Chapter 5: Problem 2
Self-diffusion involves the motion of atoms that are all of the same type; therefore it is not subject to observation by compositional changes, as with inter-diffusion. Suggest one way in which self-diffusion may be monitored.
Chapter 5: Problem 2
Self-diffusion involves the motion of atoms that are all of the same type; therefore it is not subject to observation by compositional changes, as with inter-diffusion. Suggest one way in which self-diffusion may be monitored.
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Get started for free(a) Compare interstitial and vacancy atomic mechanisms for diffusion. (b) Cite two reasons why interstitial diffusion is normally more rapid than vacancy diffusion.
An FCC iron-carbon alloy initially containing 0.55 wt \(\%\) C is exposed to an oxygen-rich and virtually carbon-free atmosphere at \(1325 \mathrm{K}\) \(\left(1052^{\circ} \mathrm{C}\right) .\) Under these circumstances the carbon diffuses from the alloy and reacts at the surface with the oxygen in the atmosphere that is, the carbon concentration at the surface position is maintained essentially at 0 wt \(\%\) C. (This process of carbon depletion is termed decarburization.) At what position will the carbon concentration be 0.25 wt\% after a 10-h treatment? The value of \(D\) at \(1325 \mathrm{K}\) is \(4.3 \times 10^{-11} \mathrm{m}^{2} / \mathrm{s}\).
(a) Briefly explain the concept of a driving force. (b) What is the driving force for steady-state diffusion?
At approximately what temperature would a specimen of \(\gamma\) -iron have to be carburized for \(4 \mathrm{h}\) to produce the same diffusion result as at \(1000^{\circ} \mathrm{C}\) for \(12 \mathrm{h} ?\)
The diffusion coefficients for nickel in iron are given at two temperatures: $$\begin{array}{cc} \boldsymbol{T}(\boldsymbol{K}) & \boldsymbol{D}\left(\boldsymbol{m}^{2} / \boldsymbol{s}\right) \\ \hline 1473 & 2.2 \times 10^{-15} \\ 1673 & 4.8 \times 10^{-14} \end{array}$$ (a) Determine the values of \(D_{0}\) and the activation energy \(Q_{d}\) (b) What is the magnitude of \(D\) at \(1300^{\circ} \mathrm{C}\) \((1573 \mathrm{K}) ?\)
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