Grain boundary contributions to deformation and solid-state flow in severe plastic deformation

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2005-11, Vol.409 (1), p.13-23
• Main Authors: Esquivel, E.V., Murr, L.E.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Deformation and plasticity (including yield, ductility, and superplasticity); Dislocation lattice; DRX; Exact sciences and technology; Grain boundary sliding; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics; SPD; Superplasticity
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2005.04.063

More than 40 years ago, Professor J.C.M. Li put forth the concept of grain boundary ledges as sources for dislocations. Since then, there have been numerous confirmations of grain boundary dislocation sources, consistent with the fundamental features of interfaces, and we will demonstrate these observations in deformed metals and alloys observed in the TEM after specific levels of plastic strain. More recently, Professor Li has proposed a new mechanism for severe plastic deformation, or superplastic flow beyond the normal realm of plasticity which involves a so-called “interfacial fluid” that allows for continuous, solid-state flow accommodating large plastic strains, and even very high strain rates. Some interesting examples of severe plastic deformation illustrating these issues, and the connectedness to the incipient and normal plastic regime (the stress–strain diagram) will be presented by examining high velocity and hypervelocity impact craters in polycrystalline metals and alloys. These exhibit varying degrees of plastic strain and associated microstructures evolving from dislocation emission and interaction, and the actual plastic flow and jetting of solid-state material from the crater rims, which are shown to be arrays of adiabatic shear bands composed of dynamically recrystallized grains. The concept of an “interfacial fluid” will be examined considering dense dislocation arrays in the grain boundary phase regime utilizing the amorphous dislocation lattice concept also originated by Professor Li several decades ago.