Coated cemented carbide endmill having...

Details Coated cemented carbide endmill having... Coated cemented carbide endmill having...

1998-09-02

2001-03-27

Turner, Archene (Department: 1574)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C051S307000, C051S309000, C407S119000, C427S402000, C427S419100, C427S419200, C427S419700, C428S212000, C428S325000, C428S336000, C428S697000, C428S698000, C428S699000, C428S701000, C428S702000

Reexamination Certificate

active

06207262

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coated cemented carbide endmill exhibiting excellent wear resistance for a long period of time.
2. Description of the Background
Conventionally, coated cemented carbide endmills are composed of a tungsten carbide (WC) based cemented carbide substrate (hereinafter “cemented carbide substrate”) having a surface portion with an average layer thickness of 0.5-5 &mgr;m of hard-material-coated-layers composed of a Ti compound. The Ti compound is one or more layers of a titanium carbide (TiC), titanium nitride (TiN), titanium carbide-nitride (TiCN), titanium oxy-carbide (TiCO), titanium oxy-nitride (TiNO) and titanium oxy-carbo-nitride (TiCNO). Each of the hard-material-coated-layers is formed by medium temperature chemical vapor deposition (MT-CVD) (a method in which vapor deposition is performed at 700-980° C., a temperature lower than the vapor deposition temperature 1000-1150° C. employed by ordinary high temperature chemical vapor deposition (HT-CVD)), as shown in, for example, in Japanese Unexamined Patent Publication No. 62-88509.
In order to save labor and energy, there has been a tendency to increase cutting speed in a cutting process. When the conventional coated cemented carbide endmills are used under these high speed conditions, the hard-material-coated layers tend to exfoliate due to insufficient adhesion, resulting in endmills which are remarkably worn and which have a relatively short life.
SUMMARY OF THE INVENTION
An object of the invention is to provide a coated cemented carbide endmill having hard-material-coated layers having excellent adhesion.
The inventors of the present invention directed their attention to the conventional coated cemented carbide endmills and made studies to improve the adhesion of the hard-material-coated layers. As a result, the inventors discovered that when a coated cemented carbide endmill is arranged as shown in the following items (a), (b) and (c), the adhesion of the Ti compound layer to the surface of the cemented carbide substrate of the endmill is greatly improved by a surface layer formed on the surface portion thereof by heating at high temperatures. The hard-material-coated layer of the coated cemented carbide endmill is not exfoliated even if the endmill is used in high speed cutting, and furthermore the endmill exhibits excellent wear resistance over a long period of time:
(a) the cemented carbide substrate has a composition of 5-20 wt % of Co (hereinafter, % means wt %) as a binder phase forming component, optionally 0.1-2% of Cr and/or V as binder phase forming components, optionally, 0.1-5% of one or more carbides, nitrides and carbonitrides of Ti, Ta, Nb and/or Zr, such as TiC, TiN, TiCN, TaC, TaN, TaCN, NbC, NbN, NbCN, ZrC, ZrN and ZRCN, as well as two or more solid solutions thereof (hereinafter “(Ti, Ta, Nb, Zr) C·N”) as a dispersed phase forming component, and the balance WC as a dispersed phase forming component and inevitable impurities, wherein the WC has a fine grained structure having an average grain size of 0.1-1. 5 &mgr;m;
(b) when the cemented carbide substrate shown in (a) is heated at a high temperature in a hydrogen atmosphere containing a carbon dioxide gas or titanium tetrachloride at a pressure of 50-550 torr, and the substrate is held at a temperature of 900-1000° C. for 1-15 minutes, a reaction-created surface layer, in which a complex carbide of Co and W (Co
m
W
n
C or cobalt tungsten carbide) is distributed, is formed on the surface portion of the base substance over a predetermined thickness;
(c) hard-material-coated layers composed of a Ti compound layer and, optionally, an aluminum oxide (Al
2
O
3
) layer, are formed on the surface of the substrate having the reaction-created surface layer which is formed by heating at high temperature and in which Co
