Coated body and method for coating a body

Abstract

The invention relates to a body, especially a cutting element, at least partially comprising a coating, whereby the coating is formed from one or more coating layers, whereby at least one coating layer comprises aluminum, titanium and nitrogen or is formed from these elements. According to the invention, the coating layer with aluminum, titanium and nitrogen at least partially comprises lamellae having a lamellar thickness of less than 100 nm, whereby the lamellae comprise successive sections having different phases. The invention further relates to a method for coating a body, especially a cutting element.

Claims

1. A body comprising: a single CVD coating layer at least partially arranged on the body; and said single CVD coating layer being at least partially lamellar and comprising aluminum, titanium and nitrogen, wherein lamellae of the single CVD coating layer comprises: a lamellar thickness of less than 100 nm; and successive portions with different phases.

2. The body of claim 1, wherein the body is a cutting element.

3. The body of claim 1, wherein the lamellar thickness is less than 50 nm.

4. The body of claim 3, wherein the lamellar thickness is one of: less than 35 nm; and less than 25 nm.

5. The body of claim 1, wherein the lamellae form crystallites having at least partially in one cross section a width of more than 50 nm.

6. The body of claim 5, wherein the width is between 50 to 200 nm.

7. The body of claim 1, wherein the lamellae comprise alternately formed first and second portions, said first portions being predominantly or exclusively composed of a cubic phase, and said second portions being predominantly or exclusively composed of a hexagonal phase.

8. The body of claim 7, wherein the first portions comprise cubic TiN and/or cubic Al.sub.xT.sub.1-xN.

9. The body of claim 7, wherein the second portions comprise hexagonal AIN.

10. The body of claim 7, wherein the first portions are thinner in cross section than the second portions.

11. The body of claim 1, wherein said single CVD coating layer comprises the following: a cubic TiN phase; a hexagonal AlN phase; and a cubic Al.sub.xTi.sub.1-xN phase, whereby, in the cubic TiN phase, aluminum is present in lower molar proportions than titanium, and whereby, in the hexagonal AlN phase, titanium is present in lower molar proportions than aluminum.

12. The body of claim 11, wherein a proportion of the hexagonal phase of AlN is at least 5%.

13. The body of claim 12, wherein the proportion of the hexagonal phase of AlN is one of: between 5% and 50%; and between 10% and 35%.

14. The body of claim 1, wherein the single CVD coating is arranged over another coating layer comprising elongated crystals of TiCN that on average extend approximately perpendicular to a surface of the other coating layer.

15. The body of claim 1, wherein the body is a hard metal base body.

16. A method for coating a body with a single CVD coating layer having an at least partially lamellar structure and comprising aluminum, titanium and nitrogen, the method comprising: applying, at least regionally, said single CVD coating layer on the body, wherein lamellae of the single CVD coating layer comprise: a lamellar thickness of less than 100 nm; and successive sections with different phases.

17. The method of claim 16, wherein the body comprises plural bodies.

18. The method of claim 17, wherein the applying occurs in a system into which the plural bodies are introduced simultaneously.

19. The method of claim 16, wherein the applying occurs at a pressure of more than 20 mbar.

20. The method of claim 19, wherein the pressure is between 20 and 80 mbar.

21. The method of claim 19, further comprising adjusting the pressure during the applying.

22. The method of claim 16, wherein the applying occurs at a temperature of from 800 C. to 830 C.

23. The method of claim 16, wherein the applying comprises depositing from a gas phase the at least one coating layer, wherein a molar ratio of aluminum to titanium is less than 5.0.

24. The method of claim 23, wherein the molar ratio of aluminum to titanium is one of: less than 4.5; and between 2.5 and 4.2.

25. A cutting tool element comprising: a metal body; plural coating layers arranged on the body; said plural coating layers comprising a single CVD outermost layer; said single CVD outermost layer comprising aluminum, titanium and nitrogen, and having an at least partially lamellar structure, wherein lamellae of said single CVD coating layer comprise: a lamellar thickness of less than 100 nm; and successive portions with different phases.

Description

(1) The invention is further explained in the following with reference to an embodiment. In the drawings, to which reference is made here, is shown:

(2) In FIG. 1, a schematic view of a coated body;

(3) In FIG. 2, a photograph of a coating layer of a body according to FIG. 1 taken with a transmission electron microscope;

(4) In FIG. 3, an enlarged detail from the representation in FIG. 2;

(5) In FIG. 4, an enlarged detail from the representation in FIG. 3;

(6) In FIG. 5, a representation of a chemical analysis by means of transmission electron microscopy.

