Example - 718 Ni-base superalloy Composition: 52.5Ni 19Cr 3Mo 19Fe 0.4Al 5Nb-1Ti 0.04C

Example - 718 Ni-base superalloy

Example - 718 Ni-base superalloy

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

Example - 718 Ni-base superalloy

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

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??

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

One way - vacancy movement Diffusion One way - vacancy movement Vacancies occur naturally in materials vacancy No. fract. of vacancies = exp (-Q/RT) For Cu @ rm T: 1/1014; @ 1080°C: 1/1600

Diffusion Vacancy movement

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

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

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 10-6 @ rm T = 2.2 x 1010 @ 1080° C

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 10-11 cm2/sec @ 500° C = 4 x 10-7 cm2/sec @ 1000° C

Diffusion For C diffusing in Fe: D(T) = 0.21 exp (-33.8/RT) = 6.7 x 10-11 cm2/sec @ 500° C = 4 x 10-7 cm2/sec @ 1000° 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