COATED CUTTING TOOL

Abstract

A coated cutting tool consisting of a substrate and a multi-layered wear resistant hard coating and a process for manufacturing the same is provided. The layers of the hard coating are deposited by chemical vapour deposition (CVD) and include a TiCN layer with a multi-sublayer structure of alternating C-type and N-type sublayers and an overall fiber texture characterized by a texture coefficient TC (4 2 2) in the range from 3.0 to 5.5, an oxygen containing Ti or Ti+Al compound bonding layer, and an -Al.sub.2O.sub.3 layer on top of the bonding layer with an overall fiber texture characterized by a texture coefficient TC (0 0 12)>5.

Claims

1. A coated cutting tool for chip-forming metal machining consisting of a substrate and a multi-layered wear resistant hard coating, comprising: a) a TiCN layer having a total thickness of from 2 m to 20 m, wherein the TiCN layer has a multi-sublayer structure of a total of p alternating C-type and N-type sublayers with p being an even or odd number in the range from 5 to 25, preferably wherein the C-type and N-type sublayers have different stoichiometries with respect to an atomic ratio of carbon and nitrogen, with the C-type TiCN sublayers having a C/N ratio in the range of 1.0C/N2.0, and the N-type TiCN sublayers having a C/N ratio in the range of 0.5C/N<1.0, and with a difference between the C/N ratio of adjacent C-type and N-type layers being 0.2, and wherein the TiCN layer has an overall fiber texture characterized by a texture coefficient TC (4 2 2) in the range from 3.0 to 5.5, the TC (4 2 2) being defined as follows: $TC\left(422\right)=\frac{I\left(422\right)}{I_0\left(422\right)}.Math.{\left(\frac{1}{n}.Math.\underset{1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hkl}\right)}{I_0\left(hkl\right)}\right)}^{-1}$ wherein I(h k l)=XRD intensity of the (h k l) reflection I.sub.0(h k l)=standard intensity of the standard powder diffraction data according to lCDD's PDF-card no 01-071-6059 n=7=number of reflections used in the calculation, whereby the seven (h k l) 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); b) a single-layer or multi-sublayer oxygen containing Ti or Ti+Al compound bonding layer on top of the TiCN layer with a total thickness of from 0.5 m to 3 m; and c) an -Al.sub.2O.sub.3 layer on top of the bonding layer with a total thickness of from 2 m to 15 m, wherein the -Al.sub.2O.sub.3 layer has an overall fiber texture characterized by a texture coefficient TC (0 0 12)>5, the TC (0 0 12) being defined as follows: $\mathrm{TC}\left(0012\right)=\frac{I\left(0012\right)}{I_0\left(0012\right)}.Math.{\left(\frac{1}{n}.Math.\underset{1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hkl}\right)}{I_0\left(hkl\right)}\right)}^{-1}$ wherein I(h k l)=XRD intensity of the (h k l) reflection I.sub.0(h k l)=standard intensity measured on the NIST standard powder SRM676a n=8=number of reflections used in the calculation, whereby the eight (h k l) reflections used are: (1 0 4), (1 1 0), (1 1 3), (0 2 4), (1 1 6), (3 0 0), (0 0 12) and (0 1 14), the standard intensities having the following values: TABLE-US-00009 {h k l} {1 0 4} {1 1 0} {1 1 3} {0 2 4} {1 1 6} {3 0 0} {0 0 12} {0 1 14} I.sub.0 (h k l) 87.93 37.68 100.00 45.76 92.43 53.93 2.05 5.16

2. The coated cutting tool of claim 1, wherein at least one base layer of TiN or TiC is deposited immediately on the substrate surface and underneath the TiCN layer, the base layer having a thickness in the range from 0.3 to 1.5 m, or from 0.3 to 1.0 m, or from 0.3 to 0.7 m.

3. The coated cutting tool of claim 1, wherein the TiCN layer has an overall fiber texture characterized by a texture coefficient TC (4 2 2) in the range from 3.5 to 5.5 or from 4.0 to 5.3.

4. The coated cutting tool of claim 1, wherein in the multi-sublayer structure of the TiCN layer in a growth direction the first sublayer on top of the base layer and a final sublayer underneath the bonding layer are C-type layers.

5. The coated cutting tool of claim 1, wherein in the multi-sublayer structure of the TiCN layer each N-type sublayer has a thickness of less than 50%, or less than 40%, or less than 30% of each of the adjacent C-type sublayers.

