Additional hindrances to metallurgical bonding from impurities during microparticle impact

Successful cold spray processing requires the formation of metallurgical bonds at the interface between particle impact sites and the substrate. While surface contamination on either the particle or substrate can interfere with metallurgical bonding, the details of particle/substrate interface chemistry are usually obscured or lost during the nanoseconds-long particle impact process. To provide a direct, detailed account of particle-substrate interfacial chemistry, we perform post-mortem scanning transmission electron microscopy and spectroscopy of impact sites of single copper microparticles, launched with a laser-induced particle impact tester, on a copper substrate. In addition to native oxides, we find that amorphous carbon and spherical copper oxide dispersoids are also present near/at the interface. Further, these features are found to influence metallurgical bonding. These results offer additional considerations for optimizing the quality of the cold spray deposition process.