Sliding bearings are critical components of the internal combustion engine. Friction and wear occur in the contact area between the shaft and the bearing. Significant wear can occur in poor working conditions or after a long service time, leading to the failure of the sliding bearing and affecting the reliability of the machinery. It is essential to investigate the wear performance of sliding bearings, understand their wear mechanism, predict their service life, and select wear-resistant materials and surface treatments. This paper reviews the current status and prospects of sliding bearing wear research, focusing on the classification of sliding bearing wear tests, wear testing machines, wear test research, wear prediction models, and future research prospects.

Powder-based layered Additive Manufacturing (AM) techniques lead to high surface roughness, due to the balling and partial melting of powders, which cannot satisfy the requirements of design and practical use. Consequently, until there is a significant step-change in the resolution of AM technology, finishing processes will be a necessary step in the additive manufacturing process. In this work, ultrasonic abrasive polishing experiments are conducted with the aim of improving the surface quality of additive manufactured components. The roles of cavitation bubbles and abrasive particles in material removal are discussed. The impact action of abrasive particles is simulated using the Smoothed Particle Hydrodynamics (SPH) method. The effects of ultrasonic output power and the concentration of abrasive suspension on machining characteristics are also examined. It is found that the cavitation bubble collapse in ultrasonic polishing can remove the partially melted structures efficiently, and further roughness improvement could be obtained using the micro-cut and impact of abrasive particles in the slurry. An increase in the ultrasonic output power and abrasive concentration within a certain range lead to a more desirable polishing effect.

Enhancing lubrication across various tribological systems in the maritime industry is essential for improving safety, efficiency, and environmental sustainability. Al₂O₃ nanoparticles, employed as additives in lubricating oils, demonstrate favorable tribological properties including anti-wear and anti-friction characteristics. In this work, nano-scale γ-Al₂O₃ particles with different shapes, i.e., nanosheet, nanorod, nanosphere, and irregular-shaped nanoparticles, were prepared and calcinated forming the same crystalline phase with nanoscale size, which dispersed well in lubricating oil. The tribological properties of Al₂O₃ nanoparticles as lubricating oil additives were examined using block-on-ring wear tests, and the effects of the particle shape and particle concentration were investigated. The results indicated that the frictional properties are largely influenced by the particle shape and the concentration of the Al₂O₃ additives, with the optimal concentration being around 0.1 wt% for each shape. The lubricating oil with nanosheet additives presented the best tribological performance, followed by those with nanorod, nanosphere, and irregular-shaped Al₂O₃ nanoparticle additives. Al₂O₃ nanosheets as the lubricating oil additives reduced the stress effect on the friction surface because of their larger bearing area and are inter-particle-sheared during sliding due to the movement of friction pairs, which can further improve the tribological properties compared to other shapes.