Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures

B. Gludovatz,A. Hohenwarter,Keli V. S. Thurston,H. Bei,Zhenggang Wu,E. George,R. Ritchie

Published 2016 in Nature Communications

ABSTRACT

High-entropy alloys are an intriguing new class of metallic materials that derive their properties from being multi-element systems that can crystallize as a single phase, despite containing high concentrations of five or more elements with different crystal structures. Here we examine an equiatomic medium-entropy alloy containing only three elements, CrCoNi, as a single-phase face-centred cubic solid solution, which displays strength-toughness properties that exceed those of all high-entropy alloys and most multi-phase alloys. At room temperature, the alloy shows tensile strengths of almost 1 GPa, failure strains of ∼70% and KJIc fracture-toughness values above 200 MPa m1/2; at cryogenic temperatures strength, ductility and toughness of the CrCoNi alloy improve to strength levels above 1.3 GPa, failure strains up to 90% and KJIc values of 275 MPa m1/2. Such properties appear to result from continuous steady strain hardening, which acts to suppress plastic instability, resulting from pronounced dislocation activity and deformation-induced nano-twinning. High-entropy alloys derive their properties from being multi-element systems that can crystallize as a single phase. Here, the authors examine a medium-entropy alloy, CrCoNi, which displays strength-toughness properties exceeding those of high-entropy alloys and resulting from steady strain hardening.

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