Anisotropic fatigue strength and status of crack initiation of Ti17 disk fabricated by through-transus-processed forging

The high-cycle fatigue tests were performed along axial direction (AD), radius direction (RD), and inclined direction (ID) of the Ti17 disk fabricated by the through-transus-processed forging. Especially, the elongated beta grains exhibits a basket-weave microstructure feature with a wavy grain boundary alpha. The AD sample presents a minimum fatigue strength. Both the RD sample and ID sample exhibit a maximum and an approximate fatigue strength. The anisotropy of the fatigue strength is determined by the alpha lath tending to occur basal slip. Meanwhile, the {10 1 2} extension twins are observed near the region of the fatigue crack initiation. Besides, the dislocation accumulates at the interface of the alpha/beta phase through the analysis of the Kernal average misorientation and transmission electron microscopy, resulting in that it becomes preferential sites for the fatigue crack nucleation and early propagation.