Alloy design, micromechanical and macromechanical properties of CoCrFeNiTax eutectic high entropy alloys

Ai, Cheng; He, Feng; Guo, Min; Zhou, Jian; Wang, Zhi Jun; Yuan, Zhanwei; Guo, Yajie; Liu, Yinliang; Liu, Lin

doi:10.1016/j.jallcom.2017.12.015

Cited by 111 publications

(28 citation statements)

References 42 publications

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“…The alloy showed a compressive yield strength (σ 0.2 ) of 517 ± 7 MPa and compressive ultimate strength (σ UTS ) of 1863 ± 12 MPa, with a total compressive fracture strain of ~34%. These compressive properties are superior to the other eutectic compositions as well 14,25 . The compressive fracture surface is shown in Fig.…”

Section: Resultsmentioning

confidence: 81%

Small-scale mechanical behavior of a eutectic high entropy alloy

Muskeri

Hasannaeimi

Salloom

et al. 2020

Sci Rep

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eutectic high entropy alloys, with lamellar arrangement of solid solution phases, represent a new paradigm for simultaneously achieving high strength and ductility, thereby circumventing this wellknown trade-off in conventional alloys. However, dynamic strengthening mechanisms and phaseboundary interactions during external loading remain unclear for these eutectic systems. In this study, small-scale mechanical behavior was evaluated for Alcocrfeni 2.1 eutectic high entropy alloy, consisting of a lamellar arrangement of L1 2 and B2 solid-solution phases. The ultimate tensile strength was 1165 MPa with ductility of ~18% and ultimate compressive strength was 1863 MPa with a total compressive fracture strain of ~34%. Dual mode fracture was observed with ductile failure for L1 2 phase and brittle mode for B2 phase. Phase-specific mechanical tests using nano-indentation and micro-pillar compression showed higher hardness and strength and larger strain rate sensitivity for B2 compared with L1 2. Micro-pillars on B2 phase deformed by plastic barreling while L1 2 micro-pillars showed high density of slip steps due to activation of more slip systems and homogenous plastic flow. Mixed micropillars containing both the phases exhibited dual yielding behavior while the interface between L1 2 and B2 was well preserved without any sign of separation or cracking. Phase-specific friction analysis revealed higher coefficient of friction for B2 compared to L1 2. These results will pave the way for fundamental understanding of phase-specific contribution to bulk mechanical response of concentrated alloys and help in designing structural materials with high fracture toughness. Multi-principal element alloys (MPEAs), also known as high entropy alloys (HEAs), offer a new paradigm in structural alloy design and development owing to their appealing physical and mechanical properties such as high fracture toughness, good wear and fatigue resistance, high strength and good elevated temperature properties 1-3. Several HEA systems have been reported with a single-phase face center cubic (FCC) or body center cubic (BCC) structure 4-6. To concurrently achieve good ductility of FCC HEAs along with high strength of BCC HEAs, eutectic high entropy alloys (EHEAs) have recently been developed to overcome the limitations of single-phase HEAs 7. EHEAs typically consist of a mixture of two solid-solution phases in the form of lamellae or rod-like dispersions in a matrix. To date, several EHEAs have been reported with excellent combination of high strength and ductility including CoFeNi 1.

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Section: Resultsmentioning

confidence: 81%

Small-scale mechanical behavior of a eutectic high entropy alloy

Muskeri

Hasannaeimi

Salloom

et al. 2020

Sci Rep

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show abstract

“…As a result, we estimated that the value of K I for our EHEA should be around ≈10 MPa · m 0.5 . Although this estimation was made on a qualitative basis, however, it is quite impressive compared to the fracture toughness of other Laves phase rich alloys with similar hardness, which is usually below 5 MPa · m 0.5 …”

Section: Resultsmentioning

confidence: 90%

“…It has been demonstrated that the strength and ductility of Laves phase rich EHEAs can be adjusted at user's disposal by changing the volume fraction of Laves phase . For example, Ai et al designed a series of CoCrFeNiTa x ( x = 0.1 to 0.7) alloys and found a eutectic composition at x = 0.43, which is Laves phase‐based composite containing ≈50% C14 Laves phase and ≈50% FCC. As a result, this Laves phase‐based composite exhibited the highest strength with good plasticity.…”

Section: Introductionmentioning

confidence: 99%

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

2018

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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.

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“…Hence, the HEAs had excellent tensile strength, fracture toughness, as well as good toughness at low temperatures [8,9]. The CoCrFeNiTa x HEAs composed of the γ phase of the FCC structure and C14 type Laves phase of the HCP structure exhibited relatively high strength and high plasticity [10]. The yield strength of CoCrFeNiNb 0.25 HEAs increased sharply because of the addition of the Nb element, which was caused by the precipitation strengthening of ductile FCC precipitate with nano basket-weave microstructure, while the ductility of the HEAs slightly decreased [11].…”

Section: Introductionmentioning

confidence: 99%

Effect of annealing heat treatment on microstructure and mechanical properties of nonequiatomic CoCrFeNiMo medium-entropy alloys prepared by hot isostatic pressing

Zhang

Jiang

Sun

et al. 2020

Nanotechnology Reviews

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AbstractIn this study, nonequiatomic Co28.5Cr21.5Fe20Ni26Mo4 medium-entropy alloys (MEAs) were prepared using hot isostatic pressing. The effect of annealing heat treatment on microstructure and mechanical properties of MEAs was investigated. The results showed that the microstructure of as-sintered alloys was mainly composed of the face-centered cubic (FCC) phase and μ phase. The presence of the μ phase could improve the compressive strength of Co28.5Cr21.5Fe20Ni26Mo4 MEAs. Meanwhile, the ductile FCC phase matrix could effectively suppress the propagation of cracks to improve its ductility. Hence, as-sintered MEAs possessed excellent compression properties, and the average compressive strength value was 2,606 MPa when the strain was 50%. Compared with as-sintered MEAs, the phase composition of as-annealed MEAs did not change. The micro-hardness of annealed MEAs was stable compared to as-sintered MEAs (342 HV), and its fluctuation was about ±30 HV. The compressive strength of the annealed MEAs did not alter greatly, and the maximum fluctuation value was only about 6.5%. Hence, Co28.5Cr21.5Fe20Ni26Mo4 MEAs had excellent thermal stability.

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Alloy design, micromechanical and macromechanical properties of CoCrFeNiTax eutectic high entropy alloys

Cited by 111 publications

References 42 publications

Small-scale mechanical behavior of a eutectic high entropy alloy

Small-scale mechanical behavior of a eutectic high entropy alloy

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

Effect of annealing heat treatment on microstructure and mechanical properties of nonequiatomic CoCrFeNiMo medium-entropy alloys prepared by hot isostatic pressing

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