CVD coated cutting tool

Abstract

A coated cutting tool for chip forming machining of metals includes a substrate having a surface coated with a chemical vapour deposition (CVD) coating. The substrate is coated with a coating having a layer of α-Al.sub.2O.sub.3, wherein the α-Al.sub.2O.sub.3 layer exhibits a texture coefficient TC(0 0 12)≥7.2 and wherein the ratio of I(0 0 12)/I(0 1 14)≥0.8. The coating further includes a MTCVD TiCN layer located between the substrate and the α-Al.sub.2O.sub.3 layer. The MTCVD TiCN layer exhibits a pole figure, as measured by EBSD, in a portion of the MTCVD TiCN layer parallel to the outer surface of the coating and less than 1 μm from the outer surface of the MTCVD TiCN, wherein a pole plot based on the data of the pole figure, with a bin size of 0.25° over a tilt angle range of 0°≤β≤45° from the normal of the outer surface of the coating shows a ratio of intensity within β≤15° tilt angle to the intensity within 0°≤β≤45° of ≥45%.

Claims

1. A coated cutting tool comprising: a substrate coated with a coating including a layer of α-Al.sub.2).sub.3, wherein a thickness of the α-Al.sub.2O.sub.3 layer is 2-4 μm and wherein said α-Al.sub.2O.sub.3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKa radiation and θ-2θscan, defined according to Harris formula $\mathrm{TC}\left(\mathrm{hkl}\right)={\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\left[\frac{1}{n}\underset{n=1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\right]}^{-1}$ where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I.sub.0(hkl) is the standard intensity according to ICDD's PDF-card No. 00-010-0173, n is the number of reflections used in the calculation, and where the (hkl) reflections used are (1 0 4), (1 1 0), (1 1 3), (0 2 4), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), wherein TC(0 0 12) ≥7.2, and wherein the ratio of I(0 0 12)/I(0 1 14) ≤0.8, and wherein said coating further includes a MTCVD TiCN layer located between the substrate and the α-Al.sub.2O.sub.3 layer, wherein the thickness of said MTCVD TiCN layer is 2-3 μm and wherein said MTCVD TiCN layer exhibits a {211} pole figure as measured by EBSD in a portion of the MTCVD TiCN layer parallel to an outer surface of the coating and less than 1 μm from an outer surface of the MTCVD TiCN, wherein a pole plot based on the data of the pole figure, with a bin size of 0.25° over a tilt angle range of 0°≤β≤45° from the normal of the outer surface of the coating shows a ratio of intensity within β≤15° tilt angle to the intensity within 0°≤β≤45° of ≥45%.

2. The coated cutting tool in accordance with claim 1, wherein said MTCVD TiCN layer exhibits a {110}pole figure as measured by EBSD, wherein a pole plot based on the data of the pole figure, with a bin size of 0.25° over a tilt angle range of 0°≤β≤45° from a normal of the outer surface of the coating shows a ratio of intensity within β≤15° tilt angle to the intensity within 0°≤β≤45° of ≤30% .

3. The coated cutting tool in accordance with claim 1, wherein the thickness of the β-Al.sub.2O.sub.3 layer is 2.5-3.5 μm.

4. The coated cutting tool in accordance with claim 1, wherein the coating further includes a bonding layer having a HTCVD deposited TiN, TiCN, TiCNO and/or TiCO or a combination thereof, the bonding layer being located outermost of the MTCVD TiCN layer and adjacent to the β-Al.sub.2O.sub.3 layer.

5. The coated cutting tool in accordance with claim 4, wherein the thickness of the bonding layer is 0.5-1 μm.

6. The coated cutting tool in accordance with claim 1, further comprising an innermost TiN layer adjacent to the substrate.

7. The coated cutting tool in accordance with claim 6, wherein the thickness of said innermost TiN layer is 0.3-0.6 μm.

8. The coated cutting tool in accordance with claim 1, wherein the substrate is cemented carbide, cermet, ceramic.

9. The coated cutting tool in accordance with claim 1, wherein the substrate is cemented carbide with a Co content of 8-15 wt %.

10. The coated cutting tool in accordance with claim 1, wherein the cutting tool is a milling insert.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 A SEM image of a cross section of coating C01 according to the invention. The coating comprises a TiN layer (E), a MTCVD TiCN layer (D), a bonding layer (B) and an outermost α-alumina layer (A). The portion (C) of the MTCVD TiCN that exhibits the EBSD pole plot is indicated in the figure.

