ZrB2-MoSi2 composites have emerged as a leading material for ultra-high-temperature thermal protection systems (TPS) due to their exceptional thermomechanical properties. Recent studies reveal that the addition of 20 vol% MoSi2 to ZrB2 enhances the flexural strength from 450 MPa to 620 MPa, while maintaining a fracture toughness of 5.2 MPa·m^1/2. This is attributed to the formation of a eutectic liquid phase at temperatures above 1600°C, which promotes densification and crack deflection. Additionally, the thermal conductivity of ZrB2-MoSi2 composites remains stable at 65 W/m·K up to 1800°C, making them ideal for hypersonic vehicle applications where rapid heat dissipation is critical.
The oxidation resistance of ZrB2-MoSi2 composites has been significantly improved through advanced sintering techniques such as spark plasma sintering (SPS). Research demonstrates that SPS-processed composites exhibit a parabolic oxidation rate constant (kp) of 1.3 × 10^-6 g^2/cm^4·s at 1600°C, compared to 5.8 × 10^-6 g^2/cm^4·s for conventionally sintered samples. This improvement is due to the formation of a dense, self-healing SiO2-B2O3 layer that effectively prevents oxygen diffusion. Furthermore, the mass loss after 100 hours of exposure at 1800°C is reduced by 40%, highlighting their potential for long-duration missions in extreme environments.
The mechanical performance of ZrB2-MoSi2 composites under cyclic thermal shock has been extensively studied, with results showing a remarkable retention of strength after 50 cycles between room temperature and 1800°C. The residual flexural strength remains above 85% of the initial value (527 MPa), while the thermal expansion coefficient remains stable at 6.8 × 10^-6 K^-1. This stability is attributed to the synergistic effect of ZrB2’s high melting point (3245°C) and MoSi2’s ability to form protective oxide layers, which mitigate microcrack propagation and delamination.
Recent advancements in microstructure tailoring have further enhanced the ablation resistance of ZrB2-MoSi2 composites. By incorporating nano-sized SiC particles (5 wt%), researchers achieved an ablation rate reduction of 35% at temperatures exceeding 2000°C, with linear ablation rates as low as 0.03 mm/s under plasma arc testing. The improved performance is due to the formation of a multi-layered oxide scale consisting of ZrO2-SiO2-SiC, which provides superior thermal insulation and erosion resistance.
The integration of additive manufacturing techniques into ZrB2-MoSi2 composite fabrication has opened new avenues for complex TPS component design. Laser powder bed fusion (LPBF) has been successfully employed to produce parts with a relative density exceeding 98% and a hardness of 18 GPa. This approach enables precise control over porosity and grain orientation, resulting in components with tailored thermal and mechanical properties for specific aerospace applications.
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