Enhanced formability of interstitial free iron at high strain rates

Microstructure development during high-velocity deformation

“…Equations [1] and [2] show that for a perfect dislocation loop, the activation-energy barrier for nucleation will depend on the level of stress and the Burger's vector, whereas, for a partial dislocation loop, the activation-energy barrier for nucleation will depend on the SFE, in addition to and b P . Assuming the Burgers vector of a perfect dislocation, b 0 ϭ a/2 Ͻ110Ͼ ϭ 2.53 ϫ 10 Ϫ10 m, [13] where a is the lattice parameter of the austenite phase, the Burgers vector of a partial dislocation is b P ϭ a/6 Ͻ112Ͼ ϭ 1.46 ϫ 10 Ϫ10 m, [13] and the SFE is ␥ ϭ 0.020 J/m 2 , [14] we can plot the activation energy of nucleation (⌬G) for a perfect and for a partial dislocation loop, as a function of the loop radius.…”

“…Of these two options, twinning is the most favorable, as no stacking faults are present and, thus, lattice distortions perpendicular to the stacking fault do not contribute to the total strain energy. [15] The superplastic behavior encountered in samples which have been deformed at high strain rates [1,2] is worth examining. Hu et al [16,17] have suggested that as a result of deformation at high strain rates, inertial effects can diffuse neck growth, # ϭ 5000 s Ϫ1 # ϭ 100 s Ϫ1 due to the adiabatic heating generated during the highvelocity deformation processes.…”

“…[1] needs to be altered, as the nucleation of an imperfect dislocation loop will involve the formation of a stacking fault. Thus, for an intrinsic stacking-fault loop, we can write…”

“…It has been shown through past studies that materials deformed at high velocities exhibit extremely high ductility (100 pct elongation was observed without failure in iron, copper, and aluminum sheets) [1,2] as well as significant strain-rate sensitivity. [3] At the microstructural level, high strain rates induce a high density of dislocations, [4] large vacancy concentrations, [5] and a higher tendency for deformation twinning to substitute for slip.…”

Formability of steel sheet in high velocity impact

“…This extended ductility at high velocity is referred to here as hyperplasticity. Balanethiram and coworkers [3][4][5][6] performed electrohydraulic forming experiments with 6061 T4 aluminum; copper and interstitial free iron, forcing the metals into a conical die with an apex angle of 90 • at velocities near 150 m/s. Altynova and coworkers [5,[7][8][9] showed that strains to failure in ring expansion of 6061 T4, 6061 T6 and annealed OFHC copper can be increased to about two-fold relative to quasi-static ductility.…”