METHOD FOR PRODUCE A HARD MATERIAL LAYER ON A SUBSTRATE AND MACHINING TOOL WITH A SUBSTRATE MADE OF HARD METAL

Description

Technical field

[0001] The present invention relates to a method for producing a hard material layer on a substrate according to claim 1, wherein a multilayer system is deposited on the substrate by means of PVD. The method is preferably used for the production of cutting tools for turning, milling or other machining processes.

[0002] Furthermore, the present invention relates to a hard material layer and a cutting tool, preferably a cutting body or an indexable insert or a solid carbide tool.

[0003] The present disclosure further relates to a method for producing a coating source and a coating source for carrying out the method for producing a hard layer on a substrate, which according to the claims do not belong to the claimed invention. State of the art

[0004] It is known to apply hard coatings to increase the wear resistance of cutting tools and other components subjected to wear, which further increases the wear resistance of the respective components.

[0005] The respective hard coating is typically deposited onto wear-resistant substrate materials using physical or chemical deposition from the gas phase. Examples of substrate materials used include cemented carbides, cermets, hard materials, or tool steels.

[0006] Hard metal is a composite material that typically comprises a main phase of tungsten carbide (WC), optionally phases of other carbides, and a metallic binder or matrix. Cobalt, nickel, and / or iron are commonly used as the metallic matrix. Other carbides can be those of metals from the fourth (titanium group), fifth (vanadium group), and sixth (chromium group) subgroups, such as tantalum, niobium, hafnium, zirconium, etc.

[0007] Cermets are composite materials that contain titanium carbide as the main carbide phase. Typically, the main component of the binder consists of nickel and / or cobalt.

[0008] Hard materials are defined as materials with a hardness of more than 10 GPa.

[0009] Tool steels, in turn, are defined according to DIN 17300 as steels that are used in tools.

[0010] In coating processes, the coating of the substrates used to manufacture cutting tools can be carried out chemically or physically. Corresponding coating processes include CVD, also known as chemical vapor deposition, and PVD, also known as physical vapor deposition. The following discussion will focus solely on the PVD process.

[0011] PVD processes include thermal evaporation, electron beam evaporation, magnetron sputtering, laser beam evaporation, and arc evaporation. All PVD processes have in common that the material to be deposited is present in solid form in the evacuated coating chamber. The material, referred to as the coating source or target, is evaporated by bombardment with, for example, laser beams, magnetically deflected ions or electrons, or by arc discharge. The proportion of atoms, ions, or larger clusters in the vapor varies from process to process.

[0012] The vaporized material moves through the chamber either ballistically or guided by electric fields, encountering the parts to be coated, where layer formation occurs.

[0013] When the vaporized materials encounter the substrate, they begin to condense and deposit on its surface. The particles do not remain at the point of contact but move along the surface (surface diffusion), their energy dependent on the location, to find a more energetically favorable position. These are areas on the crystal surface with as many atomic neighbors as possible (higher binding energy).

[0014] With the various PVD variants, almost all metals and also carbon can be deposited in very pure form. If reactive gases such as oxygen, nitrogen, or hydrocarbons are introduced into the process, oxides, nitrides, or carbides can also be deposited.

[0015] It is known from Cekada et al. (Vakuum 52, 1999 / 461-467) to apply a CrTaN hard coating to a substrate using PVD with compositions of Cr 0.58 Ta 0.42 N or Cr 0.17 Ta 0.83 N. The coatings exhibited a cubic structure and good oxidation resistance. The publication concludes that neither the chromium-rich Cr 0.58 Ta 0.42 N coating nor the tantalum-rich Cr 0.17 Ta 0.83 N coating would offer any advantages over conventional CrN or TaN binary coatings.

[0016] Chen et al. investigated single-layer crystalline Ta 48 N 52 and Cr 23 Ta 27 N 50 coatings, as well as nearly amorphous Ta 22 Si 19 N 59 and Cr 6 Ta 25 Si 11 N 58 coatings, deposited on a silicon substrate using a co-sputtering process. (YLChen, et al. Surface and Coatings Technology (2014) http: / / dx.doi.org / 10.1016 / j.surfcoat.2014.02.005) Chen et al. (Surface and Coatings Technology 2006 / 2011 / 1640-1647) also deposited single-layer CrTaN coatings on WC substrates using reactive magnetron sputtering without heating the substrates. The CrTaN layers exhibited cubic (fcc) structures with (111) preferred orientation. According to the publication, the layer is well suited as an oxidation protection for glass melting furnaces or cutting tools.

