Quiz7spring2004 - ENSC 3313, Spring 2004 Quiz 7 ANSWERS...

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ENSC 3313, Spring 2004 Quiz 7 ANSWERS Name ________________________________ Answer any 4 questions only , 1 point each 1. An OU grad prepared the micrograph of an Mg/Sn alloy shown below. However, he could not remember the composition. Please explain to this hapless Normanite why only one choice is possible. The micrograph shows an intimate two phase structure which indicates a eutectic composition. Since the phases are in near equal proportions, the eutectic at 37.6% Sn is the only possibility. 2. A phase transformation requires two steps: 1) nucleation and 2) growth. Why can undercooling increase the rate of phase transformation? Nucleation requires that the volumetric free energy advantage G v overcomes the surface energy price associated with forming a second phase. Surface energy remains largely unchanged with T, but the magnitude of G v increases with the amount of undercooling. The result is a reduced critical nucleus size (hence, an increased nucleation rate) and an overall increase in the rate of phase transformation. v
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This note was uploaded on 01/10/2012 for the course ENSC 3313 taught by Professor Staff during the Fall '11 term at Oklahoma State.

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Quiz7spring2004 - ENSC 3313, Spring 2004 Quiz 7 ANSWERS...

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