From Atoms to Sky Scrapers: The Role of Crystallography in Deformation, Damage, and Fracture
Martin A. Crimp
Chemical Engineering and Materials Science
Michigan State University
Why is copper soft and ductile while rock salt is hard and brittle? One would guess that the mechanical behavior of crystalline materials is inextricably linked to how their atoms are bonded, but just as important is how their atoms are arranged in crystal structures. Plastic (permanent) deformation is achieved through the motion of crystal defects, while failure through fracture results from the rupture of atomic bonds. In order to fully understand and optimize mechanical behavior of materials, it is therefore necessary to understand the arrangement of atoms. But how can we determine the positions of atoms in a material? Atomic arrangements are typically studied using diffraction techniques (x-ray, electron, neutron) by implementing Bragg&apos s Law and Structure Factor calculations to determine not only the size and shape of the unit cell, but also the atom positions and types within the unit cell. Armed with this information, it is possible to understand the details of mechanical behavior, in particular the anisotropic nature of plastic deformation. This talk will review and build on these concepts to illustrate how the macroscopic deformation and fracture behavior, and the ultimate performance of planes, trains, and automobiles, is a function of the crystallographic orientation distribution in both single and polycrystalline materials. Examples of the role of non-random crystallographic orientation distribution in the anisotropic behavior of a number of materials, including FeAl, TiAl, and Ti will be presented. The implications of this anisotropic behavior will be discussed.