Part II Engineering Materials
6.5 GUIDE TO THE PROCESSING OF METALS
A wide variety of manufacturing processes are available to shape metals, enhance their properties, assemble them, and finish them for appearance and protection.
Shaping, Assembly, and Finishing Processes Metals are shaped by all of the basic processes, including casting, powder metallurgy, deformation processes, and material removal. In addition, metal parts are joined to form assemblies by welding, brazing, soldering, and mechanical fastening; and finishing processes are commonly used to improve the appearance of metal parts and/or to provide corrosion protection. These finishing operations include electroplating and painting.
Enhancement of Mechanical Properties in Metals Mechanical properties of metals can be altered by a number of techniques. Some of these techniques have TABLE 6.15 Some typical superalloy compositions together with strength properties at room temperature and elevated temperature.
Chemical Analysis, %a
Tensile Strength Roomat Temperature
Tensile Strength at 870C (1600F)
Superalloy Fe Ni Co Cr Mo W Otherb MPa lb/in2 MPa lb/in2
Iron-based
Incoloy 802 46 32 21 <2 690 100,000 195 28,000
Haynes 556 29 20 20 22 3 6 815 118,000 330 48,000
Nickel-based
Incoloy 718 18 53 19 3 6 1435 208,000 340 49,000
Rene 41 55 11 19 1 5 1420 206,000 620 90,000
Hastelloy S 1 67 16 15 1 845 130,000 340 50,000
Nimonic 75 3 76 20 <2 745 108,000 150 22,000
Cobalt-based
Stellite 6B 3 3 53 30 2 5 4 1010 146,000 385 56,000
Haynes 188 3 22 39 22 14 960 139,000 420 61,000
L-605 10 53 20 15 2 1005 146,000 325 47,000
Compiled from [11] and [12].
aCompositions to nearest percent.
bOther elements include carbon, niobium, titanium, tungsten, manganese, and silicon.
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been referred to in the discussion of the various metals. Methods for enhancing mechanical properties of metals can be grouped into three categories: (1) alloying, (2) cold working, and (3) heat treatment. Alloying has been discussed throughout the present chapter and is an important technique for strengthening metals. Cold working has previously been referred to as strain hardening; its effect is to increase strength and reduce ductility. The degree to which these mechanical properties are affected depends on the amount of strain and the strain hardening exponent in the flow curve, Eq. (3.10). Cold working can be used on both pure metals and alloys. It is accomplished during deformation of the workpart by one of the shape forming processes, such as rolling, forging, or extrusion. Strengthening of the metal therefore occurs as a by-product of the shaping operation.
Heat treatment refers to several types of heating and cooling cycles performed on a metal to beneficially change its properties. They operate by altering the basic micro-structure of the metal, which in turn determines mechanical properties. Some heat treatment operations are applicable only to certain types of metals; for example, the heat treatment of steel to form martensite is somewhat specialized because martensite is unique to steel. Heat treatments for steels and other metals are discussed in Chapter 27.
REFERENCES
[1] Bauccio. M. (ed.). ASM Metals Reference Book, 3rd ed. ASM International, Materials Park, Ohio, 1993.
[2] Black, J, and Kohser, R. DeGarmo’s Materials and Processes in Manufacturing, 10th ed., John Wiley &
Sons, Hoboken, New Jersey, 2008.
[3] Brick, R. M., Pense, A. W., and Gordon, R. B.
Structure and Properties of Engineering Materials, 4th ed. McGraw-Hill, New York, 1977.
[4] Carnes, R., and Maddock, G., ‘‘Tool Steel Selection,’’
Advanced Materials & Processes, June 2004, pp. 37–40.
[5] Encyclopaedia Britannica, Vol. 21, Macropaedia.
Encyclopaedia Britannica, Chicago, 1990, under sec-tion: Industries, Extraction and Processing.
[6] Flinn, R. A., and Trojan, P. K. Engineering Materials and Their Applications, 5th ed. John Wiley & Sons, New York, 1995.
[7] Guy, A. G., and Hren, J. J. Elements of Physical Metallurgy, 3rd ed. Addison-Wesley, Reading, Mas-sachusetts, 1974.
[8] Hume-Rothery, W., Smallman, R. E., and Haworth, C. W. The Structure of Metals and Alloys. Institute of Materials, London, 1988.
[9] Keefe, J.‘‘A Brief Introduction to Precious Metals,’’
The AMMTIAC Quarterly, Vol. 2, No. 1, 2007.
[10] Lankford, W. T., Jr., Samways, N. L., Craven, R. F., and McGannon, H. E. The Making, Shaping, and Treating of Steel, 10th ed. United States Steel Co., Pittsburgh, 1985.
[11] Metals Handbook, Vol. 1, Properties and Selection:
Iron, Steels, and High Performance Alloys. ASM International, Metals Park, Ohio, 1990.
[12] Metals Handbook, Vol. 2, Properties and Selec-tion: Nonferrous Alloys and Special Purpose Materials, ASM International, Metals Park, Ohio, 1990.
