Alloys

10 Key excerpts on "Alloys"

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  eBook - ePub

  An Introduction to Metallurgy, Second Edition

  • Sir Alan Cottrell(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 14

  Alloys

  14.1  Types of Alloys

  An alloy is a metallic solid or liquid formed from an intimate combination of two or more elements. Any chemical element may be used for alloying, but the only ones used in high concentrations are metals.

  The intimate combination is usually brought about by dissolving the alloy elements in one another in the liquid state. The parent metal or solvent, in largest concentration, is melted first in a crucible and solid pieces of the alloy additions in weighed amounts are then dropped in, dissolved and stirred. Minor amounts of an element are more accurately added in the form of master Alloys, i.e. more concentrated Alloys of the element with the parent metal. Where possible, a master alloy is conveniently made up as a brittle intermetallic compound (see below) so that it can readily be broken up into pieces for weighing out. Special difficulties appear with volatile and reactive alloy additions. When zinc is added to molten copper to make brass, for example, it is put in as large pieces which are pushed and held under the surface to minimize its loss by volatilization. Even so, it is generally necessary to add up to about 2 per cent more zinc than the alloy requires, to meet such losses.

  We now consider solid Alloys. Suppose that, by freezing a liquid alloy or by some other means, we introduce into a pure solid metal some atoms of another element. The atoms are then in some way allowed to move about, rearrange themselves and change the crystal structure until they come to thermodynamical equilibrium amongst themselves. What is the structure of this alloy? To study this question it is convenient to think of the two types of atoms as (a) indifferent to one another, (b) attracting one another, or (c) repelling one another. In other words, the internal energy (a) stays unchanged, (b) decreases or (c) increases, when the atoms rearrange themselves to increase the number of unlike nearest neighbours.

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  Engineering Materials

  Volume 3

  • William Bolton(Author)
  • 2014(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  3 Alloying of metals Objectives: At the end of this chapter you should be able to: Explain what is meant by the term 'alloy' and give reasons why Alloys are generally used in engineering in preference to pure metals. Distinguish between mixtures, solutions and compounds. Explain the term 'phase'. Explain how thermal equilibrium diagrams are produced and interpret such diagrams. Deduce the structures forming on the solidification of Alloys, given the thermal equilibrium diagram. Alloys Brass is an alloy composed of copper and zinc. Bronze is an alloy of copper and tin. An alloy is a metallic material consisting of an intimate association of two or more elements. The everyday metallic objects around you will be made almost invariably from Alloys rather than the pure metals themselves. Pure metals do not always have the appropriate combination of properties needed; Alloys can, however, be designed to have them. The coins in your pocket are made of Alloys. Coins need to be made of a relatively hard material which does not wear away rapidly, i.e. the coins have to have a 'life' of many years. Coins made of, say, pure copper would be very soft; not only would they suffer considerable wear but they would bend in your pocket. Coins (British) Percentage by mass Copper Tin Zinc Nickel lp, 2p 97 0.5 2.5 — 5p, 10p, 50p 75 — — 25 Pure metals tend to be soft and to have high ductility, low tensile strength and low yield strength. Because of this they are rarely used in engineering. Alloying can produce harder materials with higher tensile strength and higher yield stress, and with a reduction in ductility. Such materials are more useful in engineering. There are, however, some circumstances in which the properties of pure metals are useful. These are where high electrical conductivity is required (alloying reduces conductivity); where good corrosion resistance is required (alloying can result in less corrosion resistance); and where very high ductility is required.

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  eBook - PDF

  Alloy Physics

  A Comprehensive Reference

  • Wolfgang Pfeiler(Author)
  • 2008(Publication Date)
  • Wiley-VCH

    (Publisher)

  44 avenue F.-A. Bartholdi 72000 Le Mans France XXVIII List of Contributors 1 Introduction Wolfgang Pfeiler 1.1 The Importance of Alloys at the Beginning of the Third Millennium An alloy is a ‘‘mixture’’ of two or more chemical elements, one of which at least is a metal. The alloying element can be distributed over the crystal lattice sites of the host element and yield a solid solution, or it can form different phases showing up as particles in a ‘‘matrix.’’ Whereas the physical properties of a solid solution are essentially determined by the chemical composition of the constituents, the properties of a multiphase alloy are determined largely by the spatial distribution of the second-phase particles. This possibility of ‘‘designing’’ physical and tech- nical properties of a material by a careful selection of alloying elements and alloy- ing concentrations put Alloys in the forefront of materials from early human his- tory up to our time at the beginning of the third millennium. We are facing tremendous progress in materials development and design of ad- vanced materials, driven by technical needs in all fields of modern production. A real revolution in materials science, however, could be observed during very re- cent years, a great leap from understanding bulk materials to the study, develop- ment, and application of nanostructured materials. In the present book we give accounts of the state-of-the-art of alloy physics and the challenges of future re- search in the field together with the basic knowledge necessary to understand the radical changes currently happening. Materials today, aside from metals and Alloys, include such different substances as ceramics, high-T c (HT c ) superconductors, liquid crystals, polymers, foams, bio- mimetic materials, nanotubes, nanocomposites .

