Fabrication of robust bifunctional composite coatings by electrodeposition

Abstract

Solid lubrication shows promising potential for advanced applications in automotive and aerospace industries where the challenging environment of high vacuum and extreme temperature have rendered it unpractical for traditional liquid lubrication. Transition metal dichalcogenides (TMD) such as molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are well-known solid lubricants and exhibit excellent friction reduction due to their unique lamellar structure. Incorporating these TMD particles into a metal matrix (e.g. nickel, cobalt, copper) via electrodeposition has been a facile and versatile method for self-lubricating composite coating synthesis. Electrodeposited Ni-MoS2 coatings demonstrate a lower coefficient of friction than electroplated nickel coatings. Under dry sliding conditions, the friction coefficient of electrodeposited nickel ranges from 0.4 to 0.6, while that of Ni-MoS2 can be as low as 0.1. However, during electroplating, the conductive nature of co-deposited TMD particles resulted in an enhanced electric field in the vicinity of particle-absorbed sites. In consequence, more metal ions would be attracted towards these sites due to greater Coulomb force, which accelerated the reduction of ions at these locations and created composite coatings with non-compact and porous structures. These porous structures become a major challenge to achieving long-term durability as they can be easily sheared off during sliding contact motion. One of the research purposes of this thesis is to develop a robust electrodeposited metal-TMD coating achieved by densifying the structure of these existing coatings.
On the other hand, TMD particles with low surface energy are also good candidates for developing superhydrophobic coatings through electro-co-deposition. However, the lack of mechanical robustness and abrasion resistance has become the major challenge inhibiting their practical industrial applications. This work presents a strategy to develop robust nickel-based hybrid composite coatings via the co-deposition of TMD and reinforcing ceramic particles (i.e., SiC and TiO2). The size of the added ceramic particle was found to have a significant effect on the surface morphology, co-deposited WS2 content and wettability of the as-deposited hybrid composite coatings. Nickel-based hybrid coating deposited from an electrolyte containing WS2 and micron-sized SiC particles showed a rough surface with uniformly distributed protrusions. The as-deposited nickel-hybrid coating exhibited excellent water repellence with a water contact angle of 166.2 ± 0.7° and a sliding angle of 3.2°. Moreover, the electrochemical tests in 3.5 wt% NaCl solution showed that the nickel hybrid coating exhibited good corrosion resistance (Ecorr = -0.14 V and Icorr = 4.29 × 10-7 A/cm2) and high corrosion inhibition efficiency (η = 97.1%.). Furthermore, the linear abrasion test proved that nickel hybrid superhydrophobic coating has one of the best abrasion resistance compared with literature (water contact angle remained above 150° after 2000 cm abrasion distance under the pressure of 2.2 kPa), indicating such coating has promising potential in robust industrial applications.

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Identifiers

ORCID for Xingyu Wang: orcid.org/0009-0001-4544-1702

ORCID for Nong Gao: orcid.org/0000-0002-7430-0319

ORCID for Zheng Jiang: orcid.org/0000-0002-7972-6175

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