Dual phase high entropy alloy

What are dual phase high entropy alloys ?

Dual phase high entropy alloys are metallurgical materials which consist of a higher number of elemental components (4 or more) with the aim to form massive solid solutions exploiting the associated enhanced configurational entropy which stabilises them.

Different from the original high entropy alloy concept such dual phase high entropy alloys are flexible in the specific number of components used and also do not need to utilize equal compositions for each of the elements. Instead the dual phase high entropy alloys can be designed by using non-equimolar atomic mixtures. The second most important difference to the original high entropy alloy concept is that the dual phase high entropy alloys consist of two or more solid solution phases with different crystal structure, where all of these phases are massive solid solutions following the original high entropy alloy concept.

 

EBSD phase maps of the quinary dual-phase Co20Cr20Fe34Mn20Ni6 HEA with increasing tensile deformation at room temperature. The results reveal deformation-induced martensitic transformation as a function of deformation; the local strain (εloc) levels of (a EBSD phase maps of the quinary dual-phase Co20Cr20Fe34Mn20Ni6 HEA with increasing tensile deformation at room temperature. The results reveal deformation-induced martensitic transformation as a function of deformation; the local strain (εloc) levels of (a
Ab initio assisted design of quinary dual-phase high-entropy alloys with transformation-induced plasticity
Acta Materialia 136 (2017) 262-270;
Here we introduce a new class of high-entropy alloys (HEAs), i.e., quinary (five-component) dual-phase (DP) HEAs revealing transformation-induced plasticity (TRIP), designed by using a quantum mechanically based and experimentally validated approach.
Acta Materialia 2017 Ab initio design qu[...]
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The mechanical properties of dual phase high entropy alloys can be improved by friction stir procesing

Dual phase high-entropy alloys (HEAs) exhibit an extraordinary combination of mechanical properties. In this project we show how an even stronger and yet very ductile non-equiatomic dual phase HEA can be obtained after friction stir processing. For this purpose a transformation-induced plasticity (TRIP) assisted
HEA with composition Fe50Mn30Co10Cr10 (at.%) was severely deformed by friction stir processing and evaluated for its microstructure-mechanical property relationships. The friction stir processing-engineered microstructure of the TRIP dual phase HEA exhibited a substantially smaller grain size, and optimized fractions of face-centered cubic (f.c.c., γ) and hexagonal close-packed (h.c.p., ε) phases, as compared to the as-homogenized reference dual phase high-entropy alloy. This results in synergistic strengthening via TRIP, grain boundary strengthening, and effective strain partitioning between the γ and ε phases during deformation, thus leading to enhanced strength and ductility of the TRIP-assisted dual-phase HEA engineered via friction stir processing.

Enhanced strength and ductility in a friction stir processing engineered dual phase high entropy alloy
SCiENTiFiC REPOrTS | 7: 16167 | DOI:10.1038/s41598-017-16509-9
Scientific Reports 7-16167 Friction Stir[...]
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Scientific Reports: True stress-true strain curves for the as-homogenized and FSP samples deformed at room temperature at an initial strain rate of 10−3 s−1, (b–d) EBSD maps showing f.c.c. γ- and h.c.p. ε-phase fractions prior to tensile deformation and, Scientific Reports: True stress-true strain curves for the as-homogenized and FSP samples deformed at room temperature at an initial strain rate of 10−3 s−1, (b–d) EBSD maps showing f.c.c. γ- and h.c.p. ε-phase fractions prior to tensile deformation and,
(a) Strength-ductility index (SDI) as a function of grain size and (b) variation of SDI as a function of ε phase fraction (prior to deformation) for grain-refined TRIP HEAs and non-TRIP HEAs. CG: coarse grained; FG: fine grained; FSP: friction stir proces (a) Strength-ductility index (SDI) as a function of grain size and (b) variation of SDI as a function of ε phase fraction (prior to deformation) for grain-refined TRIP HEAs and non-TRIP HEAs. CG: coarse grained; FG: fine grained; FSP: friction stir proces

 

 

What is the influence of interstitial atoms in dual phase and single phase high-entropy alloys ?

Interstitial atoms enable joint twinning and transformation induced plasticity in strong and ductile high-entropy alloys
Scientific Reports | 7:40704 | DOI: 10.1038/srep40704
Li_et_al-2017-Scientific_Reports interst[...]
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In this project we are concerned with the role that interstitial atoms play in dual phase and single phase high-entropy alloys.

Generally high-entropy alloys (HEAs) consisting of multiple principle elements provide an avenue for realizing exceptional mechanical, physical and chemical properties. In this project we pursued a novel strategy for designing a new class of HEAs incorporating the additional interstitial element carbon. This results in joint activation of twinning- and transformation-induced plasticity (TWIP and TRIP) by tuning the matrix phase’s instability in a metastable TRIP-assisted dual-phase HEA. Besides TWIP and TRIP, such alloys benefit from massive substitutional and interstitial solid solution strengthening as well as from the

composite effect associated with its dual-phase structure. Nanosize particle formation and grain size reduction are also utilized. The new interstitial TWIP-TRIP-HEA thus unifies all metallic strengthening mechanisms in one material, leading to twice the tensile strength compared to a single-phase HEA with
similar composition, yet, at identical ductility.

Scientific Reports: Microstructure and elemental distribution in the as-homogenized coarse-grained iHEA. (a) XRD and EBSD patterns reveal that the structure consists of f.c.c. and h.c.p. phases (DP structure). (b) EDS maps and BSE images from the region m Scientific Reports: Microstructure and elemental distribution in the as-homogenized coarse-grained iHEA. (a) XRD and EBSD patterns reveal that the structure consists of f.c.c. and h.c.p. phases (DP structure). (b) EDS maps and BSE images from the region m
Microstructure and elemental distribution in the grain-refined iHEA. (a) XRD and EBSD patterns reveal the f.c.c. matrix and a small fraction of h.c.p. phase prior to deformation. (b) ECC image and EDS maps corresponding to the identical region marked in ( Microstructure and elemental distribution in the grain-refined iHEA. (a) XRD and EBSD patterns reveal the f.c.c. matrix and a small fraction of h.c.p. phase prior to deformation. (b) ECC image and EDS maps corresponding to the identical region marked in (
Mechanical behavior of the iHEAs compared to various TRIP-DP-HEAs and single-phase HEAs. GS refers to the grain size. (a) Engineering stress-strain curves; data of Fe50Mn30Co10Cr10 (at%) TRIP-DP-HEAs (ref. 6), single-phase Fe20Mn20Ni20Co20Cr20 (at%) and F Mechanical behavior of the iHEAs compared to various TRIP-DP-HEAs and single-phase HEAs. GS refers to the grain size. (a) Engineering stress-strain curves; data of Fe50Mn30Co10Cr10 (at%) TRIP-DP-HEAs (ref. 6), single-phase Fe20Mn20Ni20Co20Cr20 (at%) and F

 

Acta Mat. 2011, 59, p. 364