| Author(s) |
Bosco Hiu Ming Yu, Jason Tam, Liyang Zheng, Dominique Poirier, Jason Giallonardo, Yu Zou, Jane Howe, Uwe Erb |
| Abstract Scope |
Cold spraying is a vital additive manufacturing process used in tools, dies, and corrosion protection for nuclear waste storage. However, achieving sufficient ductility and mechanical integrity in cold-sprayed metals remains a challenge, even for FCC-based ductile metals such as copper. This study examines the origins of brittleness in pure, as-sprayed copper, focusing on hierarchical defects and their spatial arrangements. Using electron microscopy, nanoindentation mapping, and fractography, we revealed a heterogeneous microstructure in the as-sprayed copper, featuring work-hardened crystals, nanocrystalline grains, oxide films, and microscopic pores at particle-particle interfaces. These oxide films hinder metallurgical bonding, while local hardness variations and micro-pores act as stress concentrators, leading to brittle fractures. Annealing at 350°C for one hour is enough to promote recovery, recrystallization, and oxide film coalescence, reducing stress concentrations and increasing metallurgical bonding. Thus, low-temperature heat treatment causes a shift from brittle to ductile fracture, leading to a 120-fold increase in ductility. |