Twin boundary migration creating zero shear strain: In-situ TEM observations and atomistic simulations

Atomistic simulations were conducted to study the migration of <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo><mo>&#x003C;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x003E;</mo> </mrow> </math>$$\{ 10\bar 12\} < 10\bar 1\bar 1 >$$ twin boundary. A bi-crystal that satisfies the twin orientation relationship was constructed and a tensile strain was applied in parallel to the <c> axis of one crystal. Under the tensile strain, the twin boundary starts to migrate but the migration (twin growth) does not produce any observable shear strain on the bicrystal. In-situ transmission electron microscopy (TEM) observations of a single crystal Mg under tension and compression confirm that during twinning and detwinning, no shear strain is produced. The specimen uniformly elongates and narrows during twinning, and widens across the width during detwinning.