Structure, Composition & Properties of Metals and Alloys

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  Manufacturing Technology

  Materials, Processes, and Equipment

  • Helmi A. Youssef, Hassan A. El-Hofy, Mahmoud H. Ahmed(Authors)
  • 2011(Publication Date)
  • CRC Press

    (Publisher)

  33 3 Structure of Metals and Alloys 3.1 INTRODUCTION The.structure.of.materials.influences.their.behavior.and.properties . .Therefore,.understanding.this. structure.helps.to.make.appropriate.selection.of.these.materials.for.specific.applications . .Depending. on.the.manner.of.atomic.grouping,.materials.are.classified.as.having.molecular,.crystal,.or.amor-phous.structures . .In.molecular.structures,.atoms.are.held.together.by.primary.bonds . .They.have. only.weak.attraction . .Typical.examples.of.molecular.structure.include.O 2 ,.H 2 O,.and.C 2 H 4 .(ethylene) . . Each.molecule.is.free.to.act.independently,.so.these.materials.possess.relatively.low.melting.and. boiling.points,.since.their.molecules.can.move.easily.with.respect.to.each.other . .These.materials. tend.to.be.weak . .Solid.metals.and.alloys.and.most.minerals.have.crystalline.structure,.where.atoms. are. arranged. in. a. regular. geometric. array. as. a. lattice. of. a. unit. building. block. that. is. repetitive. throughout.the.space . .In.an.amorphous.structure,.such.as.glass,.atoms.have.a.certain.degree.of.local. order.but.lack.the.periodically.ordered.arrangement.of.the.crystalline.solid . 3.2 LATTICE STRUCTURE OF METALS Metals.and.alloys.are.an.extremely.important.class.of.materials,.since.they.are.frequently.processed. to. manufacture. tools,. machinery,. and. many. metallic. products . . Metals. are. characterized. by. the. metallic.bond.in.three.dimensions,.offering.them.their.distinguishing.characteristics.of.strength,. good.electrical.and.thermal.conductivity,.luster,.the.ability.to.be.plastically.deformed.to.a.fair.degree. without.fracturing,.and.a.relatively.high.density.compared.with.nonmetallic.materials . .When.met-als.and.alloys.solidify.from.their.molten.state,.they.assume.a.crystalline.structure.in.which.atoms. arrange.themselves.in.a.geometric.lattice . 3.2.1 S PACE L ATTICES There.are.three.basic.types.of.crystal.structures.(lattice.cells).found.in.nearly.all.commercially.

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  Fundamentals of Modern Manufacturing

  Materials, Processes, and Systems

  • Mikell P. Groover(Author)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  Of course, these properties are also important in product design. Chapter 5 is concerned with several part and product attributes that are specified during product design and must be achieved in manufacturing: dimensions, tolerances, and surface finish. Chapter 5 also describes how these attributes are measured. 2.1 Atomic Structure and the Elements The basic structural unit of matter is the atom. Each atom is composed of a positively charged nucleus, surrounded by a sufficient number of negatively charged electrons so that the charges are balanced. The number of electrons identifies the atomic number and the element of the atom. There are slightly more than 100 elements (not counting a few extras that have been artificially synthe- sized), and these elements are the chemical building blocks of all matter. Just as there are differences among the elements, there are also similarities. The elements can be grouped into families and relationships established between and within the families by means of the Periodic Table, shown in Figure 2.1. In the horizontal direction, there is a certain repetition, or periodicity, in the arrangement of elements. Metallic elements occupy the left and center portions of the chart, and nonmetals are located to the right. Between them, along a diagonal, is a transition zone containing elements called metalloids or semimetals. In principle, each of the elements can exist as The Nature of Materials 2.1 Atomic Structure and the Elements 2.2 Bonding between Atoms and Molecules 2.3 Crystalline Structures 2.3.1 Types of Crystal Structures 2.3.2 Imperfections in Crystals 2.3.3 Deformation in Metallic Crystals 2.3.4 Grains and Grain Boundaries in Metals 2.4 Noncrystalline (Amorphous) Structures 2.5 Engineering Materials 28 | Chapter 2 | The Nature of Materials a solid, liquid, or gas, depending on temperature and pressure.

