Material Science

• Component


  Pure metals or compounds of which a material is formed
• System


  Series of possible alloys consisting of the same components but without regard to alloy composition
• Solubility limit


  The maximum concentration of solute atoms that may dissolve in the solvent to form solid solution
• Phases


  A chemically homogeneous portion of the microstructure. A single phase microstructure can be polycrystalline but each crystal grain differs only in crystalline orientation NOT in chemical composition
• Microstructure


  Subject to direct microscopic observation
• Phase diagram


  Equilibrium or constitutional diagram, displays much of the information about control of microstructure or phase structure of a particular alloy system
• Knowledge and understanding of phase diagrams relates to the design and control of heat treating procedures
• Some properties of materials are functions of their microstructures and thermal history
• Data from phase diagrams

  • Phases present
  • Composition of these phases
  • Percentages or fractions of the phases
• Unary phase diagram


  • Displays the melting point of a pure metal
• Binary phase diagram


  • Displays the melting points of two pure metals and the compositions of the phases present at different temperatures
• Ternary diagram (ceramics)


  • Displays the compositions of the phases present in a three-component ceramic system
• Determination of phase composition

  1. For a single phase, the composition is the same as the overall composition of the alloy

  2. For two phase regions, a tie line is constructed, and the compositions of the phases are determined from the intersections of the tie line and the phase boundaries
• The fraction of each phase in a two-phase region can be computed using the inverse lever rule
• Development of microstructure in isomorphous alloy


  As the alloy composition changes, the relative amounts of the two solid phases change, as determined by the lever rule
• Eutectic system


  A system in which a liquid solution of fixed composition solidifies at a constant temperature to form a mixture of two or more solid phases without an intermediate pasty stage
• For a 40wt%Sn-60 wt%Pb alloy at 150°C, the phases present, their compositions, and their relative amounts (mass fraction and volume fraction) can be determined using the phase diagram and the lever rule
• Eutectic reaction


  Upon cooling, a liquid solution of fixed compositions solidifies at a constant temperature, forming a mixture of two or more solid phases without an intermediate pasty stage. This process reverses on heating.
• Eutectic systems


  Systems exhibiting eutectic reaction behavior
• Solubility types


  • Unlimited solubility: Alcohol + Water
  • Limited solubility: Salt + Water
  • No solubility: Oil + Water
• Gibbs phase rule


  F = C - P + 2(1), where F = number of degrees of freedom, C = number of components, P = number of phases, 2 = variables (Temp + Pressure), 1 = if Pressure is set at 1 atm
• Degrees of freedom


  Number of externally controlled variables (Temperature, Pressure, Composition) which must be specified to completely define the state of the system. Number of these variables that can be changed independently without altering the number of phases that coexists at equilibrium.
• For single phase, F = 2
• For two phases, F = 1
• For three phases, F = 0
• Liquid-solid phase diagrams
• Eutectic system


  A binary system with a eutectic point where a liquid of a specific composition solidifies at a constant temperature to form a mixture of two solid phases
• Eutectic microstructure
• Peritectic reaction


  S1 + L = S2
• The Iron-Iron Carbide System
• Crystallography is the science that studies crystals and their structure using X-ray diffraction techniques to determine the atomic and molecular arrangement in a crystal.
• Isotopes are atoms with different numbers of neutrons but the same number of protons.
• The unit cell is the smallest repeating unit of a crystal lattice, and the arrangement of atoms within the unit cell determines the overall crystal structure.
• Crystal structure refers to the arrangement of atoms in a crystalline material, which can be categorized into different types such as cubic, hexagonal, and tetragonal.
• X-rays are used as probes to investigate the internal structure of materials at an atomic level.
• The wavelength of X-rays is similar to the spacing between atoms or molecules in a material, allowing them to be scattered by these structures.
• Lever rule


  A method to determine the weight fraction (or mole/atomic fraction if in atomic percent) of the different phases present in a two-phase region of a binary phase diagram
• Applying the lever rule

  1. Identify the total length of the tie line (the line connecting the two end compositions)

  2. For the phase you want to determine the fraction of, find the length of the segment on the tie line on the same side as that phase

  3. Divide the length of the segment from step 2 by the total length from step 1 to get the weight (or mole/atomic) fraction of that phase
• Lever rule


  Used to sketch the microstructure and determine the amount of each phase present
• Using the lever rule to sketch the microstructure

  1. At point A:

  2. - 100% liquid, 50% FA

  3. - Solid alpha (olivine) phase just starting to form, 0% alpha, 20% FA

  4. At point B:

  5. - 63.6% alpha, 36.4% liquid

  6. - Alpha composition is 38% FA

  7. - Liquid composition is 71% FA

  8. At point C:

  9. - Almost entirely solid alpha, 0% liquid

  10. - Alpha composition is 50% FA

  11. - Liquid composition is 81% FA