Process for coating an article and coating produced thereby

Abstract

The invention relates to a process for coating an article (1), wherein a coating (2) having one or more coating layers (3, 4, 5) is applied to the article (1), wherein at least one coating layer (5) is formed essentially from aluminium, titanium and nitrogen, wherein the coating layer (5) has, at least in some regions, adjoining lamellae of different chemical composition and is deposited from a gas phase comprising at least one aluminium precursor and at least one titanium precursor. According to the invention, by setting a molar ratio of aluminium to titanium, the lamellae of different chemical composition are each formed with a cubic structure, it being possible for aluminium and titanium to be partly replaced by other metals and for nitrogen to be partly replaced by oxygen and/or carbon with retention of the cubic structure. The invention further relates to a correspondingly produced coating (2).

Claims

1. A method for coating an object, comprising applying a coating having one or more coating layers to the object, wherein at least one coating layer is formed essentially from aluminum, titanium and nitrogen, wherein the at least one coating layer comprises, at least in some regions, mutually adjoining lamellae of varying chemical composition and is deposited with an average composition of Al.sub.xTi.sub.(1-x)N with 0.70x0.90, and at a pressure of 10 mbar to 80 mbar from a gas phase having at least one aluminum precursor and at least one titanium precursor, wherein the molar ratio of aluminum to titanium is adjusted so that the lamellae of varying chemical composition are each formed with a cubic structure, wherein lamellae with a composition of Al.sub.xTi.sub.(1-x)N having a higher Al content than Ti content and a cubic structure alternate consecutively with lamellae with a composition of Ti.sub.(1-x)Al.sub.xN having a higher Ti content than Al content and also a cubic structure, and wherein with the preservation of the cubic structure, aluminum and titanium can be partially replaced by other metals, and nitrogen can be partially replaced by oxygen and/or carbon.

2. The method according to claim 1, wherein for the deposition of the at least one coating layer of essentially aluminum, titanium and nitrogen, a molar Al/Ti ratio in the gas phase is, at least temporarily, limited to maximally 3.0.

3. The method according to claim 1, wherein the lamellae are deposited with a lamellar periodicity of less than 20 nm.

4. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited from a gas phase containing aluminum trichloride, titanium tetrachloride and ammonia.

5. The method according to claim 4, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited with an average composition of Al.sub.xTi.sub.(1-x)N with 0.75x0.85.

6. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited at a pressure of 20 mbar to 50 mbar.

7. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited at a temperature of approximately 750 C. to 850 C.

8. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited with a thickness of 1 m to 20 m.

9. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited epitaxially.

10. The method according to claim 1, wherein an object made of a hard metal is coated.

11. The method according to claim 1, wherein a multi-layer coating is deposited on the object, wherein as a first coating layer a bonding layer of TiN is deposited.

12. The method according to claim 11, wherein in the deposition of a first coating layer and subsequent deposition of each additional coating layer, a deposition temperature is respectively lowered or maintained.

13. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited on a coating layer of TiCN.

14. The method according to claim 1, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited by means of a CVD method.

15. The method according to claim 1, wherein with the preservation of the cubic structure, aluminum and titanium are partially replaced by other metals comprising silicon and/or chromium in an amount up to 20% by weight.

16. The method according to claim 1, wherein with the preservation of the cubic structure, nitrogen is partially replaced by oxygen and/or carbon.

17. The method according to claim 1, wherein the molar Al/Ti ratio in the gas phase is, at least temporarily, limited to maximally 2.0, the lamellae are deposited with a lamellar periodicity of 3 nm to 17 nm, and the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited with a thickness of 3 m to 8 m.

18. A coating which is applied to an object by a CVD method, wherein the coating comprises one or more coating layers and wherein at least one coating layer is formed essentially from aluminum, titanium and nitrogen with an average composition of Al.sub.xTi.sub.(1-x)N with 0.70x0.90 and, at least in some regions, comprises mutually adjoining lamellae of varying chemical composition, the lamellae of varying chemical composition are each formed with a cubic structure, wherein lamellae with a composition of Al.sub.xTi.sub.(1-x)N having a higher Al content than Ti content and a cubic structure alternate consecutively with lamellae with a composition of Ti.sub.(1-x)Al.sub.xN having a higher Ti content than Al content and also a cubic structure, and wherein with the preservation of the cubic structure, aluminum and titanium can be partially replaced by other metals, and nitrogen can be partially replaced by oxygen and/or carbon.

