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Nanotwinned Crystal Structures for Stronger Alloys

Magnesium crystals are manipulated as transmission electron micrographs (TEM) are taken, revealing the atomic-scale details of the crystal's response.
A team headed by Materials Sciences Division researcher Andrew Minor imaged the atomic-level response of magnesium crystals to mechanical strain, revealing the origin and dynamics of the crystal structure integral to mechanical properties of metal alloys. The discovery will help researchers develop new alloys with advanced mechanical properties.

In a user project at the National Center for Electron Microscopy, Minor's team used in-situ transmission electron microscopy to observe a single magnesium crystal with unprecedented spatial resolution as they stretched, compressed and bent it. The resulting strain produced crystal structures known as twin boundaries, in which two crystalline domains meet with perfect atomic registry. These features can have profound effects on macroscopic mechanical properties like strength and ductility.

TEM images show the formation of nanoscale twin boundaries, in response to strain.
The team supported their measurements with molecular dynamics simulations and identified routes to control twin-boundary nucleation and growth. The resulting picture of crystal behavior is very different from the conventional view of how larger crystals are thought to deform plastically. Alloying techniques based on this new mechanism could make Mg and other lightweight metals viable materials for fuel-efficient vehicles.

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The Nanostructured Origin of Deformation Twinning. Qian Yu, Liang Qi, Kai Chen, Raja K. Mishra, Ju Li, and Andrew M. Minor. Nano Lett. 12, 887-892, 2012. DOI: 10.1021/nl203937t