The effect of annealing on trapped copper oxides in particle-particle interfaces of cold-sprayed Cu coatings

Applying state‐of‐the‐art microscopy techniques to understand the degradation of copper for nuclear waste canisters

“…Thus, HT to reduce the presence of particle–particle interfaces and the density of cavities aids with increasing the ductility of the CS Cu, as proposed by Tam et al on bulk HT‐CS Cu samples. [ 33 ] The mechanistic interpretation of the latter benefits substantially from the microscale mechanical testing shown in this study. A subsequent study will provide further details [ 37 ] on the effect of HT on the local mechanical properties and interfaces present in nuclear waste canister Cu coatings—the Cu‐steel, and ED‐AS Cu interfaces.…”

“…In‐situ micromechanical testing of materials is more mature, and the example provided in this work applied the technique to the AS‐CS Cu material. The presence of particle–particle interfaces has previously been proposed as the source of embrittlement in the AS‐CS Cu [ 33 ] and in‐situ microscale mechanical testing confirmed that crack propagation occurred mostly along these interfaces. Future testing will include the effect of HT on the local mechanical properties of the CS Cu coating, and evaluate the mechanical properties of the Cu‐steel and ED‐AS Cu interfaces.…”

“…[ 32 ] The CS Cu is formed by accelerating particles at supersonic speeds toward the carbon steel surface of the container. This results in highly deformed particle–particle interfaces, with the peripheries of these regions having a nanocrystalline microstructure, and grain size < 100 nm, which has been thoroughly characterized by Tam et al [ 32,33 ] Furthermore, pre‐existing oxygen in the Cu powder or accumulated during the acceleration process is preferentially trapped at particle–particle interfaces, resulting in oxygen‐rich pores and interfaces. Standish et al [ 34 ] used X‐ray microcomputed tomography to reconstruct the porosity in the CS Cu in three‐dimensions (3D).…”

“…In addition to the potential of corrosion penetration at particle-particle interfaces, Yu et al showed that the CS process had a substantial effect on microstructure and mechanical properties. [32] The as-sprayed (AS) coating had low ductility (<0.2% strain), which could be recovered to approximately 25% strain using a 350°C heat treatment (HT) for 1 h. [32,33] Other HT conditions are being considered, and, while it is beneficial for bulk mechanical properties, there is a possibility that crack initiation could occur well before failure due to remnant particle-particle interfaces at the surface, which are not removed and could also lead to localized corrosion penetration. Furthermore, the presence of minor impurities, such as oxygen, in Cu materials and their role is unclear due to the size of clusters (nanoscale) and elemental sensitivity required to characterize solid solution impurities.…”

An overview of the Canadian nuclear waste corrosion program

“…One potentially significant feature of the cold spray coating is the presence of small particles of Cu 2 O which decorate the grain boundaries of the annealed material. [ 54 ] However, such particles occupy a minor percentage of the surface area of the material and are disconnected from one another. To date, all three coppers have performed similarly when subjected to electrochemical, material performance, and surface analytical testing.…”