Low cycle fatigue behavior of laser melting deposited TC18 titanium alloy

Low cycle fatigue (LCF) behavior of laser melting deposited (LMD) TC18 titanium alloy was studied at room temperature. Microstructure consisting of fine lamella-like primary alpha phase and transformed beta matrix was obtained by double annealed treatment, and inhomogeneous grain boundary alpha phase was detected. Fatigue fracture surfaces and longitudinal sections of LCF specimens were examined by optical microscopy and scanning electron microscopy. Results indicate that more than one crack initiation site can be detected on the LCF fracture surface. The fracture morphology of the secondary crack initiation site is different from that of the primary crack initiation site. When the crack grows along the grain boundary alpha phase, continuous grain boundary a phase leads to a straight propagating manner while discontinuous grain boundary alpha phase gives rise to flexural propagating mode.