6. The coated cutting tool of claim 1, wherein in the multi-sublayer structure of the TiCN layer each N-type sublayer has a thickness of at least 0.05 m, or at least 0.1 m, or at least 0.2 m.

7. The coated cutting tool of claim 1, wherein in the multi-sublayer structure of the TiCN layer in the growth direction the first C-type sublayer has a thickness in the range from 2 to 15 m, and subsequent C-type sublayers have a thickness in the range from 0.5 to 4 m, or all C-type sublayers have a thickness in the range from 0.5 to 4 m.

8. The coated cutting tool of claim 1, wherein the Ti or Ti+Al compound bonding layer has a multi-sublayer structure and a total composition of TiCNO or TiAlCNO.

9. The coated cutting tool of claim 1, wherein the substrate consists of cemented carbide, cermet, ceramics, steel or cubic boron nitride, preferably of cemented carbide.

10. The coated cutting tool of claim 1, wherein the layers of the hard coating are deposited by chemical vapour deposition (CVD), the TiCN is a MT-TiCN layer deposited by MT-CVD at a reaction temperature in the range from 600 C. to 900 C., and/or the Ti or Ti+Al compound bonding layer is deposited by HT-CVD at a reaction temperature in the range from 900 C. to 1200 C., and/or the -Al.sub.2O.sub.3 layer is deposited by HT-CVD at a reaction temperature in the range from 900 C. to 1200 C.

11. The use of the coated cutting tool of claim 1 for continuous and interrupted chip-forming machining of ISO P or ISO K steel materials, including turning operations.

12. A process for manufacturing of a coated cutting tool of claim 1, wherein the multi-layered wear resistant hard coating is deposited on the substrate by chemical vapour deposition (CVD), comprising the steps of: deposition of the TiCN layer in a multi-sublayer structure of a total of p alternating C-type and N-type sublayers with p being an even or odd number in the range from 5 to 20, by MT-CVD at a reaction temperature in the range from 600 C. to 900 C. from a process gas composition including at least TiCl.sub.4, H.sub.2, N.sub.2 and CH.sub.3CN and optionally HCl, to a total thickness of from 2 m to 20 m, wherein the C-type and N-type sublayers have different stoichiometries with respect to the atomic ratio of carbon and nitrogen, with the C-type TiCN sublayers having a C/N ratio in the range of 1.0C/N2.0, and the N-type TiCN sublayers having a C/N ratio in the range of 0.5C/N<1.0, and with the difference between the C/N ratio of adjacent C-type and N-type layers being 0.2, the C/N ratio being adjusted by the ratio of N.sub.2/CH.sub.3CN in the process gas composition; deposition of the single-layer or multi-sublayer oxygen containing Ti or Ti+Al compound bonding layer on top of the TiCN layer to a total thickness of from 0.5 m to 3 m, by thermal HT-CVD or MT-CVD from a process gas composition including at least TiCl.sub.4, H.sub.2, N.sub.2, CO and, if Al is present, AlCl.sub.3 and optionally CH.sub.4 and/or HCl; carrying out an oxidation step to the bonding layer at a temperature in the range from 900-1200 C., a pressure in the range from 30 to 150 mbar, a time from 2-20 min, and in a gas atmosphere consisting of H.sub.2, N.sub.2, 1-10 vol. % CO.sub.2 and 1-20 vol. % CO; and deposition of an -Al.sub.2O.sub.3 layer on top of the oxidation step treated bonding layer with a total thickness of from 2 m to 15 m, by HT-CVD at a reaction temperature in the range from 900 C. to 1200 C.

13. The process of claim 12, further comprising the step of deposition of at least one base layer of TiN or TiC immediately on the substrate surface to a base layer thickness in the range from 0.3 to 1.5 m by thermal HT-CVD or MT-CVD from a process gas composition comprising at least TiCl.sub.4, H.sub.2 and N.sub.2.

14. The process of claim 12, wherein the Ti or Ti+Al compound bonding layer is deposited by multiple subsequent deposition steps to obtain a multi-sublayer structure, wherein each deposition step is carried out by HT-CVD at a reaction temperature in the range from 900 C. to 1200 C.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0056] FIG. 1 shows examples of light optical micrographs (LOM) of polished calotte ground surfaces of coatings of different A adhesion classifications (FIG. 1a: A=1; FIG. 1b: A=2; FIG. 1c: A=3).