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  Parts Fabrication

  Principles and Process

  • Richard Crowson(Author)
  • 2006(Publication Date)
  • CRC Press

    (Publisher)

  Different materials require different heat treatments and different surface finishes. Subchapter 2.1 discusses metallurgy, 2.2 introduces iron and steel (ferrous metals), 2.3 talks about aluminum and other non-ferrous materials, and 2.4 describes the peculiarities of magnesium. 2.1 FUNDAMENTALS OF METALLURGY Metallurgy is the art and science concerned with metals and their alloys. It deals with the recovery of metals from their ores or other sources, their refining, alloying with other metals, forming, fabricating, testing, and a study of the relation of alloy constituents and structure to mechanical properties. 2 28 Parts Fabrication: Principles and Process The manufacturing engineer is more interested in physical metallurgy, which is concerned with the structure, properties, and associated behavior of metallic prod-ucts. The properties and behavior of metals are based on their inherent crystalline structure. They do not react as amorphous (shapeless) aggregates of atoms, with a general equality of properties in all directions. They act as crystals with preferred directions of strength, flow, cleavage, or other physical characteristics, and have many limitations due to the oriented character of their particles. 2.1.1 Crystalline Structure To illustrate crystalline formation, consider a metal in the fluid state, in the process of slowly cooling and solidifying. To begin with, we have a solution of free atoms. These atoms consist of a dense nucleus surrounded by several electrons. Figure 2.1 shows a diagram of the aluminum atom. With continued cooling, the atoms bond together in groups to form unit cells. A group of unit cells tends to collect as cooling continues, and forms branches, called dendrites, which resemble an unfinished frost pattern. Each type of metal has its own unit cell and space lattice formation. The most common are the following four basic types, depending on the metal.

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  Practical Engineering Failure Analysis

  • Hani M. Tawancy, Anwar Ul-Hamid, Nureddin M. Abbas(Authors)
  • 2004(Publication Date)
  • CRC Press

    (Publisher)

  7Structure of Engineering Alloys

  7.1 Introduction

  Modern engineering technology vividly demonstrates the intimate relationship between matter and energy, as well as the vital importance of the structure of matter in design considerations. Of the three states of matter; solid, liquid and gaseous, matter in its solid state dominates the structural and mechanical applications in engineering design. As pointed out in Chap. 1 , the properties of engineering materials are those qualities which determine their usefulness in certain applications. To effectively select and use materials for engineering applications, it is important to have a basic knowledge of the origin of these properties and how they can be controlled. Developing such a knowledge lies within the spectrum of materials science.

  Most of the technologically important properties of engineering alloys, including mechanical, chemical, and physical properties, are determined by their internal structure. Therefore, an understanding of the principles governing the internal structural features is essential in the selection of the best material or the optimum combination of material and processing for specific engineering applications. Due to the intimate relationship between matter and energy, it is first instructive to review the principles of thermodynamics.

  7.2 Principles of Thermodynamics

  Thermodynamics is the branch of physical science dealing with energy, its conservation and its transformation from one form to another. Just as mechanics introduces mass, length, and time as basic concepts, thermodynamics introduces temperature as a basic concept; it is a measure of thermal or heat energy. By means of some initial statements known as the laws of thermodynamics, it is possible to derive very useful relationships between measurable macroscopic properties of a substance such as temperature, solubility, and equilibrium constant. Such a substance which can either be a solid, liquid, gas, or any combination of these is called a system.

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  Mechanical Properties Of Complex Intermetallics

  • Esther Belin-ferre(Author)
  • 2010(Publication Date)
  • World Scientific

    (Publisher)

  A microstructure will be defined by several important parameters: - The alloy composition; the mechanical properties of pure metals are almost always very low, and useful alloys may contain 2, 3 or more species. - The number and nature of crystalline phases; their respective volume fractions, which can be found at equilibrium on a phase diagram, but which are generally out-of-equilibrium. - The chemical composition of the phases that may be determined by their crystal structure (stoechiometric phases) or may show some degree of freedom (substitution of chemical species on some of the crystal sites). - The scale and arrangement of the phases: size, morphology, percolation. - The presence of defects in the different phases, and especially crystal defects such as dislocations. All of these features of the microstructure will have strong consequences on the mechanical properties. In this chapter, we aim at presenting some laws that relate the mechanical properties to the main parameters of the microstructure. Since most of these laws relate the properties to some quantitative parameters of the microstructure (such as precipitate size, density of defects, etc.), we will first present some experimental techniques that are able to characterize these parameters in a quantitative way. In a second section we will investigate the relationship between microstructure and strength. In a third section we will investigate the influence of microstructure on strain hardening, and in the fourth section the effect of microstructure on fracture will be shortly discussed. Microstructure - Properties Relationships In Metal-Based Alloys 75 2. Quantitative Characterisation of Microstructures As written above, the main parameters needed for the characterization of microstructures are the proportion of phases, the presence of crystalline defects and the scale of phases. We will concentrate on these three topics in this section.

