The influence of titanium on the microstructure and properties of Ti/h-BN/Fe composite coatings by plasma arc cladding

Abstract

In order to improve the wear resistance and corrosion resistance of U75V steel for the application of the rail steel in high-speed railway, different concentrations of Ti (2%, 4%, 6%, and 8% by weight) were integrated into the Ti/h-BN/Fe composite coatings, fabricated on U75V steel substrates through plasma arc cladding. The study explored how variations in Ti concentration affected the coating's microstructure, hardness, residual stresses, tribological behavior, and electrochemical characteristics. SEM analysis showed that the microstructural configurations varied from dendritic to columnar to equiaxed, depending on the Ti content. The surfaces of these coatings were compact and exhibited no visible cracks or defects. Microhardness values escalated from 770.4 HV_0.5 at 2% Ti to 911.2 HV_0.5 at 8 wt.% Ti. Concurrently, compressive residual stresses on the surfaces also enhanced from 611.4 MPa to 755.6 MPa with increasing Ti percentages. The friction and wear test was carried out by using the UMT-2 multifunctional friction and wear tester with a load of 30N, and the results show that friction coefficients and wear rates initially increased, subsequently decreased, and then ascended as the Ti content was incremented. Optimal tribological properties were noted at a Ti concentration of 6 wt.%, where the friction coefficient and wear rate dropped to 0.387 and 3.7 × 10⁻³mm³·N⁻¹·m⁻¹, respectively, attributed primarily to adhesive wear. Moreover, the corrosion resistance varied inversely with Ti levels, demonstrating a decrease followed by an increase. The most effective corrosion resistance was at 6 wt.% Ti, showcasing the highest self-corrosion potential (E_oor) at −0.1972 V and the lowest corrosion current density (j_oor) at 3.1224 × 10⁻⁹A·cm⁻², signifying superior corrosion resistance at this concentration. The coating with 6 wt.% Ti content exhibits optimal wear resistance and corrosion resistance, thereby providing a theoretical foundation for the potential application of such coatings on railway tracks.