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A finite strain continuum theory is advanced for static and dynamic simulations of material response under combined mechanical and magnetic fields. The general thermomechanical theory accounts for nonlinear thermoelasticity, plastic flow from slip and twinning, damage mechanics, and phase transformations. Maxwell's equations are implemented in the Galilean approximation. Effects of electromechanical body forces, Maxwell's stress, and magnetostriction are included, as are forces and heating from electric currents in conductors. Several assumptions are newly introduced to facilitate calculations in the context of finite element methods with explicit dynamics. Of particular interest are ferrous solids whose phase changes and interactions are affected by external magnetic fields. Predictions for compression of pure iron, in comparison with experimental data and prior analytical results, verify suitability of modeling assumptions and numerical methods. Further calculations demonstrate efficacy of the model for reproducing experimental findings on ferrous alloys of the same chemical composition but with two different prior heat treatments, leading to different initial microstructures. For all materials studied, effects of magnetic field on kinetic barriers are discovered to be more influential on phase transitions than magnetic Gibbs free energy differences between phases. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

High‐entropy alloys, consisting of multiple principal elements, represent a new paradigm in structural alloy design with excellent mechanical properties and potentially promising ballistic performance. Herein, the ballistic response of a single‐phase Al0.1CoCrFeNi high‐entropy alloy is evaluated with spherical E52100 steel (RC60) projectiles at velocities ranging from 500 to 1000 m s−1 at normal obliquity, indicating failure by ductile–hole growth. A wide range of microstructural features are observed corresponding to varying degrees of deformation and the corresponding hardness maps are obtained. The microstructure in the partially penetrated condition is dominated by microbanding and microtwinning close to the crater wall. With striking velocity that result in plugging but not complete penetration, the deformation is dominated by twinning and crack initiation around adiabatic shear bands close to the exit hole. A high density of localized adiabatic shear bands and recrystallized grains are observed at impact velocities corresponding to full penetration. Highly deformed areas near the crater wall and narrow zones around shear bands show the maximum hardness, indicating significant work hardening of the material during penetration. [ABSTRACT FROM AUTHOR]

Lamellar eutectic structure in Al 0.7 CoCrFeNi high-entropy alloy (HEA) is emerging as a promising candidate for structural applications because of its high strength-ductility combination. The alloy consists of a fine-scale lamellar fcc + B2 microstructure with high flow stresses > 1300 MPa under quasi-static tensile deformation and >10% ductility. The response to shear loading was not investigated so far. This is the first report on the shear deformation of a eutectic structured HEA and effect of precipitation on shear deformation. A split-Hopkinson pressure bar (SHPB) was used to compress the hat-shaped specimens to study the local dynamic shear response of the alloy. The change in the width of shear bands with respect to precipitation and deformation rates was studied. The precipitation of L1 2 phase did not delay the formation of adiabatic shear bands (ASB) or affect the ASB width significantly, however, the deformed region around ASB, consisting of high density of twins in fcc phase, was reduced from 80 µm to 20 µm in the stronger precipitation strengthened condition. We observe dynamic recrystallization of grains within ASBs and local mechanical response of individual eutectic lamellae before and after shear deformation and within the shear bands was examined using nano-indentation.