Effect of down surface energy density on surface roughness and microstructure of pure titanium fabricated by selective laser melting

Pure titanium (Ti), known for its exceptional corrosion resistance, high specific strength, and biocompatibility, is increasingly employed in patient-specific biomedical components and aerospace applications. While Selective Laser Melting (SLM) offers superior design flexibility and near-net-shape capabilities for fabricating complex geometries, the process still faces challenges in controlling the surface quality of down surface regions, where incomplete melting, powder adhesion, and steep thermal gradients often result in surface roughness and microstructural heterogeneity. In this study, we investigated the correlation between down surface microstructure and mechanical properties of SLM-fabricated pure Ti as a function of laser power and scan speed across various energy densities, and optimized the down surface process parameters. The results showed that surface roughness deteriorated under high power and high scan speed conditions due to insufficient energy input and rapid solidification. In contrast, an appropriate energy density at low power and low scan speed promoted the formation of a uniform equiaxed microstructure and more consistent surface morphology. The lowest roughness (Ra = 19.88 μm) and highest hardness (242.85 HV) were achieved under the optimal condition of 100 W power and 700 mm/s scan speed. This study confirms that energy-density-based control of process parameters plays a critical role in determining the surface quality and mechanical performance of pure Ti produced by the SLM process, and highlights the importance of process optimization for reducing post-processing requirements and enhancing functional performance.