Materials: Structure, Properties, and Performance

1 Chapter 1 Materials: Structure, Properties, and that surrounds us is matter. The origin of the word mat-ter ismater(Latin) ormatri(Sanskrit), formother. In this sense, humanbeings anthropomorphized that which made them possible thatwhich gave them nourishment. Every scientific discipline concernsitself with matter. Of all matter surrounding us, a portion comprisesmaterials. What are materials? They have been variously defined. Oneacceptable definition is matter that human beings use and/or pro-cess. Another definition is all matter used to produce manufac-tured or consumer goods.

2 In this sense, a rock is not a material,intrinsically; however, if it is used in aggregate (concrete) by humans,it becomes a material. The same applies to all matter found on earth:a tree becomes a material when it is processed and used by people,and a skin becomes a material once it is removed from its host andshaped into an successful utilization of materials requires that they satisfy aset of properties. These properties can be classified into thermal, optic-al, mechanical, physical, chemical, and nuclear, and they are in-timately connected to the structure of materials.

3 The structure , in itsturn, is the result of synthesis and processing. A schematic frameworkthat explains the complex relationships in the field of the mechanicalbehavior of materials, shown in Figure , is Thomas s iterative tetra-hedron, which contains four principal elements: mechanical prop-erties, characterization , theory, and processing. These elements arerelated, and changes in one are inseparably linked to changes in theothers. For example, changes may be introduced by the synthesis andprocessing of, for instance, steel.

4 The most common metal, steel hasa wide range of strengths and ductilities (mechanical properties), whichmakes it the material of choice for numerous applications. While low-carbon steel is used as reinforcing bars in concrete and in the bodyof automobiles, quenched and tempered high-carbon steel is used inmore critical applications such as axles and gears. Cast iron, muchmore brittle, is used in a variety of applications, including automobile Cambridge University University Press978-0-521-86675-0 - Mechanical Behavior of MaterialsMarc Ander Meyers and Krishan Kumar ChawlaExcerptMore information2 MATERIALS.

5 structure , PROPERTIES, AND PERFORMANCEF orgingRollingStampingDrawingExtrusionCas tingPultrusionChemical vapor depositionPulsed laser ablationMolecular beam epitaxyMetal-Organic CVDL iquid-Phase epitaxyMelt spinningPowder processingMechanical testingOptical microscopyX-ray diffractionScanning electron microscopyScanning probe microscopyAuger electron spectroscopyTransmission electron microscopyCreepFatigueStrengthToughnessD ynamic responseConstitutive responseCharacterizationMechanicalProper tiesProcessingTheoryContinuum

6 MechanicsComputational mechanicsQuantum mechanicsCrystallography, defectsDiffractionThermodynamicsPhase transformationsElectrochemistryFig. materialstetrahedron applied to mechanicalbehavior of materials. (After )engine blocks. These different applications require, obviously, differ-ent mechanical properties of the material. The different propertiesof the three materials, resulting in differences in Performance , areattributed to differences in the internal structure of the understanding of the structure comes fromtheory.

7 The determina-tion of the many aspects of the micro-, meso-, and macrostructure ofmaterials is obtained bycharacterization. Low-carbon steel has a primar-ily ferritic structure (body-centered cubic; see Section ), with someinterspersed pearlite (a ferrite cementite mixture). The high hardnessof the quenched and tempered high-carbon steel is due to its martens-itic structure (body-centered tetragonal). The relatively brittle castiron has a structure resulting directly from solidification, withoutsubsequent mechanical working such as hot rolling.

8 How does oneobtain low-carbon steel, quenched and tempered high-carbon steel,and cast iron? By differentsynthesisandprocessingroutes. The low-carbon steel is processed from the melt by a sequence of mechani-cal working operations. The high-carbon steel is synthesized with agreater concentration of carbon (> ) than the low-carbon steel( ). Additionally, after mechanical processing, the high-carbonsteel is rapidly cooled from a temperature of approximately 1,000 Cby throwing it into water or oil; it is then reheated to an intermedi-ate temperature (tempering).

9 The cast iron is synthesized with evenhigher carbon contents ( 2%). It is poured directly into the molds andallowed to solidify in them. Thus, no mechanical working, except forsome minor machining, is needed. These interrelationships among Cambridge University University Press978-0-521-86675-0 - Mechanical Behavior of MaterialsMarc Ander Meyers and Krishan Kumar ChawlaExcerptMore COMPOSITE, AND HIERARCHICAL MATERIALS3structure, properties, and Performance , and their modification bysynthesis and processing, constitute the central theme of materialsscience and engineering.

10 The tetrahedron of Figure lists the princi-pal processing methods, the most important theoretical approaches,and the most-used characterization techniques in materials selection, processing, and utilization of materials have beenpart of human culture since its beginnings. Anthropologists referto humans as the toolmakers, and this is indeed a very realisticdescription of a key aspect of human beings responsible for theirascent and domination over other animals. It is the ability of humansto manufacture and use tools, and the ability to produce manufac-tured goods, that has allowed technological, cultural, and artisticprogress and that has led to civilization and its development.