Role of $${\varvec{\alpha}} \to {\varvec{\varepsilon}} \to {\varvec{\alpha}}$$ phase transformation on the spall behavior of iron at atomic scales

Shock compression of iron microstructures above a threshold stress results in a [Formula omitted] transformation, and the propagation of the release wave brings the metal back to the [Formula omitted] phase following the [Formula omitted] transformation. Predicting failure behavior under shock loading conditions (spallation) relies on understanding the evolution of defects in the microstructure as it undergoes the [Formula omitted] phase transformation. This study uses molecular dynamics (MD) simulations to investigate the role of defect evolution during the [Formula omitted] phase transformation on the spall strength values of single-crystal (sc) Fe microstructures. The MD simulations aim to characterize the [Formula omitted] phase fraction formed during shock compression and the defects during shock release for variations in loading orientations and shock stresses. The simulations are carried out for loading along the [100], [110], [111], and [112] orientations and for impact velocities ranging from 600 m/s to 1 km/s. The [Formula omitted] phase fractions during compression and defects (dislocations, twins) characterized during spall failure show an orientation dependence that affects the spall strength values. The lowest value for spall strength is observed for the [Formula omitted] loading orientation that shows a high density of twins at the spall plane, whereas the highest value is observed for the [Formula omitted] orientation and is associated with a [Formula omitted] transformation at the spall plane. The correlations of the spall strength values with the strain rates and with the [Formula omitted] phase fractions are discussed.