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 coated cutting tool has a substrate coated with a coating including a layer of α-Al2O3, wherein the α-Al2O3 layer exhibits a dielectric loss of 10−6≦tan δ≦0.0025, as measured with AC at 10 kHz, 100 mV at room temperature of 20° C.

Claims

1. A coated cutting tool comprising a substrate coated with a coating including a layer of α-Al.sub.2O.sub.3, wherein said α-Al.sub.2O.sub.3 layer exhibits a dielectric loss of 10.sup.−6≦tan δ≦25×10.sup.−4, as measured with AC at 10 kHz, 100 mV at 20° C.

2. The coated cutting tool in accordance with claim 1, wherein the thickness of the α-Al.sub.2O.sub.3 layer is 2-20 μm.

3. The coated cutting tool in accordance with claim 1, wherein the dielectric loss tan δ of the α-Al.sub.2O.sub.3 layer is higher than or equal to 10.sup.−5.

4. The coated cutting tool in accordance with claim 1, wherein the dielectric loss tan δ of the α-Al.sub.2O.sub.3 layer is lower than or equal to 20×10.sup.−4.

5. The coated cutting tool in accordance with claim 1, wherein the dielectric loss tan δ of the α-Al.sub.2O.sub.3 layer is measured on a flank face of the cutting tool.

6. The coated cutting tool in accordance with claim 1, wherein the α-Al.sub.2O.sub.3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKα radiation and θ-2θ scan, defined according to Harris formula $\begin{array}{cc}\mathrm{TC}\left(\mathrm{hkl}\right)={\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\left[\frac{1}{n}.Math.\underset{n=1}{\overset{n}{.Math.}}.Math.\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\right]}^{-1}& \left(1\right)\end{array}$ 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), the TC(hkl) value being higher than 6.

7. The coated cutting tool in accordance with claim 6, wherein TC(0 0 12) of the α-Al.sub.2O.sub.3 layer is higher than 6.

8. The coated cutting tool in accordance with claim 1, wherein the α-Al.sub.2O.sub.3 layer exhibits a residual stress level of 100-500 MPa (tensile).

9. The coated cutting tool in accordance with claim 1, wherein the coating further includes a refractory layer having a material selected from the group TiCN, TiN, TiC, ZrN, ZrCN, ZrC, HfN, HfC, HfCN or combinations thereof.

10. The coated cutting tool in accordance with claim 9, wherein the thickness of said refractory layer is 4-20 μm.

11. The coated cutting tool in accordance with claim 1, further comprising an outermost layer of TiN having a thickness of 1-3 μm.

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

13. The coated cutting tool according to claim 9, wherein the TiCN refractory layer is located between the substrate and the α-Al.sub.2O.sub.3 layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a schematic view of a cross section of a part of a cutting insert prepared for a dielectric loss measurement of the α-Al.sub.2O.sub.3 layer 3.

[0028] FIG. 2 is a schematic top view of a part of a surface of a cutting insert prepared for a dielectric loss measurement of the α-Al.sub.2O.sub.3 layer 3.

DETAILED DESCRIPTION

Methods

CVD Coating Deposition

[0029] The CVD coatings in the examples below were deposited in a radial Ion bond type CVD equipment 530 size capable of housing 10000 half-inch size cutting inserts.

Dielectric Loss Measurements

[0030] A measurement of dielectric loss properties is here disclosed based on the example of coated cutting tool disclosed in the Example section below. The TiN layer and the TiCN layer can be replaced by other conductive layer and the corresponding measurement can be performed. Alternatively an electrical conducting substrate (for example cemented carbide) can replace the TiCN in the measurement such that the substrate can be exposed and connected instead of the TiCN.

[0031] The dielectric loss properties of the deposited α-Al.sub.2O.sub.3 layer were analysed by using laser ablation to define a parallel plate capacitor structure, where an isolated area 8 of electrically conducting TiN on the α-Al.sub.2O.sub.3 layer serves as a top contact (upper plate). Below the α-Al.sub.2O.sub.3 layer an electrical conducting TiCN layer is present that is to represent the lower contact (lower plate). The contact to the lower plate is obtained by laser ablation to expose an TiCN area 6 adjacent to the top contact 8. The volume of the α-Al.sub.2O.sub.3 layer located between the two plates represents the capacitor dielectric and is to be analysed, and it is assumed to be the projected area of the isolated TiN area 8 that is affecting the resulting dielectric loss value tan δ.