[0017] Patent document US 2014 / 272391 A1 also discloses a coated cutting tool and a method for its manufacture, wherein the coating consists of several nanolayer-stacked MeAIN layers, where Me means Ti and / or Cr. Description of the invention

[0018] Starting from the known state of the art, it is an object of the present invention to provide a method for producing a hard material layer on a substrate, as well as a cutting tool with further improved properties with regard to wear resistance and hardness.

[0019] This problem is solved by a method with the features of claim 1 and a cutting tool with the features of claim 13. Advantageous embodiments are described in the dependent claims. Accordingly, a method for producing a hard coating on a substrate is proposed, wherein, according to the invention, a multilayer coating system is applied to the substrate by alternating deposition of CrTaN and AlTiN using physical vapor deposition (PVD), wherein AlTiN is applied in an atomic composition of Al x Ti 1-x N with 0.2≤x≤0.9 and CrTaN with an atomic composition of Cr 1-y Ta y N with 0.01≤y≤0.65, measured by GDOES or EDX, wherein the individual layers of the multilayer coating system are applied in thicknesses between 5 and 200 nanometers and 10 to 5000 layers are alternately deposited.

[0020] Compared to prior art methods for producing hard coatings, particularly CrTaN hard coatings, the multilayer system built up by alternating deposition of CrTaN and AlTiN achieves a significant increase in the hardness of the hard coating deposited in this way. This has a positive effect on the wear properties compared to the single CrTaN layers discussed in the prior art. A significant increase in hardness can also be achieved compared to the construction of a two-layer system of CrTaN and AlTiN.

[0021] It is known that single-layer hard coatings made of pure CrTaN have a low coefficient of friction, making them generally well-suited for cutting and machining tools. However, it is also known that the wear resistance of a hard coating made of pure CrTaN is not very high.

[0022] The proposed multilayer system made of CrTaN and AlTiN, however, achieves a significant increase in hardness, thus considerably improving the suitability of the resulting hard coating for cutting and machining tools. Furthermore, the multilayer system of CrTaN and AlTiN results in a reduced coefficient of friction compared to pure AlTiN coatings, leading to improved performance in cutting and machining tools.

[0023] Furthermore, it has been shown that the deposition of the multilayer system largely suppresses the thermal decomposition of CrTaN into GraN or Ta₂N, as would occur with a single-layer coating and as described in the literature. This makes the hard coatings produced in this manner particularly suitable for high-temperature applications. Accordingly, the presented method for producing a hard coating and the resulting hard coating are not only suitable for use as a wear-resistant coating on tools, such as carbide indexable inserts or solid carbide tools, but can also be used, for example, as oxidation protection for elements of glass melting furnaces.

[0024] It has also been shown that the alternatingly applied CrTaN layers stabilize the cubic crystal structure of the AlTIN layers, so that a largely stable cubic crystal structure can be formed via the described production of the multilayer system.

[0025] The process is preferably designed such that CrTaN is deposited from a composite target with the addition of nitrogen, preferably from a composite target with a Ta content of 1-60 at%, particularly preferably a Ta content of 20-30 at%, particularly preferably a Ta content of 25 at%.

[0026] A further preferred embodiment of the process is one in which AlTiN is deposited from a composite target with the addition of nitrogen, preferably from a composite target with a Ti content of 10-80 at%, particularly preferably with a Ti content of 25-50 at%, particularly preferably with a Ti content of 40 at%.

[0027] By depositing CrTaN and / or AlTiN from a composite target, in addition to forming a stable cubic crystal structure, single-phase deposition of the respective CrTaN and / or AlTiN layers can also be achieved, which has a beneficial effect on the service life.

[0028] The use of composite targets also eliminates the need for the more complex co-sputtem process with multiple targets, resulting in a more efficient coating process.

[0029] In the multilayer system, AlTiN is preferably deposited on the substrate in an atomic composition of Al x Ti 1-x N with preferably 0.4≤x≤0.8, particularly preferably 0.5≤x≤0.7. The layer composition is preferably measured by glow discharge optical emission spectroscopy (GDOES) or energy-dispersive X-ray spectroscopy (EDX).

[0030] In the multilayer system, CrTaN is preferably applied to the substrate with an atomic composition of Cr 1-y Ta y N with preferably 0.2≤y≤0.4, particularly preferably 0.25≤y≤0.35, measured by GDOES or EDX.

[0031] The aforementioned compositions of CrTaN and AlTiN result in a particularly hard, multi-layer system forming a stable cubic crystal structure, creating a hard coating.

[0032] A multilayer system is defined here as a system in which CrTaN and AlTiN layers are alternately deposited onto the substrate using PVD. The individual layers of the multilayer system are preferably deposited in thicknesses between 10 and 100 nanometers, particularly preferably 15 nanometers.

[0033] Preferably, 25 to 1000, and particularly preferably 50 to 250, layers are deposited alternately in the multilayer system. This allows for the deposition of a stable hard layer while simultaneously enabling efficient production of the entire hard layer.