(2) FIG. 2 Contoured versions of pole figures {211} and {110} from the coating C01, The maximum intensity is set to 3 as indicated by the label.

(3) FIG. 3 {211} pole plot from the EBSD pole figure data of coating C01 with a bin size of 0.25° over a tilt angle range of 0°≤β≤45°.

(4) FIG. 4 {110} pole plot from the EBSD pole figure data of coating C01 with a bin size of 0.25° over a tilt angle range of 0°≤β≤45°.

(5) FIG. 5 Contoured versions of pole figures {211} and {110} from the coating C06. The maximum intensity is set to 3 as indicated by the label.

(6) FIG. 6 {211} pole plot from the EBSD pole figure data of coating C06 with a bin size of 0.25° over a tilt angle range of 0°≤β≤45°.

(7) FIG. 7 {110} pole plot from the EBSD pole figure data of coating C06 with a bin size of 0.25° over a tilt angle range of 0°≤β≤45°.

EXAMPLES

(8) Exemplifying embodiments of the present invention will now be disclosed in more detail and compared to reference embodiments. Coated cutting tools (inserts) were manufactured, analysed and evaluated in a cutting test.

Example 1—Coating Preparation

(9) Coating C01

(10) Inserts with Coromant R390-11T308M-PM, Coromant R245-12T3 M-PM1 and ISO type SNMA 120408 geometry were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 2.5 μm TiCN layer by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The details of the TiN and the TiCN deposition are shown in Table 1.

(11) TABLE-US-00001 TABLE 1 Deposition of MTCVD of TiN and TiCN MT CVD of TiN and TiCN Pressure H.sub.2 N.sub.2 HCl TiCl.sub.4 CH.sub.3CN (885° C.): [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] TiN 400 48.8 48.8 — 2.44 — TiCN inner 55 59 37.6 — 2.95 0.45 TiCN outer 55 81.5 7.8 7.8 2.38 0.65

(12) Deposition time for TiCN inner and TiCN outer was 10 and 65 minutes, respectively. On top of the MTCVD TiCN layer was a 0.5-1 μm bonding layer deposited at 1000° C. by a process consisting of four separate reaction steps. First a HTCVD TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step (TiCNO-1) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar, then a third step (TiCNO-2) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and finally a fourth step (TiCNO-3) using TiCl.sub.4, CO, N.sub.2 and H.sub.2 at 70 mbar. During the third and fourth deposition step some of the gases were continuously changed as indicated by a first start level and a second stop level presented in Table 2. Prior to the start of the subsequent Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO.sub.2, CO, N.sub.2 and H.sub.2. The details of the bonding layer deposition are shown in Table 2.

(13) TABLE-US-00002 TABLE 2 Bonding layer deposition Bonding layer Pressure H.sub.2 N.sub.2 CH.sub.4 HCl CO TiCl.sub.4 CH.sub.3CN CO.sub.2 (1000° C.): [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] HTCVD 400 67.9 25.5 3.4 1.7 — 1.56 — — TiCN TiCNO-1 70 83.7 12 — 1.2 1.2 1.5 0.4 — TiCNO-2 70 63.1-61.7 31.5-30.9 — — 1.6-3.7 3.15-3.09 0.66-0.64 — TiCNO-3 70 62.1-61.5 31.1-30.8 — — 3.7-4.6 3.11-3.08 — — Oxidation 55 53.8 30 — — 12.5 — — 3.7

(14) On top of the bonding layer an α-Al.sub.2O.sub.3 layer was deposited. The α-Al.sub.2O.sub.3 layer was deposited at 1000° C. and 55 mbar in two steps. The first step using 1.2 vol-% AlCl.sub.3, 4.7 vol-% CO.sub.2, 1.8 vol-% HCl and balance H.sub.2 giving about 0.1 μm α-Al.sub.2O.sub.3 and a second step using 1.2% AlCl.sub.3, 4.7% CO.sub.2, 2.9% HCl, 0.58% H.sub.2S and balance H.sub.2 giving a total α-Al.sub.2O.sub.3 layer thickness of about 3 μm.

