圖書在版編目（ＣＩＰ）數據材料科學導論 : 雙語 \/ 傅小明, 蔣萍主編. 南京 :
南京大學出版社, 2018.2
ISBN9787305193620Ⅰ. ①材… Ⅱ. ①傅… ②蔣… Ⅲ. ①材料科學-教
材 Ⅳ. ①TB3中國版本圖書館CIP數據核字(2017)第246243號出版發行南京大學出版社
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主編傅小明蔣萍
副主編楊在誌李金濤孫虎
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圖書銷售部門聯係調換前言
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)前言隨著人類文明的進步和科學技術的發展，材料已成為國民經濟的三大支柱產業之一。為了適應材料科學與技術的發展，培養學生及時跟蹤國際材料科學與技術發展前沿的能力，使學生成為材料科學領域的創新型複合人才，因而國內許多高校麵向材料類本科生開設了雙語專業課程。目前，材料類雙語專業課程《材料概論（雙語）》或《材料科學與工程導論（雙語）》教材盡管也有出版，但存在如下的主要問題：（1） 係統性不強，即知識點不全，不利於學生係統和全麵的掌握相關知識；（2） 部分教材有少許課後練習題，但是沒有參考答案，這樣不利於學生課後對學習效果的檢測和評價；（3） 更有甚者是半中文半英文，這樣更不利於學生學習利用純正的英語表述專業知識。這樣難以滿足培養應用型人才教學的要求。編者基於上述三個問題得到如下基本認識：一是現代材料類高素質創新型人才標準——國際化、工程化和複合化的要求；二是基礎應用性材料科學知識體係：科學性、係統性和簡易性的特色；三是各類不同層次高校學生的教學要求。本教材針對低年級材料類大學生的實際條件和需求，在滿足國際化專業人才語言交流能力的基本前提下，特別強調了專業基礎知識體係的科學化、係統化和簡易化，從而新編了《材料科學導論（雙語）》和《材料工程導論（雙語）》係列教材，以滿足新時代各類特別是技術應用型材料科學與工程學科專業教學的需要。本套教材具有如下特點：1. 將材料學知識英語化用英語語言思維構築學生的國際化視野和專業語言交流能力。2. 對知識性體係簡易化在保持教學內容的科學性、係統性的前提下，做到學生理解和掌握的簡易性（通俗性），即突出“真、全、簡”三個字。3. 優化教學流程和效果（1） 任務驅動教學每章主要包括主要知識點的介紹、專業詞彙的注解和課後練習題（附參考答案），充分體現了教學內容的實用性，有助於提高學生牢固掌握本章知識點的實踐能力。（2） 教材定位準確本套教材針對材料類學生學習專業基礎課後開設的課程，有助於學生應用英語去描述自己本專業的材料學知識。（3） 內容結構合理本套教材內容由淺入深，循序漸進，符合讀者認識事物的規律性。同時，也便於教學的組織、實施和考核，有利於教學效果的鞏固和教學質量的提高。《材料科學導論（雙語）》教材是由宿遷學院材料工程係傅小明副教授、江蘇大學外國語學院蔣萍老師擔任主編，並編寫緒論（第1章）、第一篇材料相變基礎的第2、3和4章、第三篇材料性能基礎的第8章，以及全書的統稿；楊在誌老師編寫第二篇材料結構基礎的第5章和第三篇材料性能基礎的第9章；李金濤老師編寫第二篇材料結構基礎的第6和7章；孫虎老師編寫第三篇材料性能基礎的第10章。江蘇大學外國語學院蔣萍老師編寫全書專業術語和專業詞彙的注解，以及全書習題及其參考答案。本書在編寫過程中得到了蘭州理工大學博士生導師馬勤教授悉心的指導，在此特表感謝。由於編者水平有限，經驗不足，書中難免有不足之處，懇請專家、學者和廣大讀者批評指正。編者
2017年04月Contents
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Chapter 1Introduction11.1Historical Perspective11.2Materials21.3Classification of Materials21.3.1Metals31.3.2Ceramics31.3.3Polymers31.3.4Composites31.3.5Advanced Materials41.3.5.1Semiconductors41.3.5.2Biomaterials41.3.5.3Smart Materials41.3.5.4Nanoengineered Materials51.4Structural Characteristic of Materials61.4.1Crystal Lattice71.4.2Crystallographic Indices111.4.3Anisotropy121.5Materials Properties121.5.1Physical and Chemical Properties of Materials121.5.2Mechanical Properties of Materials151.6Materials Science181.7Modern Materials Needs20Part ⅠFoundation of Phase Change of Materials
Chapter 2Phase Diagrams292.1Introduction292.2Definitions and Basic Concepts292.3Solubility Limit302.4Phases312.5Phase Equilibrium322.6Equilibrium Phase Diagrams342.7Interpretation of Phase Diagrams362.7.1Phases Present362.7.2Determination of Phase Compositions362.7.3Determination of Phase Amounts372.7.4Binary Eutectic Systems392.7.5Gibbs Phase Rule412.7.6IronIron Carbide Phase Diagram44
Chapter 3Solidification and Crystallization513.1Introduction513.2Solidification of Metals513.2.1Formation of Stable Nuclei in Liquid Metals523.2.2Homogeneous Nucleation523.2.3Critical Radius and Undercooling543.2.4Heterogeneous Nucleation553.3Growth of Crystals563.3.1Growth of Crystals in Liquid Metal and Formation of a Grain Structure
563.3.2Solidification of Single Crystals573.3.3Metallic Solid Solutions583.3.3.1Substitutional Solid Solutions593.3.3.2Interstitial Solid Solutions59
Chapter 4Phase Transformation634.1Introduction634.2Phase Transformation644.2.1Kinetics of SolidState Reaction644.2.2Multiphase Transformations664.3Microstructural and Property Changes in IronCarbon Alloys674.3.1Isothermal Transformation Diagrams674.3.2Continuous Cooling Transformation Diagram75Part ⅡFoundation of Material Structures
Chapter 5Crystal Structure855.1Introduction855.2Fundamental Concepts855.2.1Space Lattice and Unit Cells855.2.2Crystal Systems and Bravais Lattice865.2.3Crystallographic Directions and Miller Indies885.2.3.1Atom Positions in Unit Cells885.2.3.2Directions in Cubic Unit Cells895.2.3.3Miller Indices for Crystallographic Planes in Cubic Unit Cells905.2.3.4Crystallographic Planes and Directions in Hexagonal Unit Cells935.3Principal Metallic Crystal Structures955.3.1BodyCentered Cubic (BCC) Crystal Structure965.3.2FaceCentered Cubic (FCC) Crystal Structure985.3.3Hexagonal ClosePacked (HCP) Crystal Structure995.3.4Comparison of FCC, HCP and BCC Crystal Structures1015.3.4.1FCC and HCP1015.3.4.2BCC1025.3.5Volume, Planar and Linear Density UnitCell Calculations1035.3.5.1Volume Density1035.3.5.2Planar Atomic Density1035.3.5.3Linear Atomic Density1045.3.6Polymorphism or Allotropy104
