Hot 3-roll longitudinal rolling and tension straightening of a superelastic Ti-Zr-Nb alloy for orthopedic implants: Microstructure, texture, mechanical and functional properties

In this study, a novel high-temperature thermomechanical treatment (HTMT) protocol, including hot longitudinal 3-roll (triangular -triangular -circular) rolling (LR) followed by hot tension straightening (HTS), was applied to Ti-18Zr-15Nb (at. %) shape memory alloy with the objective of forming long-length bar stock for the production of orthopedic implants. Evolutions of the microstructure, texture, mechanical and functional properties of the fabricated bar stock were monitored along the technological workflow. During LR, the microstructure and hardness distributions across the bar cross-section were nonuniform and correlated with the stress/strain field distribution in each LR caliber. LR led to the formation of a predominantly dynamically polygonized substructure inside elongated beta-phase grains parallel to the rolling direction and this substructure manifested a [101] beta crystallographic texture that coincided with the maximum value of a theoretical recovery strain. Next, HTS, aimed at achieving the desired bar geometry, led to the partial recrystallization of strengthened bars in their peripheral layers, while preserving a favorable [101] beta texture in their central parts. Although HTS slightly reduced the mechanical and functional properties of a semi-product, they remained the highest reclaimed to date for this alloy ( UTS = 678 MPa, epsilon r se max = 3.5 %, E = 45 GPa). Therefore, the HTMT+HTS workflow proposed in this work can be considered promising for the production of long-length bar stocks for orthopedic implants.