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  Comparative Inorganic Chemistry

  • Bernard Moody(Author)
  • 2013(Publication Date)
  • Arnold

    (Publisher)

  11 Industrial Alloys The need for Alloys Most pure metals are not used as such in engineer-ing because of poor mechanical properties. However, the properties of a metal may be modified by the addition of other elements, usually metals but sometimes metalloids or non-metals, and the resulting product, if it has metallic physical properties, is called an alloy. The physico-chemical equilibria of Alloys and their crystal structures will not be discussed in more than outline but it may be noted that compounds may be formed: cementite, Fe3C, in steel is a simple example. Alloys are generally prepared molten but this is not always possible. For very high-melting-point metals, of which molybdenum (m.p. 2895°C) and tungsten (m.p. 3400°C) are examples, the tech-nique of powder metallurgy is employed: fine powder is compressed into suitable shapes using pressures of about 750 N mm -2 followed by heating. Also, by the careful regulation of current density, electrolyte composition and temperature, direct electrodeposition of certain Alloys may be accomplished. Brass may be deposited electro-lytically under suitable conditions. In describing the characteristics of metals, including Alloys, for the purposes of this chapter, certain terms need to be defined. The general behaviour of a metal, described as its mechanical properties, depends on its strength, malleability, ductility, hardness, toughness and resistance, or otherwise, to corrosion. Strength refers to resist-ance to applied stresses and tensile strength to the load-supporting characteristics. Hardness des-cribes resistance to cutting, abrasion and indenta-tion, while toughness is the impact strength or resistance to fracture by impact. Rolling-out into sheets, which involves deformation by compres-sion, demands high malleability whereas wire-drawing, deformation by tensile stress, requires high ductility.

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  eBook - PDF

  Modern Physical Metallurgy

  • R. E. Smallman(Author)
  • 2016(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Chapter 5 The structure of Alloys 5.1 Introduction When a metal Β is alloyed to a metal A several different structures and atomic arrangements may be obtained in the alloy, depending upon the relative amounts of the component metals and upon the temperature of the alloy. Thus, if the two types of atoms behave as if they were similar and become homogeneously dispersed amongst each other, a solid solution of the type shown in Figure 1.8(a) will be formed. However, in only a few alloy systems does the solid solution exist over the entire composition range from pure A to pure B, one example being the copper-nickel system. More usually, the second element enters into solid solution only to a hmited extent and, in this case, a primary solid solution is formed which has the same crystal structure as the parent metal (see for example the copper-zinc system. Figure 3.5(a). Then at higher concentrations of the second element, new phases, generally termed intermediate phases, are formed in which the crystal structure usually differs from that of the parent metals. These intermediate phases are also called secondary solid solutions if they exist over wide ranges of composition, or intermetallic compounds if the range of homogeneity is smah. 5.2 Primary substitutional solid solutions As a result of a comparison of the solubilities of various solute elements in the noble metals, copper, silver and gold, several general rules* governing the extent of the primary solid solutions have been formulated. Extension of these experimental observations to solvents from other groups such as magnesium and iron show that, in general, these rules form a useful basis for predicting alloying behaviour. In brief the rules are as follows: (1) The atomic size factor —If the atomic diameter of the solute atom differs by more than 15 per cent from that of the solvent atom the extent of the primary solid solution is small.

