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A face-centered cubic (FCC) non-equiatomic high-entropy alloy (HEA), Cr 10 Mn 10 Fe 60 Co 10 Ni 10 , is processed via cold-rolling and subsequent annealing at 800 − 1200 °C with different cooling methods. All the annealing treatments lead to fully recrystallized microstructures with various grain sizes and precipitate types. The mechanical properties under uniaxial tension are obtained along with microstructure characterizations of postmortem samples. The sample annealed at 800 °C followed by furnace cooling yields a reasonable combination of high strength and good ductility. The yield strength and ultimate tensile strength are 43% and 19% higher than those of the sample annealed at 800 °C followed by water quenching, with only a uniform elongation ∼ 6% reduction. The yield strength variations of all the annealed samples are explained with a structure-based strength model. After fracture, all the samples show strong 〈 111 〉 texture along the tensile direction. Besides dislocation slip, deformation twinning and multiple phase transitions contribute to high strength and effective work hardening as additional deformation mechanisms. The newly formed hexagonal close-packed and body-centered cubic phases follow the Shoji–Nishiyama and Kurdjumov–Sachs orientation relations with the FCC matrix, respectively. Given the "treatment method − microstructure − mechanical property" relationship in this study, combining the advantages of the steel and HEAs, this kind of Fe-rich HEA bears great potentials to serve under practical conditions. [ABSTRACT FROM AUTHOR]

• Deformation mechanism under shock compression of an additively manufactured HEA has been revealed. • Higher strain rate promotes the phase transitions in the HEA. • Elemental segregation of Mn and Ni strongly influences the phase transitions in the HEA. [Display omitted] Shock compression of an additively manufactured high-entropy alloy, Cr 10 Mn 10 Fe 60 Co 10 Ni 10 , is investigated via gas-gun plate impact. The postmortem sample shocked to 11.3 GPa is characterized with electron back-scattered diffraction and transmission electron microscopy; two phase transitions are observed, the face-centered cubic (FCC) to hexagonal close-packed (HCP) transition, and the FCC to body-centered cubic (BCC) transition. The HCP and BCC phases with different variants are observed following specific orientation relationships with the FCC matrix. The phase transitions are strongly affected by elemental segregation during the additive manufacture (the HCP and BCC phases are absent in the Mn and Ni enriched areas), and one possible reason is the increase of local stacking fault energy caused by the Mn and Ni enrichment. [ABSTRACT FROM AUTHOR]

A typical Fe-rich non-equiatomic CrMnFeCoNi high-entropy alloy (HEA), Cr 10 Mn 10 Fe 60 Co 10 Ni 10 , and the equiatomic Cr 20 Mn 20 Fe 20 Co 20 Ni 20 HEA, are investigated via plate impact experiments along with in situ free surface velocity measurements. Both the initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. These two HEAs contain a single face-centered cubic phase, are texture-free, and have similar grain sizes. Dynamic yield stress and spall strength of the non-equiatomic CrMnFeCoNi are lower by ∼55 % and 15 % than those of its equiatomic counterpart, respectively. After shock compression, dislocation slips, stacking faults, Lomer-Cottrell locks and nanotwins are found in the postmortem samples of both HEAs. Due to the reduced stacking fault energy in the non-equiatomic HEA, more deformation twins and newly formed hexagonal close-packed phases are found. For spallation, intergranular voids are larger in size but smaller in quantity than intragranular voids for both HEAs. Both intragranular or intergranular voids show strong dependence on grain boundary misorientation. [Display omitted] • Equiatomic and non-equiatomic CrMnFeCoNi are with similar grain size and weak texture. • The yield stress and spall strength of equiatomic alloy are higher. • More nano twins and newly formed HCP phase are found in nonequiatomic alloy. • Ductile spallation occurs. The HAGBs have a higher probability of inducing a void than TBs. [ABSTRACT FROM AUTHOR]

Phase transformation in a metastable body-centered cubic (BCC) high entropy alloy HfZrTiT a 0.53 is investigated via plate impact along with in situ free surface velocity measurements, postmortem microstructure characterizations and first-principles calculations. Impact-induced BCC to hexagonal close-packed transformation is observed. Compared to the single orientation relationship (the Pitsch-Schrader relationship) under quasi-static loading, an additional orientation relationship with higher phase transformation activation barrier is also involved, given the ultrahigh strain rates and complex stress condition under planar impact. [ABSTRACT FROM AUTHOR]

The effects of strain rate on mechanical properties, microstructural evolution and underlying deformation mechanisms of two kinds of interstitial CrMnFeCoNi high entropy alloys (HEAs), (CrMnFeCoNi) 99.5 C 0.5 and (CrMnFeCoNi) 99.0 C 1.0 , are investigated under quasi-static and dynamic tension. Dynamic loading is carried out via a split Hopkinson tension bar system. The pre- and post-deformation microstructures are characterized with electron back scatter diffraction and transmission electron microscopy. Both yield strength and work hardening increase remarkably with increasing strain rate. Plastic deformation in both alloys under quasi-static and dynamic loading are dominated by dislocations, stacking faults, kink bands and deformation twins. Twinning is activated easier under dynamic loading, and twin density decreases with increasing carbon content due to the increased stacking fault energy. The Khan-Liu constitutive model can describe the experimental results for these two interstitial HEAs in a wide strain range. • Both volume fraction and size of the carbides increase with the increase of C content. • The increase of C content and strain rate lead to the increase in σ Y and σ UT. • Twin density decreases with increasing C content due to the increased SF energy. • The Khan-Liu constitutive model is used to describe the deformation. [ABSTRACT FROM AUTHOR]

Plate impact experiments are conducted on a metastable dual-phase high-entropy alloy (HEA) Cr 10 Mn 30 Fe 50 Co 10 with different matrix grain sizes and phase fractions. Free surface velocity histories are obtained along with microstructure characterizations. Postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. Multiple deformation mechanisms are observed, including dislocation slip and stacking fault in the face-center cubic (FCC) phase, dislocation slip and deformation twinning in the hexagonal close-packed (HCP) phase, and the FCC to HCP transformation. For spallation, damage is ductile in nature. Despite different microstructures, micro-voids prefer to nucleate at high-angle grain boundaries within the FCC phase, leading to similar spall strength. Upon shock loading, a dynamic plastic deformation partitioning behavior among the two phases is observed; at high shock stress, denser dislocations in the HCP phase result in increased fractions of voids around the FCC/HCP phase interface and within the HCP phase during spallation damage. • C r10 M n30 F e50 C o 10 with different FCC grain sizes and phase fractions are obtained. • Damage is ductile in nature, spall strengths for different microstructures are similar. • Multiple deformation mechanisms are observed, including FCC to HCP transition. • A dynamic plastic deformation partitioning behavior in two phases is observed. [ABSTRACT FROM AUTHOR]