Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-03-06
2003-06-24
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
Reexamination Certificate
active
06582538
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an amorphous alloy having characteristics excellent in 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 produced by a method which can attain 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 produced. For example, in 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). In 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 of Metals” (English version) issued on 1997, Vol.38, Item. No.179). These amorphous alloy ingots have tensile strength of 1700 MPa or more and Vickers hardness of 500 or more, and are expected to be used as extremely high-strength structural materials.
DISCLOSURE OF THE INVENTION
Objects to be Solved by the Invention
However, the aforementioned amorphous alloy ingots are poor in plastic workability at room temperature due to its irregular atomic structure (glass-like structure), and the bending strength and the impact strength are insufficient, resulting in poor reliability as practical structural materials. Under such circumstances, it has been desired that an amorphous alloy improved in bending strength and impact strength without causing a deterioration of high strength characteristics inherent in an amorphous structure and its producing method, are 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 improved bending strength and impact strength combined with high strength characteristics inherent in an amorphous structure. As a result, the inventors have found the facts that an amorphous alloy ingot having a structure in which fine crystals are dispersed can be obtained by pressure-solidifying a molten alloy having amorphous forming ability under a pressure exceeding one atmospheric pressure and appropriately adjusting the cooling rate during the solidification, and that the resultant amorphous alloy ingot is excellent in bending strength and impact strength. Based on the above, the present invention has been completed.
Furthermore, the inventors found the facts that the bending strength and the impact strength of the above-mentioned amorphous alloy can be further improved by infiltrating an element having an atomic diameter smaller than that of a metallic element, such as boron, carbon, oxygen, nitrogen and fluorine, into the amorphous alloy from its surface to form a high melting point compound, to thereby impart a residual compressive stress continuing from the surface caused by a volume reduction at the generation of the compound. Then, the present invention has been completed.
In other words, the present invention is to provide an amorphous alloy having excellent bending strength and excellent impact strength and having a minimum thickness of 2 mm or more by pressure-solidifying an amorphous alloy having an amorphous forming ability under a pressure of more than one atmospheric pressure, and adjusting a cooling rate during the solidification to disperse fine crystals having a mean crystal grain diameter of 1 nm to 50 &mgr;m in a crystal volume percentage of 5 to 40%.
Furthermore, the present invention is also to provide an amorphous alloy having excellent bending strength and excellent impact strength in which the texture is inclined from the surface toward the inside due to a precipitation of a high melting point compound of at least one of boron, carbon, oxygen and fluorine infiltrated from the surface of the amorphous alloy ingot manufactured by the above-mentioned method with an element forming the amorphous alloy, whereby a compressive stress layer is formed in the surface of the alloy.
The above-mentioned method for producing the amorphous alloy by dispersing fine crystal grains and the strengthening method by infiltrating an element from the surface of the amorphous alloy are similar in that both the methods utilize residual stress. However, both the methods are compatible in that the stress generating portions are different and the compounds formed by the infiltrated elements protects the surface of the amorphous alloy. In addition, the bending strength and the impact strength of the amorphous alloy can be greatly improved due to the multiplier effect.
The Best Mode for Carrying out the Invention
First, a preferred embodiment concerning an alloy according to the present invention recited in claim 1 and its producing method, will now be described as follows.
In general, a cooling rate required to form an amorphous alloy (a critical cooling rate) differs depending on an alloy to be produced because of different amorphous alloy forming ability of an alloy to be produced. It is reported that the critical cooling rate of La-alloy is about 100° C./second, that of Pd-alloy is about 1.6° C./second, and that of Fe-alloy is about 10,000° C./second. As will be apparent from the above, the critical cooling rate differs depending on an alloy to be produced.
However, in all of these amorphous forming alloys, by decreasing the critical cooling rate by about 20 to 50%, an amorphous alloy in which crystals are dispersed partially can be produced. Further, in order to produce an amorphous alloy having the crystal grain diameter and the crystal volume percentage defined in the claims, it is preferable that the manufacturing apparatus can widely control the cooling rate to any desired rate. The adjustment of the cooling rate can be performed appropriately by adjusting a die heat capacity, adjusting a water flow rate or controlling a temperature of a molten alloy during the casting.
The amorphous alloy according to the present invention is formed to have a minimum thickness of 2 mm or more by the aforementioned method. If the thickness is less than 2 mm, an amorphous alloy plate can be easily produced because a cooling rate enough for producing an amorphous alloy can be obtained. However, it is difficult to produce an amorphous alloy having the crystal grain diameter and the crystal grain volume percentage recited in the claims by solidifying the molten alloy while adjusting the cooling rate decreased by 20 to 50% from the critical cooling rate of the alloy.
In the available amorphous forming alloys as of today, the maximum thickness of the amorphous alloy is 72 mm. However, in the cooling rate range at which the crystal grain diameter and the crystal volume percentage defined by the claims can be obtained, if the thick
Inoue Akihisa
Nishiyama Nobuyuki
Zhang Tao
Armstrong Westerman & Hattori, LLP
Japan Science and Technology Corporation
King Roy
Wilkins, III Harry D.
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