[0057] FIG. 2: shows average values for A and Z adhesion of inventive and comparative examples of coated cutting tool samples plotted over the number of sublayers in the TiCN layer (FIG. 2a) and plotted over the texture coefficient TC (4 2 2) of the TiCN layer (FIG. 2b), respectively.

[0058] FIG. 3 shows light optical photographs of crater wear of inventive samples (FIG. 3a, 3b: 4WAG51; FIG. 3c, 3d: 4WAG60) and a reference sample (FIG. 3e, 3f: 1246260) after the crater wear test (turning operation in C45E steel) for 12 min cutting time (FIG. 3a, 3c, 3e) and 15 minutes cutting time (FIG. 3b, 3d, 3f).

[0059] FIG. 4 shows the flank wear of the samples 4WAG51, 4WAG60 and reference 1246260 shown in FIG. 3 after each cycle of 3 min in the crater wear test.

[0060] FIG. 5: shows the flank wear of inventive samples 4WAG51 and 4WAG55 and reference sample 1246260 in the toughness test, wherein the maximum wear width is plotted over the number of cycles, with the edge line damage (ELD) being indicated for each sample at the end of tool life (VB.sub.max on the flank face 0.3 mm).

[0061] FIG. 6 shows an example of a TEM (FIG. 5a) and an EDXS line scan (FIG. 5b) along line A-B in layer growth direction on a sample of an inventive TiCN layer. In the TEM representation the thicker C-type sublayers (bright) are interrupted by six thin N-type sublayers (dark). The EDXS line scan shows the concentrations of Ti, C and N in at-% over the length of about 4 m of the line A-B. In this sample, the average C/N ratio of the C-type sublayers was about 1.42, and the average C/N ratio of the n-type sublayers was about 0.85, determined by EDXS. The C/N ratio results could be confirmed by EELS line scan.

DEFINITIONS AND METHODS

MT-TiCN

[0062] The term MT-TICN, as it is used herein, implies that TiCN is deposited by moderate temperature CVD (MT-CVD), which distinguishes the material being deposited by high temperature CVD (HT-CVD).

X-Ray Diffraction (XRD) Measurements

[0063] X-ray diffraction measurements were performed on a Panalytical CubiX3 diffractometer using CuK-radiation and a PIXcel 1D RTMS detector. The X-ray tube was run in line focus at 45 kV and 40 mA. Measurements were done in Bragg-Brentano geometry. On primary beam side a Soller slit of 0.04 rad, a fixed divergence slit of 0.5 and an anti-scatter slit of 1 were used. To avoid a spill over of the X-ray beam over the coated face of the sample a beam mask of 1.6 mm width was inserted. On the secondary side a fixed anti-scatter slit of 8 mm, a Soller slit of 0.04 rad and a 20 m thick NiK filter were used. Symmetrical -2 scans within the angle range of 192130 with increments of 0.0158 and approximately 0.2 second counting time have been conducted.

[0064] The data analysis was done using a Matlab based peak fitting procedure by fitting Pseudo-Voigt profiles to the measured 20 scans after Cu-K.sub.2 stripping (Rachinger method) and background subtraction has been performed. Peak intensities herein are peak area intensities. Correction for thin film absorption (TF) was applied to all samples, which takes into account the limited thickness of the layer in contrast to the natural penetration depth in a bulk material. Furthermore, absorption correction (Abs) was applied for layers deposited above the respective layer of interest. The equations applied for thin film (TF) correction and absorption (Abs) correction are known to the skilled person and are shown below:

[00003]$\begin{array}{cc}{I}_{\mathrm{corr}}^{TF}=\frac{I_0}{1-\exp \left(-2S/\sin \right)}& I_{\mathrm{corr}}^{Abs}=\frac{I_0}{\exp \left(-2S/\sin \right)}\end{array}$

[0065] In the equation for thin film correction (I.sup.TF.sub.corr), S is the thickness of the layer of interest, and in the equation for absorption correction (I.sup.Abs.sub.corr), S is the thickness of an absorbing top layer, respectively. is the linear absorption coefficient of the respective layer material with (-Al.sub.2O.sub.3)=0.01258 m.sup.1 and p(TiCN)=0.08150 m.sup.1. (See also: Birkholz, Thin Film Analysis by X-ray Scattering, 2006, Wiley-VCH, ISBN 3-527-31052-5, chapter 5.5.3, pages 211-215).