m
W
n
C shown in (b) is distributed, wherein the Ti compound layer is composed of one or more layers of TiC, TiN, TiCN, TiCO, TiNO and TiCNO, using MT-CVD, and the optional aluminum oxide layer is formed using MT-CVD or HT-CVD.
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a coated cemented carbide endmill having hard-material-coated layers excellent in adhesion, the endmill comprising a tungsten carbide based cemented carbide substrate comprising 5-20% Co as a binder phase forming component, optionally 0.1-2% of Cr and/or V as a binder phase forming component, optionally 0.1-5% of one or more of (Ti, Ta, Nb, Zr) C·N as a dispersed phase forming component, and the balance being WC as the dispersed phase forming component and inevitable impurities. The WC has a fine grained structure having an average grain size of 0.1-1.5 &mgr;m, the cemented carbide substrate has a reaction-created surface layer formed on the surface portion thereof which is formed by heating at high temperature and in which Co
m
W
n
C is distributed over a thickness of 0.1-2 &mgr;m thereof, and further the substrate has coated layers composed of a Ti compound layer. Optionally, an Al
2
O
3
layer is formed thereon with an average layer thickness of 0.5-4.5 &mgr;m, the Ti compound layer being composed of one or more layers of TiC, TiN, TiCN, TiCO, TiNO and TiCNO using MT-CVD and the Al
2
O
3
layer is formed using MT-CVD or HT-CVD.
Next, reasons why the compositions of the cemented carbide substrate constituting the coated cemented carbide endmill of the present invention, the average particle size of WC particles and the average thickness of the reaction-created surface layer and the average layer thickness of the hard-material coated layers, are limited as described above, will be described.
Co Content
Co improves sinterability, thereby improving the toughness of the cemented carbide substrate. When the Co content is less than 5%, however, the desired toughness improving effect is not obtained, whereas when the Co content is larger than 20%, not only is the wear resistance of the cemented carbide substrate itself lowered, but also the cemented carbide substrate is deformed by the heat generated during high speed cutting. Thus, the Co content is 5-20%, preferably to 8-12%.
Cr and V Content
Cr and V dissolve in solid Co as the binder phase forming component, strengthening it as well as contributing to inhibit the growth of WC grains. Furthermore, Cr and V act to promote the formation of the reaction-created surface layer in which Co
m
W
n
C is distributed, formed by heating at high temperature thereby improving the adhesion of the hard-material-coated layers achieved by the reaction-created surface layer. When the content of Cr and/or V is less than 0.1%, however, it cannot be expected that the above effect is achieved, whereas when the content of Cr and/or V is larger than 2%, the above action is saturated and the improving effect is not further enhanced. Thus, the content of Cr and/or V is set to 0.1-2%, preferably 0.4-0.8%.
When the coated cemented carbide endmill is made, it is preferable that Cr and V as the binder phase forming component are used in the form of carbides, nitrides and oxides of Cr and/or V (such as Cr
3
C
2
, CrN, Cr
2
O
3
, VC, VN and V
2
O
5
) (hereinafter “(Cr, V) C·N·O as the entire group”) as material powders. Since these material powders are dissolved in solid Co as the binder phase forming component when sintering is carried out, and form a binder phase, a precipitate containing Cr and/or V as an individual component cannot be observed by optical microscopy or scanning electron microscopy.
(Ti, Ta, Nb, Zr) C·N Content
These components act to improve the wear resistance of the cemented carbide substrate. When their content is less than 0.1%, however, the desired wear resistance improving effect is not obtained. When they are present in an amount larger than 5%, toughness is lowered. Thus, the individual content of each is set to 0.1-5%, preferably 1-2.5%.
Average Particle Size of WC
The strength of the cemented carbide substrate is improved by the fine grained structure of WC grains. The fine grained structure is obtained by choosing the partic

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