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Material Science for Engineers
glossary
124
Engineering
Undergraduate 2
09/21/2008

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Term
Basal plane
Definition
The special name given to the close-packed plane in hexagonal close-packed unit cells.
Term
Basis
Definition
A group of atoms associated with a lattice point (same as motif).
Term
Blow-stretch forming
Definition
A process used to form plastic bottles.
Term
Bose-Einstein condensate (BEC)
Definition
A newly experimentally verified state of a matter in which a group of atoms occupy the same guantum ground state.
Term
Braggs's law
Definition
The relationship describing the angle at which a beam of x-rays of a particular wavelength diffract from crystallographic planes of a given interplanar spacing.
Term
Bravais lattices
Definition
The fourteen possible lattices that can be created using lattice points.
Term
Chemical vapor deposition (CVD)
Definition
A process used for production of inorganic thin films or powders involving decomposition of precursors followed by chemical reaction in the vapor phase.
Term
Close-packed directions
Definition
Directions in a crystal along which atoms are in contact.
Term
Close-packed structure
Definition
Structures showing a packing fracture of 0.74 (FCC and HCP).
Term
Coordination number
Definition
The number of nearest neighbors to an atom in its atomic arrangement.
Term
Crystal structure
Definition
The arrangement of atoms in a material into a regular repeatable lattice.
Term
Crystal systems
Definition
Cubic, tetragonal, orthorhombic, hexogonal, monoclinic, rhombohedral, and triclinic arrangements of points in space that lead to 14 Bravais lattices and hundreds of crystal structures.
Term
Crystalline materials
Definition
Materials comprised of one or many small crystals or grains.
Term
Crystallization
Definition
The process responsible for the formation of crystals, typically in an amorphous material.
Term
Cubic site
Definition
An interstitial position that has a coordination number of eight. An atom or ion in the cubic site touches eight other atoms or ions.
Term
Defect
Definition
A microstructural feature representing a disruption in the perfect periodic arrangement of atom in a crystalline material. This term is not used to convey the presence of a flaw in the material.
Term
Density
Definition
Mass per unit volume of a material, usually in units of g/m^3.
Term
Diamond cubic (DC)
Definition
A special type of face-centered cubic crystal structure found in carbon, silicon, and other covalently bonded materials.
Term
Diffraction
Definition
The constructive or reinforcement of a beam of x-rays or electrons interacting with a material. The diffracted beam provides useful information concerning the structure of the material.
Term
Directions of a form
Definition
Crytallographic directions that all have the same characteristics, although their "sense" is different. Denoted by <> brackets.
Term
Electron diffraction
Definition
A method used to determine the level of crystallinity at relatively smaller length scales. Based on the diffraction of electrons typically involving use of a transmission electron microscope.
Term
Float-glass process
Definition
A process to manufacture large pieces of flat glass in which molten glass is floated on a bath of tin.
Term
Glass-ceramics
Definition
A family of materials typically derived from molten inorganic glasses an processed into crystalline materials with very fine grain size and improved mechanical properties.
Term
Glasses
Definition
Solid, non-crystalline materials (typically derived from the molten state) that have only short-range atomic order.
Term
Grain
Definition
A small crystal in a polycrystalline material.
Term
Grain boundaries
Definition
Regions between grains of a polycrystalline material.
Term
Interplanar spacing
Definition
Distance between two adjacent parallel planes with the same Miller indices.
Term
Interstitial sites
Definition
Locations between the "normal" atoms or ions in a crystal into which another--usually different--atom or ion is placed. Typically, the size of this interstitial location is smaller than the atom or ion that is to be introduced.
Term
Isotropic
Definition
Having the same properties in all directions.
Term
Lattice
Definition
A collection of points that divide space into smaller equally sized segments.
Term
Lattice parameters
Definition
The lengths of the sides of the unit cell and the angles between those sides. The lattice parameters describe the size and shape of the unit cell.
Term
Lattice points
Definition
Points that make up the lattice. The surroundings of each lattice point are identical anywhere in the material.
Term
Linear density
Definition
The number of lattice points per unit length along a direction.
Term
Liquid crystals
Definition
Polymeric materials that are typically amorphous but can become partially crystalline when an external electric field is applied. The effect of the electric field is reversible. Such materials are used in liquid crystal displays.
Term
Long-range order (LRO)
Definition
A regular repetitive arrangement of atoms in a solid which extends over a very large distance.
Term
Metallic glass
Definition
Amorphous metals or alloys obtained using rapid solidification.
Term
Miller-Bravais indices
Definition
A special shorthand notation to describe the crystallographic planes in hexagonal close-packed unit cells.
Term
Miller indices
Definition
A shorthand notation to describe certain crystallographic directions and planes in a material. Denoted by [] brackets. A negative number is represented by a bar over the number.