[0032] Laser was used on the coated surface of the insert to define structures such that the dielectric loss properties could be measured. The laser was used to selectively remove parts of the coating.

[0033] FIG. 1 shows a schematic cross section of a part of a coated cutting tool (cutting insert) showing the substrate 1, an inner TiCN layer 2, and α-Al.sub.2O.sub.3 layer 3, an uppermost TiN layer 4, an area 5 of exposed TiCN 6, trenches of exposed α-Al.sub.2O.sub.3 7, isolated TiN areas 8 and a surrounding TiN area 9.

[0034] FIG. 2 shows a schematic top view of a surface of a coated cutting tool prepared with defined structures as shown in FIG. 1, where two isolated TiN areas 8 are shown and one exposed TiCN 6 area.

[0035] Each insert to be tested was prepared with 14 isolated areas 8 and 3 separate areas of exposed TiCN 6 evenly distributed on a flank face of the insert. The diameter of the circular isolated TiN area was 1.288 mm, the width of the trench of exposed α-Al.sub.2O.sub.3 7 surrounding the isolated TiN area 8 was 10 μm as measured in the radial direction from the centre of the isolated TiN area 8. The area of exposed TiCN 6 was a square of 1 mm×1 mm.

[0036] The dielectric loss measurement is performed using a HP 4284A Precision LCR Meter (20 Hz-1 MHz) adjusted to measure tan δ at 10 kHz, 100 mV and at room temperature (20° C.). In this measurement a parallel circuit mode (CP mode) was used. A rule of thumb is to use this CP mode if the capacitance is small and if the impedance of the capacitor is >10 kohm. In the present example each capacitor has a capacitance (C) of about 30 pF and the frequency (f) is 10 kHz. This gives the impedance (Z.sub.c) of the capacitor as Z.sub.c=1/(2πfC)≈0.5 MOhm>>10 kOhm.

[0037] One probe was connected to the isolated TiN area 8 and the other probe was connected to the exposed TiCN area 6. The duration of one measurement was about 180 ms.

[0038] It is to be noted that even if all the measurements in the present examples (as disclosed below) are based on an outer TiN layer and an inner TiCN in connection with the α-Al.sub.2O.sub.3 layer, also other layers with suitable electrical conducting properties can be used for the analyse of the dielectric properties of the α-Al.sub.2O.sub.3 layer.

X-Ray Diffraction Measurement

[0039] In order to investigate the texture of the layer(s) X-ray diffraction measurement was conducted on the flank face using a PANalytical CubiX3 diffractometer equipped with a PIXcel detector. The coated cutting tools were mounted in sample holders to ensure that the flank face of the samples are parallel to the reference surface of the sample holder and also that the flank face is at appropriate height. Cu-Kα radiation was used for the measurements, with a voltage of 45 kV and a current of 40 mA. Anti-scatter slit of ½ degree and divergence slit of ¼ degree were used. The diffracted intensity from the coated cutting tool was measured in the range 20° to 140° 2θ, i.e. over an incident angle θ range from 10 to 70°.

[0040] The data analysis, including background subtraction, Cu-K.sub.α2 stripping and profile fitting of the data, was done using PANalytical's X'Pert HighScore Plus software. The output (integrated peak areas for the profile fitted curve) from this program were then used to calculate the texture coefficients of the layer by comparing the ratio of the measured intensity data to the standard intensity data according to a PDF-card of the specific layer (such as α-Al.sub.2O.sub.3), using the Harris formula (1) as disclosed above. Since the layer was a finitely thick film the relative intensities of a pair of peaks at different 2θ angles are different than they are for bulk samples, due to the differences in path length through the layer. Therefore, thin film correction was applied to the extracted integrated peak area intensities for the profile fitted curve, taken into account also the linear absorption coefficient of layer, when calculating the TC values. Since possible further layers above for example the α-Al.sub.2O.sub.3 layer will affect the X-ray intensities entering the α-Al.sub.2O.sub.3 layer and exiting the whole coating, corrections need to be made for these as well, taken into account the linear absorption coefficient for the respective compound in a layer. Alternatively, a further layer, such as TiN, above an alumina layer can be removed by a method that does not substantially influence the XRD measurement results, e.g. chemical etching.

