Micro/nano multiscale reinforcing strategies toward extreme high-temperature applications: Take carbon/carbon composites and their coatings as the examples

Carbon fiber reinforced carbon composites (C/Cs), are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields, owing to their superior performances. However, C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures. Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics (UHTCs) are valid to enhance the oxidation/ablation resistance of C/Cs, it's not sufficient to satisfy the increasing practical applications, due to the inherent brittleness of ceramics, mismatch issues between coatings and C/C substrates, and the fact that carbonaceous matrices are easily prone to high-temperature oxidation. To effectively solve the aforementioned problems, micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades, to fabricate C/Cs with high strength and excellent high-temperature stability. This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies, including nanoparticles, nanowires, carbon nanotubes/fibers, whiskers, graphene, ceramic fibers and hybrid micro/nano structures, for C/Cs and/or the coatings, to achieve high-temperature oxidation/ablation-resistant C/Cs. Finally, this review is concluded with an outlook of major unsolved problems, challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance. It's hoped that a better understanding of this review will be of high scientific and industrial interest, since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.