Term
Motif
Definition
A group of atoms affiliated with a lattice point (same as a basis).
Term
Octahedral site
Definition
An interstitial position that has a coordination number of six. An atom or ion in the octahedral site touches six other atoms or ions.
Term
Packing factor
Definition
The fraction of space in a unit cell occupied by atoms.
Term
Packing fraction
Definition
The fraction of a direction (linear-packing fraction) or a plane (planar-packing factor) that is actually covered by atoms or ions. When one atom is located at each lattice point, the linear packing fraction along a direction is the product of the linear density and twice the atomic radius.
Term
Planar density
Definition
The number of atoms per unit area whose centers lie on the plane.
Term
Planes of a form
Definition
Crystallographic planes that all have the same characteristics, although their orientations are different. Denoted by {} braces.
Term
Polycrystalline material
Definition
A material comprised of many grains.
Term
Polymorphism
Definition
Compounds exhibiting more than one type of crystal structure.
Term
Rapid solidification
Definition
A technique used to cool metals and alloys very quickly.
Term
Repeat distance
Definition
The distance from one lattice point to the adjacent lattice point along a direction.
Term
Short-range order (SRO)
Definition
The regular and predictable arrangement of the atoms over a short distance--usually one or two atom spacings.
Term
Stacking sequence
Definition
The sequence in which close-packed planes are stacked. If the sequence is ABABAB, a hexagonal close-packed unit cell is produced; if the sequence is ABCABCABC, a face-centered cubic structure is produced.
Term
Stress-induced crystallization
Definition
The process of forming crystals by the application of an external stress. Typically, a significant fraction of many amorphous plastics can be crystallized in this fashion, making them stronger.
Term
Tranmission electron microscopy (TEM)
Definition
A technique for imaging and analysis of microstructures using a high-energy electron beam.
Term
Tetrahedral site
Definition
An interstitial position that has a coordination number of four. An atom or ion in the tetrahedral site touches four other atoms or ions.
Term
Tetrahedron
Definition
The structure produced when atoms are packed together with a four-fold coordination.
Term
Unit cell
Definition
A subdivision of the lattice that still retains the overall characteristics of the entire lattice.
Term
X-ray diffraction (XRD)
Definition
A technique for analysis of crystalline materials using a beam of x-rays.
Term
ASTM
Definition
American Society for Testing and Materials
Term
ASTM grain size number (n)
Definition
A measure of the size of the grains in a crystalline material obtained by counting the number of grains per square inch at magnification x 100.
Term
Annealing
Definition
A heat treatment that typically involves heating a metallic material to a high temperature for an extended period of time, conducted with a view to lower the dislocation density and hence impart ductility.
Term
Burgers vector
Definition
The direction and distance that a dislocation moves in each step, also known as slip vector.
Term
Dopants
Definition
Elements or compounds typically added, in known concentrations and appearing at specific places within the microstructure, to enhance the properties or processing of a material.
Term
Critical resolved shear stress
Definition
The shear stress required to cause a dislocation to move and cause slip.
Term
Cross-slip
Definition
A change in the slip system of a dislocation.
Term
Defect chemical reactions
Definition
Reactions using the Krรถger-Vink notation to describe defect chemistry. The reactions must be written in such a way that mass and electrical charges are balanced and stoichiometry of sites is maintained. The existence of defects predicted by such actions needs to be verified experimentally.
Term
Dislocation
Definition
A line imperfection in a crystalline material. Movement of dislocations helps explain how metallic materials deform. Interference with the movement of dislocations helps explain how metallic materials are strengthened.
Term
Dislocation density
Definition
The total length of dislocation line per cubic centimeter of material.
Term
Dispersion strengthening
Definition
A mechanism by which grains of an additional compound or phase are introduced in the grains of a polycrystalline metallic material. These second phase crystals serve as stop signs for dislocations thereby causing an increase in the strength of a metallic material.
Term
Domain
Definition
A small region of a ferroelectric, ferromagnetic or ferrimagnetic materials in which the direction of dielectric polarization (for ferroelectric) or magnetization (for ferromagnetic or ferromagnetic) remains the same.
Term
Domain boundaries
Definition
Region between domains in a material.
Term
Edge dislocations
Definition
A dislocation introduced into the crystal by adding an  extra half plane of atoms.
Term
Elastic deformation
Definition
Deformation that is fully recovered when the stress that is causing it is removed
Term
Etch pits
Definition
Tiny holes created at areas where dislocations meet the surface. These are used to examine the presence and number density of dislocations.
Term
Extended defects
Definition
Defects that involve several atoms/ions and thus occur over a finite volume of the crystalline material (e.g., dislocations, stacking faults, etc.).
Term
Extrinsic semiconductor
Definition
Semiconductors containing dopants or impurities.
Term

