ENGR 240 - 10.24.07

ENGR 240 - 10.24.07 - ENGR 240 October 24, 2007 Hall-Petch...

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ENGR 240 – October 24, 2007 Hall-Petch Equation o Relates σ y and grain size o σ y = σ 0 + kd -1/2 σ 0 and k are material specific constants d is the average grain size (diameter) o Brass 70% Cu, 30% Zn graph shown to the right as the yield strength decreases d decreases on a log scale Precipitation Hardening (Age Hardening) o Formation of small uniformly dispersed particles of a second phase within a parent/first phase o Effect on strength is related to the spacing between the precipitates o τ (shear strength) α 1/ℓ ℓ is the space separating precipitates smaller ℓ larger τ harder material o 3 steps Solutionize Form a solid solution by adding heat Dissolving all impurity atoms or alloying metals Example: Al-Cu solutionize Cu dissolved Al remains Quench Cool the material very quickly “Freezes” the high temperature solid solution in its current state Copper does not have time to diffuse out At room temperature, diffusion is so slow that copper does
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This note was uploaded on 04/07/2008 for the course ENGR 240 taught by Professor Gross during the Fall '07 term at Bucknell.

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ENGR 240 - 10.24.07 - ENGR 240 October 24, 2007 Hall-Petch...

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