Elements of Metallurgy and Engineering Alloys

Author: F. C. Campbell

Publisher: ASM

Publication date: 2008

Abstract:

No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or *C001wise, without the written permission of the copyright owner. THE WORD METAL, derived from the Greek metallon , is believed to have originated as a verb meaning to seek, search after, or inquire about. Today, a metal is defined as any element that tends to lose electrons from the outer shells of its atoms. The resulting positive ions are held together in crystalline structure by the cloud of these free electrons in what is known as the metallic bond. The metallic bond yields three physical characteristics typical of solid metals: (1) metals are good conductors of electricity, (2) metals are good conductors of heat, and (3) metals have a lustrous appearance. In addition, most metals are malleable, ductile, and generally denser than *C001 elemental substances. Those elements that do not display the characteristics of the metallic elements are called nonmetals. However, there are some elements that behave as metals under some circumstances and as nonmetals under different circumstances. These are now called semimetals but have also been called metalloids, meaning like metals. The boundaries separating the regions in the periodic table covered by the different classes of elements are not distinct, except that nonmetals never form positive ions. A simplified periodic table is shown in Fig. 1.1, highlighting the elements that are currently considered to be metals. NICKEL AND NICKEL ALLOYS have an excellent combination of corrosion, oxidation, and heat resistance, combined with good mechanical properties. Therefore, they are used extensively in aggressive environments, such as in the chemical processing, pollution control, power generation, electronic, and aerospace industries. Nickel is ductile and can be made by conventional processing methods into castings, powder metallurgy parts, and various hot- and cold-worked wrought products. Commercially pure nickel has a moderately high melting temperature (1468 C, or 2647 F), a density of 8.89 g/cm3 (0.322 lb/in.3), and an elastic modulus of 209 Pa (30 msi). Nickel is ferromagnetic, with a Curie temperature of 358 C (676 F), and possess good electrical (25% IACS, or International Annealed Copper Standards and thermal conductivity (7.0 W/m Á K, or 48 Btu Á in./h Á ft2 Á F). Nickel is used principally as an alloying element to increase the corrosion resistance of ferrous and copper alloys, with only approximately 13% of the annual production used for nickel-base alloys. Approximately 60% is used in stainless steel production, with an*C001 10% in alloy steels and 2.5% in copper alloys. Aside from corrosion- and heat-resistant applications, nickel is also used in special-purpose alloys, such as electrical resistance, controlled expansion, magnetic, and shape memory alloys. The cubic crystal systems are regular cubes with a lattice parameter a such that a= b= c and a=b=c=90 . Therefore, only one lattice parameter (a) is required to define the cubic lattice. Within the cubic family of systems, there are three important variations: (1) the simple or primitive cubic in which there are atoms only at the corner points of the lattice; (2) the body-centered cubic (bcc) structure, which has an additional atom located at the center of the structure; and (3) the face-centered cubic (fcc) structure, which has an extra atom located on each of the six faces. The bcc and fcc structures are extremely important in metallurgy, with approximately 90% of industrially important metals crystallizing into one of these two structures.