Dynamic shear deformation of a CrCoNi medium-entropy alloy with heterogeneous grain structures

Abstract

Dynamic shear deformation of a CrCoNi medium-entropy alloy with heterogeneous grain structures, Acta Materialia (2018), AbstractSingle-phase CrCoNi medium-entropy alloys (MEA) are emerging recently as an interesting class of metallic materials, but the dynamic response of this MEA at high strain rates remains unknown. Here we have produced this MEA with various heterogeneous microstructures, using cold rolling followed by annealing at various temperatures. The high-strain-rate response of the MEAs was characterized using hat-shaped specimens in Hopkinson-bar experiments. A combination of high dynamic shear yield strength and large uniform dynamic shear strain was observed, exceeding all other metals and alloys reported so far. Even better dynamic shear properties was revealed when the experiments were conducted at cryogenic temperature. The strong strain hardening under dynamic shear loading can be attributed to the dynamic grain refinement and deformation twinning that accompany the homogeneous shear deformation. When compared to room temperature, the efficiency of grain refinement was found to be enhanced at cryogenic temperature, with a higher density of multiple twins, stacking faults, Lomer-Cottrell locks, and hcp phase via phase transformation inside the grains, which could be responsible for the better dynamic shear properties under cryogenic environment.partitioning and strain gradients have been found to play an important role during the tensile deformation in heterogeneous structures, resulting in back stresses that enhance extra strain hardening and uniform elongation. This strategy can also be used for metals and alloys with ultra-low SFE, such as HEAs and MEAs.The un-dissipated plastic work leads to appreciable temperature rise such that the

Microstructure and properties of CoCrNi medium-entropy alloy produced by gas atomization and spark plasma sintering

“…After being sintered at a high temperature, CoCrNi MEA also has the single-phase FCC structure with no visible change in the phase composition, which is in good agreement with previous studies. [12][13][14] This also demonstrated that no impurities, such as O and C, were introduced.…”

“…[9][10][11] Particularly, the three component CoCrNi MEA exhibits a high work hardenability and excellent toughness. [12][13][14][15][16][17] Laplancche et al fabricated a CoCrNi MEA by arc melting and reported that the strength and fracture toughness of the CoCrNi MEA were improved, compared with those of CoCrFeMnNi HEAs. 18 The results indicated that the superior mechanical properties were attributed to twinning activation at higher stress and strain levels.…”

Engineering heterostructured grains to enhance strength in a single-phase high-entropy alloy with maintained ductility

“…For instance, a heterostructured multi-phase AlCoCrFeNi 2.1 HEA shows a simultaneous strength-ductility enhancement in comparison with its homogenous counterpart [24]. More recently, it has been reported that a single-phase fcc CrNiCo mediumentropy alloy (MEA), which is derived from the concept of HEA, with a heterogeneous grain structure exhibits superior mechanical properties [25]. Thus, it is reasonable to hypothesize that a good combination of strength and ductility can be achieved in singlephase fcc HEAs via the introduction of a heterogenous microstructure.…”

A Review on Heterogeneous Nanostructures: A Strategy for Superior Mechanical Properties in Metals

“…This hardness difference needs to be large enough to generate local incompatibility of plastic deformation and local extra hardening for improvement in global hardening. In a summary, larger local gradients and higher local GNDs render the better mechanical performances, such as yield strength, strain-hardening rate, and uniform elongation [16,26,53]. The local variation in hardness in the deformed state is small, but it is enhanced after recovery and partial recrystallization annealing.…”