[0034] The layer thicknesses and number of layers specified above provide an efficient balance between the hardness, stability, wear resistance and service life of the hard layer on the one hand, and the requirement for a short process time and thus cost-effective production of the hard layer on the other.

[0035] Preferably hard metals, cermets, hard materials or steels are used as substrate materials, with the substrate preferably being pretreated before the application of the respective coating.

[0036] In an alternative embodiment of the process, at least one layer of AlTiXN is deposited alternately with CrTaN in the multilayer system instead of AlTiN, wherein X=Ta, V, Si, Mo or Hf, and wherein AlTiXN is preferably deposited from a composite target.

[0037] The material properties of the hard coating can be further varied by the additional incorporation of Ta, V, Si, Mo or Hf, while retaining the fundamental advantageous properties described above.

[0038] Preferably, an AlTiN base layer is first deposited on the substrate by means of physical vapor deposition (PVD), preferably in a thickness of 0.5 to 10 µm, particularly preferably 1 to 5 µm, most preferably 2 µm, and the multilayer system is applied to this AlTiN base layer by means of alternating deposition of CrTaN and AlTiN.

[0039] The base layer provides a bonding layer between the substrate and the multilayer system, thus enabling even better adhesion of the hard layer to the substrate.

[0040] Alternatively, instead of AlTiN, a base layer of AlTiXN can be deposited, where X=Ta, V, Si, Mo, Hf, and where AlTiXN is preferably deposited from a composite target.

[0041] Furthermore, a top layer of TiN or CrTaN can be applied to the multilayer system by means of physical vapor deposition (PVD), preferably with a thickness of 0.1 to 10 µm, more preferably 0.5 to 5 µm, and particularly preferably 1 µm. Applying the top layer allows for further advantageous adjustment of the properties of the hard layer, for example, by increasing the modulus of elasticity.

[0042] The multi-layer system, preferably in combination with the respective top layer, can preferably be post-treated, for example by wet blasting, dry blasting or dyeing, whereby the surface structure and / or the surface roughness is preferably adapted to the respective intended application area.

[0043] Preferably, the CrTaN layer is deposited from a CrTa composite target, preferably from a CrTa composite target with an atomic composition of 75 / 25. Here, for example, a chemical composition of the deposited CrTaN layer of Cr 0.71 Ta 0.29 N can be measured using EDX.

[0044] The aforementioned problem is also solved by a cutting tool with a hard metal substrate according to claim 13. Advantageous further developments are described in the dependent claims.

[0045] Accordingly, a cutting tool with a hard metal substrate is proposed. According to the invention, a multilayer system is applied to the substrate by physical vapor deposition (PVD) through the alternating deposition of CrTaN and AlTiN, wherein AlTiN has an atomic composition of Al x Ti 1-x N with 0.2 ≤ x ≤ 0.9 and CrTaN has an atomic composition of Cr 1-y Ta y N with 0.01 ≤ y ≤ 0.65, as measured by GDOES or EDX. The individual layers of the multilayer system are applied in thicknesses between 5 and 200 nanometers, and 10 to 5000 layers are alternately deposited. This results in the advantages described above regarding the method of forming this hard layer on the substrate to create the cutting tool. The high hardness of the hard layer combined with a relatively low coefficient of friction is particularly advantageous.

[0046] Advantageously, an AlTiN base layer is provided between the substrate and the CrTaN / AlTiN multilayer system, preferably with a thickness of 0.5 to 10 µm, particularly preferably 1 to 5 µm, and most preferably 2 µm.

[0047] It is also advantageous to apply at least one top layer of TiN or CrTaN to the CrTaN / AlTiN multilayer system, preferably with a thickness of 0.1 to 10 µm, preferably 0.5 to 5 µm and particularly preferably 1 µm.

[0048] Advantageously, the substrate of the cutting tool is pre-treated, preferably polished, before the application of the respective coating.

[0049] To achieve a particularly advantageous applicability of the cutting tool, the CrTaN / AlTiN multilayer coating system is preferably post-treated and the surface structure and / or surface roughness are adapted to the respective application, particularly preferably by wet blasting, dry blasting and / or dyeing.

[0050] In the above-described process for producing a hard coating, a composite target is preferably used for the deposition of CrTaN. It is part of the present disclosure to specify a process for producing a coating source for carrying out the process for producing the hard coating, as well as a coating source itself.

[0051] This problem is solved by a method for producing a coating source with the features according to the disclosure, which is not part of the present invention in the claims.

[0052] Accordingly, a method for producing a coating source for the physical vapor deposition (PVD) of CrTaN is proposed, which is not part of the present invention in the claims, wherein a powder mixture of pure Cr powder and pure Ta powder is provided and the coating source is formed by hot compaction of the powder mixture.

