Depositing Aluminum onto PEKK Composites by Cold Spray
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Depositing Aluminum onto PEKK Composites by Cold Spray P. Feng1 • M. R. Rokni1,2 • S. R. Nutt1
Submitted: 17 July 2020 / in revised form: 30 October 2020 / Accepted: 9 November 2020 Ó ASM International 2020
Abstract High-pressure cold spray (HP-CS) was used to deposit aluminum onto polyetherketoneketone (PEKK) composite substrates. Aluminum powders were sprayed using N2 and He carrier gas and a bond layer (BL) of commercial-purity Al (CP Al). Dense 7075 and CP Al deposits were achieved via combinations of BL-N2, 7075/BL-N2, and 7075/BL-He. Cold spray using 7075 Al particles or using He carrier gas yielded thinner deposits because of self-erosion and bond layer erosion. Substrate roughening was more severe when using He gas and generated more polymer debris at the deposit–substrate interface, yielding lower adhesive strength values between the deposit and the composite substrates. Adhesive strength depended on the bonding of initial particle layers that fused with the substrate. Keywords adhesive strength cold spray deposition behaviors interfacial microstructure metallization of polymer composites polymer–composite substrate
Introduction To determine process conditions required to produce adherent metal deposits and understand powder–substrate interactions, the near-substrate microstructure of cold-
& P. Feng [email protected]; [email protected] 1
Department of Chemical Engineering and Materials Science, M.C. Gill Composites Center, University of Southern California, Los Angeles, CA, USA
2
Present Address: Senior Aerospace SSP, Los Angeles, CA, USA
sprayed (CS) metal on fiber-reinforced thermoplastic composites (FRTP) was investigated. Adhesion of deposits depends strongly on the interactions between the metal particles and the composite substrate, which affects the residual stress and microstructure at the deposit–substrate interface. Integration of metal coatings onto polymer composites through surface metallization could significantly broaden the use of thermoplastic composites, which is limited in some applications by low erosion resistance (Ref 1, 2) and electrical conductivity (Ref 3). Surface metallization can be an effective approach to bestow metallic properties and overcome these shortcomings, while retaining the high specific strength and modulus of the composite (Ref 4). Different processes have been utilized to metallize composite surfaces, including physical vapor deposition (Ref 5), electroless plating (Ref 6), and thermal spray techniques, including high-velocity oxygen fuel (Ref 7) and plasma spraying (Ref 8). Although thermal spray techniques have greater deposition rates (Ref 9) compared to PVD, CVD, and electroplating processes, the feedstock powders are melted during deposition, with two adverse effects: deposits develop thermally induced residual stresses (and sometimes experience oxidation), and the molten droplets damage polymer substrates. For these reasons, thermal spray processes are incompatible with polymer and composite substrates (Ref 10-14). An
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