材料科学基础_田民波_PPT_08

d A dB dA
100%
2. What is Electrochemical factor —— Electronegativity X X represents the ability of an atom of an element in the compond to attract electrons to itself.
0.85R0 R0 1.15R0 R
Dorken-Gurry graphic
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.

Ⅲ. Classification of Alloy Phases
1. According to structure
Solid Solution Compound In Solid Solution, atoms of different component share a common lattice in variable proportion.

Ⅲ. Hume-Rothery Rule for primary solid solubility
Hale Waihona Puke 1. Size factor: Size factor＝
d 0- d t
d0
×100％
If size factor ＞ 15％ solubility is very small.
Example
NiO can be added to MgO to produce a solid solution. What other ceramic systems are likely to exhibit 100% solid solubility with MgO?
②
Structure vs. e/a
for CuZn alloy system α(CuZn) —— e/a = 3/2 = 21/14 β(Cu5Zn8)—— e/a = 21/13 γ(CuZn3) —— e/a = 7/4 = 21/12
1. What is size factor metallic radii rA+rB =d Atomic radii
ionic radii r++r - =d
covalent radii single bond radius
Van der Waals radii
CN
radii
BCC
FCC
3 CN of BCC:8( a )+6(a) 2 3 3 a = rα = 0.290nm 4 4 = 0.12557nm
Pauli’s empirical rule:
n: valence
n 1 X 0.31 0.5 r(1)
r(1): simple bond radius
X A X B
2
EAA EBB ( ) EAB 2
EAA—— bonding energy between A-A atoms
§3.3 Solid Solution

Ⅰ. Classification
1. According the position of solute atoms in the lattice of the solvent Substitutional S.S. Interstitial S.S.
2. According the regularity of the position occupied by solute atoms Ordered S.S. Disordered S.S.
Lesson eight
Chapter Ⅲ
The Structures of Alloys
§3.1 Basic concepts of alloys

Ⅰ.Definition
An alloy is the combination of metal(s) with
other elements through chemical bonding.
nM exp V
∴
n
Vρexp M
M is the average atomic weigh
weighted by composition
Compare n with no (atoms per unit cell of solvent) n=no : ideal substitutional S.S. n>no : interstitial S.S. n<no : vacant S.S.
Ex. Write out in full the coordinates of all cations and anions in nucleus, Wurtzite and CaF2 referred to a b c axes of the anions sublattice.

Ⅱ. Determination of types of S.S
X ai
Wmi M i
(Xm
j 1
n
X mi
X ai M i
j
M j)
( X aj M j )
j 1
n
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 combination of atom arrangement including the types amounts and distribution of all types of material as well as grain size, defect etc.
2. According to position of the alloy in phase diagram
Terminal S.S. α α+β A B β
Intermediate S.S. or secondary S.S.
§3.2 Factors Affecting the Structure of Alloy Phase
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.
EBB—— bonding energy between B-B atoms EAB—— bonding energy between A-B atoms
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
substitutional S.S interstitial S.S ordered S.S disordered S.S primary (terminal) secondary (intermediate) continuous S.S S.S with restricted solubility
2 a) CN of FCC:12( 2 2 2 0.364nm a = rβ= 4 4 = 0.128674nm
Goldschmidt atomic radii is the radii of atom in structures with CN=12
Size factor is defined as
d
1.15d0
d0 0.85d0
Z1
Z2
Z
2. Crystal structure The materials must have the same crystal structure; otherwise there is some point at which a transition occurs from one phase to a second phase with a different structure.
0.72
0.74 1.12 0.74
9
12 70 12
NaCl
NaCl NaCl NaCl
FeO-MgO system will probably display unlimited solid solubility. CoO and ZnO systems also have appropriate radius ratios and crystal structures.
Al : 4 Fe : 12
1＋3＋12×1/4＋4＋1＝12 ∴ Fe12Al4＝Fe3Al
3. According to solid solubility
0~100% continuous series of S.S S.S with restricted solubility
summary