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

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 degrees C temperature range (1 h). Regardless of the CR intensity, Ti-Nb-Zr samples subjected to 600 degrees 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 similar to 100 nm). The second batch was atomized to produce 100-mu m-size powders in order to manufacture open-cell porous material (cell size vary from 136 to 561 mu m) 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 degrees 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 degrees 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. (C) 2012 V. Brailovski. Published by Elsevier B.V. All rights reserved.