Method for producing a hard material layer on a substrate, hard material layer, machining tool and coating source

Abstract

A process for producing a hard material layer on a substrate. A multilayer coating system is applied to the substrate by alternate deposition of CrTaN and AlTiN by way of physical vapor deposition (PVD). The CrTaN and/or the AlTiN are preferably deposited from a composite target.

Claims

1. A process for producing a hard material layer on a substrate, the method comprising: providing the substrate; and applying a multilayer coating system to the substrate by alternate deposition of CrTaN and AITiN in a physical vapor deposition (PVD) process.

2. The process according to claim 1, which comprises depositing CrTaN from a composite target.

3. The process according to claim 2, wherein the composite target has a Ta content of 1-60 at.-%.

4. The process according to claim 1, which comprises depositing AITiN from a composite target.

5. The process according to claim 4, wherein the composite target has a Ti content 10-80 at.-%.

6. The process according to claim 1, which comprises applying AITiN with an atomic composition of Al.sub.xTi.sub.1-xN to the substrate, wherein 0.2x0.9, measured by GDOES or EDX.

7. The process according to claim 1, which comprises applying CrTaN with an atomic composition of Cr.sub.1-yTa.sub.yN to the substrate, wherein 0.01y0.65, measured by GDOES or EDX.

8. The process according to claim 1, which comprises depositing individual layers of the multilayer coating system in thicknesses in a range from 5 to 200 nanometers.

9. The process according to claim 1, which comprises alternately depositing from 10 to 5000 layers in the multilayer coating system.

10. The process according to claim 1, which comprises applying at least one layer AlTiXN, where X is selected from the group consisting of Ta, V, Si, Mo and Hf, instead of AITiN alternately with CrTaN in the multilayer coating system.

11. The process according to claim 1, which comprises first depositing an AITiN base layer on the substrate by physical vapor deposition (PVD) and applying the multilayer coating system to the AITiN base layer by alternately depositing CrTaN and AITiN layers.

12. The process according to claim 11, which comprises depositing a base layer composed of AlTiXN, where X is selected from the group consisting of Ta, V, Si, Mo and Hf, instead of AITiN.

13. The process according to claim 1, which comprises applying a covering layer composed of TiN or CrTaN on top of the multilayer coating system by physical vapor deposition (PVD).

14. A cutting tool, comprising a substrate composed of cemented carbide and a multilayer coating on said substrate formed by physical vapor deposition (PVD) with alternate deposition of CrTaN and AITiN layers.

15. The cutting tool according to claim 14, comprising an AITiN base layer between said substrate and said multilayer coating of CrTaN/AlTiN.

16. The cutting tool according to claim 14, which comprises at least one covering layer composed of TiN or CrTaN formed on top of said multilayer coating of CrTaN/AlTiN.

17. A process for producing a coating source for physical vapor deposition (PVD) of CrTaN on a substrate, the process comprising providing a powder mixture of pure Cr powder and pure Ta powder, and shaping the coating source by hot densification of the powder mixture.

18. The process according to claim 17, which comprises providing the powder mixture with a Ta content of 1-60 at.-%.

19. The process according to claim 17, wherein said Cr powder and/or said Ta powder has a particle size of less than 45 m.

20. The process according to claim 17, wherein the hot densification is a process selected from the group consisting of hot pressing, pressing with direct passage of current and hot isostatic pressing (HIP).

21. The process according to claim 20, wherein the hot densification is a spark plasma sintering (SPS) process.

22. The process according to claim 17, wherein the hot densification is a hot pressing process in a temperature range of 1100-1750 C.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) Preferred further embodiments and aspects of the present invention are illustrated by the following description of the figures.

(2) The figures show:

(3) FIG. 1 a presentation of the measured values for the nanohardness H and the elastic modulus E of different CrTaN layer systems,

(4) FIG. 2 an SEM (scanning electron microscopy) image of the fracture surface of a layer system on a substrate having an AlTiN base layer and an AlTiN/CrTaN multilayer coating system,

(5) FIG. 3 a presentation of the measured values of a cutting machine test,

(6) FIG. 4 a metallographic polished section with grain boundary etching of a coating source in the form of a CrTa composite target and

(7) FIG. 5 a phase diagram of the microstructure of the CrTa composite target.

DETAILED DESCRIPTION OF PREFERRED WORKING EXAMPLES

(8) Preferred working examples are described below with the aid of the figures. Here, identical elements, similar elements or elements having the same effect are denoted by identical reference symbols and repeated description of these elements will sometimes be dispensed with in order to avoid redundancies in the description.

