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Cover of the Winter 2009 issue


VOL. 35, NO. 2






For ultra-high-temperature alloys,
new coating turns up the heat

John H. Perepezko

John H. Perepezko (large image)

Researchers in Materials Science and Engineering Professor John Perepezko’s lab have shown their new oxidation-resistant coating can take the heat. Ultra-high-temperature metals and alloys treated with this coating could enable new components for technologies ranging from airplane brakes and turbines to space vehicles.

Today, efficient combustion, greater energy efficiency and reduced emissions are the gold standard—and engines and turbines functioning at higher temperatures can accomplish all three. However, to reach those high temperatures, engine components, for example, have to be made of materials that can withstand extreme heat and pressure.

Nickel-based alloys are the industry standard for high-temperature applications, but current materials are at the limits of their potential, prompting researchers to investigate other alloys. Molybdenum alloys, particularly those with silicon and boron (Mo-Si-B), show great promise for ultra-high-temperature applications, since they maintain their strength at much greater temperatures and pressures than nickel alloys. However, even Mo-Si-B materials show some oxidation under the extreme conditions they might face in aerospace applications.

Perepezko and his students have developed a surface coating for Mo-Si-B alloys that prevents cracking, peeling, delamination and oxidation, even under extreme temperature and pressure conditions.

“According to the models, these coatings should work at very high temperatures—up to 1,800 degrees Celsius,” says Perepezko. “That’s like a tungsten filament in a light bulb. That’s hot.”

Surprisingly, the researchers’ tests exceeded what their models predicted. Oxygen torch tests have shown that both the metal and coating survive with no sign of wear at more than 2,000 degrees Celsius (about 3,600 degrees Fahrenheit).

“This is a good example of true discovery, which you wouldn’t get with any computer simulation,” says Perepezko.

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