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1、MATERIALS SCIENCE,Week 1INTRODUCTION,Material Science&Engineering,Material-something tangible that goes into the makeup of a physical object.Material Science-involves investigating the relationships that exist between the structures and properties of materialsMaterial Engineering-is,on the basis of
2、these structureproperty correlations,designing or engineering the structure of a material to produce a predetermined set of properties,Http:/四氟板、尼龙棒、有机玻璃板,Material Science&Engineering,Structure-The structure of a material usually relates to the arrangement of its internal componentsDifferent levels
3、of defining structure of a materialProperty-A property is a material trait(distinguishing feature)in terms of the kind and magnitude of response to a specific imposed stimulusSix categories of properties-mechanical,electrical,thermal,magnetic,optical,and deteriorative,Material Science&Engineering,In
4、 addition to structure and properties,two other important components are involved in the science and engineering of materialsnamely,“processing”and“performance.”Processing-preparing or putting through a prescribed procedure,e.g.the processing of ore to obtain materialPerformance-the accomplishment r
5、elative to stated goals or objectives,Relationship Among the Four Components,The structure of a material will depend on how it is processed.Furthermore,a materials performance will be a function of its properties.,processing-structure-properties-performance,Material of all three disks-Aluminum Oxide
6、Left Disk-a single crystalCenter Disk-composed of numerous and very small single crystals that are all connectedRight Disk-composed of many small,interconnected crystals,and large number of small pores or void spaces,WHY STUDY MATERIALS SCIENCEAND ENGINEERING?,As a designer we are dependent upon mat
7、erials,their properties and performanceMany times,a materials problem is one of selecting the right material from the many thousands that are availableOn only rare occasions does a material possess the ideal combination of propertiesSecond selection consideration-deterioration of properties that may
8、 occur during service operationWhat will the finished product cost?,CLASSIFICATION OF MATERIALS,Three basic classifications of solid materials:metals,ceramics,and organic polymers(or just polymers).In addition,there are the composites,combinations of two or more of the above three basic material cla
9、sses,1.METALS,Materials in this group are composed of one or more metallic elements and often also nonmetallic elements in relatively small amountsAtoms in metals and their alloys are arranged in a very orderly manner and in comparison to the ceramics and polymers,are relatively denseDistinguishing
10、characteristics-stiff,strong,ductile,resistant to fractureMetallic materials have large numbers of nonlocalized electronsSome of the metals(Fe,Co,and Ni)have desirable magnetic properties,Metallic Objects,2.CERAMICS,Ceramics are compounds between metallic and nonmetallic elements;they are most frequ
11、ently oxides,nitrides,and carbidesTraditional ceramics-clay minerals(i.e.,porcelain),as well as cement,and glassCommon(nontraditional)ceramics-alumina,silica,silicon carbide,silicon nitrideRelatively stiff and strongstiffnesses and strengths are comparable to those of the metalsVery hardThus,very br
12、ittle,2.CERAMICS(contd),typically insulative to the passage of heat and electricitymore resistant to high temperatures and harsh environments than metals and polymers.ceramics may be transparent,translucent,or opaquesome of the oxide ceramics(e.g.,Fe3O4)exhibit magnetic behavior,Ceramic Objects,3.PO
13、LYMERS,A polymer is a large molecule(macromolecule)composed of repeating structural units typically connected by covalent chemical bondsMany of them are organic compounds that are chemically based on carbon,hydrogen,and other nonmetallic elements(e.g.O,N,and Si)They have very large molecular structu
14、res,often chain-like in nature that have a backbone of carbon atomsCommon polymers-polyethylene(PE),nylon,poly vinyl chloride(PVC),polycarbonate(PC),polystyrene(PS),and silicon rubber,A Polymer at Macroscopic Level,Appearance of real linear polymer chains as recorded using an atomic force microscope
15、 on surface under liquid medium.Chain contour length for this polymer is 204nm;thickness is 0.4nm,Polymers-Properties,have low densitiesmechanical characteristics are generally dissimilar to the metallic and ceramic materials neither stiff nor strongmany of the polymers are extremely ductile and pli
