In-situ experimental investigation on fatigue crack growth behavior and crack tip plastic zone evolution of laser powder bed fused TiC/Ti6Al4V composites

In-situ fatigue crack growth tests are conducted on laser powder bed fused TiC/Ti6Al4V composites under a stress ratio of 0, utilizing digital image correlation and characterization techniques to monitor crack evolution. As a result, the major crack exhibits a microscopically sinuous zigzag path, resulting from the growth and coalescence of microcracks governed by localized shear stress. Owing to microstructural barriers such as prior β grain boundaries, the propagation of microstructurally small crack with a length of less than 200 μm exhibits notable discontinuity and retardation. In contrast, an acceleration in crack growth rate is observed along the α phase boundaries within individual grains, indicating a path of reduced resistance. Compared to the long crack, the physically small crack shows larger near-tip deformation and smaller plastic zone size, attributed to the reduced crack closure effect. The existence of fatigue steps, secondary small cracks, local fatigue striations, and pore defects further confirms the influence of microstructure on crack growth behavior.