MSE Midterm 3

Austenite

Face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure.

Cementite

Iron carbide (Fe3C)

Eutectic Reaction

A reaction in which, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases.

Eutectic Structure

A two-phase microstructure resulting from the solidification of a liquid having the eutectic composition; the phases exist as lamellae that alternate with one another

Eutectoid Reaction

A reaction in which, upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed.

Ferrite

Body-centered cubic iron; also iron and steel alloys that have the BCC crystal structure.

Hypereutectoid Alloy

For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is greater than the eutectoid composition.

Isomorphous

Having the same structure. In the phase diagram sense, isomorphicity means having the same crystal structure or complete solid solubility for all compositions

Lever Rule

A mathematical expression, such as Equation 9.1b or Equation 9.2b, by which the relative phase amounts in a two-phase alloy at equilibrium may be computed.

Liquidus Line

On a binary phase diagram, the line or boundary separating liquid- and liquid + solid-phase regions. For an alloy, the liquidus temperature is the temperature at which a solid phase first forms under conditions of equilibrium cooling.

Microconstituent

An element of the microstructure that has an identifiable and characteristic structure. It may consist of more than one phase, such as with pearlite.

Pearlite

A two-phase microstructure found in some steels and cast irons; it results from the transformation of austenite of eutectoid composition and consists of alternating layers (or lamellae) of a-ferrite and cementite.

Phase

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

Proeutectoid Ferrite

Primary ferrite that exists in addition to pearlite for hypoeutectoid steels

Proeutectoid Cementite

Primary cementite that exists in addition to pearlite for hypereutectoid steels

Solidus Line

On a phase diagram, the locus of points at which solidification is complete upon equilibrium cooling, or at which melting begins upon equilibrium heating.

Block Copolymer

A linear copolymer in which identical repeat units are clustered in blocks along the molecular chain.

Branched Polymer

A polymer having a molecular structure of secondary chains that extend from the primary main chains.

Cross Linked Polymer

A polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds.

Molecular Weight

The sum of the atomic weights of all the atoms in a molecule.

Monomer

A stable molecule from which a polymer is synthesized.

Network Polymer

A polymer produced from multifunctional monomers having three or more active covalent bonds, resulting in the formation of three-dimensional molecules.

Repeat Unit

The most fundamental structural unit in a polymer chain. A polymer molecule is composed of a large number of repeat units linked together.

Thermoplastic Polymer

A semicrystalline polymeric material that softens when heated and hardens upon cooling. While in the softened state, articles may be formed by molding or extrusion.

Thermosetting Polymer

A polymeric material that, once having been cured (or hardened) by a chemical reaction, will not soften or melt when subsequently heated.

Elastomer

A polymeric material that may experience large and reversible elastic deformations.

Glass Transition Temperature

The temperature at which, upon cooling, a noncrystalline ceramic or polymer transforms from supercooled liquid into a rigid glass.

Melting Temperature

The temperature at which, upon heating, a solid (and crystalline) phase transforms into a liquid.

Vulcanization

A nonreversible chemical reaction involving sulfur and another suitable agent in which crosslinks are formed between molecular chains in rubber materials. The rubber’s modulus of elasticity and strength are enhanced.