Molten Salt Electrochemical Synthesis, Heat Treatment and Microhardness of Ti–5Ta–2Nb Alloy

Abstract

Alloy of composition Ti–5Ta–2Nb (numbers in mass%) was synthesised directly from the corresponding mixed metal oxides via the FFC-Cambridge process. Compacted powder discs of TiO₂–Ta₂O₅–Nb₂O₅ were cathodically polarised against a graphite anode in a molten CaCl₂ electrolyte, and the effect of various process parameters on the synthesis of the alloy was investigated. The samples retained their disc-type shape throughout the oxide-to-metal conversion under appropriate processing conditions. XRD analysis showed that the electrochemically prepared alloy existed as single-phase α-Ti and changed into dual-phase (α+β)-Ti upon heat treatment. SEM/EDX analysis revealed a nodular porous microstructure and confirmed the intended chemical composition. Backscattered SEM analysis after heat treatment provided direct evidence of micron-sized β-phase precipitates at the boundaries of the α-phase particles. Microhardness of the heat-treated alloy compared well with literature data for the same material prepared by conventional metallurgical methods. Overall, the study has demonstrated the feasibility of the single-step electrochemical fabrication of Ti–5Ta–2Nb alloy bodies directly from oxides for structural application.

Schematic representation of synthesis of Ti–5Ta–2Nb alloy by electrochemical deoxidation of metal oxide mixtures in a molten salt for measurement of various properties.