Formation of TiB2/TiB layers on Ti6Al4V alloy: Adhesion and wear resistance

Abstract

This study investigates the formation of titanium boride (TiB₂/TiB) layers on Ti₆Al₄V alloy to enhance its surface hardness and wear resistance. Boride layers were synthesized via powder-pack boriding under an inert atmosphere at 1373 K for 10, 15, and 20 h. Under these parameters, a titanium diboride (TiB₂) layer with a maximum thickness of 9.7 ± 0.4 µm was obtained, achieving a total boride depth of 19.7 ± 0.4 µm. X-ray diffraction (XRD) corroborated the formation of the TiB₂ phases. Progressive scratch tests (1–60 N) identified Hertzian cracking, chipping, and spalling as the main damage mechanisms. The onset of Hertzian cracking was significantly delayed by increasing the thickness of the boride layer from 5.5 ± 0.1 to 24 ± 0.5 N, although the critical load for chipping decreased from 45 ± 0.3 to 39 ± 0.2 N due to the release of stored elastic strain energy. Multi-pass scratch tests showed 84% reduction in wear rate, achieving a minimum value of (3.7 ± 0.3) × 10⁻⁶ mm³ N⁻¹ m⁻¹ with friction coefficients below 0.05. Ultimately, the treatment fundamentally shifted the dominant wear regime from severe plastic deformation and galling to a milder regime of localized cracking, where the deep reinforcement provided by the titanium monoboride (TiB) whisker zone effectively stiffened the subsurface, preventing localized substrate collapse and conferring a superior load-bearing capacity to the thicker borided systems.