The Relationship Between the Macro- and Microstructure and the Mechanical Properties of Selective-Laser-melted Ti6Al4V Samples under Low Energy Inputs: Simulation and Experiment

The occurrence of structural defects in selective laser melting (SLM) damages the mechanical properties and fabrication accuracy of components and is closely related to the processing parameters. Therefore, having a good grasp of the interaction mechanism between the material and laser is useful for designing an improved process window. In this study, we experimentally investigated the relationship between the samples' macro- and microstructure and their mechanical properties under low energy inputs, and the response behaviour of as-built parts under these parameters was calculated using a thermal fluid flow (TFF) model with a modified and surfacetracking heat source. The results showed that Ti6Al4V parts obtained via SLM under low energy inputs exhibited a strong relationship between the macro- and microstructure and the mechanical properties. Single-track TFF models were built to better understand the underlying phenomena that are influenced by process parameters and then affects the depositing process. The models provided insight into the thermal history, deposition behaviour, densification, size accuracy, and surface morphology and by considering the velocity field, the phenomenon of powder adhesion caused by the Bernoulli effect could be investigated. Interestingly, the TFF model with a volume energy density (Ev) of 90 J/mm3 captured the formation of pores, however, high smoothness of the surface and size accuracy was obtained in the sample. It can be proved that densification is hardly related to the surface morphology or the fabrication precision. In addition, our experiments showed that the fabrication process was less sensitive to process parameters at Ev = 38 J/mm3. Densification was also more sensitive to the laser power than to the scanning speed. The results suggest that good-quality samples can be synthesised via SLM under low energy inputs, and the TFF model is a powerful tool for the systematic optimisation of the process parameters. Our findings could be applied to improve the controllability of the overhang surface with severe powder adhesion in further studies.