Metallic microparticles can acquire remarkable nanoscale morphologies after experiencing high velocity collisions, but materials science regarding the extreme events has been limited due to a lack of controlled experiments. In this work, collision dynamics and nonlinear material characteristics of aluminum microparticles are investigated through precise single particle collisions with two distinctive substrates, sapphire and aluminum, across a broad range of collision velocities, from 50 to 1,100 m/s. An empirical constitutive model is calibrated based on the experimental results, and is used to investigate the mechanics of particle deformation history. Real-time and post-impact characterizations, as well as model based simulations, show that significant material flow occurs during the impact, especially with the sapphire substrate. A material instability stemming from plasticity-induced heating is identified. The presented methodology, based on the use of controlled single particle impact data and constitutive models, provides an innovative approach for the prediction of extreme material behavior.

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Cold gas-dynamic spray is a solid-state materials consolidation technology that has experienced successful adoption within the coatings, remanufacturing and repair sectors of the advanced manufacturing community. As of late, cold spray has also emerged as a high deposition rate metal additive manufacturing method for structural and nonstructural applications. As cold spray enjoys wider recognition and adoption, the demand for versatile, high-throughput and significant methods of particulate feedstock as well consolidated materials characterization has also become more notable. In order to address the interest for such an instrument, nanoindentation is presented herein as a viable means of achieving the desired mechanical characterization abilities. In this work, conventionally static nanoindentation testing using both Berkovich and spherical indenter tips, as well as nanoindentation using the continuous stiffness measurement mode of testing, will be applied to a range of powder-based feedstocks and cold sprayed materials.

In this work, three commercially available aluminum alloy systems (Al 2024, Al 6061, and Al 7075) were considered to explicitly capture the differences in material properties associated with a rapidly solidified, gas-atomized particulate feedstock as compared with their conventionally cast counterparts. Differences between the microstructural, thermodynamic, mechanical, and kinetic behaviors associated with gas-atomized and conventionally bulk counterparts have been tacitly assumed by the cold spray community. However, many researchers continue to utilize legacy properties from bulk materials when simulating particle impact phenomena in silico, for example. By way of recognizing the fact that bulk material properties may not serve as substitutes for gas-atomized powder property input parameters for cold spray process simulation and computation in silico, enhanced cold spray research and development will be more easily achieved. Therefore, understanding the feedstock powder characteristics for use in cold spray can lead to fine-tuning the properties of cold spray consolidations. Optical microscopy, scanning electron microscopy, nanoindentation, microhardness, differential scanning calorimetry, elemental analysis, and cooling rate calculations were utilized. This work confirms preliminary findings that powder alloys may not be treated the same way as their bulk counterparts in so far as the enactment of heat treatment processing parameters are concerned. Specifically, vast discrepancies were found in the grain size, secondary phases, and mechanical behavior between the powder and cast versions of each alloy.