7.9 - A plastically deformed crystal lattice has high...

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Strengthening Mechanisms Anything that acts to restrict or hinder slip (dislocation motion) renders a material harder and stronger. The price is usually ductility. What can act as “obstacles to slip”? 1. grain boundaries (at low temperatures) 2. impurity atoms (and the strain fields around them) 3. dislocations So three common strengthening mechanisms are: 1. Grain Refinement Finer grained materials have more grain boundaries per unit volume. Grain size can be regulated by the rate of solidification or by plastic deformation followed by an appropriate heat treatment. Faster cooling during solidification will result in a finer grain structure.
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Unformatted text preview: A plastically deformed crystal lattice has high energy. This high energy lattice provides more nucleation sites during recrystallization. Hence more grains start to grow which results in a fine grained structure after recrystallization. 2. Solid solution strengthening (solution hardening) Impurity atoms are added in such a way as to maximize their effectiveness to act as an obstacle to slip. 3. Cold working (strain hardening or work hardening) Plastic deformation will increase the dislocation density, change the grain shape and increase the strain energy of the crystal lattice....
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This note was uploaded on 08/10/2009 for the course ENGN 45 taught by Professor Wendy during the Spring '09 term at City College of San Francisco.

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