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E45 - Lab 3 - Recovery Recrystallization Regrowth

E45 - Lab 3 - Recovery Recrystallization Regrowth -...

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E E n n g g i i n n e e e e r r i i n n g g 4 4 5 5 P P r r o o p p e e r r t t i i e e s s o o f f M M a a t t e e r r i i a a l l s s L L a a b b o o r r a a t t o o r r y y © Copyright 2001 Professor Ronald Gronsky the Arthur C. and Phyllis G. Oppenheimer Chair in Advanced Materials Analysis Department of Materials Science & Engineering University of California Berkeley, California 94720-1760
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E 45 2 Lab 3 Recovery, Recrystallization, And Grain Growth Objective To understand in detail the microstructural changes occurring during the three stages of annealing Background When a material is deformed plastically, the dislocation density of the material increases with the amount of deformation. Since each dislocation has a finite strain energy associated with it, the total free energy of the system increases with the number of dislocations. Because the system always tends towards minimizing its free energy, it will attempt to decrease its strain energy by either rearranging its dislocations into a more favorable configuration with a lower strain energy, and/or nucleating undeformed strain-free grains. Although thermodynamically it is advantageous for the deformed (“work-hardened”) system to be in an undeformed state, the rate of transformation is limited by the kinetics of the system, which governs the rate of change. At low temperatures the kinetics of the system is so slow that no change can be detected. However, at high temperatures many changes in the system can be directly observed. In this lab the processes of recovery, recrystallization, and grain growth will be investigated. After a material has been work hardened, the material can be softened at low temperature by recovery , a process wherein the dislocations are arranged into configurations with lower strain energy. At higher temperatures the material can be rapidly softened by
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