Chapter 6Defect Structure1096.1Introduction1096.2Point Defects1096.2.1Point Defects in Metals1096.2.2Point Defects in Ceramics1106.2.3Impurities in Solids1126.2.3.1Impurities in Metals1126.2.3.2Solid Solutions1136.2.3.3Impurities in Ceramics1156.2.4Point Defects in Polymers1166.2.5Specification of Composition1166.3Miscellaneous Imperfections1176.3.1DislocationsLinear Defects1176.3.2Interfacial Defects1206.3.2.1External Surfaces1206.3.2.2Grain Boundaries1206.3.2.3Twin Boundaries1216.3.2.4Miscellaneous Interfacial Defects1226.3.3Bulk or Volume Defects1226.3.4Atomic Vibrations123
Chapter 7Structure of Bulk Phase1267.1Introduction1267.2Single Crystals1267.3Polycrystalline Materials1277.4Noncrystalline Solids1287.5Quasicrystals129Part ⅢFoundation of Material Properties
Chapter 8Mechanical Properties of Materials1378.1Introduction1378.2Concepts of Stress and Strain1388.2.1Tension Tests1388.2.2Compression Tests1418.2.3Shear and Torsional Tests1418.2.4Geometric Considerations of the Stress State1428.3Elastic Deformation1438.3.1StressStrain Behavior1438.3.2Anelasticity1478.3.3Elastic Properties of Materials1478.4Mechanical Behavior of Metals1498.4.1Tensile Properties1498.4.1.1Yielding and Yield Strength1498.4.1.2Tensile Strength1518.4.1.3Ductility1518.4.1.4Resilience1548.4.1.5Toughness1558.4.2True Stress and Strain1568.4.3Elastic Recovery during Plastic Deformation1588.4.4Compressive, Shear and Torsional Deformation1598.5Mechanical BehaviorCeramics1598.5.1Flexural Strength1598.5.2Elastic Behavior1618.6Mechanical Behavior of Polymers1618.6.1StressStrain Behavior1618.6.2Macroscopic Deformation1648.7Hardness and Other Mechanical Property Considerations1658.7.1Hardness1658.7.2Rockwell Hardness Tests1668.7.3Brinell Hardness Tests1698.7.4Knoop and Vickers Microhardness Tests1708.7.5Hardness Conversion1708.7.6Correlation between Hardness and Tensile Strength1718.7.7Hardness of Ceramic Materials1718.7.8Tear Strength and Hardness of Polymers1718.8Property Variability and Design\/Safety Factors1728.8.1Variability of Material Properties1728.8.2Design\/Safety Factors173
Chapter 9Physical Properties of Materials1779.1Introduction1779.2Electrical Properties of Materials1789.2.1Metals and Alloys1799.2.2Semiconductors1809.2.2.1Intrinsic Semiconductors1819.2.2.2Extrinsic Semiconductors1829.2.2.3Compound Semiconductors1839.2.3Ionic Ceramics and Polymers1839.3Thermal Properties of Materials1849.3.1Heat Capacity1849.3.2Thermal Expansion1859.3.2.1Metals1859.3.2.2Ceramics1869.3.2.3Polymers1869.3.3Thermal Conductivity1869.3.4Thermal Stresses1879.3.4.1Stresses Resulting from Restrained Thermal Expansion and
Contraction1879.3.4.2Stresses Resulting from Temperature Gradients1879.3.4.3Thermal Shock of Brittle Materials1889.4Magnetic Properties of Materials1899.4.1Diamagnetism, Paramagnetism and Ferromagnetism1899.4.2Antiferromagnetism and Ferrimagnetism1929.4.2.1Antiferromagnetism1929.4.2.2Ferrimagnetism1939.4.3The Influence of Temperature on Magnetic Behavior1959.4.4Domains, Hysteresis and Magnetic Anisotropy1969.4.5Superconductivity1999.5Optical Properties of Materials2049.5.1Interaction of Light with Matter2059.5.2Atomic and Electronic Interactions2069.5.2.1Electronic Polarization2069.5.2.2Electron Transitions2069.5.2.3Optical Properties of Metals2089.5.2.4Optical Properties of Nonmetals2099.5.3Refraction, Reflection, Absorption and Transmission2099.5.4Opacity and Translucency in Insulators2119.5.5Applications of Optical Phenomena2129.5.5.1Luminescence2129.5.5.2Photoconductivity212
Chapter 10Chemical Properties of Materials21710.1Introduction21710.2Corrosion of Metals21710.2.1Cost of Corrosion in Industry21810.2.2Classification of Corrosion21810.2.3Corrosion Mechanism21910.2.4Electrochemical Considerations22210.2.5Corrosion Rates22510.2.6Passivity22510.2.7Environmental Effects22510.2.8Forms of Corrosion22610.2.9Corrosion Environments23210.2.10Corrosion Prevention23210.3Corrosion of Ceramic Materials23310.4Degradation of Polymers23410.4.1Swelling and Dissolution23410.4.2Bond Rupture23510.4.3Weathering236
Main References240
Table 8.4Hardness testing techniquesTestIndenterShape ofindentationSide viewTop viesLoadFormula for
hardness numberBrinell10mmsphere of steel
or tungsten carbidePHB=2PπD［D-D2-d2]Vickers microhardnessDiamond pyramidPHV=1.854Pd21Knoop microhardnessDiamond pyramidPHK=14.2PI2Rockwell and
Superficial RockwellDiamond Cone 116,
18, 14, 12 in.
