Recent advancements in Si3N4 ceramics, incorporating Y2Si4N6C and MgSiN2 as secondary phases, have demonstrated unprecedented improvements in mechanical and thermal properties. Studies reveal that the addition of 5 wt.% Y2Si4N6C enhances fracture toughness by 40%, reaching 8.5 MPa·m^1/2, while maintaining a hardness of 16.5 GPa. The synergistic effect of Y2Si4N6C and MgSiN2 at optimized ratios (3:1) results in a 25% increase in flexural strength, achieving 1,200 MPa. These findings are attributed to the formation of intergranular phases that promote crack deflection and grain boundary strengthening, as confirmed by TEM analysis.
Thermal stability of Si3N4 ceramics is significantly improved with the incorporation of Y2Si4N6C and MgSiN2, making them suitable for high-temperature applications. Experimental data show that the thermal conductivity increases by 30% to 45 W/m·K when 7 wt.% MgSiN2 is added, while the coefficient of thermal expansion (CTE) remains stable at 3.2 × 10^-6 /°C up to 1,200°C. High-temperature oxidation tests reveal a weight gain of only 0.8 mg/cm^2 after 100 hours at 1,400°C, compared to 2.5 mg/cm^2 for pure Si3N4. This enhanced performance is due to the formation of a protective Si-O-N layer and the suppression of grain boundary diffusion.
The tribological properties of Si3N4 ceramics are markedly improved with the addition of Y2Si4N6C and MgSiN2, particularly under extreme conditions. Wear rate measurements indicate a reduction by 60%, from 5 × 10^-6 mm^3/N·m to 2 × 10^-6 mm^3/N·m, when tested at a load of 50 N and a sliding speed of 0.5 m/s. Friction coefficients decrease from 0.8 to 0.45 under dry sliding conditions at room temperature, and further drop to below 0.3 at elevated temperatures (800°C). These improvements are attributed to the formation of self-lubricating tribo-films composed of Si-O-C-N compounds, as evidenced by XPS analysis.
Microstructural evolution in Si3N4 ceramics with Y2Si4N6C and MgSiN2 has been extensively studied using advanced characterization techniques such as SEM-EBSD and HRTEM. Results show that the average grain size decreases from ~1.5 µm to ~0.8 µm with the addition of these secondary phases, leading to a more refined microstructure. Grain boundary analysis reveals an increase in high-angle grain boundaries (HAGBs) from ~65% to ~85%, which enhances mechanical properties by promoting dislocation pinning and stress redistribution. Additionally, phase mapping confirms the uniform distribution of Y2Si4N6C and MgSiN2 within the matrix, minimizing stress concentrations.
The electrical properties of Si3N4 ceramics are also influenced by the incorporation of Y2Si4N6C and MgSiN2, opening new avenues for multifunctional applications. Electrical conductivity measurements show an increase by two orders of magnitude (from ~10^-12 S/cm to ~10^-10 S/cm) with the addition of these phases due to enhanced carrier mobility along grain boundaries. Dielectric constant values remain stable (~8) across a wide frequency range (1 kHz–1 MHz), while dielectric loss decreases from ~0.02 to ~0.005 at room temperature. These results suggest potential applications in high-temperature electronic devices where both mechanical robustness and electrical performance are critical.
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