[0066] Since the bonding layer is thin, has the same crystal structure and similar chemical composition compared to the TiCN coating, the superposed interference peaks of both layers cannot be separated or trustworthy deconvoluted. Therefore, no separate absorption correction and thin film correction, respectively, was made for the bonding layer overlaying the TiCN coating. Instead they are treated as one layer.

Texture Coefficient TC(h k l)

[0067] The term fiber texture, as it is generally used in connection with polycrystalline thin films produced by vapor deposition, describes a preferential crystallographic orientation of the grown grains compared to random orientation, in that a set of geometrically equivalent crystallographic planes {h k l} is found to be preferentially oriented parallel to the substrate surface.

[0068] A means to express preferred growth, i.e. that one set of geometrically equivalent crystallographic planes {h k l} is found to be preferentially oriented parallel to the substrate, is the texture coefficient TC(h k l) calculated using the formalism proposed by Harris on the basis of a defined set of XRD reflections measured on the respective sample (Harris, G. B., Philosophical Magazine Series 7, 43/336, 1952, pp. 113-123). According to the Harris formula, the measured peak intensities I(h k l) are correlated to the relative standard intensities I.sub.0(h k l) taken from the respective lCDD's PDF-card or measured on a standard reference powder.

[00004]$TC\left(hkl\right)=\frac{I\left(\mathrm{hkl}\right)}{I_0\left(hkl\right)}.Math.{\left(\frac{1}{n}.Math.\underset{1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hkl}\right)}{I_0\left(hkl\right)}\right)}^{-1}$

[0069] A texture coefficient TC(h k l)>1 of a layer of crystalline material is an indication that the grains of the crystalline material are oriented with their {h k l} crystallographic plane parallel to the substrate surface more frequently than in a random distribution, at least compared to the XRD reflections used in the Harris formula. For the calculation of texture coefficients TC(h k l) herein, the measured peak intensities I(h k l) mean the net peak area intensities corrected as described above.

[0070] For TiCN the lCDD's PDF-card no 01-071-6059 was applied, and the following (h k l) reflections were used in the calculation (n=7):

TABLE-US-00002 {h k l} {1 1 1} {2 0 0} {2 2 0} {3 1 1} {3 3 1} {4 2 0} {4 2 2} Std. Intensity I.sub.0 803 999 464 198 62 124 100

[0071] For -Al.sub.2O.sub.3 the standard peak area intensities I.sub.0(h k l) were obtained by measurement, as described above, on the certified NIST (National Institute of Standards and Technology) standard powder SRM676a. The following (h k l) reflections were used in the calculation (n=8):

TABLE-US-00003 {h k l} {1 0 4} {1 1 0} {1 1 3} {0 2 4} {1 1 6} {3 0 0} {0 0 12} {0 1 14} Std. Intensity I.sub.0 87.93 37.68 100.00 45.76 92.43 53.93 2.05 5.16

Scanning Electron Microscopy (SEM)

[0072] For SEM analyses inserts were cut in cross section, mounted in a holder and then treated by i) grinding with Struers Piano220 disc with water for 6 min; ii) polishing with 9 m MD-Largo Diamond suspension for 3 min; iii) polishing with 3 m MD-Dac Diamond suspension for 3:40 min; iv) polishing with 1 m MD-Nap Diamond suspension for 2 min; v) polishing/etching with OP-S colloidal silica suspension for at least 12 min (average grain size of the colloidal silica=0.04 m). The specimens were ultrasonically cleaned before SEM examination. SEM images were acquired on a Zeiss Supra 40 VP field emission scanning electron microscope using a 30 m aperture, 2.5 kV acceleration voltage and a working distance of 5 mm.

Sample Preparation for TEM Analyses

[0073] The preparation of samples for TEM was made by the in-situ lift-out technique using a combined FIB/SEM equipment Zeiss Crossbeam 540 field emission scanning electron microscope equipped with a gallium liquid metal ion source to cut a thin cross sectional piece out of the surface and thin the sample down to sufficient electron transparency.

[0074] Analytical Transmission Electron Microscopy (TEM) investigations (STEM-EDXS) Combined scanning transmission electron microscopy (STEM) imaging and element mapping via energy-dispersive X-ray spectroscopy (EDXS) was performed on an FEI Tecnai Osiris microscope at 200 keV primary electron energy with an electron current of 1 nA, the microscope is equipped with a high-brightness field emission electron gun and four silicon-drift detectors (FEI Super-X EDX system).

