Effect of Carbon in Severe Plastically Deformed Metals

In the last decades severe plastic deformation techniques have gained increasing interest as they allow the production of bulk nanostructured materials with superior mechanical and functional properties. However, because of mechanically induced grain boundary migration, the achievable grain size reduction is not indefinite but tends to stagnate once sufficient strain has been applied. Consequently, addition of solute elements or second phase particles offers the possibility to access the true nanocrystalline regime. Due to their low solubility and high mobility, interstitial elements are extremely effective at subduing boundary migration. Herein the effect of carbon on grain refinement and the resulting mechanical properties are summarized. As carbon may not only be added as graphite but could also be introduced in other forms or as allotropes such as nanotubes, nanodiamonds, or carbides, the respective advantages and problems associated with it are the center of discussion. Independent of the strategy used, strength levels hardly achievable with other alloying elements can be obtained. Moreover, as carbon does not have a negative effect on grain boundary cohesion, despite the enormous strength levels even ductility and toughness can be widely maintained.