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Influence of thermo-mechanical processing on the microstructure, mechanical properties and corrosion behaviour of a new quaternary titanium alloy



A new quaternary Ti–20Nb–10Zr–5Ta alloy was thermo-mechanically processed; applying a stress of 10 ton-forces after heat treatment at 1000 °C it resulted a very homogeneous, fine microstructure characterized by the best mechanical properties: low Young's modulus (60 GPa) and high tensile strength and hardness. The corrosion behaviour of this processed alloy after long-term soaking (5000 h) in simulated human fluid (Ringer solution) was studied. SEM micrographs of as-cast and processed alloy after immersion proved that their surfaces were covered with a layer with a porous microstructure. EDX analysis detected Ca, P, and O as constituent elements of this porous layer. XPS determined the presence of the protective TiO2, Nb2O5, ZrO2, and Ta2O5 oxides and of the hydroxyapatite deposited from solution. All electrochemical parameters exhibited more favourable values for the processed alloy indicating the beneficial influence of the applied treatment. Impedance parameters revealed a nobler behaviour of the processed alloy than of the as-cast one. EIS spectra showed a passive film with two layers: a compact, inner, electronically conducting, barrier layer and an outer, porous layer.