Eric J. Mittemeijer

Diffraction stress analysis of highly planar-faulted, macroscopically elastically anisotropic thin films and application to tensilely loaded nanocrystalline Ni and Ni(W)

The presence of planar faults complicates the diffraction stress analysis enormously owing to fault-induced displacement, broadening and asymmetry of the Bragg reflections. A dedicated stress-analysis method has been developed for highly planar-faulted, fibre-textured thin films of cubic crystal symmetry, using only specific reflections for diffraction stress analysis. The effect of unjustified use of other reflections has been demonstrated in the course of application of the method to Ni and Ni(W) thin films exhibiting excessive faulting and subjected to (1) a planar, rotationally symmetric stress state and (2) a planar biaxial stress state. In case 1 the crystallite-group method has been used, whereas in case 2 the stress-analysis method based on X-ray stress factors had to be applied. The successful separation of stress- and fault-induced reflection displacements has enabled the investigation of the mechanical behaviour of Ni and Ni(W) thin films by in situ stress measurements during tensile loading, thereby exposing pronounced stiffness and increased strength by alloying withxa0W.

Recovery, Recrystallization and Grain Growth

Recrystallization has been identified as a process in metallic solids since the “old days” (last part of the nineteenth century), when it was supposed that cold working of a metallic workpiece destroyed its crystallinity and that subsequent heating restored the crystalline nature by a process then naturally coined with the name “recrystallization”. Nowadays we would define recrystallization as a process that leads to a change of the crystal orientation (distribution) for the whole polycrystalline specimen, in association with a release of the stored strain energy as could have been induced by preceding cold work: a new microstructure results (Fig. 10.1). Recrystallization restores the properties as they were before the cold deformation. Recrystallization (and recovery and grain growth) occurs in all types of crystalline materials, so not only in metals. However, metals are the only important class of materials capable of experiencing pronounced plastic deformation at relatively low temperatures (i.e. low with respect to the melting temperatures), which explains that most of the corresponding research has been and is performed on metallic materials.

Analysis of the Microstructure; Analysis of Lattice Imperfections: Light and Electron Microscopical and X-Ray Diffraction Methods

Materials are substances that have now, or are expected to find in a not too distant future, practical use (see Chap. 1). The microstructure of a material (beautifully described by the untranslatable German word “Gefuge”) is a notion that comprises all aspects of the atomic arrangement in a material that should be known in order to understand its properties. Mostly we are concerned with crystalline materials. The conception microstructure then narrows to the description of the so-called crystal imperfection (cf. Chap. 5).

Electronic Structure of the Atom; the Periodic Table

Atoms consist of a nucleus that is surrounded by a “cloud” of electrons. Protons, elementary particles carrying positive unit charge (e = 1.602 × 10–19 C), and neutrons, elementary particles carrying no charge, form together the nucleus of diameter of the order 10–14 m. Electrons, elementary particles carrying negative unit charge, have only about 1/1836 the mass of a proton, but are located within a relatively enormously large space of diameter of the order 10–10 m. Hence, with a view to mass distribution, the atom is largely “empty”.

Chemical Bonding in Solids; with Excursions to Material Properties

Why do atoms stick together? And why do they gather in aggregates exhibiting specific types of three-dimensional (periodic) arrangements? Mankind, on its road to reveal the secrets of nature, time and again returns to these questions in order to develop an ever-growing insight on how matter is formed from its building units.

Mechanical Strength of Materials

The response of materials to applied forces concerns a field of material properties which has been of prime interest to human beings since the emergence of mankind. Even as a child, already, one gathers experiences about what we vaguely call the “strength” of a material, by feeling with our fingers how “hard” or “soft” a specific material is.

The Crystal Imperfection; Lattice Defects

Idealized presentations of atomic arrangements exhibiting long-range translation symmetry, i.e. idealized crystal structures, have been presented and discussed in the previous chapter. Very many properties of crystalline materials cannot be understood merely on the basis of such perfect atomic arrangements. As a matter of fact, defects in the atomic arrangement, as compared to the idealized ordering, strongly determine material properties as mechanical strength, diffusion, electrical conductivity and so on.