Chapter 2 - Mechanical spectroscopy of nanostructured metallic systems

Abstract

A highly attractive aspect of the mechanical behavior of solids is that kinetic processes, structural modifications, and phase transitions can be sensitively investigated by techniques that measure small deviations from the elastic behavior. These measurements, known as “mechanical spectroscopy techniques,” constitute a well-established approach to the study of a number of phenomena in a wide variety of materials, including hydrogen in metals and semiconductors, martensitic transformations in shape–memory alloys, vortex dynamics in high-temperature superconductors, viscoelasticity of polymers, glass transitions in amorphous materials, and interfacial diffusion in thin films. Two fields of mechanical spectroscopy and nanostructured materials in contact are discussed in the chapter. The nanostructured systems represent just a subclass of the nanostructured materials being investigated all around the world. Nanostructured metallic systems—more specifically nanocrystalline nickel and aluminum, granular copper–cobalt alloys, and magnetic nanocomposites obtained by devitrification of an amorphous alloy precursor—have been chosen for mechanical spectroscopy investigations. The scope of this selection is twofold: (1) to illustrate with some examples the information that can be extracted by applying mechanical spectroscopy techniques to metastable nanoscaled materials and (2) to discuss some general aspects of the structure–properties relationships in different types of nanostructured metallic systems. Irreversible structural modifications induced by thermal treatments—a feature of great interest in metastable materials—and the anelastic behavior arising from interface (grain boundaries) dynamics in ultrafine-grained systems are also discussed in the chapter.