November 8-12, 2015
Reactive metal composites (RMC) films are used in various applications from precision joining and brazing to local high heat sources for power generation and local melting. They are gasless, high heat generating, high propagation speed reactions that involve the release of energy when elemental constituents are combined to make intermetallics. These films require solid state diffusion at the nanoscale to function well, and the current method of manufacture is to sputter 20-50nm thick alternating films of the reactant elements to build up a ~50um thick composite film. This process is slow and costly, and does not lend itself well to generating unusual or three dimensional shapes. Specialized shapes must be cut using femtosecond lasers, adding to cost and complexity of the manufacturing process.
We are investigating an alternative method of using dispersion electroplating to contain a dispersed phase (Ni) within a continuous phase (Al) that is also nanostructured. The propagation speed and calorific output of the films is dependent upon the overall stoichiometry of the films, and so a 1:1 atomic ratio is the most energetic, resulting in a 40% volumetric ratio of the dispersed phase, requiring the electrodeposition of the Al. Use of ionic liquid (IL) based electrochemical baths support a clean, oxide free interface between the dispersed phase and the matrix phase with roughly the same degree of mixing at the interface as is observed in the sputtered films. However, challenges arise from the use of these ionic liquids, in that the interaction of particles dispersed in the plating solution versus particle distribution within the plated solid phase is not linear, and depends upon several other parameters, such as shear rate at the interface, viscosity of the plating fluid and suspension, and the distribution of electronic charge across the particles when interacting with ionic liquids. We investigate these plating parameters and their effect on film deposition, smoothness, and dispersed phase incorporation, revealing that the viscosity of the plating fluid is non-Newtonian, and shear thinning during deposition. We hypothesize that this effect is due to the breakup of electrostatic structure within the ionic liquid and between the ionic liquid and the dispersed particulate phase. We also investigate the electrochemistry of the Al deposition from a number of salts within the ionic liquid, since these salts affect the rate of deposition of the Al matrix phase, and by extension, the relative ratio of reactants in the film. Finally, we discuss briefly the effect of these plating properties on both the calorific output of the plated film, and the reaction rate of the resultant films.
Christopher Apblett, Jonathan Coleman, Robert Knepper, and Alexander Tappan, "Reactive Ni-Al nanostructured composites through electrochemical dispersion deposition" in "Composites at Lake Louise (CALL 2015)", Dr. Jim Smay, Oklahoma State University, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/composites_all/15