METHOD FOR COATING A TOOL PART OF A MACHINING TOOL

Abstract

A method of producing a coated tool part of a cutting tool. The tool part is coated with a coating containing at least one aluminum oxide (Al.sub.2O.sub.3) containing Al.sub.2O.sub.3-layer having an alpha-Al.sub.2O.sub.3 phase fraction and a gamma-Al.sub.2O.sub.3 phase fraction. The at least one Al.sub.2O.sub.3-layer is produced using a reactive magnetron sputtering process.

Claims

1. A method, comprising: providing a tool part of a cutting tool as a substrate comprising a substrate material selected from the group consisting of cemented carbide, cermet, cubic boron nitride, polycrystalline diamond or high speed steel; and coating the tool part with a coating comprising at least one aluminum oxide (Al.sub.2O.sub.3) containing Al.sub.2O.sub.3-layer having an alpha-Al.sub.2O.sub.3 phase fraction and a gamma-Al.sub.2O.sub.3 phase fraction, wherein the Al.sub.2O.sub.3-layer is produced by a reactive magnetron sputtering process, and wherein in the reactive magnetron sputtering process: at least one aluminum target is used; a gas mixture is used which has a noble gas as a first component and oxygen (O.sub.2) and/or a nitrogen oxide (NO.sub.x) as a second component as a reactive gas; a total gas pressure <1 Pa is set; a process temperature between 400 C. and 650 C. is set; a maximum target power density100 W/cm.sup.2 and a maximum target current 200 A is set; and a magnetic field is generated using at least one solenoid coil, which is operated with a coil current 7 A.

2. The method according to claim 1, wherein the reactive magnetron sputtering process is a pulsed magnetron sputtering process.

3. The method according to claim 1, wherein the reactive magnetron sputtering process is a pulsed magnetron sputtering process with rectangular voltage pulses.

4. The method according to claim 3, wherein the rectangular voltage pulses are bipolar voltage pulses.

5. The method according to claim 3, wherein the rectangular voltage pulses have a pulse frequency between 10 KHz and 150 KHz.

6. The method according to claim 3, wherein the rectangular voltage pulses have a pulse frequency between 40 KHz and 80 KHz.

7. The method according to claim 1, wherein the reactive magnetron sputtering process is a dual magnetron sputtering process.

8. The method according to claim 1, wherein the reactive magnetron sputtering process is a dual magnetron sputtering process with two aluminum targets.

9. The method according to claim 1, wherein the total gas pressure is set <700 mPa.

10. The method according to claim 1, wherein the coil current is 10 A.

11. The method according to claim 1, wherein in the reactive magnetron sputtering process a time-averaged target power density of 3 W/cm.sup.2 to 30 W/cm.sup.2 is set.

12. The method according to claim 1, wherein in the reactive magnetron sputtering process a time-averaged target power density of 4 W/cm.sup.2 to 20 W/cm.sup.2 is set.

13. The method according to claim 1, wherein in the reactive magnetron sputtering process a bias voltage between 125 V and 300 V is applied to the substrate.

14. The method according to claim 13, wherein the bias voltage is a pulsed bias voltage having a bias pulse frequency between 5 kHz and 80 KHz.

15. The method according to claim 13, wherein a bias current is between 10 A and 60 A.

16. The method according to claim 1, wherein the noble gas comprises argon (Ar) and/or krypton (Kr) and/or neon (Ne).

17. The method according to claim 1, wherein the Al.sub.2O.sub.3-layer is deposited directly on the substrate material, and the substrate material is a cemented carbide.

18. The method according to claim 1, wherein a plurality of layers are deposited on the substrate material, at least one layer of which is a metal oxide layer on which the Al.sub.2O.sub.3-layer is directly deposited, wherein the metal oxide layer comprises an oxide of one or more of metals selected from the group consisting of Ti, Si, V, Zr, Mg, Fe, B, Gd, La and Cr.

