Achieving ultrahigh fretting fatigue endurance in TB8 titanium alloy with hierarchical structure via triggering nanocomposite and phase transformation

Extraordinary fretting fatigue endurance is critical for engineering structures prone to contact with expected long service lifetimes. Here, we propose a strategy to achieve ultrahigh fretting fatigue endurance in titanium alloy. A special hierarchical structure, i.e. gradient amorphous-nanocrystalline grain/coarse grain, was designed in a TB8 titanium alloy via surface severe plastic deformation, which forms an nanocomposite structure comprising of amorphous-nanocrystalline and nano-lamellae and beta to alpha phase transformation upon repeated fretting wear. The nanocomposite surface and phase transformation suppress cracks initiation and propagation, resulting in the high fretting fatigue life that was 30.2-times higher than that of the original TB8 titanium alloy via triggering an exceptional fretting fatigue phenomenon where damage-crack initiate towards the interior of non-fretting contact zone. This study provides a new insight into improving the fretting fatigue endurance of titanium alloys.