The effect of thermomechanical treatment on the mechanical properties and biocompatibility of metastable β Ti-18.4Nb-5Zr alloy

Abstract

In this study, a metastable β titanium alloy, Ti-18.4Nb-5Zr, was designed. After large deformation (94 %) cold rolling, the alloy underwent a short-term annealing and aging treatment (10 min), the microstructural changes and mechanical property effects under deformation and various heat treatment conditions were investigated. The solution treated alloy consists of β and α″ phases and exhibits low yield stress (approximately 110 MPa) along with a pronounced double yielding phenomenon. It was found that during the annealing and aging process, nanoscale α and ω phases were precipitated. Both phases, together with the dislocation introduced by large deformation during cold rolling, effectively enhanced the strength of the alloy. Specifically, the α phase showed a strong correlation with the annealing temperature, and its presence was beneficial for improving the alloy's ductility. On the other hand, the ω phase was primarily influenced by the aging process, with higher aging temperatures promoting the growth of the ω phase, thereby increasing the brittleness of the alloy. The experimental alloy exhibited excellent strength-ductility balance under the 600 °C/10 min annealing + 250 °C/10 min aging conditions, while maintaining a low modulus (48 GPa) and good recoverable strain level. Further cytotoxicity testing on the alloy in this state revealed significant biological medical potential, as it showed favorable results compared to non-toxic pure titanium samples.