材科基础Fundamentals2

1、Fundamentals of Material Science and Engineering,材料科学与工程基础,Chapter 3,3. Structure of Metals and Ceramics,3.1 Introduction 3.2 Fundamental concepts 3.3 Unit cells 3.4 Metallic crystal structures 3.5 Density computations-Metal 3.6 crystal systems,Structure of Metals and Ceramics,Chapter 3,Structure of

2、 Metals and Ceramics,3.1 Introduction,Structure:,Examples for the relationship between crystal structure and property:,Deformed metals Crystalline and noncrystalline (非晶) materials,Chapter 3,Structure of Metals and Ceramics,3.2 Fundamental concepts,Crystalline materials: in which atoms are situated

3、in a repeating or periodic array over large atomic distance / “long-range order（长程有序）”,Noncrystalline / Amorphous materials:,Crystal structures:,Atomic hard sphere model lattice （晶格）,Chapter 3,Structure of Metals and Ceramics,3.3 Unit Cells (晶胞),Unit cell: the basic structure unit or building block

4、of the ctrystal structure and defines the crystal structure by virtue of its geometry and the atom position within.,Small repeat entities Parallelepiped or prism Represent the symmetry (对称性) of the crystal structure with highest level of symmetry,Chapter 3,Structure of Metals and Ceramics,3.4 Metall

5、ic crystal structures,Three simple crystal structure:,face-centered cubic （f.c.c 面心立方） body-centered cubic (b.c.c 体心立方） hexagonal close-packed (h.c.p 密排六方),Chapter 3,Structure of Metals and Ceramics,face-centered cubic: unit cell of cubic geometry, with atoms located at each corners and the centers

6、of all the cube faces,4 whole atoms are assigned to one unit cell; coordination number: 12; atomic packing factor (APF) : 0.74,Chapter 3,Structure of Metals and Ceramics,Body-centered cubic: unit cell of cubic geometry, with atoms located at each corners and a single atom at the cube center.,2 whole

7、 atoms are assigned to one unit cell; coordination number: 8; atomic packing factor (APF) : 0.68,Chapter 3,Structure of Metals and Ceramics,Hexagonal close-packed: 12 atom at each corners; each atom in top and bottom face center; and another 3 atom in the middle plane.,c/a = 1.633 6 whole atoms are assigned to one unit cell; coordination number: 12; atomic packing factor (APF) : 0.74,Chapter 3,Structure of Metals and Ceramics,3.4 Density computations-Metals,n = number of atoms associated with each unit cell A = atomic weight; Vc = volume of the unit cell; NA = Avogadros number （6.021023）,Cha