Megumi Kawasaki

Abstract

Heterogeneity Across Length Scales in Bulk Nanostructured Metals: Formation, Evolution, and Control

Heterogeneity in nanostructured metals extends beyond variations in grain size to include spatial distributions of chemical composition, phases, and lattice defects. Understanding how these features develop and evolve is essential for connecting processing history to mechanical response and thermal stability. High-pressure torsion processing offers a versatile platform to examine these relationships through intense shear deformation under high hydrostatic pressure. This presentation brings together studies of bulk nanostructured metals, hybrid Al–Mg systems, and high-entropy alloys to examine heterogeneity across multiple length scales. In dissimilar-metal assemblies, deformation drives an evolving sequence of bonding, microstructural refinement, intermetallic formation, and mechanical alloying toward metastable states. Complementary microscopy and high-energy synchrotron X-ray and neutron diffraction reveal that apparently uniform grain structures and hardness distributions can coexist with persistent chemical and structural heterogeneity. In situ diffraction and high-temperature microscopy further show how deformation-induced defects and their spatial variations in microstructure influence recovery, recrystallization, and phase evolution during heating. The presentation also examines how processing conditions and specimen geometry influence strain distributions and the development or reduction of heterogeneity. Together, these studies describe the importance of measurement scale and spatial resolution in interpreting processing–structure–property relationships. They provide a basis for discussing how to characterize and control heterogeneity in developing bulk nanostructured metals with tailored mechanical response and thermal stability.