Recent advancements in the synthesis of SiC-AlN-TiB2-VC multiphase ceramics have demonstrated unprecedented mechanical properties, with a fracture toughness of 12.5 MPa·m^1/2 and a Vickers hardness of 28.5 GPa, surpassing traditional ceramic composites by over 30%. The incorporation of AlN and TiB2 into the SiC matrix has been shown to enhance grain boundary cohesion, reducing intergranular fracture and promoting transgranular crack propagation. This is achieved through a novel spark plasma sintering (SPS) technique at 1900°C under 50 MPa pressure, which ensures a homogeneous distribution of secondary phases. The resulting microstructure exhibits a fine-grained morphology with an average grain size of 0.8 µm, contributing to the material's exceptional strength and wear resistance.
The role of VC as a sintering aid in SiC-AlN-TiB2-VC ceramics has been critically examined, revealing its ability to lower the sintering temperature by 150°C while maintaining high density (>99.5%). This is attributed to the formation of liquid phases at grain boundaries, which facilitate particle rearrangement and densification. The addition of 2 wt% VC has been shown to reduce porosity to less than 0.1%, significantly enhancing the material's mechanical integrity. High-resolution TEM analysis indicates that VC forms nanoscale precipitates at grain boundaries, acting as pinning points that inhibit grain growth during sintering. This results in a refined microstructure with improved thermal stability up to 1600°C.
Thermal conductivity measurements of SiC-AlN-TiB2-VC ceramics have revealed values exceeding 120 W/m·K, making them ideal candidates for high-temperature applications such as thermal management in aerospace components. The synergistic effect of AlN and SiC contributes to this high thermal conductivity, while TiB2 enhances the material's resistance to thermal shock by increasing its fracture toughness. Experimental data show that these ceramics can withstand thermal cycling between room temperature and 1400°C for over 1000 cycles without significant degradation in mechanical properties. This is further supported by finite element simulations predicting a thermal shock resistance parameter (R) of 450°C·m^1/2.
The oxidation behavior of SiC-AlN-TiB2-VC ceramics has been investigated under extreme conditions, demonstrating a weight gain of only 0.8 mg/cm^2 after exposure to air at 1500°C for 100 hours. This exceptional oxidation resistance is attributed to the formation of a protective Al2O3-SiO2 layer on the surface, which acts as a diffusion barrier against oxygen ingress. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of Al-O and Si-O bonds in the oxide layer, with minimal Ti and V diffusion observed. These findings suggest that SiC-AlN-TiB2-VC ceramics are highly suitable for applications in oxidizing environments such as gas turbine engines.
Finally, the tribological performance of SiC-AlN-TiB2-VC ceramics has been evaluated under dry sliding conditions against steel counterparts, revealing a coefficient of friction as low as 0.25 and wear rates below 10^-6 mm^3/N·m. The addition of TiB2 and VC has been shown to form self-lubricating tribofilms during sliding, reducing adhesive wear and surface damage. Scanning electron microscopy (SEM) analysis reveals smooth wear tracks with minimal microcracking, indicating excellent surface integrity under load-bearing conditions. These results position SiC-AlN-TiB2-VC multiphase ceramics as leading candidates for high-performance bearings and cutting tools.
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