[0075] STEM-EDXS mappings were used for the determination of the sublayer thicknesses of the C-type and the N-type layers respectively. The derived quantitative line profiles of the element distributions demonstrate a high homogeneity and reproducibility over the alternating C-type and N-type layer stack. C/N ratios were determined by line profile fitting using Matlab.

Electron Energy Loss Spectroscopy (EELS)

[0076] Electron energy loss spectroscopy (EELS) was carried out by means of a Gatan imaging energy filter of the type GIF Tridiem 865 ER on an FEI Titan 80-300 microscope at 300 kV. EELS line-profile analyses were done in the STEM mode. For the accurate quantification of the C/N ratios EELS analyses with high spatial resolution were applied. These measurements confirm the data from the STEM EDXS analyses.

Calotte Grinding/Ball Cratering

[0077] Calotte grinding was used to assess coating thickness and adhesion. The insert was placed on an inclined magnetic holder of the ball cratering set-up. A spherical calotte was ground in the coating and substrate material by a rotating 30 mm steel ball wetted with a drop of 3 m water-based diamond suspension (Struers, DP-Lubricant Green) and driven by a driving shaft at >500 rpm. The grinding process was stopped when the calotte diameter in the substrate material reached approx. 600-1100 m. The thickness measurements taking into account the geometry of the calottes were done by a dedicated software using light optical microscopy (LOM).

A Adhesion and Z Adhesion

[0078] A adhesion defines the adhesion of the -Al.sub.2O.sub.3 layer to the bonding layer and, Z adhesion defines internal adhesion within the bonding layer, i.e. between individual sublayers of the bonding layer. A and Z adhesion were assessed by LOM observation on polished calotte ground surfaces and visually classified on a scale from 1.0 (=perfect adhesion) to 3.0 (=no adhesion).

[0079] The criteria for A and Z adhesion at the interfaces of layers/sublayers are as follows: [0080] A or Z=1: no or neglectable breakouts are observable at the interfaces, the interface line is intact. [0081] A or Z=2: minor breakouts can be observed at the interface, about 51-80% of the total interface line are without deterioration. [0082] A or Z=3: mayor breakouts or a continuous delamination are observable at the interface, 50-100% of the interface line in the calotte are deteriorated.

[0083] FIGS. 1a, 1b and 1c show examples of A adhesions (FIG. 1a: A=1; FIG. 1b: A=2; FIG. 1c: A=3).

CVD Coatings

[0084] All CVD coatings herein were prepared in an industrial sized radial flow CVD coating chamber of type Bernex BPX530L with an inner reactor height of 1580 mm, an inner reactor diameter of 500 mm and an inner volume of approximately 300 litres. The reaction gas was fed into the reactor through a central gas inlet pipe and introduced into the reaction zone through openings distributed along the inlet pipe to provide an essentially radial gas flow over the substrate bodies.

[0085] It is noted that a high number of cutting tool insert substrates (in the order of up to about 15.000 inserts) may be placed in the reactor on the various tray levels and at different distances in radial direction from the reaction gas outlet openings. Accordingly, depending on the total gas flow, gas velocity and the type of deposition reaction, the reaction gas compositions, and thus, the reactivity at different substrate positions within the same reactor may vary and can result in varying coating thicknesses and other product parameters of the coated substrates within the same deposition run under the same nominal reaction conditions. This is a phenomenon well known to the skilled person. However, it is within the purview of the skilled person to lower or overcome such variations by adjustments known in the art, such as adjustment of total gas flow, gas velocity, deposition times etc., to achieve the coating properties of the present invention.

[0086] If not otherwise indicated, in the examples herein, the reactor was filled with inserts up to about its full capacity, whereby sample inserts to be investigated were placed at three different radial positions on the trays from the central inlet pipe (positions: center (C), middle (M), periphery(P)) and on six different tray levels within the height of the reactor. The remaining positions on the trays were filled with scrap inserts to simulate, as close as possible, full scale deposition conditions and volume usage within the reactor.

[0087] If not otherwise indicated, in the examples herein, measured values indicated for a sample, such as layer thicknesses, texture coefficients, A and Z adhesion etc., represent the average of 18 samples taken from the 18 various positions within the reactor, as described above.

