This research is funded in part by the Oregon Metal Initiative, Intel Corporation, and the National Science Foundation (Award No 1711994). The participation of undergraduate students to this research is supported by National Science Foundation REU-Site (Award No. 1851851). Experiments and characterization were performed at the Portland State University Nanodevice Fabrication and Nanomaterial Synthesis Labs, and the 3D printed steel manufacturing and nanoindentation tests were performed at the Nebraska Engineering Additive Technology (NEAT) Labs, Nano-engineering Research Core Facility (NERCF) of the University of Nebraska-Lincoln, which is partially funded by the Nebraska Research Initiative .
Results in Surfaces and Interfaces
Coating materials -- Thin films, Crystal structure -- Corrosion, Electrochemical reactions
This study demonstrates the feasibility of using liquid exfoliation of expandable graphite into multilayer exfoliated graphene flakes (EGFs) to form a self-assembled thin film on an air–water interface. The film can coat the surface of additive manufactured (AM) steel substrates to enhance surface properties, specifically AM 316 stainless-steel (AM316), AM 8620 steel (AM8620), and samples of the same alloys made by conventional manufacturing (CM) processes. Liquid exfoliation offers a high yield route for an EGF coating that can cover up to 95% of the sample surface with a single application. The thin, flexible EGFs can coat a rough AM metal surface, while the highly intact crystal lattice protects covered areas against diffusing ions and prevents localized corrosion compared to similar coatings made with graphene oxide (GO) or reduced GO (rGO). The EGF coating exploits a unique self-assembly process without surfactants or stabilizers, wherein the hydrophobicity and hydrophilicity of EGFs arrange the flakes, then van der Waals (vdW) forces bond them together and to the substrate for a coherent anti-corrosive coating. Electrochemical measurements indicate lower corrosion potential for coated samples, nanoindentation measurements show surface hardness protection against corrosive attack, and weight loss measurements demonstrate long-term protective capabilities. Density functional theory calculations, using the optB88-vdW exchange functional of the graphene and iron (111) interface demonstrated stronger binding and shorter interface distance compared to the well-studied graphene/nickel (111) interface. These calculations and experimental results can further elucidate the superior performance of EGF thin film coatings on high iron content steels, especially AM steels.
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Hood, K., Qian, W., Xia, Y., Krupa, S., Dao, A., Ahmed, S., ... & Jiao, J. (2023). Self-assembly of exfoliated graphene flakes as anticorrosive coatings for additive manufactured steels. Results in Surfaces and Interfaces, 100116.