Non-Arrhenius migration and structural evolution of a faceted grain boundary in Ni-Cu alloy under shock-loading: Molecular dynamics simulations

Understanding the dynamic behavior of a material under high stress is critical in developing durable materials for extreme environments and defence applications. Taking this as the motivation, the authors have utilized molecular dynamics simulations to investigate the behavior of a binary Nickel-Copper (Ni-Cu) alloy under shockloading conditions, which exhibits significant compressive deformation and abrupt stress fronts. In particular, the effect of shock-loading on a special faceted Sigma 3 [111] 60 degrees {11 8 5} grain boundary (GB) incorporated in the Ni-Cu alloy domain was predicted. Varying solute concentrations and temperatures were the other parameters considered in this investigation. Interestingly, we observed non-Arrhenius (anti-thermal) GB migration behavior for this particular faceted Sigma 3 GB under shock-loading conditions. This non-Arrhenius behavior was found to be diminishing with the increase in the solute content. Our findings also indicated that higher solute concentrations reduced the GB mobility (due to the solute drag phenomenon), which resulted in enhanced shock resistance. Additionally, the presence of solute stabilized the GB, which further enhanced the shock resistance ability of the material. Common neighbour analysis of the configurations revealed a shock-induced phase transition from the face-centered cubic (FCC) structure to hexagonal close-packed (HCP) and body-centered cubic (BCC) structures. This FCC-to-BCC transition was facilitated by the stacking faults that acted as the nucleation sites for the BCC phase. These phase transformations were more pronounced in pure nickel than in the Ni-Cu alloys.