METHOD FOR PRODUCING A COATING ON AN OBJECT AND CORRESPONDINGLY PRODUCED COATED BODY

Abstract

A method for producing a coating on an object and a correspondingly produced coated body, in particular a cutting insert such as a cutting plate for machining processes. The coating with one or more coating layers is applied to the object. At least one Al.sub.1-xTi.sub.xN coating layer is deposited using a CVD method, wherein nitrogen in the Al.sub.1-xTi.sub.xN coating layer can be partially substituted. In order to obtain a coating layer with a highest possible proportion of cubic phases, the Al.sub.1-xTi.sub.xN coating layer is deposited in the presence of a sulfur-containing gas.

Claims

1. A method for producing a coating on an object, in particular a cutting insert such as a cutting plate for machining processes, wherein a coating with one or more coating layers is applied to the object, wherein at least one Al.sub.1-xTi.sub.xN coating layer is deposited using a CVD method, wherein nitrogen in the Al.sub.1-xTi.sub.xN coating layer can be partially substituted, wherein the Al.sub.1-xTi.sub.xN coating layer is deposited in the presence of a sulfur-containing gas.

2. The method according to claim 1, wherein hydrogen sulfide is used as sulfur-containing gas.

3. The method according to claim 1, wherein the Al.sub.1-xTi.sub.xN coating layer is deposited with a hexagonal AlN volume proportion of less than 20 vol %, preferably less than 10 vol %, in particular less than 5 vol %.

4. The method according to claim 1, wherein a proportion of sulfur in the Al.sub.1-xTi.sub.xN coating layer is less than 5 at %, preferably less than 4 at %, in particular less than 3 at %.

5. The method according to claim 1, wherein the Al.sub.1-xTi.sub.xN coating layer is deposited as an outermost coating layer.

6. The method according to claim 1, wherein one or more coating layers are deposited beneath the Al.sub.1-xTi.sub.xN coating layer, wherein preferably all coating layers are deposited using a CVD method.

7. The method according to claim 6, wherein the Al.sub.1-xTi.sub.xN coating layer is deposited at a temperature of 800 C. to 850 C., preferably 810 C. to 830 C.

8. The method according to claim 1, wherein the Al.sub.1-xTi.sub.xN coating layer is deposited from a first mixture of nitrogen, hydrogen, titanium tetrachloride, aluminum trichloride, and hydrogen sulfide and from a second mixture of nitrogen and ammonia.

9. The method according to claim 1, wherein the Al.sub.1-xTi.sub.xN coating layer is at least partially embodied with regions of lamellae, wherein the lamellae preferably have an average size, determined according to Debye-Scherrer, of less than 150 nm, preferably less than 100 nm, in particular less than 80 nm.

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

11. A coated body having a coating which comprises at least one Al.sub.1-xTi.sub.xN coating layer deposited using a CVD method, wherein nitrogen in the Alix Ti.sub.xN layer can be partially substituted, wherein the Al.sub.1-xTi.sub.xN coating layer comprises sulfur.

12. The coated body according to claim 11, wherein the Al.sub.1-xTi.sub.xN coating layer is embodied with a hexagonal AlN volume proportion of less than 20 vol %, preferably less than 10 vol %, in particular less than 5 vol %.

13. The coated body according to claim 11, wherein a proportion of sulfur in the Al.sub.1-xTi.sub.xN coating layer is less than 5 at %, preferably less than 4 at %, in particular less than 3 at %.

14. The coated body according to claim 11, wherein the Al.sub.1-xTi.sub.xN coating layer is at least partially embodied with regions of lamellae, wherein the lamellae preferably have an average size, determined according to Debye-Scherrer, of less than 150 nm, preferably less than 100 nm, in particular less than 80 nm.

15. The coated body according to claim 11, wherein x lies in the range of 0.85 to 0.99.

Description

[0043] Additional features, advantages, and effects of the invention follow from the exemplary embodiment described below. In the drawings which are thereby referenced:

[0044] FIG. 1 shows a schematic illustration of a coated cutting plate;

[0045] FIG. 2 shows an image of a coated cemented carbide body taken using scanning electron microscopy;

[0046] FIG. 3 shows a further image of a coated cemented carbide body taken using scanning electron microscopy;

[0047] FIG. 4 shows an image of a coated cemented carbide body with an Al.sub.1-xTi.sub.xN coating layer having different proportions of sulfur, taken using scanning electron microscopy;

[0048] FIG. 5 shows a visual representation of reflections in an X-ray diffractogram as a function of an H.sub.2S concentration during a deposition of a coating layer according to FIG. 4 as well as the related domain size according to Debye-Scherrer:

[0049] FIG. 6 shows an X-ray diffractogram;

[0050] FIG. 7 shows a further image taken using scanning electron microscopy, with positions indicated for spectra;

[0051] FIG. 8 shows diagrams pertaining to oxygen contents and sulfur contents at the spectral positions indicated in FIG. 7.

