Superelastic Ti-Zr-Nb alloy for spinal rods: technology, microstructure, texture and functional properties
In this study, a novel combinations of radial shear rolling (RSR) and rotary forging (RF) operations at different temperatures were applied to Ti-18Zr-14Nb (at. %) shape memory alloy with the objective to form a long-length bar stock for spinal rods fabrication. Evolutions of the microstructure, crystallographic texture, mechanical properties, and functional fatigue behavior of the fabricated bar stock were monitored along the technological route. Combined hot TMT leads to the formation of a dynamically polygonized substructure of β-phase with a homogeneous across-the-section grain size distribution (d≈34-43 µm). In this structural state, the alloy demonstrates an outstanding functional fatigue resistance. TMT including cold RF and post-deformation annealing results in the formation of the well-developed polygonized substructure in β-phase with nano- to submicrometer-sized subgrains. A beneficial combination of high value of strength-to-modulus ratio with stable functional fatigue behavior was achieved in this structural state.