Solid State Manufacture of High Entropy Alloys-Preliminary Studies
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Solid State Manufacture of High Entropy Alloys-Preliminary Studies M B D Ellis and G R Doughty Metalysis Ltd, Unit 2, Farfield Park, Manvers Way, Wath-upon-Dearne, Rotherham, S63 5DB, UK Abstract For the past ten years Metalysis have produced tantalum, titanium and titanium alloy powders for high performance applications using their solid state salt electrolysis process. This low energy and environmentally friendly process is now being used to manufacture the next generation of High Entropy Alloys (HEAs). In most cases the manufacture of HEAs involves high temperatures which put all of the alloying elements into the liquid phase. This can lead to numerous problems and restrict the number of HEAs which can be made, particularly the alloys where one needs to combine low melting point elements with refractory elements and also where there are significant liquid density differences between the constituents causing melt segregation. The aim is to present the preliminary work carried out by Metalysis and to show how the solid state diffusion process based on molten salt electrolysis lends itself to the industrial scale manufacture of the next generation of HEAs. This study will focus on the HEAs whose constituent alloying elements have large differences in both their melting points and liquid densities, for example, chromium, niobium, tantalum, titanium and aluminum. Introduction High Entropy alloys (HEAs), also known as multi-principal element alloys (MPEAs) and complex, concentrated alloys (CCAs), have been around for many years. HEAs are normally made utilising a variety of techniques [1]. These are broken into liquid, solid state and vapour techniques. Due to casting constraints in the liquid phase, solid state methods are gaining favour amongst manufacturers, especially where ‘unachievable’ alloys can be fabricated. The Metalysis process is well suited to the manufacture of HEAs, including the more difficult to make alloys. This paper presents some preliminary work which looks at the solid state manufacture of a quinternary AlTiCrNbTa HEA. The Metalysis Process The Metalysis disruptive technology can transform the way metals, metallic alloys and HEAs will be produced in the future. Its clean, green technology has the potential to substantially lower the cost of production in multi-billion dollar markets. Metalysis have developed a unique electrolytic technology with a wide applicability across the periodic table, and is actively developing this potential. The process (Figure 1) involves introducing an oxide to the cathode of an electrochemical cell in a bath of molten calcium chloride at a temperature of around 800-1000˚C. The passage of current causes the oxygen in the metal oxide to be ionized and it migrates to the carbon anode where it reacts to form CO/CO2. If pure metallic oxide is used a pure metal is produced. Alternatively, a mixture of oxides can be placed on the cathode and the product will be an alloy.
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