Short-range order and its impact on the CrCoNi medium-entropy alloy

Traditional metallic alloys are mixtures of elements in which the atoms of minoriety species tend to be distributed randomly if they are below their solubility limit, or to form secondary phases if they are above it. The concept of multiple-principal-element alloys has recently expanded this view, as these materials are single-phase solid solutions of generally equiatomic mixtures of metallic elements. This group of materilas has received much interest owing to their enhanced mechanical properties. They are usually called MEA in ternary systems and HEA in quaternary or quinary systems, alluding to theri high degree of configurational entropy. However, the question has remined as to how random these solild solutions actually are, with the influence of short-range order being suggested in computational simulations but not seen experimentally. Here we report the observation, using energy-filtered TEM of structure features attibuted to short range order in the CrCoNi MEA. Increasing amounts of such order give rise to both higher stacking fault energy and hardness. These findings suggest that the degree of local ordering at the nanmetre scale can be tailored through thermomechanical processing, providing a new avenue for tuning the mechanical properties of MEAs and HEAs

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Recommended citation: Ruopeng Zhang, Shiteng Zhao (contributed equally),Jun Ding, Yan Chong, Tao Jia, Colin Ophus, Mark Asta, Robert Ritchie, Andrew Minor. (2020). “Short-range order and its impact on the CrCoNi medium-entropy alloy.” Nature. 581(283-287).