Dynamic recrystallization of Sn coatings on carbon-fiber-reinforced plastics during cold spray additive manufacturing

The metallization of carbon-fiber-reinforced plastic (CFRP) is a promising solution for increasing the electrical conductivity of CFRP components used in airplane applications to protect them from lightning strikes. Therefore, in this study, cold spraying was used to deposit Sn coating on an epoxy-based CFRP substrate with three different pass numbers (24, 48, and 96) at a gas temperature of 473 K, and the microstructural evolution of the deposited Sn coatings was examined. The grain size of the cold-sprayed Sn coatings gradually decreased as the pass number increased, with 96-pass deposition producing relatively homogeneous, finer-grained microstructures with an average grain size of 4.5 µm. Additionally, increasing the pass number enhanced the in-grain local misorientation of the Sn coatings, which can be correlated with the geometrically necessary dislocation density. The grain refinement observed in conjunction with the formation of dislocation substructures indicated that dynamic recrystallization occurred in the Sn coatings during the multipass cold spraying process, enabling synergistic strengthening. The dynamic recrystallization fraction increased with the pass number, eventually exceeding 60% after the 96-pass deposition. Consequently, as the pass number increased, the hardness of the deposited Sn coatings increased, resulting in more homogeneous hardness distributions along the building direction. Additionally, a thermomechanical effect originating from the low melting temperature of Sn was particularly observed. The findings of this study emphasize the critical nature of cold spray additive manufacturing for the metallization of CFRP components and strengthening of deposited metals.