[0041] In order to investigate the texture of the α-Al.sub.2O.sub.3 layer X-ray diffraction was conducted using CuK.sub.α radiation and texture coefficients TC (hkl) for different growth directions of the columnar grains of the α-Al.sub.2O.sub.3 layer were calculated according to Harris formula (1) as disclosed above, where I(hkl)=measured (integrated area) intensity of the (hkl) reflection, I.sub.0(hkl)=standard intensity according to ICDD's PDF-card no 00-010-0173, n=number of reflections to be used in the calculation. In this case 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).

[0042] It is to be noted that peak overlap is a phenomenon that can occur in X-ray diffraction analysis of coatings comprising for example several crystalline layers and/or that are deposited on a substrate comprising crystalline phases, and this has to be considered and compensated for by the skilled person. A peak overlap of peaks from the α-Al.sub.2O.sub.3 layer with peaks from for example TiCN layer might influence measurement and needs to be considered. It is also to be noted that for example WC in the substrate can have diffraction peaks close to the relevant peaks of the present invention.

EXAMPLES

[0043] 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 (Invention)

[0044] Cemented carbide substrates of ISO-type CNMG120408 for turning (samples E23C-1 and E23C-2) were manufactured from 7.2 wt-% Co, 2.7 wt % Ta, 1.8 wt % Ti, 0.4 wt % Nb, 0.1 wt % N and balance WC, comprising a Co enriched surface zone of about 25 μm from the substrate surface and to a depth into the body being essentially free from cubic carbides.

[0045] The inserts were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 7 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.

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

[0046] On top of the MTCVD TiCN layer was a 1-2 μm thick bonding layer deposited at 1000° C. by a process consisting of three separate reaction steps. First a TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2, HCl and H.sub.2 at 70 mbar and finally a third step using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and thereby producing a TiCNO bonding layer. During the second and third TiCNO deposition step some of the gases were continuously changed as indicated by a first and a second level in the Table. 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.

TABLE-US-00002 Dep. of TiCNO bonding layer at 1000° C., balance Pressure N.sub.2 CH.sub.4 HCl CO TiCl.sub.4 CH.sub.3CN CO.sub.2 H.sub.2: [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] TiCN 400 25.5 3.4 1.7 — 1.56 — — TiCNO-1 70 12 — 1.2 1.2 1.5 0.4  — TiCNO-2 70 31.5 — — 1.6 3.15 0.66 — 30.9 3.7 3.09 0.64 TiCNO-3 70 31.1 — — 3.7 3.11 — — 30.8 4.6 3.08 Oxidation 55 30 — — 12.5 — — 3.7

[0047] 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 as disclosed below giving a total α-Al.sub.2O.sub.3 layer thickness of about 5 μm. The second α-Al.sub.2O.sub.3 deposition step was performed using 1.2% AlCl.sub.3, 4.7% CO.sub.2, 2.9% HCl, 0.58% H.sub.2S and balance H.sub.2.

[0048] An outermost layer of about 1 μm TiN was deposited covering the α-Al.sub.2O.sub.3 layer and thereby forming the samples E23C-1 and E23C-2.

Example 2 (Reference)

[0049] Cemented carbide substrates of ISO-type CNMG120408 for turning were manufactured from 7.2 wt-% Co, 2.7 wt % Ta, 1.8 wt % Ti, 0.4 wt % Nb, 0.1 wt % N and balance WC, comprising a Co enriched surface zone of about 25 μm from the substrate surface and to a depth into the body being essentially free from cubic carbides.

[0050] Inserts were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 8 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. For the coating R25 the volume ratio of TiCl.sub.4/CH.sub.3CN in an initial part of the MTCVD deposition of the TiCN layer was 3.7, followed by a period using a ratio of TiCl.sub.4/CH.sub.3CN of 2.2.

[0051] On top of the MTCVD TiCN layer was a 1-2 μm thick bonding layer deposited at 1000° C. by a process consisting of three separate reaction steps. First a TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2, HCl and H.sub.2 at 70 mbar and finally a third step using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and thereby producing a TiCNO bonding layer. Prior to the start of the α-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.

