Inter- and intra-agglomerate fracture in nanocrystalline nickel.

In situ tensile straining transmission electron microscopy tests have been carried out on nanocrystalline Ni. Grain agglomerates (GAs) were found to form very frequently and rapidly ahead of an advancing crack with sizes much larger than the initial average grain size. High-resolution electron microscopy indicated that the GAs most probably consist of nanograins separated by low-angle grain boundaries.

Dislocation dynamics in nanocrystalline nickel.

It is believed that the dynamics of dislocation processes during the deformation of nanocrystalline materials can only be visualized by computational simulations. Here we demonstrate that observations of dislocation processes during the deformation of nanocrystalline Ni with grain sizes as small as 10 nm can be achieved by using a combination of in situ tensile straining and high-resolution transmission electron microscopy. Trapped unit lattice dislocations are observed in strained grains as small as 5 nm, but subsequent relaxation leads to dislocation recombination.

Grain boundary-mediated plasticity in nanocrystalline nickel.

The plastic behavior of crystalline materials is mainly controlled by the nucleation and motion of lattice dislocations. We report in situ dynamic transmission electron microscope observations of nanocrystalline nickel films with an average grain size of about 10 nanometers, which show that grain boundary-mediated processes have become a prominent deformation mode. Additionally, trapped lattice dislocations are observed in individual grains following deformation.

Sensitivity considerations for NMR in metal single crystals.

We report a study of the factors determining the sensitivity of NMR measurements using bulk metal single crystal samples. We show that, in an ideal case, the NMR signal intensity from such a sample can be characterized by a figure of merit which is a function of only the fractional radio-frequency power losses in the coil winding compared to the losses in the sample. This allows the Q factor of the NMR coil to be varied considerably with no appreciable change in the figure of merit, thus permitting the coil Q to be chosen on the basis of the noise characteristics of the spectrometer being used.