Blasting

[0088] If blasting of a deposited coating was performed, it was done on the rake faces of the inserts. Dry Blasting (TS) was carried out with ZrO.sub.2 round media with a diameter of 70-120 m, a blasting pressure of 5 bar (injector pressor=1.8 bar), and a blasting distance of 90 mm. Wet blasting (TT) was carried out with a blaster slurry of 20 vol-% Al.sub.2O.sub.3 in water (F240 micro grit), a blasting pressure of 2.8-3.8 bar (injector pressor=1.-2.0 bar), a blasting angle of 75, and a blasing distance of 94.5 mm.

Crater Wear Test

[0089] The coated cutting tools were tested in C45E steel using the following cutting data: [0090] Cutting speed v.sub.c: 270 m/min [0091] Cutting feed, f: 0.32 mm/revolution [0092] Depth of cut, a.sub.p: 2.5 mm [0093] Insert style: WNMG080412 [0094] (no cutting fluid)

[0095] One cutting edge per cutting tool was evaluated. In analyzing the crater wear, the area of exposed substrate was measured, using a light optical microscope. The lifetime of the tool was considered to be reached when the wear crater formed by the flowing chips breaks through/reaches the secondary cutting edge. The wear of each cutting tool was evaluated after 3 minutes cutting in the light optical microscope. The cutting process was then continued with a measurement after each 3 minutes run, until the tool life criterion was reached. Beside crater wear, flank wear was also observed.

Toughness TestEdge Line Damage (ELD)

[0096] The coated cutting tools (blasted or unblasted) were tested in an intermitted turning operation in C45E steel using the following cutting data: [0097] Cutting speed v.sub.c: 200 m/min [0098] Cutting feed, f: 0.2 mm/revolution [0099] Depth of cut, a.sub.p: 2.64 mm [0100] Insert style: WNMG080412

[0101] The work piece material consisted of C45E. The intermitted cutting process during this type of testing has shown to be critical for tool's lifetime. The end of tool life was assumed to be reached, if an edge-line damage (ELD) of 70% (criterion #1) or a wear VB.sub.max on the flank face of 0.3 mm (criterion #2) was reached or exceeded, whichever occurred earlier. Water miscible metal working fluid was used.

EXAMPLES

Substrates

[0102] In the present examples, substrates of cemented carbide with the cutting insert geometries ISO-type CNMA120412 and WNMG080412 were used. The cemented carbide composition was 86.11 wt. % WC, 5.48 wt. % Co, 3.52 wt. % TaC, 2.12 wt. % TiC, 2.33 wt. % NbC and 0.44 wt. % other carbides. The substrates have a Co binder enriched surface zone of about 20 m from the substrate surface.

[0103] For the CVD depositions, inserts of the two different geometries CNMA120412 and WNMG080412 were coated in the same deposition run under the same conditions by placing at least one insert of geometry CNMA120412 and one insert of geometry WNMG080412 next to each other at the same radial and tray level positions within the CVD reactor. Due to its more simple geometry and flat surfaces, and thus, easier handling, the CNMA120408 inserts were used for coating analytics and measurements (including A and Z adhesion analyses), whereas the WNMG080412 inserts, which is a common turning tool insert geometry for steel machining, were used in cutting tests.

Depositions

[0104] The coating sequence in the depositions of the examples herein was: TiN base layer/TiCN coating (MT-TiCN)/TiAICNO bonding layer/-Al.sub.2O.sub.3 layer. An oxidation step was applied to the bonding layer prior to the deposition of the -Al.sub.2O.sub.3 layer. In all inventive and comparative examples prepared herein, the TiN base layer, the TiAICNO bonding layer, the oxidation step and the -Al.sub.2O.sub.3 layer were deposited and carried out, respectively, under the same process conditions to make the examples comparable with respect to variations of the single-layer or multi-layer TiCN coatings.

[0105] The process parameters for the depositions of the layers of inventive and comparative samples are given in table 1, and the TiCN coating sequences are given in table 3. The process steps and parameters for the depositions of the layers of reference sample 1246260 are given in table 2. The parameters measured on the samples (average of 18 inventive and comparative samples, respectively, distributed in the reactor, as described above) are given in table 4.

[0106] The TiN base layer was about 0.3-0.5 m thick. The TiAICNO bonding layer had a thickness of about 1.0-1.5 m. The -Al.sub.2O.sub.3 layer had a thickness of about 5.5-6.5 m. The thickness of the TiCN coating was in the range of about 7.5-11.0 m.

