Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2000-03-06
2001-10-23
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S561000, C164S113000
Reexamination Certificate
active
06306228
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for producing an amorphous alloy having characteristics excellent in flexural strength (bending strength) and impact strength.
TECHNICAL BACKGROUND
It has been well known that amorphous metallic materials having various shapes, such as a thin strip shape, a filament shape and a powder particle shape, can be obtained by quickly cooling a molten alloy. Since an amorphous alloy thin strip can be easily manufactured by a method which can obtain a large cooling rate, such as a single-roll method, a dual-roll method, a rotating liquid spinning method, or the like, a number of amorphous Fe-alloy, Ni-alloy, Co-alloy, Pd-alloy, Cu-alloy, Zr-alloy and Ti-alloy have been successively obtained. Since these amorphous alloys have industrially very important characteristics such as high corrosion resistance, high strength and the like, which cannot be obtained by crystalline metallic materials, an application of these amorphous alloys in the fields of new structural materials, medical-use materials, chemical materials, or the like, has been expected.
However, according to the aforementioned manufacturing methods, amorphous alloys can only be obtained as a thin strip or a thin wire. Thus, it was difficult to form such amorphous alloys into a final product shape, resulting in an industrially limited usage.
Various studies regarding an improvement of a manufacturing efficiency of an amorphous alloy, an optimization of a composition and a manufacturing method have recently been conducted, and an amorphous alloy ingot having a size which meets the requirements of structural materials has been manufactured. For example, as a Zr—Al—Cu—Ni alloy, an amorphous alloy ingot having a diameter of 30 mm and a length of 50 mm has been successfully obtained (see “Materials Transactions, Japan Institute of Metals” (English version) issued on 1995, Vol. 36, Item. No. 1184). As a Pd—Ni—Cu—P alloy, an amorphous alloy ingot having a diameter of 72 mm and a length of 75 mm has been successfully obtained (see “Materials Transactions, Japan Institute Metals” (English version) issued on 1997, Vol. 38, Item. No. 179). These amorphous alloy ingots have a tensile strength of 1700 MPa or more and a Vickers hardness of 500 or more, and are expected to be used as unique high-strength structural materials having extremely high elastic limit.
DISCLOSURE OF THE INVENTION
(OBJECTS TO BE SOLVED BY THE INVENTION)
However, since the aforementioned amorphous alloy ingots are poor in plastic workability at room temperature due to the irregular atomic structure (glass-like structure), the dynamic strength thereof against a bending load, an impact load, and the like, tends to be insufficient, resulting in poor reliability as practical structural materials. Under such circumstances, it has been desired that an amorphous alloy which has improved dynamic strength against a bending load and an impact load without causing a deterioration of high strength high elastic limit characteristics due to the amorphous structure as well as its manufacturing method, is developed.
(MEANS FOR SOLVING THE PROBLEMS)
To solve the above mentioned problems, the present inventors have eagerly studied for the purpose of providing a practically endurable amorphous alloy having an enhanced bending strength and impact strength combined with high strength characteristics due to the amorphous structure. As a result, the inventors have found the fact that the bending strength and the impact strength can be enhanced by eliminating casting defects by pressure-solidifying molten alloy under a pressure exceeding one atmospheric pressure and solidifying it by applying a cooling rate difference with a cooling medium having an appropriate heat capacity between the surface and the interior of the molten alloy so that a compressive stress layer remains on the surface of the amorphous alloy ingot and a tensile stress layer remains in the interior thereof. By optimizing the manufacturing conditions which can effectively realize the strengthening mechanism, the present invention has been completed.
The present invention is to provide an amorphous alloy excellent in bending strength and impact strength by avoiding a stress concentration near casting detects to maintain an inner stress in the alloy.
(THE BEST MODE FOR CARRYING OUT THE INVENTION)
A preferred embodiment of the present invention will now be described as follows.
In general, a cooling rate required to form an amorphous alloy differs depending on an alloy to be manufactured because an amorphous alloy forming ability differs depending on an amorphous alloy to be manufactured. Therefore, the present invention adapts a manufacturing method including the steps of: solidifying a molten alloy at a cooling rate approximately 50% larger than a cooling rate at which the whole molten alloy forms an amorphous alloy (critical cooling rate) to quickly cool the surface of the alloy; and then cooling the alloy in a metal mold heated by a heat transmission and solidifying the inside of the alloy at nearly around the critical cooling rate to form an amorphous alloy, whereby a compression stress layer remains at the surface of the amorphous alloy and a tensile stress layer remains at the interior thereof.
Furthermore, the present invention can be preferably carried out by optimizing the manufacturing conditions which realizes the strengthening mechanism, that is to say, by making the interior of the molten alloy into an amorphous alloy at around the critical cooling rate by heating it by the transmitted heat while quickly cooling the surface of the desired molten alloy with a cooling medium having an optimum heat capacity, and by effectively generating the cooling rate difference between the surface and the interior of the amorphous alloy due to the thickness of the amorphous alloy. Therefore, it is preferable to use a manufacturing device which can control the cooling rate to a desired level in accordance with the amorphous forming ability of the amorphous alloy to be manufactured. The cooling rate adjustment can be preferably performed by, for example, adjusting the heat capacity of the mold, adjusting the amount of the mold cooling water, optimizing the minimum thickness of the alloy, or controlling the temperature of the molten alloy when the molten alloy is being cast.
Furthermore, in order to effectively eliminate casting defects which may cause a start point of fracture of an amorphous alloy according to the present invention, it is preferable that a pressure to be applied at the time of casting is controllable. In a pressure-casting apparatus, the effective applied pressure is a pressure exceeding one atmospheric pressure. More preferably, the applied pressure is a pressure exceeding two atmospheric pressure. If the applied pressure is not larger than one atmospheric pressure, it is impossible to eliminate the casting defects generated at the time of casting. The applied pressure can be preferably obtained by a die compression method which utilizes an oil-pressure, an air-pressure, an electric-driving, or the like, and an injection casting method such as a die casting or a squeeze casting.
In an amorphous alloy sheet according the present invention, the minimum thickness is set to be 1 mm or more. The minimum thickness coincides with a direction vertical to a heat flow rate caused by a cooling, and generally means the sheet thickness. The above regulation is a necessary and essential condition for manufacturing an amorphous alloy having an inner residual stress which constitutes the basis of the present invention. That means that, if the minimum thickness is less than 1 mm, although an alloy having an amorphous structure can be easily obtained, in actual, a cooling difference cannot be effectively generated between the surface of the molten alloy and the interior thereof, which fails to improve the bending strength and impact strength. On the other hand, if the minimum thickness is 10 mm or more, in currently available amorphous forming alloys, a complete amorphous st
Inoue Akihisa
Nishiyama Nobuyuki
Zhang Tao
Armstrong Westerman Hattori McLeland & Naughton LLP
Japan Science and Technology Corporation
Wyszomierski George
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