Identifying the Role of Pressure on the Response of Reactive Materials to Thermal Initiation: a Molecular Dynamics Study

Molecular dynamics (MD) simulations using a first principles-based Embedded-atom-Method (EAM) potential are used to simulate the exothermic alloying reactions of a NiAl bilayer at 1500 K and 1100 K. Both microcanonical (NVE) and isoenthalpic (NPH) MD simulations are used to demonstrate the influence of pressure on atomic mixing and subsequent alloying reaction. The NVE simulations, in which the volume is fixed and in which pressure increases as the exothermic reactions cause an increase in the system temperature, have a much slower reaction rate than those of the NPHMD simulations in which the pressure is maintained at 1 bar. The mechanism of the mixing is the same for all simulations: As mixing and reaction occurs at the interface, the heat generated first melts the Al layer, and subsequent mixing leads to further heat generation after which the Ni layer melts, leading to additional mixing until the alloying reactions are completed. The results indicate that pressure has a significant influence on the rates of atomic mixing and alloying reactions.