Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2001-12-20
2004-04-20
Chen, Bret (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S560000, C427S307000, C427S249130, C427S255394, C427S255290, C427S553000, C427S249400, C427S299000
Reexamination Certificate
active
06723389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a coated cemented carbide to be used as cutting tools represented by an insert, drill and end mill or various kinds of wear-resistant tools and parts, and a process for producing the coated cemented carbide excellent in peel strength in which a hard film is coated.
2. Prior Art
Coated cemented carbides in which a hard film such as TiC, TiCN, TiN, Al
2
O
3
, etc. is coated on the surface of a cemented carbide material by a chemical vapor deposition (CVD) or physical vapor deposition (PVD) method have both of strength and toughness of the substrate and wear resistance of the hard film in combination so that they are frequently used as cutting tools, wear resistant tools or parts, etc. However, if adhesiveness between the substrate and the film is poor, the substrate abruptly wears at the time of use due to peel off of the film, whereby the lifetime is shortened. Thus, in order to ensure adhesiveness, various attempts have been made, e.g., the surface of the substrate is treated for regulation, a film material of a subbing layer is selected, coating conditions of a subbing layer are optimized, and the like.
A substrate of a coated cemented carbide generally comprises a machined surface in which a grinding treatment, a blushing treatment or a blast treatment has been carried out, and a burnt surface in which no machining has been carried out. At the neighbor of the machining surface, a deformed layer (attachment of grinding filings, crack in hard phase particles, interfacial defect between hard phase particles or between a hard phase particle and a binder phase, or deformation of a binder phase) by processing with a thickness of 1 to 5 &mgr;m is remained. On the other hand, at the burnt surface, coarse hard phase particles are remained whereby unevenness is remarkable as compared with the surface subjected to machining.
Also, crystal faces of tungsten carbide existing at the surface particularly at which the machining has been carried out are random, and a ratio of an interface which is coherent with a crystal direction of a subbing layer (mainly TiN, TiC, TiCN, etc.) under a hard film to each other is low. Moreover, in both of the surface subjected to machining and the burnt surface, Co (cobalt) which is a binder phase is not uniformly dispersed in the surface portion so that a uniform diffusion layer is not formed in the hard film at an interface with the hard film.
Accordingly, it is necessary to carry out a surface treatment such as removal of a deformed layer, reduction of unevenness, control of crystal orientation, uniform attachment of Co, etc., to improve peel resistance at an interface between the substrate and the hard film.
As a means for improving peel strength of a coated cemented carbide by removal of the deformed layer and reduction (smoothening) of a surface roughness, there has been proposed a method of adjusting resintering and grinding conditions. The resintering method has been described in, for example, Japanese Provisional Patent Publication No. 123903/1993, and a method of reducing surface roughness has been described in, for example, Japanese Provisional Patent Publication No. 108253/1994.
Moreover, as a prior art references referring to diffusion of Co, W, etc., which are components of substrates into a hard film thereon, there may be mentioned, for example, Japanese Provisional Patent Publications No. 243023/1995, No. 118105/1996, No. 187605/1996, No. 262705/1997, No. 263252/1993, etc.
Also, electro-chemical polishing is described in, for example, Japanese Provisional Patent Publications No. 134660/1988, No. 92741/1996, and Japanese PCT Patent Provisional Publications No. 510877/1998 and No. 510877/1998, etc.
As a method for removing a deformed layer in the prior art, in Japanese Provisional Patent Publication No. 123903/1993, there is disclosed a method for producing a cutting tool member made of a surface-coated WC-base cemented carbide which comprises subjecting a surface of a cemented carbide to grinding processing, resintering the cemented carbide in a high pressure inert gas atmosphere at a temperature of appearing a liquid phase, and subjecting to a chemical vapor deposition (CVD) to form a hard coated layer. According to this method, the deformed layer can be removed by resintering and peeing strength can be improved since uneven surface is formed by grain growth of a cubic system compound. However, unevenness is remained on the surface of the alloy after a hard film is coated thereon so that a material to be processed is likely adhered to the cutting tool. Thus, there are problems that the hard film is rather easily peeled off and a finishing surface precision of the material to be processed is lowered. Moreover, it is difficult to obtain a cemented carbide by controlling a composition (an amount of Co, an amount of a cubic system compound) at the surface to be subjected to resintering, or a specific crystal face of tungsten carbide so that there is a problem that a peeling strength is insufficient and unstable.
On the other hand, as methods for reducing surface roughness and for removing a deformed layer, in Japanese Provisional Patent Publication No. 108253/1994, there is disclosed a coated cemented carbide in which a surface of the cemented carbide is subjected to brush polishing to make an average surface roughness Ra of 0.15 to 0.4 &mgr;m and a hard layer is coated on the surface thereof, at which scratches by grinding are formed to random directions. In the coated cemented carbide disclosed in this reference, whereas adhesion strength of the hard layer is heightened, removal of the deformed layer or making flat the surface of the alloy (removal of projected coarse hard phase particles) is insufficient so that there is a problem that abnormal damage due to peeling of the coating film is likely caused. Moreover, grinding filings containing Co and generated by brush abrasion are attached onto the surface of the cemented carbide but an attached amount of Co is a little and ununiform on the surface so that there is a problem that adhesiveness cannot sufficiently be improved.
With regard to diffusion of components in the substrate of the cemented carbide into a hard film provided on the surface of the cemented carbide, there are some publications. For example, in Japanese Provisional Patent Publications No. 243023/1995, No. 118105/1996, No. 187605/1996 and No. 262705/1998, there are disclosed cutting tools made of surface-coated tungsten carbide-base cemented carbide in which a hard coating layer is formed on the surface of a WC-base cemented carbide base material by the CVD method, wherein the hard coating layer comprises a first layer of TiC or TiN, a second layer of TiCN containing a columnar structure, a third layer of TiC, TiCO, etc., and a fourth layer of Al
2
O
3
containing a kappa type crystal as a basic layer constitution, and at least W and Co among the components constituting the cemented carbide base material are diffused and contained into the first and second layers, or into the first to the third layers. The coated cemented carbides described in these prior art references are somewhat improved in adhesiveness between the hard coating layer and the cemented carbide due to diffusion of Wand Co into the hard coating layer. However, when a diffusion layer in the hard coating layer is carefully observed at the portion directly above the surface of the base material, the diffusion layer is ununiformly formed markedly. That is, the diffusion layer is extremely thick and a diffused amount is too much on Co which is a binder phase, but substantially no diffusion layer exists on WC or (W,Ti,Ta)C which is a hard phase. For this reason, there is a problem that improvement in adhesiveness is insufficient.
Moreover, as a prior art using electro-chemical polishing technique, in Japanese Provisional Patent Publication No. 134660/1988, there is disclosed a method for producing a surface-coated titanium carbide-base cermet which comprises subjecting a surface of titani
Kitada Hiroshi
Kobayashi Masaki
Chen Bret
Foley & Lardner
Toshiba Tungaloy Co., Ltd.
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