1、2020/9/6,材料科學(xué)基礎(chǔ),材料科學(xué)基礎(chǔ)Fundamental of Materials,Lesson eight,2020/9/6,材料科學(xué)基礎(chǔ),Chapter ,The Structures of Alloys,2020/9/6,材料科學(xué)基礎(chǔ),3.1 Basic concepts of alloys,.Definition An alloy is the combination of metal(s) with other elements through chemical bonding. .Terminology,2020/9/6,材料科學(xué)基礎(chǔ),2020/9/6,材料科學(xué)基礎(chǔ),1.

2、 Component (or constituent) one component system two component system binary system three component system ternary system four component system quarternary system five component system quinary system,multi-component system,2020/9/6,材料科學(xué)基礎(chǔ),2. Composition It can be expressed either by atomic percentag

3、e (mol fraction) Xa or by mass percentage Xm,2020/9/6,材料科學(xué)基礎(chǔ),3. Phase A phase is a homogeneous part of the material in which no abrupt change in composition, structure and properties occurs. An alloy may be single phase or multi-phase material. 4. Structure Structure is a general term for the combin

4、ation of atom arrangement including the types amounts and distribution of all types of material as well as grain size, defect etc.,2020/9/6,材料科學(xué)基礎(chǔ),. Classification of Alloy Phases 1. According to structure Solid Solution Compound In Solid Solution, atoms of different component share a common lattice

5、 in variable proportion.,2020/9/6,材料科學(xué)基礎(chǔ),2020/9/6,材料科學(xué)基礎(chǔ),2. According to position of the alloy in phase diagram,Terminal S.S.,Intermediate S.S. or secondary S.S.,2020/9/6,材料科學(xué)基礎(chǔ),3.2 Factors Affecting the Structure of Alloy Phase,1. What is size factor metallic radii rA+rB =d ionic radii r+r - =d cov

6、alent radii single bond radius Van der Waals radii,Atomic radii,2020/9/6,材料科學(xué)基礎(chǔ),CN radii,BCC,FCC,CN of BCC:8( )+6(a) CN of FCC:12( ) r= = r= = = 0.12557nm = 0.128674nm,2020/9/6,材料科學(xué)基礎(chǔ),Goldschmidt atomic radii is the radii of atom in structures with CN=12,Size factor is defined as,2020/9/6,材料科學(xué)基礎(chǔ),2.

7、What is Electrochemical factor Electronegativity X X represents the ability of an atom of an element in the compond to attract electrons to itself.,Paulis empirical rule:,n: valence r(1): simple bond radius,2020/9/6,材料科學(xué)基礎(chǔ),EAA bonding energy between A-A atoms EBB bonding energy between B-B atoms EAB

8、 bonding energy between A-B atoms,2020/9/6,材料科學(xué)基礎(chǔ),3. Electron concentration ( e/a ) Electron concentration ( e/a ) is the number of valence electrons per atom on the average. i.g. for CuZn : e/a = 3/2 =1.5,2020/9/6,材料科學(xué)基礎(chǔ),3.3 Solid Solution,. Classification 1. According the position of solute atoms

9、in the lattice of the solvent Substitutional S.S. Interstitial S.S.,2020/9/6,材料科學(xué)基礎(chǔ),2. According the regularity of the position occupied by solute atoms Ordered S.S. Disordered S.S.,2020/9/6,材料科學(xué)基礎(chǔ),13121/44112 Fe12Al4Fe3Al,2020/9/6,材料科學(xué)基礎(chǔ),3. According to solid solubility 0100% continuous series of S

10、.S S.S with restricted solubility,2020/9/6,材料科學(xué)基礎(chǔ),summary substitutional S.S primary (terminal) interstitial S.S secondary (intermediate) ordered S.S continuous S.S disordered S.S S.S with restricted solubility Ex. Write out in full the coordinates of all cations and anions in nucleus, Wurtzite and

11、CaF2 referred to a b c axes of the anions sublattice.,2020/9/6,材料科學(xué)基礎(chǔ),. Determination of types of S.S,is the average atomic weigh weighted by composition,2020/9/6,材料科學(xué)基礎(chǔ),Compare n with no (atoms per unit cell of solvent) n=no : ideal substitutional S.S. nno : interstitial S.S. nno : vacant S.S.,2020

12、/9/6,材料科學(xué)基礎(chǔ),. Hume-Rothery Rule for primary solid solubility 1. Size factor: Size factor 100,If size factor 15 solubility is very small.,2020/9/6,材料科學(xué)基礎(chǔ),NiO can be added to MgO to produce a solid solution. What other ceramic systems are likely to exhibit 100% solid solubility with MgO?,FeO-MgO syste

13、m will probably display unlimited solid solubility. CoO and ZnO systems also have appropriate radius ratios and crystal structures.,Example,2020/9/6,材料科學(xué)基礎(chǔ),2020/9/6,材料科學(xué)基礎(chǔ),2. Crystal structure The materials must have the same crystal structure; otherwise there is some point at which a transition occ

14、urs from one phase to a second phase with a different structure.,2020/9/6,材料科學(xué)基礎(chǔ),3. Electrochemical factor If the difference in X is great, the solubility is also very restricted. Formation of stable compound will restrict the solid solubility. Parameter: Electronegativity (x),2020/9/6,材料科學(xué)基礎(chǔ),Semiem

15、peries formulas Where: r1single bond radius n valency,2020/9/6,材料科學(xué)基礎(chǔ),x0,x0+0.4,x00.4,x,R,R0,0.85R0,1.15R0,Dorken-Gurry graphic,2020/9/6,材料科學(xué)基礎(chǔ),4. Electron concentration factor, e/a e: the number of valence electrons a: the number of atoms e/a = average number of valence electrons per atom.,2020/9/6

16、,材料科學(xué)基礎(chǔ),Experimental findings: Zn, Ga, Ge, As in Cu (solute-solvent),If composition is expressed in terms of e/a rather than at%, the solid solubility of all elements in Cu will be roughly the same.,2020/9/6,材料科學(xué)基礎(chǔ),Structure vs. e/a for CuZn alloy system (CuZn) e/a = 3/2 = 21/14 (Cu5Zn8) e/a = 21/13 (CuZn3) e/a = 7/4 = 21/12,2020/9/6,材料科學(xué)基礎(chǔ),. Properties of S.S 1. lattice constants properties Vagards law ass = ao + (a - ao)x for alloy S.S a = K(ZA-ZB)2 ZA, ZB are valences of so