Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Metal and nonmetal in final product
Patent
1986-10-08
1988-08-02
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Metal and nonmetal in final product
419 23, 419 42, 419 46, 419 48, 419 68, 264 65, 264125, B22F 100
Patent
active
047612622
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to a method for the sintering a metal powder, a ceramic powder, or a mixture of a metal powder with a ceramic powder, and more particularly to a sintering method which comprises heating the aforementioned powder by means of Thermit reaction while keeping the powder under pressure.
BACKGROUND OF THE INVENTION
The so-called sintering method which uses a powder as a starting material and converts it into a mass by sintering has heretofore been widely used on metals, ceramics, and composite materials thereof.
The largest task imposed on the sintering method consists in obtaining a mass which is compact and is formed of minute crystal grains. For promoting compaction, pressure sintering methods resorting as to a hot press and a hot hydrostatic press are available. They use pressures on the order of 500 atmospheres and 2,000 atmospheres respectively. For the heating to be made under a still higher pressure, it is necessary to use such an apparatus for the generation of ultrahigh pressure and high temperature as disclosed in Japanese Patent Publication SHO 36(1961)-23,463, for example. With this apparatus, sintering can be carried out under not less than 10,000 atmospheres of pressure.
For example, a method which obtains a sintered article having a compact and fine texture by sintering an alloy powder or a nonequilibrium phase under not less than 10,000 atmospheres of pressure is conceivable.
The problems encountered by the ultrahigh pressure sintering method are as follows:
1. Since this method uses a solid pressure medium, the apparatus is deficient in capacity for hydrostatic pressure and the sintered article assumes anisotropy.
2. Since a heater installed outside the material under treatment or resistance heating caused by passage of electricity to the material under treatment itself is utilized for the heating, the apparatus requires a power source of a large capacity.
3. Since no suitable substance is available for an electrically insulating refractory material, the heating at an elevated temperature exceeding 2,000.degree. C. is not easily attained.
4. Since the speed of heating is slow, diffusion occurs and crystal grains are coarsened during the course of temperature elevation.
DISCLOSURE OF THE INVENTION
This invention has been perfected in view of the state of affairs mentioned above. An object of the invention is to provide, for elimination of disadvantages of the prior art, a method for sintering a metal powder, a ceramic powder, or a mixture thereof which attains intimate sintering of even a high melting substance by carrying out a high-temperature heating under ultrahigh pressure for a short time.
Another object of this invention is to provide a sintering method which comprises heating a metal powder, a ceramic powder, or a mixture thereof as kept under pressure with the heat of a Thermit reaction.
Yet another object of this invention is to provide a method for sintering a metal powder, a ceramic powder, or a mixture thereof, wherein the sintered article to be produced is protected so as not to be corroded by the product of Thermit reaction.
To attain the objects described above, the first embodiment of this invention provides a method for sintering a metal powder, a ceramic powder, or a mixture thereof by heating the aforementioned powder or mixture as held under pressure with the heat of Thermit reaction.
The second embodiment of this invention provides a sintering method set forth in the first embodiment mentioned above, which further comprises interposing a barrier made of hexagonal boron nitride and/or tantalum between the powder subjected to sintering and a Thermit composition.
The third embodiment of this invention provides a sintering method set forth in the first embodiment mentioned above, which further comprises disposing a Thermit composition around the entire periphery of the powder subjected to sintering, heating the powder with the heat generated by the Thermit reaction and, at the same time, fusing a part or the whole of
REFERENCES:
patent: 3865573 (1975-02-01), Newmann
patent: 3909909 (1975-10-01), Whalen et al.
patent: 3999952 (1976-12-01), Kondo et al.
patent: 4610726 (1986-09-01), King
patent: 4655830 (1987-04-01), Akashi et al.
Ogata Masaru
Takeda Shuichi
Kabushiki Kaisha Komatsu Seisakusho
Lechert Jr. Stephen J.
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