ZrB2-MoSi2 composites have emerged as a leading material for aerospace thermal protection systems (TPS) due to their exceptional high-temperature stability and oxidation resistance. Recent studies reveal that ZrB2-MoSi2 composites exhibit a thermal conductivity of 24-28 W/m·K at 2000°C, significantly higher than traditional SiC-based ceramics. This property ensures efficient heat dissipation during re-entry, reducing thermal stress. Additionally, the material demonstrates a flexural strength of 450-500 MPa at room temperature, which only decreases by 15% at 1600°C, highlighting its structural integrity under extreme conditions. Oxidation tests in simulated re-entry environments (1600°C, 20% O2) show a mass gain of less than 0.5 mg/cm² after 100 hours, underscoring its superior oxidation resistance.
The incorporation of MoSi2 into ZrB2 matrices enhances the composite’s self-healing capabilities, a critical feature for aerospace applications. Research indicates that MoSi2 forms a protective SiO2 layer at temperatures above 1200°C, which seals microcracks and prevents further oxidation. This self-healing mechanism is quantified by crack closure rates of up to 1.2 µm/hour at 1500°C. Furthermore, the addition of MoSi2 improves the composite’s fracture toughness from 3.5 MPa·m¹/² (pure ZrB2) to 5.8 MPa·m¹/² (ZrB2-20 vol% MoSi2), making it more resistant to catastrophic failure under thermal shock.
The ablation resistance of ZrB2-MoSi2 composites has been extensively studied under plasma arc jet testing, simulating re-entry conditions. Results show an ablation rate of 0.08-0.12 mm/s at heat fluxes of 10 MW/m² and surface temperatures exceeding 2200°C, outperforming traditional ultra-high-temperature ceramics (UHTCs) like HfC and TaC. The formation of a stable ZrO2-SiO2 layer during ablation reduces material loss and maintains surface integrity. Moreover, the composite’s coefficient of thermal expansion (CTE) of 6.8-7.2 ×10⁻⁶/K ensures compatibility with underlying structural materials, minimizing delamination risks.
Recent advancements in processing techniques have enabled the fabrication of ZrB2-MoSi2 composites with tailored microstructures for optimized performance. Spark plasma sintering (SPS) at 1800°C under 50 MPa pressure produces fully dense (>99% theoretical density) composites with grain sizes below 1 µm, enhancing mechanical properties and oxidation resistance. Additive manufacturing methods have also been explored, achieving layer-by-layer deposition with <1% porosity and dimensional accuracy within ±10 µm, paving the way for complex TPS geometries.
The environmental durability of ZrB2-MoSi2 composites has been validated through long-term exposure tests in simulated aerospace environments. After 1000 hours at 1200°C in air with cyclic thermal shocks (ΔT = 800°C), the material retains >90% of its initial flexural strength and shows no significant phase degradation or microstructural changes. These results position ZrB2-MoSi2 composites as a robust solution for next-generation TPS in hypersonic vehicles and reusable spacecraft.
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