Depositing Al-Based Metallic Coatings onto Polymer Substrates by Cold Spray
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Depositing Al-Based Metallic Coatings onto Polymer Substrates by Cold Spray M. R. Rokni1 • P. Feng1 • C. A. Widener2 • S. R. Nutt1
Submitted: 2 April 2019 / in revised form: 7 August 2019 ASM International 2019
Abstract The feasibility of depositing aluminum onto thermoplastic substrates via cold spray (CS) was investigated. Dense coatings of 7075 Al and CP Al (commercial purity) were achieved on three substrates—polyetheretherketone (PEEK), polyetherimide (PEI), and acrylonitrile butadiene styrene (ABS) using an iterative optimization process. 7075 Al deposition yielded low deposition efficiencies (DEs) and low thicknesses but high adhesive strengths, while CP Al deposition led to high DEs and thicknesses but relatively low adhesive strengths. PEEK and PEI were more suitable substrates for cold spray than ABS, which suffered from surface erosion and substrate distortion. Two key factors were identified that influenced the DE and adhesive strength of the coating. The first factor was the bond layer, the initial few particle layers that fused with the substrate to allow subsequent buildup. The bond layer was influenced by the substrate hardness, yield strength, glass transition temperature, and impact strength, as well as the differences in thermal expansion coefficients of Al and the polymer substrates. The second factor was the CS process parameters selected, as the bond layer and the build-up layers may require different process conditions in order to optimize both bonding strength and coating strength, respectively. Keywords adhesive strength cold spray deposition behaviors metallization of polymers polymer substrate
& M. R. Rokni [email protected]; [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
VRC Metal Systems, Rapid City, SD, USA
Introduction Polymers are widely used in land and air vehicles because of their low density, ease of forming, and weldability (Ref 1). In the last two decades, the use of polymers to reduce component weight has increased in various industries (Ref 1, 2). However, applications for polymers are limited by intrinsically inferior structural properties relative to metals, including low strength and modulus, poor erosion resistance, poor electrical conductivity, susceptibility to UV damage, and low service temperatures (Ref 2, 3). Metallization of polymers can be an effective approach to mitigate these shortcomings and broaden their applications. The objective of the present study is to investigate the feasibility of metallizing polymer substrates using a relatively mild process that does not damage or distort the polymer substrate. Presently, few conventional methods are suitable for the surface metallization of polymers. These include PVD, CVD (Ref 4), electroplating (Ref 5-7), electroforming (Ref 8), and thermal spraying techniques (Ref 9-11), all of which have attendant limitations and drawbacks. For example, both PVD
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