chap3_6 - 材材材材材材 Fundamental of Materials Prof...

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Unformatted text preview: 材材材材材材 Fundamental of Materials Prof: Tian Min Bo Prof: Tian Tel: 62795426 材 62772851 E-mail: [email protected] [email protected] Department of Material Science and Engineering Tsinghua University. Beijing 100084 Lesson ten §3.6 Intermetallic Compounds §3.6 (Intermetallic Phases) Ⅰ. Future 1. The structure of AmBn differs from those of 1. either A or B either 2. Its composition is variable to more or less extension extension 3. Mixed bonding 3. 4. Intermediate properties 4. Ⅱ. Formation A→←B The property of AmBn is between that of A and B. The Ⅲ. Factor governing the structure Factor of “compounds”. 1) Electrochemical factor 1) 2) Electron concentration 2) 3) Size factor 3) Metal Metal (X) (e/a) Nonmetal Metalloid §3.7 Normal Valence Compounds §3.7 Ⅰ. Definition: If the number of valence electrons of the cation is sufficient to complete octahedron of the anion, the compound is called the normal valence compounds. valence Example: C mA n meC 材 n(8 材 eA) sometimes: m(eC 材 eCC) = n(8 材 eA 材 eAA) Ⅱ. Classification according to structure 1. NaCl and CaF2 types NaCl: (Mg Ca Sr Ba)(Se Te) (Mg (Mn Pb Sn)(Se Te) (Mn CaF2: CaF PtSn2 PtIn2 Pt2P PtSn Anti-CaF2: Mg2(Si Ge Sn Pb) Cu2Se Li3AlN2 Mg LiMg(N As Sb Bi) AgMgAs LiMg(N 2. Diamond, Zinc blende, Wurtzite types 2. Zinc blende: Zinc (Be Zn Ca Hg)(S Se Te) (Be (Al Ga In)(P As Sb) (Al Wurtzite: Wurtzite: (Zn Cd Mn)S (Zn (Cd Mn)Se (Cd 3. NiAs structure Example: Example: (Cr Fe Co Ni)(S Se Sb) (Fe Co)Te (Fe (Mn Fe Ni Pt Cn)Sn (Mn Ni(As Sb Bi) Ni(As Structure Structure • Normal state —— Ni : As = 1 : 1 1 c 4 3 c 4 • When Ni does not full fill octahedral interspaces Ni : As < 1 : 1 • Extreme state 材 Ni occupy trigonal interspaces Ni : As > 1 : 1 4. Electron Phase 4. (Electron compounds) (Electron For Alloys of IB or transition metals, and B group metals phases with sane or similar structure occur at approximately some electron concentration(e/a) these alloys are therefore called as electron compounds §3.8 Electron Phases §3.8 (Hume-Rothery phases) Feature: ⑴ Identical on similar structure occur at approximately the same electron concentration, e/a. e/a For example: For CuZn : β Cu5Zn8 : γ CuZn3 : ε(HCP) β: (2+1)/2 = 21/14 γ: 21/13 ε: 21/12 ⑴ Components Components IB or transition metal 材 metals in B group IB ⑴ Composition range is related to e/a e/a ⑴ Metallic character Metallic §3.9 Size Factor Compounds §3.9 Ⅰ. Interstitial phases Interstitial (Interstitial compounds) (Interstitial Condition A >> B Condition >> B: H (0.46), B (0.97), C (0.77), N (0.71) B: 1. Simple interstitial compound structure rB < 0.59 rA A: Transition metals B: Interstitial elements (H, B, C, N) 2. Complex structure 2. rB > 0.59 rA M3C , (Fe3C) , M23C6 , M6C properties of interstitial compounds properties ⑴ Some metallic properties Some ⑴ Hard and brittle Hard 材 For size factor compounds For Ⅱ. Three principles for the structure 1. space-filling principle: Atoms tend to fill the space as closely as possible possible 2. Symmetry principle: 2. Atoms tend to build a configuration of high symmetry symmetry 3. Principle of multi-dimensional connection 3. Ⅲ. Intermetallic compounds Examples: Examples: 1. Laves phases 1. MgCu2 MgZn2 2 a = 4d B MgNi2 2 rB = a 8 A 材材 B 材材 rA 3 = = 1.225 rB 2 for Cu : for Mg : CN = 6(Cu − Mg ) + 6(Cu − Cu ) = 12 CN = 4(Mg − Mg ) + 12(Mg − Cu ) = 16 2. σ phase 2. A Cr Mo W V B Mn Fe Co Ni electrons atom ≈ 7 3. Topologically close-packed phase Examples and Discussions Examples Exercise Exercise Thank you ! Thank you ! 10 ...
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