Chapter 5 Slides

Chapter 5 Slides - Chapter 5 Diffusion(atomic jumping Why...

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Chapter 5 Chapter 5 Diffusion (atomic jumping) Diffusion (atomic jumping) Why study diffusion? Equilibrium state of materials changes with alloying state and with temperature Above about half the melting point (T m measured in K not C), there is enough vibrational energy in the lattice to allow atomic jumps (diffusion) Phase changes at high temperatures (HT) occur by diffusion, making quantitative study of T and t valuable Reactions often occur by diffusion reactions Sometimes we want to modify only the surface properties of a part Surface treatments can often beneficially just change surface properties Case harden gears by diffusing C into the surface And many, many more reasons…….
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Chapter 5 Chapter 5 - - Diffusion Diffusion Lectures begin on 02-19-08
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Self-diffusion : In an elemental solid, atoms migrate under the action of the thermal energy of the crystal lattice kT/atom. For long range motion to occur, one must be above ~0.5T M (K) Label some atoms After some time Self Diffusion in Crystals Self Diffusion in Crystals A B C D A B C D •Notice that with time, atoms can move substantial distances •Self diffusion experiments have to be done by simulations or by adding radioactive isotopes whose position can be tracked by radiography….
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Interdiffusion : In an alloy, atoms tend to migrate from regions of high concentration to regions of low conc. Initially Diffusion of two mutually soluble species Diffusion of two mutually soluble species into each other into each other After some time What determines the shape and extent of the diffusion profile?
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