Expanding manufacturability of sheet-based triply periodic minimal surfaces by electron beam powder bed fusion in Wafer theme

Abstract

Porous biomaterials based on triply periodic minimal surfaces (TPMS) are intensely studied and discussed in the literature. Manufacturing of these structures with a complex geometry became possible using additive manufacturing methods, having their own specifics and challenges. Previously, we demonstrated that sheet-based gyroids, one of TPMS structures, manufactured by electron beam powder bed fusion in Melt and Wafer themes could possess identical mechanical properties (quasi-elastic gradient). In the current research sheet-based gyroids were produced using Wafer Theme with five different settings, including electron beam current and scan speed variation with MultiBeam turned on and off, in attempt to obtain thin walls without losing mechanical performance. Mechanical tests revealed that the specimens manufactured with higher beam line energy on average show better mechanical properties. The specimens produced with MultiBeam showed slightly lower mechanical properties, and do not demonstrate significant improvement in the TPMS surface roughness. According to SEM studies, the average wall thickness was about 0.4 mm for specimens with high line energy, and 0.3 mm for low line energy. Through-hole defects on the horizontal surfaces, noticed and discussed by us previously, have larger average area of the hole and more irregular shape for increased beam line energy. TPMS surface morphology of the specimens produced with higher beam energy and no MultiBeam was on average more even. According to EBSD, α/α` martensite with laths oriented in a Widmanstätten basket-weave pattern was observed with no β phase in the resulting material. No significant differences in microstructure between specimens produced with different beam energy was detected. FEA modeling revealed the impact of the wall thickness, through holes size and orientation on quasi-elastic gradient of a gyroid. It was demonstrated that, through holes with small size located on the horizontal surfaces (layer plane) have only a minor impact on the mechanical properties of the samples if they are not extremely abundant.