Mechanical properties and failure behavior of silicon nitride based plate and truss lattices fabricated by vat photopolymerization 3D printing

Truss- or plate-based silicon nitride (Si₃N₄) ceramic lattices, including SC (simple cubic), SCBCC (hybrid of SC/body centered cubic truss) and plate SO (hybrid of SC/octet plates) lattices with density of ∼1.6 g/cm³ were fabricated by vat photopolymerization 3D printing. Uniaxial compression tests show that the plate SO lattices exhibited ultrahigh elastic modulus of 103 GPa and strength of 418 MPa, followed by SC (83 GPa/415 MPa) and SCBCC (71 GPa/324 MPa). The lattices displayed interesting failure characteristics, where the truss lattices tend to have failure start at horizontal or inclined struts at outer regions and proceed ‘inwards’, while plate-based lattice have outer regions breaking from the main body in a highly faceted manner. Under 3-point bending, the SCBCC lattice offered better support against shear and diagonal loads, which enabled it to exhibit similar flexural strengths to the SC lattice (∼130 MPa). The fracture failure mechanisms were thoroughly discussed with the support of finite element simulation analysis. The studied Si₃N₄ ceramic lattices have effective densities similar to conventional plastics but exhibit the compressive and flexural properties comparable to many ceramics and metals, which renders it great potential in various applications such as in automotives, aerospace and satellites.