Materials Performance

NOV 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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8 NOVEMBER 2018 W W W.MATERIALSPERFORMANCE.COM UP FRONT U.S. Airmen Make Historic Corrosion Repairs U.S. Airmen discovered corrosion on the lower skin of the aircraft, making it inoperable until repair. Photo courtesy of U.S. Air Force. Three U.S. Airmen with the 35th Mainte- nance Squadron fabrication flight recently performed a historic corrosion repair on an F-16 Fighting Falcon aircraft at Misawa Air Base, Japan. Maintainers or contractors typically conduct such depot-level repairs at Hill Air Force Base, Utah, USA, where they are certi- fied to tend to severely damaged aircraft. Many of these cases require the use of specialized resources. However, when the team discovered corrosion on the lower skin of the aircraft, making it inoperable until repair, the Hill office approved Misawa Airmen to rectify the issue in Japan. The local restoration, which saved significant time, required creative thinking along with high levels of maintenance competency and skill, accord- ing to the crew. "In one month's time, we aided in bring- ing this aircraft back to life," says Tech. Sgt. Jordon Jones, an aircraft maintenance struc- tural craftsman at Misawa. "Once we dis- covered the pinhole-sized corrosion, we removed seven major construction compo- nents, three skins, two ribs, and cut out a total longeron, which maintains the struc- tural rigidity of the airframe. In more simple terms, we cut the aircraft in half and put it back together." While making these repairs, the team stayed vigilant for quality assurance and accuracy. "My team remained cautious during the process because this was the first time in U.S. Air Force history a repair like this had been conducted at the field level," Jones World's Most Wear-Resistant Metal Alloy Researchers at Sandia National Laboratories (Albuquerque, New Mexico, USA) recently engineered a platinum-gold alloy believed to be the most wear-resistant metal in the world. According to the research team, the alloy is 100 times more durable than high- strength steel, making it the first alloy, or combination of metals, in the same class as diamond and sapphire. Although metals are typically thought of as strong, they can wear down, deform, and corrode when repeatedly rubbed against other metals, such as in an engine, the researchers explain. This is unless they have a protective barrier, like additives in motor oil. In electronics, moving metal-to-metal contacts receive similar protections with outer layers of gold or other precious metal alloys. But these coatings are expensive, and eventually they can wear out, as connections press and slide across each other. These effects are exacerbated when connections are smaller, because reduced initial material means there is less wear and tear that each connection can endure. With Sandia's platinum-gold coating, made of 90% platinum and 10% gold, the researchers say only a single layer of atoms would be lost after a mile of skidding on hypothetical tires. The coating could make electronics of all sizes and across many industries more cost-effective. While conventional wisdom says a metal's ability to withstand friction is based on its hardness, the Sandia team proposed a new theory that wear is related to how metals react to heat, not their hardness. In turn, they handpicked metals, proportions, and a fabrication process to prove their theory. The theory arose from computer simulations that calculated how individual atoms were affecting the large-scale properties of a material. "Many traditional alloys were developed to increase the strength of a material by reducing grain size," says John Curry, a postdoctoral appointee. "Even still, in the pres- ence of extreme stresses and temperatures, many alloys will coarsen or soften, especially under fatigue. We saw that with our platinum-gold alloy, the mechanical and thermal stability is excellent, and we did not see much change to the microstructure over immensely long periods of cyclic stress during sliding." For more information, visit Researchers show a computer simulation used to predict the wear resistance of their platinum-gold alloy. Photo courtesy of Sandia.

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