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1、Introduction of Materials Science,Introduction 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 producin
4、g 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 th
5、e 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
6、 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.,Chapter 1 Introduction,An advancement in the understanding of a material type is often the forerunn
7、er to 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 investig
8、ating 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
9、structure 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 at
10、oms or 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
11、naked eye 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 r
12、esponse 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.
13、 Thermal 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 mo
14、dulus and 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 t
15、he response 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 Introductio
16、n,In addition 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
17、Introduction,Furthermore, a materials performance will be a function of its properties. The interrelationship between processing, structure, properties, and performance is shown as Figure 1.1,Chapter 1 Introduction,Structure,Processing,Properties,Performance,Figure 1.1 The relationships of structure
18、, properties, precessing and performance,Chapter 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-wh
19、ich gives rise to 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
20、 makes this materials 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 th
21、is material opaque. 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 optica
22、l transmittance is 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 electri
23、cal, will at one time 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 m
24、aterial from the many 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 d
25、oes a material possess the maximum or ideal combination of properties.,Chapter 1 Introduction,Thus, 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
26、 limited ductility. 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. Fin
27、ally, the overriding 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
28、 incurred during fabrication 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.,Ch
29、apter 1 Introduction,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 b
30、ound to particular atoms.,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, y
31、et deformable, which accounts for their extensive use in structure applications,Chapter 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
32、includes ceramics are composed 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, cerami
33、cs are hard but very brittle.,Chapter 1 Introduction,POLYMERSPolymers 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 typica
34、lly have low densities and 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.,Cha
35、pter 1 Introduction,Fiberglass 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 bet
36、ween the electrical conductors 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,BIOMATERIAL
37、S Biomaterials 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.,Chapter 1 Introduction,All of the above materials-metals, ceramics, polymers,composit
38、es, and semiconductors-may be 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 Introduction,By high technology we mean a device or product that operates or functions using relative
39、ly intricate and sophisticated principles; examples include electronic equipment(VCRs, CD players, etc.), computers, fiberoptical systems, spacecraft, aircraft, and military rocketry.,Chapter 1 Introduction,These advanced materials are typically either traditional materials whose properties have bee
40、n enhanced or newly developed, high-performance materials.,Chapter 1 Introduction,Furthermore, 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 inf
41、ormation storage, liquid crystal displays(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
42、 will have a significant influence on many of our technologies.,Chapter 1 Introduction,The 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
43、 1 Introduction,In addition, this “smart” 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 a
44、daptive function).,Chapter 1 Introduction,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
45、, piezo-electric ceramics, magnetostrictive materials,Chapter 1 Introduction,and 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 re
46、sponse to an applied electric field (orvoltage); conversely, they also generate an,Chapter 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 field
47、s.,Chapter 1 Introduction,Also, electrorheological 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 no
48、ise that is created by the rotating rotor 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
49、 Introduction,NANOTECHNOLOGYUntil 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 small
50、er and simpler.,Chapter 1 Introduction,This approach 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 an