[0052] In FIG. 1, a body 1 or object is illustrated by way of example. The object is a cutting element, but can also be a different body 1. The body 1, which is merely illustrated in section, comprises a base body 2. The base body 2 is normally formed from a cemented carbide. The cemented carbide can, for example, be a cemented carbide based on tungsten carbide as a hard material, wherein the tungsten carbide can be partially replaced by titanium carbide. In addition, a metallic binder is provided, typically cobalt, though nickel and/or iron, possibly in combination with one of the other metallic binders, for example cobalt and iron, or all of these metals, can also be provided. Typically, a proportion of hard material, for example tungsten carbide, as mentioned, is 85% to 95%. The remainder is essentially formed from the metallic binder.

[0053] The base body 2 is provided with a multi-layer coating, wherein a first coating layer 3 is formed from titanium nitride (TIN). The TiN coating layer serves as a bonding layer. The bonding layer normally has a layer thickness of no more than 2 m. An additional coating layer 4 of MT-TiCN is deposited on the bonding layer of TIN. This coating layer can have a thickness of 2 m to 7 m, for example, but is merely optional. Finally, one other additional coating layer 5 is deposited on the MT-TiCN coating layer. Said additional coating layer 5 is formed from Al.sub.1-xTi.sub.xN coating layers. This additional coating layer 5 can, as illustrated, constitute the outermost coating layer, which is not mandatory, however. It is also possible that, on this additional coating layer 5, at least one additional coating layer is also deposited on the outer side.

[0054] For the production of the Al.sub.1-xTi.sub.xN coating layer, the base body 2 is first supplied and the bonding layer of TiN is then deposited, whereupon the additional coating layer 4 of MT-TiCN is, where provided, applied at reduced temperature. Finally, the coating layer of Al.sub.1-xTi.sub.xN is deposited at a once again reduced temperature. All coating layers are, even if still others should be provided, deposited in the CVD process, so that all coating layers can be created in a reactor in one procedure by simply reducing the temperature and switching the process gas.

[0055] In the production of the Al.sub.1-xTi.sub.xN coating layer, two reaction gases are separately fed to the reactor, where they are allowed to react in the reaction zone. This can be achieved if, for example, separate feed pipes open into the reactor with corresponding outlets. A first mixture of a reaction gas is thereby composed of nitrogen, hydrogen, titanium tetrachloride, aluminum trichloride, and hydrogen sulfide. The titanium tetrachloride is thereby supplied on the basis of liquid titanium tetrachloride. The aluminum trichloride is created in situ for the reaction, in that hydrochloric acid is conducted over aluminum pellets. The second mixture is composed of ammonia and nitrogen and is guided into the reaction zone separately from the first mixture, where it can then react with the first mixture, wherein the Al.sub.1-xTi.sub.xN coating layer forms.

[0056] In Table 1 below, typical reaction conditions are presented. If no MT-TicN coating layer or other intermediate layer is provided, which is advantageous for a simplest possible coating system, only the TiN bonding layer is provided.

TABLE-US-00001 TABLE 1 Typical reaction conditions for an Al.sub.1xTi.sub.xN coating layer (for H.sub.2S, see Table 3 in detail) Coating Temperature Gas composition/Gas flow rate (L/min), layer ( C.) or TiCl.sub.4 and CH.sub.3CN (mL/min) TiN 880-900 TiCl.sub.4/2.7, N.sub.2/14, H.sub.2/17 MT-TiCN 830-870 CH.sub.3CN/0.5, TiCl.sub.4/2.7, N.sub.2/19, H.sub.2/3 AlTiN 800-830 HClAlCl.sub.3/2.7-0.9, TiCl.sub.4/0.3, NH.sub.3N.sub.2/0.9-4.5, H.sub.2/64, H.sub.2S variable

[0057] In Table 2 below, general parameters corresponding to deposited coating layer are presented by way of example.

TABLE-US-00002 TABLE 2 General parameters of the coating layers Layer thickness (m) Coating layer General Preferred Composition TiN 2 0.25-0.75 TiN MT-TiCN 1-10 2-5 TiC.sub.aN.sub.1a, a = 0.4-0.6 AlTiN 1-10 3-8 Al.sub.xTi.sub.1xN, x = 0.80-0.99

[0058] In order to examine an influence of hydrogen sulfide during the deposition of Al.sub.1-xTi.sub.xN coating layers corresponding to the preceding statements, an Al.sub.1-xTi.sub.xN coating layer was produced with a varying content of hydrogen sulfide during the deposition. In Table 3 below, corresponding reaction conditions are stated in detail, wherein a TiAlN coating layer is provided as a bonding layer.

