Carbon/carbon (C/C) composites are considered as one of the most promising materials in structural applications owing to their excellent mechanical properties at high temperature. However, C/C composites are susceptible to high-temperature oxidation. Matrix modification and coating technology with ultra-high temperature ceramics (UHTCs) have proved to be highly effective to improve the oxidation and ablation resistance of C/C composites. In this paper, recent advances in oxidation and ablation resistance of C/C composites were firstly reviewed, with attention to oxidation and ablation properties of C/C composites coated or modified with UHTCs. Then, several new methods in improving oxidation and ablation resistance were discussed, such as by using nanostructures to toughen UHTCs coatings or carbon matrix and the combination of matrix modification and coating technology. In addition, relevant ablation tests with scaled models were also briefly introduced. Finally, some open problems and future challenges were highlighted in the development and application of these materials.

Advances in oxidation and ablation resistance of high and ultra-high temperature ceramics modified or coated carbon/carbon composites

Current generation carbon–carbon (C–C) and carbon–silicon carbide (C–SiC) materials are limited to service temperatures below 1800 °C and materials are sought that can withstand higher temperatures and ablative conditions for aerospace applications. One potential materials solution is carbon fibre-based composites with matrices composed of one or more ultra-high temperature ceramics (UHTCs); the latter are intended to protect the carbon fibres at high temperatures whilst the former provides increased toughness and thermal shock resistance to the system as a whole. Carbon fibre–UHTC powder composites have been prepared via a slurry impregnation and pyrolysis route. Five different UHTC compositions have been used for impregnation, viz. ZrB 2 , ZrB 2 –20 vol% SiC, ZrB 2 –20 vol% SiC–10 vol% LaB 6 , HfB 2 and HfC. Their high-temperature oxidation resistance has been studied using a purpose built oxyacetylene torch test facility at temperatures above 2500 °C and the results are compared with that of a C–C benchmark composite.

https://research.birmingham.ac.uk/portal/files/26733593/Submitted_paper.pdf

UHTC–carbon fibre composites: Preparation, oxyacetylene torch testing and characterisation

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/pdf/uhtc-composites-for-hypersonic-applications-59v44wakt9.pdf

UHTC composites for hypersonic applications

ZrC ablation protective coating for carbon/carbon composites

improved solar collectors (40) comprising glass tubing (42) attached to bellows (44) by airtight seals (56) enclose solar absorber tubes (50) inside an annular evacuated space (54;. The exterior surfaces of the solar absorber tubes (50) are coated with improved solar selective coatings {48} which provide higher absorbance, lower emittance and resistance to atmospheric oxidation at elevated temperatures. The coatings arc multilayered structures comprising solar absorbent layers (26) applied to the metal surface of the absorber tubes (50), typically stainless steel, topped wiih antireflective Savers (28) comprising at least two layers (30. 32) of refractory metal or metalloid oxides (such as titania and silica) with substantially differing indices of refraction in adjacent layers. Optionally, at least one layer of a noble metal such as platinum can be included between some of the layers. The absorbent layers cars include cermet materials comprising particles of metal compounds is a matrix, which can contain oxides of refractory metals or metalloids such as silicon. Reflective layers within the coating layers can comprise refractory metal silicides and related compounds characterized by the formulas TiSi. Ti3SiC2, TiAlSi, TiAN and similar compounds for Zr and Hf. The titania can be characterized by the formulas TiO2, Ti3O5. TiOx or TiOxN1-x with x 0 to 1. The silica can be at least one of SiO2, SiO2x or SiO2xN1-x with x = 0 to 1.

High temperature solar selective coatings

Hafnium carbide is proposed as a structural material for aerospace applications at ultra high temperatures. The chemical vapor deposition technique was used as a method to produce monolithic hafnium carbide (HfC) and tantalum carbide (TaC). The microstructure of HfC and TaC were studied using analytical techniques. The addition of tantalum carbide (TaC) in the HfC matrix was studied to improve the microstructure. The microstructure of HfC, TaC and co-deposited hafnium carbide-tantalum carbide (HfC/TaC) were comparable and consisted of large columnar grains. Two major problems associated with HfC, TaC, and HfC/TaC as a monolithic are lack of damage tolerance (toughness) and insufficient strength at very high temperatures. A carbon fiber reinforced HfC matrix composite has been developed to promote graceful failure using a pyrolytic graphite interface between the reinforcement and the matrix. The advantages of using carbon fiber reinforcement with a pyrolytic graphite interface are reflected in superior strain capability reaching up to 2%. The tensile strength of the composite was 26 MPa and needs further improvement. Heat treatment of the composite showed that HfC did not undergo any phase transformations and that the phases comprising composite were are thermochemically compatible.

Carbon fiber reinforced hafnium carbide composite

The resistance of ceramic matrix composites to combust at high oxygen pressures is expected to provide information in developing oxygen-rich propulsion systems. In contrast to metals, silicon based ceramics, SiC, Si3N4 and SiC-composites, have prevalently covalent bonding characteristics and their promoted combustion characteristics were different. These materials dissociate at very high temperatures rather than going through discrete solid—liquid phase transformation (melting). The silicon based ceramics and composites burn heterogeneously at very high oxygen pressures and the critical threshold pressure at which no test specimen sustains combustion correlated with composition, the nature of the bonding and the solubility of oxygen.

A. Sayir

Papers

Carbon fiber reinforced hafnium carbide composite

Combustion-resistance of silicon-based ceramics and composites at very high oxygen pressures