Coating processes – Applying superposed diverse coating or coating a coated base – Metal coating
Reexamination Certificate
2001-04-17
2003-07-08
Barr, Michael (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Metal coating
C427S419700, C427S419100, C427S248100, C427S255280, C205S219000, C205S238000, C205S261000
Reexamination Certificate
active
06589602
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-coated cemented carbide usable for cutting tools represented by a tip, a drill and an end mill and various wear-resistant tools and parts. Particularly, the present invention relates to a surface-coated cemented carbide which has a prolonged tool life by improving an adhesiveness at an interface between a hard film and a cemented carbide base material by having both of a cemented carbide base material and a hard film, at a proximate portion of the interface, contain at least one diffusive element selected from an iron group metal, chromium, molybdenum, manganese, copper and silicon. The present invention further relates to a method for producing the surface-coated cemented carbide comprising a step of uniformly coating a surface of the cemented carbide base material with the diffusive element in advance and a successive step of coating the surface with the hard film.
2. Prior Art
Surface-coated cemented carbides wherein cemented carbide base material is coated with a hard film of TiC, TiCN, TiN or Al
2
O
3
by a chemical vapor deposition or physical vapor deposition method exhibit strength and toughness of the base material as well as wear resistance of the hard film. Therefore, they are widely used as cutting tools and wear-resistant tools or parts. However, when the adhesiveness between the base material and the hard film is not satisfactory, the cemented carbides are rapidly worn down due to exfoliation of the film upon use, thereby shortening a tool life.
Since the adhesiveness of the film is largely affected by a diffusion state of cemented carbide components such as cobalt and tungsten in the hard film, many attempts have been made such as adjustment of the base material surface, the selection of the film materials for an undercoat layer, the optimization of coating conditions of the undercoat layer and the like. In Japanese Patent Laid-Open Publications No. 243023/1995, No. 118105/1996, No. 187605/1996, No. 262705/1997, No. 263252/1993, and so forth, there are disclosed that the base material components such as cobalt and tungsten are diffused into the hard film.
On the other hand, the base material of a surface-coated cemented carbide is formed into a shape depending on the usage, by grinding or the like. Therefore, it is consisted of the mechanically processed surface and an as-sintered surface which is not ground. At the mechanically processed surface, processing swarf containing cobalt is attached relatively uniformly to the uppermost surface, but there is a problem that there remain a degenerated layer due to processing (cracks in the hard phase particles, defect at an interface between the hard phase particles or between the hard phase particle and the binder phase, the transformation of the binder phase) near the surface. Furthermore, in the as-sintered surface, although there exists no degenerated layer, there is a problem that the binder phase is not present on the hard phase particles due to a sever surface irregularity.
Accordingly, as a means for providing suitable amount of cobalt uniformly dispersed at the cemented carbide surface and removing the degenerated layer at the mechanically processed surface, and smoothening the surface and enriching cobalt at the as-sintered surface, methods of controlling the processing conditions or re-sintering methods are proposed. Among the prior art methods, a method for reducing surface roughness is disclosed in Japanese Patent Laid-Open Publication No. 108253/1994, etc., and a re-sintering method is disclosed in Japanese Patent Laid-Open Publications No. 123903/1993, No. 097603/1995, etc.
With regard to diffusion of the base material components into the hard film, Japanese Patent Laid-Open Publications No. 243023/1995, No. 118105/1996, No. 187605/1996 and No. 262705/1997 disclose a cutting tool made of a surface coated tungsten carbide (WC)-based cemented carbide wherein a hard coating layer is formed on a surface of a WC-based cemented carbide substrate by CVD method, the layer comprising a basic film structure composed of the first layer of TiC or TiN, the second layer of TiCN with a growing columnar crystalline structure, the third layer of TiC, TiCO, etc. and the fourth layer of Al
2
O
3
containing &kgr;-type crystals, at least tungsten and cobalt among the cemented carbide components being diffused and dispersed in the first and second layers or the first to third layers. The coated cemented carbides disclosed in these publications exhibited improved adhesiveness due to diffusion of tungsten and cobalt into the hard film. However, there is a problem that the adhesiveness is not improved sufficiently by merely controlling the coating conditions such as a type of film, temperature, gas partial pressure, and the like.
Japanese Patent Laid-Open Publication No. 263252/1993 discloses a coated cemented carbide member which comprises the first coating layer comprising TiC, the second coating layer comprising TiCN having a lattice constant of 4.251 to 4.032 angstroms, and the third coating layer comprising TiC on the surface of a cemented carbide base material. The coated cemented carbide member disclosed in the publication has been improved simultaneously in wear resistance and chipping resistance as a cutting tool by preventing diffusion of tungsten, etc. and absorption of cobalt from cemented carbide base material during a coating layer formation. That is, TiC in the first coating layer and WC in the cemented carbide base material are relatively excellent in adhesiveness, and by increasing the amounts of C and N in TiCN of the second coating layer, it is intended to prevent the diffusion of C from the base material. However, there is a problem that a brittle Co—W—C type composite carbide tends to form at the interface, and improvement in adhesiveness is limited since there is no highly adhesive diffusion layer formed resulting from diffusion of cobalt and tungsten.
On the other hand, among the prior arts, as a method for reducing surface roughness, Japanese Patent Laid-Open Publication No. 108253/1994 discloses a coated cemented carbide wherein a hard film is coated on a surface of the cemented carbide having an average surface roughness Ra of 0.15 to 0.4 &mgr;m, on which scratches are formed by polishing in random directions by, for example, brushing the cemented carbide surface. The cemented carbide disclosed in the publication exhibits improved adhesiveness of the hard film to the base material by attaching cobalt uniformly on the hard particles of the cemented carbide surface through the attachment of grinding swarf caused by brushing, but the amount of cobalt is not sufficient and formation of a degenerated layer is accompanied, so that there exists a problem that improvement of the adhesiveness is not sufficient.
Moreover, as re-sintering method, Japanese Patent Laid-Open Publication No. 123903/1993 discloses a method for manufacturing a cutting tool member made of a surface-coated WC-based cemented carbide wherein a hard coating layer is formed by chemical vapor deposition using, as a substrate, a cemented carbide that has been re-sintered at a higher temperature than liquid phase-appearing temperature in a high pressure inert gas atmosphere after grinding the surface. Japanese Patent Laid-Open Publication No. 097603/1995 discloses a method for producing a ceramics based substrate for diamond coating and a substrate for coating wherein the cutting edge of a cemented carbide tip is subjected to arc honing of R=0.03 mm and then re-sintered in a 1% N
2
—Ar atmosphere to form a concavo-convex layer containing nitrogen at the surface. The re-sintered surfaces disclosed in these publications exhibit slight improvement in adhesiveness owing to the complete removal of the degenerated layer, but there is a problem that improvement of the adhesiveness is insufficient since cobalt attached on the surfaces of the hard phase particles by grinding disappears during re-sintering and therefore, no diffusion layer is formed. F
Kitada Hiroshi
Kobayashi Masaki
Barr Michael
Foley & Lardner
Toshiba Tungaloy Co., Ltd.
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