Tailoring shock-induced reaction in Ni/Al nanolaminates: Atomic insights into interfacial gradient effects and intrinsic mechanisms

In reactive nanolaminates (RNLs) with negative mixing enthalpy, the formation of premixed interlayer at sharp interface reduces both the reaction heat and rate, yet the governing factors and mechanisms are not well understood, impeding precise control of reactivity. Through molecular dynamics simulations, we systematically investigate how interfacial composition gradients affect shock-induced reaction kinetics and reactivity in Ni/Al RNLs. For the first time, corresponding piecewise and single kinetic models are proposed to accurately describe solid-liquid and liquid-liquid reaction modes. Intriguingly, while the composition gradient does not alter the fundamental reaction mode or its kinetics, it markedly enhances reactivity. The total reaction heat increases quadratically with gradient, rising from 8.8 to 18.3 kJ/mol for solid-liquid reactions and from 14 to 20 kJ/mol for liquid-liquid reactions. Energy pathway analysis reveals that the gradient modifies the competition among various exothermic processes and their respective contributions. Furthermore, the solid-liquid reaction rate decreases at lower gradients, which is attributed to weakened diffusion driving force and grain-coarsening-induced suppression of dissolution and mixing. In contrast, the liquid-liquid reaction rate remains largely independent of gradient under extreme strain rates. These findings provide atomistic insights into the relationship between interface structure and reactivity in RNLs.