lecture 8 - ME 330 Engineering Materials Lecture 8...

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Lecture 8 Diffusion and Solidification Stephen D. Downing Mechanical Science and Engineering © 2001 - 2010 University of Illinois Board of Trustees, All Rights Reserved ME 330 Engineering Materials
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 1 of 41 This Lecture . .. ± Annealing ± Diffusion ± Casting ± Solidification ± Nucleation ± Propagation
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 2 of 41 Next Lecture . .. ± Solidification ± Phase Diagram Definitions ± Eutectic Phase Diagram ± Liquidus/Solidus ± Solidification microstructures ± Invariant Points ± Intermediate compounds ± Ternary Phase Diagram
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 3 of 41 Lab 3: Cold Work and Annealing
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 4 of 41 Lab 3: Cold Work and Annealing
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 5 of 41 Lab 3: Cold Work and Annealing ± Read the lab manual ± Quiz is likely
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 6 of 41 Strengthening Mechanisms ± Eliminate dislocations ± No mechanism for plastic deformation in metals ± Whiskers and fibers ± Eliminate dislocation movement ± If they can’t move, they can’t carry plastic deformation ± Introduce barriers to movement ± Grain boundaries ± Solid-solution strengthening (alloying) ± Precipitates can pin dislocations ± Increase dislocation density ± Grain boundaries ± Solutes cause multiplication ± Strain hardening ± Cold work
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 7 of 41 “Whiskers” ± Extremely small, thin, defect free ± No dislocations to carry plastic deformation ± Usually metallic or ceramic d L >> m d μ ± Single crystal, may be grown around screw dislocation ± Applications primarily in composites
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 8 of 41 Grain Boundary Strengthening Slip Plane grain2 Grain Boundary Slip Plane grain1 ± Remember: Dislocation motion impeded at grain boundaries ± Dislocation has to change slip planes in different grains ± Boundaries posses atomic scale disorder - pins dislocation ± Smaller grains provide more barriers to dislocation motion - stronger, tougher σ σ τ τ
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ME 330 - Lecture 8 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 9 of 41 Solid Solution Strengthening Interstitial Solute ± Interstitials and solutes distort the lattice ± Introduce lattice strains ± Solutes diffuse toward dislocations ± Stress fields interact with dislocations ± Lattice strains increase if dislocations
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lecture 8 - ME 330 Engineering Materials Lecture 8...

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