19. The method according to claim 18, wherein the metal oxide layer comprises TiO.sub.2.

20. A coated tool part of a cutting tool, said tool part comprising a substrate material selected from the group consisting of cemented carbide, cermet, cubic boron nitride, polycrystalline diamond or high speed steel, and a coating comprising at least one aluminum oxide (Al.sub.2O.sub.3) containing Al.sub.2O.sub.3-layer having an alpha-Al.sub.2O.sub.3 phase fraction and a gamma-Al.sub.2O.sub.3 phase fraction, wherein the Al.sub.2O.sub.3-layer is produced by the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG. 1 shows a schematic representation of a coated tool part according to an embodiment;

[0061] FIG. 2 shows a schematic representation illustrating the layer structure of a coating according to a first embodiment;

[0062] FIG. 3 shows a schematic representation illustrating the layer structure of a coating according to a second embodiment;

[0063] FIG. 4 shows a schematic representation illustrating the layer structure of a coating according to a third embodiment;

[0064] FIG. 5 shows a schematic representation illustrating the layer structure of a coating according to a fourth embodiment;

[0065] FIG. 6 shows a first XRD diagram showing the results of a phase analysis using X-ray fine structure diffraction; and

[0066] FIG. 7 shows a second XRD diagram showing the results of a phase analysis using X-ray fine structure diffraction.

DETAILED DESCRIPTION

[0067] FIG. 1 shows a coated tool part in schematic form. The coated tool part is denoted therein in its entirety with the reference numeral 10.

[0068] The coated tool part can be an indexable insert, for example. In the present embodiment, the coated tool part 10 comprises a substrate 12 made of cemented carbide, which is coated with a coating 14 on part of its surface. Of course, the entire surface of the tool part 10 can also be coated.

[0069] In the present case, the coated surface may, for example, be a rake face 16 of an indexable cutting insert that has one or more cutting edges 18.

[0070] FIG. 2 schematically shows the layer structure of the coating 14 on the substrate 12.

[0071] According to the present embodiment, the coating 14 was carried out in a Hauzer HTC1000 coating system. A cemented carbide substrate 12 with a Co-content of 9.0 m % was used for the deposition of the coating 14. Furthermore, the substrate 12 has a mixed carbide content of approx. 1 m % and a WC content of approx. 90 m %.

[0072] According to this embodiment, the used cemented carbide substrate 12 has dimensions of 15 mm15 mm5 mm. Preferably, the cemented carbide substrate 12 has a hole (not shown) for holding it during deposition. One side surface of the substrate 12 has been polished.

[0073] It is understood that a large number of such substrates 12 were coated simultaneously in the coating system. The substrates 12 were thereby stored on a rotating substrate table. More precisely, the substrates 12 were arranged in towers, which are mounted on the substrate table and rotate together with it. A 3f-rotation was performed during the coating process.

[0074] The 2f-rotation describes a mounting method in which the substrates are rotated with both the substrate table and the towers on it. This creates a 2f-rotation around two parallel but not concentric axes. The 3f-rotation describes a mounting method in which the substrates are rotated both with the substrate table and the towers on it and also the skewers on which the substrates are mounted. This creates a 3f-rotation around three parallel but not concentric axes. The tool parts 10 were aligned in such a way that the coating thickness was measured on a rotating polished surface that was aligned parallel to the axes of rotation.

[0075] In the first embodiment shown in FIG. 2, a coating 14 with four individual layers was produced. According to the first embodiment, the coating 14 conmprises an AlTiN-layer 20, which was deposited directly on the cemented carbide substrate 12. A TiC-layer 22 was deposited on this AlTiN-layer 20. A TiO.sub.2/TiO.sub.x-layer 24 was produced on the TiC-layer 22 by oxidation. An Al.sub.2O.sub.3-layer 26 was deposited on the TiO.sub.2/TiO.sub.x-layer 24, which has both an -Al.sub.2O.sub.3-phase fraction and a -Al.sub.2O.sub.3-phase fraction.

[0076] The AlTiN layer 20 was applied using HiPIMS sputtering. An AlTi 55/45 target consisting of 55 at % Al and 45 at % Ti was used for this purpose. A target power of 15 KW was set. The pulse on-time was 150 s with a current control to 200 A and a starting voltage of 1400 V. The coil current was 4 A. An argon gas flow was set to 450 sccm. The total gas pressure in the reaction chamber was controlled to 420 mPa. Nitrogen (N.sub.2) was used as the reactive gas for pressure control. The bias voltage was 80 V DC. The rotation of the substrate table was set to 3 rpm. The deposition time was 4 h 30 s. The deposition temperature was 550 C. The layer thickness of the AlTiN layer 20 produced in this way was approx. 1.2 m.

