Materials Performance

AUG 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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12 AUGUST 2018 W W W.MATERIALSPERFORMANCE.COM Continued f rom page 11 UP FRONT U.S. Navy Engineers Develop Aluminum-Rich Primer Engineers with the U.S. Naval Air Warfare Command—Aircraft Division (NAWCAD) (Patuxent River, Maryland, USA) developed a new active Al-rich primer for coating systems. The Al-rich product is a metalized, sacrificial, chromate-free, anticorrosion primer intended as an alternative for situations where a chromated primer is currently used. The technology's first key component is the use of a specialty aluminum alloy as the pigment inside the primer. The high effi- ciency of the alumi- num alloy composi- tion, combined with aluminum's low den- sity, allows the coat- ing to be applied at normal aviation thicknesses—thus eliminating weight concerns. The second component is a pro- prietary surface treatment applied to the pigment. Because of its ability to pro- tect aluminum electrochemically, the Al-rich primer has excelled at preventing fastener-induced corrosion as well as filiform corrosion—it outperformed chro- mated primers in many of its tests. Although metal-rich primers have existed for some time, the Nav y says there were underlying problems. First, traditional zinc-rich coatings are too heav y for aviation applications and not effective on aluminum. Second, other metal-rich coatings do not have the longevity of performance in harsh environments. "Al-rich is superior based on the novel aluminum pigment that actively over- comes corrosion by electrochemical means," says NAWCAD materials engineer Craig Matzdorf. "Current coatings rely on chemical inhibitors like chromate, which are less effective at fighting galvanic corrosion. We anticipate that the Al-rich primer will reduce galvanic and other types of corrosion and its effect on the Nav y's cost and availability." Up to this point, the primer has been applied to a U.S. Army helicopter, cargo plane, two Coast Guard tail sections, and various pieces of Nav y support equip- ment. For further testing, the Nav y needs larger batch sizes, so it has begun licensing the technology to equipped businesses. Over the next few years, the Nav y plans to apply the new primer to larger portions of its assets. For more information, visit science.dodlive.mil. The U.S. Navy began testing the Al-Rich primer on applica- tions throughout the U.S. Department of Defense. Photo courtesy of the U.S. Navy. Electric Field Boosts Plasticity of Ceramic Coatings Applying an electric field to ceramics gives them metal-like characteristics needed for sustaining heavy loads. Photo by Jaehun Cho, Purdue University. Researchers with Purdue University (West Lafayette, Indiana, USA) have observed a way that historically brittle ceramic coat- ings can overcome heav y loads. The re- searchers say most ceramics fracture when strained unless exposed to high tem- peratures. Ceramic components also re- quire high temperatures to initially form via sintering, in which a powdered mate- rial coalesces into a solid mass. However, ceramic coatings used on industrial assets like metal engine blades must protect cores from many operational temperatures. This study demonstrates that applying an electric field to yttria-stabilized zirco- nia (YSZ)—a typical thermal barrier ce- ramic—makes the material almost as plas- tic as metal at room temperature. Cracks can be seen sooner as well, since they begin forming at more moderate temperatures. Historically, the researchers note, YSZ coatings have fractured when an engine heats up and cools down. "In the past, when we applied a high load at lower tem- peratures, a large number of ceramics would fail catastrophically without warn- ing," says Xinghang Zhang, professor of materials engineering. "Now we can see the cracks coming, but the material stays together." Recent studies show that applying an electric field, or "f lash," accelerates the sintering process, and at lower furnace temperatures. Flash-sintered ceramics have less porosity, which makes them denser and more likely to deform rather than break. Prior studies, however, did not test whether these ceramics could change shape at room temperature or higher. Dur- ing in situ testing, a f lash-sintered YSZ sample thinner than human hair grew in- creasingly plastic between room tempera- ture and 600 °C when compressed, with cracks slowly spreading at 400 °C. In con- trast, conventionally sintered YSZ requires 800 °C and higher to deform.

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