Ballistic penetration in thick copper plates: Microstructural characterization

Ballistic Impact Response of Al0.1CoCrFeNi High‐Entropy Alloy

“…Microbands have been reported for copper targets and their density increased with impact velocity and increasing grain size of the target. [27] Typically, in FCC alloys with low stacking fault energy (SFE), microbands are promoted due to planar dislocation arrays. In contrast, dissociated dislocations may alternatively form twins and reduce driving force for microband formation.…”

“…These equiaxed ultrafine grains likely formed by significant dynamic recrystallization adjacent to ASBs, and the thickness of these regions increased with increasing impact velocity. [27] The formation of nanostructured and ultrafine grains inside the shear band by dynamic recrystallization has been widely studied. [31,53,54] During plastic deformation at high strain rates, there is a sudden rise in temperature inside the material that leads to thermal softening of localized regions.…”

“…With further deformation, high density of dislocations accumulates inside these recrystallized grains and promote crack nucleation and propagation, [27] as shown in Figure 3f, finally resulting in detachment of plug. [27,30] The presence of recrystallized grains in the ASB region around the crack indicated that deformation and subsequent failure by crack formation was primarily guided by shear band localization. Adiabatic shear localization has been found to be an important and sometimes dominant deformation and fracture mode in metals and alloys under high strain-rate deformation.…”

“…[14][15][16][17] Deformation of HEAs at medium to high strain rates (in the range of 10 À2 -10 3 s À1 ) using Split-Hopkinson Pressure Bar (SHPB) [2,[18][19][20][21][22] indicated that the mechanism, flow stress, and strain-hardening were significantly dependent on the strain rate. [23][24][25][26][27][28][29][30] For some HEAs, a transition in deformation mechanism from dislocation slip to a mixed mode of dislocation-slip and deformation twinning was observed by increasing strain rate from 10 À3 to 10 2 s À1 . [22,[31][32][33] Several of these HEAs also show inhomogeneous deformation in the form of serrated flow with increasing applied stress.…”

“…[23] For example, in the case of copper target, high-velocity ballistic impact produced microbands on {111} planes as opposed to increased twinning seen for SHPB tested samples. [23,27] Shear localization in the form of adiabatic shear bands (ASBs) has been reported for certain target materials due to local rise in temperature. [31] ASBs represent regions of extreme strain localization and may provide preferred crack initiation sites at high strain rates.…”