(9) To produce a hard material layer by means of physical vapor deposition (PVD), a multilayer coating system is applied to a substrate by alternate deposition of CrTaN and AlTiN. The hard material layer serves, for example, as wear protection layer for cutting or machining tools.

(10) As substrate for PVD coating as mentioned above, it is possible to employ virtually all available cemented carbide substrates and cermet substrates, and all refractory metals can also be used, with the layer systems described herein also being conceivable, for example, as oxidation protection for elements in glass melting tanks. The substrates can be pretreated and in particular polished, ground or blasted in order to assist the subsequent formation of the hard material layer and the dimensional trueness of the finished coated component.

(11) Particular preference is given to carrying out the buildup of the layers by means of composite targets, i.e. targets which have a composition made up of a plurality of different phases. For example, powder-metallurgically produced composite targets can be employed here. A possible production route for CrTa composite targets is described in detail below with reference to FIGS. 4 and 5.

(12) The coatings are, for example, applied to a cemented carbide substrate at temperatures of 400-600 C. by means of PVD processes. The coating process can be carried out, for example, in an ARC-PVD coating plant, in a sputtering plant or in an HIPIMS plant.

(13) Layer systems in which CrTaN layers and AlTiN layers have been applied to the substrate are presented by way of example below, with different layer sequences having been applied and a plurality of relevant parameters then having been measured in each case.

(14) Illustrative layer sequences of the specimens having AlTiN and CrTaN layers are shown in table 1:

(15) TABLE-US-00001 TABLE 1 Illustrative combinations of substrate, layer and after-treatment Substrate Layer After-treatment Unrestricted AlTiN/CrTaN Dry or wet AlTiN/(AlTiN/CrTaN multilayer coating blasting system) (AlTiN/CrTaN multilayer coating system) AlTiN/(AlTiN/CrTaN multilayer coating system)/CrTaN

(16) To be able to deposit the layers, the following compositions of the targets indicated in table 2 below, for example, were provided in the PVD plant. When single-layer coatings were provided, they were deposited separately for determination of the chemical composition and the composition was determined by means of GDOES. For better comparability with the target composition, the nitrogen is not shown in the following table. Accordingly, in the case of the target compositions indicated in the first double column, the layer composition indicated in the second column sequence, which was correspondingly determined by means of GDOES, is obtained. Instead of or in addition to the GDOES measurement, an EDX measurement can also be carried out.

(17) TABLE-US-00002 TABLE 2 Illustrative target composition and layer composition (in each case atomic) Individual layers of the coating Target (GDOES) Ti 100 Ti AlTi 60/40 AlTi 63/37 CrTa 75/25 CrTa 71/29

(18) It has been found to be advantageous in the deposition of the layers to deposit CrTaN with addition of nitrogen from a composite target, preferably from a composite target having a Ta content of 1-60 at.-%, particularly preferably a Ta content of 20-30 at.-%, particularly preferably a Ta content of 25 at.-%.

(19) Particularly advantageous composition ranges for the Cr.sub.1-yTa.sub.yN layer are thus 0.01y0.65, preferably 0.2y0.4, particularly preferably 0.25y0.35.

(20) The CrTaN layer can be deposited from a CrTa composite target, which has the advantage over the cosputtering of a plurality of metallic targets that a single-phase cubic structure is deposited, as can be confirmed, for example, by XRD. Correspondingly, an improved structure of the hard material layer, which is achieved by stabilization of the cubic crystal structure, is obtained as a result of the use of composite targets.

(21) For deposition of the AlTiN layer, it has been found to be advantageous to deposit AlTiN in a nitrogen atmosphere from a composite target, preferably from a composite target having a Ti content of 10-80 at.-%, particularly preferably a Ti content of 25-50 at.-%, particularly preferably a Ti content of 40 at.-%.

(22) A composition range of the Al.sub.xTi.sub.1-xN layer is thus advantageously 0.2x0.9, preferably 0.4x0.8, particularly preferably 0.5x0.7.

(23) Here too, an at least largely single-phase cubic structure is obtained by deposition from the composite target, which can be confirmed, for example, by XRD.

(24) To build up the multilayer coating system, the individual layers of the multilayer coating system are preferably deposited in thicknesses in the range from 5 to 200 nanometers, preferably from 10 to 100 nanometers, particularly preferably 15 nanometers. In the samples having the illustrative structure here, the thickness of the individual layers was about 15 nanometers.

(25) Furthermore, preference is given to depositing from 10 to 5000, preferably from 25 to 1000, particularly preferably from 50 to 250, alternating layers to build up the multilayer coating system. In the specimens built up here, about 100 alternating layers were deposited for the multilayer coating system.

