Tribologically transformed structure of titanium alloy (TiAl6V4) in surface fatigue induced by repeated impacts

Under repeated impact solicitation in the elasto-plastic regime, Ti-6 wt.% Al-4 wt.% V (TiAl6V4) titanium alloy undergoes surface fatigue that leads to microstructural transformation and to wear. This tribologically transformed structure (TTS) appears after a given number of cycles, which depends on the impact parameters (kinetic energy, speed impact, indenter radius) and on the materials properties of the sample. Microstructural characterizations have been performed using different techniques i.e. optical microscopy, scanning electron microscopy, energy-dispersive X-ray fluorescence analyses. Transmission electron microscopy as well as nano-indentation tests reveal that the TTS structure has a typical grain size of less than 100 μm without preferential orientation and consists of α(hcp) phase with a very high (nano) hardness of 7.5 GPa.