Effect of Fatigue Test Temperature on Microstructure and Properties of TC11 Titanium Alloy after Surface Nanocrystallization

The high cycle fatigue experiments of TC11 titanium alloy strengthened by supersonic fine particles bombarded (SFPB) were carried out at different temperatures (-30 degrees C, 25 degrees C, 150 degrees C). The fatigue fracture morphology and microstructure evolution at different fatigue test temperatures were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that gradient nanostructured layer with a thickness of 30 similar to 50 mu m is formed on the surface of TC11 titanium alloy after SFPB treatment and the average grain size is about 10 nm. After high cycle fatigue testing at different temperatures, the grain size of surface layer still remains in the nanometer scale, which is similar to that before fatigue testing. Surface hardening of TC11 titanium alloy induced by SFPB treatment causes the change of crack initiation site from surface to subsurface layer. The fatigue fracture morphology of TC11 titanium alloy is composed of three parts: fatigue source zone, crack growth zone and instantaneous fracture zone. In particular, the fatigue stripe width increases with the increase of fatigue test temperatures.