LR754 battery.New smart materials could open new areas of research

　　A new group of smart materials discovered by Texas A&M University researchers and colleagues has the potential to significantly improve jet engine fuel-burning efficiency and reduce flight costs. These materials can also reduce aircraft noise in residential areas and have other applications in a variety of other industries. "What excites me is that we have just touched upon something new that not only opens up a whole new field of scientific research but also enables new technologies," said Dr. Ibrahim Karaman, Chevron Professor I and University Department Chair. Materials Science and Engineering. This work is published in ScriptaMaterialia. Klarman's co-authors are Demircan Canada, William Trehern and Ji Ma of Texas A&M, and United Technology Research Center (UTRC) technical fellows Fanping Sun and Zaffir Chaudhry. The discovery is based on bringing together two relatively new fields of materials science involving metal alloys, or metals composed of two or more elements. The first area involves shape memory alloys, "smart" materials that can switch from one shape to another via a specific trigger, in this case temperature. Think of a straight metal rod bent into a spiral screw. By changing the temperature, the corkscrew changes back into a rod and vice versa. Many Applications Many potential applications of shape memory alloys involve extremely hot environments, such as operating jet engines. However, so far, economical high-temperature shape memory alloys (HTSMA) have only worked at temperatures up to about 400 degrees Celsius. Adding elements such as gold or platinum can significantly increase temperatures, but the resulting materials are too expensive, among other limitations. Klarman began this research while working on a NASA project with UTRC and colleagues to solve a specific problem: controlling the gap, or space, between turbine blades and the casing of a jet engine's turbine. Jet engines are most fuel efficient when the gap between the turbine blades and casing is minimized. However, such permission must allow a reasonable margin to deal with special operating conditions. HTSMA incorporated into the turbine casing can allow minimum clearances to be maintained in all flight states, thereby improving thrust-specific fuel consumption. Another important potential application of HTSMA is reducing the noise of aircraft entering airports. Aircraft with larger exhaust nozzles are quieter but less air efficient. HTSMA can automatically change the size of the core exhaust nozzle depending on whether the aircraft is in flight or landing. This change, triggered by the temperatures associated with these operating modes, could allow for more efficient operation in the air and quieter conditions on landing. Klarman and his colleagues decided to try to increase the operating temperature of HTSMA by applying the principles of another new class of materials: high-entropy alloys, which are materials composed of four or more elements mixed together in roughly equal amounts. The team created materials composed of four or more elements known to form shape memory alloys (nickel, titanium, hafnium, zirconium and palladium) but purposefully omitted gold or platinum. "When we mixed these elements in the same proportions, we found that the resulting materials could operate at temperatures in excess of 500 degrees Celsius - one worked at 700 degrees Celsius - without gold or platinum. That was a discovery," Klarman said. "It was also unexpected because the literature said otherwise." How does the new material work? Klarman said they have an idea of how to operate at such high temperatures, but don't yet have a solid theory. To this end, future work includes trying to understand what is happening at the atomic scale through computer simulations. The researchers are also working to explore ways to further improve the material's properties. However, Klarman points out that there are many other issues. "That's why I think this could open up a whole new field of research," he said. "While we will continue our efforts, we are excited for others to join us now so that together we can advance the science." This joint project between UTRC and Texas A&M is funded by NASA's Frontier Special Research Initiative.

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