lecture 9 - ME 330 Engineering Materials Lecture 9...

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Lecture 9 Solidification and Phase Diagrams 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 9 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 1 of 31 This 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 9 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 2 of 31 Example Problem Consider a single crystal of silver oriented such that a tensile stress is applied along a [001] direction. If slip occurs on a (111) plane and in a [101] direction, and is initiated at an applied tensile stress of 1.1 MPa (160 psi), compute the critical resolved shear stress.
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ME 330 - Lecture 9 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 3 of 31 Example Problem Two previously undeformed specimens of the same metal are to be plastically deformed by reducing their cross-sectional areas. One has a circular cross section, and the other is rectangular; during deformation the circular cross section is to remain circular, and the rectangular is to remain as such. Their original and deformed dimensions are as follows: 13.7x55.1 15.9 Deformed dimensions 20x50 18.0 Original dimensions Rectangular (mm) Circular (diameter,mm) Which of the specimens will be the hardest after plastic deformation, and why?
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ME 330 - Lecture 9 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 4 of 31 Development of Microstructure ± Begin with molten metal ± Remove heat (lower temperature) ± Solid metal forms ± Nucleation ± Need to overcome energy barrier to initiate nucleation ± Usually large number of nucleation sites ± Growth ± Competitive - multiple nucleation sites fight for remaining liquid ± Certain growth directions are preferred
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ME 330 - Lecture 9 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 5 of 31 Controlling Microstructure (Nucleation) ± Heterogeneous Nucleation ± “Grain refiners” promote nucleation ± Add solid second phase which act as nucleation sites ± Change alloy which changes melting temperature from pure metal ± Decrease the critical nucleation size more nucleation sites ± Mold walls also can act as nucleation sites ± Mold vibration ± Break off dendrites ± Broken dendrites act as nucleation sites ± Heat mold ± Suppress chill zone at wall ± Superheat molten metal
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ME 330 - Lecture 9 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 6 of 31 Terminology ± System : For our purposes, alloy under consideration ± Fe/C or Pb/Sn ± Component : Pure elements of which an alloy is composed ± Fe or C, Pb or Sn ± Solute : Component of solution being dissolved ± Solvent : Component of solution in greatest amount ± Solubility
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lecture 9 - ME 330 Engineering Materials Lecture 9...

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