Process for conditioning shape memory alloys

Details Process for conditioning shape memory alloys Process for conditioning shape memory alloys

1998-05-26

2000-11-21

Ip, Sikyin

Metal treatment

Process of modifying or maintaining internal physical...

Heating or cooling of solid metal

337139, 337140, C21D 1000

Patent

active

061497428

ABSTRACT:
A process for conditioning shape memory alloys is disclosed. The process preferably includes force application/release cycling of a shape memory alloy at a temperature above the martensitic-austenitic transformation (A.sub.f) finish temperature of the alloy, but below the maximum temperature at which an austenitic-martensitic transformation will be effected by the force application. The alloy is preferably cold-worked and annealed prior to force application/release cycling. The invention yields greater control over martensitic-austenitic and austenitic-martensitic transformation temperatures and yields reduced hysteresis variability. In certain disclosed embodiments a TiNi or CuAl containing alloy may be cold-worked between about 20% and 45%, and annealed to maintain between about 3% and 8% of the cold working. The alloy may then be heated to between about A.sub.f and 5.degree. C. and A.sub.f 15.degree. C. and conditioned via the application/release of a force for at least about 50 cycles, wherein an austenitic-martensitic phase transformation is induced. The conditioned alloy may then be cooled and integrated into an application mechanism for subsequent selective activation upon heating.

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