[0053] In this way, a coating source for the deposition of CrTaN in a PVD system can be easily provided, by means of which a deposition of CrTaN in a predetermined atomic composition can be achieved, whereby the resulting layer has a stable cubic crystal structure and is single-phase.

[0054] Preferably, the powder mixture is provided with a Ta content of 1-60 at.%, particularly preferably with a Ta content of 20-30 at.%, and most preferably with a Ta content of 25 at.%, prior to hot compaction. In this way, the compositions of the deposited layers that have been found to be advantageous can be achieved.

[0055] Preferably, the particle size of the Cr powder and / or the Ta powder is below 45 µm to achieve a particularly homogeneous mixture of the powder mixture and to achieve a particularly fine distribution of the Cr 2 Ta phase during hot compaction.

[0056] Hot compaction is preferably carried out by hot pressing, spark plasma sintering (SPS) or hot isostatic pressing (HIP), and the powder is preferably heated during compaction using heating conductors and / or directly with an electric current and / or inductively.

[0057] To achieve an advantageous microstructure of the coating source, hot pressing preferably takes place in a temperature range of 1100-1750°C, particularly preferably in a temperature range of 1300-1500°C.

[0058] The treatment time is preferably less than one hour to avoid recrystallization and maintain the fine grain structure. Furthermore, short sintering times do not result in a complete conversion of Ta to the Cr₂Ta phase, so that the resulting microstructure of the coating source contains three phases: a pure Ta phase, a pure Cr phase, and the Cr₂Ta phase. Short Description of the characters

[0059] Preferred further embodiments and aspects of the present invention are explained in more detail by the following description of the figures.

[0060] This shows: Figure 1 shows the measured values ​​for the nanohardness H and the modulus of elasticity E of different CrTaN coating systems, Figure 2 shows an SEM (scanning electron microscopy) fracture image of a coating system on a substrate with an AlTiN base layer and an AlTiN / CrTaN multilayer coating system, Figure 3 shows the measured values ​​of a machining test, Figure 4 shows a metallographic cross-sectional view with a grain boundary etching of a coating source in the form of a CrTa composite target, and Figure 5 shows a phase diagram of the microstructure of the CrTa composite target. Detailed description of preferred embodiments

[0061] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements are designated with identical reference numerals, and repeated descriptions of these elements are sometimes omitted to avoid redundancy.

[0062] A multilayer system is applied to a substrate by alternating deposition of CrTaN and AlTIN to produce a hard coating using physical vapor deposition (PVD). This hard coating serves, for example, as a wear-resistant coating for cutting or machining tools.

[0063] Almost all available hard metal and cermet substrates can be used as substrates for the aforementioned PVD coating. Furthermore, all refractory metals can also be used, and the coating systems described herein are also conceivable, for example, as oxidation protection for elements in glass melting furnaces. The substrates can be pretreated, in particular by polishing, grinding, or blasting, to support the subsequent build-up of the hard coating layer and the dimensional accuracy of the finished coated component.

[0064] It is particularly preferred to build up the layers using composite targets, i.e., targets that have a composition of several different phases. For this purpose, powder metallurgy-produced composite targets can be used, for example. A possible method for manufacturing CrTa composite targets will be discussed further below. Figures 4 and 5 received.

[0065] The coatings are applied to a hard metal substrate using, for example, a PVD process at temperatures of 400-600°C. This can be carried out, for example, in an ARC-PVD coating system, a sputtering system, or a HIPIMS system.

[0066] The following are examples of layer systems in which CrTaN layers and AlTiN layers were applied to the substrate, with different layer sequences being applied and several relevant parameters then being measured in each case.

[0067] Exemplary layer structures of the samples exhibiting AlTIN and CrTaN layers are shown in Table 1: Table 1: Exemplary combinations of substrate, layer and post-treatment substrate layer Post-treatment AlTiN / CrTaN unrestricted AlTiN / (AlTiN / CrTaN multilayer system) Dry or wet blasting (AlTiN / CrTaN multilayer system) AlTiN / (AlTiN / CrTaN multilayer system) / CrTaN

[0068] To enable layer deposition, the following target compositions, listed in Table 2 below, were used in the PVD system. If single-layer layers were used, they were deposited separately to determine their chemical composition, which was then determined using GDOES. For better comparability with the target composition, nitrogen is not included in the table below. The resulting layer compositions for the target compositions listed in the first double column are shown in the second column, and these were determined using GDOES. An EDX measurement can be performed instead of, or in addition to, the GDOES measurement. Table 2: Example target composition and layer composition (atomic level) Target Layer Single Layers (GDOES) Ti 100 Ti Alti 60 / 40 Alti 63 / 37 CrTa 75 / 25 CrTa 71 / 29

[0069] It has proven advantageous in the deposition of the layers to deposit CrTaN from a composite target with the addition of nitrogen, preferably from a composite target with a Ta content of 1-60 at%, particularly preferably a Ta content of 20-30 at%, particularly preferably a Ta content of 25 at%.