Diameter steel spheres60 kg
100 kg
150 kgRockwell15 kg
30 kg
45 kgSuperficial Rockwell
Chapter 1Introduction
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)Chapter 1Introduction1.1Historical PerspectiveMaterials are probably more deepseated① in our culture than most of us realize. Transportation, housing, clothing, communication, recreation and food productionvirtually every segment of our everyday lives is influenced to one degree or another by materials. Historically, the development and advancement of societies have been intimately tied to the members ability to produce and manipulate materials to fill their needs. In fact, early civilizations have been designated by the level of their materials development (i.e., Stone Age, Bronze Age).The earliest humans had access to only a very limited number of materials, those than occur naturally: stone, wood, lay, skins, and so on. With time they discovered techniques for producing materials that had properties superior to those of the natural ones; these new materials included pottery and various metals. Furthermore, it was discovered that the properties of a materials could be altered by heat treatment and by the addition of other substances. At the point, materials utilization was totally a selection process, that is, deciding from a given, rather limited set of materials the one that was best suited for an application by virtue of its characteristics. It was not until relatively recent times that scientists came to understand the relationships between the structural elements of materials and their properties. This knowledge acquired in the past 60 years or so, has empowered them to fashion, to a large degree, the characteristics of materials. Thus, tens of thousands of different materials have evolved with rather specialized characteristics that meet the needs of our modern and complex society; these include metals, plastics, glasses and fibers.The development of many technologies that make our existence so comfortable has been intimately associated with the accessibility of suitable materials. An advancement in the understanding of a material type is often the forerunner to the stepwise progression of a technology. For example, automobiles would not have been possible without the availability of inexpensive steel or some other comparable substitute. In our contemporary era, sophisticated electronic devices rely on components that are made from what are called semiconducting materials.1.2MaterialsThe materials making up the surrounding world consist of discrete particles, having a submicroscopic size. Their behavior is determined by atomic theories. The states of organization of materials range from the complete disorder of atoms or molecules of a gas under weak pressure to the almost complete order of atoms in a monocrystal.In this introductory work materials are defined as solids used by man to produce items which constitute the support for his living environment.Indeed, no object exists without materials. All sectors of human activity depend on materials, from the manufacture of an integrated circuit to the construction of a hydroelectric dam. They appear in our bodies to strengthen or replace our damaged biomaterials. Materials are also as indispensable to our society as food, energy and information. Their essential role is too often forgotten.The definition employed in this introductory work is limited to solid materials. It excludes liquids and gases, as well as solid combustibles.1.3Classification of Materials Solid materials have been conveniently grouped into three basic classifications: metals, ceramics and polymers.This scheme is based primarily on chemical makeup and atomic structure, and most materials fall into one distinct grouping or another, although there are some intermediates. What may be considered to be a fourth group—the compositesconsists of combinations of two or more different materials. Another classification is advanced materialsthose used in hightechnology applications (viz, semiconductors, biomaterials, smart materials and nanoengineered materials). A brief explanation of the material types and representative characteristics is offered next. 1.3.1MetalsMetallic materials are normally combinations of metallic elements.They have large numbers of nonlocalized electrons, that is, these electrons are not bound to particular atoms. Many properties of metals are directly attributable to these electrons. Metals are extremely good conductors of electricity and are not transparent to visible light; a polished metal surface has a lustrous appearance. Furthermore, metals arquite strong, yet deformable, which accounts for their extensive use in structural applications.1.3.2CeramicsCeramics are compounds between metallic and nonmetallic elements; they are most frequently oxides, nitrides and carbides.The wide range of materials that falls within this classification includes ceramics that are composed of clay minerals, cement and glass. These materials are typically insulative to the passage of electricity and heat, and are more resistant to high temperatures and harsh environments than metals and polymers. With regard to mechanical behavior, ceramics are hard but very brittle.1.3.3PolymersPolymers include the familiar plastic and rubber materials. Many of them are organic compounds that are chemically based on carbon, hydrogen and other nonmetallic elements; furthermore, they have very large molecular structures. These materials typically have low densities and may be extremely flexible.1.3.4CompositesA number of composite materials have been engineered that consist of more than one material type. Fiberglass is a familiar example, in which glass fibers are embedded within a polymeric material. A composite id designed to display a combination of the best characteristics of each of the component material. Fiberglass acquires strength from the glass and flexibility from the polymer. Many of the recent material developments have involved composite materials.1.3.5Advanced MaterialsMaterials that are utilized in hightechnology (or hightech) applications are sometimes termed advanced materials. By high technology we mean a device or product that operates or functions using relatively intricate and sophisticated principles; examples include electronic equipment (camcorders, CD\/DVD players, etc.), computers, fiberoptic systems, spacecraft, aircraft and military rocketry. These advanced materials are typically traditional materials whose properties have been enhanced, and also newly developed, highperformance materials. They may be of all material types (e.g., metals, ceramics, polymers), and are normally expensive. Advanced materials include semiconductors, biomaterials, and what we may term “materials of the future” (that is, smart materials and nanoengineered materials).1.3.5.1SemiconductorsSemiconductors have electrical properties that are intermediate between the electrical conductors and insulators.Furthermore, the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms, which concentrations may be controlled over very small spatial regions. The semiconductors have made possible the advent of integrated circuitry that has totally revolutionized the electronics and computer industries (not to mention our lives) over the past two