Self-diffusion in ordered pseudo-binary multicomponent aluminides is investigated. Equiatomic substitution of transition metal sublattice in aluminides is performed to produce multicomponent alloys Al(CoNi), Al(FeNi), Al(CoFe), Al(CoFeNi), Al(CoFeMnNi) and Al(CoCuFeMnNi). X-ray diffraction and electron microscopy confirm the presence of single phase ordered BCC structure for all the alloys. Radioactive isotopes of 57Co, 59Fe, 54Mn, 63Ni and 65Zn are used to measure the tracer diffusion coefficients in all the alloys at 1273 K. The influence of multi-principal element alloying of the transition metal sublattice on self-diffusion is mapped to its impact on the defect structure in these ordered alloys. © 2019 Acta Materialia Inc.

Budaraju Srinivasa Murty

Department of Metallurgical and Materials Engineering

Mayur Vaidya

Alloying elements

Crystal Structure

Diffusion

HIGH-ENTROPY ALLOYS

INTERMETALLICS

Transition metals

Aluminides

B2 ORDERING

EQUIATOMIC SUBSTITUTION

MULTI-COMPONENT ALLOY

Multicomponents

PSEUDO-BINARIES

Tracer diffusion

TRACER DIFFUSION COEFFICIENTS

Transition metal alloys

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IIT Madras

Scripta Materialia

High entropy alloys (HEAs) have emerged as a new class of multicomponent materials, which have potential for high temperature applications. Phase stability and creep deformation, two key selection criteria for high temperature materials, are predominantly influenced by the diffusion of constituent elements along the grain boundaries (GBs). For the first time, GB diffusion of Ni in chemically homogeneous CoCrFeNi and CoCrFeMnNi HEAs is measured by radiotracer analysis using the 63Ni isotope. Atom probe tomography confirmed the absence of elemental segregation at GBs that allowed reliable estimation of the GB width to be about 0.5 nm. Our GB diffusion measurements prove that a mere increase in number of constituent elements does not lower the diffusion rates in HEAs, but the nature of added constituents plays a more decisive role. The GB energies in both HEAs are estimated at about 0.8-0.9 J/m2, they are found to increase significantly with temperature and the effect is more pronounced for the CoCrFeMnNi alloy. © 2017 The Author(s).

Fulltext

Scientific Reports

Radioactive isotopes reveal a non sluggish kinetics of grain boundary diffusion in high entropy alloys

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

Acta Materialia

Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy

Journal of Materials Science & Technology

Experimental and numerical studies on the sluggish diffusion in face centered cubic Co-Cr-Cu-Fe-Ni high-entropy alloys

Diffusion Foundations

A Mystery of "Sluggish Diffusion" in High-Entropy Alloys: The Truth or a Myth?

Tracer diffusion in ordered pseudo-binary multicomponent aluminides

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