Exceptional resistance to grain growth in nanocrystalline CoCrFeNi high entropy alloy at high homologous temperatures

Sathiyamoorthi, Praveen; Basu, Joysurya; Kashyap, Sanjay; Kottada, Ravi Sankar

doi:10.1016/j.jallcom.2015.12.020

Cited by 164 publications

(41 citation statements)

References 28 publications

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“…On one hand, when an atom jumps into a low-energy site, it can be trapped. On the other hand, if the site has a high energy, the atom has a higher chance to hop back to its original site so it does not contribute to diffusion effectively [29]. The combination of both scenarios may (on average) slow down the diffusion, as being demonstrated in the modeling of bulk diffusion in CoCrFeMnNi [30]; we believe that similar mechanisms may also slow down the migration of high-entropy GBs.…”

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 77%

“…An additional scheme/strategy to stabilize nanoalloys is to utilize kinetic effects, which is often coupled with the thermodynamic effects. Multicomponent segregation at GBs may maximize the solute-drag effects, which can be further enhanced through a so-called high-entropy "sluggish kinetics" effect [28,29]. First, a multicomponent alloy with different atomic sizes and bonding characteristics usually has local sites with a wider distribution of metastable energy levels (than those in unary and binary alloys).…”

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

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Stabilization of nanocrystalline alloys at high temperatures via utilizing high-entropy grain boundary complexions

et al. 2016

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Multicomponent alloying can be utilized to enhance the thermal stability of nanocrystalline alloys. The grain boundary energy can be reduced significantly via both bulk and grain-boundary high-entropy effects with increasing temperature at/within the solid solubility limit, thereby reducing the thermodynamic driving force for grain growth. Moreover, grain boundary migration can be hindered by sluggish kinetics. Although nanocrystalline metals can exhibit superior properties such as high strength and hardness [1][2][3][4], their applications are often hindered by the extreme susceptibility to grain growth. For example, nanocrystalline Al, Sn, Pb, and Mg are subjected to grain growth even at room temperature [5][6][7]. There are two general approaches to stabilize nanocrystalline materials against grain growth [8][9][10][11]. First, kinetic stabilization by the solute-drag effects and/or Zener (particle) pinning can slow down grain boundary (GB) migration [12][13][14], which become less effective at high temperatures. Second, thermodynamic stabilization can be achieved by reducing the GB energy (γ GB ) via solute segregation (a.k.a. GB adsorption) to reduce the thermodynamic driving force for grain growth. Specifically, Weismuller originally proposed that an "equilibrium" grain size can be reached when the effective γ GB vanishes [15,16]. Yet, Kirchheim [17] showed that the equilibriumgrain-size binary nanocrystalline alloys generally represent metastable states in supersaturated regions if (and only if) the precipitation is hindered kinetically. In such cases, the kinetic inhibition of the precipitation also becomes more difficult with increasing temperature, triggering abrupt grain growth. These challenges motivate the present study to develop and test new theories and strategies to enhance the thermal stability of nanocrystalline alloys at high temperatures via utilizing highentropy GB complexions (where the term "complexion" refers to an interfacial "phase" that is thermodynamically two-dimensional [18] The Gibbs adsorption theory states:where S XS (entropy) and Γ i (adsorption) are the GB excess quantities, T is temperature, and μ i is the chemical potential of the i-th element. Eq.(1) implies that the GB energy (γ GB ) can be reduced by segregation at a constant T and this effect can be enhanced for multicomponent (high-entropy) GBs under certain conditions. We should note that generally (∂γ GB /∂ T) P , X i N 0 for a specimen of a constant bulk composition (X Bulk i ) due to thermally-induced desorption. In a recent article [26], we proposed that a high-entropy GB effect can be achieved for a saturated specimen (in equilibrium with precipitates), when the bulk composition moves long the solvus line, where the solutes' bulk chemical potentials are pinned by the precipitates so that (∂ γ GB / ∂ T) P , X Bulk i on solvus ≈ (∂ γ GB /∂ T) P , μ i = − S XS ; thus, γ GB can be reduced with increasing temperature for a high-entropy GB with positive and

