Laser surface treatment for enhanced surface quality of Si3N4 + SiO2 wave-transparent ceramics

Si₃N₄ + SiO₂-based wave-transparent ceramics are valued for their excellent mechanical strength and superior dielectric properties, making them suitable for radome applications. A recent study explored the production of these ceramics through compression molding of green pellets, followed by sintering (at 1500 °C). However, further improvements in mechanical properties without compromising dielectric performance are essential for use in harsh conditions. In this study, surface treatment using a CO₂ laser with a 10.6 μm wavelength was applied to green Si₃N₄ + SiO₂ ceramic compacts (GP), prepared by compression molding at 1912 MPa, to investigate changes in surface integrity, microstructure, and chemical composition before and after sintering. Thermal gravimetric analysis (TGA) confirmed that oxidation began at 700 °C, with a mass gain of 18 % up to 1500 °C. XRD and XPS confirmed Si₃N₄ and SiO₂ phases in the green pellets, with optimal laser parameters (10 W power, 15 mm/s) maximizing SiO₂ formation and inducing compressive residual stresses, of up to −128 MPa on green ceramic surface to −2045 MPa after sintering. This treatment significantly improved microhardness, increasing from 1566 ± 6.7 HV₀.₁ in untreated sintered samples to 1651 ± 7.1 HV₀.₁ in sintered, laser-treated samples. XRD results confirmed the formation of Si₃N₄, cristobalite-SiO₂, and Si₂N₂O phases in the laser-treated sintered ceramics which was also confirmed by the SEM micrograph. Line EDS (energy-dispersive spectroscopy) verified that the elemental composition of the laser-treated sintered surface remained consistent with that of the untreated sintered surface. These findings demonstrate that CO₂ laser treatment significantly enhances the mechanical properties of Si₃N₄-SiO₂ ceramics without compromising their dielectric performance, thereby greatly improving the material's suitability for radome applications in challenging environmental conditions.