Hao Chen,Jianjun Chen,Jiahao Yang,Zahoor Ahmad,Mingming Zhu,Yilian Xiong,Jiyu Tao,Jinxia Li
In this work, stacked SiC fibers paper-reinforced SiC ceramic matrix composites (SiC nf /SiC CMCs) were prepared by nanoimpregnation and transient eutectic (NITE) process using ultra-long single-crystal SiC nanofibers. The effect of the SiC nf surface modification via boron nitride (BN) interphase deposition as well as the sintering additive (Al 2 O 3 –Y 2 O 3 ) content on the density, microstructure, and mechanical properties of SiC nf /SiC CMCs has been investigated systematically. The results revealed that the laminated SiC nf /SiC CMCs feature a significant saw-tooth-like curve on the load–displacement test, which indicates that the obtained laminated structure with the weak interlayer binding owning to the BN coating treatment possesses significant toughening to the SiC ceramics. Specifically, the SiC nf /SiC CMCs with the sintering additive content of 12 wt% revealed a fracture toughness of over 10 MPa m 1/2 after 60 min of BN interface deposition, which is 104.31% higher than that of the composites prepared without BN coating.
Yuan Fang,Aoxuan Wang,Keze He,Hongying Pan,Jiajun Liao,Zhu Ding,Feng Xing,Huirong Le,Xianfeng Wang
This article investigates the key interface properties of geopolymers reinforced by SiC whiskers loaded with BN coating (BN/SiCw) and the insight of mechanical performance and microstructures of the resulting composites. The interesting diverse strength evolutions of geopolymer composites calcinated at various temperatures suggest a result of rivalries of multiple factors including BN coating, geopolymer matrix transformations, SiC whiskers. A positive effect on whisker pull-out phenomenon has been achieved via the chemical bonding between SiC whisker (SiCw) and BN coating and the rough physical interface between BN coating and geopolymers; the addition of SiCw and BN/SiCw promotes the polycondensation reaction of geopolymers and the addition of the latter is superior. Through changing the pore structure characteristics of the composites, the SiCw in composites can release their excessive vapor pressure in the closed pores which is the main reason attributing to the strength loss of geopolymers at 900 °C. In addition, BN coating can make up for the mismatch of thermal expansion coefficient between SiCw and geopolymers, increasing the strength of the composites by 30.9% at 900 °C, whereas whisker pull-out and crack deflection are the main toughening effect for BN/SiCw.
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