Study of new multifunctional shape memory and low elastic modulus Ni-free Ti alloys

Two new Ni-free Ti alloys, Ti-8.8Zr-19.1Nb and Ti-15.7Ta-19.0Nb, have been produced and studied in order to obtain shape memory and low elastic modulus materials for employment in the biomedical field. The new alloys were designed by means of a theoretical molecular orbitals method using nontoxic alloying elements. In the present study, the phases and mechanical properties obtained after solution treatment at 1100 degrees C by 1.5 hours following an ice-water quenching were characterized. Also, special attention on exploring the elastic modulus and shape memory properties via instrumented nanoindentation was given. The microstructural observation revealed beta-grain in both alloys with an average size of 268 and 500 mu m for Ti-15.7Ta-19.0Nb and Ti-8.8Zr-19.1Nb alloys, respectively. This latter presented also fine and disperse plates inside the grains. X-ray results confirmed the existence of beta phase in both alloys and orthorhombic alpha '' phase on Ti-8.8Zr-19.1Nb alloy. A reversible phase transformation was detected by differential scanning calorimetry in the former alloy, which confirms the presence of shape memory effect. The elastic modulus of the new alloys was smaller than the commercial alloys employed as implant materials. Evidence of phase transformation was detected by nanoindentation, as hysteresis loops between unloading/reloading cycles on the P-h curves obtained at nanometer scale. These results suggest the possibility of using instrumented indentation for shape memory characterization.