Effect of Cooling and Annealing Conditions on the Microstructure, Mechanical and Superelastic Behavior of a Rotary Forged Ti-18Zr-15Nb (at. %) Bar Stock for Spinal Implants

In this work, the microstructure, phase state, texture, superelastic and mechanical properties of a Ti-18Zr-15Nb (at. %) shape memory alloy subjected to a combined thermomechanical treatment, including hot rotary forging with either air cooling or water quenching and post-deformation annealing are studied. It was revealed that the main structural component of the deformed and annealed alloy is BCC beta-phase. With an increase in the forging temperature from 600 to 700 degrees C, the average grain size increases from 5.4 to 17.8 mu m for the air-cooled specimens and from 3.4 to 14.7 mu m for the water-quenched specimens. Annealing at 525 degrees C after forging at 700 degrees C with water quenching leads to the formation of a mixed statically and dynamically polygonized substructure of beta-phase. In this state, the alloy demonstrates the best combination of functional properties in this study: a Young's modulus of similar to 33 GPa, an ultimate tensile strength of similar to 600 MPa and a superelastic recovery strain of similar to 3.4%.