Phase Diagrams and Crystalline Imperfections

Flashcards covering material science concepts including phase diagrams, alloy classification, crystalline defects (point, line, surface, volume), and diffusion mechanisms based on Unidad III lecture notes.

Phase Diagram

Graphical representations of temperature vs. composition at constant pressure that identify phases present, solubility, and solidification temperatures.

Binary Phase Diagram

A phase diagram representing a system with 2 components ($r = 2$).

Alloy

A product resulting from the union of two or more chemical elements, where at least one has a metallic character.

Substitutional Solid Solution

A homogeneous mixture where solute atoms occupy positions normally held by solvent atoms in the crystal lattice.

Interstitial Solid Solution

A mixture where solute atoms occupy the interstitial positions (holes) within the solvent's crystal lattice.

Intermetallic Compound

A homogeneous alloy with a defined composition and properties, such as duralumin ($CuAl_2$) or cementite ($CFe_3$).

Solubility Limit

The maximum concentration of solute atoms that can be dissolved in a solvent to form a solid solution at a specific temperature.

Eutectic Reaction

An isothermal three-phase equilibrium reaction where a liquid transforms into two solid phases upon cooling: $Líquido \rightarrow Sólido A + Sólido B$.

Gibbs Phase Rule

The equation $P + F = C + N$, where $P$ is the number of phases, $F$ is the degrees of freedom, $C$ is the number of components, and $N$ is the number of non-composition variables (usually pressure and temperature).

Free Energy ($G$)

A thermodynamic potential defined as $G = H - TS$, representing the driving force for phase changes.

Eutectoid Reaction

A reaction where one solid phase transforms into two other solid phases: $Sólido 1 \rightarrow Sólido 2 + Sólido 3$.

Peritectic Reaction

A reaction where a liquid and a solid phase react to form a new solid phase: $Líquido + Sólido 1 \rightarrow Sólido 2$.

Lever Rule

A formula used to determine the phase fractions (liquid and solid) for an alloy at a given temperature in a two-phase region.

Vacancy

A zero-dimensional (point) defect representing a missing atom or ion from its regular lattice site.

F-center (Farbe center)

A type of crystalline defect where an anion vacancy is occupied by one or more electrons, causing a material to absorb visible radiation and become colored.

Hume-Rothery Rules

Criteria for solid solubility including atomic size factor (difference < $15$%), crystal structure, valency, and electronegativity.

Schottky Defect

A point defect in ionic crystals where a pair of oppositely charged ions is missing, maintaining electrical neutrality.

Frenkel Defect

An imperfection in ionic crystals created when a cation moves into an interstitial site, leaving a vacancy at its original position.

Edge Dislocation

A line defect (one-dimensional) symbolized by $\bot$, involving an extra half-plane of atoms within the crystal structure.

Screw Dislocation

A line defect created by shear stress where the Burgers vector is parallel to the dislocation line.

Burgers Vector

A vector that defines the magnitude and direction of the lattice distortion associated with a dislocation.

Grain Boundary

A surface (two-dimensional) defect representing the interface between crystals of different orientations in a polycrystalline material.

Twin Boundary (Macla)

A special type of surface defect where the atoms on one side of the boundary are in a mirror-image position to the atoms on the other side.

Strain Hardening

Increasing the strength of a material by increasing the number of dislocations through plastic deformation.

Precipitates

Three-dimensional (volume) defects consisting of clusters of particles with a different composition from the matrix phase.

Diffusion

The mass transport phenomenon involving atomic movement through a material, driven by thermal energy.

Fick's First Law

Describes the steady-state diffusion flux as proportional to the concentration gradient.

Sintering

A processing method where atoms diffuse across contact points of particles, creating bridges and reducing porosity.

Metallography

Experimental techniques used to identify microstructures and defects, often involving sample polishing and etching.