Chapter 10.4

Chapter 10.4 - Rate of phase transformations Total rate of...

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16 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Rate of phase transformations m T temperature nucleation rate Total rate of a phase transformation induced by cooling is a product of the nucleation rate and growth rate (diffusion controlled - slows down with T decrease). overall transformation rate growth rate high T (close to T m ): low nucleation and high growth rates Æ coarse microstructure with large grains low T (strong undercooling): high nucleation and low growth rates Æ fine structure with small grains
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17 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Example of solidification under conditions of extreme undercooling Localized excitation of a metal film by a short laser pulse results in very steep temperature gradients, fast heat conduction and extreme cooling rates exceeding 10 12 K/ s Æ deep undercooling of the melt Æ high nucleation rate Æ nanocrystalline structure of the surface feature generated by the laser pulse
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Chapter 10.4 - Rate of phase transformations Total rate of...

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