A new type of ceramic coating developed at the University of Manchester has the potential to “revolutionise” hypersonic flight, according to its creators.
(Credit: University of Manchester)
Hypersonic flight – defined as Mach five or above – would see aircraft subjected to external temperatures between 2,000 and 3,000°C, leading to structural challenges caused by oxidation and ablation. Amongst other materials, current spacecraft and missiles rely on ultra-high temperature ceramics (UHTCs) to combat high temperatures. However, according to Manchester University, conventional UHTCs can’t currently satisfy the associated ablation requirements of hypersonic flight.
“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 such temperatures cause to excess during flight,” said Philip Withers, Regius Professor at Manchester University.
Working in collaboration with Central South University (CSU), China, and the Royce Institute, Withers and his colleagues developed a carbide coating that performs 12 times better than Zirconium carbide (ZrC), a widely used UHTC often found in tool bits.
According to the team, the performance of the coating is due to its unique structural make-up, which provides excellent heat resistance and improved oxidation resistance. The coating is manufactured using a process called reactive melt infiltration (RMI) – which reduces the time needed to make such materials -and reinforced with carbon–carbon composite (C/C composite), making it extremely resistant to typical surface degradation.
“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,” said Ping Xiao, Professor of Materials Science, who led the study at the University of Manchester.
“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.”
Very interesting, but a bit jargonistic and lacking in useful details: more a sales shot than a technical explanation.
I have always considered that ablation in hypersonic flow meant carbon ablation e.g. in re-entry vehicles. Ceramic coatings generally are used in components of gas turbines and other heat engines, commonly rare-earth carbides to reduce surface temperatures at relatively low heat fluxes compared with hypersonic flow.
I am intrigued as to why people will always look first for high-tech solutions to a problem, as this often results in “treating the symptoms, not curing the illness”, which I believe to be the case here.
The basic problem is high temperatures, generated by friction between essentially static air and an aircraft pushing through it at supersonic speed.
The aircraft designers can make ingenious tweaks to the shape of the vehicle; but the law of diminishing returns applies. So, a point is eventually reached where it is necessary to “bite the bullet” and investigate exotic materials resistant to high temperatures, in order to prevent loss of strength and/or deterioration of the basic skin material.
But what if, instead, they were to look at eliminating the disease itself: skin friction?
Not so long ago a video appeared on the Web showing the effect on aerodynamic drag – aka skin friction – of providing a plasma skin to an aircraft wing. The reduction in drag was apparently significant, and comparable to the results of experiments carried out to show the same effect by providing a bubble skin to ships’ hulls.
In both cases the principle was the same: preventing interface friction by disrupting the boundary layer, rather than finding some high-tech way of living with it.
My question therefore is: would the provision of such a plasma skin for SSTs be a more practical way of making such travel economically feasible, by at least lowering skin temperatures enough to permit the use of “normal” aircraft construction materials?
“why people will always look first for high-tech solutions to a problem,”
because they are of so-called ‘pure’ science and have forgotten the first rule of Engineers (applied scientists) “who should try to do for 10p what any fool can do for £1.00”
Of course, there are less grants -‘for more research’ -available once the problem is solved!
Does any individual’s increased reward and continued employment depend on the Conflict or its outcome? The great question of our time. Now what we need is more money for more research?