2. Some of the Diffusional transformations
Allotropic Transformation
Precipitation
Reaction
Eutectoid Transformation
Order-disorder Transformation
Massive Transformation

3. HOMOGENEOUS NUCLEATION IN SOLID STATE
’    
Supersaturated B-rich precipitate
solid solution
G = V GV + V Gs A 
= - (4/3)  r3 GV + (4/3)  r3 GS +4 r2 a/b
= - (4/3)  r3 [GV - GS] +4 r2 a/b

4. G = - (4/3)  r3 [GV - GS] +4 r2 /

5. Gn = G G1
Gv = Gn / Vm
 X where X = X0 - Xe

7. Gheterogeneous = - V [ GV - Gs] + A   A 
Heterogeneous Nucleation
2  Cos  = 
Gheterogeneous = - V [ GV - Gs] A   A 
A =  (r Sin )2
A = 4  r2 (1-Cos)
V = (2/3) r3 (2 + Cos ) (1-Cos)2
G*heterogeneous = [- (4/3)  r*3 (GV - Gs) + 4 (r*)2 a/b ]
. [(2 + Cos ) (1-Cos)2 /2]
= G*homogeneous . S ()

8. S () = (1/2) (2 + Cos ) (1-Cos )2
= (G*heterogeneous /G*homogeneous)
= V*heterogeneous / V*homogeneous
C*hom = C0 exp [ - G*hom / kT ]
C*I,het. = Ci exp [ - G*i, het. / kT ]
i refers to heterogeneous nucleation site type “i”,
Ci refers to number of heterogeneous nucleation sites of type “i” per unit volume,
C*i refers to rate of formation of stable nucei per unit volume at heterogeneous nucleation sites of type “i”.

9.  - Grain boundary width, D- Grain size
Defect site type
Ci/C0
Grain boundary
(/D)
Grain corner
(/D)3
Grain edge
(/D)2
 - Grain boundary width, D- Grain size
Grain corner
Grain edge

10. Ci
G*
Type of site
Homogeneous sites
Vacancies
Dislocations
Stackin faults
Grain boundaries and interface boundaries
Surfaces
(Chet., i / C0 ) = exp [- (G*het.,i - G*hom) / kT ]