[0070] Particularly advantageous composition ranges for the Cri-yTayN layer are therefore 0.01≤y≤0.65, preferably 0.2≤y≤0.4, and particularly preferably 0.25≤y≤0.35.

[0071] The CrTaN layer can be deposited from a CrTa composite target, which has the advantage over co-sputtering multiple metallic targets that a single-phase cubic structure is deposited, which can be verified, for example, by XRD. Accordingly, the use of composite targets results in an improved structure of the hard coating, achieved through the stabilization of the cubic crystal structure.

[0072] For depositing the AlTiN layer, it has proven advantageous to deposit AlTiN in a nitrogen atmosphere from a composite target, preferably from a composite target with a Ti content of 10-80 at%, particularly preferably with a Ti content of 25-50 at%, particularly preferably with a Ti content of 40 at%.

[0073] This results in a composition range of the Al x Ti 1-x N layer of 0.2≤x≤0.9, preferably 0.4≤x≤0.8, and particularly preferably 0.5≤x≤0.7. Here too, the deposition from the composite target results in at least a largely single-phase cubic structure, which can be verified, for example, by XRD.

[0074] For the construction of the multilayer system, the individual layers are deposited in thicknesses between 5 and 200 nanometers, preferably between 10 and 100 nanometers, and particularly preferably 15 nanometers. In the samples constructed here as examples, the thickness of the individual layers was approximately 15 nanometers.

[0075] For the construction of the multi-layer system, 10 to 5000, preferably 25 to 1000, and particularly preferably 50 to 250 alternating layers are deposited. In the samples constructed here, approximately 100 alternating layers were deposited for the multi-layer system.

[0076] Against this background, the following layer systems were constructed as examples and then measured: BL: AlTiN / CrTaN double layer, wherein AlTiN with a thickness of 2 µm and CrTaN with a thickness of 2.9 µm were deposited on the substrate. ML: An AlTiN base layer with a CrTaN / AlTiN multilayer system built upon it, wherein the AlTiN base layer was 1.8 µm thick and the CrTaN / AlTiN multilayer system was 3 µm thick. The individual layers of the multilayer system had a thickness of approximately 15 nm. ML+DS: An AlTiN base layer on which an AlTiN / CrTaN multilayer ethic system was built, and on which a CrTaN top layer was deposited, wherein the CrTaN top layer had a thickness of 1.1 µm, the AlTiN / CrTaN multilayer system had a thickness of 2 µm, and the AlTiN base layer had a thickness of 1.9 µm. The individual layers of the multilayer system had a thickness of approximately 15 nm. SL: CrTaN as a single layer with a layer thickness of 2.5 µm CrTaN. Ref.1-PM: Reference layer made of AlTiN as a single layer, deposited from a 60 / 40 AlTiN composite target with a thickness of 2.8 µm. Ref.2-CC: Reference layer made of AlTiN as a single layer, deposited from a 60 / 40 AlTiN plug target with a thickness of 3 µm.

[0077] Table 3 below shows a layer structure of a system consisting of an AlTIN base layer with a single CrTaN layer applied on top, where, accordingly, a multilayer system has not been chosen. This structure corresponds to the sample designated BL above. Table 3: Exemplary layer structure, layer thickness and chemical composition of the layer, starting from the substrate Nr. Layer type Layer thickness [µm] Chemical composition Measurement methods should min max 2 CrTaN 3,0 0,5 7,0 (Cr 0.71 Ta 0.29 )N EDX 1 AltiN 2,0 0,5 7,0 (Al 0.63 Ti 0.37 ) N EDX Total thickness 5 1,0 14

[0078] In Table 4 below, a multilayer system was applied to an AlTiN substrate, with a single-layer thickness of approximately 15 nm. This structure corresponds to the sample ML mentioned above. Table 4: Exemplary layer structure, layer thickness and chemical composition of the layer, starting from the substrate Nr. Layer type Layer thickness [µm] Chemical composition Measurement methods should min max 2 CrTaN / AlTiN 3,0 0,5 7,0 1 AltiN 2,0 0,5 7,0 (Al 0.63 Ti 0.37 ) N EDX Total thickness 5 1,0 14

[0079] Finally, a hard layer was applied to the hard metal substrate, consisting of a CrTaN top layer, a CrTaN / AlTiN multilayer system, and an AlTiN base layer, as shown in Table 5 below. This structure corresponds to the aforementioned sample ML+DS. Table 5: Exemplary layer structure, layer thickness and chemical composition of the layer, starting from the substrate Nr. Layer type Layer thickness [µm] Chemical composition Measurement methods should min max 3 CrTaN 1,0 0,1 4,0 (Cr 0.71 Ta 0.29 )N EDX 2 CrTaN / AlTiN 2,0 0,5 5,0 1 AltiN 2,0 0,5 7,0 (Al 0.63 Ti 0.37 ) N EDX Total thickness 5 1,1 16

[0080] Figure 1 shows values ​​of the nanohardness H and the modulus of elasticity E for different layer systems, each containing at least one CrTaN layer.

