In-situ observations of single micro-particle impact bonding

We study supersonic impact of individual metallic microparticles on metallic substrates, that is, the unit process of materials buildup in cold spray coatings/additive manufacturing. We resolve the moment of impact bonding through real-time observations of single particle impacts with micron-scale and nanosecond-level resolution. We offer the first in-situ observation of a material-dependent threshold velocity, above which the particle undergoes an impact-induced jet-like material ejection and adheres to the substrate. We report direct measurements of critical velocities for structural metals, which unlike in nozzle experiments, are not affected by process-related complexities obscuring particles' kinetic and thermal histories. Keyword: Cold spray; Adhesion; Additive manufacturing; ImpactUnited States. Army Research Office (Contract W911NF-13-D-0001)United States. Office of Naval Research (Grant N00014-13-1-0676