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Flashcards in Chapter 2 Deck (21):

Define: Valance Electrons

Outer shell electrons; determine much of an atom's chemical affinity for other atoms


Define: Primary vs. Secondary Bonds
(Intra vs. Inter Molecular Forces)

Primary Bonds: characterized by strong atom-to-atom attractions that involve the exchange of valence electrons (ionic, covalent, metallic)

Secondary Bonds: Involve attraction forces between molecules, or inter-molecular forces (dipole, London, hydrogen)


Define: Ionic Bonds

Bonds in which atoms of an element that give up an outer electron(s) to atoms of another element in order to increase both atom's electron count in the outermost shell to 8.


Define: Covalent Bonds

Bonds in which electrons are share between atoms in their outermost shell to achieve a stable set of 8.


Define: Metallic Bonding

To fill incomplete outermost orbits of most metallic elements, electrons are shared atom-to-atom in a continuously flowing manner, providing good conductivity.


Define: Alloptropic

Name given to metals or other materials that change their lattice structure due to temperature changes. (ex. BCC to FCC to HCP)


Define: Point Defects

Imperfections in the crystal structure involving either a single atom or a few atoms. Imperfections include vacancy, ion-pair vacancy, interstitial (extra atom), or displaced ions (atom misplaced in lattice strucutre)


Define: Vacancy

Missing atom within a lattice structure.


Define: Interstitialcy

Produced by the presence of an extra atom in the strucuture


Define: Line Defect

A connected group of point defects taht form a line in the lattice structure (dislocations)


Define: Edge Dislocation

Edge of an extra plane of atoms that exists in the lattice


Define: Screw Dislocation

Spiral within the lattice structure wrapped around an imperfection line (shearing)


Define: Plastic Deformation

If mechanical stress reaches a high value relative to the electrostatic forces holding the atoms in their lattice positions, a permanent shape change occurs


Define: Slip

Involves the relative motion of atoms on opposite sides of a plane in the lattice, called the slip plane.


Define: Slip Plane

Plane of lattice in which atoms on opposite sides move apart from one another


Define: Slip Direction

Preferred directions in which slip is more likely to occur; depends on the lattice structure


Define: Grains

In metals, the millions of individual crystals with their own unique lattice and orientation.


Define: Polycrystalline

When grains are collectors oriented randomly within a block of metal, it is known as polycrystalline.


Define: Grain Boundary

As crystals grow within the metal, they interfere with one another, forming at their interference a surface defect, or grain boundary. Consists of a transition zone I which the atoms are not aligned with either grain.


Define: Strain Hardening

Grain boundaries (imperfections) in metals that interrupt the continued movement of dislocations, make the metal stronger as it is deformed. Therefore, the more grains and grain boundaries, the stronger the metal.


Define: Amorphous

When materials have a noncrystalline form in their solid state