Role of interlayer bonding in mechanical-dielectric properties of Si ₃ N ₄ via heat-assisted vat photopolymerization

Silicon nitride (Si3N4) ceramics serve as key load-bearing and electromagnetic wave-transmitting materials for radomes in hypersonic vehicles. Vat photopolymerization (VPP) additive manufacturing technology enables integrated forming of complex structures, yet Si3N4’s strong ultraviolet absorption and scattering cause insufficient cured depth and weak interlayer bonding, limiting mechanical-electromagnetic synergistic regulation. Herein, a heat-assisted vat photopolymerization (H-VPP) technique is proposed to accelerate slurry polymerisation kinetics, thereby increasing interlayer crosslinking density and strengthening green body bonding strength. These effects compress interparticle spacing and reduce inherited pores after debinding, providing a denser initial value for sintering. Consequently, increasing the forming temperature from 30°C to 60°C at an exposure energy density of 37.95 mJ/cm2 boosted the sintered Si3N4’s flexural strength by 6.25% (reaching 674 MPa) while decreasing dielectric loss by 56% (tanδ = 0.012). To further synergize performance, a horsetail-inspired bionic structure was designed with optimised high volume porosity (68%) and radial/circumferential ribs. This integration dispersed mechanical loads, mitigated electric field concentration, and thereby simultaneously enhanced load-bearing efficiency and wave-transmitting performance. Ultimately, the bionic Si3N4 structure achieved > 92% transmittance in the Ku band and ∼1000 MPa compressive strength.