Coated cutting tool and a process for the production of the same

Details Coated cutting tool and a process for the production of the same Coated cutting tool and a process for the production of the same

1995-03-09

1999-06-22

Gorgos, Kathryn

Stock material or miscellaneous articles

All metal or with adjacent metals

Having metal particles

428627, 428698, 428699, 75235, B22F 300

Patent

active

059151625

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a coated cutting tool having a tenacious and high wear resistance coating formed on the surface of a substrate such as cemented carbides and a process for the production of the same.


BACKGROUND TECHNIQUE

Improvement of the service life of a cutting tool has been carried out by vapor deposition of a coating layer of titanium carbide (TiC) on a surface of cemented carbides, cermets or ceramics and in general, a coated cutting tool having a coating layer formed by a thermal or heat-assisted chemical vapor deposition method (hereinafter referred to as heat-assisted CVD method) or plasma CVD method has widely been spread.
However, in the case of carrying out a working using these coated cutting tools, for example, working which requires wear resistance of the coating layer at high temperatures, such as high speed cutting, and a working requiring a number of workings and a number of thrusting-in workpieces, such as the working of small-sized parts, results in a decrease in service life of the tool resulting from the poor wear resistance of the coating layer or damaging of the coating layer.
In the coating film by the heat-assisted CVD method, the adhesiveness thereof to a substrate is excellent, and depending upon the variety of the substrates, the .eta. phase as a brittle layer tends to be deposited thick on the interface with the substrate, in particular, near the cutting edge ridge line. During cutting, the coating layer falls away with this .eta. phase to promote wearing of the tool and a reduction in the service life of the tool. Thus, the presence of the coating layer does not necessarily result in the improvement in the wear of the tool.
In these coated cutting tools, factors affecting the wear resistance and peeling resistance are the chlorine content in components for forming the coating layer, and the preferred orientation.
Coating of titanium carbide or titanium nitride (TiN) by the heat-assisted CVD method is generally carried out by the use of titanium tetrachloride (TiCL.sub.4) as a titanium source, methane (CH.sub.4) as a carbon source and nitrogen gas as a nitrogen source. Thus, in the coating using these gases, chlorine resulting from the titanium tetrachloride is taken in the coating layer, resulting in deterioration of the film quality.
As a report as to the chlorine in the film, there are disclosed techniques in which coating is carried out at a low temperature side using a plasma CVD method, for example, in "Hyomen Gijitsu (Surface Techniques)" Vol. 40, No. 10, 1889, p 51-55, "Hyomen Gijitsu" Vol. 40, No. 4, 1889, p 33-36, etc. This report tells that the level of the chlorine content in the film can be reduced to about 1 atom % by film making by the plasma CVD method at a temperature of up to 700.degree. C., whereby good film quality can be obtained.
Japanese Patent Laid-Open Publication. No. 13874/1992 describes that a titanium carbide film with excellent film adhesiveness as well as good wear resistance is composed of two titanium coating layers consisting of one having a chlorine content of 0.025 to 0.055 atom % up to a thickness of less than 0.5 .mu.m from the surface of a substrate and the other having a chlorine content of 0.055 to 1.1 atom % at a thickness of at least 0.5 .mu.m therefrom. In the method described in this publication, since titanium tetrachloride is used as a raw material gas and free carbon (C) from methane is used as a carbon source, the chlorine (Cl) from the titanium tetrachloride and the free carbon from the methane are taken in the film, thus unfavourably affecting the property of the film. In particular, precipitation of C in the film lowers the wear resistance, which should preferably be avoided, but the presence of chlorine in a proportion of at least 0.055 atom % suppresses the precipitation of C to give a titanium carbide film excellent in wear resistance without depositing carbon. According to this method, therefore, it is required that the chlorine content is adjusted to 0.025 to 0.055 atom % near the substrate

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