Simulation and experimental investigation of the reaction behavior of morphologically modified reactive multilayers

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Reactive metallic multilayers form a subclass of reactive materials. They are capable of self-propagating reactions and their reaction behavior is essentially determined by the type, size, shape and distribution of the reactants. In the first funding phase, results were obtained on the reaction behavior of planar, binary Ni/Al and Ru/Al multilayers in self-propagating reactions in free-standing samples as well as in controlled heat treatments at low heating rates on substrates. A phase field model for simulating the microstructure evolution in Ru/Al during and after self-propagating reaction was established and validated with experimental results. Heat treatment experiments were conducted to elaborate the effect of the bilayer thickness on the phase sequence in Ru/Al. Based on the results of the first funding phase, several new approaches were identified to modify the architecture of Ni/Al and Ru/Al multilayers in a controlled manner in order to gain a deeper understanding of the governing processes on the microscale through key experiments at high and low heating rates in combination with phase field simulations. Here, mainly mass and heat transport processes play a dominant role, and two approaches are followed in this project. The first approach involves utilizing laser-structured substrates for layer deposition to generate pores through shadowing effects at distinct locations within the multilayer. These locally inhibit mass and heat transport during the reaction. The strict localization of the pores thereby allows the before-after comparison with the reacted material. The second approach is based on the insertion of intermediate layers of B2-RuAl or B2-NiAl between the single layers of Ru and Al or Ni and Al, respectively. This reduces the stored energy density without changing the overall composition of the multilayer and will further have an inhibitory effect on mass transfer. The latter is relevant for both the self-propagating reaction and the phase transformation at low heating rates. With respect to self-propagating reactions, the focus is on free-standing samples to investigate fundamentals of the reaction without substrate influence. Both approaches will be investigated experimentally as well as by phase field simulations to determine their effects. For this purpose, the model used for microstructure evolution during the first funding phase will be extended to incorporate the simulation of heat release.