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Section: Contents Lists Available At Sciencedirectmentioning

confidence: 77%

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

Stabilization of nanocrystalline alloys at high temperatures via utilizing high-entropy grain boundary complexions

et al. 2016

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“…They concluded that both thermodynamics and kinetics effects contribute to the stabilization of NC HEAs. Praveen et al [102] demonstrated an exceptional resistance to grain growth in NC CrFeCoNi HEA at a high homologous temperature of %0.68 T m for a prolonged duration of 600 h. They observed that the average grain size of CrFeCoNi HEA increased from %120 to 260 nm after heat treatment at 900 C for 600 h They attributed the enhanced grain growth resistance to the formation of composite microstructure, due to the unsolicited contamination during processing. The recent overview article by Chokshi [103] on hightemperature deformation in fine-grained HEAs discusses the possible high-temperature deformation mechanisms and also highlights the deformation mechanism maps in fine-grained HEAs.…”

Section: Introductionmentioning

confidence: 99%

“…Manzoni et al [221] attempted to optimize an HEA based on Al-Ti-Cr-Fe-Co-Ni-Cu system for high-temperature applications. They concluded that the Al 10 [102,222] They observed an exceptional resistance to anneal softening at the temperature range of 700-900 C for a prolonged duration of 600 h. It is reported that the fractional decrease in hardness and the increase in grain size after annealing at 700 C for 600 h are negligible. They attributed the remarkable thermal stability of this alloy to the composite microstructure achieved after sintering due to the contamination during synthesis.…”

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confidence: 99%

High‐Entropy Alloys: Potential Candidates for High‐Temperature Applications – An Overview

2017

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Multi-principal elemental alloys, commonly referred to as high-entropy alloys (HEAs), are a new class of emerging advanced materials with novel alloy design concept. Unlike the design of conventional alloys, which is based on one or at most two principal elements, the design of HEA is based on multi-principal elements in equal or near-equal atomic ratio. The advent of HEA has revived the alloy design perception and paved the way to produce an ample number of compositions with different combinations of promising properties for a variety of structural applications. Among the properties possessed by HEAs, sluggish diffusion and strength retention at elevated temperature have caught wide attention. The need to develop new materials for high-temperature applications with superior high-temperature properties over superalloys has been one of the prime concerns of the high-temperature materials research community. The current article shows that HEAs have the potential to replace Ni-base superalloys as the next generation hightemperature materials. This review focuses on the phase stability, microstructural stability, and high-temperature mechanical properties of HEAs. This article will be highly beneficial for materials science and engineering community whose interest is in the development and understanding of HEAs for high-temperature applications.

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“…HEAs also exhibit the inherent potential to be alloyed with high concentrations of Al and/or Cr to promote enhanced oxidation resistances without necessarily forming various intermetallic phases that can be deleterious to strength [5][6][7]. In addition, HEAs have been reported to exhibit sluggish diffusion kinetics [8][9][10] and high thermal stabilities [11][12][13], making them ideal candidates for use in high temperature applications. However, a fundamental understanding of the active oxidation mechanisms are required in order to effectively implement HEAs in these environments.…”

Section: Introductionmentioning

confidence: 99%

Influence of Annealing on the Microstructures and Oxidation Behaviors of Al8(CoCrFeNi)92, Al15(CoCrFeNi)85, and Al30(CoCrFeNi)70 High-Entropy Alloys

Butler

Weaver

2016

Metals

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Abstract:The understanding of the oxidation behaviors of as-cast and annealed high-entropy alloys (HEAs) is currently limited. This work systematically investigates the influence of annealing on the microstructures and oxidation behaviors of AlCoCrFeNi-based HEAs. Annealing was found to alter the distribution of Al-rich phases which caused a change in the oxidation mechanisms. In general, all three of the investigated HEAs displayed some degree of transient oxidation at 1050 • C that was later followed by protective, parabolic oxide growth. The respective oxidation behaviors are discussed relative to existing oxide formation models for Ni-Cr-Al alloys.

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Exceptional resistance to grain growth in nanocrystalline CoCrFeNi high entropy alloy at high homologous temperatures

Cited by 164 publications

References 28 publications

Stabilization of nanocrystalline alloys at high temperatures via utilizing high-entropy grain boundary complexions

Stabilization of nanocrystalline alloys at high temperatures via utilizing high-entropy grain boundary complexions

High‐Entropy Alloys: Potential Candidates for High‐Temperature Applications – An Overview

Influence of Annealing on the Microstructures and Oxidation Behaviors of Al8(CoCrFeNi)92, Al15(CoCrFeNi)85, and Al30(CoCrFeNi)70 High-Entropy Alloys

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