Abstract
High-entropy alloys1–3 are an intriguing new class of metallic materials that
derive their properties not from a single dominant constituent, such as iron in
steels, nor from the presence of a second phase, such as in nickel-base
superalloys, but rather comprise multi-element systems that crystallize as a
single phase4–7, despite containing high concentrations (~20 at.%) of five or
more elements with different crystal structures5–7. Indeed, we have recently
reported on one such single-phase high-entropy alloy, NiCoCrFeMn, which
displays exceptional strength and toughness at cryogenic temperatures8. Here
which displays unprecedented strength-toughness properties that exceed those
of all high-entropy alloys and most multi-phase alloys. With roomtemperature
tensile strengths of almost 1 GPa and KJIc fracture-toughness
values above 200 MPa.m1/2 (with crack-growth toughnesses exceeding 300
MPa.m1/2), the strength, ductility and toughness of the NiCoCr alloy actually
improve at cryogenic temperatures to unprecedented levels of strengths above
1.3 GPa, failure strains up to 90% and KJIc values of 275 MPa.m1/2 (with crackgrowth
toughnesses above 400 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.