High Cycle Fatigue Properties and Fracture Behavior of TC4 Titanium Alloy at Room and Elevated Temperatures

Abstract

AbstractThe high cycle fatigue properties and fracture characteristics of TC4 titanium alloy at room temperature, 200 ℃ and 400 ℃ under the stress concentration factors Kt = 1 and Kt = 3 were studied. The S-N curves of rotary bending fatigue under different conditions were plotted by power function fitting of three parameters, and the fatigue limit of Nf = 3 × 107 cycles was obtained. The results indicated that TC4 alloy had a high fatigue notch sensitivity at both room and elevated temperatures, which led to the significant decline of fatigue properties. It was found that the smooth specimen was more sensitive to the effect of temperature, whose high cycle fatigue performance decreased obviously with the increase of temperature. There was only one fatigue crack source region in the smooth specimen, and obvious fatigue bands and a small number of secondary cracks can be seen in the propagation region. With the propagation of cracks, instantaneous fracture occurred in the inner side of the specimen opposite the source region. Multiple fatigue crack sources were formed on the surface of the notched specimen, and then the fatigue cracks expanded from the circumference inward. Finally, instantaneous fracture occurred in the inner part of the specimen. TC4 alloy was characterized by ductile fatigue fracture.KeywordsTC4 titanium alloyStress concentration factorTemperatureHigh cycle fatigueFatigue fracture morphology