[0107] The bonding layer consisted of multi-sublayer structure deposited in five coating steps BL-a to B-e. The deposition of the -Al.sub.2O.sub.3 was carried out in two steps, Step 1 and Step 2.

Adhesion Analyses

[0108] Average values for A and Z adhesion from the inventive and comparative samples (see tables 3 and 4) were determined and plotted over the number of multilayers (FIG. 2a; #-ML) and the texture coefficient TC (4 2 2) of the TiCN layer (FIG. 2b), respectively. In the dashed box in FIGS. 2a and 2b the mono-layer samples (#-ML=1) using TiCN-C and TiCN-D are marked. The results show that #-ML and TC (4 2 2) have only very little influence on Z adhesion, even for the mono-layer samples. However, a strong negative linear dependency of the A-adhesion over #-ML and a strong positive linear dependency of the A adhesion over TC (4 2 2) was observed. Both mono-layer examples show very weak A adhesion. The multi-sublayer samples within the #-ML and TC(4 2 2) ranges of the TiCN layer of the present invention show improved A adhesion and, at the same time, improved cutting properties.

TABLE-US-00004 TABLE 1 Process parameters and reaction gases during deposition for layers in inventive and comparative samples Temp Pressure Time H.sub.2 N.sub.2 TiCl.sub.4 CH.sub.4 CH.sub.3CN HCl AlCl.sub.3 CO.sub.2 CO H.sub.2S Total Layer Type [ C.] [mbar] [min] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol % [vol %] [vol %] [l/min] TiN (base layer) 885 300 60 54.9 43.9 1.2 90.9 TiCN-A (N type) 885 70 var. 57.3 41.7 0.9 0.1 96.0 TiCN-B (C type) 885 70 var. 81.8 14.9 2.7 0.6 67.2 TiCN-C (C type) 885 55 320 87.8 8.8 2.7 0.7 113.9 TiCN-D (C type) 885 70 320 81.5 14.8 3.0 0.7 67.5 TiCN-E (N type) 885 70 var. 63.1 36.0 0.8 0.1 96.0 TiCN-F (C type) 885 70 var. 85.1 12.2 2.2 0.5 67.2 BL-a 1000 400 25 67.5 25.9 1.5 3.4 1.7 88.9 BL-b 1000 70 12 83.1 12.5 1.5 0.4 1.3 1.2 120.4 BL-c 1000 70 5 71.6 23.1 2.3 0.5 0.2 2.3 129.9 BL-d 1000 70 7 71.9 23.2 2.3 0.3 2.3 129.3 BL-e 1000 55 10 99.5 0.5 65.3 Oxidation step 1000 65 5 57.1 31.7 3.2 8.0 63.0 -Al.sub.2O.sub.3 (step 1) 1000 65 30 93.2 1.4 1.4 2.7 1.3 74.0 -Al.sub.2O.sub.3 (step 2) 1000 65 270 93.7 1.8 0.8 3.4 0.3 135.2 BL = Bonding Layer (multi-layer)

TABLE-US-00005 TABLE 2 Process steps and parameters for the layer deposition in reference sample (1246260 = prior art) Temp Pressure Time H.sub.2 N.sub.2 TlCl.sub.4 CH.sub.3CN CH.sub.4 HCl AlCl.sub.3 CO.sub.2 CO H.sub.2S Total Layer Type [ C.] [mbar] [min] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol % [vol %] [vol %] [vol %] [l/min] TiN (base layer) 900 160 51 59.4 39.6 1.0 88.4 TiCN (step 1) 900 75 90 71.5 25.7 2.2 0.6 69.9 TiCN (step 2) 900 70 240 89.4 7.9 2.0 0.7 76.1 BL-1 1000 400 20 67.7 25.4 1.9 3.3 1.7 59.1 BL-2 1000 70 4 84.1 12 1.5 1.2 1.2 83.2 BL-3 1000 70 14 83.8 12 1.4 0.4 1.2 1.2 83.6 BL-4 1000 70 6 65.3 28.1 2.7 0.6 0.5 2.8 71.2 BL-5 1000 70 14 64.8 27.9 2.7 0.4 4.2 71.8 BL-6 1000 45 10 99.5 0.5 62.8 Oxidation step 1000 55 6 57.1 31.7 3.2 8 63.0 -Al.sub.2O.sub.3 (step 1) 1000 55 30 93 1.4 1.4 2.8 1.4 71.5 -Al.sub.2O.sub.3 (step 2) 1000 75 320 95.2 0.9 0.8 2.8 0.3 130.3 BL = Bonding Layer (multi-layer)

