03E45 Recovery Recrystallization Regrowth Lab Report

03E45 Recovery Recrystallization Regrowth Lab Report - E45...

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Image 1: Work-hardening diagram for bar Image 2: Apparatus setup Image 3: Rockwell hardness test sites E45 Lab Report (March 3, 2008) Norbert Wang Recovery, Recrystallization, and Regrowth Abstract Hardness of a material usually correlates directly with its strength, which is a prime concern for engineers when making products that will be under a lot of stress and strain. The main focus of this lab was to explore the relationship of hardness with two types of annealing: “cold working” and heating. The “cold work” will be in terms of rolling a brass bar of varying thickness to a constant thickness. Thus a gradient of “cold work” will be established along one axis of the bar. A heat gradient will be applied to the other axis. Rockwell A tests will be conducted along each axis to measure hardness of a brass bar as a function of “cold work” and heat. As the local temperature of the bar increased, the material becomes softer. As more work is applied to a material, its hardness will increase. Introduction Plastic deformation increases the local dislocation density of material. This deformation can come in the form of rolling the material to a thinner thickness. Dislocations have an associated free energy. Whenever there’s free energy involved, the system will always try to minimize its free energy as much as possible. To achieve this it must undergo reconfiguration of dislocations into a lower energy state or it can create new grains free of strain. Cold work is an example of plastic deformation due to force only. The reason it is called “cold” is because no external heat is applied. The material is merely smashed or bent at constant temperature. “Cold working” a material to new shapes causes a lot of dislocations and raises the energy of the material. The system is highly stressed but it cannot lower its free energy without the help of energy input. Energy input can usually come in the form of heat. Heating a highly dislocated material causes it to go through three transformations: recovery, recrystallization, and regrowth. Recovery refers to early rearrangements of dislocations to lower the free
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energy of the system. Recrystallization begins when enough heat is applied. It will essentially purge the material of dislocations. After more heat is added, new strain-free grains will start to nucleate, contributing to the regrowth transformation. Grain boundaries will start to disappear as more heat is applied and soon merge into large grains with no strain. The amount of heat applied will ultimately determine how far into this 3 stage process the material will go. Each stage requires a certain minimal amount of energy to activate. The mechanical property of hardness will be measured in this lab. Hardness has a distinct relationship
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This note was uploaded on 01/21/2010 for the course ENGIN 45 taught by Professor Devine during the Fall '07 term at Berkeley.

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03E45 Recovery Recrystallization Regrowth Lab Report - E45...

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