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.

Polyurethane elastomers are anticipated to be applied in the field of cavitation erosion (CE) resistance, but their protection and damage mechanisms are not clear, which greatly restricts their further development. In this article, five polyether polyurethanes (PU_x) with different crosslinking densities were prepared. Their mechanical properties, thermal properties, water absorption, surface morphology and chemical structure before and after CE tests were compared with ESEM, OM, TG-DSC, FTIR and XPS in detail. The results showed that with an increase in crosslinking density, the tensile strength of PU_x increased first and then decreased, elongation at break and water absorption reduced gradually and thermal decomposition temperature and adhesion strength increased steadily. During the CE process, cavitation load aggravated the degree of microphase separation and made brittle hard segments concentrate on the coating surface; meanwhile, cavitation heat accelerated hydrolysis, pyrolysis, oxidation and the fracture of molecular chains. As a result, the mechano-thermal coupling intensified the formation and propagation of fatigue cracks, which should be the fundamental reason for the CE damage of polyurethane elastomer. PU_0.4 exhibited the best CE resistance among the five coatings thanks to its good comprehensive properties and may find potential applications on the surface of hydraulic components.

A facile in situ synthesis approach and a size control strategy were established to obtain Ag₂S nanoparticles in polyimide (PI) composite coatings. Such Ag₂S nanoparticles in the composite coatings were characterized, and the effects of the as-obtained Ag₂S nanoparticles of different sizes on the mechanical and tribological properties of the nanocomposite coatings were investigated. Results indicate that the in situ synthesized Ag₂S nanoparticles exhibited good dispersibility and bimodal and multimodal size distribution in the nanocomposite coatings. The size of the Ag₂S nanoparticles can be effectively controlled by adjusting the substituent alkyl chain length of single-source precursor, and these Ag₂S nanoparticles exhibited superior improvement to mechanical and tribological properties of the nanocomposite coatings. More importantly, the Ag₂S nanoparticles with the proper grain size and bimodal size distribution provided the optimal mechanical and tribological properties for the nanocomposite coatings, and the excellent tribological properties were attributed to their outstanding mechanical properties and strong ability to form a homogenous and stable protective tribofilm.