Chapter 10.5

Chapter 10.5 - Superheating / supercooling Upon crossing a...

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21 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Superheating / supercooling ¾ Upon crossing a phase boundary on the composition- temperature phase diagram, phase transformation towards equilibrium state is induced. ¾ But the nucleation and growth of the equilibrium structure takes time and the transformation is delayed. ¾ During cooling, transformations occur at temperatures less than predicted by phase diagram: supercooling. ¾ During heating, transformations occur at temperatures greater than predicted by phase diagram: superheating. ¾ Degree of supercooling/superheating increases with rate of cooling/heating. ¾ Metastable states can be formed as a result of fast temperature change. Microstructure is strongly affected by the rate of cooling. ¾ Below we will consider the effect of time on phase transformations using iron-carbon alloy as an example.
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Let us consider eutectoid reaction as an example eutectoid reaction: γ (0.76 wt% C) α (0.022 wt% C) + Fe 3 C
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This note was uploaded on 02/14/2012 for the course MSE 2090 taught by Professor Leoindzhiglei during the Fall '10 term at UVA.

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Chapter 10.5 - Superheating / supercooling Upon crossing a...

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