Interfacial bonding mechanisms in TiB2/Ti systems fabricated by molten salt electrophoretic deposition: Experimental and first-principles calculation

Superhard ceramics are suitable materials to improve the surface characteristics of titanium. In this study, TiB 2 nanopowder was coated on titanium substrate using electrophoretic deposition in NaF-AlF 3 -Al 2 O 3 molten salts. The effects of varying deposition voltages and deposition times on TiB 2 coatings were investigated. Additionally, the microstructure of the coating surface was observed by scanning electron microscopy. With an applied cell voltage of 1.2 V and a deposition time of 1.5 h, a dense, defect-free TiB 2 /TiB composite coating (including the outer TiB 2 layer and the inner TiB whiskers layer) approximately 74 μm thick was produced, exhibiting a strong metallurgical bond to the substrate. A densely packed TiB whisker layer forms at the TiB 2 /Ti interface. The work of adhesion, interfacial energy, and electronic structure of the α-Ti(0001)/TiB 2 (0001) interfaces have been calculated using first-principles methods. Simultaneously, the diffusion of B atoms at the TiB 2 /Ti interface was computed to explain the formation process of TiB whisker layers. The work of adhesion calculations indicated that the B-HCP-Ti interfacial model exhibited the highest interfacial bond strength. The electronic structure of the interfacial model was analyzed to show that the Ti-terminated interface model was primarily formed through metallic bonds, while the B-terminated interface model was primarily formed through covalent bonds. Compared to the Ti-terminated interface, the B-terminated interface facilitates the diffusion of boron from TiB 2 into the titanium substrate more effectively.