As the need for higher efficiency of engineering components increases, so does the demand for functional surfaces. While various tribosurfaces (e.g., texturing and coatings) have been developed, many researches are aimed at static functionality. On the other hand, due to a wide range of environmental adaptability and active control, active-morphing surfaces can be highly efficient and robust. In this paper, we demonstrate a novel morphing surface and its realization using additive manufacturing (AM). By using a diaphragm structure, morphing performance is achieved even if a hard resin material is used. When air pressure is applied to the backside of the diaphragm, it changes to a convex shape and vice versa. The concept requires a complex structure for arranging airflow and a solid morphing system. The AM is one great technique to create such complex structures. As a result of actual manufacturing, the created morphing structure realizes a large morphing of 600 μm or more. In addition, the shape changes reversibly depending on the air pressure. The surface also exhibits very interesting tribological characteristics. The surface shows a friction coefficient of about 0.3 with a concavity, and then increases to 0.5–1.7 with a convexity. A real-contact area measurement reveals that the novel property occurs due to change in the real-contact area depending on surface morphology. In conclusion, the present paper provides a new concept of a novel morphing tribosurface, which selectively performs as a low-friction or break-like surface, created using AM.

When the lubricating oil flowing between the contact surfaces contains simulated wear particles, it is considered that there is a high possibility for the particles to enter between the contact surfaces if the particles are present on the disk side in a friction test between a fixed ball and a rotating disk. For particles with a diameter of 0.8 μm, it has been previously shown that the entrainment frequency changes with the outside oil film thickness, but the effect of the disk material on the amount of particle deposition and the visualization of particle movement direction due to vortices generated between the contact surfaces had not been performed. In this study, by using SiO₂ disks and sapphire disks with different Hamaker constants, the effect on the amount of particle deposition in front of the contact surfaces was experimentally clarified by changing the van der Waals forces acting between the particles and the disks. Additionally, assuming that vortices generated in the oil film between the contact surfaces move the particles to the disk surface side, the flow direction of the lubricating oil was visualized using Navier-Stokes simulation.

Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses surface damage in a high-temperature operating environment; however, it causes a detrimental effect that hinders the formation of a competent tribofilm. In this study, we dispersed highly reactive TiO₂ nanoparticles (TDONPs) in molybdenum dithiocarbamate (MoDTC)-containing lubricant for adhering triboproducts on the DLC surface. In addition, TDONPs contributed to the decomposition of triboproducts by promoting the decomposition of MoDTC through its catalytic role. Rutile TDONPs were more helpful in reducing friction than anatase TDONPs and improved the friction performance by up to ~100%.