(7) FIG. 1 shows a body (1) according to the invention. The body (1) comprises a base body (2), which is usually composed of a hard metal, which is selected from carbides and/or carbonitrides of tungsten, titanium, niobium or other metals, and a binder metal selected from the group cobalt, nickel and/or iron. As a rule, a binder metal content is up to 10 wt %. Typically, the body (1) is composed of up to 10 wt % of cobalt and/or other binder metals, the remainder being tungsten carbide, and up to 5 wt % of other carbides and/or carbonitrides of other metals. A coating layer (3) of TiN serving as a bonding layer is deposited on the base body (2). The coating layer (3) typically has a thickness of less than 2 m, preferably 0.4 to 1.2 m. A coating layer (4) of TiCN serving as an intermediate layer is deposited on the coating layer (3). This coating layer (4) is a medium-temperature TiCN (MT-TiCN) coating layer. Such a coating layer (4) typically has a columnar structure with columnar crystals, which are aligned substantially parallel to the surface normal to the body (1). Finally, an outermost coating layer (5) is deposited on the coating layer (4). The coating layer (5) is formed with aluminum, titanium and nitrogen, and is deposited by means of a CVD method as with the other coating layers (3) and (4). Depending on the procedure and gases used, smaller proportions of chlorine and oxygen can also be present in the coating layer (5).

(8) A coating as shown in FIG. 1 can be deposited on a cutting element, in particular a cutting plate, wherein the body (1) is prepared, whereby in a first step the bonding layer and/or coating layer (3) of TiN is deposited at a process temperature of from 880 C. to 900 C. from a gas containing nitrogen, hydrogen and titanium tetrachloride. Then the temperature is lowered, and at a temperature from 830 to 870 C. a coating layer (4) formed from MT-TiCN having a thickness of 2-5 m is deposited. The deposition is thus carried out from a gas composed of nitrogen, hydrogen, acetonitrile, and titanium tetrachloride. The corresponding process temperature and the use of acetonitrile as the carbon and/or nitrogen source ensures formation of the intermediate layer with columnar growth and/or columnar crystals of TiCN.

(9) The TiCN coating layer thus has longitudinally extending crystals in cross-section, which preferably extend predominantly at an angle of 30 to a surface normal of the body (1). A corresponding TiCN coating layer produces a good bonding of the subsequently deposited coating layer (5) with an average Al.sub.xTi.sub.1-xN. In this regard, it is advantageous for the TiCN coating layer to have an average composition of TiC.sub.aN.sub.1-a with a in the range of 0.3 to 0.8, especially 0.4 to 0.6.

(10) To enhance a hardness, finally the coating layer (5) with aluminum, titanium and nitrogen can be applied to the intermediate layer of TiCN, whereby the titanium can be replaced by up to 40 mole % aluminum, whereby the temperature is lowered to about 800 C. to 830 C. The coating layer (5), which is, but need not be, an outermost coating layer, is prepared from a gas containing aluminum trichloride, nitrogen, hydrogen, titanium tetrachloride, and a separately supplied 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), each can have a lowered process temperature, which is highly economical and allows for rapid preparation of the coating on the cutting element.

(11) For the production of coated bodies (1), a respective plurality of bodies (1) is introduced into a system where coating takes place simultaneously in the manner described above. A process pressure in the CVD coating steps is thus adjusted through the supply of the process gas. During production of the coating layer (5) with aluminum, titanium and nitrogen, a molar ratio of aluminum to titanium is adjusted such that that it is less than 5.0.

(12) The following tables show typical process parameters for the production of a coating and properties of individual coating layers.

(13) TABLE-US-00001 TABLE 1 Process parameters Temperature Gas composition/gas flow rate (L/min) Coating layer ( C.) and/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.3/2.7-0.7, TiCl.sub.4/0.3, NH.sub.3N.sub.2/0.9-4.5, H.sub.2/64

(14) TABLE-US-00002 TABLE 2 Properties 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

(15) FIGS. 2 to 4 show transmission electron micrographs of the outermost coating layer (5) with different resolution. As can be seen in FIG. 2, lamellar structures are present in the coating layer (5), which are visible partially in cross-section. It is assumed that these are individual crystallites that are differently aligned with respect to the viewing direction, so that the lamellar structure is fully visible only for individual, suitably positioned crystallites. According to the cross-section, the crystallite size is approximately 50 to 200 nm.

(16) FIG. 3 shows an enlarged detail of a region according to FIG. 2. As can be seen, individual lamellae are formed. A lamella respectively comprises a first portion that appears darker in FIG. 3 and a thicker second section that appears brighter. A plurality of such lamellae in a crystallite follow each after the other with a lamellar thickness, namely the thickness of the sum of a first portion and a second portion, of less than 25 nm. The first sections are composed of cubic TiN that can have lower proportions of aluminum, whereby the molar fraction of aluminum is preferably a maximum of 10% of the titanium content. The thicker second portions are formed from a hexagonal phase, which in terms of metals predominantly comprises aluminum. In addition, an Al.sub.xTi.sub.1-xN phase is still present in the coating layer, wherein the aluminum content far outweighs the titanium content. Thus, a total of three phases are present, whereby two of the phases form a lamellar structure that is shown enlarged in FIG. 4.

(17) It is confirmed through chemical analysis by means of transmission electron microscopy that the thinner, first portions of the lamellae are formed predominantly with titanium as the metal (the darker regions in FIG. 5), whereas in the thicker, second portions aluminum is the predominant metal (lighter regions in FIG. 5).

(18) Cutting elements with a coating layer (5) as described previously have proven in use especially for the machining of cast materials, but also other metallic materials, to be extremely wear-resistant and oxidation resistant, whereby individual cases have shown service life increases of up to 220% as compared with cutting plates that were coated with a cubic Al.sub.xTi.sub.1-xN coating layer using a PVD method.