Large Diameter Hot Rolled NiTiCo Bars for Civil Engineering Structures

Great efforts have been made to develop and commercialize Nitinol in retrofitting and building new structures to enhance damping capacity in civil engineering applications. Binary Nitinol bars have been studied and a good combination of superelasticity, strength and ductility at room temperature has been obtained through proper thermo-mechanical process. This study is our continuous efforts to develop a new material which can sustain superelastic properties under extreme weather conditions.

Large diameter NiTiCo bars were manufactured through vacuum induction melting and vacuum arc remelting followed by thermal-mechanical processing. Subsequent heat treatment was optimized to obtain excellent mechanical properties. A set of mechanical engineering properties including tensile and cyclic properties were chosen to evaluate the NiTiCo bars for seismic design. Tensile tests were carried out at temperatures ranging from -38^oC to 38^oC and this material exhibits good superelasticity within such a broad testing temperature range. In addition, significant higher yield strength has been achieved in this material compared to binary Nitinol. Microstructure characterization and phase transformation tests confirmed the effect of heat treatment on the mechanical behavior.