Powder metallurgy (PM) of titanium is a potentially cost-effective alternative to conventional wrought titanium. This article examines both traditional and emerging technologies, including the production of powder, and the sintering, microstructure, and mechanical properties of PM Ti. The production methods of powder are classified into two categories: (1) powder that is produced as the product of extractive metallurgy processes, and (2) powder that is made from Ti sponge, ingot, mill products, or scrap. A new hydrogen-assisted magnesium reduction (HAMR) process is also discussed. The mechanical properties of Ti-6Al-4V produced using various PM processes are analyzed based on their dependence on unique microstructural features, oxygen content, porosity, and grain size. In particular, the fatigue properties of PM Ti-6Al-4V are examined as functions of microstructure. A hydrogen-enabled approach for microstructural engineering that can be used to produce PM Ti with wroughtlike microstructure and properties is also presented.

Molten oxide electrolysis (MOE) is a carbon-free, electrochemical technique to decompose a metal oxide directly into liquid metal and oxygen gas. From an environmental perspective what makes MOE attractive is its ability to extract metal without generating greenhouse gases. Hence, an inert anode capable of sustained oxygen evolution is a critical enabling component for the technology. To this end, iridium has been evaluated in ironmaking cells operated with two different electrolytes. The basicity of the electrolyte has been found to have a dramatic effect on the stability of the iridium anode. The rate of iridium loss in an acidic melt with high silica content has been measured to be much less than that in a basic melt with high calcia content. Electrolysis is being investigated by the steel industry as a carbon-lean route that copes with the potential environmental constraints on emissions.1-3 Of all the new methods under consideration, only molten oxide electrolysis (MOE) produces liquid metal, 4,5 which occurs by the decomposition of iron oxide dissolved in an appropriately designed solvent melt according toThe reduction mechanism of MOE is similar to that of the HallHéroult process for aluminum production, which consists of the electrolytic decomposition of aluminum oxide dissolved in a molten fluoride solvent comprising cryolite. However, the two processes are fundamentally different with regards to the compensating oxidation reaction at the anode. In the Hall-Héroult cell, oxidation requires the attendant consumption of the carbon anode resulting in the generation of carbon dioxide. In MOE the compensating reaction is the generation of oxygen, which is predicated on the existence of a so-called inert anode whose development is nontrivial given the extreme conditions in the cell including:-temperatures in excess of the melting point of iron (1538 C) -high solubilizing power of a multicomponent oxide melt -evolution of pure oxygen gas at atmospheric pressure.Furthermore, to meet the production requirements of an industrial process, the anode must sustain high current densities, potentially exceeding 1 A cm À2 . Under these conditions, most metals are poor candidates due to the oxidizing atmosphere surrounding the anode and the extreme anodic potential to which the electrode is subjected. Furthermore, passivating oxide layers, which would normally protect a metallic surface, are dissolved by the molten oxide electrolyte resulting in unabated oxidation of the metal. 6,7 Previous work in this laboratory demonstrated that iridium can serve as an oxygen-evolving anode. 4,8 Furthermore, the anodic current density and, hence, the rate of oxygen evolution was found to increase with the optical basicity of the electrolyte at a given value of potential. The focus of the present study is the assessment of the chemical stability of iridium as a function of electrolyte composition. While the cost and scarcity of this metal make it unsuitable for industrial applications, it has a role to play in laboratory-scale studies ...

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