Question

4. a.) Sketch the strength versus aging time for a typical ppt strengthened aluminum alloy for two temperatures (T1 and T2 with T1 > T2). b.) Define overaging and show the region where overaging occurs on one of the curves from part a. 5. a.). Describe the vacancy mechanism for solid state diffusion. b.) Describe the interstitial mechanism for solid state diffusion. c.) Which mechanism would you expect for: i.) diffusion of boron (B) in nickel (Ni)? Explain. li.) diffusion of chromium (Cr) in iron (Fe)? Explain. 6. Given the following data set for the diffusion of iron in cobalt: T(C) 500 700 900 1100 1200 Dm-/s) 8.81 x 10-20 2.88 x 10-15 5.96 x 10-17 2.61 x 10-15 1.17 x 10-14 a.) Calculate the values for the activation energy for diffusion, Qo, and the pre- exponential constant, D. (Note: use all of the data, not just two pairs). b.) What will the diffusion rate, D, be at 1500°C? 7. A process to grow a 100 um thick wear resistant layer on the surface of a plate is completed in 1 hr (3600 s). Assuming that the process is controlled by diffusion through the product layer: a.) If the layer thickness is to be increased to 500 um, how long will the process take (in hrs and s). b.) If the temperature is increased to a temperature where the diffusion rate is increased by a factor of 10 (D2 = 10 Di), how long will it take to grow the 100 um thick layer (in hrs and s). 8. Given Qp = 76,150 J/mol and D. = 3.0 x 10 m/s. A diffusion-controlled phase transformation requires approximately 100 hrs to complete at 300°C. a.) What T in °C) would be required to complete the transformation in 1 hr? b.) What T (in °C) would be required to complete the transformation in 0.01 hr? c. How long would it take to complete the transformation at RT (20°C)? Give your answer in hrs and years)

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Answer 1

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