MSE_2610_HW_8_solutions - MSE 2610 Introduction to the...

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MSE 2610 Introduction to the Mechanical Properties of Materials Fall 2008 Homework Assignment #8 Due: 13 November 2008 1.) Answer the following about recrystallization: a. What is the driving force for recrystallization? The driving force for recrystallization is the reduction of dislocation energy. Recrystallization nucleates new, dislocation free grains. This reduces the dislocation density in the material and the dislocation energy. b. What atomistic mechanism is required for recrystallization? What external variables are important to controlling recrystallization? Diffusion is required for recrystallization. It is for the atoms to rearrange to nucleate and grow stress free grains. Diffusion in recrystallization is controlled by temperature and time. While not specifically tied to diffusion, the driving force for recrystallization is the dislocation energy. The dislocation density can be controlled externally by cold work, usually expressed as a percent reduction in area. c. What is the driving force for grain growth? The driving force for grain growth is the reduction of interface energy. Larger grains have lower d. What is the motivation for doing a recrystallization process? Recrystallization is done primarily for one of two reasons. The first reason is that the heavily cold-worked material is not the proper shape and requires more rolling, drawing, or pressing. Without recrystallization, the material would not plastically deform and would fracture. Recrystallization reduces dislocation density and allows further plastic deformation. Another possible reason for recrystallization is to control grain size. Cold work and recrystallization is a pathway to create a particular grain size and tune the mechanical properties of a materials. 2.) You perform a series of creep experiments on an aluminum alloy at various temperatures and applied stresses. Your first experiment gives you strain as a function of time at 400ºC and a constant stress of 25 MPa. Time (min) Strain Time (min) Strain 0 0.000 16 0.135 2 0.025 18 0.153 4 0.043 20 0.172 6 0.065 22 0.193 8 0.078 24 0.218 10 0.092 26 0.255 12 0.109 28 0.307 14 0.120 30 0.368
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You perform similar experiments to find the steady state strain rate by holding the stress constant at 25MPa and varying the temperature and also by holding the temperature
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MSE_2610_HW_8_solutions - MSE 2610 Introduction to the...

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