Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2001-05-21
2004-01-06
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C427S185000, C427S355000, C427S372200, C427S376100, C427S376200, C428S325000, C428S408000, C428S698000
Reexamination Certificate
active
06673439
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a coated diamond to which an SiC coating is applied, a method of manufacturing and a composite material thereof. In particular, the invention relates to a coated diamond with an enhanced density as well as a superior adherence compared with those that have been accomplished, a method of manufacturing and a composite material thereof.
BACKGROUND ART
Diamond has the highest hardness among terrestrial materials and thus has been employed as tool materials. As diamond also has a considerably high thermal conductivity, application to heat sink materials is expected. When diamond is used as tool and heat sink materials, the diamond is molded with metal, ceramic, resin or the like into one piece by means of powder metallurgy and accordingly a composite thereof is produced. On the other hand, when the temperature of diamond is increased in the air, oxidation of the diamond begins at approximately 650° C. A further shortcoming of the diamond is transformation into graphite resultant from dissolution of the diamond in molten metal of Co, Ni, Fe and the like. Then, in order to prevent oxidation as well as chemical reaction between diamond and these materials and to enhance a bonding strength between diamond and metal, ceramic and resin, studies have been conducted on application of a coating layer onto a surface of diamond (Japanese Patent Laying-Open Nos. 5-105560, 6-263516 and 8-113774).
However, conventional techniques of forming a coating layer on a surface of diamond are insufficient in terms of optimization of density, nonuniform thickness, surface properties and coating film thickness which affect quality of the coating layer. In addition, the bonding strength between the coating film and diamond is also insufficient.
The present invention aims to provide a diamond with a coating film that is dense and superior in adherence to enable diamond to exhibit its excellent characteristics, a method of manufacturing the coated diamond and a composite material of the coated diamond.
DISCLOSURE OF THE INVENTION
A coated diamond according to the present invention includes a diamond and a film including SiC as a main component to coat the diamond (hereinafter referred to as SiC film). The SiC is substantially formed of &bgr;-SiC. For the SiC film, a value of ratio I (220)/I (111) is at least 0.38 and at most 0.55, I (220) representing peak intensity of Miller index (220) of SiC and I (111) representing peak intensity of Miller index (111) thereof.
The &bgr;-SiC is SiC which belongs to one of Nos. 29-1129, 29-1128 and 39-1196 of JCPDS (Joint Committee on Powder Diffraction Standards) card. The film including &bgr;-SiC as a main component preferably has at least a partial region which is in a crystallographically identical orientation relationship with respect to adjacent diamond, since such a coating film is unlikely to separate. The crystallographically identical orientation relationship (epitaxial relation) can be determined by irradiating a region in the vicinity of the boundary between the diamond and the SiC film with X-rays or electron beam to take an X-ray diffraction image or electron diffraction image where diffraction patterns of the diamond and SiC film occur. The present invention includes a structure having an intermediate layer between the diamond and the SiC film for alleviating lattice distortion to achieve a regular orientational relation between the diamond and SiC film, i.e., the diamond and SiC film are not directly adjacent to each other.
The &bgr;-SiC can be identified by means of X-ray diffraction to measure a lattice constant of SiC, which is approximately 4.36 angstrom. The value of ratio I (220)/I (111) can be calculated by determining peak intensity in X-ray diffraction of Miller indices (220) and (111). As shown by JCPDS card, the value of I (220)/I (111) is usually 0.35. The value of ratio can be set at 0.38 or higher to considerably improve adherence of the &bgr;-SiC film to diamond. The ratio is more desirably 0.4 or higher. However, the adherence deteriorates when the ratio exceeds 0.55 and thus the value is desirably 0.55 or lower, more desirably 0.5 or lower.
When &bgr;-SiC is of equi-axial grains, the coating film has an enhanced strength and thus is unlikely to separate. Further, toughness of the &bgr;-SiC is combined with the property of equi-axial grains to make the coating film more unlikely to separate. Here, “equi-axial grains” refers to the shape of polycrystal grains having no anisotropy, as compared with columnar grains and extended grains having anisotropy. In the coated diamond according to the present invention, carbon atoms in the SiC film are supplied substantially from diamond. As C is supplied from diamond, the surface of diamond is readily coated completely with the &bgr;-SiC film which is dense.
The &bgr;-SiC film of equi-axial grains is not porous and the film coats the surface of diamond densely and completely. Accordingly, the bonding strength between the coating film and diamond can be enhanced. Here, “film densely coats” means that a uniform coating film covers diamond without leaving a non-coated part.
The SiC film of the coated diamond discussed above could have an Si ratio which is lower near the diamond and higher near the surface of the SiC film. On the contrary, the ratio of carbon atoms could be higher near the diamond and lower near the surface of the SiC film. The Si and carbon ratios in the SiC film can be determined by spectroscopic analysis or EPMA (Electron Probe X-ray Microanalyser) and wavelength dispersive type X-ray spectrometer. For quantitative analysis of a light element like carbon having atomic number 10 or smaller, multi-layer crystal is used as a spectrometer in a wavelength dispersive type spectrometer, the spectrometer is placed in vacuum, and a proportional counter is used as a detector. Alternatively, secondary ion mass spectrometry (SIMS) may be used.
The film containing SiC as a main component of the coated diamond according to the present invention preferably has a thickness of 0.001 to 0.3 &mgr;m.
The coating film having the thickness mentioned above prevents the diamond with superior characteristics from deteriorating. Specifically, oxidation resistance can be enhanced and prevention is possible of reaction between the diamond and molten metal of Co, Ni, Fe and the like. The coating film includes SiC with the carbon supplied from the diamond. Therefore, it is difficult to form the coating film with its thickness exceeding 0.3 &mgr;m. On the other hand, a smaller thickness less than 0.001 &mgr;m lessens the effect of applying the coating. Accordingly, the coating film has a thickness of 0.001 to 0.3 &mgr;m.
More preferably, the film containing SiC as a main component of the coated diamond according to the present invention has a thickness ranging from 0.005 to 0.1 &mgr;m.
The film thickness of 0.005 &mgr;m or greater enables oxidation resistance to be sufficient and superior characteristics of the diamond to be retained. On the other hand, the film thickness can be limited to 0.1 &mgr;m or smaller to prevent occurrence of crack in the coating film due to difference in thermal expansion coefficient between the diamond and SiC and to facilitate maintenance of the epitaxial relation between &bgr;-SiC and adjacent diamond. Resistance to separation is thus significantly improved.
The SiC of the coated diamond according to the present invention desirably has a mean grain diameter of at most 50 nm for example.
When the mean grain diameter of SiC is 50 nm or smaller, the SiC has an improved strength. The mean grain diameter of SiC is desirably at most 15 nm. The SiC with the mean grain diameter in this range can have a further enhanced strength.
Diamond of the coated diamond according to the present invention is of particulate for example and the mean particle diameter of the diamond is 0.1 to 100 &mgr;m.
When the diamond is formed of minute particles with a mean particle diameter of 0.1 to 100 &mgr;m, a dense and uniform SiC film is difficult to produce by conven
Miyamoto Yoshinari
Moriguchi Hideki
Fasse W. F.
Fasse W. G.
Sumitomo Electric Industries Ltd.
Turner Archene
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