PVD process for the deposition of Al.SUB.2.O.SUB.3 .and a coated cutting tool with at least one layer of Al.SUB.2.O.SUB.3

Abstract

A coated cutting tool including a substrate and a single layer or multi-layer hard material coating is provided. The substrate is selected from cemented carbide, cermet, ceramics, cubic boron nitride (cBN), polycrystalline diamond, steel or high-speed steel. The hard material coating includes at least one layer of gamma-Al.sub.2O.sub.3, exhibiting particularly high hardness and reduced Young's modulus. The gamma-Al.sub.2O.sub.3 layer of the coated cutting tool is obtainable by means of a reactive magnetron sputtering process using at least one Al target, wherein the deposition is carried out using a reaction gas composition of argon (Ar) and oxygen (O.sub.2) at a total reaction gas pressure within the range from at least 1 Pa to at most 5 Pa, at an O.sub.2 partial pressure within the range from 0.001 Pa to 0.1 Pa, and at a temperature within the range from 400° C. to 600° C.

Claims

1. A process for manufacturing of a coated cutting tool consisting of a substrate and a single layer or multi-layer hard material coating, the substrate being selected from cemented carbide, cermet, ceramics, cubic boron nitride (cBN), polycrystalline diamond (PCD), steel or high-speed steel (HSS), and the hard material coating including at least one layer of gamma-Al.sub.2O.sub.3 being deposited by means of a reactive pulsed magnetron sputtering process using at least one Al target, wherein the at least one gamma-Al.sub.2O.sub.3 layer has a Vickers hardness HV(0.0015) of 3000 HV to 3500 HV, and wherein the deposition is carried out using a reaction gas composition comprising or consisting of argon (Ar) and oxygen (O.sub.2) at a total reaction gas pressure within the range from at least 1 Pa to at most 5 Pa, at an O.sub.2 partial pressure within the range from 0.001 Pa to 0.1 Pa, at a temperature within the range from 400° C. to 600° C., wherein a power density at the magnetron is from 4 to 20 W/cm.sup.2, the bias voltage is from 80 V to 200 V and the bias current is from 20 A to 60 A.

2. The process according to claim 1, further comprising controlling the flow of oxygen during the deposition process in order to provide a substantially constant cathode voltage and/or substantially constant oxygen partial pressure.

3. The process according to claim 1, wherein the power density at the magnetron is from 6 to 13 W/cm.sup.2.

4. The process according to claim 1, wherein the bias voltage is from 100 V to 180 V.

5. The process according to claim 1, wherein the reactive pulsed magnetron sputtering process has a pulse frequency within the range from 20 kHz to 100 kHz.

6. The process according to claim 1, wherein the bias current is from 26 A to 50 A.

7. The process according to claim 1, wherein a portion of the O.sub.2 gas in the reactive gas composition is replaced by a nitrogen and oxygen containing gas, selected from nitrous oxide, N.sub.2O, nitric oxide, NO, nitrogen dioxide, NO.sub.2, and dinitrogen tetroxide, N.sub.2O.sub.4.

8. A coated cutting tool comprising a substrate and a single layer or multi-layer hard material coating, the substrate being selected from cemented carbide, cermet, ceramics, cubic boron nitride (cBN), polycrystalline diamond, steel or high-speed steel, and the hard material coating comprising at least one layer of gamma-Al.sub.2O.sub.3, wherein the at least one layer of gamma-Al.sub.2O.sub.3 is deposited by the process of claim 1.

9. A coated cutting tool comprising a substrate and a single layer or multi-layer hard material coating, the substrate being selected from cemented carbide, cermet, ceramics, cubic boron nitride (cBN), polycrystalline diamond (PCD), steel or high-speed steel (HSS), and the hard material coating comprising at least one layer of gamma-Al.sub.2O.sub.3, wherein the entire at least one gamma-Al.sub.2O.sub.3 layer has a Vickers hardness HV(0.0015) of 3000 HV to 3500 HV.

10. The coated cutting tool according to claim 9, wherein the at least one gamma-Al.sub.2O.sub.3 layer has a reduced Young's modulus of 350 GPa to 390 GPa.

11. The coated cutting tool according to claim 9, wherein the at least one gamma-Al.sub.2O.sub.3 layer is deposited directly onto the substrate.

12. The coated cutting tool according to claim 9, wherein at least one further layer of a nitride, carbide, carbonitride or boride of an element, selected from the group, consisting of Ti, Al, Cr, Si, V, Nb, Ta, W, Zr and Hf, is deposited between the substrate and the at least one gamma-Al.sub.2O.sub.3 layer and/or on top of the at least one gamma-Al.sub.2O.sub.3 layer.

