Effects of shock-induced α (bcc) → ɛ (hcp) phase transition on spall failure in Fe–Mn alloys

Plate-impact experiments were conducted on Fe–Mn alloys containing 4, 7, and 11 at. % Mn to investigate the role of shock-induced α(bcc) → ɛ(hcp) phase transformations on wave dissipation and subsequent spall failure. Increasing Mn content systematically reduced the transformation threshold pressures from 13 GPa for pure Fe to 9.19 ± 0.56, 7.66 ± 0.45, and 4.64 ± 0.31 GPa for Fe–4Mn, Fe–7Mn, and Fe–11Mn, respectively. In addition, the phase transformation broadened the shock front, with rise times nearly doubling due to kinetic delays, latent heat absorption, and structural rearrangements. Time-resolved metrics including the decompression strain rate, velocity pullback, recompression slope, and oscillation periods, respectively, link the transformation-induced changes in effective stiffness, wave attenuation, and void-growth kinetics to the observed spall failure response, including generation of multiple spall planes revealed in soft-recovered impacted samples of Fe–Mn alloys. The spall strength, determined from analysis of pullback signals, increased by 78%–90% due to the preceding phase transformation, demonstrating that transformation-mediated loading and unloading strongly influences spall failure. The findings highlight that compositional tuning promoting shock-induced phase transformation can enable damage mitigation caused by spall failure.