2材料科學(xué)基礎(chǔ)英文版8PPT課件

1、Assessment Structure Written examination (50%) Oral presentation (20%, any topics in Chapter 7 Mechanical Properties, 4 students as a group, 15 minutes) Report (20%, any topics in materials science and engineering) Assignment (10%)第1頁/共27頁Outline Introduction Atomic bonding in solids Structures of m

2、etals and ceramics Imperfections in solids Diffusion Mechanical properties Deformation and strengthening mechanisms Failure Phase diagrams and phase transformations Types and applications of materials第2頁/共27頁Chapter OneIntroduction Materials science and engineering (MSE) Why study materials science

3、and engineering Classification of materials Advanced materials第3頁/共27頁What is materials science and engineering Materials science Concerned with the relationship between composition, structure and properties of materials Materials engineering Concerned with designing or engineering the structure to

4、produce a predetermined set of properties The structure of a material depends on what composition it has and how it is processed. Also, the performance of a material is a function of its properties MSE: Composition-processing-structure- properties-performance relationship第4頁/共27頁Why study materials

5、science and engineering All applied scientists and engineers in any engineering areas: design problems involving materials To select a right material from many thousands according to service conditions and property requirements, we need to have the knowledge of MSE To modify existing materials and d

6、evelop new materials, we need to know MSE第5頁/共27頁Classification of materials In terms of chemical makeup and atomic structure Metals; Ceramics; Polymers 1) Metallic: combinations of metallic elements Free electrons good electrical and thermal conductivities Strong but deformable extensive use in str

7、uctural applications 2) Ceramic: compounds between metallic and nonmetallic elements oxides, nitrides, and carbides Very insulative to electricity and heat very low electrical and thermal conductivities Highly resistant to high temperatures and corrosive environments Very hard but very brittle 3) Po

8、lymeric: organic compounds based on carbon, hydrogen and other nonmetallic elements plastics and rubbers Normally low density and relatively flexible第6頁/共27頁Additional types of material Composites; Semiconductors; and BiomaterialsThey originate from the three basics (metals, ceramics and polymers),

9、but they have special uses and functions1) Composites Composed of more than one material type one: matrix; other(s): reinforcing addition Matrix polymeric, metallic, or ceramic materials Reinforcing addition: glass fibers, carbon fibers, ceramic fibers (e.g. basalt fibers) or nanoparticles (e.g. SiC

10、, SiN, etc) Designed to display a combination of the best properties of each of the components2) Semiconductors Electrical properties being intermediate between conductors and insulators and being very sensitive to their composition and environmental conditions (e.g., functional ceramics: microwave

11、dielectric ceramics, ferroelectric and piezoelectric ceramics)3) Biomaterials Used for components implanted into the human body for replacement of the diseased or damaged body parts第7頁/共27頁Advanced materials Materials used in high technology electronic equipment, computers, spacecraft, aircraft, nuc

12、lear equipment, etc. Including: Traditional materials whose properties are enhanced by some modifications (new processing technology) Newly developed materials第8頁/共27頁Chapter TwoAtomic bonding in solids Introduction Primary interatomic bonds Secondary bonds Condensed states of matter Interatomic for

13、ces第9頁/共27頁Atomic bonding in solids Introduction (1)To understand the origin of some material properties, e.g. the modulus of elasticity need to look at materials on the atomic level Two important things:1) The force which holds two atoms together (the interatomic bond), working like a little spring

14、The spring-like bond between two atoms第10頁/共27頁Atomic bonding in solids Introduction (2)2) The ways in which atoms pack together (atom packing) determining the number of little springs per unit area and the bond-angle Atom packing and bond-angle第11頁/共27頁 The ways in which atoms can be bound together

15、 include:Atomic bonding in solids Introduction (3)(1) Primary bonds ionic, covalent, and metallic bonds - strong(2) Secondary bonds Van der Waals and hydrogen bonds - weak第12頁/共27頁P(yáng)rimary interatomic bonds (1) All ceramics and metals are bound together by primary bonds Ionic and covalent bonds in ce

16、ramic materials Metallic bonds in metallic materials Both primary and secondary bonds in polymeric materials e.g., in liquid N2, N-N N-N第13頁/共27頁P(yáng)rimary interatomic bonds (2)1) Ionic bondsSodium chloride: NaCl Cl-Formation of an ionic bond between a sodium atom and a chlorine atom2o2A4rqFrqrFUro2AA4

17、dnRrBUBonding energy:Ubonding = Ui (UA + UR)Ui =energy of isolated ionsRAUUUb第14頁/共27頁P(yáng)rimary interatomic bonds (3)The formation of an ionic bond, viewed in terms of energyUbonding第15頁/共27頁P(yáng)rimary interatomic bonds (4)2) Covalent bonds The bond is formed by sharing of electrons between adjacent atom

18、s e.g. Methane (CH4) The formation of covalent bonds in CH4第16頁/共27頁P(yáng)rimary interatomic bonds (5)Bond energy: Ub = -A/rm + B/rn (mn)The formation of a covalent bond, viewed in terms of energyUbonding第17頁/共27頁P(yáng)rimary interatomic bonds (6) Compound partially ionic bonding and partially covalent bondin

19、g Degree of either bonding type difference in the electronegativity of component atoms For a compound composed of two elements A and B % ionic character = 1- exp-(0.25)(XA-XB)2 100 XA and XB electronegativities of elements A and BIncreasing with increasing electronegativity difference第18頁/共27頁3) Met

20、allic bonds Dominant interatomic bonding in metalsMetal ion cores + free electrons (valence electrons)Primary interatomic bonds (7)Bonding in a metal第19頁/共27頁Secondary bonds (1) Much weaker than primary bonds, but important Links between polymer molecules solids Keep water liquid at room temperature

21、; water boil at 80oC without them Two types of secondary bonds Van der Waals bonds Hydrogen bonds 第20頁/共27頁Secondary bonds (2)1)Van der Waals bonds Describe a dipolar attraction between uncharged atoms with stable electron structures or between molecules in molecular structures e.g. inert gases heli

22、um (He), neon (Ne), argon (Ar), and H2, N2, F2; when they are in the liquid state, their atoms or molecules are bonded by Van der Waals bonds Reason: Electronic charge on an atom is always in motion; on the average spherically symmetric relative to the nucleus, but at any instant unsymmetric dipole moment Two dipoles on two adjacent atoms attract each otherBond energy: 第21頁/共27頁Secondary bonds (3)Van der Waals bonding the atoms are held together by the dipole charge distribution Typical example: liquid nitrogen at 198oC covalently bonded N2 molecules are glued together by Van der Waals for