Fatigue behavior of notched Ti-6Al-4V not STOA treated in inert environment

The paper investigates the fatigue behavior of Ti-6Al-4V in inert environment when the alloy is not subjected to Solution Treatment and Over-Aging (STOA). The case study of a plain and notched specimen with a stress concentration factor (Kt) of 3.11 without STOA tested axially in air is presented. The load ratio in the fatigue test is R ~ 0, with a maximum applied axial load of 13 kN. The specimen fails at 139,458 cycles. The lack of STOA treatment increases the fatigue strength, compared with specimens under STOA conditions. In order to understand the failure mechanism, the fracture surface is macroscopically observed with a stereo microscope. The fracture surface has no symmetry planes. The crack initiation point is on a vertex of the fracture surface and the final fracture area on the opposite vertex. The presence of defects in the specimen, machining errors and mounting misalignments can be responsible for the unexpected asymmetric behavior observed.