[13] Moore, C., and Marshall, R. I. Steelmaking. The Institute for Metals, The Bourne Press, Ltd., Bourne-mouth, U.K., 1991.
[14] Wick, C., and Veilleux, R. F. (eds.). Tool and Man-ufacturing Engineers Handbook, 4, Vol. 3, Materials, Finishing, and Coating. Society of Manufacturing Engineers, Dearborn, Michigan, 1985.
REVIEW QUESTIONS
6.1. What are some of the general properties that dis-tinguish metals from ceramics and polymers?
6.2. What are the two major groups of metals? Define them.
6.3. What is an alloy?
6.4. What is a solid solution in the context of alloys?
6.5. Distinguish between a substitutional solid solution and an interstitial solid solution.
6.6. What is an intermediate phase in the context of alloys?
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6.7. The copper-nickel system is a simple alloy system, as indicated by its phase diagram. Why is it so simple?
6.8. What is the range of carbon percentages that de-fines an iron–carbon alloy as a steel?
6.9. What is the range of carbon percentages that de-fines an iron–carbon alloy as cast iron?
6.10. Identify some of the common alloying elements other than carbon in low alloy steels.
6.11. What are some of the mechanisms by which the alloying elements other than carbon strengthen steel?
6.12. What is the predominant alloying element in all of the stainless steels?
6.13. Why is austenitic stainless steel called by that name?
6.14. Besides high carbon content, what other alloying element is characteristic of the cast irons?
6.15. Identify some of the properties for which aluminum is noted.
6.16. What are some of the noteworthy properties of magnesium?
6.17. What is the most important engineering property of copper that determines most of its applications?
6.18. What elements are traditionally alloyed with copper to form (a) bronze and (b) brass?
6.19. What are some of the important applications of nickel?
6.20. What are the noteworthy properties of titanium?
6.21. Identify some of the important applications of zinc.
6.22. What important alloy is formed from lead and tin?
6.23. (a) Name the important refractory metals. (b) What does the term refractory mean?
6.24. (a) Name the four principal noble metals. (b) Why are they called noble metals?
6.25. The superalloys divide into three basic groups, according to the base metal used in the alloy.
Name the three groups.
6.26. What is so special about the superalloys? What distinguishes them from other alloys?
6.27. What are the three basic methods by which metals can be strengthened?
MULTIPLE CHOICE QUIZ
There are 20 correct answers in the following multiple choice questions (some questions have multiple answers that are correct). To attain a perfect score on the quiz, all correct answers must be given. Each correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, and each additional answer beyond the correct number of answers reduces the score by 1 point. Percentage score on the quiz is based on the total number of correct answers.
6.1. Which of the following properties or characteristics are inconsistent with the metals (two correct answers): (a) good thermal conductivity, (b) high strength, (c) high electrical resistivity, (d) high stiff-ness, and (e) ionic bonding?
6.2. Which one of the metallic elements is the most abundant on the earth: (a) aluminum, (b) copper, (c) iron, (d) magnesium, or (e) silicon?
6.3. The predominant phase in the iron–carbon alloy sys-tem for a composition with 99% Fe at room sys- tempera-ture is which one of the following: (a) austenite, (b) cementite, (c) delta, (d) ferrite, or (e) gamma?
6.4. A steel with 1.0% carbon is known as which one of the following: (a) eutectoid, (b) hypoeutectoid, (c) hypereutectoid, or (d) wrought iron?
6.5. The strength and hardness of steel increases as carbon content (a) increases or (b) decreases?
6.6. Plain carbon steels are designated in the AISI code system by which of the following: (a) 01XX, (b) 10XX, (c) 11XX, (d) 12XX, or (e) 30XX?
6.7. Which one of the following elements is the most important alloying ingredient in steel: (a) carbon, (b) chromium, (c) nickel, (d) molybdenum, or (e) vanadium?
6.8. Which one of the following is not a common alloy-ing alloy-ingredient in steel: (a) chromium, (b) manga-nese, (c) nickel, (d) vanadium, (e) zinc?
6.9. Solid solution alloying is the principal strengthening mechanism in high-strength low-alloy (HSLA) steels: (a) true or (b) false?
6.10. Which of the following alloying elements are most commonly associated with stainless steel (two best answers): (a) chromium, (b) manganese, (c) molyb-denum, (d) nickel, and (e) tungsten?
6.11. Which of the following is the most important cast iron commercially: (a) ductile cast iron, (b) gray cast iron, (c) malleable iron, or (d) white cast iron?
6.12. Which one of the following metals has the lowest density: (a) aluminum, (b) magnesium, (c) tin, or (d) titanium?
6.13. Which of the following metals has the highest den-sity: (a) gold, (b) lead, (c) platinum, (d) silver, or (e) tungsten?
6.14. From which of the following ores is aluminum derived: (a) alumina, (b) bauxite, (c) cementite, (d) hematite, or (e) scheelite?
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6.15. Which of the following metals is noted for its good electrical conductivity (one best answer): (a) cop-per, (b) gold, (c) iron, (d) nickel, or (e) tungsten?