Ferrimagnetic

Definition

A material that also develops a spontaneous and reversible magnetization (e.g., Fe3O4). It is different from a ferromagnetic material in that the magnetic moments of different ions are not all in the same direction.

Term

Ferroelectric

Definition

A dielectric material that develops a spontaneous and reversible electric polarization (e.g., PZT, BaTiO3).

Term
Ferromagnetic
Definition
A material that develops a spontaneous and reversible magnetization.
Term
Frenkel defect
Definition
A pair of point defects produced when an ion moves to create an interstitial site, leaving behind a vacancy.
Term
Grain
Definition
One of the crystals present in a polycrystalline material.
Term
Grain boundary
Definition
A surface defect representing the boundary between two grains. The crystal has a different orientation on either side of the grain boundary.
Term

Hall-Petch equation

Definition

The relationship between yield strength and grain size in a metallic material--that is, σy = σ0 + Kd-1/2.

Term
Image analysis
Definition
A technique that is used to analyze images of microstructures to obtain quantitative information on grain size, shape, grain size distribution, etc.
Term
Impurities
Definition
Elements or compounds that find their way into a material, often originating from processing or raw materials and typically have a deleterious effect on the properties or processing of a material.
Term
Interstitial defect
Definition
A point defect produced when an atom is placed into the crystal at a site that is normally not a lattice point.
Term
Interstitialcy
Definition
A point defect caused when a  normal atom occupies an interstitial site in the crystal.
Term
Intrinsic semiconductor
Definition
A semiconductor that contains no dopants or impurities.
Term
Line defects
Definition
Defects such as dislocations in which atoms or ions are missing in a row.
Term
Metallography
Definition
Preparation of a metallic sample of a material by polishing and etching so that the structure can be determined using a microscope.
Term
Mixed dislocation
Definition
A dislocation that contains partly edge components and partly screw components.
Term
n-type semiconductor
Definition
A semiconductor that is doped with elements that donate electrons (e.g., P-doped Si).
Term
p-type semiconductor
Definition
A semiconductor that is doped with elements that accept electrons (e.g., B-doped Si).
Term

Peierls-Nabarro stress

Definition

The shear stress, whichdepends on the Burgers vector and the interplanar spacing, required to cause a dislocation to move--that is, τ = c exp(-kd/b).

