Materials Science: Metallic Materials and Phase Diagrams

These flashcards cover the fundamental definitions, phase reactions, cooling processes, and microstructures of metallic materials including binary systems and the iron-carbon system.

Component

An individual chemical substance (element or compound) that forms part of a system.

Phase

Any fraction of a system that is physically and chemically homogeneous and separated from the rest by a surface that makes it mechanically separable.

System

The set of all possible mixtures and combinations of two or more components.

Phase Diagrams

A graphical representation of the phases present in a system and their boundaries as a function of pressure ($P$), temperature ($T$), and/or composition.

Gibbs Phase Rule

A formula that indicates the number of degrees of freedom ($L$) or variables to be fixed to describe a system: $Fases + Graus\, de\, llibertat = Components + 2$ (or $+ 1$ if pressure is constant).

Microstructure

The microscopic observation of the structure of a material and its components.

Microconstituent

A phase or set of phases that precipitate together with a characteristic appearance.

Clausius-Clapeyron Equation

An equation used to calculate the slope of phase boundaries in a one-component diagram: $\frac{dP}{dT} = \frac{\Delta H}{T \Delta V}$.

Isomorphism

A characteristic of binary systems where components are completely soluble in each other in both liquid and solid states, such as the $Ni-Cu$ system.

Liquidus

The line in a phase diagram representing the temperature above which a material is completely liquid.

Solidus

The line in a phase diagram representing the temperature below which a material is completely solid.

Lever Rule

A method to determine the relative quantity of each phase in a two-phase region: $\text{\%} m_L = \frac{C_{\alpha} - C_0}{C_{\alpha} - C_L} \times 100$.

Monel

A specific nickel-copper alloy containing approximately $60\,\text{\%}$ Nickel which provides maximum resistance.

Eutectic Point

A point in a phase diagram with an invariant composition that has a lower melting temperature ($T_{fus}$) than the surrounding compositions.

Eutectic Reaction

An isothermal reaction where a liquid phase transforms into two different solid phases upon cooling: $L \rightarrow \alpha + \beta$.

Hypoeutectic

A composition in a binary system that is to the left of the eutectic point.

Hypereutectic

A composition in a binary system that is to the right of the eutectic point.

Solvus

The line on a phase diagram that separates a solid-phase region from a region of two solid phases, indicating the limits of solid solubility.

Intermetallic Compound

A combination of two components that produces a new phase with a specific structure and properties, typically being hard and brittle.

Peritectic Reaction

A phase reaction where a solid and a liquid phase transform into a different solid phase: $\alpha + L \rightarrow \beta$.

Eutectoid Reaction

A phase reaction where one solid phase transforms into two different solid phases: $\gamma \rightarrow \alpha + \beta$.

Precipitation Hardening

A mechanism to increase hardness by the appearance of a precipitated phase, which reduces the mobility of dislocations.

$\alpha$-Ferrite

A magnetic phase of iron ($Fe$) with a body-centered cubic ($bcc$) structure and a lattice parameter $a = 2.8$.

Austenite ($\gamma$-Fe)

A non-magnetic phase of iron with a face-centered cubic ($fcc$) structure, stable between $912\,^{\circ}C$ and $1394\,^{\circ}C$.

Cementite ($Fe_3C$)

An intermetallic iron-carbon compound with $6.70\,\text{\%}$ carbon content, which is very hard and brittle.

Pearlite

A microconstituent formed by the eutectoid reaction consisting of alternating lamellae of ferrite and cementite.

Ledeburite

The eutectic microconstituent in the iron-carbon system composed of austenite and cementite.

AISI-SAE Nomenclature

A numeric system for identifying steels where the first two digits indicate alloying elements and the last two digits indicate the weight percentage of carbon multiplied by 100.

TTT Diagram

Time-Temperature-Transformation diagrams used to describe the kinetics of phase transformations under isothermal conditions.

Bainite

A microconstituent of ferrite and cementite that forms at temperatures between the pearlite and martensite ranges.

Martensite

A metastable phase formed by rapid cooling (athermal transformation) of austenite, resulting in a body-centered tetragonal ($BCT$) structure.

Shape Memory Alloy (SMA)

Smart metals, like Nitinol ($Ni-Ti$), that can be deformed when cold but recover their original shape when heated.

Austempering

An isothermal heat treatment used to produce a $100\,\text{\%}$ bainite microstructure.

Martempering

A cooling process designed to produce a $100\,\text{\%}$ martensitic structure while minimizing internal stresses and cracking.

CCT Diagram

Continuous Cooling Transformation diagrams, which describe phase changes in materials subjected to steady cooling rates rather than isothermal holds.

Spheroidite (Esferoidita)

A microconstituent produced by maintaining steel below the eutectoid temperature for a long time, resulting in globules of cementite in a ferrite matrix.

Tempered Martensite (Martensita Revinguda)

A microconstituent produced by heating martensite below the eutectoid temperature to improve its ductility and toughness.