Engineering 45 Lab 3 - Engineering 45 Lab 3: Recovery,...

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Engineering 45 Lab 3: Recovery, Recrystallization, and Grain Growth Introduction to Mechanical Properties Lab Section 103 Riti Gupta Partner: Lena Luu GSI: Matt Sherburne 10/14/09 1
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Introduction : Annealing is when a material is heated and altered, causing changes in its properties such as strength and hardness. This treatment is used to induce ductility, relieve internal stress, and improve mechanical properties such as cold work. The purpose of this lab was to understand the microstructural changes that occur during each stage of annealing. These three stages are recovery, recrystallization, and grain growth. After a material has been hardened by cold work, which strengthens the material through plastic deformation, the material can be softened through a process called recovery, where the dislocations formed by heating can be arranged in such a way to have less strain energy. Recovery removes crystal defects and the internal stress these defects cause. After recovery comes recrystallization. In this stage, new, strain-free, grains nucleate and grow to replace those that were deformed due to internal stresses. This process eliminates most of the dislocations in the material, and the end of this stage is when all the deformed grains are replaced. Yet, although all the dislocations are taken out, there is still a very high “surface energy” that surrounds the new grains. In order to get rid of this energy and decrease the free energy of the material even further, grain growth needs to take place. This is when the microstructure of the material starts to get harder and coarsen, and large grains overtake smaller grains. However, this process might result in unsatisfactory mechanical properties. Procedure : First, a brass specimen that was seventy percent copper and thirty percent zinc (and reduced by a fifty percent reduction of thickness by cold rolling) was hung from a nichrome wire 2
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into the furnace and about one eighth inch into a bowl of water. A thermocouple was inserted
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This note was uploaded on 12/01/2009 for the course ENGIN 45 taught by Professor Devine during the Fall '07 term at University of California, Berkeley.

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Engineering 45 Lab 3 - Engineering 45 Lab 3: Recovery,...

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