材科基础Fundamentals3

1、Fundamentals of Material Science and Engineering,材料科学与工程基础,Chapter 3,3. Structure of Metals and Ceramics,3.10 Polymorphism and allotropy 3.11 Crystal systems 3.12 Crystallographic directions 3.13 Crystallographic planes 3.14 / 3.15 Close-packed crystal structures,Structure of Metals and Ceramics,Cha

2、pter 3,Structure of Metals and Ceramics,3.10 Polymorphism and allotropy,Polymorphism: 同质多晶现象,The same material with different crystal structures Termed “Allotropy” in elemental solids Depends on temperature and external pressure Familiar examples:,Polymorphism:,Allotropy: 同素异形现象,Graphite / Diamond P

3、ure iron at room temperature / at 912 C or above,3.11 Crystal Systems,Coordinate system in crystal structures,Origin x, y, and z axe Lattice parameters: x, y, z, , , ,7 Crystal systems,Cubic / hexagonal tetragonal / orthorhombic / rhombohedral Monoclinic / triclinic,crystal system 晶系,lattice paramet

4、ers 晶格常数,coordinate system 坐标系,Chapter 3,Structure of Metals and Ceramics,Chapter 3,Structure of Metals and Ceramics,3.12 Crystallographic Directions,Steps to determine the directional indices:,Translate: A vector passing through the origin measure the vector length with a, b and c Multiply or divid

5、e by a common factor Enclosed in square brackets,Negative indices are possible: a bar over the index; Change the signs of all indices: an antiparallel direction; 1 0 0 1 1 0 1 1 1 are common crystalline directions,index / indices 指数,translate 平移,vector 向量,antiparallel 反方向,Chapter 3,Structure of Meta

6、ls and Ceramics,Chapter 3,Structure of Metals and Ceramics,Crystalline direction family (晶向族):,Some nonparallel directions with different indices are actually equivalent the spacing of atoms along the direction is the same.,Example: in cubic crystal 100 100 010 010 001 001,Enclosed in angle brackets

7、, in cubic crystals:,nonparallel 不平行的,equivalent 等价的,Chapter 3,Structure of Metals and Ceramics,3.13 Crystallographic Planes,Steps to determine the directional planes:,Translate: a parallel plane not through the origin measure the planar intercept with a, b and c Take the reciprocals Multiply or div

8、ide by a common factor Enclosed in parentheses,Negative indices are possible: a bar over the index; Change the signs of all indices: an parallel plane; Perpendicular: if the directions and the planes have same indices in cubic crystals.,translate 平移,plane 平面,perpendicular 垂直,Chapter 3,Structure of Metals and Ceramics,braces 大括号,tetragonal 四方的,Atomic arrangement,Crystalline plane family (晶面族): crystal-lographically equivalent Planes.,Enclosed in braces. In cubic crystal:,How about in tetragonal crystals ?,六方晶系晶面指数：,采用了四个轴，a1、a2、a3位于同一平面且互呈120度角。 晶面指数的标定方法与三轴坐标系相同。 （h k i l）其