• Fused filament fabricated large-sized alumina tetrahedra were rapidly (pSPS) sintered. • Accelerated densification observed as compared to the conventional sintering in air. • Tetrahedron`s base edges more prone to reductive discolouration than lateral ones. • Thermal gradients led to microstructural anisotropy and microcracking. Rapid radiation techniques, such as pressureless spark plasma sintering (pSPS) and ultra-fast high-temperature sintering (UHS), have proven effective in achieving rapid densification of ceramics, including additively manufactured components. However, sintered component sizes tend to be small, disk-shaped or having thin-strutted geometries. Here, fused filament fabrication (FFF) of a commercial filament was used for manufacturing complex-shaped and large-sized alumina tetrahedra with edge thickness of 5 mm, varying the edge size (15‒40 mm). The aim was to investigate the effect of heating rate (33‒300°C/min) and tetrahedron size on the pSPS outcome. The pSPS reductive environment discoloured the tetrahedra, but were all successfully rapidly sintered to full density irrespective of their size and heating rate employed. The evolved thermal gradient contributed to differential, anisotropic densification related shrinkage, microstructure and mechanical properties specific to tetrahedra` edge position, i.e., core versus shell and base versus lateral, also triggering cracking of the largest tetrahedra.
Ivekovič et al. (2026) studied this question.