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HW5Solutions - MSE280 Introduction to Engineering Materials...

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MSE280: Introduction to Engineering Materials Homework 5: Solutions 1. (8 points) The two factors that contribute to the activation energy for substitutional diffusion are the energies required to break bonds and distort the lattice. Both bond breaking and lattice distortion are needed to initiate diffusion. 2. Problem 6.2b from Callister (8 points) Interstitial diffusion is normally more rapid than vacancy diffusion because: (1) interstitial atoms, being smaller, are more mobile; and (2) the probability of an empty adjacent interstitial site is greater than for a vacancy adjacent to a host (or substitutional impurity) atom. Problem 6.5 from Callister (8 points) Let us first convert the carbon concentrations from weight percent to kilograms carbon per meter cubed using Equation 5.12a. For 0.015 wt% C C C " = C C C C ρ C + C Fe ρ Fe × 10 3 = 0.015 0.015 2.25 g /cm 3 + 99.985 7.87 g /cm 3 × 10 3 1.18 kg C/m 3 Similarly, for 0.0068 wt% C C C " = 0.0068 0.0068 2.25 g /cm 3 + 99.9932 7.87 g /cm 3 × 10 3 = 0.535 kg C/m 3 Now, using a rearranged form of Equation 6.3
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