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  Steel-Rolling Technology

  Theory and Practice

  • Ginzburg(Author)
  • 1989(Publication Date)
  • CRC Press

    (Publisher)

  Part I Main Properties and Classifications of Steels and Alloys 1 The Crystalline Structure of Metals 1 . 1 S P A C E L A T T I C E S S u b s t a n c e s c a n e x i s t i n e i t h e r a m o r p h o u s o r c r y s t a l l i n e s t a t e . I n t h e a m o r p h o u s s t a t e t h e e l e m e n t a r y p a r t i c l e s a r e i n t e r m i x e d i n a d i s o r d e r l y m a n n e r ; t h e i r p o s i t i o n s a r e n o t f i x e d r e l a t i v e t o t h o s e o f t h e i r n e i g h b o r s . I n t h e c r y s t a l l i n e s t a t e t h e s u b s t a n c e c o n s i s t s o f a t o m s , o r m o r e p r o p e r l y , i o n s w h i c h a r e a r r a n g e d a c c o r d i n g t o s o m e r e g u l a r g e o m e t r i c p a t t e r n . T h i s p a t t e r n v a r i e s f r o m o n e s u b s t a n c e t o a n o t h e r . A l l m e t a l s a r e c r y s t a l l i n e i n n a t u r e . C r y s t a l l i z a t i o n o f t h e m e t a l s t a k e s p l a c e d u r i n g s o l i d i f i c a t i o n w h e n a t o m s o f t h e l i q u i d m e t a l g r o u p t h e m s e l v e s i n a n o r d e r l y a r r a n g e m e n t , f o r m i n g a d e f i n i t e s p a c e p a t t e r n . T h i s p a t t e r n i s k n o w n a s a ' s p a c e l a t t i c e ' . T h e r e a r e s e v e r a l t y p e s o f t h e l a t t i c e s i n w h i c h m e t a l l i c a t o m s c a n a r r a n g e t h e m s e l v e s u p o n s o l i d i f i c a t i o n , b u t t h e t h r e e m o s t c o m m o n a r e s h o w n i n F i g . 1 . 1 a n d a r e k n o w n a s t h e b o d y - c e n t e r e d c u b i c ( b . c . c . ) , f a c e - c e n t e r e d c u b i c ( f . c . c . ) , a n d c l o s e - p a c k e d h e x a g o n a l ( c . p . h . ) c r y s t a l l a t t i c e s [ 1 ] . 1 . 2 L A T T I C E C O N S T A N T T h e s i d e o f t h e e l e m e n t a r y c u b e o r h e x a g o n i s k n o w n a s t h e l a t t i c e c ' o n s t a n t ( F i g . 1 . 2 ) .

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  Introduction to the Physics and Chemistry of Materials

  • Robert J. Naumann(Author)
  • 2008(Publication Date)
  • CRC Press

    (Publisher)

  5 The Structure of Matter The properties of matter are intimately tied to its structure, as we shall see in subsequent chapters, and the structure of matter is primarily determined by the sizes of the atoms and ions of its constituents and by the types of bonding between them. In this chapter, we will explore some of the myriads of ways nature has found to assemble materials, starting with simple one-component systems and then moving to compounds and fi nally to polymeric molecular structures. 5.1 Structure of Metals Because the metallic bond is nondirectional and because the positive ion cores attract each other through the intervening sea of electrons that fl ows between them, metals tend to form close-packed structures, meaning they try to get as close together as they can in order to maximize their coordination number. Johannes Kepler (a mathematician as well as the famous astronomer) conjectured that the maximum number of identical spheres that could surround and touch another sphere was 12. Now, let us see what kinds of structures are possible with a coordination number of 12. 5.1.1 Face-Centered Cubic Versus Hexagonal Close-Packed Structures Imagine packing oranges into a crate and you want to put as many oranges as possible into a given volume. There are two possible ways of doing this in such a way as to fi ll all space with repeating structures. You would start by arranging the fi rst layer in a hexagonal array so that each orange had six nearest neighbors (label this layer A). You would put the next layer in three of the six vertices formed by the oranges in the fi rst layer (label this layer B).

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