Shutong Dai

Selective laser melting (SLM) fabricated Ti6Al4V (TC4) has broad application potential, though its mechanical behavior is highly sensitive to processing conditions. However, the coupled response of Young’s modulus, Poisson’s ratio, and impact toughness to SLM process parameters remains insufficiently understood. In this study, laser ultrasonic testing (LUT), Charpy impact testing, fractographic observation, and defect statistical analysis were combined to systematically investigate the effects of laser power, scan speed, and hatch spacing on the mechanical behavior of SLM-fabricated TC4 samples. The results show that the three properties exhibit a similar non-monotonic dependence on process parameters, with an overall parabola-formed trend. The optimized process parameters for Young’s modulus, Poisson’s ratio, and impact toughness were identified as laser powers of 315, 348, and 336 W, scan speeds of 1230, 1277, and 1193 mm/s, and hatch spacings of 77, 82, and 87 μm respectively. The data fitting indicated that impact toughness is the most affected by changes in both laser power, scan speed, and hatch spacing. It was followed by Young’s modulus. And Poisson’s ratio received the least impact. The combined defect, fracture, and microstructural analysis further reveal that both excessively low and excessively high volumetric energy density increase porosity and defect size, as well as reduce the β phase volume fraction and area weighted mean value of the transformed-phase plates’ width, thereby degrading mechanical performance. These results establish a process–defect/microstructure–property relationship for SLM TC4 and provide useful guidance for the optimization of mechanical performance in additively manufactured titanium alloy components.