined immediately before entry into the reaction zone, i.e. after the outlet of the gas distribution tube.

(32) The Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a) according to the present invention is deposited at a temperature in the range of 600° C. to 900° C. Depending on the desired layer composition, the reaction gases comprise TiCl.sub.4, AlCl.sub.3, CH.sub.3CN, NH.sub.3, N.sub.2, H.sub.2.

(33) The κ-Al.sub.2O.sub.3 layer (b) is then deposited directly on top of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a) at a temperature in the range of 600° C. to 950° C. The reaction gases comprise AlCl.sub.3, COO.sub.2 and H.sub.2, and may additionally comprises CO, HCl, H.sub.2S and/or SF.sub.6. The deposition of the κ-Al.sub.2O.sub.3 layer (b) was typically carried out in two deposition steps, wherein in the first step a nucleation layer is grown, and in the second step the κ-Al.sub.2O.sub.3 layer is grown to the desired thickness. In the second step H.sub.2S and/or SF.sub.6 was used as a catalyst. It is also within the scope of this invention to grow the κ-Al.sub.2O.sub.3 layer without using the said first deposition step, however, in that case a higher amount of porosity at the interface between the lower Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer (a) and the κ-Al.sub.2O.sub.3 layer (b) was observed.

(34) The example coatings according to the invention and the comparative examples have been obtained using the herein described equipment and the process conditions as given in the following table 1. However, it is well known in the art that the process conditions to produce CVD coatings may to a certain degree vary depending on the equipment used. It is therefore within the purview of the person skilled in the art to modify the deposition conditions and/or the equipment used to achieve the coating properties of the present invention.

(35) Cross-section SEM microphotographs were prepared from the example coatings and are shown in FIGS. 1 and 4. Pole figures from the TiAlN layers and the κ-Al.sub.2O.sub.3 layers of the example coatings were measured and are shown in FIGS. 2, 3, 5 and 6.

(36) The position (tilt angle) of an intensity maximum relative to the sample normal in the {111} pole figures of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer and in the {002} pole figures of the κ-Al.sub.2O.sub.3 layer for the coatings of example 1 (Invention) and example 2 (Comparative Example) are shown in Table 2. Table 2 also shows the relative intensity within ≤20 tilt angle from the sample normal as measured over an angle range of 0°≤α≤60° in the {111} pole figures of the Ti.sub.1-xAl.sub.xC.sub.yN layer and as measured over an angle range of 0°≤α≤80° in the {002} pole figures of the κ-Al.sub.2O.sub.3 layer for the coatings of Example 1 (Invention) and Example 2 (Comparative Example).

(37) TABLE-US-00001 TABLE 1 Process Conditions Gas concentration (volume %) Precursor Precursor gas stream gas stream Coating Time Thickness Temperature Pressure (PG1) (PG2) (deposition step) [min] [μm] [° C.] [kPa] TiCl.sub.4 AlCl.sub.3 HCl CO.sub.2 CO H.sub.2S N.sub.2 H.sub.2 NH.sub.3 H.sub.2 Example 1 (Invention) TiN 90 0.5 850 15 1.03 0 0 0 0 0 44.0 33.0 0 22.0 Ti.sub.1−xAl.sub.xN 75 4 675 0.38 0.028 0.23 0 0 0 0 0 49.5 1.09 49.2 κ-Al.sub.2O.sub.3 (nucleation step) 30 2 850 7.5 0 1.32 1.32 1.84 1.32 0 13.2 54.2 0 27.1 κ-Al.sub.2O.sub.3 (growth step) 210 850 10 0 0.93 1.16 2.32 1.16 0.35 0 70.5 0 23.5 Example 2 (Comparative Example) TiN (step 1) 100 2.6 815 15 1.03 0 0 0 0 0 44.0 33.0 0 22.0 TiN (step 2) 75 790 2 0.44 0 0 0 0 0 43.3 32.5 2.16 21.6 Ti.sub.1−xAl.sub.xN 10 0.5 700 1 0.014 0.23 0 0 0 0 0 49.5 1.09 49.2 κ-Al.sub.2O.sub.3 (nucleation step) 30 2 850 7.5 0 1.32 1.32 1.84 1.32 0 13.2 54.2 0 27.1 κ-Al.sub.2O.sub.3 (growth step) 210 850 10 0 0.93 1.16 2.32 1.16 0.35 0 70.5 0 23.5

(38) TABLE-US-00002 TABLE 2 Pole figure data Example 1 Example 2 Sample (Invention) (Comparative) Ti.sub.1−xAl.sub.xC.sub.yN.sub.z layer Position of intensity maximum in 0° 65° {111} pole figure Percentage of relative intensity of 78.2% 21.5% {111} pole figure within ≤20° tilt angle from sample normal (0° ≤ α ≤ 60°) κ-Al2O3 layer Position of intensity maximum in 0° 15° {002} pole figure Percentage of relative intensity of 71.2% 30.4% {002} pole figure within ≤20° tilt angle from sample normal (0° ≤ α ≤ 80°)
Cutting Tests

(39) The cutting tools prepared according to Example 1 (Invention) and Example 2 (Comparative Example) were used in milling operations under the following conditions:

(40) Workpiece material: Steel (DIN 42CrMo4)

(41) Coolant: none

(42) Feed per tooth: f.sub.z=0.2 mm

(43) Depth of cut: a.sub.p=3 mm

(44) Cutting speed: v.sub.c=283 m/min

(45) Setting angle: κ=45°

(46) The development of the maximum flank wear, V.sub.Bmax, on the main cutting edge and the number of comb cracks were observed over a milling distance of 4000 mm in 800 mm steps. The following table 3 shows the development of V.sub.Bmax and the number of comb cracks over the milling distance. In the milling test the cutting tool with the coating according to the present invention showed a significantly higher resistance against flank wear and against the formation of comb cracks than the comparative example.

(47) TABLE-US-00003 TABLE 3 Cutting Test Results Example 1 Example 2 (Invention) (Comparative Example) Milling Maximum Maximum Distance Flank Number of Flank Number of [mm] Wear V.sub.Bmax Comb Cracks Wear V.sub.Bmax Comb Cracks 0 0 0 0 0 800 0.02 0 0.02 1 1600 0.04 0 0.06 1 2400 0.08 0 0.12 3 3200 0.12 1 0.20 3 4000 0.16 1 0.34 4