Development of nanostructures in metallic materials with low stacking fault energies during surface mechanical attrition treatment (SMAT)

Surface mechanical attrition treatment (SMAT) technique was developed to synthesize a nanostructured surface layer on metallic materials for upgrading their overall properties and performance. In this paper, the grain refinement process during SMAT was investigated in materials with low stacking fault energies (SFE, Inconel 600 alloy and AISI 304 stainless steel) by means of transmission electron microscopy and high-resolution electron microscopy, respectively. Grain subdivision was performed by the interaction of mechanical microtwins with dislocations in Inconel 600. For AISI 304 stainless steel with a lower SFE, twin-twin intersections subdivide initial grains into refined blocks with sizes ranging from nanometers to submicrometers. Such grain subdivision processes of the interaction of microtwins with dislocations or microtwins obviously differ from those observed in the high SFE materials in which dislocation interactions predominate the grain refinement.