Nanoscale electronic theory of mechanical
behavior
One
of the major topics in the field of Materials Science is to understand the
dependence of the properties of a material on its structure. Traditionally,
“structure” has meant microstructure, which includes the more macroscopic
structural parameters (the ones that can be determined with traditional
characterization methods such as a scale or a light microscope). However, the
chemical bonding and thus the electronic structure of the different atoms in
their respective configuration in the material are the basis for this behavior
and thus are necessary for a real physical understanding of the materials
properties starting from the nanoscale. However, little work has been done in
this area to date.
Example: Grain Boundary
Embrittlement of Ni3Al Alloys*
Ni3Al
has excellent high-temperature properties and is thus an excellent candidate
material for highly demanding environments such as airplane turbines. However,
in its clean form, it is very brittle and breaks already under small
deformations. Addition of B has been found to fix this problem and make the
material highly ductile. We have developed an “electronic theory of
embrittlement” and find a low electron density to be the reason for the high
grain-boundary brittleness. Addition of B accumulates electrons (which can be
thought of as “glue” between the atoms) around the B atoms, which segregate to
the grain boundary. Thus, the accumulated electrons around the B atoms “staple”
the grains together and prevent fracture at the grain boundaries (Fig. 4).
*
M. Chisholm, G. Duscher and