Louisiana State University Mechanical Engineering Department Professor Meletis ME 2733 Fall 2004 Materials of Engineering Homework Assignment #4 (due: in class Wednesday, October 13, 2004) 1. The free energy of vacancy formation for Ni is 1.2 eV. (a) Calculate the equilibrium concentration of vacancies at 400oC. (b) What is the maximum concentration of vacancies that can exist in solid Ni? 2.The diffusivity of Cu in a commercial brass alloy is 10-20m2/s at 400oC. The activation energy for diffusion of Cu in this system is 195 kJ/mol. Calculate the diffusivity at 500oC. 3. A thick low carbon steel plate (initial composition 0.1 wt% C) is heated to 1000°C in a carbonaceous atmosphere (CH4) to be carburized (hardened by diffusing C). The carburization conditions keep the carbon surface concentration constant at 0.8% C (assume that only one
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