40. Effect of Ultrasonic Deep Rolling on High-Frequency and Ultrasonic Fatigue Behavior of TC4

A gradient nanostructured (GNS) surface layer was produced on TC4 samples by means of ultrasonic deep rolling (UDR). Grain size refined to nano-scale and increased to macro-scale with the increasing depth. The microstructure of the UDRed sample was observed and the mechanical properties of UDRed samples were measured. The Roughness of samples after rolling is reduced by 60% with the comparison of un-treated sample. The micro-hardness increased with the increasing rolling passes. After the measurement of mechanical properties, the fatigue tests were carried out and the fatigue life of UDRed samples shows were lower than that of un-UDRed samples on high-frequency and ultrasonic fatigue. The fatigue fracture and the initiation of cracks have been investigated to clarify the fatigue mechanism of the UDRed samples. The results showed that the decrement of fatigue life of UDRed samples compared with coarse-grain samples was attributed to the fever in cyclic loading induced by the heterogeneity of the material.