A team of scientists from Britain and China have developed a new ceramic material that could one day make hypersonic air travel a reality. The ceramic carbide coating can withstand the high temperatures of flying at over five times the speed of sound without the degradation experienced by similar materials.
Engineering isn't simply a matter of coming up with a good idea and slapping the bits together before flipping the "on" switch. In many cases, it's a long, frustrating search to find the materials needed to build the device. Look, for example, at a smartphone with all its compact intricacy and try to imagine making one without any of the sophisticated plastics used in its design. If you could build one at all, it would be the size of a suitcase and scarcely portable.
The same is true in aerospace engineering. The idea of hypersonic flight has been around for a long time, but building an aircraft or missile that could make velocities of at or above Mach 5 (3,800 mph, 6,125 km/h) – think two hours from New York to London – requires materials that are still in the experimental stage. This is because the impact of the air at such speeds generates temperatures of as high as 3,000º C (5,400º F).
Even if this doesn't melt or warp wing edges, nose tips, turbine blades and other components, it will certainly cause them to degrade in short order due to oxidation and ablation. This causes the surface layers of metals to evaporate in part, making them weaker and more prone to scouring and pitting.
The team from the University of Manchester and Central South University in China is working on a new class of ultra-high temperature ceramics (UHTCs) that are less susceptible to oxidation and ablation, giving them more resilience and longer life. The key is a new carbide coating that the scientists claim is 12 times better than current UHTCs, like zirconium carbide (ZrC).
The new ceramic was made by the Powder Metallurgy Institute at Central South University and evaluated at Manchester. It's produced by means of Reactive Melt Infiltration (RMI), which involves the penetration of elements including zirconium, boron, and titanium into a matrix made of a composite of different types of carbon. Normally, high temperature on ceramics drives off protective elements and leaves the remaining ceramic vulnerable to degradation, but RMI makes the ceramic much harder and extremely resistant to surface degradation at hypersonic temperatures.
"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," says Professor Ping Xiao, Professor of Materials Science at Manchester. "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."
The research was published in Nature Communications.
Source: University of Manchester
