The present Review addresses current developments related to polymer-derived ceramic nanocomposites (PDC-NCs). Different classes of preceramic polymers are briefly introduced and their conversion into ceramic materials with adjustable phase compositions and microstructures is presented. Emphasis is set on discussing the intimate relationship between the chemistry and structural architecture of the precursor and the structural features and properties of the resulting ceramic nanocomposites. Various structural and functional properties of silicon-containing ceramic nanocomposites as well as different preparative strategies to achieve nano-scaled PDC-NC-based ordered structures are highlighted, based on selected ceramic nanocomposite systems. Furthermore, prospective applications of the PDC-NCs such as high-temperature stable materials for thermal protection systems, membranes for hot gas separation purposes, materials for heterogeneous catalysis, nano-confinement materials for hydrogen storage applications as well as anode materials for secondary ion batteries are introduced and discussed in detail.

https://www.mdpi.com/2079-4991/5/2/468/pdf

Ceramic Nanocomposites from Tailor-Made Preceramic Polymers

Damage investigation and modeling of 3D woven ceramic matrix composites from X-ray tomography in-situ tensile tests

Laser ablation behavior and mechanism of C/SiC composite

Tension–compression fatigue of a SiC/SiC ceramic matrix composite at 1200 °C in air and in steam☆

The evolution of matrix cracks in a melt-infiltrated SiC/SiC ceramic matrix composite (CMC) under uniaxial tension was examined using scanning electron microscopy (SEM) combined with digital image correlation (DIC) and manual crack opening displacement (COD) measurements. CMC modeling and life prediction strongly depend a thorough understanding of when matrix cracks occur, the extent of cracking for given conditions (time-temperature-environment-stress), and the interactions of matrix cracks with fibers and interfaces. In this work, strain relaxation due to matrix cracking, the relationship between CODs and applied stress, and damage evolution at stresses below the proportional limit were assessed. Direct experimental observation of strain relaxation adjacent to regions of matrix cracking is presented and discussed. Additionally, crack openings were found to increase linearly with increasing applied stress, and no crack was found to pass fully through the gage cross-section. This calls into question the modeling assumption of through-cracks for all loading conditions and fiber architectures, which can obscure oxidation mechanisms that are active in realistic cracking conditions. Finally, the combination of SEM with DIC is demonstrated throughout to be a powerful means for damage identification and quantification in CMCs at stresses well below the proportional limit.

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Crack opening behavior in ceramic matrix composites

The oxidation kinetics and mechanisms of SiC-matrix composites fabricated by chemical vapor infiltration, and of their constituents (C or SiC-fibers, C or BN interphases and SiC matrix) are studied on the basis of an experimental approach and modelling. The oxidation of carbon fibers is rate-controlled by a combined diffusion/chemical reaction mechanism at low temperatures and its rate reduced by a 1600°C heat treatment. The oxidation rate of the pyrocarbon is similar to that of the fibers when they have been heat-treated. The oxidation kinetics of both the SiC-based fibers and matrix are parabolic and assumed to be rate-limited by the diffusion of gaseous species in the silica scale. A full kinetics law is given. The occurrence of water in the atmosphere increases the oxidation rate of the fibers and decreases the activation energy, water becoming the main oxidizing agent. The oxidation of the BN-interphase is complex and strongly anisotropic, its kinetics depending on composition, structure and texture. Finally, the oxidation of SiC-matrix composites, depicted for 1D-SiC/C/SiC and 2D-C/C/SiC composites, involves both diffusion of gaseous species in the composite porosity and heterogeneous oxidation reactions. Oxidation occurs through the thickness of the composites at low temperatures which consumes the carbon-based constituents. Conversely, it tends to be limited to near the composite surface at high temperatures, due to the formation of silica-based phases healing the material porosity and preventing the in-depth oxidation of the carbon-based constituents.

C. Louchet

Papers

Oxidation mechanisms and kinetics of SiC-matrix composites and their constituents