On the strain rate-dependent deformation mechanism of CoCrFeMnNi high-entropy alloy at liquid nitrogen temperature

Abstract

(2017) On the strain rate-dependent deformation mechanism of CoCrFeMnNi highentropy alloy at liquid nitrogen temperature, Materials Research Letters, 5:7, 472-477, DOI: 10.1080/21663831.2017 ABSTRACTIn the present work, the deformation mechanisms of the CoCrFeMnNi high-entropy alloy at 77 K were investigated using thermal activation analyses. The strain rate jump test was performed to estimate strain rate sensitivity and the activation volume of the alloy. Transmission electron microscopy analyses were performed to identify the evolution of twins at low temperatures. The insensitivity of activation volume to strain observed in the CoCrFeMnNi alloy at 77 K was different from the observed increase in the activation volume with strain at room temperature, which occurred due to the shearing of nanoscale inhomogeneities, such as co-clusters and short-range orders. IMPACT STATEMENTThe insensitivity of the activation volume to plastic strain in the CoCrFeMnNi alloy at 77 K can be attributed to the increasing fraction of mechanical twinning with strain. ARTICLE HISTORY

Small-scale mechanical behavior of a eutectic high entropy alloy

“…However, in ordered FCC phase (L1 2 ), dislocation glide (edge or screw or mixed) over obstacles is the dominant mechanism. The B2 phase showed a higher SRS than L1 2 phase, which is consistent with literature [37][38][39] . To evaluate the bulk response, overall SRS of the EHEA was determined at a load of 5 N at strain rates of 4 × 10 −2 s −1 , 1.2 × 10 −1 s −1 and 4 × 10 −1 s −1 .…”

Probing deformation mechanisms of a FeCoCrNi high-entropy alloy at 293 and 77 K using in situ neutron diffraction

“…High-entropy alloys (HEAs) were first introduced in 2004 [1,2], which aimed to maximise the configuration entropy to form a single phase microstructure via combining four or more principle elements in equimolar or near equimolar ratios. The high configuration entropy, sluggish diffusion, cocktail effect and large lattice distortion lead to their promising properties such as high strength, excellent ductility, and superior fracture toughness [3][4][5][6][7][8].…”

“…One type of HEA and its variants, based on five 3d transition elements (Fe, Co, Cr, Mn, Ni), can form a single phase face-centered-cubic (fcc) structure, displaying an excellent combination of high strength, ductility and fracture toughness at both room and cryogenic temperatures. Their mechanical properties improve significantly with decreasing deformation temperatures [3][4][5][6][7]. We termed this group of HEA as tHEA to distinguish them from other high entropy alloys (such as multi-phase HEAs [8]).…”

Effects of Adiabatic Heating and Strain Rate on the Dynamic Response of a CoCrFeMnNi High-Entropy Alloy

“…For a high-entropy alloy, the lattice friction (Peierls stress) can be much higher than for a low alloy FCC metal due to its large lattice distortions, strong solid solution strengthening, and higher interaction energy between dislocations and solute atoms [27,28]. Hong et al [10] and Moon et al [9] have investigated the rate controlling mechanism of the CoCrFeMnNi alloy and reported that its activation volume for deformation is closer to that observed in BCC metals. The authors concluded that the high friction stress for dislocation motion to be the rate controlling mechanism in this alloy.…”

“…The authors also reported that its mechanical behavior was similar to those of materials with low stacking fault energy. Moon et al [9] and Hong et al [10] have studied the thermally activated deformation of a CoCrFeMnNi high entropy alloy at room and cryogenic temperatures, and have concluded that the rate controlling mechanism in this alloy is the overcoming of nanoscale obstacles such as short range orders (SROs) and clusters. However, the exact microstructural evolution and especially the high rate thermomechanical behavior of the alloy is still largely unknown.…”