nanograins

Nanograins are crystalline domains with dimensions on the nanometer scale that constitute the basic building blocks of nanocrystalline materials. In a polycrystalline solid, the material contains many such grains, separated by grain boundaries. Typical grain sizes range from about 1 to 100 nanometers, and the large grain-boundary area strongly influences properties. Compared with coarse-grained materials, nanograined metals often show increased hardness and strength due to grain-boundary strengthening, though at very small sizes some materials exhibit deviations from the conventional Hall-Petch trend.

Synthesis and processing: Nanograins form through processes that limit grain growth during synthesis or processing, including severe plastic deformation (e.g., equal-channel angular pressing, high-pressure torsion), rapid solidification, mechanical alloying, electrodeposition of nanocrystalline films, and chemical synthesis routes such as solvothermal methods. Deposition and annealing strategies can tailor grain size, distribution, and texture. Controlling oxidation and coarsening is a major challenge.

Characterization and applications: Transmission electron microscopy, scanning electron microscopy, X-ray diffraction with peak broadening analysis, and electron backscatter diffraction are commonly used to assess grain size and structure. Nanograined materials find applications in structural components with enhanced strength, catalytic supports with high surface area, magnetic materials with unique domain behavior, and energy storage or protective coatings.