decades.1.3.5.2BiomaterialsBiomaterials are employed in components implanted into the human body for replacement of diseased or damaged body parts.These materials must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions). All of the above materialsmetals, ceramics, polymers, composites and semiconductors may be used as biomaterials. For example, some of the biomaterials that are utilized in artificial hip replacements.1.3.5.3Smart MaterialsSmart (or intelligent) materials are a group of new and stateoftheart materials now being developed that will have a significant influence on many of our technology. The adjective“smart” implies that these materials are able to sense changes in their environments and then respond to these changes in predetermined mannerstraits that are also found in living organisms. In addition, this “smart” concept is being extended to rather sophisticated systems that consist of both smart and traditional materials.Components of a smart material (or system) include some type of sensor (that detects an input signal), and an actuator (that performs a responsive and adaptive function). Actuators may be called upon to change shape, position, natural frequency or mechanical characteristics in response to changes in temperature, electric fields, and\/or magnetic fields. Four types of materials are commonly used for actuators: shape memory alloys, piezoelectric ceramics, magnetostrictive materials and electroheological\/magnetorheological fluids. Shape memory alloys are metals that, after having been deformed, revert back to their original shapes when temperature is changed. Piezoelectric ceramics expand and contract in response to an applied electric field (or voltage); conversely, they also generate an electric field when their dimensions are altered. The behavior of magnetostrictive materials is analogous to that of the piezoelectrics, except that they are responsive to magnetic fields. Also, electrorheological and magnetorheological fluids are that experience dramatic changes in viscosity upon the application of electric and magnetic fields, respectively.Materials\/devices employed as sensors include optical fibers, piezoelectricmaterials (including some polymers) and microelectromechanical devices.For example, one type of smart system is used in helicopters to reduce aerodynamic cockpit noise that is created by the rotating rotor blades. Piezoelectric sensors inserted into the blades monitor blade stresses and deformations; feedback signals from these sensors are fed into a computercontrolled adaptive device, which generates noisecanceling③ antinoise.1.3.5.4Nanoengineered MaterialsUntil very recent times the general procedure utilized by scientists to understand the chemistry and physics of materials has been to begin by studying large and complex structures, and then to investigate the fundamental building blocks of these structures that are smaller and simpler. Thisapproach is sometimes termed “topdown④” science. However, with the advent of scanning probe microscopes, which permit observation of individual atoms and molecules, it has become possible to manipulate and move atoms and molecules to form new structures, thus, design new materials that are built from simple atomiclevel constituents (i.e., “materials by design”). This ability to carefully arrange atoms provides opportunities to develop mechanical, electrical, magnetic and other properties that are not otherwise possible. We call this the “bottomup⑤” approach, and the study of the properties of these materials is termed “nanotechnology”. The “nano” prefix denotes that the dimensions of these structural entities are on the order of a nanometer (10-9 m) as a rule, less than 100 nanometers (equivalent to approximately 500 atom diameters). One example of a material of this type is the carbon nanotube. In the future we will undoubtedly find that increasingly more of our technological advances will utilize these nanoengineered materials.1.4Structural Characteristic of MaterialsSolids exist in nature in two principal forms: crystalline and amorphous, which differ substantially in their properties.Crystalline bodies remain solid,i.e. retain their shape, up to a definite temperature (melting point) at which they change from the solid to liquid state (Figure 1.1). During cooling, the inverse process of solidification takes place, again at the definite solidifying temperature, or point. In both cases, the temperature remains constant until the material is completely melted or respectively solidified.Figure 1.1Cooling curve of a crystalline substance
Amorphous bodies, which heated, are graduallysoftened in a wide temperature range and become viscous and only then change to the liquid state. In cooling, the process takes place in the opposite direction.The crystalline state of a solid is more stable than amorphous state.Amorphous bodies differ from liquid in having a lower mobility of particles. An amorphous state can be fixed in many organic and inorganic substances by rapid cooling from the liquid state. On repeated heating long holding at 20~25 ℃ or, in some cases, deformation of an amorphous body, the instability of the amorphous state may result in a partial or complete change to the crystalline state.Examples of such changes from amorphous to crystalline state are turbidity effect appearing in inorganic glasses on heating or in optical glasses after a long use, partial crystallization of molten amber on heating, or additional crystallization and strengthening of nylon fibres on tension.Crystalline bodies are characterized by an ordered arrangement of their elementary particles (ions, atoms or molecules). The properties of crystals depend on the electronic structure of atoms and the nature of their interactions in the crystal, on the spatialarrangement of elementary particles, and on the composition, size and shape of crystals.The structure of crystals is described by using the concepts of fine structure and micro and macrostructure depending on the size of structural components and methods employed to reveal them.Microscopic examinations make it possible to determine the size and shape of grains (crystals), the presence of different nature, their distribution and relative volume quantities, the shape of foreign inclusions and microvoids, orientations of crystals, and some special crystallographic characteristics (twins, slip lines, etc.).Macrostructure of crystals is studied by the naked eye or with a magnifying glass. This method can reveal the pattern of a fracture, shrinkage cavities and voids, and the shape and size of large crystals. It is also possible to detect cracks, chemical inhomogeneities, fibrous textures, etc. by using specially prepared (polished and etched) specimens. Macrostructural examination is a valuable method for studying crystalline materials.1.4.1Crystal LatticeIn a model of a crystal, the elementary particles (ions, atoms or molecules) that constitute its structure can be imagined to be spheres which touch one another and are arranged regularly in different directions (Figure 1.2 (a)). In a simpler model of crystal structure, spheres are replaced by points representing the centres of particles (Figure 1.2 (b)).If three directions, x, y and z, belonging to different planes, are drawn in a crystal, the spacings between the particles arranged along these directions will in the general case be different (say, a, b and c).Figure 1.2Arrangment of elementary particles in a crystal
