Processing and Use Of Nitico High Stiffness Alloys

The industrial and medical device industry trend towards reducing device size while maintaining mechanical properties has led to renewed interest in Nitinol based alloys with increased elastic modulus and higher superelastic plateaus.  NiTiCo is one such alloy.  Previous studies have documented that a 1 to 2 wt.% Co addition increases the modulus approximately 30% compared to binary NiTi.  The microstructural features of the material and the substitution of Co for some of the Ni lattice sites is believed to account for the increased stiffness of the material.  This change in structure necessitates changes in processing steps to achieve similar superelastic properties to binary NiTi.  This study will document the specific thermo-mechanical processing requirements of NiTiCo.  TEM (Transmission Electron Microscopy) analysis will be used to characterize the microstructural features and the substitution of Co for some of the Ni lattice sites.  Rotating beam fatigue data will be analyzed and a method to relate elastic modulus to fatigue results for NiTi alloys will be presented.