Tuning The Shape Memory Behavior Of Nitihf Alloys
S. M. Saghaian1, H. Tobe1, H. E. Karaca1, R. Noebe2
1University of Kentucky, Dept. of Mechanical Engr., Lexington, KY, 40504, USA
2NASA Glenn Research Center, M.S. 23-2, Cleveland, OH 44135, USA
Composition alteration and heat treatments can be effectively employed to tune the transformation temperatures and shape memory characteristics of Ni-rich NiTiHf alloys. Extensive thermal, microstructural and mechanical characterization has been conducted to determine the shape memory and superelastic behavior of aged NiTiHf single and polycrystalline alloys. It was found that aged Ni-rich NiTiHf alloys have the ability to recover their shape against high bias stresses (~ 1500 MPa) and can show perfect superelasticity even at stress levels as high as 2000 MPa at temperatures between -40 ºC and 160 ºC. Moreover, heat treatments can be employed to improve the strength of the alloys and to further manipulate the transformation temperatures, strains, hysteresis, and cyclic stability. Addition of quaternary element such as Cu improves its ductility and decreases the thermal hysteresis and transformation temperatures. These alloys can be used as high temperature actuators and sensors as well as dampers and high strength alloys.