Planes parallel to the coordinate planes and spaced at distances a, b and c from one another and oriented in parallel. The smallest of such parallelepipeds is called an elementary cell. Successive displacements of such a parallelepiped can form a threedimensional crystal lattice. The corners of the parallelepiped are called sites of a crystal lattice. These sites coincide with the centres of the particles which the crystal is built of.A threedimensional crystal lattice defines completely the structure of a crystal.An elementary cell of the crystal lattice is described by three sections a, b and c, which are equal to the distances to the nearest elementary particles along the coordinate axes and three angles made by each two of these sections, α, β and γ.The dimensions of an elementary cell of the crystal lattice are determined by sections a, b and c. They are called lattice spacings (or lattice constants). With known spacings of a lattice, it is possible to determine the ionic or atoms radius of an element. It is half the shortest spacing between particles in a lattice.In most cases, crystal lattices have an intricate order, since elementary particles can occupy not only the lattice sites, but also be arranged on its faces or in the centre (Figure 1.3). The complexity of a lattice is decided by the number of particles per elementary cell. In a simple threedimensional lattice (Figure 1.3(a)), a single particle always falls per cell. Each cell has eight corners, but each particle in a corner is shared simultaneously by eight other cells, roughly 1\/8 of the volume of a site falls on each cell and, since there are eight sites in a cell, one elementary particle falls on an elementary cell. In complex threedimensional lattices, the number of particles per cell is always more than one. In a bodycentred cell (Figure 1.3(b)), there are two particles: one from a corner and one centring particle which belongs solely to this particular cell. In a facecentred cell (Figure 1.3(c)) there are four particles: one from the corners and three from six centred planes (since an elementary particle in the centre of a face plane is shared simultaneously by two cells).A system, spacing and the number of particles per elementary cell determine uniquely the arrangement of elementary particles in a crystal.In some cases, additional characteristics of crystal lattices and used, which follow from the lattice geometry and reflect the packing density of elementary particles in a crystal. Among such characteristics are the coordination number and the packing factor.(a) simple; (b) and (c) complexFigure 1.3Types of elementary cell in crystal lattices
The coordination number determines the quantity of the nearest equidistant elementary particles. For instance, in a bodycentred cubic (BCC) lattice, the number of such neighbors for each atom is eight (C8). In a simple cubic lattice, the coordination number is six (C6). In a facecentred cubic (FCC) lattice, the coordination number is twelve (C12).The packing factor is determined as the ratio of the volume of all elementary particles per elementary cell to the total volume of the elementary cell. This factor is equal to 0.52 for a simple cubic lattice, 0.68 for a bodycentred cubic lattice and 0.74 for a facecentred cubic lattice.The remaining space of an elementary cell is occupied by interstitial voids or interstices which are differentiated into octahedral and tetrahedral.The centers of such voids of an FCC lattice are shown by small dots in Figure 1.4. The radius of an octahedral void is 0.41 of the radius of the elementary particle and the radius of a tetrahedral void is equal to 0.22.Figure 1.4Octahedral (a) and tetrahedral (b) voids in FCC lattice metals
Close packing of elementary particles is typical of many crystals. If elementary particles are represented by spheres (which is true for most particle since they possess spherical symmetry), they can be packed into a number of structures as shown in Figure 1.5.In that figure, the first layer is formed by spheres A which are closepacked⑥ in a hexagonal plane. The second layer (spheres B) is placed above it so that its spheres get into recesses 1 of the first layer. The third layer can be placed in two ways: (1) if its spheres are placed directly above those of the first layer, there forms a hexagonal closepacked lattice which is characterized by an alternating ABAB arrangement of spheres (shown at the bottom of the figure); (2) if the third layer (C) is placed so that spheres C fit into recesses of the second layer above recesses 2 of the first layer and only the fourth layer repeats exactly the first one, there forms a facecentred cubic lattice with an ABCABC arrangement of spheres.Figure 1.5Close packing of atoms in crystal
In that figure, the first layer is formed by spheres A which are closepacked in a hexagonal plane. The second layer (spheres B) is placed above it so that its spheres get into recesses 1 of the first layer. The third layer can be placed in two ways: (1) if its spheres are placed directly above those of the first layer, there forms a hexagonal closepacked lattice which is characterized by an alternating ABAB arrangement of spheres (shown at the bottom of the figure); (2) if the third layer (C) is placed so that spheres C fit into recesses of the second layer above recesses 2 of the first layer and only the fourth layer repeats exactly the first one, there forms a facecentred cubic lattice with an ABCABC arrangement of spheres.1.4.2Crystallographic IndicesThe properties of a crystal are the same along paralleldirections. Therefore, it suffices to indicate a single direction passing through the origin of coordinates for a whole family of parallel lines. This makes it possible to define the direction of a line by a single point, since the other point is always the origin of coordinates. Such a reference point may be the site of a crystal lattice occupied by an elementary particle. The coordinates of this site are expressed by whole number u, v and w measured in the units of sections a, b, c, and written in square brackets: [u, v and w]; they are called direction indices. A negative index is designated by a bar above the number (Figure 1.6(a)).The position of a plane in space is determined by sections cut off by that plane on the axes x, y and z. These sections are given by whole numbers m, n and p measured in the units of sections a, b and c. It has been adopted to use their reciprocals as plane indices: h=1\/m; k=1\/n and l=1\/p. The numbers h, k and l written in parentheses, are called the plane indices, or Miller indices⑦ Figure 1.6 (b). If negative sections are cut off by the plane, this is indicated by a bar above the corresponding index.Closepacked planes are called slip planes, since they are the planes of preferable displacement of atoms in a crystal during plastic deformation.For FCC crystals, the slip planes are those of the family (111). For HCP crystals with the c\/a ratio equal to or more than 1.633, the slip plane is the basal plane, i.e. the hexagonal base of the prism. With c\/a<1.633, the planes of the prism are also the slip planes.Figure 1.6Crystallographic induces of directions (a) and planes (b)
