Plastic deformation of materials occurs by the motion of defects known as dislocations and disclinations. High-resolution transmission electron microscopy was used to directly reveal the individual dislocations that constitute partial disclination dipoles in nanocrystalline, body-centered cubic iron that had undergone severe plastic deformation by mechanical milling. The mechanisms by which the formation and migration of such partial disclination dipoles during deformation allow crystalline solids to fragment and rotate at the nanometer level are described. Such rearrangements are important basic phenomena that occur during material deformation, and hence, they may be critical in the formation of nanocrystalline metals by mechanical milling and other deformation processes.

The effects of hydrogen on microstructural change and surface originated flaking in rolling contact fatigue were investigated using JIS-SUJ2 bearing steel specimens charged with hydrogen. Under clean lubrication conditions, subsurface originated flaking occurred and the rolling contact fatigue life was reduced and the amounts of the microstructural change called white structure that formed in the specimens increased as the hydrogen content increased. The localized microstructural changes were found in the hydrogen-charged specimens by electron microscope observations. It is supposed that the localization of plasticity was enhanced by hydrogen during the process of rolling contact fatigue. Under contaminated lubrication conditions, which included debris in the lubricating oil, surface originated flaking occurred and the rolling contact fatigue life of the hydrogen-charged specimens became shorter than the uncharged specimens, although white structure was not observed around the flaking. Enhancement of fatigue crack formations due to hydrogen was observed in specimens with artificial dents. It is presumed that hydrogen facilitated the formation of fatigue cracks on the raceway surface.

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