Tribological Properties of Ti-DLC Coatings on Piston-pin Surfaces

A magnetically filtered cathode vacuum arc deposition system was used to deposit Ti-doped diamond-like carbon coatings (Ti-DLC) on pin surfaces to improve the wear resistance of high-power density diesel engine piston pins. The coating structure, composition, and morphology were characterised using field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and other techniques. Friction tests were carried out using a universal tribometer to study the tribological properties of pins with or without coatings under dry friction and oil lubrication. The surface morphology and cross-sectional morphology of the Ti-DLC coating show that the coating has a uniform cross-section and good surface properties. The XPS spectrum shows that the coating contains Ti-C, Ti-C*, sp2-C, sp3-C, and C-O/C=O. Raman spectroscopy shows that there is an amorphous carbon phase in the Ti-DLC coating. The friction test shows that the friction temperature increase of the pin with the Ti-DLC coating is lower than that without the coating, especially under dry-friction conditions. At the end of the test, the difference in temperature increase is 16.7%. The friction coefficient when using high-viscosity lubricating oil with a coating is relatively lower than that without a coating, especially under low-speed and heavy-duty conditions. In the dry-friction state, the coated surface has better wear resistance than the uncoated surface, which primarily manifests as abrasive wear, and the surface without a coating mainly experiences adhesive wear.