Microstructures of Ti6Al4V matrices induce structural evolution of bioactive surface oxide layers via cold compression and induction heating

Highlights: • Structural evolution of oxide layers on Ti6Al4V surfaces were achieved by conducting cold-compression and induction heating. • Metallographic microstructures determined the size and structures of oxide crystallites formed via a seeding mechanism. • The formation of submicroscale TiO₂ crystallites considerably improved the HAp deposition in vitro. • The promotion effect of oversized oxide crystallites on HAp deposition was diminished. Considerable efforts have been devoted to the construction of micro- and nanostructured surfaces to improve the clinical application of Ti-based orthopedic implants. However, the preparation of bioactive microstructures with tunable characteristics remains challenging. Herein, we investigated the structural evolution of oxide layers on Ti6Al4V surfaces by conducting a cold compression and induction heating protocol. We found that the properties of the metallographic microstructures determined the size and structure of oxide crystallites formed via a seeding mechanism: the finer the matrix grains, the smaller the oxide crystallites. In addition, the alloy matrix grain sizes steadily increased with increasing axial compression because of recrystallization during induction heating. The formation of nanoscale rutile (TiO₂) crystallites caused an increase of surface roughness and hardness, and considerably improved the bioactivity of Ti6Al4V, as measured by the degree of hydroxyapatite deposition in simulated body fluid in vitro. However, oversized oxide crystallites had a negative effect on the promotion of hydroxyapatite deposition. This important finding offers a feasible method for the controllable in-situ construction of bioactive oxide layers by designing the required matrix microstructures of Ti-based implant materials.