Treatment of alloys

Abstract

A method of making a heat-recoverable article in which an alloy comprising an intermetallic compound, which on cooling transforms into a banded martensite by shear with or without working, deformed after appropriate heat treatment so that on reheating it at least partly resumes its original shape. It is preferred to use a copperbase alloy which transforms into a martensite of pseudocubic symmetry.

We claim: 
     
       1. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy comprising an intermetallic compound of copper which compound undergoes a shear transformation to a banded martensite .Iadd.below the A F  temperature .Iaddend.and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first shape.Iadd., said alloy containing at least 50% by weight of copper in the form of an intermetallic compound and said martensite having pseudo-cubic symmetry. .Iaddend. .[.2. A method according to claim 1 in which the alloy contains at least 50% by weight of copper in the form of an intermetallic compound 
     
     
        and said martensite has pseudo-cubic symmetry..]. 3. A method according to claim .[.2.]. .Iadd.1 .Iaddend.in which the alloy contains zinc, the balance (except for any impurities and incidental constituents which may 
     
     
        be present) being copper. 4. A method according to claim .[.2.]. .Iadd.1 .Iaddend.in which the alloys contains aluminium, the balance (except for any impurities and incidental constituents which may be present) being 
     
     
        copper. 5. A method according to claim .[.2.]. .Iadd.1 .Iaddend.in which the alloy contains aluminium and zinc, the balance (except for any impurities and incidental constituents which may be present) being copper. 
     
     
        . A method according to claim .[.2.]. .Iadd.1 .Iaddend.in which the alloy contains zinc and tin, the balance (except for any impurities and 
     
     
        incidental constituents which may be present) being copper. 7. A method according to claim .[.2.]. .Iadd.`.Iaddend.in which the alloy contains zinc and silicon, the balance (except for any impurities and incidental 
     
     
        constituents which may be present) being copper. 8. A method according to claim .[.2.]. .Iadd.1 .Iaddend.in which the alloy contains aluminium and manganese, the balance (except for any impurities and incidental 
     
     
        constituents which may be present) being copper. 9. A method according to claim .[.2.]. .Iadd.1 .Iaddend.in which the alloy contains aluminium and iron, the balance (except for any impurities and incidental constituents 
     
     
        which may be present) being copper. 10. A method according to claim 1 in which said rate of cooling and lower temperature are such that the alloy has undergone a shear transformation to a banded martensite before being 
     
     
        plastically deformed into said second shape. 11. A method according to claim 1 in which said rate of cooling and lower temperature are such that the alloy retains its first temperature structure or a related ordered structure at said lower temperature and the plastic deformation into said 
     
     
        second shape causes a shear transformation into a banded martensite. 12. A method according to claim 11 in which after deformation into said second shape the alloy is cooled to below the temperature at which transformation 
     
     
        into martensite would have been caused by cooling alone. 13. A method according to claim 1 including the step of raising the temperature of the alloy after it has been deformed into said second shape so that it changes 
     
     
        shape towards said first shape. 14. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy comprising an intermetallic compound of silver which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on 
     
     
        reheating the article at least partly resumes its first shape. 15. A method according to claim 14 in which the alloy contains not more than 10% 
     
     
        by weight of aluminium. 16. A method according to claim 14 in which the 
     
     
        alloy contains not more than 55% by weight of cadmium. 17. A method according to claim 14 in which the alloy contains not more than 30% by 
     
     
        weight of magnesium. 18. A method according to claim 14 in which the alloy 
     
     
        contains not more than 50% by weight of platinum. 19. A method according to claim 14 in which the alloy contains not more than 46% by weight of 
     
     
        zinc. 20. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a gold-aluminium intermetallic compound containing not more than 4% by weight of aluminium which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 21. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a gold-indium intermetallic compound containing not more than 12% by weight of indium which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 22. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a gold-magnesium intermetallic compound containing not more than 15% by weight of magnesium which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 23. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a gold-manganese intermetallic compound containing not more than 38% by weight of manganese which compound undergoes a shear trasnsformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 24. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a gold-zinc intermetallic compound containing not more than 30% by weight of zinc which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 25. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a gold-copper intermetallic compound containing not more than 80% by weight of gold which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 26. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of a cobalt-platinum intermetallic compound containing not more than 30% by weight of cobalt which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 27. A method of making a heat-recoverable article, which method comprises cooling an alloy in a first shape from a first temperature to a lower temperature, said alloy consisting of an iron-platinum intermetallic compound containing not more than 30% by weight of iron which compound undergoes a shear transformation to a banded martensite and which compound in the cooled condition has an anomalously low modulus of elasticity during loading, and then plastically deforming the alloy into a second shape at the lower temperature, the temperature and rate of cooling being such that on reheating the article at least partly resumes its first 
     
     
        shape. 28. A heat-recoverable article made by the method according to 
     
     
        claim 1. 29. Apparatus including a heat-recoverable article according to claim 28, the article performing a function in said apparatus by virtue of its property of changing shape with temperature. .Iadd. 30. A thermally actuated device comprising at least one element consisting of an intermetallic compound containing at least 60 weight percent of copper which has been plastically deformed at a first temperature and which has the capability of retaining the deformed shape until heated to a predetermined transition temperature at which it reverts back to its original shape, said intermetallic compound having a crystal structure which below the said transition temperature has a pseudo -cubic symmetry and an atomic packing density which is higher than the atomic packing density above the said transition temperature. .Iaddend..Iadd. 31. A thermally actuated device as claimed in claim 30 in which the crystal structure of said intermetallic compound, below said transition temperature, has a dodecahedral atom arrangement. .Iaddend. .Iadd. 32. A thermally actuated device comprising at least one element consisting of an intermetallic compound containing at least 60 weight percent of copper which has been plastically deformed at a first temperature and which has the capability of retaining the deformed shape until heated to a predetermined transition temperature at which it reverts back to its original shape, said intermetallic compound having a crystal structure which below the said transition temperature has an atomic packing density which is higher than the atomic packing density above the said transition temperature, said intermetallic compound being a binary copper-aluminum alloy containing 10.0 to 13.0 weight percent aluminum. .Iaddend..Iadd. 33. A thermally actuated device comprising at least one element consisting of an intermetallic compound containing at least 60 weight percent of copper which has been plastically deformed at a first temperature and which has the capability of retaining the deformed shape until heated to a predetermined transition temperature at which it reverts back to its original shape, said intermetallic compound having a crystal structure which below the said transition temperature has an atomic packing density which is higher than the atomic packing density above the said transition temperature, said intermetallic compound being a binary copper-zinc alloy containing 38.6 to 41.5 weight percent zinc. .Iaddend. .Iadd. 34. A thermally actuated device comprising at least one element consisting of an intermetallic compound containing at least 50 weight percent of copper which has been plastically deformed at a first temperature and which has the capacity of retaining the deformed shape until heated to a predetermined transition temperature at which it reverts back to its original shape, said intermetallic compound having a crystal structure which below the said transition temperature has an atomic packing density which is higher than the atomic packing density above the said transition temperature. .Iaddend. .Iadd. 35. A thermally actuated device comprising at least one element consisting of an intermetallic compound containing at least 50 weight percent of copper which has been plastically deformed at a first temperature and which has the capability of retaining the deformed shape until heated to a predetermined transition temperature at which it reverts back to its original shape, said intermetallic compound having a crystal structure which below the said transition temperature has an atomic packing density which is higher than the atomic packing density above the said transition temperature, said intermetallic compound being a binary copper zinc alloy containing 38.6 to 41.5 weight percent zinc. .Iaddend.