| Résumé | The current study details an experimental analysis that elucidates the relationship between the processing history, microstructural evolution, and bulk properties of cold-sprayed pure FCC copper coatings. Particular attention is paid to determining the effect of low temperature ex situ and in situ annealing (350 °C; 1 h) on the evolution of microstructure (i.e. grains and subgrains) and porosity, as well as the combined influence of these defects on the bulk properties (microhardness, and electrical conductivity) and fracture mechanics of cold-sprayed copper.
SEM, TEM, in situ TEM, and fractography analysis together revealed that the inherently brittle nature of the cold-sprayed metals cannot be explained solely by their porosity or microstructure; their fracture mechanics is most likely governed by the coupling interaction between porosity and the nanocrystalline dynamically/static recrystallized (RX) grains adjacent to the pores. Under tensile loading, pores (0.5–20 µm) in the as-sprayed copper can easily act as crack tips which then propagate along the adjacent RX grains (∼100 nm), resulting in a brittle cleavage fracture. Although low-temperature annealing was not sufficient to remove the porosity, it was capable of promoting recovery and grain growth in these RX grains. The ductility of the region ahead of the crack tips was therefore enhanced to promote dimpling and potentially crack blunting. Consequently, this low-temperature annealing improved the tensile ductility of the cold-sprayed copper by 2 orders of magnitude (from ∼0.2% to ∼25% strain). |
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