1、Introduction of Materials ScienceIntroduction of Materials Science Chapter 1 Introduction1.1 Historical Perspective Materials are more deep-seated in our culture than most of us realize. Transportation, housing, clothing, communication, recreation, and food production-virtually every segment of our
2、everyday lives is influenced to one degree or another by materials. Chapter 1 Introduction Historically, the development and advancement of societies have been intimately tied to the members ability to produce and manipulate materials to fill their needs. Early civilizations have been designated by
3、the level of their materials development (Stone Age, Bronze Age, et al.,) Chapter 1 Introduction Firstly, the earliest human had access to only a very limited number of materials, those that occur naturally: stone, wood, clay, skins, and so on. Secondly, the human discovered techniques for producing
4、 materials that had properties superior to those of the natural ones, these new materials included pottery and various metals.Chapter 1 Introduction Furthermore, it was discovered that the properties of a materials could be altered by heat treatments and by the addition of other substances. Now the
5、scientists come to understand the relationships between the structural elements of materials and their properties.Chapter 1 Introduction Thus, tens of thousands of different materials have evolved with rather specialized characteristics that meet the needs of our modern and complex society; these in
6、clude 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.Chapter 1 Introduction An advancement in the understanding of a material type is often the forerunner t
7、o the stepwise progression of a technology. In our contemporary era, sophisticated electronic devices rely on components that are made from what are called semiconducting materials.Chapter 1 Introduction 1.2 Materials Science and Engineering The discipline of materials science involves investigating
8、 the relationships that exist between the structures and properties of materials. Materials engineering is, on the basis of these structure-property to produce a predetermined set of properties.Chapter 1 Introduction “Structure” is a nebulous term that deserves some explanation. In brief, the struct
9、ure of a material usually relates to the arrangement of its internal components. Subatomic structure involves electrons within the individual atoms and interactions with their nuclei. (Electronic Structure)Chapter 1 Introduction On an atomic level, structure encompasses the organization of atoms or
10、molecules relative to one another.(Atomic Structure) The next larger structural realm, which contains large groups of atoms that are normally agglomerated together, is termed “microscopic”. (Microscopic Structure)Chapter 1 Introduction Finally, structural elements that may be viewedwith the naked ey
11、e are termed “macroscopic.”(Macroscopic structure)The notion of “property” deserves elaboration. While in service use, all materials are exposed to external stimuli that evoke some type of response. Chapter 1 Introduction A property is a material trait in terms of the kind and magnitude of response
12、to a special imposed stimulus. Generally, definitions of properties are made independent of material shape and size. Virtually all important properties of solid materials may be grouped into six different categories:Chapter 1 Introduction 1. Mechanical properties 2. Electrical properties 3. Thermal
13、properties 4. Magnetic properties 5. Optical properties 6. Deteriorative properties Chapter 1 Introduction For each there is a characteristic type of stimulus capable of provoking different responses. Mechanical properties relate deformation to an applied load or force (including elastic modulus and
14、 strength).Chapter 1 Introduction For electrical properties, such as electrical conductivity and dielectric constant, the stimulus is an electric field. The thermal properties of solids can be represented in terms of heat capacity and thermal conductivity. Magnetic properties demonstrate the respons
15、e of a material to the application of magnetic field.Chapter 1 Introduction For optical properties, the stimulus is electro-magnetic or light radiation.(index of refraction and reflectivity) Deteriorative characteristics indicate the chemical reactivity of materials. Chapter 1 Introduction In additi
16、on to structure and properties, two other important components are involved in the science and engineering of materials namely“processing”and“performance.” With regard to the relationships of these four components, the structure of a material will depend on how it is processed. Chapter 1 Introductio
17、n Furthermore, a materials performance will be a function of its properties. The interrelationship between processing, structure, properties, and performance is shown as Figure 1.1Chapter 1 Introduction StructureProcessingPropertiesPerformanceFigure 1.1 The relationships of structure, properties, pr
18、ecessing and performanceChapter 1 Introduction We now present an example of these processing-structure-properties-performance principles. All of these specimens are of the same materials: aluminum oxide (Al2O3) Chapter 1 Introduction A single crystal-that is, it is highly perfect-which gives rise to
19、 its transparency, so it is transparent; The other one is composed of numerous and very small single crystals that are all connected (polycrystals); Chapter 1 Introduction the boundary between these small crystals scatter a portion of the light reflected from the printed page, which makes this mater
20、ials optically translucent. Finally, the third specimen is composed not only of many small, interconnected crystals, but also of a large number of very small pores or void spaces.(Ceramics) Chapter 1 Introduction These pores also effectively scatter the reflected light and render this material opaqu
21、e. Thus, the structures of these three specimens are different in terms of crystal boundaries and pores, which affect the optical transmittance properties. Chapter 1 Introduction Furthermore, each material was produced using a different processing techniques. And of cause, if optical transmittance i
22、s an important parameter relative to the ultimate in-service application, the performance of each material will be different.Chapter 1 Introduction 1.3 Why study Materials Science and Engineering?Many an applied scientist or engineer, whether mechanical, civil, chemical, or electrical, will at one t
23、ime or another be exposed to a design problem involving materials. Chapter 1 Introduction Of course, materials scientists and engineers are specialists who are totally involved in investigation and design of materials. Many times, a materials problem is one of selecting the right material from the m
24、any thousands that are available. There are several criteria on which the final decision is normally based. Chapter 1 Introduction First of all, the in-service conditions must be characterized, for these will dictate the properties required of the material. On only rare occasions does a material pos
25、sess the maximum or ideal combination of properties. Chapter 1 IntroductionThus, it may be necessary to trade off one characteristic to another. Chapter 1 Introduction The classic example involves strength and ductility; normally, a material having a high strength will have only a limited ductility.
