Phase diagram

• Crystalline materials


  Metals, ceramics
• Amorphous materials


  Glass, polymers
• Overview of type of bonding

  • Molecular
  • Crystal structure
• Properties of Engineering Materials

  • Physical
  • Mechanical
• Types of phase diagrams

  • Unary
  • Binary
• Classification of reinforced composites

  • Types of fibers
  • Their physical properties
• Why study Phase Diagrams?
• There is a strong correlation between microstructure and mechanical properties, and the development of microstructure of an alloy is related to the characteristics of its phase diagram

  
• Information provided by phase diagrams

  • Melting
  • Crystallization
  • State of the material
  • Designing of heat treatments of Alloys
  • Aero space engineering to understand the behaviors of materials
• Alloy


  A metal mixed with one or more other elements (metallic or non metallic)
• Principal element


  Generally a metal
• Other elements

  Can be metallic or non-metallic
• A useful alloy can be produced only if the elements concerned are soluble in each other in the molten stage
• Alloys


  • Brass - Cu + Zn
  • Steel - Fe + C
• Microstructure


  The size and shape of the grains of the different phases, their orientation and distribution

  
• Techniques to observe microstructure

  • Optical Microscope
  • Scanning Electron Microscope (SEM)
  • Atomic Force Microscope (AFM)
  • Transmission Electron Microscope (TEM)

  
• TEM image showing arrangement of atoms at grain boundaries

  
• Optical microscopic image of brass
• SEM image showing grain boundaries
• Common Lattice Types


  • FCC
  • BCC
  • HCP
• Classification of Alloys

  • Solid Solutions
  • Compounds

  
• Solid solution

  A phase in which atoms of both metals are soluble in each other (above melting points)
• Solvent


  Host or major component in solution
• Solute


  Dissolved, minor component in solution
• Solubility

  The ability to dissolve
• Types of solid solutions

  • Interstitial
  • Substitutional

  
• Interstitial solid solution

  Small solute vs. large solvent, more common for H, O, C, and N as solutes, more easily dissolved in transition metal solvents, solubility is limited

  
• Interstitial solid solution

  • Steel (Fe-C)
• Substitutional solid solution

  Solute and solvent atomic radii should be within ~15%, similar in electronegativity, identical valence, identical crystallized form

  
• Substitutional solid solutions


  • Cu and Ni (FCC)
  • Cu and Ag (FCC)

  
• Types of compounds

  • Intermetallic
  • Interstitial
  • Electron
• Intermetallic compounds

  Formed between metallic elements in the left hand-side of the Periodic Table and the metallic elements in the right hand-side, have strong bonds (ionic or covalent) and the crystal structure differs from those of the parent metals, usually very hard, brittle and have a high melting point than their parent metals
• Intermetallic compounds


  • Mg2Sn, Ca3Al
• Interstitial compounds


  Formed when the solubility of an interstitially dissolved element is exceeded, have a more complex crystal structure, generally carbides, nitrides, hydrides, and borides of the transition metals

  
• Interstitial compounds

  • TiN, WC, TiC
• Electron compounds


  Formed between copper, gold, silver, iron and nickel with the metals cadmium, magnesium, tin, zinc, and aluminum, have a definite ratio of valence electrons to atoms, wide range of composition, high ductility, low hardness
• Electron compounds


  • AgCd, Ag5Cd8, AgCd3
• Phase

  Homogeneous, physically distinct, mechanically separable portion of a material with a given chemical composition
• Component


  Chemically recognizable species
• A phase may contain one or more components