Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2000-08-24
2002-09-10
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C427S532000, C427S557000, C428S325000, C428S697000, C428S698000, C428S699000, C428S336000, C051S307000, C051S309000
Reexamination Certificate
active
06447912
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coated cemented carbide cutting tools with improved properties obtained by a heat treatment of the cemented carbide before the application of a wear resistant coating. More particulary, the invention is in particular related to a body coated with diamond. However, the invention can also be used for other wear resistant coatings, such as any CVD- or PVD wear resistant coatings.
BACKGROUND OF THE INVENTION
The adhesion of wear resistant coatings on cemented carbide is due to several mechanisms of which mechanical adhesion constitutes one part, i.e. a rough surface grips mechanically into the applied coating. Several approaches have been made in order to achieve good mechanical adhesion see EP-A-500 253. For the case of diamond layers, the achievement of adhesion is particularly difficult since the presence of binder metal deteriorates the adhesion. A common method for achieving good diamond layer adhesion on cemented carbide is to etch away the binder metal from a surface region, see EP-A-0 500 253. This, however, increases the risk of bad adhesion due to loosely bound carbide grains. Other methods involve carburising sintering of an eta phase containing body (U.S. Pat. No. 4,843,039) so as to deplete a surface region of binder phase. The treatment gives a relatively brittle surface zone together with a likewise brittle core which is less than adequate for certain toughness demanding cutting applications.
Another method for preparing a cemented carbide for diamond coating is described in WO 95/15258 according to which a rough surface is obtained through a heat treatment in N
2
containing atmosphere. The surfaces treated in this way are free of binder phase. However, during a heat treatment as described in WO 95/15258 grain growth occurs not only at the surface but also within the body generally resulting in formation of large WC-grains in the structure.
U.S. Pat. No. 4,830,886 describes a method to avoid the presence of the eta phase layer formed during a CVD deposition of a TiCN layer by carburizing the eta phase layer through the TiCN-layer after the CVD process.
EP-A-759 480 describes a cemented carbide body containing triangular WC-platelets. The platelets are oriented with their triangular surfaces parallel to the surface of the body. The toughness of the body is said to be improved.
U.S. Pat. No. 5,100,703 describes a diamond-coated sintered body, comprising a film of diamond and/or diamond-like carbon deposited on the surface of a sintered body of a hard phase composed mainly of a mixture of W
2
C and WC and inevitable impurities.
SUMMARY OF THE INVENTION
It has now surprisingly been found that within a surface zone of a cemented carbide body, a controlled change in WC grain orientation, size and shape can be obtained by an initial decarburization or decarburization+heat treatment in neutral gas atmosphere or vacuum through which an eta phase containing surface zone is obtained and then a complete recarburization of said zone in order to completely transform the eta phase therein to WC+Co. (Eta phase is a common name for low carbon content containing carbides usually comprising W—Co—C in proportions (M
6
C or M
12
C, M=W and Co and/or Fe and/or Ni) such as M
12
C=Co
6
W
6
C and M
6
C=Co
3
W
3
C, W
4
Co
2
C). The shape of the WC grains is triangular platelets. The platelet containing region can be combined with different binder phase gradient zones. The adhesion of a subsequently deposited wear resistant coating to this body is found to be excellent.
According to one aspect, the present invention provides a body of cemented carbide comprising 4-12 wt-% binder phase coated with at least one wear resistant layer, the body comprises a surface zone with a thickness up to 100 &mgr;m, the zone comprises essentially triangular WC platelets having a texture coefficient ratio >1.75.
According to another aspect, the present invention provides a method for producing diamond coated cemented carbide body with a surface zone in the cemented carbide being different from the rest of the carbide body, the method comprising: decarburizing the body to form an eta phase containing surface zone 3-100 &mgr;m thick and comprising >60% by volume of at least partially interconnected eta phase and recarburizing the body whereby the eta phase is completely transformed into WC+Co.
REFERENCES:
patent: 4731296 (1988-03-01), Kikuchi et al.
patent: 4830886 (1989-05-01), Cho et al.
patent: 4843039 (1989-06-01), Akesson et al.
patent: 5100703 (1992-03-01), Saijo et al.
patent: 5391422 (1995-02-01), Omori et al.
patent: 5585176 (1996-12-01), Grab et al.
patent: 5716170 (1998-02-01), Kammermeier et al.
patent: 5725932 (1998-03-01), Iio et al.
patent: 5891522 (1999-04-01), Olson
patent: 0 500 253 (1992-08-01), None
patent: 0 701 006 (1996-03-01), None
patent: 0 759 480 (1997-02-01), None
patent: WO 95/12009 (1995-05-01), None
patent: WO 95/15258 (1995-06-01), None
Mikus Marian
Reineck Ingrid
Burns Doane , Swecker, Mathis LLP
Sandvik AB
Turner Archene
LandOfFree
Coated cemented carbide cutting tool and method of coating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coated cemented carbide cutting tool and method of coating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coated cemented carbide cutting tool and method of coating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2828712