Thermal and Mechanical Ignition of Exothermic Reactions in Ni+Al Nano-laminates

In this paper, we report on the factors influencing the thermal and mechanical ignition of highly exothermic reactions in intermetallic forming Ni+Al nano-layered laminate structures. In particular, the variations in ignition conditions for as-fabricated nano-laminate samples and those subjected to natural or accelerated aging via heat- treatment, are investigated. Thermal ignition of reactions is determined based on heating the nanolaminate samples in a DSC at different heating rates to obtain the activation energy and enthalpies of reactions associated with the formation of various aluminide phases. Mechanical ignition is studied using 80-mm gas gun impact experiments, employing planar-parallel for uniaxial strain and inclined-plate for shear loading geometries, while measuring free surface velocity profiles using multi-probe PDV interferometry. The generation of an intermixed inter-phase layer between Ni and Al due to natural/accelerated aging becoming a diffusion barrier in addition to consuming the reactants, can affect the threshold conditions for the onset and propagation of intermetallic forming reactions. The results obtained to date, with respect to how stored energy associated with these effects of aging influence the thermal and mechanical ignition of nano-layered Ni+Al laminate structures, will be presented.