[0077] Subsequently, the TiC layer 22 was also applied using HiPIMS sputtering. A Ti target was used for this. The target power was set to 15 KW. The pulse on-time was 60 s with a current control to 500 A and a starting voltage of 1800 V. The coil current was set to 4 A. The bias voltage was set to 60 V DC. An argon gas flow of 500 sccm was used. Acetylene (C.sub.2H.sub.2) with a flow of 32.5 sccm was used as the reactive gas. The coating time was 3 h. The substrate temperature was set to 550 C. The rotation of the substrate table was set to 3 rpm. The TiC layer 22 has a layer thickness of approx. 0.4 m.

[0078] Subsequently, the upper part of the TiC layer 22 was converted into the TiO.sub.2/TiO.sub.x-layer 24 by means of an oxidation process. The oxidation of the TiC layer 22 to the TiO.sub.2/TiO.sub.x-layer 24 was carried out at a substrate temperature of 600 C., an oxygen gas flow of 994 sccm and for a duration of 45 min. In this way, a TiO.sub.2/TiO.sub.x-layer 24 having a layer thickness of approx. 0.1 m was produced.

[0079] After the oxidation process, the Al.sub.2O.sub.3-layer 26 was applied to the existing layer composite using a dual magnetron sputtering process. Two aluminum targets were used for this. The two targets used were located on opposite sides of the reaction chamber. The pulse shape of the power supply used was in bipolar mode and rectangular. The power of the pulsed power supply was set to a constant 20 KW during deposition. The frequency of the power supply was 40 kHz. The duty cycle of the rectangular pulses was 50% (i.e. 50% positive voltage pulses and 50% negative voltage pulses). A gas mixture of argon and oxygen was used inside the reaction chamber. The argon gas flow was set to a constant 500 sccm. The oxygen gas flow was adjusted via the set operating point of the process control at 430 V. The oxygen gas flow was approx. 105 sccm. The total gas pressure was approx. 457 mPa. A negative bipolar pulsed bias voltage (substrate bias voltage) with a frequency of 30 kHz and an off time of 10 s was applied to the substrates 12 during deposition. The level of the negative bias voltage was 175 V. The rotation of the substrate table was 2 rpm. The substrate temperature during deposition was 570 C. The coil current was set to 10 A. The deposition time was 2 h 10 min. The --Al.sub.2O.sub.3-layer 26 deposited in this way has a layer thickness of approx. 1.2 m.

[0080] The deposition of the --Al.sub.2O.sub.3-layer on the TiO.sub.2/TiO.sub.x-layer 24 has proven to be particularly advantageous, as this increased the formation of the -Al.sub.2O.sub.3-phase components. Further tests by the applicant have shown that the TiO.sub.2/TiO.sub.x-layer 24 should have a minimum layer thickness of 5 nm and the Al.sub.2O.sub.3-layer 26 should have a layer thickness of at least 10 nm.

[0081] The layer structure of the coating 14 according to the second embodiment shown in FIG. 3 is principally similar to the layer structure according to the first embodiment shown in FIG. 2. Accordingly, the layers 20, 22, 24 were also produced by means of the same manufacturing processes using the same process parameters. For the sake of simplicity, these are therefore not repeated again.

[0082] In contrast to the first embodiment, during the deposition of the Al.sub.2O.sub.3-layer 26, the voltage was varied from 175 V to 125 V in the form of a time gradient. The bias current of about 21 A was slightly lower than in the first embodiment (about 26 A). The temporal variation of the bias voltage resulted in the Al.sub.2O.sub.3 layer 26 having a higher --Al.sub.2O.sub.3-phase fraction towards the upper end of the layer 26. The layer thickness of the --Al.sub.2O.sub.3-layer 26 was 1.4 m according to the second embodiment.

