Investigation On The Properties Of Ti₃SiC₂Modified C/SiC Composites

Carbon fiber reinforced SiC matrix composites (C/SiC) and carbon fiber reinforcedcarbon/silicon carbide binary matrix composites (C/C-SiC) are promising candidates forapplication in thermal protection system (TPS) and aircraft braking due to the low density, goodmechanical strength, high thermal stability and good oxidation resistance. Compared withporous C/SiC, dense C/SiC has a lower porosity, which is beneficial to improving theperformance of as-fabricated composites, but the dense C/SiC usually shows lower strength andtoughness.MAX phases (general formula Mn+1AXnphase-where n=1,2, or3; M is an early transitionmetal; A is an A-group element; and X is C and/or N) own special bonding and nano-laminatedstructure, so they not only show good oxidation resistance and high-temperature mechanicalproperties like ceramic, but also can occur plastic micro-deformation like metal, which leads tohigh damage tolerance and various toughening mechanism. Therefore, the introduction of MAXphases into dense C/SiC is expected to simultaneously improve their mechanical properties andperformance. Up to now, there is lack of systematically study on the properties of C/SiCcomposties containing MAX phases.Ti3SiC2is one of representative MAX phases. In this paper, C/C-SiC-Ti3SiC2, C/SiC-Ti3SiC2and C/SiC-Ti3Si(Al)C2composites were prepared by a combined process of slurryinfiltration and reactive melt infiltration (RMI). The microstructure and mechanical propertiesof modified C/SiC were studied, and then their friction performance, oxidation resistance andablation resistance were systematically studied. The main contents and results are as follows.1) The effect of composition of the initial perform, alloy and infiltration temperature onthe formation of Ti3SiC2and Ti3Si(Al)C2in RMI process was studied. In the infiltration processof liquid silicon, the existence of carbon is beneficial to the formation of Ti3SiC2. Only whenthere’s enough carbon exsiting in the preform, the formation of Ti3SiC2can be promoted due tothe reaction of carbon and silicon. Carbon can react with TiSi2to form new TiC grains withmore carbon vacancies than the initial TiC, promoting the formation of TiC twins andnucleation of Ti3SiC2. In the infiltration process of Al-Si alloy, the existence of Al caneffectively decrease the twin boundary energy of TiC grains, leading to the formation of TiCtwins and the nucleation of Ti3SiC2, and the solution of Al into Ti3SiC2can form Ti3Si(Al)C2.2) The effect of Ti3SiC2on the microstructure, mechanical properties, and friction andwear properties of C/C-SiC was studied. The results show that the introduction of Ti3SiC2canreplace the residual silicon, enriching the toughening mechanism of dense matrix. Compared with C/C-SiC, C/C-SiC-Ti3SiC2shows higher bending strength and fracture toughness. Theresidual silicon increases the wear rate and leads to the instability of friction behavior, whilethe self-lubricious film-like debris can be formed by the oxidation of Ti3SiC2at hightemperatures, therefore, C/C-SiC-Ti3SiC2shows lower wear rate and higher friction stabilitythan those of C/C-SiC.3) The effect of Ti3SiC2on microstructure, mechanical and thermophysical properties,oxidation resistance and ablation resistance of C/SiC were studied. The results show that theintroduction of Ti3SiC2can improve the damage tolerance of inter-bundle matrix, suspendingthe crack propagation of dense matrix, thereby confining the damage of thermal residual stresson the dense matrix. With the densification of matrix and the inhibition of crack propagation,C/SiC-Ti3SiC2shows the higher young’s modulus, interlaminar shear strength and thermaldiffusivity than those of C/SiC and C/SiC-Si.In the temperature range from1000to1200oC, the cracks in SiC coating would be healedby the formation of SiO2. At the same time, the matrix of C/SiC-Ti3SiC2would show the self-healing properties due to high oxidation parabolic constant of Ti3SiC2, and the matrix crackswould be filled by the oxidation product, decreasing the inward diffusion path of oxygen.Therefore, the strength retention rate of C/SiC after oxidation at1000~1200oC for10h wouldbe above90%, revealing the excellent oxidation resistance. In the ablation process, theformation of TiO2and SiO2can cover the ablation surface of C/SiC-Ti3SiC2, forming oxide filmto prevent the inward diffusion of oxygen and alleviate the scouring effect of high speed flame,leading to the better ablation resistance of C/SiC-Ti3SiC2than C/SiC and C/SiC-Si.4) The microstructure and mechanical behavior of C/SiC-Ti3Si(Al)C2fabricated by Al-Sialloy infiltration were studied.The infiltration temperature of Al-Si alloy is only1300oC, revealing the lowerdensification temperature than that of liquid silicon, which is beneficial to the decrease of TRSin as-fabricated composites. C/SiC-Ti3SiC2shows a bending strength of556±33MPa and afracture toughness of21.6±0.9MPa·m1/2, both of which are higher than those of C/SiC-Si andC/SiC-Ti3SiC2and reach to the level of CVI-based C/SiC, revealing the advantage of in-situformation of MAX phases into C/SiC. At the same time, due to the low densificationtemperature of Al-Si alloy infiltration, it is possible to introduce MAX phases into Al2O3fiberand SiC fiber reinforced ceramic matrix composites, avoding the degradation of fibers at hightemperatures and obtaining the high-performance composites.