Phase diagram (Muda Ibrahim)

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Phase diagram (Muda Ibrahim)

  1. 1. 2.0) PHASE DIAGRAM <ul><li>LECTURE OUTLINE: </li></ul><ul><li>Define phase diagram, cooling curve, liquidity and solidification. </li></ul><ul><li>Connection between cooling curve and phase diagram. </li></ul><ul><li>Dissolvable alloy system. </li></ul><ul><li>Pure metals,Gibb’s order, lever order ,dual system and eutectic point. </li></ul>
  2. 2. Introduction <ul><li>Many of the engineering materials possess mixtures of phases, e.g. steel, paints, and composites. </li></ul><ul><li>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. </li></ul>
  3. 3. Define Phase Diagram <ul><li>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. </li></ul>
  4. 4. PHASE DIAGRAMS THEORY AND APPLICATIONS
  5. 5. Some basic concepts <ul><li>Phase </li></ul><ul><ul><li>A homogeneous region with distinct structure and physical properties </li></ul></ul><ul><ul><li>In principle, can be isolated </li></ul></ul><ul><ul><li>Can be solid, liquid or gas </li></ul></ul><ul><li>Phase Diagram </li></ul><ul><ul><li>Representation of phases present under a set of conditions (P, T, Composition etc.) </li></ul></ul>
  6. 6. Concepts…... <ul><li>Phase transformation </li></ul><ul><ul><li>Change from one phase to another </li></ul></ul><ul><ul><li>E.g. L S, S S etc. </li></ul></ul><ul><ul><li>Occurs because energy change is negative/goes from high to low energy state </li></ul></ul><ul><li>Phase boundary </li></ul><ul><ul><li>Boundary between phases in a phase diagram </li></ul></ul>
  7. 7. A simple phase diagram Triple point (Invariant point) Solid Liquid Vapor Pressure Temperature Phase boundary System: H 2 O
  8. 8. 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
  9. 9. 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
  10. 10. Solidification(cooling) curves L S L S Pure metal Alloy T m L S L + S Solidification complete Soldification begins T L T S
  11. 11. Construction of a simple phase diagram <ul><li>Conduct an experiment </li></ul><ul><li>Take 10 metal samples(pure Cu, Cu-10%Ni, Cu-20%Ni, Cu-30%Ni………, pure Ni) </li></ul><ul><li>Melt each sample and then let it solidify </li></ul><ul><li>Record the cooling curves </li></ul><ul><li>Note temperatures at which phase transformations occur </li></ul>
  12. 12. 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
  13. 13. 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
  14. 14. Microstructural changes during solidification L S L S T t T m L S Pure metal S
  15. 15. Microstructural changes during solidification L S Alloy L + S T L T S L S T t
  16. 16. 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
  17. 17. Notes <ul><li>This is an equilibrium phase diagram (slow cooling) </li></ul><ul><li>The phase boundary which separates the L from the L+S region is called LIQUIDUS </li></ul><ul><li>The phase boundary which separates the S from the L+S region is called SOLIDUS </li></ul><ul><li>The horizontal (isothermal) line drawn at a specific temperature is called the TIE LINE </li></ul><ul><li>The tie line can be meaningfully drawn only in a two-phase region </li></ul><ul><li>The average composition of the alloy is C O </li></ul>
  18. 18. Notes….. <ul><li>The intersection of the tie line with the liquidus gives the composition of the liquid, C L </li></ul><ul><li>The intersection of the tie line with the solidus gives the composition of the solid, C S </li></ul><ul><li>By simple mass balance, </li></ul><ul><li> C O = f S C S + f L C L </li></ul><ul><li>and f S + f L = 1 </li></ul><ul><li> C O = f S C S + (1- f S ) C L </li></ul>Lever Rule
  19. 19. Some calculations <ul><li>In our diagram at T 3 , C O = A-40%B, </li></ul><ul><li>C S =A-90%B and C L =A-11%B </li></ul><ul><li>Therefore, f S =29/79 or 37% and </li></ul><ul><li>f L =50/79 or 63% </li></ul><ul><li>If we take an initial amount of alloy =100 g, </li></ul><ul><li>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) </li></ul>
  20. 20. 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 
  21. 21. 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  +   + 
  22. 22. T A B Wt%B L  +L  +L  +  E T E C E   Solidification for alloy of eutectic composition L S  +   + 
  23. 23. Eutectic microstructure Lamellar structure
  24. 24. T A B Wt%B L  +L  +L  +  T E C E   L Proeutectic   +   + 
  25. 25. L T A B Wt%B L  +L  +L  +  T E C E   L   particles
  26. 26. The Eutectoid Phase Diagram T A B Wt%B   +   +   +  E T E C E     +  T E , C  =C E 
  27. 27.  T A B Wt%B   +   +   +  E T E C E   Cooling of an alloy of eutectoid composition S  +   +  
  28. 28.  T A B Wt%B   +   +   +  E T E   Cooling of an alloy of hypoeutectoid composition S  +   +    Pro-eutectiod  Pro-eutectiod 
  29. 29. 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  
  30. 30. 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  
  31. 31. 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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