[0083] In the third embodiment shown in FIG. 4, the Al.sub.2O.sub.3-layer 26 was also deposited using a dual reactive magnetron sputtering process. However, the Al.sub.2O.sub.3 layer 26 was deposited here directly on the cemented carbide substrate 12 (layers 20, 22, 24 therefore do not exist here). The deposition of the --Al.sub.2O.sub.3-layer 26 was carried out at a substrate temperature of approx. 550 C. in an argon-oxygen gas mixture. The power of the two aluminum targets was set to 20 kW. The total gas pressure during deposition was 454 mPa. A negative bias voltage of 200 V was applied to the substrates during the deposition process. The rotation of the substrate table was 2 rpm. The layer thickness of the --Al.sub.2O.sub.3-layer 26 was 0.8 m according to the third embodiment.

[0084] FIG. 5 shows a fourth embodiment of a coating 14. According to this fourth embodiment, the coating 14 has the following coating sequence starting from the substrate 12: An AlTiN layer 20 having a layer thickness of approx. 2000 nm, a thin Al.sub.2O.sub.3-layer 26 having a layer thickness of approx. 15 nm, a TiO.sub.2/TiO.sub.x-layer 24 having a layer thickness of approx. 60 nm, a --Al.sub.2O.sub.3-layer 26 having a layer thickness of approx. 500 nm and a four-layer composite, each of which has an AlTiN layer having a layer thickness of approx. 150 nm, an Al.sub.2O.sub.3-layer 26 arranged above it having a layer thickness of 15 nm, a TiO.sub.2/TiO.sub.x-layer having a layer thickness of 60 nm and a --Al.sub.2O.sub.3-layer 26 having a layer thickness of approx. 150 nm. According to the fourth embodiment, the uppermost layer of the coating 14 is an AlTiN layer 20 having a layer thickness of approximately 150 nm.

[0085] The --Al.sub.2O.sub.3-layers 26 contained in the coating 14 according to the fourth embodiment were produced in a similar manner as previously mentioned. The following tables summarize again the process parameters during the production of the --Al.sub.2O.sub.3-layers 26 for all four embodiments:

TABLE-US-00001 Invention Oxygen Argon Process Bias Example gas flow gas flow temperature voltage No. in sccm in sccm in C. in V 1 ca. 105 500 570 175 2 ca. 104 500 570 175 > 125 3 ca. 73 500 550 200 4 ca. 104 500 570 175

TABLE-US-00002 Invention Bias Bias Bias Table Example current frequency off-time rotation No in A in kHz in s in rpm 1 ca. 26 30 10 2 2 ca. 21 30 10 2 3 ca. 24 20 1 2 4 ca. 34 30 10 2

TABLE-US-00003 Invention Pulse Pulse DMS Operating Example shape frequency power point No. DMS DMS in kHZ in kW in V 1 rectangular 40 20 430 2 rectangular 40 20 430 3 rectangular 80 20 430 4 rectangular 40 20 430

TABLE-US-00004 Invention Example Deposition time Coil current total gas pressure No. in min in A in mPa 1 130 10 ca. 457 2 130 10 ca. 455 3 180 10 ca. 454 4 65 + 4*20 10 ca. 465

[0086] As can be seen from the tables above, the total gas pressure in the four embodiments was selected in the range of 454 mPa-465 mPa. However, further tests by the applicant have shown that the total gas pressure can also be selected somewhat higher without the positive properties of the Al.sub.2O.sub.3-layer being lost. However, the total gas pressure should always be selected <1 Pa.

[0087] The process temperature was selected at 550 C. or 570 C. according to the four embodiments shown here. However, tests by the applicant have shown that other process temperatures in the range from 400 C. to 650 C. are also possible.

[0088] The coil current was selected at 10 A in each case. Tests by the applicant have shown that the coil current should generally be selected at 7 A to achieve the desired properties of the Al.sub.2O.sub.3-layer.

[0089] The following modifications to the above-mentioned embodiments are conceivable in principle: Instead of producing the TiO.sub.2/TiO.sub.x-layers 24 via an oxidation process, a TiO.sub.2 layer could also be produced by direct deposition. Furthermore, it should be noted with regard to the oxidized TiC-layers to TiO.sub.2/TiO.sub.x-layers 24 that these may also have C as a further component, so that it could be a TiCO layer.