(15) A SEM image of a cross section of the blasted coating C01 is shown in FIG. 1. As seen from the substrate the coating C01 comprises a TiN layer, an MTCVD TiCN layer, i.e. the inner and the outer MTCVD TiCN, a bonding layer, i.e. HTCVD TiCN, TiCNO-1, TiCNO-2, TiCNO-3, and an outermost α-Al.sub.2O.sub.3 layer. The thicknesses of these layers can for example be studied in an SEM image.

(16) Coating C02

(17) Same type of geometry used as in Coating C01 were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 1.5 μm TiCN layer by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The volume ratio of TiCl.sub.4/CH.sub.3CN in an initial part of the MTCVD deposition of the TiCN layer was 6.6, followed by a period using a ratio of TiCl.sub.4/CH.sub.3CN of 3.7. The details of the TiN and the TiCN deposition are shown in Table 1.

(18) Deposition time for TiCN inner and TiCN outer was 30 and 10 minutes, respectively. On top of the MTCVD TiCN layer was a 1-2 μm bonding layer deposited at 1000° C. by a process consisting of four separate reaction steps. First a HTCVD TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step (TiCNO-1) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar, then a third step (TiCNO-2) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and finally a fourth step (TiCNO-3) using TiCl.sub.4, CO, N.sub.2 and H.sub.2 at 70 mbar. During the third and fourth deposition step some of the gases were continuously changed as indicated by a first start level and a second stop level presented in Table 2. The growth steps time of the bonding layer were doubled as compared to Coating C01. Prior to the start of the subsequent Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO.sub.2, CO, N.sub.2 and H.sub.2. The details of the bonding layer deposition are shown in Table 2.

(19) On top of the bonding layer an α-Al.sub.2O.sub.3 layer was deposited. The α-Al.sub.2O.sub.3 layer was deposited at 1000° C. and 55 mbar in two steps. The first step using 1.2 vol-% AlCl.sub.3, 4.7 vol-% CO.sub.2, 1.8 vol-% HCl and balance H.sub.2 giving about 0.1 μm α-Al.sub.2O.sub.3 and a second step using 1.2% AlCl.sub.3, 4.7% CO.sub.2, 2.9% HCl, 0.58% H.sub.2S and balance H.sub.2 giving a total α-Al.sub.2O.sub.3 layer thickness of about 3 μm.

(20) Coating C03

(21) The coating C03 corresponds to coating C01 but with the difference that the outer TiCN was deposited for 105 minutes instead of 65, and that the α-Al.sub.2O.sub.3 layer thickness was deposited to about 2 μm.

(22) Coating C04

(23) The coating C04 corresponds to coating C01 but with the difference that the outer TiCN was deposited for 25 minutes instead of 65, and that the Al.sub.2O.sub.3 layer thickness was deposited to about 4 μm.

(24) Coating C05

(25) Same type of geometries as for previous coatings were first coated with a thin approximately 0.4 μm TiN-layer, then with an approximately 1.5 μm TiCN layer by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The volume ratio of TiCl.sub.4/CH.sub.3CN in the MTCVD deposition of the TiCN layer was 2.2. The details of the TiN and the TiCN deposition are shown in Table 3.

(26) TABLE-US-00003 TABLE 3 Deposition of TiN and MTCVD of TiCN Temper- ature Pressure H.sub.2 N.sub.2 HCl TiCl.sub.4 CH.sub.3CN [° C.] [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] TiN 930 160 60.1 38.3 — 1.50 — TiCN 885 55 59.8 38.05 — 1.49 0.67 inner TiCN 885 55 82.7 7.9 7.9 1.08 0.49 outer

(27) On top of the MTCVD TiCN layer was a 0.5-1 μm bonding layer deposited at 1010° using 3.03 vol-% TiCl.sub.4, 6.06 vol-% CO and 90.1 vol-% H.sub.2 at 55 mbar. Prior to the start of the subsequent Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 2 minutes in a mixture of H.sub.2, CO.sub.2 and HCl.

(28) On top of the bonding layer an α-Al.sub.2O.sub.3 layer was deposited. The α-Al.sub.2O.sub.3 layer was deposited at 1010° C. and 55 mbar in two steps. The first step using 2.3 vol-% AlCl.sub.3, 4.6 vol-% CO.sub.2, 1.7 vol-% HCl and balance H.sub.2 giving about 0.1 μm α-Al.sub.2O.sub.3 and a second step using 2.2% AlCl.sub.3, 4.4% CO.sub.2, 5.5% HCl, 0.33% H.sub.2S and balance H.sub.2 giving a total α-Al.sub.2O.sub.3 layer thickness of about 2.7 μm.

