Members with multi-layer coatings

Details Members with multi-layer coatings Members with multi-layer coatings

1999-03-15

2001-07-03

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

C428S697000, C428S698000, C428S699000, C428S701000

Reexamination Certificate

active

06254984

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a multi-layer-coated member constituted by an ultra-hard alloy substrate of high-speed steel, cemented carbides, cermets, etc. coated with a plurality of layers excellent in oxidation resistance and/or wear resistance, particularly those suitable for cutting tools such as drills, end mills, throwaway chips for milling machines, etc.
Many attempts have already been reported to provide ultra-hard alloy substrates such as high-speed steel, cemented carbides, cermets, etc. with ceramic coatings excellent in oxidation resistance and wear resistance, thereby achieving long life due to an effective combination of their properties. The coating layers of coated tools have widely been composed of TiN, TiCN, etc. excellent in wear resistance. However, metal nitrides such as TiN are easily oxidized at high temperatures, resulting in extreme deterioration of wear resistance.
To solve the problems of the oxidation of TiN coatings, proposal has recently be made to add Al to these coatings to improve their wear resistance, oxidation resistance, etc. See Japanese Patent Laid-Open No. 62-56565, and Japanese Patent Publication Nos. 4-53642 and 5-67705.
The coating methods of ultra-hard alloy substrates are generally classified to chemical vapor deposition (CVD) methods and physical vapor deposition (PVD) methods. It is known that coatings formed by the PVD methods such as an ion plating method, a sputtering method, etc., serve to improve the wear resistance of the substrates without deteriorating their mechanical strength. Accordingly, cutting tools such as drills, end mills, and throwaway chips for milling machines that require high mechanical strength and chipping resistance are coated by the PVD methods at present.
In the above Al-containing coating layers proposed by Japanese Patent Laid-Open No. 62-56565, for instance, coating layers composed of carbides, nitrides or carbonitrides of Ti and Al provide ultra-hard alloy substrates with higher oxidation resistance and wear resistance than those containing no Al. It is, however, pointed out that the Al-containing coating layers rather deteriorate the mechanical properties of the ultra-hard alloy substrates. While the inclusion of Al into the coatings leads to improvement in the chemical properties of the coating surfaces, it deteriorates the fracture toughness of the coatings. Particularly when coated ultra-hard alloys are used for high-speed cutting tools, their teeth are extremely heated, resulting in oxidation and rapid wearing of the coatings and deterioration of the coatings by thermal shock and galling, and thus a decrease in life.
Cutting speeds are recently increasing, and severe cutting conditions are required in many cases as in the cutting of heat-treated high-speed steel. To cope with such conditions, improvement is desired.
Also proposed is the formation of an outermost layer of TiAlON, etc. to improve the oxidation resistance of the coated members (Japanese Patent Laid-Open No. 7-328811). However, the mere formation of an outermost layer consisting of oxides of Ti and Al fails to provide enough oxidation resistance to withstand severe working conditions.
It is further proposed that alumina layers generally formed by CVD methods are formed as outermost layers by ion plating methods (Japanese Patent Laid-Open No. 9-192906). However, the alumina layers formed by the PVD methods do not have sufficient adhesion to the underlying layers, resulting in peeling of the alumina layers by impact in actual cutting operation.
OBJECT AND SUMMARY OF THE INVENTION
In view of the fact that in a high-speed cutting operation which has become commonplace recently, cutting tools are extremely heated at their teeth, sometimes higher than temperatures at which oxidation starts in the coating layers, the present invention is aimed at providing coated members capable of carrying out a stable cutting operation under such severe conditions with a long life.
As a result of research on the oxidation mechanism of a TiAIN layer to achieve the above objects, the inventor has found that alternately laminating first layers each and second layers each can provide a multi-layer coating having excellent oxidation resistance and wear resistance. The present invention has been completed based upon this finding.
Thus, the multi-layer-coated member according to the present invention is composed of an ultra-hard alloy substrate and a multi-layer coating formed thereon, wherein the multi-layer coating comprises two or more first layers and two or more second layers laminated alternately, the first layer being composed of at least one selected from the group consisting of carbides, nitrides and carbonitrides of at least one element of Groups 4a, 5a and 6a of the Periodic Table and Al, and the second layer being composed of at least one selected from the group consisting of oxides, carboxides, oxinitrides and carboxinitrides of at least one element of Groups 4a, 5a and 6a of the Periodic Table and Al.
In a preferred embodiment, the first layers adjacent via the second layer have crystals whose orientations are substantially the same, because the second layer is extremely thin as compared with the first layer. The state that the first layers have the same crystal orientation may be called that the first layers have “crystal continuity” via the second layer. The crystal orientation of the first layer determined by the maximum intensity of X-ray diffraction is aligned along the (200) face. The first layer preferably has an fcc crystal structure.
The first layer may comprise 1-30 atomic % of at least one additional element selected from the group consisting of Si, Y, Nd, Sm and Sc.
In another preferred embodiment, the multi-layer coating has an outermost layer composed of at least one selected from the group consisting of oxides, carboxides, oxinitrides and carboxinitrides of at least one element of Groups 4a, 5a and 6a of the Periodic Table and Al. The outermost layer is preferably composed of at least one selected from the group consisting of oxides, carboxides, oxinitrides and carboxinitrides of Ti and Al, particularly Ti, Si and Al, more particularly Al. The outermost layer may be amorphous or crystalline.
In a further preferred embodiment, the multi-layer coating has an innermost layer having excellent adhesion to the substrate, the innermost layer is composed of at least one of TiN, TiCN, Ti and TiAl and having a thickness from 2 nm to 5000 nm.


REFERENCES:
patent: 4554201 (1985-11-01), Andreev et al.
patent: 4643951 (1987-02-01), Keem et al.
patent: 4984940 (1991-01-01), Bryant et al.
patent: 5035957 (1991-07-01), Bartlett et al.
patent: 5330853 (1994-07-01), Hofmann et al.
patent: 5503912 (1996-04-01), Setoyama et al.
patent: 5549975 (1996-08-01), Schulz et al.
patent: 5679448 (1997-10-01), Kawata
patent: 5879823 (1999-03-01), Prizzi et al.
patent: 197 52 644 (1998-06-01), None
patent: 0 709 353 (1996-05-01), None
patent: 62-142768 (1987-06-01), None
patent: 62-56565 (1987-12-01), None
patent: B 5-67705 (1993-09-01), None
patent: A 7-328811 (1995-12-01), None
patent: 7-328812 (1996-04-01), None
patent: 9-323204 (1997-12-01), None
patent: 10-128605 (1998-05-01), None

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