Chapter 4

Types of defects in a crystal structure

Vacancies, interstitial atoms, substitutional impurity atoms, dislocations, and grain boundaries.

Solidification

Result of casting molten material, involving nucleation of solid phase and growth of crystals until boundaries meet.

Equiaxed grains

Grains that have roughly the same dimensions in all directions.

Columnar grains

Grains that are elongated in one direction.

Grain Boundaries

Regions between grains characterized by crystallographic misalignment, slight atomic disorder, high atomic mobility, and high chemical reactivity.

Crystalline imperfections

Lattice irregularities with dimensions on the order of an atomic diameter that affect the properties of materials.

Point defects

0-Dimensional defects, such as vacancies and interstitial atoms.

Line defects

1-Dimensional defects, such as dislocations.

Planar defects

2-Dimensional defects, such as grain boundaries and stacking faults.

Frenkel defect

A type of point defect where an atom leaves its lattice site and occupies an interstitial site.

Schottky defect

A type of point defect in ionic solids where an equal number of cations and anions are missing, creating vacancies.

Burgers vector

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

Slip System

The combination of slip plane and slip direction along which dislocations move during deformation.

Hall-Petch relationship

A relationship that describes how the yield strength of a material increases as grain size decreases.

Dislocation slip

The movement of dislocations under applied shear stress, which facilitates plastic deformation.

Temperature effect on vacancy concentration

The number of vacancies increases with increasing temperature.

Stacking faults

Errors in the stacking sequence of close-packed planes in crystalline structures.

Types of dislocations

Edge dislocations, screw dislocations, and mixed dislocations.

Factors for substitutional solid solutions

1. Atomic radius difference < 15%, 2. Proximity in the periodic table, 3. Similar crystal structure, and 4. Valences.