| Abstract: | Laser additive manufacturing(LAM)technique has unique advantages in producing geometrically com-plex metallic components.However,the poor low-cycle fatigue property(LCF)of LAM parts restricts its widely used.Here,the microstructural features of a Ti-6Al-4 V alloy manufactured via high power laser directed energy deposition subjected to low-cycle fatigue loading were studied.Before fatigue loading,the microstructure of the as-deposited parts was found to exhibit a non-homogeneous distribution of columnar prior-β grains(200-4000 μm)at various scanning velocities(300-1500 mm/min)and rela-tively coarse α-laths(1.0-4.5 μm).Under cyclic loading,fatigue microcracks typically initiated within the aligned α phases in the preferred orientation(～45° to the loading direction)at the surface of the fatigue specimens.Fatigued Ti-6Al-4V exhibited a single straight dislocation character at low strain amplitudes(＜0.65％)and dislocation dipoles or even tangled dislocations at high strain amplitudes(＞1.1％).In addition,dislocation substructure features,such as dislocation walls,stacking faults,and disloca-tion networks,were also observed.These findings may provide opportunities to understand the fatigue failure mechanism of additive manufactured titanium parts. |
