Nanocrystalline Metals and Alloys

Dear Colleagues,

The strength of metals and alloys is strongly influenced by grain size with materials in the nanocrystalline regime characterized by superior yield and fracture strength, improved wear resistance and superplasticity observed at relatively low temperatures and high strain rates as compared with their microcrystalline counterparts. This has led to increased attention towards charactering their mechanical properties and deformation mechanism, these work summarized in recent review articles. The current attention to the potential industrial application of nanopolycrystals leads to the necessity of deep investigations of their mechanical physical and chemical properties both in static and dynamic conditions. Several laboratory-scale processing techniques are currently available to produce nanocrystalline (nc<100nm) and ultra-fine crystalline (ufc<1mm) materials. Today, the materials community realizes that the hopes for ultra-strong and ductile bulk nanocrystalline materials have not materialized yet. The reduction of the grain size down to the nanometer regime opened new and fascinating avenues for research in several aspects of material science, including mechanical properties. In polycrystalline metals with grain sizes in the micron range, the traditional view of plasticity is based on dislocation activity: dislocation sources are active within a grain, dislocations repel each other and they distribute themselves over available area within the slip plane delimited by the grain boundaries. Additionally, dislocations are attracted to the boundaries of the slip plane as a result of image forces and consequently, their distribution peaks close to the boundaries in the so-called pile-up effect. When the stress field resulting from the addition of individual dislocation contributions reaches some critical value, it activates sources in neighboring grains.

As a result of all this, the material becomes harder to deformScientifically, the study of nanocrystalline materials is of great interest because the potential breakdown of classical scaling laws and the accompanying need for new materials physics in the nanostructured state. Understanding the basic deformation mechanisms and the key microstructural parameters that influence the materials macroscopic behavior at such small grain size, the way to the development of ductile and high performance nanocrystalline structures is open. At a nanometric scale, different mechanisms take place during monotonic or cyclic loading respect to the microcrystalline metals; The nanocrystalline metals and alloys contain a very high fraction of grain boundary volume; therefore grain boundaries and their interactions with crystal defects play a significant role in the deformation of these materials. Advances in the processing alloys along with the precipitous rise in the sophistication of routines, commonly available tools capable of characterizing materials with force, displacement and spatial resolution smaller and smaller, permit to obtain scientific data very precise on the mechanical response on nanocrystalline materials. Large improvements in computer hardware and software permit the simulation of the structures and deformation of nanostructures helping scientists in the well-understanding of the processes on nanoscale.

The main goal of the special issue “Nanocrystalline metals and alloys” is to represent a miliar stone in the field of nanostructured materials from synthesis, to processing to industrial application.

Dr. Pasquale Daniele Cavaliere
Guest Editor

• nanostructured materials
• syntesis
• production
• deformation
• elasticity
• plasticity
• applications
• future prospective