Synopsis: Finding strength in small places

X-ray diffraction reveals why some nanostructured metals are stronger than others.

Pulling, rolling, or bending a metal such as steel introduces dislocations in its structure that allow it to absorb energy under stress and resist fracture. Scientists and engineers have tried to find a similar process to toughen nanocrystalline metals, as these materials are prone to fracture despite their ultrahigh strength and hardness.

Writing in Physical Review Letters, Yinmin Wang and colleagues at Lawrence Livermore National Laboratory, in collaboration with researchers at Ames Laboratory and Argonne National Laboratory, all in the US, present experiments on specific ways in which nanostructured metals deform under stress.

Wang et al. prepared bulk pieces of nanocrystalline nickel and cobalt, which have similar grain sizes but different crystal structures. Each metal contained a large number of nanograins (“domains”) with a different crystalline orientation than those around them. With synchrotron x-ray diffraction and electron microscopy, Wang et al. tracked changes in the structure and defect accumulations within the domains in response to tensile (pulling) stress.

In the experiments, cobalt proved to be more resistant to fracture than nickel. Wang et al. suggest that this is because the domains in cobalt reorient, or “twin”, more easily than those in nickel, thus offering an effective strain-hardening mechanism. However, they note that even for cobalt the twinning mechanism is less effective for grains smaller than $15$ nanometers, which may be one reason why truly nanoscale materials are so resistant to toughening. – Jessica Thomas

More Features »

Announcements

More Announcements »

Subject Areas

Materials Science

Magnetism

Next Synopsis

Superconductivity

Related Articles

Condensed Matter Physics

Synopsis: Tackling Electronic Correlations

A new “first principles” simulation method could broaden the range of strongly correlated materials whose properties can be theoretically predicted. Read More »

Condensed Matter Physics

Viewpoint: Hydrogen Hides Surprises at High Pressure

Measurements of the melting curve of hydrogen at unprecedentedly high pressures call for a refinement of the theories describing the material. Read More »

Materials Science

Viewpoint: Porous Materials Exhibit Granular-Like Stress Chains

Simulations of porous materials exhibit internal stress patterns like those in granular materials, despite the fact that these two systems are practically “negative images” of each other. Read More »