The steel products containing metals and semiconductors are formed by crystalline grains. The solar panels and knife blades are made up of crystalline grains. These grains have tendency in combining and build up mechanical strength, electrical conductivity, thermal properties and flexibility.
Coherent Twin Boundary (CTB)
The borders between the grains of different type known as Coherent Twin Boundary (CTB) it is a useful property for some materials on nanoscale. This makes material stronger in its ability to be in disfigure.
Researchers have found the deformation technique between the twin crystal boundaries. It helps to use CTB to characterizing the properties of other materials. The study led by Ming Dao, a principal research scientist from 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.
The structure of crystal grain is three-dimensional array of atoms in a lattice structure. Lattice forms a mirror-image of the structure on the other side. Every atom on either side of the coherent twin boundary exactly matches by an atom in a mirror-symmetrical location on the other side.
Ductility- Stretching property
In recent years the research has shown that lattices that incorporate nanoscale CTBs have more strength than same material with random grain boundaries, without losing another useful property which describes a material’s ability in stretching called Ductility.
A high-strength nano crystalline materials with grains sizes measured in less than 100 nanometers have low ductility and fatigue properties. Metals that combine CTBs,enhances the strength and preserves the good ductility. But understanding the materials various mechanical stresses is important to be able to harness them for structural uses. The way the material deforms is quite uneven. Distortions in the direction of the planes of the CTBs might happen readily than in other directions.
CTB Sliding
The experiment carried out with copper. But the results should apply to some other metals with similar crystal structures, such as gold, silver, and platinum. These materials widely used in electronic devices, Dao says. The sliding, once understood can implement for significant advantages. Researchers design extremely strong nano structures based on the known orientation dependence. Otherwise knowing the type and direction of force that requires to start the sliding. It is possible to design a device to activate it, such as an alarm, in response to a specific level of stress.
This study confirmed CTB sliding, which was previously considered impossible, and its particular driving conditions,” says Zhiwei Shan
Nano Twinned Materials
Both systematic experiments and analysis of mechanical characteristic identified by this work. It found only in certain special types of interfaces and at the nano scale. Given that this phenomenon applied to broad range of crystalline materials. One can envision new materials design approaches involving nano structures to optimize a different types of mechanical and functional characteristics,” Suresh says.
Gao adds that “CTBs are key to engineering novel Nano twinned materials with superior mechanical and physical properties such as strength, ductility, toughness, electrical conductivity, and thermal stability. This paper significantly advances our knowledge in this field by revealing large-scale sliding of CTBs.”
[source:MIT]
