scholarly journals High-entropy materials for catalysis: A new frontier

2021 ◽  
Vol 7 (20) ◽  
pp. eabg1600
Author(s):  
Yifan Sun ◽  
Sheng Dai
Keyword(s):  
Structural Engineering ◽  
Configurational Entropy ◽  
Side Surface ◽  
Reaction Pathways ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Structures And Properties ◽  
New Frontier ◽  
Simple Systems ◽  
Entropic Effects

Entropy plays a pivotal role in catalysis, and extensive research efforts have been directed to understanding the enthalpy-entropy relationship that defines the reaction pathways of molecular species. On the other side, surface of the catalysts, entropic effects have been rarely investigated because of the difficulty in deciphering the increased complexities in multicomponent systems. Recent advances in high-entropy materials (HEMs) have triggered broad interests in exploring entropy-stabilized systems for catalysis, where the enhanced configurational entropy affords a virtually unlimited scope for tailoring the structures and properties of HEMs. In this review, we summarize recent progress in the discovery and design of HEMs for catalysis. The correlation between compositional and structural engineering and optimization of the catalytic behaviors is highlighted for high-entropy alloys, oxides, and beyond. Tuning composition and configuration of HEMs introduces untapped opportunities for accessing better catalysts and resolving issues that are considered challenging in conventional, simple systems.

scholarly journals Temperature-Dependent Configurational Entropy Calculations for Refractory High-Entropy Alloys

2021 ◽  
Author(s):  
Chiraag M Nataraj ◽  
Axel van de Walle ◽  
Amit Samanta
Keyword(s):  
Cluster Expansion ◽  
Configurational Entropy ◽  
Temperature Limit ◽  
Design Guidelines ◽  
Alloy Design ◽  
Solid Solution Alloy ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Entropy Of Mixing ◽  
The Ideal

AbstractThe cluster expansion formalism for alloys is used to construct surrogate models for three refractory high-entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr). These cluster expansion models are then used along with Monte Carlo methods and thermodynamic integration to calculate the configurational entropy of these refractory high-entropy alloys as a function of temperature. Many solid solution alloy design guidelines are based on the ideal entropy of mixing, which increases monotonically with $$N$$ N , the number of elements in the alloy. However, our results show that at low temperatures, the configurational entropy of these materials is largely independent of $$N$$ N , and the assumption described above only holds in the high-temperature limit. This suggests that alloy design guidelines based on the ideal entropy of mixing require further examination.

scholarly journals Computational property predictions of Ta–Nb–Hf–Zr high-entropy alloys

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shashank Mishra ◽  
Soumyadipta Maiti ◽  
Beena Rai
Keyword(s):  
Shear Stress ◽  
Yield Strength ◽  
Configurational Entropy ◽  
Annealing Treatment ◽  
Nuclear Radiation ◽  
Solid Solution Alloy ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Principal Axes ◽  
Edge Dislocations

AbstractRefractory high entropy alloys (R-HEAs) are becoming prominent in recent years because of their properties and uses as high strength and high hardness materials for ambient and high temperature, aerospace and nuclear radiation tolerance applications, orthopedic applications etc. The mechanical properties like yield strength and ductility of TaNbHfZr R-HEA depend on the local nanostructure and chemical ordering, which in term depend on the annealing treatment. In this study we have computationally obtained various properties of the equimolar TaNbHfZr alloy like the role of configurational entropy in the thermodynamic property, rate of evolution of nanostructure morphology in thermally annealed systems, dislocation simulation based quantitative prediction of yield strength, nature of dislocation movement through short range clustering (SRC) and qualitative prediction of ductile to brittle transition behavior. The simulation starts with hybrid Monte Carlo/Molecular Dynamics (MC/MD) based nanostructure evolution of an initial random solid solution alloy structure with BCC lattice structure created with principal axes along [1 1 1], [− 1 1 0] and [− 1 − 1 2] directions suitable for simulation of ½[1 1 1] edge dislocations. Thermodynamic properties are calculated from the change in enthalpy and configurational entropy, which in term is calculated by next-neighbor bond counting statistics. The MC/MD evolved structures mimic the annealing treatment at 1800 °C and the output structures are replicated in periodic directions to make larger 384,000 atom structures used for dislocation simulations. Edge dislocations were utilized to obtain and explain for the critically resolved shear stress (CRSS) for the structures with various degrees of nanostructure evolution by annealing, where extra strengthening was observed because of the formations of SRCs. Lastly the MC/MD evolved structures containing dislocations are subjected to a high shear stress beyond CRSS to investigate the stability of the dislocations and the lattice structures to explain the experimentally observed transition from ductile to brittle behavior for the TaNbHfZr R-HEA.

scholarly journals The formation and stability of bulk amorphous and high entropy alloys

2021 ◽  
Vol 4 (1) ◽  
pp. 51-57
Author(s):  
Attila Szabó ◽  
Krisztián Bán ◽  
József Hlinka ◽  
Judit Pásztor ◽  
Antal Lovas
Keyword(s):  
Amorphous Alloys ◽  
Configurational Entropy ◽  
Temperature Stability ◽  
High Entropy Alloy ◽  
Alloy Formation ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Phase Stabilization ◽  
Fcc Phase