16、able(i.e.,plastic)relatively inert chemically and nonreactive in a large number of environmentsmajor drawback-tendency to soften and/or decompose at modest temperatureslow electrical conductivities and nonmagnetic,Polymer Objects,COMPOSITES,Composites are engineered materials made from two or more c
17、onstituent materials with significantly different physical or chemical properties,which remain separate and distinct on a macroscopic level within the finished structure,COMPOSITES(contd),The design goal of a composite is to achieve a combination of properties that is not displayed by any single mat
18、erialSome naturally-occurring materials are also considered to be compositesOne of the common composites is fiberglass,in which small glass fibers are embedded within a polymeric materialGlass Fiber-Strong+Stiff+BrittlePolymer-Ductile+Weak+Flexible,Glass-Fiber Reinforced Polymer,COMPOSITES(contd),CF
19、RP-carbon fibers that are embedded within a polymerThese materials are stiffer and stronger than the glass fiber-reinforced materials,thus they are more expensiveCFRPs are used in some aircraft and aerospace applications,as well as high-tech sporting equipment,CFRP microstructure,Comparison Chart-1,
20、Bar-chart of room temperature density,Comparison Chart-2,Bar-chart of room temperature stiffness(elastic modulus),Comparison Chart-3,Bar-chart of room temperature strength(tensile strength),Comparison Chart-4,Bar-chart of room temperature resistance to fracture(fracture toughness),Comparison Chart-5
21、,Bar-chart of room temperature electrical conductivity ranges,Advanced Materials,Materials that are utilized in high-tech applicationsHi-Tech-device or product that operates or functions using relatively intricate and sophisticated principlesThese advanced materials are typically traditional materia
22、ls whose properties have been enhanced,and,also newly developed,high-performance materials.include semiconductors,biomaterials,and materials of the future(i.e.,smart materials and nanoengineered materials),1.Semiconductors,Semiconductors have electrical properties that are intermediate between the c
23、onductors(e.g.metals and metal alloys)and insulators(e.g.ceramics and polymers)Common semiconducting materials are crystalline solids but amorphous and liquid semiconductors are known.These include hydrogenated amorphous silicon and mixtures of arsenic,selenium and tellurium in a variety of proporti
24、onsElectrical characteristics are extremely sensitive to the presence of minute concentrations of impurity atomsSemiconductors have caused the advent of integrated circuitry,2.Biomaterials,A biomaterial is any material,natural or man-made,that comprises whole or part of a living structure or biomedi
25、cal device which performs,augments,or replaces a natural functionmust not produce toxic substances and must be compatible with body tissuesAll of the above materialsmetals,ceramics,polymers,composites,and semiconductorsmay be used as biomaterialsExamples-Artificial hip,bone plates,heart valves,conta
26、ct lenses,dental implants,etc,Materials of the Future Smart Materials,Smart materials are materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli,such as stress,temperature,moisture,pH,electric or magnetic fieldsSmart material(or syste
27、m)include some type of sensor,and an actuatorFour types-shape memory alloys,piezoelectric ceramics,magnetostrictive materials,and electrorheological/magnetorheological fluids,Smart Materials(contd),Shape Memory Alloys-alloy that remembers its original shape and returns the pre-deformed shape by heat
28、ingMain types of shape memory alloys are the copper-zinc-aluminum-nickel,copper-aluminum-nickel,and nickel-titaniumPiezoelectric ceramics-produce a voltage when stress is applied.Since this effect also applies in the reverse manner,a voltage across the sample will produce stress within the sample,Sm
29、art Materials(contd),Magnetostrictive materials-analogous to piezoelectrics,except that they are responsive to magnetic fieldsElectrorheological and Magnetorheological fluids-liquids that experience dramatic changes in viscosity upon the application of electric and magnetic fields,respectivelyMateri
30、als for sensors-Optical fibers,Piezoelectrics,Microelectromechanical devices,Materials of the Future Nanoengineered Materials,It has become possible to manipulate and move atoms and molecules to form new structures and design new materials that are built from simple atomic-level constituentsThis ability to carefully arrange atoms provides opportunities to develop mechanical,electrical,magnetic,and other properties that are not otherwise possibleOne example of a material of this type is the carbon nanotube,
