Rapid Solidification of High Entropy Alloys

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High entropy alloys (HEA's) are an exciting new class of metallic materials in which typically 5 or more constituent elements are combined in approximately equal quantities. They represent a paradigm shift from conventional alloy metallurgy, in which small additions are made to a single, dominant, base element, usually with the intention of improving one or more of the alloys properties. Remarkably, despite their chemical complexity, such HEA's are structurally very simple, generally containing just one, or at most two, simple crystalline phases. This is again in contrast to conventional alloys which may contain dozens of both desired and spurious intermetallic phases, often with complex crystal structures. High entropy alloys possess a number of remarkable mechanical properties, including the retention of high yield strengths at elevated temperature. Consequently, multiple applications have been proposed. In this research we will look at a range of HEA's, studying the phase composition, microstructure and mechanical properties as a function of both composition and cooling rate, with drop-tube experiments giving access to cooling rates in the range 500-80,000 K s-1. A range of analytical technique will be used to characterise the resulting materials, including SEM, TEM, X-ray diffraction and mechanical testing.