(29) Coating C06

(30) The coating C06 corresponds to coating CO.sub.2 but with the difference that the outer TiCN was deposited for 40 minutes instead of 10 minutes and that the deposition process was stopped after this step.

Example 2—Texture Analysis

(31) The layer thicknesses were analysed in a light optical microscope by studying a cross section of each coating at 1000× magnification. The thicknesses can also be studied in a SEM image. The results are presented in Table 4

(32) XRD was used to analyse the TC values of the α-Al.sub.2O.sub.3 and the MTCVD TiCN in accordance with the method as disclosed above. The texture analysis was made on coated ISO type SNMA120408 cemented carbide substrates. It is to be noted that the TC(311) of the MTCVD TiCN is disturbed by a WC peak and that this is not corrected for when calculating the TC(220) and TC(422) as presented in the Table 5.

(33) TABLE-US-00004 TABLE 4 Layer thicknesses and TC Layer Layer Layer thick- thick- Layer thick- ness ness thick- I(0 0 12)/ ness MTCVD Bonding ness TC(0 0 I(0 1 14) TiN TiCN layer α-Al.sub.2O.sub.3 12) of α- of α- Coating [μm] [μm] [μm] [μm] Al.sub.2O.sub.3 Al.sub.2O.sub.3 C01 0.5 2.4 0.8 3.0 7.50 1.05 C02 0.5 1.5 1.7 3.2 4.19 0.39 C03 0.4 3.3 0.8 2.1 7.12 1.49 C04 0.4 1.7 0.8 3.9 7.45 0.81 C05 0.4 1.7 0.8 2.7 0 0 C06 0.5 2.0 — — — —

(34) A high TC(0 0 12) is advantageous in providing a high crater wear resistance. The texture of the α-Al.sub.2O.sub.3 layer is controlled by the process parameters during deposition and is developed with increased layer thickness of the α-Al.sub.2O.sub.3 layer. The texture of the α-Al.sub.2O.sub.3 layer is also influenced by the texture of the preceding MTCVD TiCN layer. If the α-Al.sub.2O.sub.3 layer is too thin its orientation is less pronounced. The C01 and C04 have very high TC(0 0 12) and are also the most crater wear resistant as seen below. The C03 is probably too thin to give this very high TC(0 0 12) value. The references C02 and C05 are deposited on a different TiCN and with a different α-Al.sub.2O.sub.3 CVD process and do not show high TC(0 0 12) values.

(35) TABLE-US-00005 TABLE 5 Texture coefficients for MTCVD TiCN Coating TC(220) TC(422) C01 0.56 1.96 C02 0.71 0.95 C03 0.46 2.36 C04 0.75 0.78 C05 1.76 0.47 C06 1.05 1.06

(36) It can be noted from the TC values of the MTCVD TiCN that both the TC(422) and the TC(220) are relatively low. It can also be noted that the thicker the MTCVD TiCN the higher the TC(422) and the lower TC(220) values when comparing C04 (1.7 μm), C01 (2 μm) and C03 (3.3 μm) that were deposited with the corresponding MTCVD TiCN processes.

(37) Pole figures were measured by EBSD in a portion of the MTCVD TiCN layer parallel to the outer surface of the coating and less than 1 μm from the outer surface of the MTCVD TiCN of coatings C01, C02, C03, C04 and C06. For this measurement the coatings C01 and C06 were provided with the MTCVD layer being the outermost layer, while the outer layers of the coatings C02, C03 and C04 were removed by polishing with said Dimple Grinder as disclosed above before the measurement. Any outer layer can be removed by the skilled person prior to any EBSD analysis, for example by grinding and polishing.

