Effect of the Spatial Arrangement of Floating Builds with Minimum Support on the Microstructural and Mechanical Characteristics of Electron Beam Additively Manufactured Biomedical Ti-6Al-4V Alloys.

In this study, normal and floating builds of Ti-6Al-4V were fabricated by electron beam additive manufacturing. The effects of the spatial arrangement on the microstructure, mechanical properties, and surface roughness of the parts were investigated. Both the normal and floating builds exhibited an α+β lamellar microstructure, but the normal builds had finer grains compared to the floating builds. The microstructural characteristics were correlated with the thermal history, specifically the cooling rate, resulting from the connection plate (S45C for the normal builds and the powder bed for the floating builds). The compressive yield strength and hardness of the normal builds were higher than those of the floating builds, regardless of build location owing to the grain refinement effects on the normal builds. The top surface (TS) of the sample was smoothest, and the lateral surface of the sample was the roughest for both the normal and floating builds; however, the roughness of the TS and bottom surface samples did not differ significantly between normal and floating builds. There were no noticeable differences in the microstructure and mechanical properties of the builds in five different positions, that is, the center and four corners. Finally, these findings were used to develop a set of conceptual spatial arrangement designs, including floating builds, to optimize the microstructure and mechanical properties.