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Phase Diagrams

melting / production process / alloying (strength, T m ...) heat treatment. material properties. microstructure. system (e.g. Cu-Ni). components (pure substances or compounds). phases (uniform physical/chemical characteristic). solid solution – solvent + solute

kennethewilliams
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Phase Diagrams

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  1. melting / production process / alloying (strength, Tm...) heat treatment material properties microstructure system (e.g. Cu-Ni) components (pure substances or compounds) phases (uniform physical/chemical characteristic) solid solution – solvent + solute solubility limit=> precipitation pure materials – 2 phases: liquid + solid Phase Diagrams

  2. Phase Equilibria G=min =min G=H-TS Gibbs free energy: =f(T,c,p) entropy (disorder of molecules entropy of mixing) internal energy (bonding enthalpy) metastable stable

  3. melting point Tm Phase Equilibrium phase composition <=> G minimization

  4. Ni Cu Cu-x%Ni Phase Diagram (p=const)isomorphous phase composition =f (T,c) liquid phase Gibbs phase rule F=K-P+2 (F degrees of freedom depends on number of components K and number of phases P) liquid+solid phase solid phase

  5. Equilibrium Cooling first solid nuclei two-phase solidification polycrystalline solid Cu %Ni

  6. Amounts W WSolid=Wa: length of tie line from CL to Co divided by length of tie line 100% liquid tie line Phase Composition %Ni

  7. segregation Non-Equilibrium Cooling first solid nuclei concentration changes in solid AND liquid phase required!! by diffusion Ni concentration in solid nuclei remains high: low Dsolid

  8. steady state diffusion Diffusion flux

  9. solution (c(0)=0): Non-Steady-State DiffusionFicks‘s 2nd Law diffusion coefficient:

  10. a and b solid solution solid phase limited solubility eutectic reaction a(18.3%Sn) +b (97.8%Sn ) Binary Eutectic Phase Diagrams (Pb-Sn) liquid phase %Sn Pb

  11. Lamellar Eutectic Microstructure Tm, similar to pure components, but: two phases!!

  12. Sub-Eutectic Microstructure lead-rich a phase eutectic: white b dark a

  13. Microstructural Examination - Metallography preparation of cross section -cutting -grinding (SiC paper)-polishing (e.g. 1µm diamond suspension) -etching (selective chemical attack of grains/grain boundaries) optical microscopy electron microscopy (transmission (TEM) or scanning (SEM))

  14. Metallography (SEM) detector electron beam secondary electrons specimen

  15. Binary Eutectic Phase Diagrams a phase solvus line: precipitation of b phase Pb %Sn

  16. CaZr4O9 Intermetallic Phases/Compounds(e.g. ceramics)

  17. peritectic subsystem Fe3C precipitation eutectoid subsystem ferrite precipitation Steel Cast Iron The Iron-Carbon Phase Diagram eutectic system bcc d ferrite fcc g austenite bcc a ferrite cementite Fe3C

  18. Hypoeutectoid Steels (CC<0.76%)( hypereutectoid) Ck45Cc=0.45% dark pearlite: lamellae of Fe3C and ferrite light a ferrite

  19. Hypoeutectoid Steels (CC<0.76%)( hypereutectoid) Ck15Cc=0.15% dark pearlite: light a ferrite

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