Printability and microstructural evolution of Ti-5553 alloy fabricated by modulated laser powder bed fusion

In this research, the printability of Ti-5553 alloy is assessed using a modulated laser powder bed fusion method. Cylindrical samples were printed with a wide range of volumetric energy density (VED). Density evaluation was practiced by the Archimedes method and X-ray computed tomography (XCT). Surface roughness analysis and hardness mapping were further used to characterize the as-built samples. In addition, the microstructure was studied using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. It was observed that low and high VED values resulted in an increase in the level of porosity. The highest relative density of 99.92% and surface roughness of < 12 μm were achieved while using the VED of 112 J/mm³, resulting in a uniform hardness distribution equal to 295 ± 10 HV. In addition, the characterization by electron microscopy revealed evidence for the presence of ω phase in the sample with the highest density. It was also observed that the use of rather high VEDs gave rise to the in situ precipitation hardening due to nucleation of α-Ti needles in the β-Ti phase matrix. However, due to the inhomogeneous size distribution and volume fraction of the α-Ti needles along the building direction, a non-uniform hardness was obtained when high VEDs were applied.