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  Materials Technology NQF3 SB

  TVET FIRST

  • Business Programme Development (PTY) Ltd(Author)
  • 2013(Publication Date)
  • Macmillan

    (Publisher)

  People have been using Alloys for thousands of years. In this module you will learn why we use Alloys and how different alloying elements affect the properties of the base metal to which they are added. There are more than 4 000 different Alloys in use today but you will learn about some of the more commonly used Alloys. You will: • identify the reasons for alloying • describe the effect of alloying on physical properties • describe the effect of alloying on machining processes. Unit 3.1 Reasons for alloying Unit 3.2 Aluminium Alloys Unit 3.3 Copper Alloys Unit 3.4 Lead Alloys Unit 3.5 Magnesium Alloys Unit 3.6 Manganese Alloys Unit 3.7 Nickel Alloys Unit 3.8 Tin Alloys Unit 3.9 Zinc Alloys Unit 3.10 The effect of alloying on machinability At the end of this unit, you will be able to: • discuss reasons for alloying. You learned in Module 1 Unit 1.2 that an alloy is a mixture of one metal called the base metal with other metals or non-metals called alloying elements. Pure metals have some useful properties such as Figure 3.1 Fourteen carat gold is an alloy of gold with other elements high thermal and electrical conductivity but they are not often used in structural or mechanical engineering because of their low strength. The most important way in which the strength of metals can be improved is by alloying. Several thousand Alloys are used commercially. Most Alloys are made to standard specifications and are widely used in industry. When suitable metals are mixed, it is possible to produce Alloys whose properties are quite different from those of the original metals. For example, when a soft, weak metal is alloyed with another soft, weak metal or non-metal it may produce a strong alloy with very different properties. Pure iron is a soft metal and carbon, a non-metal, is mechanically weak. When you add as little as 0,5% carbon to iron, steel is produced. This steel is hard and strong enough to be used to make railway lines and rifles.

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  eBook - PDF

  The Study of Metal Structures and Their Mechanical Properties

  Pergamon Unified Engineering Series

  • W. A. Wood, William F. Hughes, Arthur T. Murphy, William H. Davenport(Authors)
  • 2014(Publication Date)
  • Pergamon

    (Publisher)

  CHAPTER FOUR Alloys and Dispersions 4.1 Solid Solution A solid with crystal structure A may dissolve foreign atoms (ions) B by one or both of the processes depicted by Fig. 4.1(a), (b). In (a), interstitial solid-solution, B atoms lodge between atoms of the host structure A. In (b), substitutional solid solution, the B atoms replace A atoms. In both, the B atoms may locally expand, contract, or distort the A structure but they do not upset it. The result is a crystal structure A with variable composition and lattice spacings. (a) (b) * o ß · · A O B · Figure 4.1. (a) Interstitial solid solution and (b) substitutional solid solution. The A structure may be complex, like a zeolite silicate where whole water molecules can enter interstitially into tunnels between its atoms. It may be covalent, like graphite where interstitial ions can lodge between the carbon layers, affecting the way one layer slips over another and thus their lubricating quality. Or it may be ionic, like the silver halides Ag(I/Br) of photographic emulsions where iodine can replace bromine ions in an NaCl-type structure and form substitutional solutions or mixed crystals with various photographic responses. But the structure which above all lends itself to solid solution is the metallic because of its tolerant non-directional bonds. Solid solution then becomes alloying. 59 The Study of Metal Structures and their Properties In the following survey of basic principles in alloying we can without much loss first take as host structure A a simple metal like copper or iron, while allowing B to be metallic or nonmetallic. 4.2 Interstitial Alloying This must depend primarily on two factors, as follows. (i) Ion Size The size of the B atoms or ions must be of the same order as the gaps they are to occupy in A. Since A is a metal, with ions packed closely like spheres, it can provide small gaps only.

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  Metal Failures

  Mechanisms, Analysis, Prevention

  • Arthur J. McEvily, Jirapong Kasivitamnuay(Authors)
  • 2013(Publication Date)
  • Wiley-Interscience

    (Publisher)

  5 Alloys and Coatings I. INTRODUCTION The characteristics of the materials involved in a failure are obviously of importance in carrying out a failure analysis. This chapter reviews the microstructural features and related matters, such as equilibrium and isothermal transformation diagrams of some of the more common Alloys, as influenced by alloying and heat treatment. The nature of the coatings used in high-temperature applications is also discussed. 105 106 Alloys AND COATINGS II. ALLOYING ELEMENTS Figure 5-1 shows the periodic table of the elements. In solid form the elements are characterized by their crystal structure, with the elements considered to be ordered arrays of hard spheres. The three principal crystal structures are the face-centered cubic (fcc) with four atoms per unit cell, as in the case of aluminum and copper; the hexagonal close-packed (hcp) with six atoms per unit cell, as in the case of zinc and magnesium; and the body-centered cubic (bcc) with two atoms per unit cell, as in the case of iron. The unit cells of these crystal structures are shown in Fig. 5-2. If no atom is present on a lattice site, then a point defect, known as a vacancy, exists. Vacancies are important agents in diffusion processes, as we shall see. The yield strength of a pure element is usually quite low and unsuitable for structural application. A combination of elements is known as an alloy. The main purpose in alloying is to increase the strength properties. Additional reasons for alloying include the improvement in corrosion resistance, wear properties, and performance at elevated temperatures. There are other reasons for alloying as well. For example, if sulfur is present in a steel, during heat treatment the sulfur atoms may diffuse to the grain boundaries and cause temper embrittlement.

