Shengguo Zhou

Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

Friction has a direct relation with the energy efficiency and environmental cleanliness in all moving mechanical systems. To develop low friction coatings is extremely beneficial for preserving not only our limited energy resources but also the earth’s environment. This study proposes a new design for low friction carbon-based nanocomposite coatings by tailoring the microstructure and phase segregation, and thereby it contributes to better controlling the mechanical and tribological properties. Experimental findings and theoretical calculations reveal that high-hardness (18.2 GPa), high-adhesion strength (28 N) as well as low-internal stress (−0.8 GPa) can be achieved by a nanocrystallite/amorphous microstructure architecture for the nc-WC/a-C(Al) carbon-based nanocomposite coating; in particular low friction (∼0.05) can be acquired by creating a strong thermodynamic driving force to promote phase segregation of graphitic carbon from the a-C structure so as to form a low shear strength graphitic tribo-layer on the friction contact surfaces. This design concept is general and has been successfully employed to fabricate a wide class of low friction carbon-based nanocomposite coatings.

Corrosion resistance and self-cleaning behaviour of Ni/a-C:H superhydrophobic films

ABSTRACT Superhydrophobic nickel-incorporated carbon-based (Ni/a-C:H) nanocomposite films were prepared successfully on Si substrate via the one-step electrochemical deposition method using methanol as the carbon source and nickel (II) acetylacetonate as the dopant under high voltage, atmospheric pressure and low temperature. Surprisingly, this one-step electrochemical deposited Ni/a-C:H nanocomposite films could achieve superhydrophobic surface. Results showed that without any further modifications by low surface energy materials, the water contact angle of 154.21° and sliding angle of 7.96° were obtained, which attribute to the irregular petaloid structures. In addition, the corrosion resistance tests demonstrated the Ni/a-C:H films deposited at a Ni content of 0.08 mg/ml had excellent corrosion resistance. And the self-cleaning test revealed that the Ni/a-C:H films surface had excellent self-cleaning properties, which indicated this kind of film might have a promising application in the field of drag reduction and self-cleaning.

Rare earth Ce-modified (Ti,Ce)/a-C:H carbon-based film on WC cemented carbide substrate*

WC cemented carbide suffers severe wear in water environments. A novel carbon-based film could be a feasible way to overcome this drawback. In this study, a rare earth Ce-modified (Ti,Ce)/a-C:H carbon-based film is successfully prepared on WC cemented carbide using a DC reactive magnetron sputtering process. The microstructure, mechanical properties, and tribological behavior of the as-prepared carbon-based film are systematically investigated. The results show that the doping Ti forms TiC nanocrystallites that are uniformly dispersed in the amorphous carbon matrix, whereas the doping Ce forms CeO2 that exists with the amorphous phase in the co-doped (Ti,Ce)/a-C:H carbon-based film. The mechanical properties of this (Ti,Ce)/a-C:H film exhibit remarkable improvements, which could suggest higher hardness and elastic modulus as well as better adhesive strength compared to solitary Ti-doped Ti/a-C:H film. In particular, the as-prepared (Ti,Ce)/a-C:H film presents a relatively low friction coefficient and wear rate in both ambient air and deionized water, indicating that (Ti,Ce)/a-C:H film could feasibly improve the tribological performance of WC cemented carbide in a water environment.

Testing Atmosphere Effect on Friction and Wear Behaviors of Duplex TiC/a-C(Al) Nanocomposite Carbon-Based Coating

Due to strongly tribological atmosphere sensitivity of carbon-based coatings, it is of extreme significance to investigate their friction and wear behaviors in different atmospheres. In this letter, duplex nc-TiC/a-C(Al) nanocomposite carbon-based coating coupled with high hardness, low internal stress and high adhesion strength was successfully fabricated using magnetron sputtering process. The friction and wear behaviors of as-fabricated coating were evaluated in dry N2, humid N2, air, dry O2, and humid O2 atmospheres, respectively. Results show that the as-fabricated coating possesses very high friction and wear due to the strong covalent bond interactions at the sliding interface caused by the free σ-bonds on the coating surface in dry N2 atmosphere. Whereas the free σ-bonds can be efficiently terminated and passivated by water and/or oxygen molecules to weaken the strong covalent bond interactions to result in low friction and wear of coating in humid N2, air, dry O2, and humid O2 atmospheres. The compact and homogeneous carbonaceous tribo-layer on the counterpart is mainly responsible for the lowest friction and wear of coating in humid N2 atmosphere. Whereas the tribo-layer can be restrained to a certain extent by the tribo-chemical reaction, especially it results in a nearly negligible carbonaceous tribo-layer on the counterpart in dry O2 atmosphere, which is mainly responsible for largely increased friction and wear of coating.