Nguyen-Manh, A. Horsfield, and S. Dudarev Phys.
B 73 , R — Published 3 January Abstract We present an investigation of systematic trends for the self-interstitial atom SIA defect behavior in body-centered cubic bcc transition metals using density-functional calculations. Issue Vol.
Authorization Required. Log In. Data for bcc Fe is taken from Ref. Figure 4 Fields of atomic displacements in the central string of the crowdion configuration evaluated for bcc metals.
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Editors: H. Ullmaier | ISBN: (Print) ( Online) | DOI: /b | SpringerMaterials Atomic or point defects are disturbances of the periodicity of the crystal lattice extending over only a few atomic distances. Many physical and mechanical.
Journal: Phys. X Rev.
A Phys. B Phys. Linear defects, or more precisely edge dislocations, occur when a layer remains incomplete so that the layers above and below it must take a step. As the length of the linear defects in a cubic metre of steel can add up to one light year, the discovery ought to have great practical significance since the structure of a steel depends on, among other factors, how malleable, rigid and ductile it is — properties which material scientists want to continuously optimize.
Atom probe tomography shows them the distribution of the iron blue and manganese atoms green. They have put green iso-surfaces into the image where the concentration of the manganese atoms is In the superimposed images, the researchers can see that the manganese atoms accumulate along the linear defects; the crystal structure which forms there is different to the surrounding material. Dislocations can save lives. This stems from the fact that the one-dimensional defects in a metal play an important role when the material deforms: for example, when a car body panel crumples in an accident, thus absorbing a large part of the impact energy and hopefully protecting the passengers from injury.
In such a case, the dislocations act as nano-hinges along which a metal bends. The fact that the crystal structure differs from the structure immediately around the linear defect should therefore also affect how the metal deforms. In the worst case, it tears rather than deforms.
He and his team had been investigating the micro- and nano-structure of a particularly rigid and ductile manganese steel which is strengthened with the aid of nanoparticles and is used in the landing gear of large aircraft, for example. They analysed this material with the aid of atom probe tomography.
The analysis involves a sample being vaporized atom by atom with short pulses of an electric voltage. From the time-of-flight to a detector it is possible to determine to which element the vaporized detached atom belongs; its position in the sample can be determined from the location where the atom impinges on the detector. The fine tubes in which the manganese collects are only two nanometres wide.
And this happens not along the whole length, but more in the form of a chain of manganese-rich nano-beads. In order to accommodate the larger number of manganese atoms in these minute areas, the crystal structure of the material must change. Iron and manganese atoms normally sit at the corners and centers of a cubic unit cell, the smallest structural unit.
The researchers call this a body-centred cubic or martensite structure. The manganese concentration in the chain of nano-beads corresponds to an arrangement in which the atoms are located on each face and corner of the unit cell, in technical terms, a face-centred cubic or austenite structure.