Yongfeng Gong

Aggregation of Nb filaments in Cu-Nb/Sn composite during low-temperature intermetallic growth

Abstract The solid-state diffusion behavior in the layered Cu–Sn/Cu intermetallic phase system was investigated by using Cu–20 wt.% Nb (filament)/Sn diffusion couple at 400–450°C. Very thin Nb filament is used as an inert marker for studying the Kirkendall effect-like phenomena. Experimental results show that the Nb filaments near the interface of Cu–Nb/Sn are shifting toward the Cu–Nb side and forming a Nb filament aggregating zone with the concentration of Nb up to 27–40 wt.% and a width about 10–15 μm. The study proved that the shift of Nb filament originated from volume expansion caused by the formation of e phase (Cu3Sn). The convoluting or coarsening of ribbon-like Nb filament resulting from stress relaxation during annealing plays a role of driving force for the aggregation of Nb, making the density of Nb filaments in the aggregating zone dependent on temperature.

Tribocorrosion behaviours of cold-sprayed diamond–Cu composite coatings in artificial sea water

ABSTRACT Frictional components in the marine environment always face a synergistic effect of wear and corrosion. Diamond-based composite coatings are known for their excellent wear performances, but few studies were conducted relating to their marine applications. Herein, diamond–copper composite coatings were successfully deposited on stainless steel 316L plates by the cold spraying, employing diamond powder coated with thin copper (Cu) layer. The diamond–Cu composite coatings with a diamond content of 31.79% were successfully fabricated. The coatings showed significantly enhanced wear resistance tested in artificial sea water with the reduced friction coefficient from 0.32 for the Cu coating to 0.10 for the diamond–Cu coating. Further electrochemical testing showed promoted anti-corrosion performances of the diamond-containing coatings. The newly constructed diamond–Cu coatings show encouraging promises as anti-tribocorrosion layers for marine structures.

Suspension Flame Spray Construction of Polyimide-Copper Layers for Marine Antifouling Applications

Individual capsule-like polyimide splats have been fabricated by suspension flame spray, and the polyimide splat exhibits hollow structure with an inner pore and a tiny hole on its top surface. Enwrapping of 200-1000-nm copper particles inside the splats is accomplished during the deposition for constrained release of copper for antifouling performances. Antifouling testing of the coatings by 24-h exposure to Escherichia coli-containing artificial seawater shows that the Cu-doped splat already prohibits effectively attachment of the bacteria. The prohibited adhesion of bacteria obviously impedes formation and further development of bacterial biofilm. This capsulated splat with releasing and loading of copper biocides results in dual-functional structures bearing both release-killing and contact-killing mechanisms. The suspension flame spray route and the encapsulated structure of the polyimide-Cu coatings would open a new window for designing and constructing marine antifouling layers for long-term applications.

Incorporation of Copper Enhances the Anti-Ageing Property of Flame-Sprayed High-Density Polyethylene Coatings

High-density polyethylene (HDPE)-copper (Cu) composite coatings were prepared through depositing HDPE-Cu core-shell particles by flame spraying. The HDPE-Cu composite coatings and the HDPE coatings were aged in xenon lamp ageing testing chamber. The variations of chemical compositions and surface morphology of the coatings before and after the ageing testing were analyzed using infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and ultraviolet-visible spectrophotometer. Results show that there is no chemical composition variation in the HDPE-Cu coatings. Cracks were found on the surfaces of the HDPE coatings, while the HDPE-Cu coating shows almost intact surface morphology. These results suggest that the HDPE-Cu coatings present better anti-ageing performances than the HDPE coatings. Further assessment of the function of Cu shells on the anti-ageing property reveals that Cu shells not only enhanced the absorption of the coatings to ultraviolet, but also increased their reflectivity to visible light. Additionally, the Cu shells enhanced the decomposition temperature and thermal stability of HDPE in the composite coatings. These results give bright insight into potential anti-ageing applications of the polymer-based structures.