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Wings:
Hypersonic travel heats up with new materials discovery

Researchers at The University of Manchester in the U.K., in collaboration with Central South University (CSU), China, have created a new kind of ceramic coating that could revolutionize hypersonic travel for air, space, and defense purposes.

Hypersonic travel means moving at Mach 5 or above, which is at least five times faster than the speed of sound. When moving at such velocity, the heat generated by air hitting the aircraft can reach anywhere from 2,000 C to 3,000 C, which can have a serious impact on structural integrity.

The structural problems are primarily caused by processes called oxidation and ablation. This is when extremely hot air and gas remove surface layers from the metallic materials of the aircraft or object travelling at such high speeds. To combat the problem, materials called ultra-high-temperature ceramics (UHTCs) are needed in aero engines and hypersonic vehicles such as rockets, re-entry spacecraft, and defense projectiles.

But even conventional UHTCs can't currently satisfy the associated ablation requirements of travelling at such extreme speeds and temperatures. However, the researchers at the University of Manchester and the Royce Institute, in collaboration with the Central South University of China, have designed and fabricated a new carbide coating that is vastly superior in resisting temperatures up to 3,000 C, when compared to existing UHTCs.

Professor Philip Withers, Regius Professor from the University of Manchester, says, "Future hypersonic aerospace vehicles offer the potential of a step jump in transit speeds. A hypersonic plane could fly from London to New York in just two hours and would revolutionize both commercial and commuter travel.

"But at present, one of the biggest challenges is how to protect critical components such as leading edges, combustors, and nose tips so that they survive the severe oxidation and extreme scouring of heat fluxes at such temperatures during flight."

So far, the carbide coating developed by teams from both University of Manchester and Central South University is proving to be 12 times better than the conventional UHTC, Zirconium carbide (ZrC). ZrC is an extremely hard refractory ceramic material commercially used in tool bits for cutting tools.

The much improved performance of the coating is due to its unique structural makeup and features manufactured at the Powder Metallurgy Institute, Central South University, and studied in University of Manchester's School of Materials. This includes extremely good heat resistance and massively improved oxidation resistance.

What makes this coating unique is it has been made using a process called reactive melt infiltration (RMI), which dramatically reduces the time needed to make such materials, and has been reinforced with carbon-carbon composite (C/C composite). This makes it not only strong but extremely resistant to the usual surface degradation.

Professor Ping Xiao, Professor of Materials Science, who led the study at the University of Manchester, explains, "Current candidate UHTCs for use in extreme environments are limited, and it is worthwhile exploring the potential of new single-phase ceramics in terms of reduced evaporation and better oxidation resistance. In addition, it has been shown that introducing such ceramics into carbon fiber-reinforced carbon matrix composites may be an effective way of improving thermal-shock resistance."

Reference: "Ablation-resistant carbide Zr0.8Ti0.2C0.74B0.26 for oxidizing environments up to 3,000?°C" Yi Zeng, Dini Wang, Xiang Xiong, Xun Zhang, Philip J. Withers, Wei Sun, Matthew Smith, Mingwen Bai & Ping Xiao Article number: 15836 (2017) doi:10.1038/ncomms15836

Published July 2017

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