Reactive Nanofoils Research Articles

In-situ investigation of the thermal reaction properties of multilayered aluminum–nickel nanofoils

The reduction of the overall mass is a well-established strategy to improve the resource efficiency of vehicles. In terms of lightweight construction, the trend is to produce components consisting of dissimilar materials. Consequently, joining techniques are required that best fulfill the associated requirements. Joining based on reactive nanofoils represents an innovative approach to produce components in a multi-material design. However, nanofoils are not yet used in the industry due to the limited knowledge concerning the effective reaction characteristics during joining. Therefore, this study addresses the characterization of the thermal reaction properties of commercially available aluminum–nickel nanofoils. An experimental setup based on high-speed two-color infrared pyrometry was developed to ascertain the reaction temperature profile during the reaction time of ignited nanofoils. The layer composition of the samples and the ignition strategy were varied within the study. As a result, the effective reaction temperature profile and the duration of the reaction were determined in-situ with high temporal and spatial resolution for the first time. Furthermore, an analytic model was developed to accurately predict the reaction period with respect to the layer structures of the nanofoils. Finally, the sequence of developed intermediate aluminum-nickel phases during the reaction process was ascertained.

Assessment of the technological potential and maturity of a novel joining technique based on reactive nanofoils

Manufacturing companies in the automotive industry are confronted with the rising demand for long-range electromobiles. The traction battery must be interconnected internally with low electrical resistance within the joints to achieve a high-performance powertrain. Joining based on reactive nanofoils represents an innovative manufacturing technology to meet the aforementioned demand. However, the integration of a new technology or the substitution of a well-established technology in a running production environment represents a strategic management decision associated with high risks. The awareness of the industry concerning the technological capability of reactive nanofoils is currently low, as this technology is classified as new and emerging. Therefore, this study addresses the assessment of the technological potential and the maturity of reactive nanofoils by presenting a use case, in particular the interconnection of a traction battery. The assessment was carried out for reactive nanofoils as well as for screwing, as the latter is ranked as the established technology in this matter. In the case of the former technology, the design of a state-of-the-art traction battery was adapted and manufactured.

Study of the kinetic and energetic reaction properties of multilayered aluminum–nickel nanofoils

Manufacturers are facing the demand to produce resource efficient electromobiles. This is a challenging task as the heavy traction battery significantly increases the overall mass of the vehicle. Using light-weight components is an engineering strategy to improve the power-to-mass ratio. The current trend is to produce components consisting of dissimilar materials. Joining by using reactive nanofoils is a promising technique to produce components in a multi-material design. However, the reaction characteristics during joining must be known to enable an industrial application. Therefore, this study addresses the analysis of the kinetic and energetic reaction properties of commercially available aluminum–nickel nanofoils with different layer structures. An experimental setup based on a monochromatic high-speed camera and a test device was applied to evaluate the shape and the velocity of the propagating combustion front during the reaction process. A combustion calorimeter was used to determine the reaction enthalpy. Existing analytical models to predict kinetic and energetic reaction properties of multilayered foils were reviewed using the experimental findings. A pre-exponential factor was determined empirically to account for nanofoils with individual foil thicknesses. Finally, the kinetic and energetic properties of commercially available nanofoils were predicted with a high degree of accuracy by using the analytical models in combination with the pre-exponential factor.

Reactive nanofoils for joining refractory and dissimilar materials

Heterogeneous nanostructured foils produced by magnetron deposition or mechanical processing represent a new class of reactive materials. They are composed of layers or clusters of different phases (typically with a size of 10–100 nm) that can react with each other with strong heat release. The reaction, being initiated locally, spontaneously propagates across the entire foil in the form of high-temperature wave. Some examples of promising practical applications of these foils in advanced technologies, such as joining dissimilar materials, were presented.

Modeling self-sustaining waves of exothermic dissolution in nanometric Ni-Al multilayers

The self-sustained propagating reaction occurring in nanometric metallic multilayers was studied by means of molecular dynamics (MD) and numerical modeling. We focused on the phenomenon of the exothermic dissolution of one metallic reactant into the less refractory one, such as Ni into liquid Al. The exothermic character is directly related to a negative enthalpy of mixing. An analytical model based on the diffusion-limited dissolution [1] coupled with heat transfer was derived to account for the main aspects of the process. Together, several microscopic simulations were carried out. The first series were set up to obtain all the parameters governing the process, including the heat release by dissolution. The second series of MD simulations was set up to detect the very possibility of self-sustaining propagation driven by exothermic dissolution. We aimed at developing a consistent multiscale description by numerically solving the model with the MD extracted parameters. The study proves that the exothermic intermixing of Ni and Al is a driving mechanism of self-sustaining propagation in reactive nanofoils.

Combustion in reactive multilayer Ni/Al nanofoils: Experiments and molecular dynamic simulation

A comparative study, including experiments and molecular dynamic simulation, of the combustion waves in the Ni/Al multilayer reactive nanofoils reveals unknown mechanisms of the process. High speed macro-video recording, brightness pyrometry and thermal imaging proved that the combustion wave consists of two stages; the first stage can propagate independently with the same velocity as the complete wave. Products of the first stage of combustion are nano-grains of NiAl separated by liquid gaps of the Al-Ni melt. SEM and TEM study of the intermediate and final products of combustion allow us to suggest a new mechanism of “mosaic” dissolution-precipitation describing nano-heterogeneous reaction at the first stage of the process, which explains dynamics of the combustion wave and resultant microstructure. It was shown also that most of the heat released in the second stage of combustion is generated by grain coarsening. Thus, a conclusion is made that the combustion wave in the Ni/Al reactive multilayer nanofoil is proposed to be a sequential, two stage process involving chemical (first stage) and physical (second stage) exothermic transformations.