Abstract Two kinds of phase stabilization mechanism are discussed and compared: the first is characteristic of the formation of bulk amorphous alloys, in which the high supercooling ability of multicomponent liquids is responsible for the glassy phase stabilization. Here the hindered nucleation of crystalline phases is the center phenomenon. The origin of this hindering is the slowing atomic mobility in the supercooling melt. In contrast the melt supercooling is negligible during the high entropy alloy formation. It is believed that stability of the crystalline single fcc phase is the consequence of the characteristic of high configurational entropy at high temperatures. However, the significance of this entropy-dominated stabilization is overestimated in several references. It has been concluded that transition metal contraction (arising from the d electron participation in the overall bonding state) does also contribute to the high temperature stability of fcc single phase in the high entropy alloys.

scholarly journals Kinetically Limited Phase Formation of Pt-Ir Based Compositionally Complex Thin Films

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2298
Author(s):  
Aparna Saksena ◽  
Dimitri Bogdanovski ◽  
Hrushikesh Sahasrabuddhe ◽  
Denis Music ◽  
Jochen M. Schneider
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Surface Diffusion ◽  
Phase Formation ◽  
Single Phase ◽  
Configurational Entropy ◽  
High Entropy Alloys ◽  
X Ray ◽  
High Entropy ◽  
Two Phases

The phase formation of PtIrCuAuX (X = Ag, Pd) compositionally complex thin films is investigated to critically appraise the criteria employed to predict the formation of high entropy alloys. The formation of a single-phase high entropy alloy is predicted if the following requirements are fulfilled: 12 J∙K−1 mol−1 ≤ configurational entropy ≤ 17.5 J∙K−1 mol−1, −10 kJ∙mol−1 ≤ enthalpy of mixing ≤ 5 kJ∙mol−1 and atomic size difference ≤ 5%. Equiatomic PtIrCuAuX (X = Ag, Pd) fulfill all of these requirements. Based on X-ray diffraction and energy-dispersive X-ray spectroscopy data, near-equiatomic Pt22Ir23Cu18Au18Pd19 thin films form a single-phase solid solution while near-equiatomic Pt22Ir23Cu20Au17Ag18 thin films exhibit the formation of two phases. The latter observation is clearly in conflict with the design rules for high entropy alloys. However, the observed phase formation can be rationalized by considering bond strengths and differences in activation energy barriers for surface diffusion. Integrated crystal orbital Hamilton population values per bond imply a decrease in bond strength for all the interactions when Pd is substituted by Ag in PtIrCuAuX which lowers the surface diffusion activation energy barrier by 35% on average for each constituent. This enables the surface diffusion-mediated formation of two phases, one rich in Au and Ag and a second phase enriched in Pt and Cu. Hence, phase formation in these systems appears to be governed by the complex interplay between energetics and kinetic limitations rather than by configurational entropy.

Microstructure and Corrosion Properties Investigations of AlCrNiCuMn High-Entropy Alloy

2015 ◽  
Vol 1128 ◽  
pp. 127-133
Author(s):  
Iulia Florea ◽  
Gheorghe Buluc ◽  
Romeu Chelariu ◽  
Elena Raluca Baciu ◽  
Ioan Carcea
Keyword(s):  
Electron Microscopy ◽  
Configurational Entropy ◽  
Microstructural Characterization ◽  
Electron Gun ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Corrosion Properties ◽  
High Entropy ◽  
Disordered Structures ◽  
Corrosion Resistance Property

Using new high entropy alloy with chemical formula AlCrNiCuMn produced by high technology (induction melt method), in manufacture of new composite materials will enable the creation of new structures resistant to stress used dynamic collective protection. Specify that High Entropy Alloys are characterized as alloys consisting of approximate equal concentrations of at least five metallic elements and are claimed to favor close-packed, disordered structures due to high configurational entropy. In this study, we investigate the microstructure and corrosion properties of AlCrNiCuMn high-entropy alloys. The type of high entropy alloys manufactured was a five-component alloy of AlCrNiCuMn. The microstructure and corrosion resistance property of high-entropy alloys AlCrNiCuMn were determined by scanning electron microscopy and electrochemical workstation. Microstructural characterization was performed by electron microscopy on LMHII VegaTescan equipment using a secondary electron detector (SE) at a voltage of 30 kV electron gun.

scholarly journals Entropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range

Entropy ◽  
2018 ◽  
Vol 20 (9) ◽  
pp. 654 ◽  
Author(s):  
Sebastian Haas ◽  
Mike Mosbacher ◽  
Oleg Senkov ◽  
Michael Feuerbacher ◽  
Jens Freudenberger ◽  
...  
Keyword(s):  
Single Phase ◽  
Configurational Entropy ◽  
Solid Solution Phase ◽  
High Entropy Alloys ◽  
Scanning Calorimetry ◽  
High Entropy ◽  
Thermal Entropy ◽  
Fcc Alloys ◽  
Good Agreement

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy.

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