[0090] It would also be conceivable to use a layer of WCCo instead of TiO.sub.2-layers 24 as sub-layers for the --Al.sub.2O.sub.3-layers 26.

[0091] The following table summarizes the analysis results of the coating properties of the four coatings 14 shown in FIGS. 2-5. For comparison, this table shows the coating properties of a reference coating consisting of an AlTiN-coating having a thickness of approx. 1.2 m, which was deposited directly on the cemented carbide substrate 12.

TABLE-US-00005 Invention Layer red. modulus of XRD Al.sub.2O.sub.3 Example thickness Hardness H.sub.IT elasticity phase No. in m in MPa in GPa analysis reference 1.2 26.3 543 1 2.9 34.5 431 alpha + gamma 2 3.1 29.2 389 alpha + gamma 3 0.8 36.3 464 alpha + gamma 4 4.2 27.7 418 alpha + gamma

[0092] The coating thickness was determined in each case by grinding a spherical cap with a steel ball with a diameter of 20 mm. The steel ball was used to grind a spherical cap. The rings visible in the spherical cap were then measured using an optical microscope. The measurements were carried out on the polished free surface of the carbide substrates 12.

[0093] The instrumented coating hardness H.sub.IT and the instrumented modulus of elasticity E.sub.IT were determined by nanoindentation using the Oliver-Pharr method. An NHT1 device from the manufacturer CSM Instruments with a Berkovich indenter made of diamond was used for the measurement. During the measurement, the maximum load was 10 mN, the loading time 30 s, the creep time 10 s and the unloading time 30 s. Loading and unloading curves were recorded. The hardness values and the values for the reduced modulus of elasticity (red. modulus of elasticity E.sub.IT) were determined from these load and unloading curves using the Oliver-Pharr method. The measurements were carried out on the coating surface. A transverse contraction coefficient of 0.25 was used to determine the reduced modulus of elasticity.

[0094] FIGS. 6 and 7 show the results of a phase analysis of the coating 14 using X-ray fine structure diffraction. The phase analysis was carried out using grazing incidence X-ray diffraction (GIXRD) at an angle of incidence of 1. A diffractometer from Malvern Panalytical (Empyrean) with Cu K.sub. radiation at 40 kV and 40 mA was used. The measurements were carried out in line focus with a parallel beam via a mirror. A 2 mm mask, a slit diaphragm to reduce the divergence and a 0.04 rad set point were used. A 0 D proportional detector with a 0.27 plate collimator was used for the measurement. For the measurements shown in FIG. 6, for example, a 2-theta measuring range of 20-65 with a step width of 0.07 and a counting width of 60 s was selected. The angle of incidence was kept constant at 1. The resulting diffractograms were used for phase analysis. For better comparability, the background of the XRD diagrams was corrected, the diffractograms were normalized to the maximum intensity and a y-offset was added if necessary.

[0095] In addition to the reflections of the cemented carbide substrate 12 (hexagonal WC, space group P-6m2, space group no. 187, PDF no. 51-939 of the ICDD database, dot-dashed vertical line), several reflections of both -Al.sub.2O.sub.3 (rhombohedral Al.sub.2O.sub.3, space group R-3c, space group no. 167, PDF No. 42-1468 of the ICDD database, dashed vertical lines) as well as from -Al.sub.2O.sub.3 (cubic Al.sub.2O.sub.3-space group Fd-3m, space group No. 227, PDF No. 10-425 of the ICDD database, vertical lines). For reasons of clarity, the TiO.sub.2 and AlTiN phases were not marked in the diffractograms. The coatings exhibit the (024) reflex of -Al.sub.2O.sub.3 at 2theta of approx. 52.559. This demonstrates the existence of the -Al.sub.2O.sub.3-phase in the coating 14. Furthermore, the -Al.sub.2O.sub.3-phase is also present.

[0096] It is to be understood that the foregoing is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.

[0097] As used in this specification and claims, the terms for example, e.g., for instance, such as, and like, and the verbs comprising, having, including, and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.