Coherent Nanodispersion-Strengthened Shape-Memory Alloys

Abstract

High-strength, low-hysteresis TiNi-based shape-memory alloys (SMAs) employing fully coherent low-misfit nanoscale precipitates, wherein the precipitate phase is based on an optimized composition for high parent-phase strength and martensite phase stability, and compensating the stored elastic energy through the addition of martensite stabilizers. The alloys, with a yield strength in excess of 1200 MPa, are useful for applications such as self-expanding stents, automotive actuators, and other applications wherein SMAs with high output force and long cyclic life are desired.

1 . A shape memory alloy comprising, in combination: 
 a temperature sensitive alloy characterized by a displacive transformation between a first parent phase and a second product phase, said first parent phase maintaining a deformed shape below the M s  temperature following stress and unloading and transformable to an original shape upon reheating above an A f  temperature;    said alloy further characterized by a coherent, nanodispersion of an additional phase providing a misfit of less than about 2.5% in the lattice structure between the nanodispersion and the parent phase.    
   
   
       2 . The alloy of  claim 1  comprising a CuZnAl combination having a β parent phase and a nanodispersion selected from the group consisting of α or δ phase.  
   
   
       3 . The alloy of  claim 1  comprising a CuAlNi combination and a δ 2  intermetallic nanodispersion.  
   
   
       4 . The alloy of  claim 1  comprising a FeMnSi combination and a NbC nanodispersion.  
   
   
       5 . The alloy of  claim 1  comprising a NiTiAl combination with a Huesler nanodispersion in a B2 parent phase.