MSE 1500

Austentite

  • Face-centered cubic iron; also includes iron and steel alloys with the FCC crystal structure.
  • Known as Gamma phase iron.

Cementite

  • Also known as Iron Carbide (Fe₃C).
  • Forms through a ceramic eutectic reaction where, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases.
  • Chemical reaction: L→S+SL \rightarrow S + S

Eutectic Structure

  • A two-phase microstructure resulting from solidification of a liquid with eutectic composition.
  • Phases exist as alternating lamellae of solids.

Eutectoid Reaction

  • A reaction where, upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases.
  • Chemical reaction: S→S+SS \rightarrow S + S

Ferrite

  • Body-centered cubic iron; also includes iron and steel alloys with the BCC crystal structure (alpha iron).
  • Known for its ductility.

Alloy Types

  • Hypereutectoid Alloy:
    • Contains a concentration of solute greater than the eutectoid composition (RIGHT side of the phase diagram).
  • Hypoeutectoid Alloy:
    • Contains a concentration of solute less than the eutectoid composition (LEFT side of the phase diagram).

Isomorphous

  • Refers to materials that have the same structure.
  • In the context of alloys, it indicates complete solid solubility for all compositions.

Lever Rule

  • A mathematical expression that computes the relative phase amounts in a two-phase alloy at equilibrium.
  • Considered essential for understanding phase diagrams.

Liquidus Line

  • On a binary phase diagram, this is the line separating liquid-phase and liquid + solid-phase regions.
  • Represents the temperature at which a solid phase first forms under equilibrium cooling conditions.

Solidus Line

  • The set of points where solidification is considered complete during equilibrium cooling.
  • Indicates where melting begins during equilibrium heating.

Solvus

  • The locus of points representing the limit of solid solubility as a function of temperature on a phase diagram.

Microconstituent

  • An identifiable element of the microstructure that has specific physical characteristics, can be composed of more than one phase.

Pearlite

  • A two-phase microstructure found in some steels and cast irons.
  • Forms from the transformation of austenite of eutectoid composition, consisting of alternating layers of α-ferrite and cementite.

Phase

  • A homogeneous portion of a system that maintains uniform physical and chemical characteristics.

Proeutectoid Ferrite

  • Primary ferrite that exists in addition to pearlite in hypoeutectoid steels.

Proeutectoid Cementite

  • Primary cementite that coexists with pearlite in hypereutectoid steels.

Copolymers

  • Block Copolymer:
    • A linear copolymer with identical repeat units clustered in blocks along the chain.
  • Branched Polymer:
    • Similar to block copolymers but structured with branched chains.
  • Crosslinked Polymer:
    • Comprises adjacent linear chains joined by covalent bonds.

Molecular Weight

  • The total atomic weight sum of all atoms in a molecule.

Monomer

  • A stable molecule used as a building block for polymer synthesis.

Network Polymer

  • Formed from multifunctional monomers with three or more active covalent bonds, resulting in a three-dimensional structure.

Repeat Unit

  • The fundamental structural unit in a polymer chain, resulting in a long molecule composed of many linked repeat units.

Thermoplastic Polymer

  • A semicrystalline material that softens upon heating and hardens when cooled; can be molded or extruded while in the soft state.

Thermosetting Polymer

  • A polymer that will not soften or melt upon reheating once it has been cured or hardened.