Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1999-04-21
2001-10-16
Jenkins, Daniel J. (Department: 1742)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S420200, C030S350000, C030S357000, C051S307000, C407S032000
Reexamination Certificate
active
06302225
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a polycrystal diamond tool excellent in, in particular, heat resistance, strength and anti-adhesion property and more particularly, it is concerned with a polycrystal diamond tool having an improved heat resistance, strength and anti-adhesion property as a tool, provided by removing binding materials and modifying a porosity of a diamond sintered compact.
DESCRIPTION OF THE PRIOR ART
Diamond has been used for various tools such as cutting tools, dies, bits, etc. from old times because of its excellent properties, for example, high hardness and high thermal conductivity. Particularly, a diamond compact obtained by sintering diamond powder with a binder predominantly consisting of an iron group metal such as cobalt, etc. under ultra-high pressure and high temperature has widely been used for cutting non-ferrous metals, plastics, ceramics, dressers, drill bits, wire drawing dies, etc. because of being free from disadvantages of single crystal diamond that breakage due to cleavage takes place.
However, the diamond sintered compact using a binder of an iron group metal such as cobalt has a disadvantage that the heat resistance is not sufficient. That is, when this sintered compact is heated at a temperature of at least 750° C., occurrence of microcracks and lowering of the hardness or strength appear and at a temperature of at least 900° C., the sintered compact is broken.
This phenomenon is caused by two actions, in combination, that (1) graphitization of diamond by an iron group metal such as Co is accelerated to decrease the bonding strength between grains or the hardness of grains and (2) when using at a high temperature, cracks occur due to difference of thermal expansion coefficients of between an iron group metal such as Co (e.g. linear thermal expansion coefficient of Co: 18×10
−6
) and diamond (thermal expansion coefficient: 4.5×10
−6
), thus weakening the bonding strength between grains.
Several methods have been proposed to solve these problems and improve the heat resistance. For example, Japanese Patent Laid-Open Publication No. 114589/1978 discloses a diamond sintered compact in which diamond is sintered using a binder such as Co, etc. and the binder is removed by treatment with an acid to obtain the iron group metal-removed diamond sintered compact. However, this diamond sintered compact has a problem that the fracture strength is remarkably lowered depending upon an amount of the residual metal or pores and accordingly, the use thereof is limited.
Furthermore, Japanese Patent Laid-Open Publication No. 187603/1985 discloses a diamond sintered compact in which a binder consisting of an iron group metal such as Co, etc. is removed by an acid treatment and then pores remained in the sintered compact is permeated with a metallic brazing agent consisting mainly of Cu or Ag to obtain pores-free diamond sintered compact. In this case, it is reported that the strength or fracture strength of the sintered compact are improved by removing pores, but application ranges thereof as a tool are limited, since the quality of a worked surface is so bad as not to be practical due to adhesion of a workpiece to a tool edge during working.
As a method of using a binder other than iron group metals such as Co, etc., it has been proposed to use SiC as a binder, as disclosed in U.S. Pat. No. 4,124,401. In this case, however, a diamond sintered compact has been sintered under conditions of relatively low pressure and low temperature by a hot press or the like, so when it is used as a tool, the wear resistance is inferior because of less bonding among diamond grains.
Furthermore, a proposal to obtain a diamond sintered compact with a high heat resistance by impregnating diamond grains with liquid phase Si at a high pressure and high temperature is disclosed in Japanese Patent Laid-Open Publication No. 33865/1986. However, this method comprising reacting Si with diamond to form SiC to be used as a binder, has a disadvantage that unreacted Si remains to decrease the strength and wear resistance.
In order to remove influences of the unreacted and remaining Si, use of Si
3
N
4
as a raw material for a binder of a sintered compact has been proposed in Japanese Patent Laid-Open Publication No. 260858/1988. According to this method, however, bonding of Si
3
N
4
and SiC is not so strong that the strength and wear resistance are not satisfied.
Of late, such a knowledge has been attained that not only iron group metals such as Co, etc., but also carbonates of alkaline earth metals such as Mg, Ca, Sr, Ba, etc. are also effective similarly to the iron group metals such as Co, etc. and sintered compacts using these materials as a binder has been proposed (Japanese Patent Laid-Open Publication Nos. 74766/1992, 9271/1994 and 9272/1994). The diamond sintered compacts obtained by these methods are excellent in heat resistance, strength and wear resistance, but when using these carbonates for obtaining diamond sintered compacts, a pressure of 7 to 10 GPa and a temperature of 2000 to 2500° C., much higher than those in the case of using the iron group metals such as Co, etc., i.e. 5 GPa and 1400° C., are required, which are, therefore, not practically used from the standpoint of the cost.
As described above, a number of proposals have hitherto been made noting a binder of a diamond sintered compact, in particular, the presence of pores replacing the binder or a material to be filled in the pores, but a diamond sintered compact having more excellent properties as to application ranges, heat resistance, anti-adhesion property etc. of the diamond tool using the diamond sintered compact has not been developed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polycrystal diamond tool in which the porosity in a binder material of a diamond sintered compact is modified to improve the heat resistance, strength and anti-adhesion property as a tool.
It is another object of the present invention to markedly improve tool properties by modifying a composition of a heat resistance diamond sintered compact described in Japanese Patent Laid-Open Publication No. 187603/1985.
It is a further object of the present invention to provide a process for the production of a polycrystal diamond tool in economical manner.
These objects can be attained by a polycrystal diamond tool comprising a diamond sintered compact, sintered under ultra-high pressure and high temperature, brazed onto a tool substrate, in which the cutting edge vicinity part consists of 85 to 99 volume % of the diamond sintered compact material consisting of diamond grains bonded with each other and the balance of pores, and the other part than the cutting edge vicinity part consists of diamond grains and the balance of a brazing material.
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Nakai Tetsuo
Ogata Yasunobu
Shiraishi Junichi
Yoshida Katsuhito
Jenkins Daniel J.
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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