Mechanical properties of porous metastable beta Ti–Nb–Zr alloys for biomedical applications

Highlights: ► Effect of cold rolling and annealing of Ti–Nb–Zr bulk alloys is studied. ► Effect of post-sintering heat treatment of Ti–Nb–Zr foams is studied. ► Cold-rolled and annealed bulk alloy with 100 nm subgrain size is superelastic. ► Cold-rolled and annealed bulk alloy demonstrates high fatigue resistance. ► Ti–Nb–Zr foams show significant softening after post-sintering heat treatment. -- Abstract: For this study, Ti–(20–22)Nb–(5–6)Zr (at%) ingots were manufactured by vacuum and argon arc melting. The obtained ingots were divided into two batches: the first subjected to cold rolling (CR) from 30 to 85% of thickness reduction, and subsequent annealing in the 450–600 °C temperature range (1 h). Regardless of the CR intensity, Ti–Nb–Zr samples subjected to 600 °C annealing showed the highest fatigue resistance during room-temperature cumulative cycling due to the stress-induced martensitic transformation occurring in the polygonized dislocation substructure (average subgrain size ∼ 100 nm). The second batch was atomized to produce 100-μm-size powders in order to manufacture open-cell porous material (cell size vary from 136 to 561 μm) of 46% porosity by means of powder metallurgy using a polymer-based foaming process. Tensile, compression and bending testing were performed at RT on foam samples annealed at 450–600 °C (1 h). Results indicated that Young's modulus of Ti–Nb–Zr foams significantly decreases as compared to the as-sintered material: when annealing temperature increases from 450 to 600 °C, Young's modulus decreases from 10 ± 2 GPa to 6 ± 1 GPa. Under the same testing conditions, Ti-CP foams produced by the same technology and having similar porosity remain fairly insensible to post-sintering annealing