The top-down approach on the other hand, consists of refining existing coarse structure primarily by severe plastic deformation 2 (SPD).
Bottom-up refers to the assembly of the material by agglomeration of atoms or molecules (as a rule, in non-equilibrium conditions), such as processes based on vapor deposition or fast solidification.
Traditional methods for fabricating nanostructured metals have been classified as bottom-up and top-down 1. As a consequence of the reduction of mobility of linear defects (dislocations), confined between close grain boundaries (GBs), the hardness and ultimate strength of nanostructured metals is very high, which might provide certain technological benefits. Nanostructured metallic materials typically have very different mechanical properties as compared to their coarse-grained counterparts.
The microscopic analysis suggests a reassembly of the elements in a new lattice of carbon supersaturated nano-ferrite. Analysis of the mechanical properties has shown extraordinary results at the surface, over 2000 MPa of strength on AISI1045 steel, more than three times the strength of the base material, demonstrating at the same time a reduction of 15% in the elastic modulus. In this work the machining method is considered to be a testing platform for the formation and study of frictional nanostructured steel, assembly of which is stabilized by fast cooling of the produced chip.
One approach towards achieving these nanostructures resides in frictional treatments on manufactured parts, leading to differential refinement of the surface structure as compared to the bulk material. Nanocrystalline structured variants of commercially available alloys have shown potential for boosting the mechanical properties of these materials, leading to a reduction in waste and thereby retaining feasible supply chains.
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