ICMCTF2019 Session C4-ThA: Fundamentals of Metallurgy in Thin Films and Coatings

The ignition of sputter deposited bimetallic nanolaminate films results in rapid, self-propagating reactions. Analytical models of the measured propagation velocities have been typically performed using a framework developed by Mann et al. (J. Appl. Phys. 1997). This work seeks to expand upon this model to handle electron transparent Co/Al samples for experiments in dynamic TEM. This work utilizes a three resistor thermal circuit model to account for thermal conductivity in the intermixed zone that is an order of magnitude less than that predicted by rule of mixtures. Also, this work utilizes cross-sectional scanning transmission electron microscope energy-dispersive X-ray spectroscopy data to calculate the Fourier coefficients in the Mann et al. model from the physical composition profile in the intermixed region. The effect of radiation loss for 150 nm thick foils is calculated as a perturbation to the difference in the heat of reaction measured in calorimetry and the adiabatic heat of product formation. Finally, the model considers two independent activation energies for when the reaction proceeds via co-melted reactants versus solid Co dissolution into molten Al.

This work was supported by the Sandia National Laboratory Directed Research and Development

(LDRD) program. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under Contract No. DE-NA0003525. This work describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S.

Department of Energy or the U.S. Government.

There has been a growing interest in additive manufacturing technologies for the repair of metallic structural components. Among the proposed techniques, twin-wire arc plasma spraying offers the advantage of providing high deposition and growth rate capabilities, coupled with process robustness and versatility, which are always desirable in real-life applications. In addition to these considerations, the fundamental materials science of these plasma-sprayed coatings is surprisingly still under-explored. Nanostructured depositions and coatings should be achievable with this additive technique given its high temperature and fast quenching rate. Motivated by these considerations, we have performed a study on the deposition of metallic coatings on steel substrates using an Oerlikon Metco FlexiArc 300 twin-wire arc plasma spraying system. We used 1.6mm diameter stainless steel wires and compressed air as a carrier gas. The process conditions that were varied include power, standoff distance and coating thickness. Dense coatings, approximately 150 micrometers thick, were achievable at the highest electrical input power of 10 kW within a few seconds of deposition time. Structural and morphological characterization has been performed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). We have found that substrate temperature has a significant influence on the adhesion layer between the substrate and the coating.

This work was supported by a Sandia Laboratory Directed Research and Development (LDRD) program. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.