Mechanical Performance Improvement by Nitrogen Addition in N-CoCrNi Compositionally Complex Alloys
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RECENTLY, new classifications of alloys called medium-entropy alloys (MEAs) and high-entropy alloys (HEAs) have gained wide attention as one of the latest developments in materials science. MEAs and HEAs exhibit a fundamental characteristic of being composed of numerous elements in an equiatomic or near-equiatomic ratio.[1,2] The mixing of multi-elements in MEAs and HEAs generally results in the formation of a solid-solution phase instead of forming intricate intermetallic compounds as in conventional alloys.[3–5] MEAs and HEAs also tend to possess outstanding properties such as an excellent combination of strength and ductility at very low temperatures,[6,7] outstanding corrosion resistance,[8,9] good magnetic properties,[10] and high wear resistance.[11–14] Various element combinations to construct MEAs and HEAs were discovered previously. Among them, CoCrNi MEA is one of the most prominent MEAs.[15] CoCrNi exhibits outstanding mechanical properties,
DENNIS EDGARD JODI is with the School of Materials Science and Engineering, Yeungnam University, 280 Daehak-ro, Gyeongbuk 38541, Republic of Korea. NURI CHOI and JOOHYUN PARK are with the Department of Materials Engineering, Hanyang University, Republic of Korea. Contact e-mail: [email protected] NOKEUN PARK is with the School of Materials Science and Engineering, Yeungnam University and also with the Institute of Materials Technology, Yeungnam University, 280 Daehak-ro, Gyeongbuk 38541, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted November 12, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
particularly with regard to its strength–ductility balance and fracture resistance at cryogenic temperatures.[15,16] These interesting properties are caused by the early presence of nanotwinning in the matrix of the single face-centered cubic (FCC) phase, which provides a high work-hardening rate and improved ductility.[17,18] On the other hand, the mechanical properties of MEAs and HEAs were reported to decrease under several circumstances, e.g., at elevated temperature conditions.[16] This implied that the sole solid-solution matrix in MEAs and HEAs was not adequate, especially for engineering applications.[19] Therefore, more appropriate strengthening mechanisms are required to resolve this issue. Previously, it was reported that the application of precipitation hardening was feasible to be implemented in the systems of MEA and HEA. For example, the addition of Ti and Al was observed to be able to form nanoscale precipitates on the matrix of MEAs and HEAs, which subsequently improved the mechanical properties considerably.[20,21] This indicated that precipitation hardening, in which the strengthening magnitude in metals and alloys is affected by the precipitate size, fraction, and the complex precipitate–matrix and precipitate–dislocation interaction,[22,23] is highly feasible to be implemented as a potential strengthening mechanism in MEAs and HEAs. On the other hand, the formation of precipitate indicates that the original defin
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