The non-equilibrium response of a high entropy alloy CoCuFeNiTa0.5 has been studied using undercooling as a control parameter. The solidification growth rates are rapid (30–50 m/s) at deep undercooling (&gt;150 °C) and are comparable with conventional alloys. The elemental segregation especially that of Cu as predicted by phase field simulations in lower (&lt;50 °C) undercooling regime matches with the experimental observations. This study indicates that even extreme non-equilibrium conditions during solidification could not avoid elemental segregation at the atomic scale. © 2019 Acta Materialia Inc.

Konda Gokuldoss Pradeep

Department of Metallurgical and Materials Engineering

Phanikumar Gandham

M. R. Rahul

Sumanta Samal

A. Marshal

V. I.Nithin Balaji

Cobalt alloys

Copper

entropy

HIGH-ENTROPY ALLOYS

Iron alloys

Phase separation

Solidification

TANTALUM ALLOYS

Atomic scale

control parameters

Conventional alloys

ELEMENTAL SEGREGATION

GROWTH VELOCITY

Non equilibrium

NONEQUILIBRIUM CONDITIONS

PHASE-FIELD SIMULATION

UNDERCOOLING

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IIT Madras

Scripta Materialia

High entropy alloys (HEAs) are multicomponent alloys in equiatomic or nearly equiatomic composition. Anticipated sluggish atomic diffusion is reported to be one of the core effects in HEAs which is presumably responsible for their many unique properties. For the first time, in the present study, tracer (Ni) diffusion in CoCrFeNi and CoCrFeMnNi alloys is measured by the radiotracer technique in the temperature range of 1073–1373 K using the 63 Ni isotope. Chemically homogeneous alloys of equiatomic composition were prepared by a vacuum arc melting route. The microstructure and phase stability of the alloys in the given temperature range is confirmed by differential thermal analysis and X-ray diffraction. Ni diffusion in both CoCrFeNi and CoCrFeMnNi alloys is found to follow Arrhenius behavior. When plotted against the homologous temperature, a tendency to a successive slow down of the tracer diffusion rate with an increased number of components in equiatomic alloys is unambiguously established. Both the entropy term as well as the energy barriers is revealed to contribute to this trend. The current results indicate that diffusion in HEAs cannot a priori be considered as sluggish. © 2016 Elsevier B.V.

Journal of Alloys and Compounds

Ni tracer diffusion in CoCrFeNi and CoCrFeMnNi high entropy alloys

The decomposition of an equiatomic AlCoCrCuFeNi high-entropy alloy produced by splat quenching and casting was investigated by the analytical high resolution methods: transmission electron microscopy and three-dimensional atom probe. It could be shown that splat-quenched alloy consisted of an imperfectly ordered body-centred cubic phase with a domain-like structure, whereas normally cast alloy formed several phases of cubic crystal structure. The cast alloy decomposed into both dendrites and interdendrites. A detailed local compositional analysis carried out by atom probe within the dendrites revealed that the alloying elements in the Ni-Al-rich plates and Cr-Fe-rich interplates are not randomly distributed, but segregate and form areas with pronounced compositional fluctuations. Cu-rich precipitates of different morphologies (plate-like, spherical and rhombohedron-shaped) could also be found in the dendrites. The results are discussed in terms of segregation processes governed by the enthalpies of mixing of the binary systems. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Acta Materialia

Decomposition in multi-component AlCoCrCuFeNi high-entropy alloy

Bulk samples of Fe-25 at.% Ge peritectic alloy are undercooled up to 260 K using electromagnetic levitation technique. The growth rate of the primary phase is measured using a capacitance proximity sensor technique. Solidification microstructure is studied as a function of undercooling. The microstructure of samples at low undercoolings consists of a residual primary phase α2, peritectic phase ε and inter-dendritic ε-β eutectic. Microstructure at higher undercoolings is nearly phase-pure ε. Time resolved diffraction analysis of the levitated droplets using synchrotron radiation indicates the nucleation of primary α2 in all cases. The growth rate is analysed using current theories to explain the experimental observations. Interfacial undercooling is found to play an important role in the growth kinetics. Our results also suggest suppression of peritectic reaction. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fulltext

Solidification of undercooled peritectic Fe-Ge alloy

A novel face-centered-cubic high-entropy alloy strengthened by nanoscale precipitates

Metallurgical and Materials Transactions A

Microstructural Quantification of Rapidly Solidified Undercooled D2 Tool Steel

Nano-sized Cu clusters in deeply undercooled CoCuFeNiTa high entropy alloy

Journal	Scripta Materialia
Publisher	Acta Materialia Inc
ISSN	13596462
Open Access	No