Materials Science and Engineering Flashcards

Flashcards covering the structure of materials, crystalline solids, crystal systems, crystallographic points, directions, and planes, imperfections in solids.

What is a crystalline material?

A material in which atoms are arranged in a repeating, periodic array over large atomic distances.

What is crystal structure?

The description of the manner in which atoms, ions, or molecules are spatially arranged in a crystalline material.

What is a lattice?

A three-dimensional array of points coinciding with atom positions or sphere centers.

What is a motif?

The list of atoms associated with each lattice point.

What is a unit cell?

The smallest building block of a crystal, whose repetition in space produces a crystal lattice.

What is the Face-Centered Cubic (FCC) crystal structure?

Cubic geometry with atoms at each corner and the centers of all cube faces; examples include copper, aluminum, silver, and gold.

What is coordination number?

The number of nearest-neighbor or touching atoms; for FCC, it is 12.

What is Atomic Packing Factor (APF)?

The sum of the sphere volumes of all atoms within a unit cell divided by the unit cell volume; for FCC, it is 0.74.

What is the Body-Centered Cubic (BCC) Crystal Structure?

Cubic geometry with atoms at all eight corners and a single atom at the cube center; examples include chromium, iron, and tungsten.

What is 8?

The coordination number for the BCC crystal structure is?

What is the Hexagonal Close-Packed (HCP) Crystal Structure?

Hexagonal geometry with specific atom arrangements in the unit cell; examples include cadmium, magnesium, titanium, and zinc.

What parameters are needed to calculate theoretical density for metals?

n = number of atoms per unit cell, A = atomic weight, Vc = volume of the unit cell, NA = Avogadro’s number.

What is polymorphism?

The phenomenon where some metals and nonmetals have more than one crystal structure.

What is allotropy condition?

When polymorphism is found in elemental solids.

What are the seven crystal systems?

Cubic, tetragonal, hexagonal, orthorhombic, rhombohedral, monoclinic, and triclinic.

What are lattice parameters?

The three edge lengths (a, b, c) and the three interaxial angles (α, β, γ) that define the unit cell geometry.

What are point coordinates?

Specifies the position of a point within a unit cell as fractional multiples of the unit cell edge lengths (a, b, c).

What is a crystallographic direction?

A unit vector used to represent various directions within the crystal system.

What is Miller-Bravais coordinate system?

A four-axis coordinate system used for hexagonal crystals, with three axes (a1, a2, a3) in the basal plane and the z-axis perpendicular to it.

What are Crystallographic Planes represented by?

Represent the orientations of planes in a crystal structure.

What is Linear Density (LD)?

Number of atoms per unit length whose centers lie on the direction vector for a specific crystallographic direction.

What is Planar Density (PD)?

Number of atoms per unit area that are centered on a particular crystallographic plane.

What are stacking sequences for FCC and HCP crystals?

FCC: ABCABCABC…; HCP: ABABAB…

What is a single crystal?

Periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen without interruption.

What are Polycrystalline materials?

Composed of a collection of many small crystals or grains.

What is Grain boundary?

Area where two grains meet in a polycrystalline material.

What is Anisotropy?

Properties vary with direction.

What is Isotropy?

Properties are independent of the direction of measurement.

What are Non-crystalline materials?

Lack a systematic and regular arrangement of atoms over relatively large atomic distances.

What is a Crystalline defect?

Lattice irregularity having one or more of its dimensions on the order of an atomic diameter.

What are point defects?

Associated with one or two atomic positions.

What is a vacancy?

A vacant lattice site where an atom is missing.

What is a self-interstitial?

An atom from the crystal crowded into an interstitial site.

What is a dislocation?

A linear defect around which some of the atoms are misaligned.

What is an edge dislocation?

An extra portion of a plane of atoms, the edge of which terminates within the crystal.

What is screw dislocation?

Formed by shear stress applied to produce distortion, shifting one part of the crystal relative to another.

What is a mixed dislocation?

Exhibits components of both edge and screw dislocations.

What is Burgers vector?

Magnitude and direction of the lattice distortion associated with a dislocation.

What is a slip system?

Set of symmetrically identical slip planes and associated family of slip directions for which dislocation motion can easily occur.

What is Burgers vector?

The magnitude and direction of slip are represented by what?

What are Planar defects?

Boundaries that have two dimensions and separate regions of materials with different crystal structures or orientations.

Give examples of Planar defects.

External surfaces, grain boundaries, phase boundaries, twin boundaries, and stacking faults.

What is a Grain Boundary?

A planar defect that separates regions of different crystalline orientation within a polycrystalline solid.

What is a Twin boundary?

A special type of grain boundary across which there is a specific mirror lattice symmetry.

What is a Stacking fault?

Error in the stacking sequence of close-packed planes in FCC metals.

Give examples of Volume defects.

Pores, cracks, foreign inclusions, and other phases.