Although the friction and wear behavior of plasma sprayed aluminum matrix ceramic coatings have been extensively discussed in the last decades, only few researches have been carried out the wear mechanisms sliding against different pairs. The tribological behaviors of plasma sprayed Al2O3 coating sliding against ZrO2, Si3N4, Al2O3 and stainless steel balls in air were comparatively investigated in this study. It was showed that Al2O3 coating sliding against different counterparts exhibited diverse tribological behaviors, which could be mainly ascribed to the different mechanical properties of counterparts. Meanwhile, the tribochemical reactions influenced the friction performances significantly. Moreover, the transform of γ-Al2O3 to α-Al2O3 occurred during the friction, which was closely related to the coefficient of friction and thermal conductivities of counterparts. The main wear of Al2O3 coating sliding against ceramic materials resulted from the brittle fracture and abrasive wear. While it was dominated by adhesive wear when sliding against stainless steel, and accompanied with abrasive wear.

Hydroxyl-polysiloxane prepolymers were prepared via refluxing methyltriethoxysilane (METS) and dimethoxydimethylsilane (MSDS) at 75 °C in the presence of hydrochloric acid as the reactant. As-obtained prepolymers were used to modify aluminum chromium phosphate binder; and the modified aluminum chromium phosphate binder was adopted to fabricate bonded solid lubricating coatings with MoS2 and Sb2O3 as the solid lubricants. The structure of the modified aluminum chromium phosphate binder was investigated by infrared spectrometry and X-ray photoelectron spectroscopy. The corrosion behavior of the organosiloxane-modified phosphate solid lubricating coatings was examined by salt spray test. Moreover, an MM-200 friction and wear tester and an Optimol SRV-IV oscillating friction and wear tester were performed to evaluate the tribological behavior of the solid lubricating coatings at room temperature and 500 °C. The worn surfaces of the solid lubricating coatings were observed and analyzed with a scanning electron microscope. It was found that P–O–Si bond was formed in the organosiloxane-modified aluminum chromium phosphate binder, which confirmed that there occurs chemical reaction between hydroxyl-polysiloxane prepolymer and the aluminum chromium phosphate binder. As a result, the flexible organic structure bonded in the aluminum chromium phosphate binder favored to improve the toughness, corrosion resistance and tribological behavior of the molybdenum disulfide bonded solid lubricating coatings.

•Mullite coating is fabricated by plasma spraying with spray-dried feedstock.•The wedging action of water leads to the largest wear rate of the coating in water.•The boundary and hydrodynamic lubrication produce the lowest COF in acid solution.•Self-produced micro-texturing is formed on worn coating surface in acid condition.Spray-dried mullite powder was plasma sprayed onto steel substrates to form mullite coating. The microstructure of mullite coating and its tribological properties coupled with Si3N4 ball under dry sliding as well as water and hydrochloric acid solution were investigated. Results indicate that mullite coating exhibits high porosity and retains an amorphous phase. The mullite coating-Si3N4 exhibits greatly reduced coefficient of friction under HCl solution, due to the boundary lubrication of the hydrated silica layer and the hydrodynamic lubrication of the acid solution. Moreover, since the wedging action of water, the mullite coating has the highest specific wear rate under water environment.

WC-(W,Cr)2C-Ni coatings were prepared by atmospheric plasma spraying (APS) with different spraying powers. The effect of spraying power on microstructure, phase composition, hardness, fracture toughness, and oscillating dry friction and wear behaviors of the coatings were studied. Simultaneously, the microstructure and properties of the as-sprayed coatings were compared with those of WC-17Co coating prepared under the optimal spraying power. It was found that spraying power had significant effect on the molten degree of feedstock powder and phase composition as well as microstructure and properties of WC-(W,Cr)2C-Ni coatings. WC-(W,Cr)2C-Ni coating deposited at a moderate spraying power of 22.5 kW had the highest fracture toughness and the best wear resistance. WC-17Co coating obtained under the moderate spraying power had poor fracture toughness and wear resistance. Moreover, the four kinds of coatings were all dominated by subsurface cracking and removal of materials when sliding against Si3N4 ball under unlubricated conditions.

•The ZrO2 ceramic coatings were fabricated via atmospheric plasma spraying.•MoS2 with flowerlike microsphere structure is synthetized by hydrothermal method.•Nano-layered MoS2 is interconnected to grow in the micro-defects of ZrO2 coating.•The ZrO2/MoS2 composite coatings exhibit excellent tribological properties.A novel method was introduced in this article to fabricate hybrid materials by virtue of thermal sprayed ceramic coatings as templets to improve their tribology performance. MoS2 was in-situ synthesized in the pores and micro-cracks of ceramic coatings using hydrothermal method coupled with vacuum impregnation. The resultant MoS2 appeared flowerlike microsphere structure and constructed with many ultrathin nanosheets, which were curly and interconnected to grow in the pores and micro-cracks of ZrO2 coatings. The results of tribological test revealed that the composite coatings have excellent tribological properties due to the formation of MoS2 lubricating film on frictional surfaces in comparison with pure ZrO2 coatings.