(26) In view of this background, the following layer systems were built up by way of example and then measured:

(27) BL: AlTiN/CrTaN double layer, with AlTiN being deposited in a thickness of 2 m on the substrate and CrTaN having been deposited in a thickness of 2.9 m on top of this.

(28) ML: AlTiN base layer with CrTaN/AlTiN multilayer coating system built up thereon, with the AlTiN base layer having been applied in a thickness of 1.8 m and the CrTaN/AlTiN multilayer coating system having been applied in a thickness of 3 m. The individual layers of the multilayer coating system had a thickness of about 15 nm.

(29) ML+DS: AlTiN base layer on top of which an AlTiN/CrTaN multilayer coating system had been built up and a CrTaN covering layer having been deposited thereon, with the CrTaN covering layer having a thickness of 1.1 m, the AlTiN/CrTaN multilayer coating system having a thickness of 2 m and the base layer AlTiN having a thickness of 1.9 m. The individual layers of the multilayer coating system had a thickness of about 15 nm.

(30) SL: CrTaN as single layer having a layer thickness of 2.5 m of CrTaN.

(31) Ref.1-PM: Reference layer composed of AlTiN as single layer, deposited from a 60/40 Al/Ti composite target in a thickness of 2.8 m.

(32) Ref.2-CC: Reference layer composed of AlTiN as single layer, deposited from a 60/40 AlTiN plug target in a thickness of 3 m.

(33) Table 3 below shows a layer sequence of a system made up of an AlTiN base layer with a CrTaN single layer applied thereon, with a multilayer coating system accordingly not being selected here. This structure corresponds to the specimen designated as BL above.

(34) TABLE-US-00003 TABLE 3 Illustrative layer sequence, layer thickness and chemical composition of the layer, starting from the substrate Layer thickness [m] Measure- Layer intend- Chemical ment No. type ed min max composition method 2 CrTaN 3.0 0.5 7.0 (Cr.sub.0.71Ta.sub.0.29)N EDX 1 AlTiN 2.0 0.5 7.0 (Al.sub.0.63Ti.sub.0.37)N EDX Total thickness 5 10 14

(35) In table 4 below, a multilayer coating system was applied to an AlTiN base layer, with the individual layer thickness being about 15 nm in the multilayer coating system. This structure corresponds to the abovementioned specimen ML.

(36) TABLE-US-00004 TABLE 4 Illustrative layer sequence, layer thickness and chemical composition of the layer, starting from the substrate Mea- Layer thickness [m] sure- Layer intend- Chemical ment No. type ed min max composition method 2 CrTaN/AlTiN 3.0 0.5 7.0 1 AlTiN 2.0 0.5 7.0 (Al.sub.0.63Ti.sub.0.37)N EDX Total thickness 5 10 14

(37) Finally, a hard material layer having a CrTaN covering layer, a CrTaN/AlTiN multilayer coating system and an AlTiN base layer was built up on the cemented carbide substrate, giving the structure shown in table 5 below. This structure corresponds to the abovementioned specimen ML+DS.

(38) TABLE-US-00005 TABLE 5 Illustrative layer sequence, layer thickness and chemical composition of the layer, starting from the substrate Mea- Layer thickness [m] sure- Layer intend- Chemical ment No. type ed min max composition method 3 CrTaN 1.0 0.1 4.0 (Cr.sub.0.71Ta.sub.0.29)N EDX 2 CrTaN/AlTiN 2.0 0.5 5.0 1 AlTiN 2.0 0.5 7.0 (Al.sub.0.63Ti.sub.0.37)N EDX Total thickness 5 11 16

(39) FIG. 1 shows values of the nanohardness H and the elastic modulus E for different layer systems having at least one CrTaN layer.

(40) The nanohardness was measured here by means of a nanoindenter (Ultra-Micro-Indentation SystemUMIS) having a Berkovich diamond indentation body. 16 indentations per specimen were carried out for each of the measurements and the nanohardness and the Young's modulus were determined.

(41) It can be seen immediately from FIG. 1 that, compared to the single layer SL and the double layer BL, which each comprised a CrTaN layer, a significant increase in hardness was obtained by the use of the multilayer coating system ML. Starting out from the SL and BL specimens, which had a nanohardness of from 16.0 to 15.5 GPa, the nanohardness increased to from about 25 to 30 GPa in the case of the ML specimens.

(42) It can be seen from the results shown in FIG. 1 that the multilayer coating system ML has a greater hardness and thus also improved wear properties compared to the single layers SL and double layers BL.