6.16. Traditional brass is an alloy of which of the follow-ing metallic elements (two correct answers):
(a) aluminum, (b) copper, (c) gold, (d) tin, and (e) zinc?
6.17. Which one of the following metals has the lowest melting point: (a) aluminum, (b) lead, (c) magne-sium, (d) tin, or (e) zinc?
PROBLEMS
6.1. For the copper-nickel phase diagram in Figure 6.2, find the compositions of the liquid and solid phases for a nominal composition of 70% Ni and 30% Cu at 1371C (2500F).
6.2. For the preceding problem, use the inverse lever rule to determine the proportions of liquid and solid phases present in the alloy.
6.3. Using the lead–tin phase diagram in Figure 6.3, determine the liquid and solid phase compositions for a nominal composition of 40% Sn and 60% Pb at 204C (400F).
6.4. For the preceding problem, use the inverse lever rule to determine the proportions of liquid and solid phases present in the alloy.
6.5. Using the lead–tin phase diagram in Figure 6.3, determine the liquid and solid phase compositions for a nominal composition of 90% Sn and 10% Pb at 204C (400F).
6.6. For the preceding problem, use the inverse lever rule to determine the proportions of liquid and solid phases present in the alloy.
6.7. In the iron–iron carbide phase diagram of Figure 6.4, identify the phase or phases present at the following temperatures and nominal compositions:
(a) 650C (1200F) and 2% Fe3C, (b) 760C (1400F) and 2% Fe3C, and (c) 1095C (2000F) and 1% Fe3C.
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7 CERAMICS
Chapter Contents
7.1 Structure and Properties of Ceramics 7.1.1 Mechanical Properties
7.4.1 Chemistry and Properties of Glass 7.4.2 Glass Products
7.4.3 Glass-Ceramics
7.5 Some Important Elements Related to Ceramics 7.5.1 Carbon
7.5.2 Silicon 7.5.3 Boron
7.6 Guide to Processing Ceramics
We usually consider metals to be the most important class of engineering materials. However, it is of interest to note that ceramic materials are actually more abundant and widely used. Included in this category are clay products (e.g., bricks and pottery), glass, cement, and more modern ceramic materials such as tungsten carbide and cubic boron nitride.
This is the class of materials discussed in this chapter. We also include coverage of several elements related to ceramics because they are sometimes used in similar applications.
These elements are carbon, silicon, and boron.
The importance of ceramics as engineering materials derives from their abundance in nature and their mechanical and physical properties, which are quite different from those of metals. A ceramic material is an inorganic compound consist-ing of a metal (or semimetal) and one or more nonmetals. The word ceramic traces from the Greek keramos meaning pot-ter’s clay or wares made from fired clay. Important examples of ceramic materials are silica, or silicon dioxide (SiO2), the main ingredient in most glass products; alumina, or aluminum oxide (Al2O3), used in applications ranging from abrasives to artifi-cial bones; and more complex compounds such as hydrous aluminum silicate (Al2Si2O5(OH)4), known as kaolinite, the principal ingredient in most clay products. The elements in these compounds are the most common in Earth’s crust; see Table 7.1. The group includes many additional compounds, some of which occur naturally while others are manufactured.
The general properties that make ceramics useful in engineered products are high hardness, good electrical and thermal insulating characteristics, chemical stability, and high melting temperatures. Some ceramics are translucent—win-dow glass being the clearest example. They are also brittle and possess virtually no ductility, which can cause problems in both processing and performance of ceramic products.
The commercial and technological importance of ceramics is best demonstrated by the variety of products and applications that are based on this class of material. The list includes:
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å Clay construction products, such as bricks, clay pipe, and building tile
å Refractory ceramics, which are capable of high temperature applications such as furnace walls, crucibles, and molds
å Cement used in concrete, used for construction and roads (concrete is a composite material, but its components are ceramics)
å Whiteware products, including pottery, stoneware, fine china, porcelain, and other tableware, based on mixtures of clay and other minerals
å Glass used in bottles, glasses, lenses, window panes, and light bulbs
å Glass fibers for thermal insulating wool, reinforced plastics (fiberglass), and fiber optics communications lines
å Abrasives, such as aluminum oxide and silicon carbide
å Cutting tool materials, including tungsten carbide, aluminum oxide, and cubic boron nitride
å Ceramic insulators, which are used in applications such as electrical transmission components, spark plugs, and microelectronic chip substrates
å Magnetic ceramics, for example, in computer memories å Nuclear fuels based on uranium oxide (UO2)
å Bioceramics, which include materials used in artificial teeth and bones
For purposes of organization, we classify ceramic materials into three basic types:
(1) traditional ceramics—silicates used for clay products such as pottery and bricks, common abrasives, and cement; (2) new ceramics—more recently developed ceramics based on nonsilicates such as oxides and carbides, and generally possessing mechanical or physical properties that are superior or unique compared to traditional ceramics; and (3) glasses—based primarily on silica and distinguished from the other ceramics by their noncrystalline structure. In addition to the three basic types, we have glass ceramics—
glasses that have been transformed into a largely crystalline structure by heat treatment.