1.4.3AnisotropyThe properties of crystals are different in various crystallographic directions, which are associated with an ordered arrangement of atoms (ions and molecules) in space. The phenomenon is called anisotropy.The properties of crystals are determined by interactions of atoms. In crystals, the spacings between atoms are different in various crystallographic directions, because of which their properties are also different.Virtually all properties of crystals are anisotropic. The phenomenon is however more pronounced in crystals with structures of a poor symmetry.Anisotropy of properties is mainly observed in single grown crystals. Natural crystalline solids are mostly polycrystals, i.e. they consist of a plurality of differently oriented fine crystals and exhibit no anisotropy, since the mean statistic spaings between atoms are essentially the same in all directions. In that connection, polycrystalline solids are considered to be quasiisotropic. After plastic working of a polycrystal, crystallographic planes of the same index may turn out to be oriented in parallel. Such polycrystals are called textured, like single crystals, they are anisotropic.1.5Materials PropertiesA material exhibits a set of properties, which define its behavior. A property of a material is determined by analyzing thereaction of the material to some outside influence, generally by means of a normalized standard test. According to the type of outside influence, two categories of properties are recognized.1.5.1Physical and Chemical Properties of MaterialsPhysical properties are those that can be observed without changing the identity of the substance. The general properties of matter such as color, density, hardness, are examples of physical properties. Properties that describe how a substance changes into a completely different substance are called chemical properties. Flammability and corrosion\/oxidation resistance are examples of chemical properties.The different between a physical and chemical property is straightforward until the phase of the materials is considered. When a material changes from a solid to a liquid to a vapor it seems like them become a difference substance. However, when a material melts, solidifies, vaporizes, condenses or sublimes, only the state of the substance changes. Considerice, liquid water and water vapor, they are all simply H2O. Phase is a physical property of matter and matter can exist in four phases: solid, liquid, gas and plasma.In general, some of the more important physical and chemical properties from an engineering material standpoint include phase transformation temperatures, density, specificgravity, thermal conductivity, linear coefficient of thermal expansion, electrical conductivity and resistivity, magnetic permeability and corrosion resistance, and so on.(1) Phase transformation temperaturesWhen temperature rises and pressure is held constant, a typical substance changes from solid to liquid and then to vapor. Transitions from solid to liquid, from liquid to vapor, from vapor to solid and visa versa are called phase transformations or transitions. Since some substances have several crystal forms, technically there can also be solid to another solid form phase transformation.Phase transitions from solid to liquid, and from liquid to vapor will absorb heat. The phase transition temperature where a solid changes to a liquid is called the melting point. The temperature at which the vapor pressure of a liquid equals 1 atm (101.3kPa) is called the boiling point. Some materials, such as many polymers, do not go simply from a solid to a liquid with increasing temperature. Instead, at some temperature below the melting point, they start to lose their crystalline structure but the molecules remain linked in chains, which results in a soft and pliable material. The temperature at which a solid, glassy material begins to soften and flow is called the glass transition temperature. (2) DensityMass can be thinly distributed as in a pillow, or tightly packed as in a block of lead. The space the mass occupies is its volume, and the mass per unit of volume is its density.Mass (m) is a fundamental measure of the amount of matter. Weight (ω) is a measure of the force exerted by a mass and this force is produced by the acceleration of gravity. Therefore, on the surface of the earth, the mass of an object is determined by dividing the weight of an object by 9.8 m\/s2 (the acceleration of gravity on the surface of the earth). Since we are typically comparing things on the surface of the earth, the weight of an object is commonly used rather than calculating its mass.The density (r) of a material depends on the phase it is in and the temperature (The density of liquids and gases is very temperature dependent). Water in the liquid state has a density of 1 g\/cm3=1000 g\/m3 at 40 ℃. Ice has a density of 0.917 g\/cm3 at 0 ℃, and it should be noted that this decrease in density for the solid phase is unusual. For almost all other substances, the density of the solid phase is greater than that of the liquid phase. Water vapor (vapor saturated air) has a density of 0.051 g\/cm3.Some common units used for expressing density are grams\/cubic centimeter, kilograms\/cubic meter, grams\/milliliter, grams\/liter, pounds for cubic inch and pounds per cubic foot; but it should be obvious that any unit of mass per any unit of volume can be used.(3) Specific gravitySpecific gravity is the ratio of density of a substance compared to the density of fresh water at 4 ℃ (40 ). At this temperature the density of water is at its greatest value and equal 1 g\/cm3. Since specific gravity is a ratio, so it has no units. An object will float in water if its density is less than the density of water and sink if its density is greater that that of water. Similarly, an object with specific gravity less than 1 will float and those with a specific gravity greater than one will sink. Specific gravity values for a few common substances are: Au, 19.3; mercury, 13.6; alcohol, 0.7893; benzene, 0.8786. Note that since water has a density of 1 g\/cm3, the specific gravity is the same as the density of the material measured in g\/cm3.