Cold-sprayed copper and tantalum coatings — Detailed FESEM and TEM analysis

In cold spraying, a high level of plastic deformation and adiabatic shear instability are required for the tight bonding between powder particles and thus, formation of a dense microstructure. Cold-sprayed copper and tantalum coatings have fully dense structures according to microscopic evaluations and corrosion tests, indicating coatings' impermeability. Actually, denseness, i.e., existing through-porosity is a crucial coating characteristic which is reflected to the structural properties. In this study, the microstructure and fracture behavior are characterized using a field-emission scanning electron microscope (FESEM) and the inter-particle structures with a transmission electron microscope (TEM). Furthermore, a long-time impermeable behavior of these coatings was performed with open-cell potential measurements. Cold-sprayed copper and tantalum coatings possessed highly and localized deformed micro- and grain structures with high amount of dislocations and shear bands in their structures. Additionally, metal–metal particle bonds were attained as an important factor in the tight particle bonding. Moreover, partly ductile fracture behavior and material jets due to the thermal softening were observed from the fracture surfaces.