Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1998-08-14
2001-05-15
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S672000, C148S668000
Reexamination Certificate
active
06231697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an amorphous alloy having high hardness and strength, excellent ductility, high corrosion resistance, and excellent workability, and a process for preparing the same.
2. Description of the Prior Art
Conventional Zr-based alloys having specified alloy compositions causes glass transition before crystallization, have a wide supercooled liquid region, and have a high capability of forming an amorphous phase. Since these alloys have such a high amorphizing capability, they become amorphous not only by any method wherein a high cooling rate can be secured like a liquid quenching method, but also by any ordinary casting method wherein the cooling rate is slow like a copper mold casting method, whereby tough bulk amorphous alloys can be prepared. When, however, a quenched tough thin strip formed by, for example, the liquid quenching method is heated at a temperature around the crystallization temperature thereof to precipitate crystals, the toughness thereof is deteriorated so that it can hardly be subjected to 180° contact bending. On the other hand, according to the copper mold casting method, a good amorphous bulk can be formed when cooled at a given or higher cooling rate, while the toughness thereof is deteriorated when the cooling rate is lowered to precipitate crystals.
SUMMARY OF THE INVENTION
The present invention aims at providing a high-strength amorphous alloy while solving the problem of deterioration of toughness either when a formed quenched tough thin strip or bulk material is heat-treated to precipitate crystals or when the cooling rate is lowered in the mold casting method to precipitate crystals.
The present invention provides a high-strength amorphous alloy represented by the general formula: X
a
M
b
Al
c
T
d
(wherein X is at least one element selected between Zr and Hf; M is at least one element selected from the group consisting of Ni, Cu, Fe, Co and Mn; T is at least one element having a positive enthalpy of mixing with at least one of the above-mentioned X, M and Al; and a, b, c and d are atomic percentages, provided that 25≦a≦85, 5≦b≦70, 0<c≦35 and 0<d≦15) and having a structure comprising at least an amorphous phase.
The most effective element mentioned above as T is Ag. The addition of such an element T can bring about a change in the bonding of the constituent elements of the resulting amorphous alloy so as to allow it to attain a high strength without deterioration of toughness. Further, the structure of the alloy of the present invention is a mixed phase comprising an amorphous phase and a microcrystalline phase. The formation of the mixed phase structure provides excellent mechanical strength and ductility. When particular consideration is given to ductility, the amorphous phase preferably accounts for at least 50% in terms of volume fraction.
The present invention also provides a process for preparing a high-strength amorphous alloy, comprising preparing an amorphous alloy having a composition represented by the aforementioned general formula and containing at least an amorphous phase, and heat-treating the alloy in the temperature range from the first exothermic reaction-starting temperature (Tx
1
: crystallization temperature) thereof to the second exothermic reaction-starting temperature (Tx
2
) thereof to decompose the amorphous phase into a mixed phase structure consisting of an amorphous phase and a microcrystalline phase.
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Inoue et al., “Effect of Additional Elements on Glass Transition Behavior and Glass Formation Tendency of Zr-AL-Cu-Ni Alloys,”Materials Transactions, JIM, vol. 36, No. 12 (1995), pp. 1420 to 1426.
Rao, “Stoichiometry and Thermodynamics of Metallurgical Processes,” 1985 Cambridge University Press, XP00208 7231, pp. 243 and 892-894.
Derwent Abstract (English Language) for Japanese Patent JP 09020968 A, Jan. 21, 1997.
Inoue Akihisa
Nagahama Hidenobu
Zhang Tao
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Inoue Akihisa
Oltmans Andrew L.
Sheehan John
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