26、 A second selection consideration is any deterioration of material properties that may occur during service operation. Chapter 1 Introduction For example, significant reductions in mechanical strength may result from exposure to elevated temperatures or corrosive environments. Finally, the overridin
27、g consideration is that of economics: what will the finish product cost? Chapter 1 Introduction A material may be found has the ideal set of properties but is prohibitively expensive. Hear again, some compromise is inevitable. The cost of a finished piece also includes any expense incurred during fa
28、brication to produce the desired shape.Chapter 1 Introduction 1.4 Classification 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.Chapter 1 Introduction
29、In addition, there are three other groups of important engineering materials-composites, semiconductors and biomaterials. METALS Metallic materials are normally combinations of metallic elements. They have large numbers of nonlocated electrons: that is, these electrons are not bound to particular at
30、oms.Chapter 1 Introduction Many properties of metals are directly attributable to these electrons. Metals are extremely good conductors of electricity and heat and are not transparent to visit light; a polished metal surface has a lustrous appearance. Metals are quite strong, yet deformable, which a
31、ccounts for their extensive use in structure applicationsChapter 1 Introduction CERAMICS Ceramics are compounds between metallic and nonmetallic elements; they are most frequently oxides, nitrides, and carbides. The wide range of materials that fall within this classification includes ceramics are c
32、omposed of clay minerals, cement, and glass. Chapter 1 Introduction Ceramics 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 br
33、ittle.Chapter 1 IntroductionPOLYMERSPolymers include the familiar plastic and rubber materials. Many of them are organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements; they have very large molecular structures. These materials typically have low densities an
34、d maybe extremely flexible.Chapter 1 Introduction COMPOSITES A number of composite materials have been engineered that consist of more than one material type. A composite is designed to display a combination of the best characteristics of each of the component material.Chapter 1 Introduction Fibergl
35、ass is a familiar example, in which glass fibers are embedded within a polymeric material. Fiberglass acquires strength from the glass and flexibility from the polymer.Chapter 1 Introduction SEMICONDUCTOR Semiconductors have electrical properties that are intermediate between the electrical conducto
36、rs and insulators. Furthermore, the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms; these concentrations may be controlled over very small spatial regions. Chapter 1 Introduction BIOMATERIALS Biomaterials are employed
37、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.Chapter 1 IntroductionAll of the above materials-metals, ceramics, polymers,composites, and semiconductors-may be
38、used as biomaterials.1.5 Advanced Materials Materials that are utilized in high-technology (or high-tech) application are sometimes termed advanced materials.Chapter 1 IntroductionBy high technology we mean a device or product that operates or functions using relatively intricate and sophisticated p
39、rinciples; examples include electronic equipment(VCRs, CD players, etc.), computers, fiberoptical systems, spacecraft, aircraft, and military rocketry. Chapter 1 IntroductionThese advanced materials are typically either traditional materials whose properties have been enhanced or newly developed, hi
40、gh-performance materials.Chapter 1 IntroductionFurthermore, they may be of all material types(e.g.,metals, ceramics, polymers)and are normally relatively expensive.For example, advanced materials are materials that used for lasers, integrated circuits, magnetic information storage, liquid crystal di
41、splays(LCDs), fiber optics and the thermal protection system for the Space Shutter Orbiter. Chapter 1 Introduction 1.6 METRIALS OF THE FUTURE SMART MATERIALS Smart (or intelligent) materials are a group of new and state-of-the-art materials now being developed that will have a significant influence
42、on many of our technologies. Chapter 1 IntroductionThe adjective “smart” implies that these materials are able to sense changes in their environments and then respond to these changes in predetermined manners-traits that are also found in living organisms.Chapter 1 IntroductionIn addition, this “sma
43、rt” concept is beingextended to rather sophisticated systems thatconsist of both smart and traditional materials.Components of a smart material (or system)include some type of sensor (that detects aninput signal), and an actuator (that performs aresponsive and adaptive function).Chapter 1 Introducti
44、on Actuators may be called upon to change shape, position, natural frequency, or mechanical characteristics in response to change in temperature, electric fields, and/or magnetic fields.Four types of materials are commonly usedfor actuators: shape memory alloys, piezo-electric ceramics, magnetostric
45、tive materials,Chapter 1 Introductionand electrorheological/magnetorheologicalfluids.Shape memory alloys are metals that, after having been deformed revert back to theiroriginal shapes when temperature is changed.Piezoelectric ceramics expand and contractin response to an applied electric field (orv
46、oltage); conversely, they also generate anChapter 1 Introduction electric field when their dimensions are altered. The behavior of magnetostrictive materials is analogous to that of the piezoelectric ceramics, except that they are responsive to magnetic fields. Chapter 1 Introduction Also, electrorh
47、eological and magneto-rheological fluids are liquids that experience dramatic changes in viscosity upon the application of electric and magnetic field, respectively. For example, one type of smart system is used in helicopters to reduce aerodynamic cockpit noise that is created by the rotating rotor
48、 blades.Chapter 1 Introduction Piezoelectric sensors inserted into the blades, monitor blade stress and deformations; feedback signals from these sensors are fed into a computer-controlled adaptive device, which generates noise-canceling antinoise.Chapter 1 IntroductionNANOTECHNOLOGYUntil very recen
49、t 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. Chapter 1 IntroductionThis a
50、pproach is sometimes termed “top-down” science.However, with the advent of scanning probe microscopes, which permit observation of individual atoms and molecules, it has become possible to manipulates and move atoms and molecules to form new structures and, thus, design new materials that are built
