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Homework+4+Solutions-+Exam+format_2_ - HOMEWORK 4 Solutions...

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HOMEWORK 4 Solutions PART A. DEFINITIONS/NOMENCLATURE (5 points) 1. Cu dissolved in Ni is an example of a substitutional solid solution. 2. The effective penetration distance of a diffusing species is proportional to Dt . 3. Small cation and anion vacancy clusters that are formed in ionic solids are referred to as Schottky defect. 4. The time dependent change in composition is related to the curvature (look at Fick’s Second law) of the composition versus distance relationship. 5. The movement of atoms in a pure material is termed self-diffusion .
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PART B. CIRCLE THE APPROPRIATE ANSWER (10 points) 1. Fick’s second law defines diffusion that is time dependent . 2. The activation energy for bulk diffusion is higher than the activation energy for grain boundary diffusion. 3. Decreasing temperature decreases the concentration of vacancies. 4. Diffusion along a dislocation has lower activation energy than bulk diffusion. (Note: this question is from Chapter 5 and not covered in this chapter.) 5. Because it is a thermally activated process, diffusivity increases as temperature increases. 6. Frenkel defects involving anions are less common than those involving cations. 7. As temperature decreases, bulk diffusion becomes less important than grain boundary diffusion. 8. Increasing the dislocation density by plastic deformation increases the strength of an alloy. (Note: this question is from Chapter 5 and not covered in this chapter.) 9. Diffusion of C in BCC iron is faster than in FCC iron. 10. Substitutional diffusion has higher activation energy than interstitial diffusion.
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PART C. CONCEPTS PROBLEMS (55 points) 1. (10 points) List Hume-Rothery’s rules and explain how they account for solid solubility of solute in a solvent. Explain how you might modify Hume-Rothery’s
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Homework+4+Solutions-+Exam+format_2_ - HOMEWORK 4 Solutions...

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