Tool and process for coating a basic tool component

Details Tool and process for coating a basic tool component Tool and process for coating a basic tool component

1995-05-16

1997-12-02

Turner, Archene

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

428698, 428699, 428702, 427249, 4272552, 4272557, 51307, 51309, C23C 3000

Patent

active

056934084

DESCRIPTION:

BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT application PCT/DE93/01111 filed 18 Nov. 1993 with a claim to the priority of German application P 42 39 234.9 filed 21 Nov. 1992.


FIELD OF THE INVENTION

The invention relates to a tool having a base body of hard metal, cermet, or steel and a multilayer surface coating applied to the base body of the hard materials titanium carbide, titanium carbonitride, titanium nitride, zirconium carbonitride, and/or aluminum oxide.
The invention further relates to a method of coating a base body of hard metal or cermet with several layers consisting of carbides, nitrides and/or carbonitrides of titanium and/or zirconium and/or aluminum oxide by means of a deposition process from the gas phase.


BACKGROUND OF THE INVENTION

The German publication "Angewandte Chemie" (69th year, no. 9, pages 281 through 312, 7 May 1957) describes how the brittleness of hard materials can be overcome by using them in the form of thin surface layers in order to protect other materials against mechanical or chemical attack. Thus for example a sheet coated with a 6 .mu.m thick layer of TiN is described.
In addition a base body is for example known from Swiss patent 507,094 which consists of a hard-metal substrate and at least one hard-material layer, the hard-metal substrate being constituted of one or more hard materials and at least one binder metal, the hard-material layer containing hard carbides or nitrides. Such shaped bodies can be used as tools for chip-removing or noncutting shaping since they have good resistance to wear. The bodies can be made by the CVD (chemical vapor deposition) method as described for example in Swiss patent 452,205. The CVD process today is the most common coating method and is carried out by precipitating a surface layer onto a substrate from a reactive gas atmosphere which generally has a temperature between 900.degree. C. and 1200.degree. C. The gas atmosphere contains several compounds which react with one another at the reaction temperature and form the material in the surface layer. It is nowadays generally standard to sheath metallic substrates with hard-material layers of carbides, nitrides, or carbonitrides with the overall atmosphere containing halogenides of the elements from the group III to VI of the periodic table and including a nitrogen-containing compound and a carbon-containing compound. Thus a titanium-carbide layer is coated onto a hard-metal base body at about 1000.degree. C. from a gas atmosphere which contains titanium tetrachloride and methane. As the carbon compounds, gaseous hydrocarbons are used while N.sub.2, NH.sub.3 or amines are used as the nitrogen-containing compounds.
In order to work at a low precipitating temperature the so-called plasma-assisted CVD process has been suggested. A nonequilibrium plasma is added to the reaction gas in a low-pressure glow discharge so that the charge carriers in the gas are accelerated by the created electrical field. The free path between successive collisions is dependent on the particle density and the pressure. When the particle energy reaches the applied voltage, molecules or atoms are excited to disassociation or ionization. Thus chemical reactions are possible which otherwise could only take place at relatively high temperatures. The low-pressure plasma can be produced mainly by applying a constant direct-current voltage to a workpiece as cathode, by means of a high-frequency alternating-current voltage, or by a pulsed direct-current voltage.
The high-frequency excitation, which adds its energy inductively or capacitatively from outside into the reaction vessel, is mainly used to deposit very pure layers in the electronics field, e.g. with microchips. Since it works without electrodes directly connected to the substrate there is no problem whether the workpiece is conductive or not. Disadvantageously this method is very expensive.
The simplest way to produce a low-pressure discharge is to connect the workpiece to be coated as a cathode and the

REFERENCES:
patent: 4643951 (1987-02-01), Keem
patent: 4746563 (1988-05-01), Nakano
patent: 4943450 (1990-07-01), Sarin
patent: 5077091 (1991-12-01), Nowak et al.
patent: 5093151 (1992-03-01), Van Den Berg
patent: 5223337 (1993-06-01), Van Den Berg
patent: 5250367 (1993-10-01), Santhanam et al.
patent: 5403628 (1995-04-01), Konig
patent: 5496594 (1996-03-01), Konig

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