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Metallurgy ( Help please )

  1. Jan 22, 2012 #1
    Use the diffusion data in the table below
    for atoms in iron to answer the questions
    that follow. Assume metastable equilibrium
    conditions and trace amounts of C
    in Fe. The gas constant in SI units is
    8.314 J (mol K).

    Diffusion Diffusion
    Couple Mechanism Q (J mol) D0 (m2 s)
    C in FCC iron Interstitial 1.38 * 105 2.3 * 10-5
    C in BCC iron Interstitial 8.74 * 104 1.1 * 10-6
    Fe in FCC iron Vacancy 2.79 * 105 6.5 * 10-5
    Fe in BCC iron Vacancy 2.46 * 105 4.1 * 10-4




    (a) Plot the diffusion coefficient as a function
    of inverse temperature (1 T) showing
    all four diffusion couples in the
    table.
    (b) Recall the temperatures for phase transitions
    in iron, and for each case, indicate
    on the graph the temperature range
    over which the diffusion data is valid.
    (c) Why is the activation energy for Fe diffusion
    higher than that for C diffusion
    in iron?
    (d) Why is the activation energy for diffusion
    higher in FCC iron when compared
    to BCC iron?
    (e) Does C diffuse faster in FCC Fe than in
    BCC Fe? Support your answer with a
    numerical calculation and state any
    assumptions made.
     
  2. jcsd
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