Molten salt electrochemical synthesis, heat treatment and microhardness of Ti5Ta2Nb alloy

Abstract

Alloy of composition Ti5Ta2Nb (numbers in mass%) was synthesised directly from the corresponding mixed metal oxides via the FFC-Cambridge process. Compacted powder discs of TiO 2 Ta 2 O 5 Nb 2 O 5 were cathodically polarised against a graphite anode in a molten CaCl 2 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 ¡-Ti and changed into dual-phase (¡+¢)-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 ¢-phase precipitates at the boundaries of the ¡-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 Ti5Ta2Nb alloy bodies directly from oxides for structural application.