Bonding Mechanisms in Cold Spray: Influence of Surface Oxidation During Powder Storage
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Bonding Mechanisms in Cold Spray: Influence of Surface Oxidation During Powder Storage Maryam Razavipour1 • Saeed Rahmati1 • Alejandro Zu´n˜iga2 • Denise Criado3 Bertrand Jodoin1
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Submitted: 24 May 2020 / in revised form: 3 September 2020 / Accepted: 2 November 2020 Ó ASM International 2020
Abstract Cold spray is a solid-state process in which solid particles are subjected to severe plastic deformation to form a coating. The effect of naturally occurring oxides on bonding in the cold spray was investigated in this work. Deposition characteristics of copper powder with different surface oxide thicknesses on steel substrate were examined using a local pull-off test. This enables the investigation of individual particle/substrate interfaces. X-ray photoelectron spectroscopy was used to study thoroughly the powder surface chemistry and the oxide thickness as a function of exposure time. This study revealed that the oxide film thickness grew from 6 nm for the as-received powder to 11.6 nm after 2 months of exposure to atmospheric conditions. Scanning electron microscopy and x-ray energy dispersive spectroscopy were used to characterize the particle/substrate interfacial bonding. Adhesion test results show that the bond strength is highly influenced by the surface oxide thickness. Different bonding behaviors and a drop in coating deposition efficiency were observed as the oxide thickness increased. Finite element simulations supplemented our understanding of the particle adhesion dynamics as the oxide film thickness increases. They were also used to study the surface oxide cleanup and bonding mechanism for particles with different oxide film thicknesses. & Maryam Razavipour [email protected] 1
Cold Spray Research Laboratory, University of Ottawa, Ottawa, ON, Canada
2
CECS, Universidade Federal do ABC, Santo Andre´, SP, Brazil
3
CCNH, Universidade Federal do ABC, Santo Andre´, SP, Brazil
Keywords cold spray process finite element simulation (FEM) interfacial bonding local pull-off test oxide thickness scanning electron microscopy (SEM) X-ray photoelectron spectroscopy (XPS)
Introduction Cold spray (CS) is a solid-state manufacturing process by which feedstock powder is deposited on a substrate following intensive plastic deformation due to high-velocity impact (Ref 1–4). This enables the formation of highly dense coatings with low oxide content since the feedstock powder is kept well below their melting temperature during their flight in an inert environment (Ref 1, 5). According to the prevailing bonding theories in solidstate joining processes such as cold welding (Ref 6, 7), all metals and alloys are capable of forming bonds when their clean surfaces are brought together within the range of interatomic forces (Ref 8). However, different metals exhibit different abilities to form bonds, which has been attributed to differences in their oxide films (Ref 8). Depending on their chemical composition and thickness, these oxide films may have different mechanical properties tha
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