Impact response of dual-phase cobalt at elevated temperatures: Experiments and molecular dynamics simulations

JH Liu and ZH Lin and SH Guo and K Li and YJ Deng and Y Cai and L Lu and NB Zhang and SN Luo, JOURNAL OF ALLOYS AND COMPOUNDS, 1036, 181416 (2025).

DOI: 10.1016/j.jallcom.2025.181416

In order to investigate impact response of dual-phase cobalt at elevated temperatures (300-725 K), plate impact experiments are conducted along with postmortem microstructure analyses and large-scale molecular dynamics simulations. Based on the in situ synchrotron diffraction results, dual-phase cobalt consists of hexagonal close-packed (HCP) and face-centered cubic (FCC) phases at room temperature and undergoes the heating-induced HCP to FCC phase transition at 675 K. Upon shock loading, the elastic-plastic transition is obscure with no evident Hugoniot elastic limit within the temperature range of this study. With increasing temperature, its spall strength decreases from 2.9 GPa at 300 K to 1.9 GPa at 725 K, as a result of thermal softening. Given the postmortem characterizations, dislocation slip in both phase, deformation twins in the HCP phase and FCC to the HCP phase transition are observed. At higher temperatures, only 1012 twinning is activated, in contrast with 10 (1) over bar2, 10 (1) over bar1 and 11 (2) over bar1 twinning at room temperature. Besides, impact-induced FCC to the HCP phase transition is also impeded. Regardless of the preheating temperature, the HCP phase accommodates more plastic deformation under shock loading than the FCC phase. Thus, the voids are basically restricted within the HCP phase for spallation damage. The molecular dynamics simulations reveal the evolution of dislocation densities, phase fractions and intergranular damage at different temperatures. The increased stacking fault energy heightens the stability of the FCC phase, then impede the FCC to the HCP phase transition.

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