Coated cemented carbide body and method for use

Details Coated cemented carbide body and method for use Coated cemented carbide body and method for use

2002-12-20

2004-04-13

Lam, Cathy (Department: 1775)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S699000, C428S701000, C428S702000, C428S704000

Reexamination Certificate

active

06720095

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present application relates generally to coatings. More specifically, the present application relates to multilayer coatings including an alumina layer.
2. Background of the Invention
In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
From U.S. Pat. No. 6,221,469, it appears that the use of a &kgr;-Al
2
O
3
coated metal cutting insert is better than an &agr;-Al
2
O
3
coated cutting insert, particularly where high-speed turning is concerned. However, it has been found that in interrupted turning and in turning with coolant, the &agr;-Al
2
O
3
coated insert performs better. This appears to be so because between the &agr;- and &kgr;-forms, the a form is more ductile.
&kgr;-Al
2
O
3
cannot deform plastically due to its defect structure. When the application temperature is lower, e.g., with coolant, &kgr;-Al
2
O
3
cannot transform to &agr;-Al
2
O
3
either. On the other hand, the temperature and especially the pressure are obviously high enough to activate sufficient amount of slip systems in the &agr;-Al
2
O
3
phase. Consequently, the insert containing the &kgr;-Al
2
O
3
is more brittle due lack of plasticity during cutting.
SUMMARY OF THE INVENTION
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide a particularly efficacious coated cemented carbide body for the cutting of steel or cast iron.
An exemplary embodiment of a coated sintered cemented carbide body comprises a cemented carbide body, a first layer adjacent the cemented carbide body, the first layer including Ti(C,N) and having a thickness of from about 3 to about 20 &mgr;m, an alumina layer adjacent said first layer, the alumina layer including &agr;-Al
2
O
3
or K-Al
2
O
3
and having a thickness of from about 1 to about 15 &mgr;m, and a further layer adjacent the alumina layer of a carbide, carbonitride or carboxynitride of one or more of Ti, Zr and Hf, the further layer having a thickness of from about 1 to 15 &mgr;m.
In an exemplary embodiment of a coated sintered cemented carbide body, a friction-reducing layer is adjacent to the further layer, the friction-reducing layer including one or more of &ggr;-Al
2
O
3
, &kgr;-Al
2
O
3
and nanocrystalline Ti(C,N). The friction-reducing layer has a thickness of from about 1 to about 5 &mgr;m.
In one aspect, the coated sintered cemented carbide body, in which the Al
2
O
3
is &agr;-Al
2
O
3
, can be used to cut cast iron.
In another aspect, the coated sintered cemented carbide body, in which the Al
2
O
3
layer is &agr;-Al
2
O
3
, can be used for the cutting of steel.


REFERENCES:
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patent: 2003/0054159 (2003-03-01), Ruppi et al.
Anette Sulin et al. U.S. patent application No. 09/717,006 entitled “Coated Cutting Insert for Milling and Turning Applications” filed Nov. 22, 2000.
Sakari Ruppi U.S. patent application No. 09/498,344 entitled “Deposition of &ggr;-AI2O3by Means of CVD” filed Feb. 4, 2000.

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