Study of New Multifunctional Shape Memory and Low Elastic Modulus Ni-Free Ti Alloys

Abstract

Two new Ni-free Ti alloys, , 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°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 b-grain in both alloys with an average size of 268 and 500 lm 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 b phase in both alloys and orthorhombic a¢¢ 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.

Thermoelastic phase transformation in TiNi alloys under cyclic instrumented indentation

“…Phase transformations can be evidenced on the load vs. displacement into surface (P-h) curves as events on the loading and unloading portions, such as pop-in, pop-out or hysteresis loops produced between load and reload cycles [27]. These latter have been well reported by Domnich and Gogotsi in other transforming materials, such as silicon, gallium arsenide and zirconium oxide [28], by Ma and Komvopoulos [29] in TiNi shape memory thin films and by Frick et al [30] in nickel-titanium sub-micron compression pillars.…”

Quantum parameters for guiding the design of Ti alloys with shape memory and/or low elastic modulus

“…displacement into surface (P-h) curves as events on the loading and unloading portions, such as pop-in, pop-out or hysteresis loops produced between load and reload cycles [27].…”

Development of Ti-Nb-Zr shape memory alloys

“…The selection of the alloy's composition was made using the Bo-Md diagram [27] that allows the analysis of the phase stability based on parameters are determined by calculating electronic structures of various alloys by using a molecular orbital method (Discrete-Variational (DV)-Xα cluster method) [28], where:…”

“…1). Such Ti-based alloys, including in the composition elements with full biocompatibility, can also be advantageous due to their elastic modulus, which -in the phase -is significantly lower than the one of the alpha or alpha-beta Ti alloy, currently used in a large number of biomedical applications [27]. The further development of Ti-Nb-Zr shape memory alloys can expand the limits and increase the possibilities for such alloys to be used in practical applications.…”