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  Production Technology

  Processes, Materials and Planning

  • William Bolton(Author)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  The everyday metallic objects around you will be made almost invariably from Alloys rather than the pure metals themselves. Pure metals do not always have the appropriate combination of properties needed; Alloys can, however, be designed to have them. The coins in your pocket are made of Alloys. Coins need to be made of a relatively hard material which does not wear away rapidly, i.e. the coins have to have a 'life' of many years. Coins made of, say, pure copper would be very soft; not only would they suffer considerable wear but they would bend in your pocket. Coins (Bntish) Percentage by mass Copper Tin Zinc Nickel lp 5 2p 97 0.5 2.5 — 5p, 10p, 50p 75 — — 25 If you put sand in water, the sand does not react with the water but retains its identity, as does the water. The sand in water is said to be a mixture. In a mixture, each component retains its own physical structure and properties. Sodium is a very reactive substance, which has to be stored under oil to stop it interacting with the oxygen in the air, and chlorine is a poisonous gas. Yet when these two substances interact, the product, sodium chloride, is eaten by you and me every day. The product is common salt. Sodium chloride is a compound. In a compound the components have interacted and the product has none of the properties of its constituents. Alloys are generally mixtures though some of the components in the mixture may interact to give compounds as well. 188 Production Technology 7.2 Solutions If you drop a pinch of common salt, sodium chloride, into cold water it will dissolve. The sodium chloride is said to be soluble in the cold water. Up to 36 g of sodium chloride can be dissolved in 100 g of cold water; more than that amount will not dissolve. With the 36 g dissolved in 100 g the resulting solution is said to be saturated. The solubility of sodium chloride in cold water is said to be 36 g per 100 g of water.

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  Alloys

  Preparation, Properties, Applications

  • Fathi Habashi(Author)
  • 2008(Publication Date)
  • Wiley-VCH

    (Publisher)

  10.2.1 Composition Many alloying elements are added to alu- minum to enhance its properties (Table 10.1) [13, 141. The major elements increasing strength are copper (Figure 10.21), magne- sium (Figure lO.l), manganese (Figure 10.2), silicon (Figure 10.3), and zinc (Figure 10.4). All these have maximum solid solubility lim- its in excess of 1.5% (Table 10.2) [l, pp. 362- 3631. Elements with lower solubilities, e.g., chromium (Figure 10.5), zirconium, and tita- nium, are added to certain Alloys to aid in con- trolling aspects of metallurgical structure, e. g., as-cast grain size and the nature of recrystalli- zation, and thus to affect the characteristics of the Alloys. Of the elements commonly added, copper, magnesium, silicon, and zinc have high diffusion coefficients; other elements dif- fuse only slowly [ 1, p. 1 181. Commercial Alloys are usually multicom- ponent systems, and the phase diagrams are frequently complex. One important precipita- tion-hardening system, Al-Mg-Si, is shown in Figure 10.6 in the form of contour maps representing the solvus, solidus, and liquidus surfaces. Magnesium, mol % - 0 L R 17 i h Magnesium, % - Figure 10.1: Aluminum-magnesium phase diagram (up to 16% Mg). Manganese, mol O/O - 0.5 1.0 1 .s 2.0 I 1 1 Al 1 2 3 4 Manganese, % - Figure 10.2: Aluminum-manganese phase diagram 4% Mn). The composition of a specific alloy is often written as, e.g., A1-5.1Mg-0.79Mn-0.11Cr (Aluminum Association Number 5456), 167 meaning an alloy consisting of 5.1% Mg, 0.79% Mn, 0. I1 % Cr, and the rest aluminum and the usual impurities. Silicon, mol 'A - Silicon, - Figure 10.3: Aluminuni-silicon phase diagram (up to 40% Si). 10.2.2 Solidification and Cast Structure 10.2.2.1 Grain Size and Dendrite Arm Spacing The transformation from the liquid to the solid state in aluminum Alloys is assisted by heterogeneous nucleation.

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