Abstract
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.
Highlights
The microstructure of the thermomechanically processed A l0.3CoCrFeNi high entropy alloys (HEAs) alloy is shown in Fig. 1a, consisting of bimodal microstructure with some recrystallized fine grains from high temperature annealing and strained elongated coarse grains from hot rolling
The microstructural features and mechanical response of Al0.3CoCrFeNi high entropy alloy was characterized in a wide range of strain rates including quasi-static deformation, Split-Hopkinson pressure bar testing, and ballistic impact
The alloy exhibited an excellent combination of strength and ductility from the bimodal microstructure, nano-scale L 12 phase in face centered cubic (FCC) matrix and grain-boundary B2 precipitates
Summary
The mechanical response of Al0.3CoCrFeNi alloy, with unique bimodal microstructure, was evaluated at quasistatic, dynamic, and ballistic strain rates. Deformation mechanisms at quasistatic and dynamic strain rates were primarily characterized by extensive dislocation slip and low density of stacking faults.
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