Homework 5 -solutions

# Homework 5 -solutions - MAT33Fall2008Homework#5Solutions...

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Homework #5 - Solutions Due: 10/06/08 1.) The diffusion coefficient of Ni in an austenitic stainless steel is 10 -22 m 2 /s at 500 o C and 10 -15 m 2 /s at 1000 o C. From this information, calculate the activation energy (in kJ/mol) for the diffusion of nickel in this alloy. D (m 2 /s) T (K) 10 -22 773 10 -15 1273 Using D = D o exp - Q d RT we set up two simultaneous equations with Q d and D o as unknowns. Solving for Q d and eliminating D o in terms of temperatures T 1 and T 2 and D 1 and D 2 we get Q d = - R ln D 1 - ln D 2 1 T 1 - 1 T 2 = - 8.31J/mol-K [ ln 10 -22 - ln10 -15 ] [1/773 – 1/1273] = 263,000 J/mol = 263 kJ/mol 2.) For the diffusion data given below, answer the following questions; a.) Which process has the higher activation energy: i.) the diffusion of C in BCC Fe or ii.) the diffusion of Fe in BCC Fe. What is the graphical basis of your argument? b.) From the limited data here would you expect that the grain boundaries in a polycrystal constitute overall a faster or a slower diffusive path? Why? c.) What is the activation energy for the diffusion of Cu in Cu?

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## This note was uploaded on 02/10/2009 for the course MAT 33 taught by Professor Keith during the Spring '07 term at Lehigh University .

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Homework 5 -solutions - MAT33Fall2008Homework#5Solutions...

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