Materials with a special kind of boundary between crystal grains can deform in unexpected ways | 10/25/2017 | Staff
MireilleMireille (Posted by) Level 3
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Most metals and semiconductors, from the steel in a knife blade to the silicon in a solar panel, are made up of many tiny crystalline grains. The way these grains meet at their edges can have a major impact on the solid's properties, including mechanical strength, electrical conductivity, thermal properties, flexibility, and so on.

When the boundaries between the grains are of a particular type, called a coherent twin boundary (CTB), this adds useful properties to certain materials, especially at the nanoscale. It increases their strength, making the material much stronger while preserving its ability to be deformed, unlike most other processes that add strength. Now, researchers have discovered a new deformation mechanism of these twin crystal boundaries, which could help engineers figure out how to more precisely use CTBs to tune the properties of some materials.

Expectations - Material - Grains - CTBs - Finding

Contrary to expectations, it turns out that a material's crystal grains can sometimes slide along these CTBs. The new finding is described in a paper published this week in the journal Nature Communications by Ming Dao, a principal research scientist in MIT's Department of Materials Science and Engineering; Subra Suresh, the Vannevar Bush Professor Emeritus of Engineering and president-designate of Nanyang Technological University in Singapore; Ju Li, the Battelle Energy Alliance Professor in MIT's Department of Nuclear Science and Engineering; and seven others at MIT and elsewhere.

While each crystal grain is made up of an orderly three-dimensional array of atoms in a lattice structure, CTBs are places where, on the two sides of a boundary, the lattice forms a mirror-image of the structure on the other side. Every atom on either side of the coherent twin boundary is exactly matched by an atom in a mirror-symmetrical location on the other side. Much research in recent years has shown that lattices that incorporate nanoscale CTBs can...
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