Effect of Nb on phase composition, microstructure and corrosion resistance of electrochemically synthesised porous Ti-xNb-13Zr for use as a bio-alloy

Abstract

Porous Ti-xNb-13Zr alloys (x = 13, 24, 35 mass%) have been synthesised from TiO2-Nb2O5-ZrO2 oxide discs by molten salt electro-deoxidation at 1173 K. The aim has been to assess the dependence of the alloys’ phase composition, microstructure, chemical homogeneity, oxidation resistance and corrosion resistance on their Nb contents. Phase analysis revealed that Ti-xNb-13Zr alloys with 13 and 24 mass% Nb were α/β-alloys, whereas the alloy with the highest content of 35 mass% had exclusively the β-structure. The alloys displayed significant open porosities of 50–54 %; particle size increased with increase in Nb content from 13 to 24 mass% and then decreased with further increase to 35 mass%; and the distribution of Ti, Nb and Zr was uniform. Thermokinetic examination of the alloys in air showed that the oxidation was slowest for Ti‐24Nb‐13Zr which was due to its comparatively larger particles. Open circuit potential measurements in Hanks’ simulated body fluid solution and surface spectroscopic characterisation of a long-term immersed sample indicated the formation of a passive oxide film and a hydroxyapatite layer on the surface. Overall, the study has brought out that the Nb content of the alloys has a crucial influence on all of the above properties.

Keywords

• Titanium alloy
• Biomedical alloy
• Electro-deoxidation
• FFC-Cambridge process
• Phase composition
• Oxidation resistance