Effect of a combined thermomechanical treatment on the microstructure, texture and superelastic properties of Ti-18Zr-14Nb alloy for orthopedic implants

Abstract

In this study, different thermomechanical treatment (TMT) routes, combining hot, warm and cold rotary forging with post-deformation annealing at different temperatures, were applied to Ti-18Zr-14Nb shape memory alloy to study the influence of these TMTs on the phase composition, structure, texture, mechanical properties, and superelastic behavior of long-length rod stock for fabrication of load-bearing orthopedic implants. The warm and hot forging routes led to the formation of a dynamically recrystallized structure, most likely combined with a dynamically polygonized structure, with an average β-phase grain size of 9 μm (warm forging) and 30 μm (hot forging). After the combination of warm/hot and cold forging with annealing at 525 °С, the alloy exhibited a polygonized β-phase substructure and the best combination of functional properties: low Young’s modulus (37 GPa), large difference between the dislocation and transformation yield stresses (320 GPa), and significant total amount of superelastic and elastic recovery strains (∼4%).