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Homework 6

# Homework 6 - 3 How far into the sheet from this...

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ENMA 300/ENME 382 Homework 6 Due: Monday Oct. 24, 2011 1a) How can you distinguish between steady state and non-steady state diffusion? b) What is the driving force for steady state diffusion? c) What is the difference between self diffusion and interdiffusion? 2a) When would you expect a vacancy diffusion mechanism? b) When would you expect an interstitial diffusion mechanism? c) Briefly describe one situation where diffusion is beneficial. d) Briefly describe one situation where diffusion is problematic. 3a) A sheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200°C and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6x10 -11 m 2 /s and the diffusion flux is found to be 1.2 x 10 -7 kg/m 2 s. Also, it is known that the concentration of nitrogen in the steel on the high pressure side is 4 kg/m
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Unformatted text preview: 3 . How far into the sheet from this high-pressure side will the concentration be 2.0 kg/m 3 ? Assume a linear concentration profile. b) By what mechanism will the nitrogen diffuse? Why? 4) Callister 6.6 Determine the carburizing time necessary to achieve a carbon concentration of 0.30 wt% at a position 4 mm into an iron–carbon alloy that initially contains 0.10 wt% C. The surface concentration is to be maintained at 0.90 wt% C, and the treatment is to be conducted at 1100°C. Use the diffusion data for γ-Fe in Table 6.2. 5) Callister 6.12 The diffusion coefficients for carbon in nickel are given at two temperatures: T (°C) D (m 2 /s) 600 5.5 × 10 –14 700 3.9 × 10 –13 (a) Determine the values of D and Q d . (b) What is the magnitude of D at 850°C?...
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