(43) Compared to the AlTiN layers, in particular Ref. 1-PM and Ref. 2-CC layers, too, a higher nanohardness can be achieved, as can likewise be seen from FIG. 1.

(44) A multilayer coating system made up of CrTaN and AlTiN thus gives a hardness increase compared to the single layers or a double layer composed of these materials.

(45) Furthermore, it is found that the thermal decomposition of CrTaN into Cr.sub.2N and Ta.sub.2N, as would occur, for example, in the case of single-layer coatings and as is described in the literature, is largely suppressed in the multilayer coating system.

(46) Accordingly, the proposed multilayer coating system gives a coating system which is particularly suitable for high-temperature use. In the case of the multilayer coating system, it is found that the thermal decomposition is prevented by the stabilization of the cubic crystal structure, so that the applied layer is also thermally stable, as a result of which longer operating lives are possible. This property profile is accordingly suitable for use as wear protection layer on cemented carbide indexable cutting plates and also in solid cemented carbide tools.

(47) Furthermore, a lower coefficient of friction of the multilayer coating system ML was found in the tribometer test (at room temperature, 500 C. and 700 C.).

(48) A ball-on-disc tribometer from CSM Instruments in the configuration with a counterbody composed of Al.sub.2O.sub.3 having a diameter of 6 mm was used for this purpose and measurements were carried out at room temperature (RT), 500 C. and 700 C. The load set was 5N, the slide distance was 300 m and the speed was 10 cm/s. The radius of the wear groove was 5 mm. Measurement of the wear groove was carried out by means of a Veeco white light profilometer and a 2D cross section and a 3D depiction were produced.

(49) The measurements on the abovementioned specimens are shown in table 6 below. It can immediately be seen that the achievable coefficients of friction (p) for the multilayer coating system ML are 0.7, at best even 0.6. The specimen having the multilayer coating system ML is accordingly particularly suitable for use in tools for which the coefficients of friction have to be low, for example in thread-cutting tools, reamers and solid metal tools.

(50) TABLE-US-00006 TABLE 6 Measured coefficients of friction and wear coefficients Layer Coefficient of friction thickness [] Wear coefficient K [m.sup.3/(Nm)] Designation [m] RT 500 C. 700 C. RT 500 C. 700 C. BL 2/2.0 0.71 0.66 0.60 1.27*10.sup.15 1.55*10.sup.14 1.65*10.sup.14 ML 1.8/3 0.67 0.57 0.56 1.67*10.sup.15 6.67*10.sup.15 1.25*10.sup.14 ML + DS 1.9/2/1.1 0.60 0.58 0.58 1.14*10.sup.15 9.70*10.sup.15 1.45*10.sup.14 SL 2.4 0.61 0.59 0.51 1.81*10.sup.15 9.32*10.sup.15 8.19*10.sup.15 Ref. 1-PM 2.8 0.85 0.96 0.86 2.28*10.sup.14 5.37*10.sup.16 4.60*10.sup.15 Ref. 2-CC 3 0.88 1.02 0.88 1.87*10.sup.14 5.79*10.sup.16 4.45*10.sup.15

(51) Furthermore, the residual stress states of the layer systems are listed in table 7 below. The stresses were determined in the as deposited state by the wafer curvature method on silicon specimens. However, depending on the method by which the layers are produced, these values can vary.

(52) TABLE-US-00007 TABLE 7 Residual stresses in the layers measured by the wafer curvature method on Si specimens Designation Layer Stresses [MPa] BL TiAlN/TaCrN ~370 ML TiAlN/TiAlN TaCrN ~450 ML + DS TiAlN/TiAlN TaCrN/TaCrN ~450 SL TaCrN ~500 Ref. 1-PM TiAlN PM targets ~550 Ref. 2-CC TiAlN plug targets ~1200

(53) It can be seen that the multilayer coating system ML also has relatively low intrinsic stresses in the coating, as a result of which the life and period of operation are additionally positively influenced.

(54) An illustrative structure of a multilayer coating system ML is shown as an image of a fracture surface in FIG. 2, in which an AlTiN base layer was provided on a cemented carbide substrate and the AlTiN/CrTaN multilayer coating system was then applied on top of this.

(55) Accordingly, a tremendous increase in hardness combined with low coefficients of friction and a long operation life are obtained in the case of the above-described multilayer coating system ML.

(56) When a multilayer coating system ML was used, it was confirmed in cutting machining tests that a coating is particularly advantageous for thread-cutting tools, reamers and solid cemented carbide tools, namely everywhere where the coefficient of friction should be low and a high hardness is required at the same time.