13. The coated cutting tool according to claim 9, wherein the at least one gamma-Al.sub.2O.sub.3 layer has a thickness in the range from 0.3 μm to 20 μm.

14. The coated cutting tool according to claim 9, wherein the at least one layer of gamma-Al.sub.2O.sub.3 is deposited by a reactive pulsed magnetron sputtering process using at least one Al target, wherein the deposition is carried out using a reaction gas composition comprising or consisting of argon (Ar) and oxygen (O.sub.2) at a total reaction gas pressure within the range from at least 1 Pa to at most 5 Pa, at an O.sub.2 partial pressure within the range from 0.001 Pa to 0.1 Pa, at a temperature within the range from 400° C. to 600° C., wherein a power density at the magnetron is from 4 to 20 W/cm.sup.2, the bias voltage is from 80 V to 200 V and the bias current is from 20 A to 60 A.

15. The process according to claim 5, wherein the reactive magnetron sputtering process is a bipolar pulsed magnetron sputtering process or HIPIMS.

16. The coated cutting tool according to claim 9, wherein the at least one gamma-Al.sub.2O.sub.3 layer has a reduced Young's modulus of 370 GPa to 390 GPa.

17. A coated cutting tool comprising a substrate and a single layer or multi-layer hard material coating, the substrate being selected from cemented carbide, cermet, ceramics, cubic boron nitride (cBN), polycrystalline diamond (PCD), steel or high-speed steel (HSS), and the hard material coating comprising at least one layer of gamma-Al.sub.2O.sub.3, wherein the at least one gamma-Al.sub.2O.sub.3 layer has a Vickers hardness HV(0.0015) of 3000 HV to 3500 HV and a reduced Young's modulus of 361 GPa to 390 GPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a coated substrate.

DETAILED DESCRIPTION

(2) Referring to FIG. 1, the coated substrate 10 comprises a substrate 11 and a coating 12 deposited thereon. The coating 12 includes at least one gamma-Al2O3 layer.

Example 1—Deposition of Gamma-Al.SUB.2.O.SUB.3 .Coating Layers According to the Invention and Comparative Coatings

(3) In the following examples of the preparation of cutting tools according to the present invention and of comparative examples cemented carbide cutting tool substrate bodies (composition: 12 wt-% Co, 1.6 wt-% (Ta, Nb)C, balance WC; WC grain size: 1.5 μm; geometry: ADMT160608R-F56); were coated by bipolar pulsed magnetron sputtering in a PVD system as indicated above.

(4) Prior to the deposition, the installation was evacuated to 8×10.sup.−5 mbar, and the substrates were pre-treated at 550° C. For the depositions of A.sub.2O.sub.3, two Al-targets (800 mm×200 mm×10 mm each) were used and a dual magnetron was applied. The bias power supply was used in a bipolar pulsed mode with 45 kHz and an off-time of 10 ms. The magnetron power supply was pulsed with 60 kHz (±2 kHz), and the pulse form was sinus shape. The cathode voltage at the stabilized stage of the process was 390 V. Each of the depositions experiments was carried out with three-fold rotated substrates. The essential deposition parameters and measurement results (measured on products positioned in the middle of the reactor height) are indicated in the following table 1.

(5) TABLE-US-00001 TABLE 1 1 2 3 4 5 Sample # (Inv.) (Inv.) (Inv.) (Inv.) (Comp.) Ar flow [sccm] 1220 2255 1915 1220 500 O.sub.2 flow [sccm] 101 104 101 156 105 Total pressure [mPa] 1000 2070 4180 1000 450 O.sub.2 part. press. [mPa] 10.2 6.8 6.1 18.1 8.0 Bias current [A] 35.3 28.0 24.0 58.0 30.8 Bias voltage [V] 125 125 125 165 125 Magnetron target 20 20 20 39 20 power [kW] Magnetron target 6.2 6.2 6.2 12.2 6.2 power density [W/cm.sup.2] Coil current [A] 4.5 4.0 5.0 2.5 6.5 Deposition time [min] 90 120 120 90 90 Deposition rate [μm/h] 0.55 0.48 0.43 0.73 0.55 Thickness [μm] 0.82 0.96 0.86 1.1 0.83 Vickers Hardness [HV] 3112 3120 3002 3164 2792 Reduced Young's 381 361 368 367 340 modulus [GPa]

(6) XRD measurements on the samples prepared according to the invention and on the comparative sample showed only peaks of gamma-Al.sub.2O.sub.3 phase.

