Tribological Performance of High-Speed Laser Cladded Cbn Reinforced Composite Coatings: The Influence of Ag Additions

Abstract

This study investigates the effects of Ag addition on the microstructure, microhardness, and tribological properties of Ti-based cBN composite coatings with high-speed laser cladding. The effect of Ag addition on the solidification process of Ti-based cBN composite coatings was investigated. At low concentrations, Ag is fully dissolved in the Ti matrix in solid solution. However, with increasing Ag content, precipitation of elemental Ag and Ag-Ti intermetallic compounds occurs. On this basis, the hardness and tribological properties of the coatings after Ag addition were comparatively investigated at room temperature and elevated temperatures (300°C–500°C). The results indicated that the hardness of the coatings increased with rising Ag content due to solid solution strengthening and the formation of Ag-Ti intermetallic compounds. However, when the Ag content exceeded 2.5 wt.%, the hardness exhibited a decreasing trend. With increasing Ag content, both the room-temperature friction coefficient and wear volume of the coatings decreased gradually. When 10 wt.% Ag was added, the friction coefficient reached 0.56, representing a 15% reduction, and the wear volume decreased by 28%. Additionally, the primary wear mechanisms gradually evolved from adhesive and fatigue wear to oxidative wear. Under high-temperature conditions (300°C, 400°C, and 500°C), the friction coefficients of 0 wt.% Ag and 5 wt.% Ag coatings decreased as the temperature increased, primarily due to the formation of oxide films. Notably, for coatings with 5 wt.% Ag, the friction-reducing effect was further enhanced due to the precipitation of Ag onto the friction surface in the form of “sweating” as a result of thermal expansion. Simultaneously, the formation of hard phases improved the resistance of the coatings to thermal softening and enhanced their wear resistance. Compared with 0 wt.% Ag coatings, 5 wt.% Ag coatings exhibited reductions in friction coefficient by 18%, 13%, and 7% at 300°C, 400°C, and 500°C, respectively. Furthermore, at 500°C, the wear volume of coatings with 5 wt.% Ag was reduced by 85% compared to those without Ag.

Keywords: High-speed laser cladding, coating, cBN, Ag, wear resistantance