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# Phase diagram (Muda Ibrahim)

## on Jul 05, 2011

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## 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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