19. The coating according to claim 18, wherein the lamellae are formed with a lamellar periodicity of less than 20 nm.

20. The coating according to claim 18, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen has an average composition of Al.sub.xTi.sub.(1-x)N with 0.75x0.85.

21. The coating according to claim 18, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen has a thickness of 1 m to 20 m.

22. The coating according to claim 18, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is grown epitaxially.

23. The coating according to claim 18, wherein the coating has a multi-layer structure.

24. The coating according to claim 23, wherein a first coating layer is provided as a bonding layer on the object, wherein the first coating layer is formed from TiN with a thickness of less than 1.0 m.

25. The coating according to claim 23, wherein the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited on a coating layer of TiCN.

26. An object comprising a cutting tool having a coating according to claim 18.

27. The coating according to claim 18 wherein with the preservation of the cubic structure, aluminum and titanium are partially replaced by other metals comprising silicon and/or chromium in an amount up to 20% by weight.

28. The coating according to claim 18, wherein with the preservation of the cubic structure, nitrogen is partially replaced by oxygen and/or carbon.

29. The coating according to claim 18, wherein the lamellae are deposited with a lamellar periodicity of 3 nm to 17 nm, and the at least one coating layer of essentially aluminum, titanium and nitrogen is deposited with a thickness of 3 m to 8 m.

Description

(1) Additional features, advantages and effects of the invention follow from the exemplary embodiments described below. The drawings which are thereby referenced show the following:

(2) FIG. 1 A basic structure of a coating on an object;

(3) FIG. 2 An image taken using a transmission electron microscope (TEM);

(4) FIG. 3 A diffraction pattern for the image according to FIG. 2;

(5) FIG. 4 An X-ray diffractogram;

(6) FIG. 5 A chart for the hardness and elasticity modulus

(7) FIG. 6 A TEM image;

(8) FIG. 7 An illustration of pole figures.

(9) In FIG. 1, an object 1 according to the invention is illustrated schematically. The object 1 is typically formed from a sintered hard metal which is composed of carbides and/or carbonitrides of tungsten, titanium, niobium or other metals and a binder metal selected from the group comprising cobalt, nickel and/or iron. A binder metal content is thereby normally up to 10 wt. %. Typically, the object 1 is composed of up to 10 wt. % cobalt and/or other binder metals, the remainder being tungsten carbide and up to 5 wt. % other carbides and/or carbonitrides of other metals.

(10) A coating layer 3 of TiN serving as a bonding layer is deposited on the object 1. The coating layer 3 normally has a thickness of less than 2 m, preferably 0.4 to 1.2 m. On the coating layer 3, a coating layer 4 of TiCN serving as an intermediate layer is deposited. This coating layer 4 is an MT-TiCN coating layer. A coating layer 4 of this type normally has a columnar structure with spiky crystals, which are essentially aligned parallel to the surface normals on the object 1. Finally, an additional coating layer 5 is deposited on the coating layer 4. The coating layer 5 is formed essentially from aluminum, titanium and nitrogen and deposited by means of a CVD method. Depending on the process management or the gases used, smaller contents of chlorine and oxygen can also be present in the coating layer 5. The other coating layers 3, 4 can also be deposited using a CVD method.

(11) The object 1 can in particular be a cutting insert such as an indexed cutting plate. To coat said cutting plate, or to create a coating 2, the bonding layer or coating layer 3 of TiN is deposited in a first step at a process temperature from 880 C. to 900 C. from a gas containing or composed of nitrogen, hydrogen and titanium tetrachloride. The temperature is then lowered, and at a temperature from e.g. 820 C. to 840 C., a coating layer 4 formed from MT-TiCN is deposited with a thickness of 2 m to 5 m. The deposition thereby takes place from a gas composed of nitrogen, hydrogen, acetonitrile and titanium tetrachloride. The corresponding process temperature and the use of acetonitrile as a carbon or nitrogen source ensures a formation of the intermediate layer with columnar growth or spiky crystals of TiCN. The TiCN coating layer thereby comprises in cross-section longitudinally extended crystals, which preferably run parallel, but at least mostly at an angle of 30, to a surface normal of the object 1. With a corresponding TiCN coating layer, there results a suitable bonding of the subsequently deposited coating layer 5 with an average composition of Al.sub.xTi.sub.1-xN. In this regard, it is expedient that the TiCN coating layer has an average composition of TiC.sub.aN.sub.1-a, with a in the range from 0.3 to 0.8, in particular 0.4 to 0.6.

