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

Abstract

Metal oxide precursors (ca. 90 wt pct Ti, 6 wt pct Al, and 4 wt pct V) were prepared with a hollow structure in various shapes such as a sphere, miniature golf club head, and cup using a one-step solid slip-casting process. The precursors were then electro-deoxidized in molten calcium chloride [3.2 V, 1173 K (900°C)] against a graphite anode. After 24 hours of electrolysis, the near-net-shape Ti-6Al-4V product maintained its original shape with controlled shrinkage. Oxygen contents in the Ti-6Al-4V components were typically below 2000 ppm. The maximum compressive stress and modulus of electrolytic products obtained in this work were approximately 243 MPa and 14 GPa, respectively, matching with the requirement for medical implants. Further research directions are discussed for mechanical improvement of the products via densification during or after electrolysis. This simple, fast, and energy-efficient near-net-shape manufacturing method could allow titanium alloy components with desired geometries to be prepared directly from a mixture of metal oxides, promising an innovative technology for the low-cost production of titanium alloy components.

Electroreduction of Iron(III) Oxide Pellets to Iron in Alkaline Media: A Typical Shrinking-Core Reaction Process

“…The difference between the morphologies of the electroreduction-generated dendritic iron crystals and the initial Fe 2 O 3 powder suggests that the dissolution of Fe 2 O 3 may occur during the electroreduction process. [14] Actually, comparing to the typical current-time curves of the electrodeoxidation of solid oxides in molten salts, [9,24,27,28,53] the current-time curves shown in Figures 5, 8(a), and 11 display a small difference. The currents generated during the electrodeoxidation of solid oxides in molten salts generally increase to their maximum values and then decrease immediately.…”

“…[20][21][22][23][24][25][26][27][28][29][30][31][32] Moreover, the gaseous reduction of iron oxides to metal iron by hydrogen gas has also been recognized as an environmental friendly way. [33][34][35][36] However, high cost of hydrogen production is still a challenge for iron and steel industry.…”

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

“…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.…”

“…To address these issues, the FFC-Cambridge process has therefore been successfully employed to fabricate Ti-W alloys in one step. 34,35,81 Since its initial conception, the FFC-Cambridge process has been used to fabricate numerous titanium alloys, such as Ti-6Al-4V, 36 Ni-35Ti-15Hf, 37 Ti-10V-2Fe-3Al, 20,38 Ti-W 34,35,81 Ti-Ni, 6,[39][40][41] TiFe, [42][43][44][45][46] and Ti-Mo. 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.…”

“…20,28 Another feature of the FFC-Cambridge process is that it proceeds in the solid state, and the electrolytic products retain the shape closely to the original shape of the oxide precursors, although shrinkage would occur. 36,58,84 By taking advantage of this unique ability, different shapes of Ti-6Al-4V components (such as hollow spheres, hollow miniature golf club heads, and cylindrical cups) were produced from their slip-cast oxide precursors. 36 Figure 4 displays the photographs of different nearnet-shape products from the FFC-Cambridge process.…”