Oxide coated cutting tool

Details Oxide coated cutting tool Oxide coated cutting tool

2001-11-02

2004-03-30

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Including a second component containing structurally defined...

C051S307000, C051S309000, C407S118000, C407S119000, C428S697000, C428S698000, C428S699000, C428S701000

Reexamination Certificate

active

06713172

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a coated cutting tool for chipforming machining. The coating includes at least one alumina (Al
2
O
3
) layer characterized by fine, equiaxed grains.
DESCRIPTION OF THE RELATED ART
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Cemented carbide cutting tools can be coated with various types of Al
2
O
3
layers by using Chemical Vapour Deposition (CVD), e.g., pure &kgr;-Al
2
O
3
, mixtures of &kgr;- and &agr;-Al
2
O
3
, coarse grained &agr;-Al
2
O
3
, and fine grained textured &agr;-Al
2
O
3
have been commercially available for years generally in multilayer combinations with other metal carbide and/or nitride layers, the metal being selected from transition metals of the IVB, VB and VIB groups of the Periodic Table.
Al
2
O
3
crystallizes in several different phases: &agr;, &kgr;, &ggr;, &dgr;, &thgr; etc. The two most frequently occurring phases of CVD-produced wear resistant Al
2
O
3
layers are the thermodynamically stable &agr;-phase and the metastable &kgr;-phase, or a mixture thereof. Generally, the &kgr;-phase exhibits a grainsize in the range 0.5-3.0 &mgr;m and the grains predominately grow through the whole coating forming a columnar type coating morphology. Furthermore, the &kgr;-Al
2
O
3
layers are free from crystallographic defects and also free from micropores and voids.
Coarse-grained (3-6 &mgr;m) &agr;-Al
2
O
3
often possesses porosity and crystallographic defects, while fine-grained textured &agr;-Al
2
O
3
are free of defects with very pronounced columnar-shaped grains.
In U.S. Pat. No. 5,674,564 is disclosed a method of growing a fine-grained &kgr;-alumina layer by employing a low deposition temperature and a high concentration of a sulphur dopant.
In U.S. Pat. No. 5,487,625 a method is disclosed for obtaining a fine grained, (012)-textured &agr;-Al
2
O
3
layer consisting of columnar grains with a small cross section (about 1 &mgr;m).
In U.S. Pat. No. 5,766,782 a method is disclosed for obtaining a fine-grained (104)-textured &agr;-Al
2
O
3
layer.
As mentioned above, all Al
2
O
3
layers produced by the CVD technique possess a more or less columnar-like grainstructure. An Al
2
O
3
layer with an equiaxed grainstructure is, however, expected to show some favorable mechanical properties, e.g.—resistance to crack propagation, as compared to a layer with a columnar grainstructure. One well-known and possible technique to avoid columnar grain growth is to deposit a so-called multilayer structure in which the columnar growth of Al
2
O
3
is periodically interrupted by the growth of a thin, 0.1-1 &mgr;m second layer such as disclosed in U.S. Pat. No. 4,984,940. The second layer should preferably have a different crystal structure or at least different lattice spacings in order to be able to initiate renucleation of the first layer. One example of such a technique is when the Al
2
O
3
growth periodically is interrupted by a short TiN deposition process resulting in a (Al
2
O
3
+TiN)xn multilayer structure with a thickness of the individual TiN layers of about 0.1-1 &mgr;m (see, e.g.—Proceedings of the 12th European CVD Conference, page pr.8-349). However such multilayer structures very often suffer from a low adherence between the two different types of layers.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide onto a hard substrate, or preferably onto a hard substrate coated with a TiC
x
N
y
O
z
layer, at least one single phase &agr;-Al
2
O
3
layer with a microstructure which is different from the prior art columnar &agr;- or &kgr;-Al
2
O
3
CVD layers mentioned above. It is also the object of the present invention to provide a high performance tool coating comprising the invented Al
2
O
3
layer.
It is a further object of the invention to provide an alumina coated cutting tool insert with improved cutting performance in steel, stainless steel, cast iron and in particular nodular cast iron.
According to one aspect, the present invention provides a cutting tool comprising a body of sintered cemented carbide, cermet, or ceramic superhard material, the body comprising a surface, and a hard and wear resistant coating on at least a portion of the surface, said coating comprising: one or more refractory layers of which at least one layer essentially consists of &agr;-Al
2
O
3
, said &agr;-Al
2
O
3
layer having equiaxed grains with an average grainsize of <1 &mgr;m and further containing striated zones containing >5 at % titanium, but no nitrogen or carbon.
According to another aspect, the present invention provides a method of coating a body with an &agr;-alumina layer comprising: (i) bringing the body into contact with a hydrogen carrier gas containing one or more halides of aluminum and a hydrolyzing and/or oxidizing agent while the body is at a temperature of 950-1000° C.; (ii) maintaining the oxidation potential of the CVD-reactor atmosphere prior to the nucleation of Al
2
O
3
at a low level, using a total predetermined concentration of oxidizing species; (iii) starting Al
2
O
3
growth by introducing the following gases into the reaction chamber: AlCl
3
, HCl and CO
2
; (iv) adding a sulphur dopant after 20-60 min; (v) repeatedly stopping the CO
2
, AlCl
3
, HCl and the sulphur dopant for intervals of 10-50 min during which TiCl
4
is allowed to enter the reactor for 1-10 min in a concentration of 1-10%; and (vi) then reintroducing AlCl
3
, HCl, CO
2
and the sulphur dopant, in that order.


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patent: 5674564 (1997-10-01), Ljungberg et al.
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patent: 5851687 (1998-12-01), Ljungberg
patent: 5861210 (1999-01-01), Lenander et al.
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patent: 0 753 602 (1997-01-01), None
patent: 0 784 103 (1997-07-01), None
patent: 95 19457 (1995-07-01), None
S. Ruppi et al., “Microstructure and deposition characteristics of K-Al2O3”,J. Phys. IV France, 9 (1999), pp. 349-355.
U.S. patent application No. 10/155,168, Björn Ljungberg, “Oxide Coated Cutting Tool”, filed May 28, 2002.

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