Solution heat treatment of Ti-Nb alloys using a molten salt shield

Ti-Nb alloys have attracted growing attention for biomedical implant application due its low elastic modulus. Nb is a β-stabilizer in Ti alloys and retains its high biocompatibility. Thermal treatment plays a key role for optimization of mechanical properties and microstructure of Ti-Nb alloys. However, high oxygen affinity of Ti alloys requires the use of a protective atmosphere during their processing at high temperatures. In this context, we propose the use of molten salt as novel atmosphere protection during solution heat treatment of Ti-Nb alloys avoiding elaborated encapsulation. For that, Ti-Nb parts were solution treated in molten KCl followed by water quenching. Microstructure and phase transformation were evaluated by SEM, EDS, X-ray Diffraction, Elastic Modulus and Vickers microhardness measurements. No evidence of oxidation of Ti-Nb parts was found, which suggested that molten salt was an effective measure to protect Ti alloys from oxidation. After treatment, a martensitic microstructure was achieved. A martensitic structure enables to decrease elastic modulus to ca. 35 GPa, which can avoid stress shield in the case of bone implant application