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 Fickss 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. 1m 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