[0081] The nanohardness was measured using a nanoidentifier (Ultra-Micro-Indentation System - UMIS) with a Berkovich diamond indenter. Sixteen indentations were made to each sample for the measurements, and the nanohardness and the Young's modulus were determined.

[0082] From the Figure 1It is immediately apparent that, compared to the single-layer SL and double-layer BL, each comprising a single CrTaN layer, the use of the multilayer system ML resulted in a significant increase in hardness. Starting with the SL and BL samples, which exhibited a nanohardness of 16.0 to 15.5 GPa, the nanohardness of the ML samples increased to approximately 25 to 30 GPa.

[0083] From the in Figure 1 The results shown indicate that the multilayer system ML has a higher hardness and therefore also improved wear properties compared to the single layers SL and double layers BL.

[0084] Even compared to AlTiN layers, especially Ref. 1-PM and Ref. 2-CC layers, a higher nanohardness can be achieved, as can also be seen from the Figure 1 results.

[0085] The construction of a multi-layer system made of CrTaN and AlTIN therefore results in an increase in hardness compared to single layers or a double layer made of these materials.

[0086] Furthermore, it is evident that in the multilayer coating system, the thermal decomposition of CrTaN into Cr₂N and Ta₂N, as would occur in single-layer coatings and as described in the literature, is largely suppressed. Accordingly, the proposed multilayer coating system is particularly suitable for high-temperature applications. Due to the stabilization of the cubic crystal structure, thermal decomposition is prevented in this multilayer system, resulting in temperature stability and thus longer tool life. This property profile makes it suitable for use as a wear-resistant coating on carbide indexable inserts as well as in solid carbide tools.

[0087] Furthermore, a low coefficient of friction of the multilayer system ML was observed in the tribometer test (at room temperature, 500°C and 700°C).

[0088] For this purpose, a tribometer from the manufacturer CSM Instruments in a ball-disc configuration with a counterbody made of Al₂O₃ with a diameter of 6 mm was used, and measurements were taken at room temperature (RT), 500°C, and 700°C. The set load was 5 N, the sliding distance 300 m, and the speed 10 cm / s. The radius of the wear trench was 5 mm. The wear trench was surveyed using a Veeco white light profilometer, generating a 2D cross-section and a 3D representation.

[0089] The measurements on the aforementioned samples are shown in Table 6 below. It is immediately apparent that the achievable coefficients of friction (µ) for the multilayer system ML are s 0.7, and in the best case even s 0.6. Accordingly, the sample with the multilayer system ML is particularly suitable for use in tools where low coefficients of friction are required, such as threading tools, reamers, and solid metal tools. Table 6: Measured coefficients of friction and wear coefficients Designation Layer thickness [µm] Coefficient of friction µ ∼] Wear coefficient K [m 3< / (Nm)] RT 500°C 700°C RT 500°C 700°C BL 212,0 0,71 0,66 0,60 1,27*10 -15< 1,55*10 -14< 1,65°10 -14< : ML 1,8 / 3 0,67 0,57 0,56 1,67*10 -15< 6,67*10 -15< 1,25*10 -14< ML+DS 1,9 / 2 / 1,1 0,60 0,58 0,58 1,14*10 -15< 9,70*10 -15< 1,45*10 -14< SL 2,4 0,61 0,59 0,51 1,81*10 -15< 9,32*10 -15< 8,19*10 -15< Ref. 1-PM 2,8 0,85 0,96 0,86 2.28*10 -14< 5,37*10 -16< 4,60*10 -15< Ref. 2-CC 3 0,88 1,02 0,88 1,87*'10 -14< 5,79*10 -16< 4,45*10 -15<

[0090] Furthermore, the residual stress states of the layer systems are listed in Table 7 below. The stresses were determined in the "as deposited" state using the wafer curvature method on silicon samples. However, these values ​​can vary depending on the fabrication method of the layers. Table 7: Layer residual stresses measured via wafer curvature method on Si samples Designation layer Voltages [MPa] BL TiAIN / TaCrN ∼ -370 ML TiAIN / TiAlN TaCrN ∼ -450 ML+DS TiAlN / TiAlN TaCrN / TaCrN - -450 SL TaCrN ∼ -500 Ref. 1-PM TlAIN PM Targets ∼ -550 Ref.2-CC TlAIN plug targets ~ -1200

[0091] It turns out that the multilayer system ML also exhibits relatively low layer residual stresses, which further positively influences the service life and maintenance time.

