Microstructure and corrosion behavior of SLM–Ti6Al4V with different fabrication angles in F⁻-containing solutions

Selective laser fusion (SLM) is an emerging 3D printing technology that can greatly shorten the processing cycle and reduce the production cost of medical implants, thus offering broad prospects for application in the biomedical field. In addition, its excellent corrosion resistance is a crucial characteristic for its application as a biomedical material. However, the corrosion behavior of SLM–TI6AL4V, especially its corrosion resistance, has not been a focus of extensive study to date. In this study, the microstructures and corrosion behavior of SLM–Ti6Al4V, which was produced via selective laser melting with fabrication angles of 30°, 45°, and 60°, in NaF-containing solutions were investigated using metalloscopy, scanning electron microscope, electrochemical measurement, and immersion test. According to microstructural analysis, SLM–Ti6Al4V is characterized by prior β grains with needle α' phases; the prior β grains for the sample with the fabrication angle of 45° are most like equiaxed, and the α' phase are the smallest. In addition, the sample with the fabrication angle of 45° has the smallest lattice distortion compared to the others. The electrochemical measurements reveal that with increasing NaF concentration, the corrosion resistance of all three samples deteriorates, and the critical fluoride concentration of the samples with fabrication angles of 30°, 45°, and 60° are in the range of 0.0005–0.00075 mol·L⁻¹, 0.00075–0.001 mol·L⁻¹, and 0.0005–0.00075 mol·L⁻¹, respectively. From the results of the immersion test, in the solution with NaF concentrations less than the critical value, the surfaces of the three samples remain nearly intact, while in the solutions with more added NaF, active dissolution takes place on the sample surface. Comparing the results of the electrochemical measurements and the immersion test, the sample with the fabrication angle of 45° exhibits superior corrosion resistance.