Shape-memory alloy based on copper, zinc and aluminum and process for preparing it
AssigneeBBC Brown, Boveri & Company, Limited
InventorsKeith Melton, Olivier Mercier, Helmut Riegger
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Abstract
A fine-grained shape-memory alloy of the Cu/Zn/Al type, prepared by powder metallurgy, exhibiting the beta-high temperature phase, having dispersed in the matrix dispersoids in the form of Y.sub.2 O.sub.3 and or TiO.sub.2 particles which limit grain growth, and a process for preparing this alloy using mechanical alloying.
Claims12
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 in an amount of 0.5 to 2% by weight of the entire mass of the alloy as a dispersoid in the matrix formed by the beta phase.
A process for preparing a shape-memory alloy based on copper, zinc and aluminum, characterized by the following steps:
- (a) preparing a Powder A having a particle size of 10 to 200 micrometers 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% by 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;
- (b) mixing 0.5 to 15% by weight of Powder B, 0 to 80% by weight of Powder C 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;
- (c) isostatically pressing the dried powder mixture in a plastic or rubber tube at a pressure of at least 3000 bar;
- (d) reducing and pre-sintering the compact prepared in step (c) in a hydrogen or hydrogen/nitrogen atmosphere at a temperature between 700.degree. and 1000.degree. C. for at least 30 minutes;
- (e) sintering the reduced and pre-sintered compact in an argon atmosphere at at least 700.degree. C. for at least 10 hours;
- (f) alternately hot working at a temperature between 700.degree. and 1000.degree. C. and homogenizing in an inert gas atmosphere at a temperature of at least 700.degree. C. for at least 30 minutes;
- (g) finally annealing in an argon atmosphere at a temperature between 700.degree. and 1050.degree. C. for 10 to 15 minutes and immediately thereafter quenching in water.
A shape-memory alloy based on copper, aluminum and zinc, these metals present in the beta-phase, having a metal oxide present in an amount of 0.5 to 2% by weight of the entire mass of the alloy as a dispersoid in the matrix formed by the beta-phase and characterized by having a fine grain size.
A shape-memory alloy based on copper, aluminum and zinc, these metals present in the beat-phase, consisting essentially of 95-50% Cu, 0.5-15% Al, 6-20% zinc, these percentages being percent by weight, and 0.5 to 2% of a metal oxide present as a dispersoid in the matrix formed by the beta-phase, characterized by having a fine grain size.
Dependencies are inferred from the claim text.