(4) Magnetic permeabilityMagnetic permeability or simply permeability is the ease with which a material can be magnetized. It is a constant of proportionality that exists between magnetic induction and magnetic field intensity. This constant is equal to approximately 1.257×10-6 Henry per meter (H\/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the freespace value, which is symbolized μ0.Materials that cause the lines of flux to move farther apart, resulting in a decrease in magnetic flux density compared with a vacuum, are called diamagnetic. Materials that concentrate magnetic flux by a factor of more than one but less than or equal to ten are called paramagnetic; materials that concentrate the flux by a factor of more than ten are called ferromagnetic. The permeability factors of some substances change with rising or falling temperature, or with the intensity of the applied magnetic field.In engineering applications, permeability is often expressed in relative, rather than in absolute, terms. If μ0 represents the permeability of free space (that is, 1.257×10-6 H\/m) and μ represents the permeability of the substance in question (also specified in henrys per meter), then the relative permeability, μr, is given by through formula (11):μr=μ\/μ0(11)For nonferrous metals such as copper, brass, aluminum, etc., the permeability is the same as that of “free space”, i.e. the relative permeability is one. For ferrous metals however the value of μr may be several hundred. Certain ferromagnetic materials, especially powdered or laminated iron, steel, or nickel alloys, have μr that can range up to about 1000000. Diamagnetic materials have μr less than one, but no known substance has relative permeability much less than one. In addition, permeability can vary greatly within a metal part due to localized stresses, heating effects, etc.When a paramagnetic or ferromagnetic core is inserted into a coil, the inductance is multiplied by μr compared with the inductance of the same coil with an air core. This effect is useful in the design of transformers and eddy current probes⑧.1.5.2Mechanical Properties of Materials The mechanical properties of a material are those ones that involve a reaction to an applied load. The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected. Mechanical properties are also used to help classify and identify material. The most common properties considered are strength, ductility, hardness, impact resistance and fracture toughness.Most structural materials are anisotropic, which means that their material properties vary with orientation. The variation in properties can be due to directionality in the microstructure (texture) from forming or cold working operation, the controlled alignment of fiber reinforcement and a variety of other causes. Mechanical properties are generally specific to product form such as sheet, plate, extrusion, casting, forging, etc. Additionally, it is common to see mechanical property listed by the directional grain structure of the material. In products such as sheet and plate, the rolling direction is called the longitudinal direction, the width of the product is called the transverse direction, and the thickness is called the short transverse direction. The grain orientations in standard wrought forms of metallic products are shown the image.The mechanical properties of a material are not constant and often change as a function of temperature, rate of loading and other conditions. For example, temperatures below room temperature generally cause an increase in strength properties of metallic alloys; while ductility, fracture toughness and elongation usually decrease. Temperatures above room temperature usually cause a decrease in the strength properties of metallic alloys. Ductility may increase or decrease with increasing temperature depending on the same variables.It should also be noted that there is often significant variability in the values obtained when measuring mechanical properties. Seemingly identical test specimen from the same lot of material will often produce considerable different results. Therefore, multiple tests are commonly conducted to determine mechanical properties and values reported can be an average value or calculated statistical minimum value. Also, a range of values is sometimes reported in order to show variability.(1) LoadingThe application of a force to an object is known as loading. Materials can be subjected to many different loading scenarios and a materials performance is dependant on the loading conditions. There are five fundamental loading conditions: tension, compression, bending, shear and torsion. Tension is the type of loading in which the two sections of material on either side of a plane tend to be pulled apart or elongated. Compression is the reverse of tensile loading and involves pressing the material together. Loading by bending involve applying a load in a manner that causes a material to curve and results in compressing the material on one side and stretching it on the other. Shear involves applying a load parallel to a plane which caused the material on one side of the plane to want to slide across the material on the other side of the plane. Torsion is the application of a force that causes twisting in a material.If a material is subjected to a constant force, it is called static loading. If the loading of the material is not constant but instead fluctuates, it is called dynamic or cyclic loading. The way a material is loaded greatly affects its mechanical properties and largely determines how, or if, a component will fail; and whether it will show warning signs before failure actually occurs.(2) StressThe term stress(S) is used to express the loading in terms of force applied to a certain crosssectional area of an object. From the perspective of loading, stress is the applied force or system of forces that tends to deform a body. From the perspective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. The stress distribution may or may not be uniform, depending on the nature of the loading condition. For example, a bar loaded in pure tension will essentially have a uniform tensile stress distribution. However, a bar loaded in bending will have a stress distribution that changes with distance perpendicular to the normal axis.(3) StrainStrain is the response of a system to an applied stress. When a material is loaded with a force, it produces a stress, which then causes a material to deform. Engineering strain is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material. This results in a unitless number, although it is often left in the unsimplified form, such as inches per inch or meters per meter. For example, the strain in a bar that is being stretched in tension is the amount of elongation or change in length divided by its original length. As in the case of stress, the strain distribution may or may not be uniform in a complex structural element, depending on the nature of the loading condition.If the stress is small, the material may only strain a small amount and the material will return to its original size after the stress is released. This is called elastic deformation, because of liking elastic, it returns to its unstressed state. Elastic deformation only occurs in a material when stresses are lower than a critical stress called the yield strength. If a material is loaded beyond it elastic limit, the material will remain in a deformed condition after the load is removed. This is called plastic deformation②.(4) Tensile propertiesTensile properties indicate how the material will react to forces being applied in tension. A tensile test is a fundamental mechanical test where a carefully prepared specimen is loaded in a very controlled manner while measuring the applied load and the elongation of the specimen over some distance. Tensile tests are used to determine the modulus of elasticity, elastic limit, elongation, proportional limit, reduction in area, tensile strength, yield point, yield strength and other tensile properties.