Chapter 5s - 1200C 5min 680C 5 sec water quench Fe...

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1 1200 ° C ሺ5minሻ 680 ° C ሺ5 secሻ water quench Fe‐ 0.84 wt% Ni‐0.1wt% C
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Are solids inert? That is, once a solid forms is its structure fixed forever? movement of atoms within a solid ሺcrystalline or amorphousሻ 2
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3
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A Copper‐Nickel Diffusion couple before a high‐temperature heat treatment A Copper‐Nickel Diffusion couple after a high‐ temperature heat treatment Diffusion couple : Formed by joining bars of two different metals together, creating contact between the two faces. The couple is then heated for extended periods of time at high temperatures. 4
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5 CuAl 2 precipitates in Al matrix. Heated at 320 o C for 15 minutes.
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Remember, all crystals have vacancies. ሺX v 10 ‐4 at T ൌ T M Atoms easily hop into adjacent vacant lattice positions We can equal think of the vacancy jumping or of an atom jumping. Atomic motion occurs in the opposite direction as that of the vacancies An atomic jump is successful only if there is a vacancy next to the atom and the atom jumps into this vacancy. Both Self‐diffusion and substitutional impurity diffusion occur by this mechanism 6
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7 Vacancy diffusion Interstitial diffusion
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8 Interstitial atoms are small Atoms migrate from an interstitial position to a neighboring one that is empty Occurs more rapidly than vacancy diffusion because interstitial atoms are small and more mobile plus most neighboring interstitial sites are vacant Courtesy P. M. Anderson (Click to Play)
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Activation barriers 9
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Courtesy P. M. Anderson 10 (Click to Play)
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Chapter 5s - 1200C 5min 680C 5 sec water quench Fe...

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