(12) On the intermediate layer of TiCN, in which the titanium can be replaced by aluminum at up to 40 mol % in order to increase a hardness, the coating layer 5 with aluminum, titanium and nitrogen is finally applied, for which the temperature is lowered to approximately 800 C. to 830 C. The coating layer 5, which is, but does not have to be, an outermost coating layer, is created from a gas containing aluminum trichloride, nitrogen, hydrogen, titanium chloride and a separately introduced mixture of ammonia and nitrogen. Thus, in a second step for producing the intermediate layer and in a third step for producing the coating layer 5, a process temperature for each is lowered, which is extremely cost-efficient and allows a rapid creation of the coating 2 on the cutting insert. The coating layer 5 is preferably deposited at a pressure of 20 mbar to 80 mbar, in particular 25 mbar to 55 mbar, wherein the pressure is regulated via the volume flow rate of the introduced gases.

(13) In Tables 1 and 2 below, typical process parameters and compositions are provided.

(14) TABLE-US-00001 TABLE 1 Process parameters for coating with AlTiN CVD coating layer having alternating cubic lamellae Temperature Gas composition in [L/min], TiCl.sub.4 Coating layer [ C.] and CH.sub.3CN for MT-TiCN in [mL/min] TiN 880-900 TiCl.sub.4/2.2, N.sub.2/14, H.sub.2/17 MT-TiCN 750-850 CH.sub.3CN/0.5, TiCl.sub.4/2.5, N.sub.2/12, H.sub.2/4 AlTiN 750-850 HClAlCl.sub.3/3.3 to 1.1, TiCl.sub.4/1.2, NH.sub.3N.sub.2/0.9 to 4.5, H.sub.2/61

(15) TABLE-US-00002 TABLE 2 Properties of the AlTiN coating layer Layer thickness [m] Coating layer general preferred Composition AlTiN 1-20 3-8 Al.sub.xTi.sub.1xN, x = 0.75-0.85

(16) In FIG. 2, a TEM image of a coating structure is shown, in which structure an AlTiN gradient layer is applied to a hard metal, which layer was applied essentially as described above, although the content of the titanium precursor was steadily increased and that of the aluminum precursor was kept constant. The gradient layer starts at Al.sub.90Ti.sub.10N and ends at Al.sub.70Ti.sub.30N. In the range therebetween, the structure known from WO 2013/134796 A1 with alternating lamellae of a hexagonal and cubical structure initially forms while contents of the titanium precursor are still low. At higher contents, a structure then forms in which only cubic phases are still present, which follows from FIG. 3. Thus, by varying a ratio of the precursors, the structure can be set in a targeted manner on the nanometer scale. The lamellar periodicity is approximately 9 nm.

(17) In FIG. 4, an X-ray diffractogram for a coating layer 5 can be seen, from which it follows in an evaluation that a coating layer 5 is formed with a cubic structure and hexagonal phases are not detectable, which confirms the results from FIG. 3 for the gradient layer.

(18) Surprisingly, a coating layer 5 exhibits not only a high hardness, but also a suitable toughness. As the measurement results shown in FIG. 5 for the gradient layer according to FIG. 2 indicate, the gradient layer reaches a maximum for both hardness and toughness in the range of the exclusively cubic formation.

(19) In FIG. 6, a high-resolution TEM image of a coating layer 5 is shown, which layer was produced as described above. In this image, the formed lamellae which have a lamellar periodicity of a few nanometers can be seen. Lamellae with a composition of Al.sub.xTi.sub.1-xN having a higher Al content than Ti content and a cubic structure alternate consecutively with lamellae Ti.sub.1-xAl.sub.xN lamellae having a higher Ti content than Al content and also a cubic structure. It is assumed that this special nanostructure causes the excellent properties of the coating layer 5, in particular the high hardness and strength. The coating layer 5 is not only embodied as particularly oxidation-stable and having high hardness and strength, but also as very thermally stable. Continuous thermal loads at 950 C. to 1050 C. for one hour showed that cracks occur in hard metal substrates starting at 1000 C., whereas a coating layer 5, aside from the concurrent breakaway with hard metal parts, withstands the thermal loading.

(20) If a coating layer 5 is deposited on a suitable substrate such as sapphire, epitaxial growth can also occur, which can be derived from the pole figures in FIG. 7, which are based on a coating layer 5 directly deposited on sapphire.

(21) Even though a coating layer 5, possibly also together with additional coating layers 3, 4, is preferably used for cutting inserts such as indexed cutting plates, any other desired cutting tools that are exposed to high temperatures and mechanical stresses during use and must thereby also exhibit a high oxidation resistance can of course also be coated.