Structure and functional properties of metastable beta Ti-18Zr-14Nb (at.%) alloy for biomedical applications subjected to radial shear rolling and thermomechanical treatment

In this preliminary study, a novel combination of radial shear rolling with thermomechanical treatment including cold rolling and post-deformation annealing at different temperatures was applied to Ti-18Zr-14Nb shape memory alloy with the objective of forming various structures in long-length bars dedicated for bone implants fabrication. The static mechanical properties and the functional fatigue behavior of Ti-18Zr-14Nb alloy in different structural states were studied. The dynamically polygonized substructure of β-phase formed as a result of radial shear rolling led to an outstanding combination of high ductility (δ = 35%) and superior functional fatigue resistance. After additional TMT (CR e = 0.3 + PDA at 500 °C), the alloy exhibited a highly-dislocated nanosubgrained structure of β-phase with subgrain size below 100 nm and a small quantity of α-phase. PDA at 550 °C led to the formation of the polygonized structure in β-phase with nano-to submicrometer-sized subgrains without α-phase present. The latter TMT improved further the functional properties of the alloy, by increasing its strength-to-modulus ratio and ensuring stable functional fatigue behavior with low level of accumulated strain.