Physical Metallurgy (eBook)

Kazuhiro Hono, David E. Laughlin (Herausgeber)

eBook Download: PDF | EPUB

2014 | 5. Auflage
2960 Seiten
Elsevier Science (Verlag)
978-0-444-53771-3 (ISBN)

Infos

This fifth edition of the highly regarded family of titles that first published in 1965 is now a three-volume set and over 3,000 pages. All chapters have been revised and expanded, either by the fourth edition authors alone or jointly with new co-authors. Chapters have been added on the physical metallurgy of light alloys, the physical metallurgy of titanium alloys, atom probe field ion microscopy, computational metallurgy, and orientational imaging microscopy. The books incorporate the latest experimental research results and theoretical insights. Several thousand citations to the research and review literature are included. - Exhaustively synthesizes the pertinent, contemporary developments within physical metallurgy so scientists have authoritative information at their fingertips - Replaces existing articles and monographs with a single, complete solution - Enables metallurgists to predict changes and create novel alloys and processes

Textauszug

1

Crystal Structures of Metallic Elements and Compounds

Walter Steurer     Laboratory of Crystallography, ETH Zurich, Zurich, Switzerland

Abstract

Besides reviewing the most frequent structure types as well as those of technologically and commercially important materials, we will illustrate the major structural building principles on typical examples and underline interesting structural interrelationships wherever existing. We will exclusively discuss ideal structures of macroscopic single-crystalline elements and compounds in thermodynamic equilibrium and, consequently, will not deal with any size- or processing-related topics. First, some factors governing the formation of crystal structures, in general, are introduced. This is followed by a comprehensive discussion of the structures of the metallic elements and, subsequently, by a presentation of the most relevant (frequency, properties, didactical content) structure types of intermetallic phases. Finally, a few representative examples of the structures of quasicrystals will be given.

Keywords

Crystal structures; Metallic elements; Intermetallic phases

1.1 Introduction?2

1.2 Factors Governing Formation and Stability of Crystal Structures?5

1.3 Crystal Structures of the Metallic Elements?24

1.4 Crystal Structures of Intermetallic Phases?47

1.5 Crystal Structures of Quasicrystals?78

References?94

Further Reading List?100

Glossary

Allotrope

    Modification of an element at a given temperature and pressure range.

Alloy

    A homogenous mixture of two or more (inter)metallic phases that may form a solid solution or remain phase separated.

Aperiodic crystal

    The signature of ideal aperiodic crystals is that they show a pure-point Fourier spectrum (Bragg diffraction pattern) as periodic crystals do but have no translationally periodic structures. Examples are incommensurately modulated structures, composite (host/guest) structures and quasicrystals.

Atomic environment type (AET)

    Local coordination of an atom by the surrounding atoms (first coordination polyhedron).

Cluster

    Polyhedral arrangement of atoms in several cluster shells.

Crystal structure

    It is defined by its chemical composition, metrics (lattice parameters), space group symmetry, equipoint (Wyckoff) positions occupied by the different types of atoms (crystallographic orbits) and their specific coordinates in one asymmetric unit. The metrics may differ for all chemical compounds or phases adopting one particular structure type.

Intermetallic compound

    Special case of an intermetallic phase with sharply defined composition (“line compound”).

Intermetallic phase

    A phase, constituted by two or more metallic elements, which may have a narrow or an extended compositional stability range.

Intermetallics

    Short form for intermetallic phase.

Pearson notation

    Symbol for the shorthand characterization of crystal structures in combination with the structure type. It consists of a lower-case letter denoting the crystal system, an upper-case letter giving Bravais lattice type and the number of atoms per unit cell.

Quasicrystal

    Intermetallic phase with noncrystallographic symmetry and quasiperiodic structure. The Fourier module of a quasiperiodic structure is of rank n > d, with d, the dimension of the quasiperiodic structure in physical space, and n, the number of basis vectors spanning the Fourier module.

Solid solution

    Solution of one or more elements in the structure of another element or of an intermetallic phase by substituting atoms without changing the structure type.

