Yongkun Qin

Compositions and tribological properties of PEO coatings on Ti6Al4V alloy

ABSTRACT Hard oxide coatings were deposited on Ti6Al4V alloy using plasma electrolytic oxidation process from mixed aluminate/phosphate electrolytes. The influence of aluminate/phosphate proportion on the phase compositions, mechanical and tribological properties was systematically investigated. The results showed that plasma electrolytic oxidation (PEO) coatings with high compactness and hardness were formed in high aluminate/phosphate ratio electrolyte and the wear resistance and load bearing capacity were greatly improved due to the presence of hard γ- and α-Al2O3 phases. Low aluminate/phosphate ratio electrolyte led to thin and loose coatings without α-Al2O3 phase. It was shown that a thicker coating could provide only a limited improvement in wear resistance unless it is hard and free of porosity.

Wide temperature lubrication of LST/PEO/Ag/MoS2 multilayer coating

ABSTRACT The Ag film and MoS2 film were successively deposited onto the LST/PEO duplex-treated titanium alloy substrate. The friction tests were conducted at 25°C, 350°C and 600°C, respectively. The worn morphologies were analysed by optical microscopy and Raman spectrum. The results showed that the LST/PEO/Ag/MoS2 coating exhibited more excellent friction behaviour in comparison to the LST/PEO coating at 25–600°C. The combined lubrication of Ag diffused from surface micro-pores and Ag2MoO4 formed on the surface is responsible for the decrease of friction coefficient at 600°C. It also revealed that the friction heat can promote the formation of Ag2MoO4 in comparison to the high test temperature.