Phase Diagrams melting / production process / alloying (strength, Tm...) heat treatment microstructure material properties 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 Equilibria G=min G=H-TS =min Gibbs free energy: =f(T,c,p) internal energy (bonding enthalpy) entropy (disorder of molecules entropy of mixing) metastable stable

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

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

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

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

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 segregation

Diffusion steady state diffusion flux

Non-Steady-State Diffusion Ficks‘s 2nd Law solution (c(0)=0): diffusion coefficient:

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

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

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

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))

Metallography (SEM) detector electron beam secondary electrons specimen

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

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

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

Hypoeutectoid Steels (CC<0.76%) ( hypereutectoid) Ck45 Cc=0.45% dark pearlite: lamellae of Fe3C and ferrite light a ferrite

Hypoeutectoid Steels (CC<0.76%) ( hypereutectoid) Ck15 Cc=0.15% dark pearlite: light a ferrite