Journal
SCIENCE
Volume 378, Issue 6623, Pages 978-+Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.abp8070
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Funding
- US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, through the Damage-Tolerance in Structural Materials program at the Lawrence Berkeley National Laboratory (LBNL) [KC13, DE-AC02-CH11231]
- Multiscale Mechanical Properties and Alloy Design program at the Oak Ridge National Laboratory [ERKCM06]
- Office of Science, Office of Basic Energy Sciences of the US Department of Energy [DE-AC02-05CH11231]
- UK Engineering and Physical Sciences Research Council [EP/N004493/2, EP/T000368/1]
- ARC Future Fellowship [FT190100484]
- UNSW Scientia Fellowship
- Australian Research Council [FT190100484] Funding Source: Australian Research Council
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This study found that CrCoNi alloy displays exceptional crack growth toughness at 20 Kelvin, with high crack-initiation fracture toughness values and crack growth toughness values. The crack-tip deformation structures at 20 K involve nucleation and restricted growth of stacking faults, fine nanotwins, and transformed epsilon martensite, with coherent interfaces.
CrCoNi-based medium- and high-entropy alloys display outstanding damage tolerance, especially at cryogenic temperatures. In this study, we examined the fracture toughness values of the equiatomic CrCoNi and CrMnFeCoNi alloys at 20 kelvin (K). We found exceptionally high crack-initiation fracture toughnesses of 262 and 459 megapascal-meters(1/2) (MPa center dot m(1/2)) for CrMnFeCoNi and CrCoNi, respectively; CrCoNi displayed a crackgrowth toughness exceeding 540 MPa center dot m(1/2) after 2.25 millimeters of stable cracking. Crack-tip deformation structures at 20 K are quite distinct from those at higher temperatures. They involve nucleation and restricted growth of stacking faults, fine nanotwins, and transformed epsilon martensite, with coherent interfaces that can promote both arrest and transmission of dislocations to generate strength and ductility. We believe that these alloys develop fracture resistance through a progressive synergy of deformation mechanisms, dislocation glide, stacking-fault formation, nanotwinning, and phase transformation, which act in concert to prolong strain hardening that simultaneously elevates strength and ductility, leading to exceptional toughness.
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