1. Example - 718 Ni-base superalloy
Composition:
52.5Ni 19Cr Mo 19Fe 0.4Al Nb-1Ti 0.04C

2. Example - 718 Ni-base superalloy

3. Example - 718 Ni-base superalloy

4. Example - 718 Ni-base superalloy
Possibilities for strengthening 718:

5. Example - 718 Ni-base superalloy

6. Example - 718 Ni-base superalloy
52.5Ni Provides friendly matrix for alloying elements
19Cr Oxidation and corrosion resistance, solid solution strengthening
3Mo Solid solution strengthening, stabilizes chromium oxide film,
carbide formation for Hi T strength
19Fe Solid solution strengthening
0.4Al Increases oxidation resistance, forms strengthening pptates
5Nb-1Ti Form strengthening pptates
0.04C Carbide formation for creep resistance

7. Movement of atoms (or molecules) down a concentration gradient
Diffusion
Movement of atoms (or molecules) down a concentration gradient
concn
distance
concn
distance
concn
distance
concn
distance
How??

8. One way - vacancy movement
Diffusion
One way - vacancy movement
Vacancies occur naturally in materials
vacancy
No. fract. of vacancies = exp (-Q/RT)

9. One way - vacancy movement
Diffusion
One way - vacancy movement
Vacancies occur naturally in materials
vacancy
No. fract. of vacancies = exp (-Q/RT)
For rm T: 1080°C: 1/1600

10. Diffusion
Vacancy movement

11. Movement of atoms (or molecules) down a concentration gradient
Diffusion
Movement of atoms (or molecules) down a concentration gradient
concn
distance
concn
distance
concn
distance
concn
distance
I lied

12. Diffusion
Movement of atoms (or molecules) over a hump
Where do we get the activation energy?

13. Diffusion
Where do we get the activation energy?
From energy stored as thermal vibrations
# jumps/sec = A exp (-Q/RT)
For Cu:
# jumps/sec = 1015 exp (-29/RT)
= 1.1 x rm T
= 2.2 x 1080° C

14. Diffusion
Diffusion coefficient:
D(T) = Do exp (-Q/RT) flux J = D(T) dC/dx
For C diffusing in Fe:
D(T) = 0.21 exp (-33.8/RT)
= 6.7 x ° C
= 4 x ° C

15. Diffusion
For C diffusing in Fe:
D(T) = 0.21 exp (-33.8/RT)
= 6.7 x ° C
= 4 x ° C
Ex - carburizing a steel shaft:
how long to carburize to depth of 1 mm
x2 = D t
D(1000° C) = 3 x 10-7 cm2/sec t = 10 hr
D(1200° C) = 1.8 x 10-6 cm2/sec t = 1.5 hr