Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-10-29
2001-08-14
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S704000, C428S627000, C428S472000, C428S699000, C428S208000, C428S208000, C428S208000, C428S208000, C428S208000, C164S138000, C249S135000, C249S134000, C249S114100
Reexamination Certificate
active
06274257
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to forming members such as molds, dies and the like for shaping aluminum and other reactive metals. More particularly, the invention relates to forming members having a coating thereupon of doped chromium nitride and to methods for their fabrication and use.
BACKGROUND OF THE INVENTION
Molds, dies, cores, pins and other such forming members for shaping molten metals are frequently manufactured from steel because of its low cost and ease of fabrication. Problems arise when such forming members are used to shape reactive metals, such as aluminum, magnesium and zinc containing alloys. It has been found that such alloys, particularly low iron content aluminum alloys, are reactive in the molten state and can corrode and/or erode the surface of molds, dies and other forming members significantly reducing their surface life.
A number of approaches have been taken in an attempt to solve this problem. One approach involves nitriding the surface of the forming member. Nitrided surfaces do provide some protection from attack by certain alloys; but this protection is fairly limited, and nitrided surfaces are ineffective against more reactive metals, such as aluminum alloys, particularly those aluminum alloys having an iron content of 1.2% or less, and aluminum alloys with a silicon content of up to 18%. Another approach involves implanting tungsten into the surface of steel forming members. Generally, such implantation processes are fairly expensive; furthermore, protection provided thereby is still somewhat limited.
A further approach, which is disclosed in U.S. Pat. 5,476,134, comprises coating a surface of the forming member with a layer of chromium nitride. As disclosed therein, the chromium nitride coating has good resistance to attack by reactive metal alloys, including low iron content aluminum alloys. While such prior art chromium nitride coatings provide good erosion resistance, it has been found that these coatings tend to fail, particularly in the region of sharp features on the forming member such as edges, textured surfaces and the like. While not wishing to be bound by speculation, the inventors herein theorize that stresses in such prior art coatings concentrate at sharp edges and provide cracks and fissures which allow molten metal to contact underlying substrate material and cause erosion.
The foregoing makes clear that there is a need for a surface treatment which can be applied to forming members such as molds and dies, which will protect such members from attack by reactive metals. The treatment should be easy to apply, low in cost, and should not interfere with use of the forming members. In addition, the treatment should be durable and provide long service life. The present invention, as will be described in detail hereinbelow, utilizes a doped coating of chromium nitride as a protective treatment for forming members. While chromium nitride coatings have previously been used in molds for shaping aluminum, doped coatings have not; and it has been found, unexpectedly, that the addition of relatively small amounts of dopant greatly enhance the resistance of chromium nitride coatings to attack by molten metal. These and other advantages of the present invention will be apparent from the drawings, discussion and description which follow.
BRIEF DESCRIPTION OF THE INVENTION
There is disclosed herein a forming member for shaping a reactive metal. The forming member comprises a substrate having a forming surface defined thereupon, and a protective coating on at least a portion of the forming surface. The protective coating comprises doped chromium nitride. In specific embodiments, the chromium nitride is in the form of a polycrystalline CrN matrix having a dopant dispersed therein, and the CrN crystals have a slightly preferred bias in the 220 orientation. Preferred dopant ranges comprise 1-10 atomic percent, and some specifically preferred dopants comprise transition metals, such as tungsten or molybdenum, as well as oxygen. Coating thicknesses are typically in the range of 2-40 microns.
Also disclosed herein is a method for forming the protective coating, which method comprises depositing the coating by a physical vapor deposition process. In some specific embodiments of the process, the physical vapor deposition process is a cathodic arc process. In some versions of the cathodic arc process, the dopant is a metal, and is incorporated into a chromium cathode, and the deposition process is carried out in a working atmosphere of nitrogen so as to deposit the doped chromium nitride coating. In other versions of the cathodic process, the dopant is oxygen, and the cathode consists essentially of chromium. The working atmosphere in such instance comprises nitrogen and oxygen, and operates to deposit an oxide doped chromium nitride coating. Also disclosed herein are methods for using the coated forming members in a metal forming process.
REFERENCES:
patent: 4556098 (1985-12-01), Hintermann et al.
patent: 4753854 (1988-06-01), Gavrilov et al.
patent: 4852542 (1989-08-01), Kamo et al.
patent: 5114470 (1992-05-01), Biancaniello et al.
patent: 5236661 (1993-08-01), Hidaka et al.
patent: 5318091 (1994-06-01), Pavoni et al.
patent: 5413821 (1995-05-01), Ellis et al.
patent: 5476134 (1995-12-01), Whittle et al.
patent: 5575902 (1996-11-01), Heyse et al.
patent: 5601293 (1997-02-01), Fukutome et al.
patent: 5603072 (1997-02-01), Kouno et al.
patent: 5618590 (1997-04-01), Naruse et al.
patent: 5690759 (1997-11-01), Wang
patent: 5723800 (1998-03-01), Yoshimoto et al.
patent: 5806336 (1998-09-01), Sunaga et al.
patent: 5841046 (1998-11-01), Rhodes et al.
patent: 5851680 (1998-12-01), Heau
Robert R. Aharonov, Bernard J. Janoss and Mark A. Pellman “How chromium nitride performs on metal forming dies-striving for abrasive, adhesive protection for tooling” article reprinted from the Jun. 1995 issue of The Fabricator.
Aharonov Robert R.
Chellapilla Sridhar
Fontana Raymond P.
Janoss Bernard J.
Boss Wendy
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
IonBond Inc.
Jones Deborah
LandOfFree
Forming members for shaping a reactive metal and methods for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Forming members for shaping a reactive metal and methods for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Forming members for shaping a reactive metal and methods for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2442835