In nanometric metallic multilayers such as Ni/Al, the alloying reaction proceeds in the form of a propagating wave. We studied the different phase transformations involved in the reactive wave propagation by means of molecular dynamics. The focus was on a specific regime that involves melting of reactants, intermixing of reactants, and formation of an intermetallic compound. We found that the wave consists of two stages. The first front is associated with a dissolution process and propagates at several meters per second, while the second front is due to the crystallization of the final product and is slower, leading to a specific microstructure with alternated large grains of NiAl and liquid regions in the front propagation direction. Three main exothermic processes were identified, including grain coarsening. Their respective contributions were evaluated. We developed a new texture analysis tool that allowed us to follow the evolution of the microstructure and the dynamics of the grain orientation.

Fluctuation theorem for entropy production is revisited in the framework of stochastic processes. The applicability of the fluctuation theorem to physico-chemical systems and the resulting stochastic thermodynamics were analyzed. Some unexpected limitations are highlighted in the context of jump Markov processes. We have shown that these limitations handicap the ability of the resulting stochastic thermodynamics to correctly describe the state of non-equilibrium systems in terms of the thermodynamic properties of individual processes therein. Finally, we considered the case of diffusion processes and proved that the fluctuation theorem for entropy production becomes irrelevant at the stationary state in the case of one variable systems.

The reactivity of the Ti–Al system was investigated experimentally in the case of reactive laminated particles produced by high energy ball milling. The ignition temperature for a self-sustaining reaction was measured as a function of the heating rate. By means of the Kissinger analysis, two activation energies were evaluated. The first one is associated with the solid-state transformation at the interface below the melting point of Al. The second one corresponds to the exothermic dissolution of Ti into Al liquid together with the formation of ${\mathrm{TiAl}}_3$ . A complementary microscopic approach was developed in order to detect all elemental processes associated with the reactivity of the Ti–Al system in composite materials. Above the melting temperature of Al, the exothermic dissolution of Ti into the liquid layer starts and induces a self-sustaining behavior until the reaction is complete. The dissolution step is limited by the low solubility of Ti in Al. The formation of the intermetallic compound ${\mathrm{TiAl}}_3$ was observed. The microscopic analysis of the dissolution at the interface explains some specific features of reactive particles.