[0052] Thereafter an 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 1.16% 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 5 μm.

[0053] The samples formed, R25C-1, R25C-2, also comprises an outermost layer of about 1 μm thick TiN.

Example 2b (Reference)

[0054] Cemented carbide substrates of ISO-type CNMG120408 for turning were manufactured from 7.2 wt-% Co, 2.7 wt % Ta, 1.8 wt % Ti, 0.4 wt % Nb, 0.1 wt % N and balance WC, comprising a Co enriched surface zone of about 25 μm from the substrate surface and to a depth into the body being essentially free from cubic carbides.

[0055] Inserts were first coated with a thin approximately 0.3 μm TiN-layer then with an approximately 8 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 during the MTCVD deposition of the TiCN layer was 2.2.

[0056] On top of the MTCVD TiCN layer was an about 1 μm thick bonding layer deposited at 1000° C. (HTCVD) by a process consisting of two reaction steps. First a TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 55 mbar, then a second step using TiCl.sub.4 and CO at 55 mbar. Prior to the start of the α-Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO.sub.2 and HCl.

[0057] Thereafter an α-Al.sub.2O.sub.3 layer was deposited at 1000° 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 5 μm.

[0058] The samples formed, R225C-1, R225C-2, also comprises an outermost layer of about 1 μm thick TiN.

Example 3 (Texture Analysis)

[0059] X-ray diffraction measurement was used to analyse the TC values of the α-Al.sub.2O.sub.3 and the TiCN in accordance with the method as disclosed above. Two sample individuals of the coated CNMG120408 substrate were texture analysed and subsequently wear tested. The layer thicknesses were analysed in a light optical microscope by studying a cross section of each coating and the bonding layer is included in the TiCN layer thickness given in Table 2. The results are presented in Table 2.

[0060] The dielectric loss properties were analysed by measuring the tan δ in a method as disclosed above. The value given below is an average value of 14 measurements at separate structures provided on the flank face of each cutting tool.

TABLE-US-00003 TABLE 2 (Thickness and diffraction data) Layer Layer tan δ thickness thickness α- TC(0 0 12) of (average of 14 Sample TiCN [μm] Al.sub.2O.sub.3 [μm] α-Al.sub.2O.sub.3 measurements) E23C-1 9.1 5.1 7.66  21 × 10.sup.−4 E23C-2  11 × 10.sup.−4 R25C-1 8.6 5.2 6.87  26 × 10.sup.−4 R25C-2 142 × 10.sup.−4 R225C-1 8.3 4.3 0 320 × 10.sup.−4 R225C-2 300 × 10.sup.−4

Example 4 (Cutting Test)

[0061] 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 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 turning test.

[0062] The coated cutting tools of the ISO type CNMG120408 as blasted were tested in longitudinal turning in ball bearing steel (100CrMo7-3) using the following cutting data;

Cutting speed v.sub.c: 220 m/min
Cutting feed, f: 0.3 mm/revolution
Depth of cut, a.sub.p: 2 mm

[0063] Water miscible metal working fluid was used.

[0064] One cutting edge per cutting tool was evaluated.

[0065] In analyzing the crater wear, the area of exposed substrate was measured, using a light optical microscope. When the surface area of the exposed substrate exceeded 0.2 mm.sup.2 the life time of the tool was considered to be reached. The wear of each cutting tool was evaluated after 2 minutes cutting in the light optical microscope. The cutting process was then continued with a measurement after each 2 minutes run, until the tool life criterion was reached. When the size of the crater area exceeded 0.2 mm.sup.2 the time until the tool life criterion was met was estimated based on an assumed constant wear rate between the two last measurements. Beside crater wear, flank wear was also observed, but did not in this test influence the tool life. Two parallel tests were run for each type of coating, for example sample E23C-1 was tested in wear test 1 and the samples E23C-2 was tested in wear test 2. The results are shown in Table 3.

TABLE-US-00004 TABLE 3 (Wear performance) Coating Crater wear test 1 [min] Crater wear test 2 [min] E23C 51 55 R25C 27 28 R225C 16 18

[0066] 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.