[0092] An exemplary structure of a multilayer system (ML) is shown in Figure 2 shown in the fracture image, where an AlTIN base layer was provided on a hard metal substrate, onto which the AlTIN / CrTaN multilayer system was then applied.

[0093] The multi-layer system ML described above results in a massive increase in hardness with simultaneously low friction coefficients and a long service life.

[0094] When using a multi-layer coating system ML, machining tests have shown that a coating for threading tools, reamers and solid carbide tools is particularly advantageous, namely wherever the coefficient of friction should be low and at the same time a high hardness is required.

[0095] In Figure 3The measurement results of machining tests for the different multilayer coating systems are presented. The tool life of a milling cutter insert during wet milling is given in minutes. The machining test was specifically performed with the following test parameters: climb milling with a single tooth, with a helical cut in the block plane. SP300 high-performance steel was used as the material, and the tool was an ISCAR F45ST D050-22 for indexable inserts, guided in an SK50 tool holder. The workpiece had dimensions of 400 x 200 x 96 mm and a tensile strength of 1000 N / mm². The milling cutter had a diameter of 50 mm and was driven at a lead angle of 45° with a cutting speed vc of 250 m / min (dry) and 150 m / min (wet), a feed rate fa of 0.25 mm, and a cutting width ae of 32 mm.

[0096] From the Figure 3It is immediately apparent that the multilayer coating system ML exhibits the best tool life. In wet machining, this results in an approximately 20% improvement in tool life compared to the reference coating systems. However, in dry machining (not shown in the figure), the multilayer coating system ML does not perform significantly better than the reference coating systems. Furthermore, a cutting tool for a machining device can also be manufactured, which features a suitable substrate, preferably a carbide substrate, in the specified geometry. The cutting tool can, for example, be in the form of a cutting element for turning and milling devices or in the form of an indexable insert.

[0097] A hard coating with a multi-layer surface system of CrTaN and alternating AlTiN is then applied to this substrate using the above-described method, with low layer thicknesses.

[0098] Furthermore, to adapt the surface structure and / or surface roughness to the specific application, the hard coating can undergo post-treatment. This post-treatment can be carried out, for example, by wet blasting, dry blasting, and / or dyeing. Any applied topcoat and / or functional layer can also be subjected to such post-treatment.

[0099] The following section describes the production of coating sources in the form of CrTa composite targets which, according to the claims, do not belong to the present invention, and how they were advantageously used in the above-described processes for the production of hard coatings for the deposition of the CrTaN coatings by PVD.

[0100] To produce the composite targets, pure Cr and pure Ta powder are first provided as raw materials. Preferably, the particle size of the powders is less than 45 µm. The two powders are mixed together in the desired ratio of the CrTa composite target to be produced from the powder, and as homogeneously as possible. Due to the fine particle size, the mixture of the two powders can be prepared particularly homogeneously, and during the subsequent compaction process, a TaCr₂ phase can form finely dispersed within the target.

[0101] As described above, the mixture of the CrTa composite target to be produced preferably contains a Ta content of 1-60 at.%, particularly preferably 20-30 at.%, and most preferably 25 at.%.

[0102] The CrTa composite target is then produced from the essentially homogeneous powder mixture in a press mold using a sintering process. This sintering process is carried out, for example, by hot pressing, spark plasma sintering (SPS), or hot isostatic pressing (HIP). In each case, the powder may be heated during pressing in a chamber with heating elements or directly with an electric current and / or inductively.

[0103] Sintering using PLC or hot pressing to produce the CrTa composite targets takes place in a temperature range of 1100-1750°C, preferably in a temperature range of 1300-1500°C. The sintering time is kept as short as possible, preferably less than one hour, to avoid recrystallization and to maintain the fine grain structure.

[0104] In Figure 4A metallographic section showing a grain boundary etch through the composite target created in this way is shown. After the sintering process, the microstructure consists of three phases: a pure Cr or Cr solid solution (phase 1), a pure Ta or Ta solid solution (phase 2), and a TaCr₂ phase (phase 3). The TaCr₂ phase (phase 3) is present at the interfaces where Ta and Cr meet. To produce the CrTa composite target as proposed, all three phases must be present. The corresponding phase diagram is shown in Figure 5 shown.

[0105] The measured density after sintering is at least 90% of the theoretical density, preferably 95% or 98%.

