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Samples of the new carbide were put through ablation testing. (a) Green and orange flames are seen in tests of Zr0.8Ti0.2C0.74B0.26 and Zr0.8Ti0.2C, respectively. (b) Comparison of surface of the 30-mm diameter samples before and after ablation. Black-gray sample is before test, and middle and right samples experienced 120 s of ablation of 2000 and 2500°C, respectively. (c) Surface profile of central region of sample ablated at 3000°C, showing the ablated traces due to evaporation of oxides with low melting points. But no ablated hollows appeared on surface. (Source: Nat. Commun.)

Researchers develop new carbide coating for hypersonic flight

Researchers from the University of Manchester have designed and fabricated a carbide coating that can withstand the speed and temperature associated with hypersonic travel. To develop the unique coating—a type of ultra-high temperature ceramic (UHTC)—the researchers collaborated with China’s Central South University (CSU).

Conventional UHTCs, developed as thermal protection systems for air, space, and defense applications, have been in use since the 1960s. However, for hypersonic travel (at a speed of Mach 5 or above), UHTCs still had trouble coping with oxidation and ablation, where hot gases flowing past the aircraft strip away layers of the metallic surface material.

“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,” said Philip Withers, Regius Professor, University of Manchester.

These temperatures experienced during hypersonic flight can reach between 2000 to 3000°C. (As a reference, surface temperatures for Lockheed's SR-71 Blackbird during sustain supersonic flight at Mach 3.1 were recorded as high as 315°C—which necessitated the extensive use of titanium in the aircraft.)

At this point, the carbide coating developed by the University of Manchester and CSU researchers is proving to be 12 times more resilient to ablation than conventional zirconium carbide (ZrC)—an extremely hard refractory UHTC used in commercial cutting tools.

The new carbide (Zr0.8Ti0.2C0.74B0.26) coating is fabricated through reactive melt infiltration and pack cementation onto a carbon-carbon composite. According to the research team’s abstract, “the sealing ability of the ceramic’s oxides, slow oxygen diffusion and a dense and gradient distribution of ceramic result in much slower loss of protective oxide layers formed during ablation than other ceramic systems, leading to the superior ablation resistance.”

“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,” said Ping Xiao, Professor of Materials Science, who led the study in University of Manchester.

Hypersonic development for spacecraft and launch vehicles (e.g., NASA’s Hypersonic International Flight Research Experimentation Program and continued research into ramjet and scramjet nanosatellite delivery) will continue to require advanced coatings research. Beyond that, as Boom Technology develops supersonic commercial aircraft like the XB-1, supersonic travel may soon become an everyday occurrence. Hypersonic travel could be close on the horizon, soon to be incorporated into commercial designs.

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