Fatigue cracking behavior and life assessment of TC11 titanium alloy in very high cycle regime at two working temperatures

Axial loading fatigue tests were conducted with two stress ratios to investigate fracture surface behavior and associated failure analysis governing crack nucleation of TC11 titanium alloy at two working temperatures, spanning high-cycle and very high-cycle fatigue regimes. Furthermore, scanning electron microscopy, optical microscopy, and electron-backscattered diffraction techniques were employed to analyze the cracking mechanism. The interior failure is attributed to the cleavage of the large equiaxed α_p-grains and facet-facet cluster area-fisheye formation. Moreover, the crack growth threshold values and the transition sizes from small to long cracks decrease with temperature rise. In addition, small cracks follow the path that requires minimum energy for propagation as per the microstructural orientation and are governed by maximum shear stress, resulting in the formation of crystallographic facets. Based on the analysis above, the interior fracture mechanism was summarized as related to the microstructure characteristics. Considering the fatigue cracking behavior and microstructural features, a model for predicting crack nucleation life is developed, exhibiting a better consistency between predicted and experimental fatigue lives.