Multi-principal element alloys represent a new paradigm in structural alloy design with superior mechanical properties and promising ballistic performance. Here, the mechanical response of Al0.3CoCrFeNi alloy, with unique bimodal microstructure, was evaluated at quasistatic, dynamic, and ballistic strain rates. The microstructure after quasistatic deformation was dominated by highly deformed grains. High density of deformation bands was observed at dynamic strain rates but there was no indication of adiabatic shear bands, cracks, or twinning. The ballistic response was evaluated by impacting a 12 mm thick plate with 6.35 mm WC projectiles at velocities ranging from 1066 to 1465 m/s. The deformed microstructure after ballistic impact was dominated by adiabatic shear bands, shear band induced cracks, microbands, and dynamic recrystallization. The superior ballistic response of this alloy compared with similar AlxCoCrFeNi alloys was attributed to its bimodal microstructure, nano-scale L12 precipitation, and grain boundary B2 precipitates. Deformation mechanisms at quasistatic and dynamic strain rates were primarily characterized by extensive dislocation slip and low density of stacking faults. Deformation mechanisms at ballistic strain rates were characterized by grain rotation, disordering of the L12 phase, and high density of stacking faults.
High-performance energy storage devices (HPEDs) play
a critical
role in the realization of clean energy and thus enable the overarching
pursuit of nonpolluting, green technologies. Supercapacitors are one
class of such lucrative HPEDs; however, a serious limiting factor
of supercapacitor technology is its sub-par energy density. This report
presents hitherto unchartered pathway of physical deformation, chemical
dealloying, and microstructure engineering to produce ultrahigh-capacitance,
energy-dense NiMn alloy electrodes. The activated electrode delivered
an ultrahigh specific-capacitance of 2700 F/cm3 at 0.5
A/cm3. The symmetric device showcased an excellent energy
density of 96.94 Wh/L and a remarkable cycle life of 95% retention
after 10,000 cycles. Transmission electron microscopy and atom probe
tomography studies revealed the evolution of a unique hierarchical
microstructure comprising fine Ni/NiMnO3 nanoligaments
within MnO2-rich nanoflakes. Theoretical analysis using
density functional theory showed semimetallic nature of the nanoscaled
oxygen-vacancy-rich NiMnO3 structure, highlighting enhanced
carrier concentration and electronic conductivity of the active region.
Furthermore, the geometrical model of NiMnO3 crystals revealed
relatively large voids, likely providing channels for the ion intercalation/de-intercalation.
The current processing approach is highly adaptable and can be applied
to a wide range of material systems for designing highly efficient
electrodes for energy-storage devices.
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