Materials Science and Engineering: An Introduction

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262 12.18 It is not possible to produce malleable iron in pieces having large cross-sectional dimensions. White cast iron is the precursor of malleable iron, and a rapid cooling rate is necessary for the formation of white iron, which may not be accomplished at interior regions of thick cross- sections. 12.19 The principal difference between wrought and cast alloys is as follows: wrought alloys are ductile enough so as to be hot or cold worked during fabrication, whereas cast alloys are brittle to the degree that shaping by deformation is not possible and they must be fabricated by casting. 12.20 Both brasses and bronzes are copper-based alloys. For brasses, the principal alloying element is zinc, whereas the bronzes are alloyed with other elements such as tin, aluminum, silicon, or nickel. 12.21 Rivets of a 2017 aluminum alloy must be refrigerated before they are used because, after being solution heat treated, they precipitation harden at room temperature. Once precipitation
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Unformatted text preview: hardened, they are too strong and brittle to be driven. 12.22 Strengthening of a 3003 aluminum alloy is accomplished by cold working. Welding a structure of a cold-worked 3003 alloy will cause it to experience recrystallization, and a resultant loss of strength. 12.23 The chief difference between heat-treatable and nonheat-treatable alloys is that heat-treatable alloys may be strengthened by a heat treatment wherein a precipitate phase is formed (precipitation hardening) or a martensitic transformation occurs. Nonheat-treatable alloys are not amenable to strengthening by such treatments. 12.24 This question asks us for the distinctive features, limitations, and applications of several alloy groups. Titanium Alloys Distinctive features: relatively low density, high melting temperatures, and high strengths are possible. Limitation: because of chemical reactivity with other materials at elevated temperatures, these alloys are expensive to refine....
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