Coating processes – Coating by vapor – gas – or smoke – Carbon or carbide coating
Reexamination Certificate
2003-08-04
2004-11-30
Turner, Archene (Department: 1775)
Coating processes
Coating by vapor, gas, or smoke
Carbon or carbide coating
C427S249170, C427S255230, C427S255280, C427S348000, C427S372200
Reexamination Certificate
active
06824823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cutting tool formed by coating a substrate such as hard metal, cermet or ceramic with a hard coating film, which has improved cutting ability due to the co-presence of particles having particle diameters in a direction horizontal to the base material is large and particles having particle diameters in the same direction are small in a columnar crystal layer and the presence of agglomerations dispersed in the columnar crystal layer, and a method for producing the same.
2. Prior Art
A variety of coating techniques for forming a hard layer on a cutting tool or the like have been practiced. In recent years, a technique relating to a columnar crystal structure of the coating film which comprises titanium compounds has been developed, and an invention relating to particle diameters thereof has been disclosed. For example, Japanese Patent Application Laid-Open No. 285001/1995 discloses an invention in which the average crystal particle diameter of columnar crystals is limited to 0.1 to 1 &mgr;m when the film thickness of TiCN is not larger than 4 &mgr;m and the average crystal particle diameter is limited to 0.5 to 3 &mgr;m when the film thickness of TiCN is 4 to 20 &mgr;m. Japanese Patent Application Laid-Open No. 71814/1996 discloses an invention in which columnar crystals have a tapered shape, the average crystal particle diameter is 0.012 to 0.5 &mgr;m when the film thickness is not larger than 2 &mgr;m, and the average crystal particle diameter is 0.05 to 1.3 &mgr;m when the film thickness is 2 to 10 &mgr;m. Japanese Patent Application Laid-Open No. 15711/1998 discloses an invention in which the average particle diameter in a horizontal direction is 0.3 to 1.2 &mgr;m, the average particle diameter in a vertical direction is at least 2.5 times that in the horizontal direction, and the thickness of columnar crystal layer comprising TiCN corresponds to at least 60% of the total thickness of the film. Japanese Patent Application Laid-Open No. 109206/1998 discloses an invention in which the average particle diameter of particles in the columnar crystal layer changes depending on the position from the interface and the average crystal particle diameter is 0.15 to 1.5 &mgr;m.
In prior art, it is provided that the columnar crystals in the columnar crystal layer have uniform particle diameters in a direction horizontal to the interface between the coating film and the base material in the same plane as described in Japanese Patent Application Laid-Open No. 285001/1995, and the average particle diameter and the range of the particle diameters of the columnar crystals, e.g., TiCN, are limited.
Further, in Japanese Patent Application Laid-Open Nos. 71814/1996, 15711/1998 and 109206/1998, there has been disclosed an invention in which the particle diameters of columnar crystals in the same plane are uniform while the particle diameters of columnar crystals change in a thickness direction.
The columnar crystals in the same plane have a uniform particle diameter in these inventions, so that there is a problem that they are liable to have cracks caused by thermal shock whereas abrasion resistance is excellent.
In the developments of the conventional coated hard metal cutting tools, abrasion resistance has been considered extremely important in terms of cutting capability so that the development of a technique for prolonging the useful life of a cutting tool by improving thermal shock resistance by controlling the columnar crystal structure has not been carried out.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to overcome the above-mentioned problems and to provide a cutting tool having excellent cutting properties. The present invention has been achieved by conducting various experiments and studies with regard to the controls of the diameters of the columnar crystal particles and columnar crystal structure to solve the above problem.
That is, a coated cutting tool of the present invention comprises a base material of a hard alloy comprising a hard phase of tungsten carbide and at least one material selected from the group consisting of a carbide, a nitride and a carbonitride of a metal selected from the group consisting of the Group 4, 5 and 6 (IVa, Va and VIa) of the Periodic Table and a mutual solid solution thereof and a binder phase of at least one element selected from the group consisting of Fe, Ni and Co, and a hard coating film formed on the surface of the base material by a chemical vapor deposition (CVD) method, wherein the hard coating film has a columnar crystal layer comprising at least one material selected from the group consisting of a carbide, a nitride and a carbonitride of titanium, the columnar crystal layer contains particles having crystal particle diameters in a direction horizontal to the interface between the hard coating film and the base material are large and particles having crystal particle diameters in the same direction are small, and the ratio of the average particle diameter of the large particles to the average particle diameter of the small particles is 3 to 50.
Also, a method for producing the coated cutting tool of the present invention comprises forming a hard coating film by a chemical vapor deposition method on a surface of a hard metal base material of a hard alloy comprising a hard phase of tungsten carbide and at least one material selected from the group consisting of a carbide, a nitride and a carbonitride of at least one metal selected from the group consisting of the Group 4, 5 and 6 of the Periodic Table and a mutual solid solution thereof and a binder phase of at least one element selected from the group consisting of Fe, Ni and Co, wherein the hard coating film comprises at least one material selected from the group consisting of a carbide, a carbonitride and a carbonitroxide of titanium, and a hydrocarbon gas mainly comprising ethane is used as a carbon element-feeding gas for forming the hard coating film.
Here, the largest diameter is used as a representative value when the columnar crystal particles have a nearly circular shape. Also, when the columnar crystal particles have an oval shape having an aspect ratio of larger than 1.2, an average value of the particle diameter in a longitudinal direction and that in a direction perpendicular to the longitudinal direction is used as a representative value.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, the present invention is explained in more detail.
The present invention has been completed by finding that thermal cracks are less liable to occur and a tool lasts longer when the structure of a coating film is a columnar crystal structure comprising large and small crystal particles than when it is a columnar crystal structure comprising crystal particles of the same particle diameter.
The base material of hard alloy to be used for the cutting tool according to the present invention comprises a hard phase and a binder phase. The hard phase of the hard alloy of the present invention comprises tungsten carbide as a main component and, as an auxiliary component, at least one material selected from the group consisting of carbides, nitrides and carbonitrides of a metal selected from the group consisting of the Group 4, 5 and 6 (IVa, Va and VIa) of the Periodic Table and mutual solid solutions thereof. The binder phase of the hard alloy comprises at least one element selected from the group consisting of Fe, Ni and Co. An amount of the binder phase is preferably 1 to 30% by weight based on the total amount of the hard alloy composition and the reminder is the hard phase. If an amount of the binder phase is less than 1% by weight, the resulting cutting tool is easily chipped off, while if it exceeds 30% by weight, wear resistance is markedly lowered. The hard alloy of the present invention can be prepared by the above materials by sintering with a powder metallurgy method under the conditions conventionally known in the art.
The hard coating film formed on the surface of t
Kodama Hiroyuki
Yazaki Itsuo
Yoshikawa Nobukazu
Toshiba Tungaloy Co., Ltd.
Turner Archene
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