Phase diagram (Muda Ibrahim)
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Phase diagram (Muda Ibrahim)

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Phase diagram (Muda Ibrahim) Phase diagram (Muda Ibrahim) Presentation Transcript

  • 2.0) PHASE DIAGRAM
    • LECTURE OUTLINE:
    • Define phase diagram, cooling curve, liquidity and solidification.
    • Connection between cooling curve and phase diagram.
    • Dissolvable alloy system.
    • Pure metals,Gibb’s order, lever order ,dual system and eutectic point.
  • Introduction
    • Many of the engineering materials possess mixtures of phases, e.g. steel, paints, and composites.
    • The mixture of two or more phases may permit interaction between different phases, and results in properties usually are different from the properties of individual phases.
  • Define Phase Diagram
    • An equilibrium state of solid system can be reflected in terms of characteristics of the microstructure, phases present and their compositions, relative phase amounts and their spatial arrangement or distribution.
  • PHASE DIAGRAMS THEORY AND APPLICATIONS
  • Some basic concepts
    • Phase
      • A homogeneous region with distinct structure and physical properties
      • In principle, can be isolated
      • Can be solid, liquid or gas
    • Phase Diagram
      • Representation of phases present under a set of conditions (P, T, Composition etc.)
  • Concepts…...
    • Phase transformation
      • Change from one phase to another
      • E.g. L S, S S etc.
      • Occurs because energy change is negative/goes from high to low energy state
    • Phase boundary
      • Boundary between phases in a phase diagram
  • A simple phase diagram Triple point (Invariant point) Solid Liquid Vapor Pressure Temperature Phase boundary System: H 2 O
  • Gibb’s Phase Rule P + F = C + 2 P=number of phases C=number of components F=number of degrees of freedom (number of independent variables) Modified Gibbs Phase Rule (for incompressible systems) P + F = C + 1 Pressure is a constant variable F = C - P + 2 F = C - P + 1
  • Application of the phase rule At triple point, P=3, C=1, F=0 i.e. this is an invariant point At phase boundary, P=2, C=1, F=1 In each phase, P=1, C=1, F=2
  • Solidification(cooling) curves L S L S Pure metal Alloy T m L S L + S Solidification complete Soldification begins T L T S
  • Construction of a simple phase diagram
    • Conduct an experiment
    • Take 10 metal samples(pure Cu, Cu-10%Ni, Cu-20%Ni, Cu-30%Ni………, pure Ni)
    • Melt each sample and then let it solidify
    • Record the cooling curves
    • Note temperatures at which phase transformations occur
  • Results L S L S t T L L + S T L T S S L L + S T L T S Pure Cu Cu-10%Ni Cu-20%Ni L L S Pure Ni S T Ni T Cu
  • Binary isomorphous phase diagram x x x x x x x x x x x x x x x x x x x x L+S L S Composition Temp T Cu T Ni 10 60 70 80 90 30 40 50 20 0 100 Cu Ni %Ni Cu Ni
  • Microstructural changes during solidification L S L S T t T m L S Pure metal S
  • Microstructural changes during solidification L S Alloy L + S T L T S L S T t
  • L Binary isomorphous phase diagram L+S L S Composition T 10 60 70 80 90 30 40 50 20 0 100 A B %B L L S T 1 T 2 T 3 T 4 C L C 0 C S
  • Notes
    • This is an equilibrium phase diagram (slow cooling)
    • The phase boundary which separates the L from the L+S region is called LIQUIDUS
    • The phase boundary which separates the S from the L+S region is called SOLIDUS
    • The horizontal (isothermal) line drawn at a specific temperature is called the TIE LINE
    • The tie line can be meaningfully drawn only in a two-phase region
    • The average composition of the alloy is C O
  • Notes…..
    • The intersection of the tie line with the liquidus gives the composition of the liquid, C L
    • The intersection of the tie line with the solidus gives the composition of the solid, C S
    • By simple mass balance,
    • C O = f S C S + f L C L
    • and f S + f L = 1
    • C O = f S C S + (1- f S ) C L
    Lever Rule
  • Some calculations
    • In our diagram at T 3 , C O = A-40%B,
    • C S =A-90%B and C L =A-11%B
    • Therefore, f S =29/79 or 37% and
    • f L =50/79 or 63%
    • If we take an initial amount of alloy =100 g,
    • amt. of solid=37 g (3.7 g of A and 33.4 g of B) and amt. of liquid=63 g (56.07 g of A and 6.93 g of B)
  • The Eutectic Phase Diagram T A B Wt%B L  +L  +L  +  E T E C E   Liquidus Solidus Solvus L  +  T E , C L =C E 
  • T A B Wt%B L  +L  +L  +  E T E C E   Pure A or B Other alloys between A and B C E L S L  +  L  +  L L L+  L  +   + 
  • T A B Wt%B L  +L  +L  +  E T E C E   Solidification for alloy of eutectic composition L S  +   + 
  • Eutectic microstructure Lamellar structure
  • T A B Wt%B L  +L  +L  +  T E C E   L Proeutectic   +   + 
  • L T A B Wt%B L  +L  +L  +  T E C E   L   particles
  • The Eutectoid Phase Diagram T A B Wt%B   +   +   +  E T E C E     +  T E , C  =C E 
  •  T A B Wt%B   +   +   +  E T E C E   Cooling of an alloy of eutectoid composition S  +   +  
  •  T A B Wt%B   +   +   +  E T E   Cooling of an alloy of hypoeutectoid composition S  +   +    Pro-eutectiod  Pro-eutectiod 
  • The Peritectic Phase Diagram T A B Wt%B L  + L  + L  +  P T P C P    L  at T P  N M Note:  and L will react only in a certain proportion= NP:PM L L  
  • T A B Wt%B L  + L  + L  +  P T P C P    L  at T P  N M Note:  and L will react only in a certain proportion= NP:PM 10 25 85 NP:PM=1:2 60 L L  L  
  • T A B Wt%B L  + L  + L  +  P T P C P    L  at T P  N M Note:  and L will react only in a certain proportion= NP:PM L L  L  
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