When moving at five times faster than the speed of sound the heat generated by air and gas in the atmosphere can reach 2000 to 3000°C which can have a serious impact on the structural integrity on an aircraft.
The structural problems are primarily caused by oxidation and ablation, where extremely hot air and gas remove surface layers from the metallic materials of the aircraft. 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 defence projectiles.
But, at present, even conventional UHTCs can’t currently satisfy the associated ablation requirements of travelling at such extreme speeds and temperatures. However, the researchers have designed and fabricated a carbide coating that they say is vastly superior in resisting temperatures up to 3000°C, when compared to existing UHTCs.
Professor Philip Withers from The University of Manchester, said: “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 revolutionise 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 cause to excess during flight.”
So far, the carbide coating developed by teams at both the University of Manchester and CSU 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.
According to the researchers, the improved performance of the coating is due to its unique structural make-up and features manufactured at the Powder Metallurgy Institute, CSU and studied in University of Manchester, School of Materials.
The coating is made using a process called reactive melt infiltration, which dramatically reduces the time needed to make such materials, and has been in reinforced with carbon–carbon composite. This makes it not only strong but extremely resistant to the usual surface degradation.
Ping Xiao, Professor of Materials Science, who led the study in University of Manchester explained: “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 fibre- reinforced carbon matrix composites may be an effective way of improving thermal-shock resistance.”