Excellent ballistic impact resistance of Al0.3CoCrFeNi multi-principal element alloy with unique bimodal microstructure

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.

New insights into the role of porous microstructure on adiabatic shear localization

This paper provides new insights into the role of porous microstructure on adiabatic shear localization. For that purpose, we have performed 3D finite element calculations of electro-magnetically collapsing thick-walled cylinders. The geometry and dimensions of the cylindrical specimens are taken from the experiments of Lovinger et al. (2015), and the loading and boundary conditions from the 2D simulations performed by Lovinger et al. (2018). The mechanical behavior of the material is modeled as elastic-plastic, with yielding described by the von Mises criterion, an associated flow rule and isotropic hardening/softening, being the flow stress dependent on strain, strain rate and temperature. Moreover, plastic deformation is considered to be the only source of heat, and the analysis accounts for the thermal conductivity of the material. The distinctive feature of this work is that we have followed the methodology developed by Marvi-Mashhadi et al. (2021) to incorporate into the finite element calculations the actual porous microstructure of 4 different additively manufactured materials --aluminium alloy AlSi10Mg, stainless steel 316L, titanium alloy Ti6Al4V and Inconel 718-- for which the initial void volume fraction varies between 0.001% and 2%, and the pores size ranges from ≈ 6 µm to ≈ 110 µm. The numerical simulations have been performed using the Coupled Eulerian-Lagrangian approach available in ABAQUS/Explicit (2016) which allows to capture the shape evolution, coalescence and collapse of the voids at large strains. To the authors' knowledge, this paper contains the first finite element simulations with explicit representation of the material porosity which demonstrate that voids promote dynamic shear localization, acting as preferential sites for the nucleation of the shear bands, speeding up their development, and tailoring their direction of propagation. In addition, the numerical calculations bring out that for a given void volume fraction more shear bands are nucleated as the number of voids increases, while the shear bands are incepted earlier and develop faster as the size of the pores increases.

The Correlation of Texture and the Formation of the Adiabatic Shear Band in 7XXX Aluminum Alloy during Dynamic Loading

The mechanical behavior of the extruded 7003-T6 aluminum profiles used as automotive buffer beams is investigated. The correlation of the texture and the formation of the adiabatic shear band is analyzed. Copper texture, R texture, and S texture are the main reasons for the anisotropy of mechanical behavior of the profile, resulting in that the stress of the profile along the extrusion direction is higher than that perpendicular to the extrusion direction. Through finite element modeling (FEM), it can be found that the adiabatic shear band is developed in the sample if the dynamic loading direction is parallel to the extrusion direction, but it does not appear if the loading direction is perpendicular to the extrusion direction. When the dynamic loading direction is parallel to the extrusion direction, higher stress results in a lower energy barrier for shear localization. Therefore, the formation of the adiabatic shear band is susceptible along but is not sensitive perpendicular to the extrusion direction. This study provides technical support for the service of 7003 aluminum alloy in automobiles, which has important academic and engineering application value.

Penetration Damaging Behavior of ATI425 Titanium Alloy

The penetration damaging behavior of ATI425 titanium alloy was studied by 7.62 mm diameter armor piercing projectiles. The damage characteristics and the mechanism were analyzed by observing and analyzing the craters of ATI425 titanium alloy target. It can be found that local temperature-rise of the target plate occurred, even sputtering phenomenon in the opening stage. The shear bands extended upward along the cater wall could be seen in the stable stage. The large non-homogeneous deformation in adiabatic shear bands caused microcracks and micropores. A large number of macro-cracks were observed on the side wall and at the bottom of the crater.