[0106] The CrTa composite targets produced in this way can either be used directly or, for improved handling, attached to a backplate via bonding, brazing, or diffusion bonding. This backplate then allows the targets to be mounted in the PVD system for CrTaN deposition. Multiple CrTa composite targets can also be mounted on a single backplate, for example, to accommodate the desired geometry in the PVD system.

Claims

1. A method for producing a hard material coating on a substrate, characterized in that a multilayer coating system is deposited on the substrate by physical vapor deposition (PVD) through alternating deposition of CrTaN and AlTiN, wherein AlTiN is deposited with an atomic composition of AlxTi1-xN with 0.2 ≤ x ≤ 0.9 and CrTaN is deposited with an atomic composition of Cr1-yTayN with 0.01 ≤ y ≤ 0.65, as measured by GDOES or EDX, wherein the individual layers of the multilayer coating system are deposited with thicknesses between 5 and 200 nm, and 10 to 5000 layers are deposited in alternation.

2. The method according to claim 1, wherein the method is configured for producing a cutting tool.

3. The method according to claim 1 or 2, characterized in that CrTaN is deposited from a composite target, preferably from a composite target having a Ta content of 1-60 at.%, more preferably a Ta content of 20-30 at.%, most preferably a Ta content of 25 at.%.

4. The method according to claim 1, 2 or 3, characterized in that AlTiN is deposited from a composite target, preferably from a composite target having a Ti content of 10-80 at.%, more preferably a Ti content of 25-50 at.%, most preferably a Ti content of 40 at.%.

5. The method according to any one of the preceding claims, characterized in that AlTiN is deposited on the substrate with an atomic composition of AlxTi1-xN, preferably with 0.4 ≤ x ≤ 0.8, more preferably 0.5 ≤ x ≤ 0.7, as measured by GDOES or EDX.

6. The method according to any one of the preceding claims, characterized in that CrTaN is deposited on the substrate with an atomic composition of Cr1-yTayN, preferably with 0.2 ≤ y ≤ 0.4, more preferably 0.25 ≤ y ≤ 0.35, as measured by GDOES or EDX.

7. The method according to any one of the preceding claims, characterized in that the individual layers of the multilayer coating system are deposited with thicknesses preferably between 10 and 100 nm, more preferably 15 nm.

8. The method according to any one of the preceding claims, characterized in that< / b> preferably 25 to 1000, more preferably 50 to 250 layers are alternately deposited in the multilayer coating system.

9. The method according to any one of the preceding claims, characterized in that, in the multilayer coating system, at least one layer of AlTiXN is alternately deposited with CrTaN in place of AlTiN, wherein X = Ta, V, Si, Mo or Hf, and wherein AlTiXN is preferably deposited from a composite target.

10. The method according to any one of the preceding claims, characterized in that an AlTiN base layer is first deposited on the substrate by physical vapor deposition (PVD), preferably with a thickness of 0.5 to 10 µm, more preferably 1 to 5 µm, most preferably 2 µm, and the multilayer coating system is applied on this AlTiN base layer by alternating deposition of CrTaN and AlTiN layers.

11. The method according to claim 10, characterized in that, instead of AlTiN, a base layer of AlTiXN is deposited, wherein X = Ta, V, Si, Mo or Hf, and wherein AlTiXN is preferably deposited from a composite target.

12. The method according to any one of the preceding claims, characterized in that a top layer of TiN or CrTaN is applied onto the multilayer coating system by physical vapor deposition (PVD), preferably with a thickness of 0.1 to 10 µm, preferably 0.5 to 5 µm, and most preferably 1 µm.

13. A cutting tool comprising a substrate of cemented carbide, characterized in that a multilayer coating system is applied to the substrate by physical vapor deposition (PVD) through alternating deposition of CrTaN and AlTiN layers, wherein AlTiN is present with an atomic composition of AlxTi1-xN with 0.2 ≤ x ≤ 0.9 and CrTaN is present with an atomic composition of Cr1-yTaγN with 0.01 ≤ y ≤ 0.65, as measured by GDOES or EDX, and wherein the individual layers of the multilayer coating system have thicknesses between 5 and 200 nm and 10 to 5000 layers are alternately deposited.

14. The cutting tool according to claim 13, characterized in that an AlTiN base layer is provided between the substrate and the CrTaN / AlTiN multilayer coating system, preferably with a thickness of 0.5 to 10 µm, more preferably 1 to 5 µm, most preferably 2 µm.

15. The cutting tool according to claim 13 or 14, characterized in that at least one top layer of TiN or CrTaN is applied onto the CrTaN / AlTiN multilayer coating system, preferably with a thickness of 0.1 to 10 µm, preferably 0.5 to 5 µm, and most preferably 1 µm.