Hierarchical Eutectic Structure Enabling Superior Fracture Toughness and Superb Strength in CoCrFeNiNb0.5 Eutectic High Entropy Alloy at Room Temperature

Abstract

Laves phase is hard but notorious for its brittleness at a low temperature. Over the past decades, a great deal of efforts is paid to toughen Laves phase by forming Lave phase-based metal-metal composites. In this work, the authors demonstrate that, through the mixing of carefully selected elements, one can obtain the CoCrFeNiNb0.5 eutectic high entropy alloy (EHEA), which exhibits a hierarchical eutectic lamellar structure consisting of Laves and face centered cubic (FCC) phases mixed in a nearly equal volume fraction. Compared to the conventional Laves phase matrix composites, their EHEAs possess a unique combination of superb hardness (%9.2 GPa) and superior fracture toughness (%15 MPa Á m 0.5 ) at room temperature. Through the combined experiments and modeling, the authors are able to show quantitatively this high fracture toughness is derived from the hierarchical eutectic structure and the interplay of a series of extrinsic and intrinsic toughening mechanisms, which are strongly dependent on local lamellar size and orientation. At the fundamental level, their current research demonstrates that the tradeoff between strength and fracture toughness, as commonly perceived for conventional alloys, may be evaded in chemically complex alloys through the formation of hierarchical eutectic structures.

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

“…Laves phase (see, for example, [554,557,1071,[1077][1078][1079][1080]) as well as fcc ? Laves phase (see, for example, [553,[1081][1082][1083][1084][1085][1086][1087][1088][1089][1090]) two-phase HEAs were reported in the literature. Sometimes ordering of the solid solution phase is observed as, for example, B2ordering of the bcc solid solution in B2 ?…”

High Entropy Intermetallic–Oxide Core–Shell Nanostructure as Superb Oxygen Evolution Reaction Catalyst

“…[ 12 ] Recently, a similar design principle was proposed by metallurgists to enhance the chemical complexity of alloys through the synthesis of multi‐principal element alloys, also known as high entropy alloys (HEAs), [ 13,14 ] for enhanced mechanical properties. [ 13,15,16 ] In addition, some HEAs also show promising functional properties, such as super‐paramagneticity and superconductivity. [ 17,18 ] Interestingly, it is noteworthy that most HEAs reported so far contain active transition metals, [ 19 ] such as Ni, Co, and Fe, which are commonly used for electrochemical catalysis; however, to our best knowledge, the research on HEAs for electrocatalysis is still rare.…”

Phase Engineering of High‐Entropy Alloys

“…Similarly, Yang et al designed a hierarchical eutectic lamellar HEA consisting of Laves and FCC phases. [145] The HEAs exhibited high fracture toughness (≈15 MPa m 1/2 ) due to the hierarchical eutectic structure and toughening mechanisms. Liu et al realized a novel design to effectively address the strength-ductility tradeoff.…”

“…Ultimately, the HEAs exhibited a desirable strength–ductility balance, where the yield strength reached to 1.5 GPa and the ductility up to 14%. Similarly, Yang et al designed a hierarchical eutectic lamellar HEA consisting of Laves and FCC phases 145. The HEAs exhibited high fracture toughness (≈15 MPa m 1/2 ) due to the hierarchical eutectic structure and toughening mechanisms.…”