Example 2—Comparison of the Layer Thicknesses

(7) The following table 2 shows the ratios of the measured layer thicknesses on the rake face (RF) and on the flank face (FF) [ratio RF/FF] of samples produced as described for sample #1 (invention) and sample #5 (comparative example) in example 1, respectively. The ratios RF/FF were measured on samples positioned at the top position, the middle position and the bottom position within the PVD reactor. Thereby, the layer thicknesses on the rake face (RF) were measured on the upper rake face for the samples at the top and middle positions in the reactor, whereas the layer thickness on the rake face (RF) of the sample at the bottom position of the reactor was measured on the lower rake face.

(8) TABLE-US-00002 TABLE 2 Sample Reactor layer thickness layer thickness ratio according to position RF [μm] FF [μm] RF/FF #1 (Inv.) top 0.38 0.69 0.55 middle 0.62 0.82 0.77 bottom 0.37 0.62 0.60 #5 (Comp.) top 0.28 0.62 0.45 middle 0.57 0.83 0.69 bottom 0.27 0.64 0.43

(9) The obtained results show that the thickness ratio RF/FF obtained according to the process of the present invention was at least 10% higher than obtained by the prior art process, i.e., a more even thickness distribution between rake face and flank face was obtained by the inventive process, independent of the position of the samples within the reactor.

Example 3—Cutting Tests on Multi-Layer Coated Cutting Tools

(10) In order to assess the effect of the Al.sub.2O.sub.3 layer according to the invention, compared to conventional coating, with respect to cutting properties, multi-layer coated cutting tools were produced and tested in a milling test. The cemented carbide substrates were the same as used above in example 1. In each case the multi-layer coating structures consisted of a total of seven layers, four of them were conventional TiAlN layers, alternating with inventive gamma-Al.sub.2O.sub.3 layers in the tool according to the invention, or with conventional Al.sub.2O.sub.3 layers in the comparative tool. The thicknesses of the layers corresponding to each other were the same in both sequences.

(11) The TiAlN layers were each deposited in an Arc-PVD process at a total pressure of 10 Pa. The ratio Al/(Al+Ti) in the layers was 0.61 with 50 at. % nitrogen. The deposition conditions were adjusted to achieve the desired layer thicknesses.

(12) In the layer sequence of the inventive tool, the Al.sub.2O.sub.3 layers were all prepared according to the present invention using the process parameters as described for sample #1 in example 1 above. In the layer sequence of the comparative tool, the Al.sub.2O.sub.3 layers were all prepared using the process parameters as described for sample #5 in example 1 above, whereby the substrate was three-fold rotated.

(13) The layer structures were as follows:

(14) TABLE-US-00003 Layer # Layer Thickness Layer (from substrate) [μm] Composition 1 4 μm TiAlN 2 0.5 μm Al.sub.2O.sub.3 3 0.25 μm TiAlN 4 0.1 μm Al.sub.2O.sub.3 5 0.25 μm TiAlN 6 0.1 μm Al.sub.2O.sub.3 7 0.6 μm TiAlN

(15) Using the above described tools, cutting tests were performed on a Heller FH 120-2 machine under the following conditions:

(16) Cutting tests were performed on a Heller FH 120-2 machine under the following conditions.

(17) Cutting Conditions: Tooth Feed f.sub.z [mm/tooth]: 0.2 Feed v.sub.f [mm/min]: 120 Cutting speed v.sub.c [m/min]: 235 Cutting depth a.sub.p [mm]: 3 Workpiece material: 42CrMo4; tensile strength Rm: 950 N/mm.sup.2

(18) The following table 3 shows the results of the cutting tests, wherein V.sub.B is the minimum wear at the flank faces of the tool, V.sub.Bmax is the maximum wear, i.e. the deepest crater observed on the flank face of a tool, and VR is the wear at the cutting edge radius

(19) TABLE-US-00004 TABLE 3 Cutting Inventive Tool Comparative Tool length V.sub.B V.sub.Bmax V.sub.R V.sub.B V.sub.Bmax V.sub.R [mm] [mm] [mm] [mm] [mm] [mm] [mm] 800 0.02 0.02 0.02 0.02 0.03 0.03 1600 0.02 0.03 0.03 0.03 0.04 0.06 2400 0.02 0.05 0.04 0.04 0.06 0.08 3200 0.02 0.07 0.07 0.07 0.1 0.12 4000 0.02 0.10 0.10 0.10 0.12 0.17 4800 0.03 0.13 0.18 0.12 0.35 0.45

(20) The results clearly show the advantageous behaviour of a cutting tool comprising at least one layer of Al.sub.2O.sub.3 according to the invention. In particular, the wear is considerably reduced with increasing cutting lengths.