Sphere packing

    Infinite set of noninterpenetrating hard spheres with the property that any pair of spheres is connected by a chain of spheres with mutual contact. A sphere packing is called homogenous for all spheres being symmetrically equivalent, otherwise it is called heterogenous.

Structure type

    Crystal structure representing a whole set of similar crystal structures, i.e. structures with the same space group symmetry and atomic environment types (AET).

Superspace group

    The symmetry of modulated structures can be described by superspace groups. The symbol describing a (3 + 1)-dimensional superspace group, for instance, consists of the space group of the basic structure and the components of the modulation wave vector. For instance, the superspace group I4/mcm(00?) refers to a tetragonal basic structure that is periodically distorted by a modulation wave along the [001] direction, i.e. along the fourfold axis.

Tiling

    A tessellation of the plane or the space where the unit tiles (copies of prototiles) fill the plane or space without gaps or overlaps.

-module

    A vector module of rank n is an infinite set of vectors resulting from all possible linear combinations of its n basis vectors. It is also called -module to emphasize that the coefficients of all linear vector combinations are integers.

1.1. Introduction

Intelligent materials design depends on a deep understanding of the relationships between chemical composition, crystal structure and physical properties. Particularly, in case of multiphase materials, the microstructure, which strongly depends on processing parameters, can drastically modify physical properties provided by individual components. One also has to keep in mind that structure and properties of materials on the nanoscale can strongly differ from those on the macroscale due to size effects. However, in the present chapter, we will exclusively discuss ideal structures of macroscopic single-crystalline elements and compounds in thermodynamic equilibrium and, consequently, will not have to deal with any size- or processing-related topics.

Although only a very few technologically and commercially important materials consist of metallic elements in their (almost) pure form such as Cu, Au, Ag, Pd, Pt, etc., their crystal structures are of more than academic interest. Just to give an example, the crystal structure of a pure metal remains unchanged if it forms a solid solution (single-phase alloy) when one or several other elements are added for tuning or modifying its properties. This technique has been used since time immemorial by alloying gold with copper or silver, for instance, to make jewelry or coins more mechanically resistant. Especially, closest packed structures and their derivatives, typical for many metallic elements, are also characteristic for numerous materials consisting of multicomponent solid solutions.

Even though elements are chemically simpler model systems than intermetallic phases, their structures can be quite complex, mainly originating from intricate electronic interactions. Most elements are polymorphous, i.e. they adopt several different crystal structures as a function of ambient conditions (temperature, pressure, …). The understanding of the phase transformations in these homoatomic cases is not only of interest on its own but also very helpful for understanding in general why a phase with given chemical composition is adopting a particular crystal structure under given conditions.

The structural chemistry and crystallography of intermetallic phases is incredibly rich. More than 2000 different structure types are known, with the number of atoms per unit cell ranging between one and more than 20,000; in the case of aperiodic crystals such as incommensurate structures, composite crystals or quasicrystals (QCs), three-dimensional (3D) unit cells even do not exist at all. However, only a comparably small number of intermetallics have found so far important applications since their physical properties have rarely been studied in the past. Well known is the usage of some intermetallics as strengthening phases in precipitation hardening systems such as LiAl3 in Al–Li alloys or Ni3Al in superalloys (both of the cP4-AuCu3 type). There are also several intermetallic phases known that have important applications as functional materials such as cP8-Cr3Si (A15)-type structures as superconductors (Nb3Sn), cF24-Cu2Mg-type Laves phases as magnetostrictive materials (Terfenol D) or hP6-CaCu5-type structures as powerful permanent magnets (SmCo5).

Neither is it possible nor would it make sense to discuss all structure types of intermetallic phases in a similar way as we do for the metallic elements; their crystallographic data can be found in Pearson’s Handbook of Crystallographic Data for Intermetallic Phases (Villars and Calvert, 1991) or in the database Pearson’s Crystal Data (Villars and Cenzual, 2011), anyway. Besides reviewing the most frequent structure types as...

Produkt-Details

• Erscheint lt. Verlag: 24.7.2014
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie
• Themenwelt: Technik
• ISBN-10: 0-444-53771-6 / 0444537716
• ISBN-13: 978-0-444-53771-3 / 9780444537713