Term
Point defects
Definition
Imperfections, such as vacancies, that are located typically at one (in some cases a few) sites in the crystal.
Term
Precipitation strengthening
Definition
Strengthening of metals and alloys by formation of tiny precipitates inside the grains. The small precipitates help resist dislocation motion.
Term

Schmid's law

Definition

The relationshop between shear stress, the applied stress, and the orientation of the slip system--that is, τ = σ cos λ cos φ.

Term
Schottky defect
Definition
A point defect in ionically bonded materials. In order to maintain a neutral charge, a stoichiometric number of cation and anion vacancies must form.
Term
Screw dislocation
Definition
A dislocation produced by skewing a crystal so that one atomic plane produces a spiral ramp about the dislocation.
Term
Second-phase strengthening
Definition
A mechanism by which grains of an additional compound or phase are introduced in the grains of a polycrystalline material. These second phase crystals serve as stop signs for dislocations thereby causing an increase in the strength of a metallic material.
Term
Sintering
Definition
A process for forming a dense mass by heating compacted powders.
Term
Slip
Definition
Deformation of a metallic material by the movement of dislocations through the crystal.
Term
Slip band
Definition
Collection of many slip lines, often easily visible.
Term
Slip direction
Definition
The direction in the crystal in which the dislocation moves. The slip direction is the same as the direction of the Burgers vector.
Term
Slip line
Definition
A visible line produced at the surface of a metallic material by the presence of several thousand dislocations.
Term
Slip plane
Definition
The plane swept out by the dislocation line during slip. Normally the slip plane is a close-packed plane, if one exists in the crystal structure.
Term
Slip system
Definition
The combination of the slip plane and the slip direction.
Term
Small angle grain boundary
Definition
An array of dislocations causing a small misorientation of the crystal across the surface of the imperfection.
Term
Stacking fault
Definition
A surface defect in FCC metals caused by the improper stacking sequence of close-packed planes.
Term
Substitutional defect
Definition
A point defect produced when an atom is removed from a regular lattice point and replaced with a different atom , usually of a different size.
Term
Surface defects
Definition
Imperfections, such as grain boundaries, that form a two-dimensional plane within the crystal.
Term
Thermal grooving
Definition
A technique used for observing microstructures in ceramic materials, involves heating, for a short time, a polished sample to a temperature slightly below the sintering temperature.
Term
Tilt boundary
Definition
A small angle grain boundary composed of an array of edge dislocations.
Term
Transmission electron microscope (TEM)
Definition
An instrument that, by passing an electron beam through a material, can detect microscopic structural features.
Term
Twin boundary
Definition
A surface defect across which there is a mirror image misorientation of the crystal structure. Twin boundaries can also move and cause deformation of the material.
Term
Twist boundary
Definition
A small angle grain boundary composed of an array of screw dislocations.
Term
Vacancy
Definition
An atom or an ion missing from its regular crystallographic site.
Term
Allotropy
Definition
The characteristic of an element being able to exist in more than one crystal structure, depending on temperature and pressure.
Term
Amorphous materials
Definition
Materials, including glasses, that have no long-range order, or crystal structure.
Term
Anisotropic
Definition
Having different properties in different directions.
Term
Atomic level defects
Definition
Defects such as vacancies, dislocations etc. occurring over a length-scale comparable to few interatomic distances.
Term
Atomic radius
Definition
The apparent radius of an atom, typically calculated from the dimensions of the unit cell, using close-packed directions (depends upon coordination number).
Term
Packing factor
Definition
The fraction of space in a unit cell occupied by atoms.
Term
Kepler's conjecture
Definition
A conjecture made by Johannes Kepler in 1611 that stated that the maximum packing fraction with spheres of uniform size could not exceed π/√18. In 1998 Thomas Hales proved this to be true.
Term
Kröger-Vink notation
Definition
A system used to indicate point defects in materials. The main body of the notation indicates the type of defect or the element involved. The subscript indicates the location of the point defect and the superscript indicates the effective positive (.) or negative (')charge.
Term
Source
Definition
Askeland, Donald and Pradeep Phulé. The Science and Engineering of Materials, 4E. ISBN 0-534-95373-5.
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