(38) Crystallographic orientation data extraction of the acquired EBSD data was made using Oxford Instruments “HKL Tango” software version 5.12.60.0 (64-bit) and Oxford Instruments “HKL Mambo” software version 5.12.60.0 (64-bit). Pole figures using equal area projection and upper hemisphere projection were retrieved from the acquired EBSD data using the “HKL Mambo” software. The retrieved pole figures were for both the {211} and {110} poles with the Z direction being perpendicular to the outer surface of the coatings. Pole plots of both the {211} and {110} pole figures were extracted using a class width of 0.25° for the bin size in the pole plot and for an angular measuring range β from β=0° to β≤45°. The intensity in the pole plot ranging from β=0 to β≤15° was related to the total intensity in the pole plot ranging from β=0° to β≤45°. The pole plots of {211} and {110} of coating C01 are shown in FIG. 3 and FIG. 4, respectively. The pole plots of {211} and {110} of coating C06 are shown in FIG. 6 and FIG. 7, respectively. The signal in the pole plot ranging from β=0 to β≤15° related to the total signal in the pole plot ranging from β=0° to β≤45° for the coatings C01, C02, C03, C04 and C06 are presented in Table 6.

(39) TABLE-US-00006 TABLE 6 EBSD data Ratio of intensity Ratio of intensity within β = 0°-15° within β = 0°-15° to intensity to intensity within β = 0°-45° within β = 0°-45° in pole plot {211} in pole plot {110} Coating [%] [%] C01 51 25 C02 43 32 C03 55 14 C04 43 32 C06 43 37

(40) Contoured versions of the pole figures were calculated using a half width of 10.0° and a data clustering of 5.0° to illustrate the texture. The contoured pole figures {211} and {110} of coating C01 are shown in FIG. 2 and of coating C06 in FIG. 5. The maximum so called global intensity is set to 3MUD in these contoured versions of the pole figures.

Example 3—Cutting Tests

(41) Prior to cutting wear tests the inserts were blasted on the rake faces in a wet blasting equipment using a slurry of alumina in water and the angle between the rake face of the cutting insert and the direction of the blaster slurry was about 90°. The alumina grits were F220, the pressure of slurry to the gun was 1.8 bar, the pressure of air to the gun was 2.0 bar, the average time for blasting per area unit was 5 seconds and the distance from the gun nozzle to the surface of the insert was about 137 mm. The aim of the blasting is to influence the residual stress in the coating and the surface roughness and thereby improve the properties of the inserts in the subsequent wear test.

(42) The coatings C01-C05 were evaluated in five separate cutting tests.

(43) Cutting Test 1

(44) This test is to evaluate the resistance against crater wear at the rake face of the cutting tool. In the crater wear test the coatings C01-C05 were deposited on a cemented carbide substrate with a composition of about 9.14 wt % Co, 1.15 wt % Ta, 0.27 wt % Nb, 5.55 wt % C and the rest W.

(45) The coated cutting tools of type Coromant R39011-T308M-PM as blasted were tested in down milling in the work piece material Toolox 33 using the following cutting data:

(46) Cutting speed v.sub.c: 300 m/min

(47) Cutting feed per tooth, f.sub.z: 0.2 mm/tooth

(48) Axial depth of cut, a.sub.p: 2 mm

(49) Radial depth of cut, a.sub.e: 50 mm

(50) Number of teeth, z: 1

(51) No cutting fluid was used.

(52) In analyzing the crater wear, the area of exposed substrate was measured, using a light optical microscope. The wear of each cutting tool was evaluated after 4 cuts, i.e. 8 minutes cutting. Three parallel tests were run for each type of coating and the average values of the results are shown in Table 7.

(53) Cutting Test 2

(54) This is a test to evaluate the resistance towards chippings in the edge line. In the edge line toughness wear test the coatings C01-C05 were deposited on a cemented carbide substrate with a composition of about 13.5 wt % Co, 0.57 wt % Cr, 5.19 wt % C, and the rest W.

(55) The coated cutting tools of the type Coromant R39011-T308M-PM as blasted were tested in number of cut entrances into work piece material Dievar unhardened using the following cutting data:

(56) Cutting speed v.sub.c: 150 m/min

(57) Cutting feed per tooth, f.sub.z: 0.15 mm/tooth

(58) Axial depth of cut, a.sub.p: 3 mm

(59) Radial depth of cut, a.sub.e: 12 mm

(60) Number of teeth, z: 1

(61) Length of cut: 12 mm

(62) No cutting fluid was used.

(63) In analyzing the edge line toughness, the number of entrances until the cut-off criterion was reached was studied. The cut-off criterion in the test was a chipping of at least 0.5 mm of the edge line or a measured depth of 0.2 at either the flank or the rake face. The chipping was studied using a light optical microscope. Between eight and ten parallel tests were run for each type of coating. The results are shown in Table 7 as an average value.

