Tribological behavior of core-shell structured porous Ti-TiN composites under lubrication condition

In this study, core-shell structured porous Ti-TiN composites were fabricated by powder metallurgy route, and their microstructure and tribological performance were investigated. The composites were produced througth heat treatment of sintered pure titanium samples in a nitrogen gas atmosphere. During the heat treatment, nitrogen atoms diffused into the interior of the titanium powder particles (core), while a nitride-based shell layers were formed on their outer surfaces. To evaluate their tribological properties, ball-on-disk wear test was conducted under lubrication conditions in using SUS440C steel balls as the counter materials. Compared to pure titanium, the Ti-TiN composites exhibited a significantly lower and more stable coefficient of friction, along with enhanced wear resistance. These improvements are attributed to the synergistic effects of: (i) oil retention within the porous structure, enabling stable lubrication at the sliding interface; (ii) solid solution strengthening of Ti matrix by nitrogen atoms; and (iii) prevention of direct contact with the counter material by hard TiN shell layers. As a result, the Ti-TiN composites exhibited reduced wear loss and superior tribological performance under lubrication compared to pure titanium.