TABLE-US-00006 TABLE 4 Measured Parameters TiCN TiCN Thickness TiCN Al.sub.2O.sub.3 A Z # sublayers # Sample [m] TC(4 2 2) TC(0 0 12) Adhesion Adhesion [#-ML] 1 WAG1719_V40 13.8 6.1 7.4 3.0 2.0 1 2 4WAG25 10.1 5.1 6.0 3.0 2.2 1 3 4WAG44 9.0 5.3 6.3 2.2 1.9 6 4 4WAG48 10.4 5.2 6.1 2.2 1.6 7 5 4WAG28.1 7.9 3.9 5.5 1.1 1.6 19 6 4WAG28.2 7.7 3.9 5.4 1.1 1.9 19 7 4WAG49 8.7 4.1 5.9 1.4 1.6 19 8 4WAG51 10.3 5.2 6.2 2.3 1.4 7 9 4WAG55 9.2 4.5 6.0 1.5 2.0 25 10 4WAG56 9.6 4.8 5.8 1.5 1.9 21 11 4WAG59 9.7 4.9 6.2 2.0 1.8 17 12 4WAG60 10.4 4.9 6.2 1.8 1.5 17

TABLE-US-00007 TABLE 3 TiCN coating sequences in inventive and comparative samples MT-TICN -,,X Depos. Time Total Thickness # Sample # Layer Sequence [min] layer no. [m] 1 WAG1719_V40 1x C 320 1 13.8 2 4WAG25 1x D 320 1 10.1 3 4WAG44 1x B 270 6 9.0 2x (A + B) 2x (7 + 25) 1x A 32 4 4WAG48 1x B 300 7 10.4 3x (A + B) 3x (7 + 25) 5 4WAG28.1 9x (B + A) 9x (25 + 7) 19 7.9 1x B 32 6 4WAG28.2 9x (B + A) 9x (25 + 7) 19 7.7 1x B 32 7 4WAG49 9x (B + A) 9x (30 + 10) 19 8.7 1x B 30 8 4WAG51 1x B 300 7 10.3 3x (A + B) 3x (7 + 25) 9 4WAG55 1x F 25 25 9.2 12x (E + F) 12x (7 + 25) 10 4WAG56 1x B 70 21 9.6 10x (A + B) 10x (7 + 25) 11 4WAG59 1x B 134 17 9.7 8x (A + B) 8x (7 + 25) 12 4WAG60 1x B 134 17 10.4 8x (A + B) 8x (7 + 25) 12x (A + B)

Toughness Tests

[0109] Edge line toughness tests were carried out on a reference sample (1246260) and on two inventive samples (4AG51 and 4WAG5). Each sample was post-treated T+TT=dry blasting and subsequent wet blasting, as described above. All samples reached or exceeded a flank wear B.sub.max of 0.3 mm (end of tool life criterion #2) long before an edge-line damage (EL) of 70% (end of tool life criterion #1) was reached. Therefore, ELD was determined for each sample after end of tool life de to flank wear. The results are shown in the following table 5and FIG. 5.

TABLE-US-00008 TABLE 5 Edge Line Toughness Test # of cycles flank wear flank wear ELD until width after width after after VBmax >0.3 4 cycles 6 cycles end of Sample # mm VBmax [mm] VBmax [mm] tool life Ref. 1246260 4 0.36 35% 4WAG51 >7 0.15 0.26 31% 4WAG55 6 0.22 0.34 29%

Crater Wear

[0110] Inventive samples 4WAG51 and 4WAG60 and reference sample 1246260 were subjected to the crater wear test, as described above, (turning operation in C45E steel) for 12 min and 15 min, respectively. FIG. 3 shows the observed (LOM) wear of an inventive samples. (FIG. 3a=4WAG51, 12 min; 3b=4WAG51, 15 min, 3c=4WAG60, 12 min; 3d=4WAG60, 15 min; 3e=1246260, 12 min; 3f=1246260, 15 min). The results show similar crater wear of the inventive samples and the reference sample after 12 min, but after 15 min wear of the inventive samples was still acceptable, whereas the cutting edge and the rake and flank faces of the reference sample were almost completely destroyed. FIG. 4 shows the flank wear of the samples after each cycle of 3 min in the crater wear test.