TABLE-US-00003 TABLE 3 Reaction conditions for the deposition of Al.sub.1xTi.sub.xN coating layers in the presence of hydrogen sulfide. TiN AlTiN AlTiN Batch temperature [ C.] 890 800 800 AlCl.sub.3 temperature, generator [ C.] 365 365 365 AlCl.sub.3 flow rate [L/min] 0 1.2 1.2 H.sub.2S flow rate [mL/min] 0 0 10* HCl flow rate [L/min] 0 0.35 0.35 N.sub.2 flow rate [L/min] 14 5.5 5.5 H.sub.2 flow rate [L/min] 17 61 61 TiCl.sub.4 flow rate [mL/min] 2.2 0.7 0.7 NH.sub.3 flow rate [L/min] 0 1 1 Pressure [mbar] 160 23 23 *The H.sub.2S bypass is subsequently increased in steps by 10 mL/min each, ultimately to 100 mL/min, so that a gradient layer results.

[0059] In FIG. 2, an image taken using scanning electron microscopy is shown in which a corresponding coating layer can be seen on a cemented carbide body. The coating layer was deposited in the presence of hydrogen sulfide at a varying content, as noted for Table 3.

[0060] In FIG. 3, a correspondingly produced Al.sub.1-xTi.sub.xN coating layer is depicted in an enlarged manner using scanning electron microscopy. The Al.sub.1-xTi.sub.xN coating layer comprises lamellae that have a lamellar thickness (sum of the segments of one higher-aluminum segment and one higher-titanium segment each) of less than 100 nm, as is known from corresponding coating layers. In FIG. 4, this is shown in further enlargement, and is once again visible.

[0061] FIG. 5 shows a visual representation of reflections in an X-ray diffractogram as a function of an H.sub.2S concentration during a deposition of a coating layer according to FIG. 4 as well as the related domain size according to Debye-Scherrer. As can be seen, the typical cubic reflections become stronger as the H.sub.2S concentration increases, which indicates that the cubic phases are stabilized by an increasing H.sub.2S concentration. The domain size shows a certain fluctuation, but it can be observed that the lamellae size runs in the range of approximately 20 nm to 60 nm. It can be stated that the presence of H.sub.2S facilitates the formation of cubic phases, that is, lamellae with alternating cubic segments of higher aluminum concentration and cubic segments of higher titanium concentration. This, in turn, introduces the possibility of creating corresponding coating layers with higher aluminum contents, since a collapse into the hexagonal AlN structure is opposed. The formation of a correspondingly cubic structure is confirmed in the X-ray diffractogram, as is shown in FIG. 6.

[0062] The sulfur contents in the Al.sub.1-xTi.sub.xN coating layer are relatively low and lie, as can be seen in FIG. 7 viewed in combination with FIG. 8, below an oxygen concentration in the Al.sub.1-xTi.sub.xN coating layer. In FIG. 7, a corresponding coating layer can be seen, wherein different measurement positions for spectra are recorded, and wherein the measurement positions are accompanied by an increasing H.sub.2S content in the first reaction mixture. As can be seen in FIG. 8, an aluminum content in the created Al.sub.1-xTi.sub.xN coating layer also increases as the H.sub.2S concentration increases. The sulfur content remains in a predetermined range within statistical significance.

[0063] Cutting plates with a coating system according to FIG. 1 or as described above were produced in the presence of hydrogen sulfide during the deposition of the Al.sub.1-xTi.sub.xN coating layer and compared with analogous coated cutting plates produced, however, without the presence of hydrogen sulfide during the deposition. Corresponding machining results are presented in Table 4 below.

TABLE-US-00004 TABLE 4 Machining results KV/K factor Wear V.sub.b at cm.sup.3 Cutting plate mm 250 500 750 1000 1250 1500 1750 2000 Total Invention 1 0.0296/1.047 0.070 0.079 0.086 0.108 0.121 0.156 1500 0.095 0.102 0.102 0.102 0.105 0.105 Invention 2 0.0337/1.209 0.073 0.079 0.092 0.124 0.137 0.163 1500 0.099 0.105 0.121 0.134 Comparison 1 0.0424/1.167 0.029 0.048 0.086 0.089 0.092 0.096 0.099 0.105 0.0432/1.189 0.076 0.077 0.083 0.093 Comparison 2 0.0457/1.093 0.048 0.060 0.067 0.095 0.102 0.111 0.111 0.111 0.0522/1.010 0.070 0.083 0.083 0.102

[0064] As can be seen, in the coating systems with an outer Al.sub.1-xTi.sub.xN coating layer, which, in any case, already function excellently, additional improvements can still be achieved if the deposition of the Al.sub.1-xTi.sub.xN coating layer takes place in the presence of hydrogen sulfide.