E4511ps8-txt - Engineering 45 The Structure and Properties...

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Page 1 Engineering 45 The Structure and Properties of Materials Spring, 2011 Problem Set No. 8 Problem 1: (a) Carbon is an interstitial specie in BCC iron that has an activation energy for diffusion of about 1 eV (the value of kT a ~ 10 4 K) and a pre-exponential factor (D 0 ) of about 10 -2 cm 2 /sec. A sample of iron is cast and cooled to form BCC, and is found to have an inhomogeneous distribution of carbon with a scale of about 1 micron. Roughly how long would it take for the carbon distribution to homogenize at room temperature (273 K)? At 500 o C (773 K)? (b) If the temperature is high or the iron is highly alloyed with Ni it has the FCC structure. The activation energy for diffusion of Ni in iron is about 2.3 eV, and the pre- exponential factor is about 0.5 cm 2 /sec. Assuming that a sample is cast with a Ni inhomogeneity on a scale of about 1 micron, roughly how long would the sample have to be heated and held (annealed) at 1000 o C to achieve homogenization? (c) I was once shown a sample of a meteorite that astronomers estimated had a
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This note was uploaded on 04/05/2011 for the course ENGIN 45 taught by Professor Devine during the Spring '07 term at University of California, Berkeley.

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E4511ps8-txt - Engineering 45 The Structure and Properties...

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