Investigating on the microstructure of cross-section and surface of Ti-10Mo alloy produced by selective laser melting

Considering the nature of the additive manufacturing process and the produced layered structure, the possible gradient in microstructure can be predictable. For this purpose, the morphology and microstructure of the cross-section from top to bottom was evaluated. The morphology of the last and first printed layers, were also investigated.

Ti-10Mo was printed using mixed powder in 120 layers, each thickness of 25µm, by selective laser melting (SLM) with a laser power of 95 W, a scanning speed of 600 mm.s-1, and a hatching distance of 88 µm under argon atmosphere. Density was measured, and the constituent phases were identified by XRD. The microstructural feature was studied by optical and scanning electron microscopies.

The printed samples were dense, and the relative density was about 98.53%. Details in microstructural evaluation show spectacular Mo-enriched rims, which reveal the circumstance of Mo dissolution in molten Ti and homogenization, consequently. Also, a gradient in Mo dissolution is seen along the cross-section. So that, at the top, the sides of molten pools that are mostly Mo enriched are seen as thick white and bright rims in electron microscopy and as white to light purple in optical microscopy. However, at the bottom, the rims seem to be really thinner and smoother, which can be in consequence of enhanced diffusion of the Mo to Ti matrix. Here, the promoted diffusion could be in the result of heat transfer from the newly printed layer to the previous printed ones.