Developing Superplasticity in High-Entropy Alloys Processed by Severe Plastic Deformation
High-entropy alloys (HEAs) are currently attracting much interest because they offer unique properties and good ductility at low temperatures. These materials are of interest primarily because they contain five or more principal elements, with each element having a concentration between 5 and 35 at. %, and yet they have very simple structures based on solid solution phases. Superplasticity is defined formally as a tensile elongation without failure of at least 400% and very recent experiments have shown that the HEAs also have a potential for exhibiting superplastic ductilities when testing at elevated temperatures. Since superplasticity requires a very small grain size, typically <10 μm, it is feasible to process HEAs using severe plastic deformation in order to introduce significant grain refinement. The objective of this review is to summarize the recent results showing superplasticity in HEAs and to compare directly the superplastic flow in HEAs and superplasticity in conventional metallic alloys.