Fabrication And Properties Of SiC Whisker Enhancing And Toughenng ZrC-Based Ultra High Temperature Ceramics Composites

Ultra-high temperature ceramics(UHTCs) have received much attention in theaviation, aerospace, military and other fields due to its unique characteristics. Thispaper selects ultra-high temperature ceramics typical representative of ZrC as thebase material, and adding SiC whiskers to ceramic materials improves its brittleness,sintering properties and oxidation resistance.After optimization to design the content of SiC whiskers, ZrC+5%SiCwcomposites, ZrC+10%SiCw composites, ZrC+15%SiCw composites andZrC+20%SiCw composites are developed. The influence of the SiC whisker on themicrostructure, mechanical properties, thermal shock resistance and ablationresistance of the composites is discussed. The strengthening and tougheningmechanisms, thermal shock resistance mechanisms and oxidation and ablationresistance behavior were analysized deeply, which provide experimental andtheoretical foundation for the application of the new type ZrC matrix composites ashigh-temperature structure materials.Compared with the single-phase ZrC ceramics, the addition of SiC whiskerscan promote the sintering performance, reduces internal defects in the materials, andrestrict the grain growth of matrix. Meanwhile, the density, the flexural strength andfracture toughness of the materials are improved, and they increase with the contentof SiC whiskers growing. We obtained maximum values 99.2%, 626.17MPa and5.03MPa·m1/2 respectively when SiC whiskers content is 20vol.%. The interfaces ofcomposites combine well, and the boundary phase is not found. The strengtheningand toughening mechanisms of the materials is the grain refinement, residual stressand crack deflection, bridging and branching.The thermal shock resistance of four type of composite systems are studiedusing the water quenching– residual strength method in the temperature range from200℃to 500℃. The results show that: there is no obvious change in the thermalshock residual strength of ZrC/SiCw composite systems when the temperaturedifferenceΔT = 200℃; The residual strength of four composites are dramaticallyreduced when the thermal shock temperature differenceΔT increasing from 200℃to 300℃; then as the temperature difference increasing, the residual strength of thecomposites have been slowly decline; ZrC/20SiCw composite system has thehighest thermal shock temperature difference, it's 237℃. The thermal shockresistance of ZrC/SiCw composites improving is due to the addition of SiC whiskers,which significantly increases the density, the flexural strength, the fracturetoughness and thermal conductivity rates of composites, thus affects the thermal shock capability.The performance evaluation of the oxidation and ablation of ZrC matrixcomposites with different SiC whisker is given, and the ablation mechanism of thecomposites is analysed. The results show that the weight ablation rate and the linearablation rate of the ZrC/20SiCw composite is lowest. After 120 seconds ablation ofoxyacetylene flame, the weight ablation rate of ZrC/20SiCw composite is (2.52×10-4)g/s, and the linear ablation rate is (30.83×10-4)mm/s, which is due to formedoxidation film on the surface of composites. The structure of oxidation film ismainly the outermost ZrO₂ and SiO₂ protective film and the transition layer oxideZrCxO1-x between the oxidation layer and matrix; the oxidation film effectivelyprevents the proliferation of oxygen, thus improves the ablation resistance ofmaterials.