(64) Cutting Test 3

(65) In the plastic deformation resistance wear test the resistance against plastic deformation of the cutting edge when the cutting edge is impressed is evaluated. The coatings C01-C05 were deposited on a cemented carbide substrate with a composition of about 9.14 wt % Co, 1.15 wt % Ta, 0.27 wt % Nb, 5.55 wt % C and the rest W.

(66) The coated cutting tools of type Coromant R39011-T308M-PM as blasted were tested in down milling in the work piece material Toolox 33 using the following cutting data:

(67) Cutting speed v.sub.c: 300 m/min

(68) Cutting feed per tooth, f.sub.z: 0.15 mm/revolution

(69) Axial depth of cut, a.sub.p: 1.5 mm

(70) Radial depth of cut, a.sub.e: 75 mm

(71) Number of teeth, z: 1

(72) No cutting fluid was used.

(73) In analyzing the resistance against plastic deformation at edge line impression, the area of exposed substrate was measured, using a light optical microscope. The tool life criterion is set to when the width of the exposed substrate is ≥0.2 mm. Three parallel tests were run for each type of coating. The average values of the results are shown in Table 7.

(74) Cutting Test 4

(75) The thermal crack resistance test is a test of the resistance against the formation of thermal cracks and chipping as a consequence of these cracks. In this test the coatings C01-C05 were deposited on a cemented carbide substrate with a composition of about 13.5 wt % Co, 0.57 wt % Cr, 5.19 wt % C, and the rest W.

(76) The coated cutting tools of type Coromant R39011-T308M-PM as blasted were tested in up milling in the work piece material Toolox 33 using the following cutting data:

(77) Cutting speed v.sub.c: 250 m/min

(78) Cutting feed per tooth, f.sub.z: 0.2 mm/revolution

(79) Axial depth of cut, a.sub.p: 3 mm

(80) Radial depth of cut, a.sub.e: 40 mm

(81) Number of teeth, z: 1

(82) Cutting fluid was used.

(83) In analyzing the wear, the chipping of the coating was studied using a light optical microscope. The life time criterion was set to a chipping depth of ≥0.3 mm or chipping width of ≥1.0 mm. Between 2 and 5 parallel tests were run for each type of coating. The results are shown as an average value in Table 7.

(84) Cutting Test 5

(85) This test evaluates the resistance to thermal cracks in dry machining. When thermal cracks have formed, the edge will suffer from plastic deformation. In this wear test the coatings C01-C05 were deposited on a cemented carbide substrate with a composition of about 9.14 wt % Co, 1.15 wt % Ta, 0.27 wt % Nb, 5.55 wt % C and the rest W.

(86) The coated cutting tools of the type Coromant R245-12T3M-PM as blasted were tested in down milling in the work piece material Toolox 33 using the following cutting data:

(87) Cutting speed v.sub.c: 300 m/min

(88) Cutting feed per tooth, f.sub.z: 0.46 mm/tooth

(89) Axial depth of cut, a.sub.p: 2 mm

(90) Radial depth of cut, a.sub.e: 20 mm

(91) Number of teeth, z: 1

(92) No cutting fluid was used.

(93) In analyzing the crater wear, the area of exposed substrate was measured, using a light optical microscope. The tool life criterion was set to a width of exposed substrate exceeding 0.25 mm. Two parallel tests were run for each type of coating. The average value results are shown in Table 7.

(94) TABLE-US-00007 TABLE 7 Results of cutting tests Cutting test: 3 4 5 Plastic Thermal Thermal 1 2 deformation crack crack Crater Edge line resistance- resistance resistance area toghness impression wet dry Coating: [mm.sup.2] [no. of cuts] [minutes] [minutes] [minutes] C01 0.06 44.5 32.6 9.4 45.2 C02 0.1 33.3 24.6 7 36.9 C03 0.07 38.9 27.9 8.8 38.4 C04 0.08 31.5 32.2 9.2 39.1 C05 0.17 13.3 14 5.9 27

(95) It can be concluded that the C01 is the overall best performing coating. A selection of specific thicknesses and orientations of the layers of the coating gives an unexpected optimum in properties. The inventive coated cutting tool performs best in a wide spectrum of demanding metal cutting applications.

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