Mechanical And Ablation/Oxidation Properties Of ZrC-SiC_w-SiC_nm Composites

As a typical refractory carbide ceramic, the ultra-high-temperature ceramicZrC has excellent performance and many unique characteristics, it has receivedmuch attention in the fields of aviation, aerospace, energy,et al. According to theservice requirement and the inherent feature of ZrC,SiC whiskers （the SiC_w） andSiC nanoparticles (SiC_nm), ZrC-SiC_w-SiC_nmcomposites reinforced by SiC_wandSiC_nmwas fabricated to improve single-phase ZrC ceramic properties, such assintering properties, mechanical properties, thermal shock resistance andablation/oxidation resistance properties.Different content of ZrC-SiC_w-SiC_nmcomposites were prepared byhot-pressing at1900℃under20MPa and30MPa in a flow argon atmosphere. Bymeans of different analyzing and testing methods, the composites’ microstructure,mechanical properties, thermal shock resistance and ablation/oxidation resistanceproperties were systematically investigated. The relationship between itspreparation technology, microstructure and properties was also studied,thestrengthening and toughening mechanisms and oxidation/ablation resistancebehavior were analyzed deeply.The introduction of SiC_wand SiC_nmwas found to have a significant effect onthe density, flexural strength and fracture toughness of ZrC-SiC_w-SiC_nm. Thestrengthening and toughening mechanisms of the composites was the crackdeflection and branching, whisker bridging and pull-out, particle pinning, grainrefinement, residual stress, the elastic modulus mismatch and thermal expansioncoefficient misfit of components. The results showed that the maximum flexuralstrength of ZrC-SiC_w-SiC_nmcomposites with10vol%of SiC_wand15vol%of SiC_nm was481.12MPa, and the fracture toughnesses of the composites reached4.9MPam1/2.The thermal shock resistance of ZrC-SiC_w-SiC_nmcomposites were studiedusing the water quenching–residual strength method.It was found that the residualstrength of the composites dramatically decreased when the thermal shocktemperature reached about300℃. The critical thermal shock temperature ΔTcwasused to evaluate thermal shock resistance properties of the composites, the ΔTcofZrC-SiC_w-SiC_nmcomposites with15vol%of SiC_wand5vol%of SiC_nmreached343℃. The results show that the thermal shock resistance of ZrC was improvedmore significantly with the addition of SiC_wthan SiC_nm.ZrC-SiC_w-SiC_nmcomposites was ablation by oxygen-acetylene flame, and itsablation/oxidation resistance properties was evaluated by weight ablation rate andthe linear ablation rate of the composites. The weight ablation rate ofZrC-SiC_w-SiC_nmcomposites with5vol%of SiC_wand15vol%of SiC_nmand thecomposites with15vol%of SiC_wand10vol%of SiC_nmwere3.63×10-4mm/s and3.85×10-4mm/s respectively, it showed a zero-ablation. After ablation ofoxyacetylene flame, an oxidation film was observed on the surface of composites,the oxidation film was mostly made of ZrO₂and SiO₂（ZrO₂/SiO₂）. By analysis ofthe structure of cross-section, SiC-depletion layers and transition layers wereformed in oxidation layers, molten SiC, SiO₂, and ZrO₂filled the ablation holes,and the transition layers is structure that ZrO₂was a backbone, ZrO₂and SiO₂formed a kind of viscous glassy mixture which can fill the holes,meanwhile,amorphous ZrC_xO_1-xwas found in transition layers. The ZrO₂/SiO₂oxidation film,SiC-depletion layers and transition layers can effectively prevent the penetration ofoxygen, so ZrC-SiC_w-SiC_nmcomposites possessed good ablation and oxidationresistance properties.