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6306 |
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Friday, June 12, 2020, Hall K1 11:20 AM Cold Gas Spraying III |
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Interfacial bonding characteristics of copper powders with different oxide films in the cold spray process
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Maryam Razavipour* / University of Ottawa, Canada Bertrand Jodoin / University of Ottawa, Canada Saeed Rahmati/ University of Ottawa, Canada Alejandro Zúñiga/ Universidade Federal do ABC, Brazil Denise Criado/ Universidade Federal do ABC, Brazil |
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Cold spray is a solid-state additive manufacturing process for which the feedstock material quality is of utmost importance for the efficient production of homogenous and uniform coatings. Powders with the lowest oxygen content are known to be the most favorable for coating production but are typically costly. Furthermore, these high-quality powders must be well preserved and thus kept from oxygen and humid environment exposure to maintain their quality. The effect of powder aging on the powder particle bonding characteristics in cold spray was investigated in this work. Copper powders were kept at ambient atmospheric condition for different periods of time and their deposition characteristics were examined using micrometric pull-off test. X-ray photoelectron spectroscopy (XPS) was used to study thoroughly the surface chemistry of the copper powders and the oxide thicknesses as a function of exposure time. Identical nano-hardness values were observed for all powders interfaces while the oxide layer thicknesses varied from 6 nm to 11.6 nm. A considerable reduction of deposition efficiency was observed between the freshest (6 nm oxide thickness) and most oxidized powder (11.6 nm oxide layer thickness), confirming the importance of the oxide layer in the deposition/bonding mechanism. SEM along with EDS analysis was used to characterize the metallurgical bonding at the particle/substrate interfaces. Only a small portion of the interfaces revealed fracture surfaces that are typical of metallurgical bonded surfaces for all the deposited powders. These dimpled structures reached an area fraction of 16% for the as-received powder (6nm oxide film) while this value was reduced to less than 10% for aged powders (11.6nm oxide film thickness). These findings demonstrate the detrimental effect of oxide film on the deposition behavior even for small oxidation scale (0.14 vol%-0.27 vol%) and emphasize the importance of proper powder maintenance for consistent coating quality. |