(57) The measurement results of cutting machining tests for the different multilayer coating systems are shown in FIG. 3. Here, the operating life of a cutting insert of a milling cutter in wet milling in minutes is reported. In detail, the cutting machining test was carried out using the following test parameters:

(58) Climb milling with a single tooth, with a spiral cut in the plane of the block being made. SP300 high-speed steel was used as material and the tool was an ISCAR F45ST D050-22 for accommodating indexable cutting plates, which was installed in an SK50 tool seat. The workpiece in each case had dimensions of 40020096 mm and a strength of 1000 N/mm.sup.2. The milling cutter had a diameter of 50 mm and was advanced at a pitch of 45 with a cutting speed v.sub.c of 250 m/min (dry) and 150 m/min (wet), a tooth advance f.sub.z of 0.25 mm and an engagement width a.sub.e of 32 mm.

(59) It can immediately be seen from FIG. 3 that the multilayer coating system ML has the best operating life. In the case of wet machining, an about 20% better operating life compared to the reference layer systems is obtained. In the case of the dry machining which is not shown in the figure, the multilayer coating system ML is, however, not significantly better than in the case of the reference layer systems.

(60) Furthermore, a cutting tool for cutting machining apparatus, which has a suitable substrate, preferably a cemented carbide substrate, having the prescribed geometry, can also be produced. The cutting tool can, for example, be in the form of a cutting body for lathes and milling machines or in the form of an indexable cutting plate.

(61) A hard material layer having a multilayer coating system made up of CrTaN alternating with AlTiN in low layer thicknesses is then applied to this substrate using the process indicated above.

(62) Furthermore, in order to match the surface structure and/or the surface roughness to the respective application, the hard material layer can be subjected to an after-treatment. This after-treatment can, for example, be carried out by wet blasting, dry blasting and/or coloring. Any covering layer and/or functional layer applied can also be subjected to such an after-treatment.

(63) The production of coating sources in the form of CrTa composite targets, as were advantageously used in the above-described processes for producing hard material layers for the deposition of the CrTaN layers by PVD, will be discussed in detail below.

(64) To produce the composite targets, pure Cr and pure Ta powder are firstly provided as raw materials. The particle size of the powders is preferably below 45 m in each case. The two powders are mixed very homogeneously with one another in the desired ratio of the CrTa composite targets to be produced from the powder. Due to the fine particle size, the mixture of the two powders can be made particularly homogeneous and a TaCr.sub.2 phase finely dispersed in the target can be formed in the subsequent densification process.

(65) As stated above, a Ta content of 1-60 at. %, particularly preferably 20-30 at. %, very particularly preferably 25 at. %, is preferably produced in the mixture for the CrTa composite target to be produced.

(66) The CrTa composite target is then produced in a pressing mold from the essentially homogeneous powder mixture by means of a sintering operation. The sintering operation is, for example, carried out by hot pressing, spark plasma sintering (SPS) or hot isostatic pressing (HIP). In each case, the powder can be treated in a chamber by means of heating conductors or directly with an electric current and/or inductively heated during pressing.

(67) The sintering by means of SPS or hot pressing in order to produce the CrTa composite targets takes place in the temperature range of 1100-1750 C., preferably in the temperature range of 1300-1500 C. The sintering time is kept quite short, preferably less than one hour, in order to avoid recrystallization and obtain the fine-grained nature of the microstructure.

(68) A metallographic polished section with grain boundary etching through the composite target produced in this way is shown in FIG. 4. After the sintering process, the microstructure consists of three phases, namely a pure Cr or Cr mixed crystal phase 1, a pure Ta or Ta mixed crystal phase 2 and a TaCr.sub.2 phase 3. The TaCr.sub.2 phase 3 is present at the grain boundaries at the transitions from Ta to Cr. In order to provide the CrTa composite target in the proposed manner, all three phases mentioned have to be present. The corresponding phase diagram is shown in FIG. 5.

(69) The measured density after sintering is at least 90% of the theoretical density, preferably 95% or 98%.

(70) The CrTa composite targets produced in this way can either be used directly, or can, in order to improve handling, be fastened on their rear side to a backing plate, e.g. by bonding, hard soldering or diffusion bonding, by means of which the targets can then be fastened in the PVD plant for deposition of CrTaN. It is also possible for a plurality of CrTa composite targets to be fastened to a single backing plate, for example in order to take account of the desired geometry in the PVD plant.

(71) If applicable, all individual features which are presented in the individual working examples can be combined with one another and/or exchanged without going outside the scope of the invention.