Interior Cracking Behavior of Laser Powder Bed Fused TiC/Ti6Al4V Composites under Vacuum Environment

High and very high cycle fatigue tests were carried out to elucidate the interior crack nucleation behavior in a vacuum environment of a TiC-reinforced Ti6Al4V composite fabricated by laser powder bed fusion. To investigate the failure mechanisms, advanced microscopy techniques such as scanning electron microscopy and electron backscatter diffraction are employed. The first failure mode is the cracking of the inhomogeneous hardening zone (IHZ). The cleavage planes observed inside IHZ suggest that the essence of cracking is lamellar α′-grain fracture. The second failure mode is the lack of fusion (LOF) assisted IHZ cracking. The presence of LOF increases stress concentration and reduces the effective bearing capacity of the material, leading to a significant decrease in fatigue life. The knowledge gained can be utilized to optimize the fabrication process and design of composites, ultimately improving their fatigue resistance and extending their service life in applications.