Metal treatment – Compositions – Heat treating
Patent
1981-11-03
1983-08-16
Stallard, W.
Metal treatment
Compositions
Heat treating
148 115P, 148402, 148413, 148434, 148436, C22C 901, C22C 904
Patent
active
043989691
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a shape-memory alloy Cu/Zn/Al and to a process for preparing it.
2. Description of the Prior Art
Memory alloys based on the Cu/Zn/Al system are known and have been described in various publications (e.g., U.S. Pat. No. 3,783,037). Such memory alloys, which belong generally to the type having a beta-high temperature phase, are usually produced by fusion techniques.
When these alloys are cast they usually exhibit a coarse texture, which becomes still coarser because of grain growth during subsequent annealing in the temperature range of the beta-phase solid solution, and which cannot be eliminated by hot working. As a result, the mechanical characteristics, particularly elongation and notch ductility, of shape-memory alloys produced in this manner are relatively poor, and their field of application is limited.
Accordingly, a need has existed to improve the metallurgy and preparative technology of these shape-memory alloys so that additional practical applications may be open to them.
It has already been proposed to produce shape-memory alloys of the Cu/Zn/Al type by powder metallurgy, starting with previously prepared alloys corresponding to the final composition (e.g., M. Follon, E. Aernoudt, Powder-metallurgically processed shape-memory alloys, 5th European Symposium on Powder Metallurgy, Stockholm 1978, pp. 275-281). In such processes the prepared powder is encapsulated, cold compacted, hot pressed and extruded.
However, these methods are not adapted to all practical requirements and the finished articles often leave something to be desired in their mechanical properties.
SUMMARY OF THE INVENTION
The basic object of the invention is to provide shape-memory alloys based on copper, zinc, and aluminum and a process for their preparation which provides dense, compact articles having good mechanical properties and at the same time accurately reproducible values of the transition temperature and other properties associated with the shape-memory effect.
This object is attained according to the invention by providing a shape-memory alloy based on copper, zinc and aluminum, which is present in the beta-phase, characterized in that it is prepared by powder metallurgical techniques from pre-alloys and pre-mixtures, that it has a fine-grained structure with a grain size of at most 100 micrometers and that at least one metal oxide is present as a dispersoid in the matrix formed by the beta-phase.
This object is further attained by providing a process for preparing a shape-memory alloy based on copper, zinc and aluminum, characterized by the following steps: from a copper-rich pre-alloy containing 60 to 80% by weight Cu, 0 to 1% by weight Al, balance Zn; preparing a Powder B having a particle size from 5 to 100 micrometers by mixing and/or alloying of 95 to 99.5% by weight aluminum powder with 0.5 to 5% weight of copper powder; preparing a Powder C of pure copper having a particle size of 10 to 100 micrometers; preparing a Powder d of Y.sub.2 O.sub.3 or TiO.sub.2 or any mixture of these oxides having a particle size of 10 to 100 micrometers; and 0.5 to 2% by weight of Powder D, and the balance Powder A, under toluene, ethyl alcohol or another organic solvent in a ball mill or an attrition mill for at least 5 hours at room temperature and finally evaporating the solvent; tube at a pressure of at least 3000 bar; hydrogen or hydrogen
itrogen atmosphere at a temperature between 700.degree. and 1000.degree. C. for at least 30 minutes; at least 700.degree. C. for at least 10 hours; 1000.degree. C. and homogenizing in an inert gas atmosphere at a temperature of at least 700.degree. C. for at least 30 minutes; 700.degree. and 1050.degree. C. for 10 to 15 minutes and immediately thereafter quenching in water.
The nucleus of the invention lies in starting with neither elemental powders nor with powders corresponding to one of the ultimate alloys, but rather with a mixture of pre-alloyed powders and specially formulated powder mixtures, and mecha
REFERENCES:
patent: 4144104 (1979-03-01), Brooks
patent: 4285739 (1981-08-01), Deruyttere et al.
Melton Keith
Mercier Olivier
Riegger Helmut
BBC Brown Boveri & Company Limited
Stallard W.
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