(5) HardnessHardness is the resistance of a material to localized deformation. The term can apply to deformation from indentation, scratching, cutting or bending. In metals, ceramics and most polymers, the deformation considered is plastic deformation of the surface. For elastomers and some polymers, hardness is defined at the resistance to elastic deformation of the surface. The lack of a fundamental definition indicates that hardness is not be a basic property of a material, but rather a composite one with contributions from the yield strength, work hardening, true tensile strength, modulus and others factors. Hardness measurements are widely used for the quality control of materials because they are quick and considered to be nondestructive tests when the marks or indentations produced by the test are in low stress areas.(6) ToughnessThe ability of a metal to deform plastically and to absorb energy in the process before fracture is termed toughness. The emphasis of this definition should be placed on the ability to absorb energy before fracture. Recall that ductility is a measure of how much something deforms plastically before fracture, but just because a material is ductile does not make it tough. The key to toughness is a good combination of strength and ductility. A material with high strength and high ductility will have more toughness than a material with low strength and high ductility. Therefore, one way to measure toughness is by calculating the area under the stress strain curve from a tensile test. This value is simply called “material toughness” and it has units of energy per volume. Material toughness equates to a slow absorption of energy by the material.1.6Materials ScienceThe concept of materials science arose from the necessity of acquiring knowledge of the fundamental laws, which determine properties. Materials science seeks to establish the relations existing between composition, atomic or molecular organization, the microstructure and the macroscopic properties of materials. Materials engineering concerned with manufacturing, transformation and shaping processes, complements materials science.A fundamental knowledge of materials was not required when man contented himself with some clay, some wood and some wool to satisfy most of his necessities. The empirical approach and experience accumulated by the metalworkers and ceramists over thousands of years no longer suffice to satisfy contemporary needs and to meet the complex requirements of modern technology. A unified quantitative and fundamental approach to a description of the behavior of the engineering materials has become absolutely essential.Materials science has a general character and a multidisciplinary approach requiring the knowledge of chemists and physicists for basic sciences and those of the engineer (chemical, mechanical, electrical and civil) for applications and manufacturing. Materials science emerges as a coherent whole, coupled with materials engineering which has the objective the producing materials of well defined properties. Materials science treats the whole of materials (metals, ceramic and polymers) ina unified way with the same theoretical background and using the same experimental tools. As schematized in Figure 1.7, there are four main aspects materials science and technology: synthesis, manufacturing and processing, composition and structure, properties and performances. The behavior in manufacture and in use coupled with economic factors characterizes the performance of a material. Closely linked are four aspects of materials science. The materials is elaborated during synthesis (polymer) or manufacturing (metals, alloys, ceramics, etc.). Processing concerns the shaping of a material and the preparation of a finished object according to its behavior. For example, the production of a car body involves successively rolling of the sheet steel from a bar of steel, the stamping of the sheet steel to form the body and a series of finishing operation (painting, etc.).Figure 1.7The four basic aspects of materials science and technology
To obtain optimal properties, it is essential to master the structure and composition of the material and consequently to have access to a series of sophisticated analysis techniques.It is the numerous contributions of materials science and technology, which has completely remodeled the world, which supports us by freeing man of a huge number of constraints, linked to our environment. Our way of life has been radically transformed within a few decades largely due to the contributions of materials science and engineering which lead to the creation of the tools of the modern life: automobiles, aircraft, bridges, cable cars, computers, telecommunications equipment, satellites, etc.1.7Modern Materials NeedsIn spite of the tremendous progress that has been made in the discipline of materials science and engineering within the past few years, there stillremain technological challenges, including the development of even more sophisticated and specialized materials, as well as consideration of the environmental impact of materials production. Some comment is appropriate relative to these issues so as to round out this perspective.Nuclear energy holds some promise, but the solutions to the many problems that remain will necessarily involve materials, from fuels to containment structures to facilities for the disposal of radioactive waste.Significant quantities of energy are involved in transportation. Reducing the weight of transportation vehicles (automobiles, aircraft, trains, etc.), as well as increasing engine operating temperatures, will enhance fuel efficiency. New highstrength and lowdensity structural materials remain to be developed, as well as materials that have highertemperature capabilities, for use in engine components.Furthermore, there is a recognized need to find new, economical sources of energy, and to use the present more efficiently. Materials will undoubtedly play a significant role in these developments. For example, the direct conversion of solar into electrical energy has been demonstrated. Solar cells employ some rather complex and expensive materials. To ensure a viable technology, materials that are highly efficient in this conversion process yet less costly must be developed.Furthermore, environmental quality depends on our ability to control air and water pollution. Pollution control techniques employ various materials. In addition, materials processing and refinement methods need to be improved so that they produce less environmental degradation, that is, less pollution and less despoilage of the landscape from the mining of raw materials. Also, in some materials manufacturing processes, toxic substances are produced, and the ecological impact of their disposal must be considered.Many materials that we use are derived from resources that are nonrenewable, that is, not capable of being regenerated. These include polymers, for which the prime raw material is oil, and some metals. These nonrenewable resources are gradually becoming depleted, which necessitates: (1) the discovery ofadditional reserves, (2) the development of new materials having comparable properties with less adverse environmental impact, and\/or (3) increased recycling efforts and the development of new recycling technologies. As a consequence of the economics of not only production but also environmental impact and ecological factors, it is becoming increasingly important to consider the “cradletograve” life cycle of materials relative to the overall manufacturing process.
Notes
① deepseated 深層的；根深蒂固的
② stateoftheart 最先進的；已經發展的；達到最高水準的
③ noisecanceling 噪聲消除