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Nanocrystals not small enough to avoid defects - 11/2/2002—Nanocrystals as protective coatings for advanced gas turbine and jet engines are receiving a lot of attention for their many advantageous mechanical properties, including their resistance to stress. However, contrary to computer simulations, the tiny size of nanocrystals apparently does not safeguard them from defects. In a study by researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab)and collaborators from multiple institutions, nanocrystals of nickel subjected to high pressure continued to suffer dislocation-mediated plastic deformation even when the crystals were only three nanometers in size. These experimental findings, which were carried out at Berkeley Lab's Advanced Light Source (ALS), a premier source of X-rays and ultraviolet light for scientific research, show that dislocations can form in the finest of nanocrystals when stress is applied. "We cannot ignore or underestimate the role of dislocations – defects or irregularities – in fine nanocrystals as external stress can change the entire picture," says Bin Chen, a materials scientist with the ALS Experimental Systems Group who led this research. "Our results demonstrate that dislocation-mediated deformation persists to smaller crystal sizes than anticipated, primarily because computer models have not given enough consideration to the effects of external stress and grain boundaries." Chen is the lead and corresponding author of a paper in Science describing this work. The paper is titled "Texture of Nanocrystalline Nickel: Probing the Lower Size Limit of Dislocation Activity." Co-authoring this paper were Katie Lutker, Selva Vennila Raju, Jinyuan Yan, Waruntorn Kanitpanyacharoen, Jialin Lei, Shizhong Yang, Hans-Rudolf Wenk, Ho-kwang Mao and Quentin Williams.

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