Phase-Tunable Fabrication of Consolidated (α+β)-TiZr Alloys for Biomedical Applications through Molten Salt Electrolysis of Solid Oxides

Abstract

Electrochemical reduction of a solid TiO2−ZrO2 mixture (molar ratio = 1:1) to the TiZr alloys in a consolidated porous structure was studied by constant cell voltage electrolysis in molten CaCl2 at 900 °C. For the first time, and surprisingly, it was found that tuning the α- and β-phases in the TiZr alloys could be easily realized by controlling the electrolysis time or, specifically, the oxygen content in the alloys. Oxygen acted as a phase-transition inhibitor from the high-temperature β-TiZr to the low-temperature α-TiZr, leading to metastable β-TiZr or (α+β)-TiZr as the product at room temperature. However, if the oxygen content decreased to <1100 ppm, only α-TiZr was collected, even when the electrolytic alloy was directly quenched in water. The consolidated porous (α+β)-TiZr alloys possessed elastic moduli in the range of 20−40 GPa, matching closely to that of natural bone (10−30 GPa). They also exhibited excellent corrosion resistance in the Ringer solution. These novel findings promise a simple, one-step, low-energy, and environmentally friendly electrochemical process for the production of β-phase containing TiZr alloys as medical implant materials without any added expensive and/or bio-incompatible elements.

Development of the Fray-Farthing-Chen Cambridge Process: Towards the Sustainable Production of Titanium and Its Alloys

“…20,47 It was also noted that the a-and b-phases in the Ti-Zr alloys could be easily tuned by controlling the electrolysis duration, which adjusts the oxygen content in the Ti-Zr alloys. 48 Most recently, the high-entropy alloys (e.g., TiNbTaZr and TiNbTaZrHf) have been fabricated using the FFC-Cambridge process, which further demonstrates its capabilities for alloy making. 83 …”

“…6,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] In the process, the preformed metal compound (e.g., pellet of TiO 2 ) is attached on a cathode which is then electrolysed against a suitable anode under a cell voltage that is high enough to ionise the oxygen in the metal compound without decomposing the electrolyte (e.g., molten CaCl 2 ). The FFC-Cambridge process can be represented by the following reactions where M represents a metal.…”

Near-Net-Shape Production of Hollow Titanium Alloy Components via Electrochemical Reduction of Metal Oxide Precursors in Molten Salts

“…This unusual finding was attributed to the effects of quenching, but more importantly an appropriate amount of oxygen remaining in the alloy might have functioned as an inhibitor to the phase transition at low temperatures. [33] It can be seen in Figures 8(a) through (e) that all electrolytic products retained the original shape of their metal oxide precursors (Figures 1(d) and 4(a)), while some shrinkage happened. The diameter of the electrolytically reduced hollow sphere was about 40 pct less than its metal oxide precursor, i.e., reduced from ca.…”

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

“…27) The process also offers the opportunity of preparing three-dimensional metallic bodies, by using solid oxide bodies of defined geometry as the starting material and maintaining this geometry throughout the reduction. Examples are the near-net-shape fabrication of solid bodies of ¡-Zr and ¡-Zr/Nb, 28) (¡+¢)-Ti/Zr, 29) Ti 6Al4V, 30) and ¢-Ti/Nb. 31) Heat treatment of Ti and its alloys is key to establishing the ratio between the low-temperature ¡-phase and the hightemperature ¢-phase as well as the microstructure.…”