Material Science Exam 2 Review

grain boundary

the enhanced atomic flow along the relatively open structure of the grain-boundary region.

surface diffusion

the enhanced atomic flow along the relatively open structure of a material’s surface.

activation energy

the energy barrier that must be overcome by atoms in a given process or reaction.

Arrhenius equation

An equation that is a general expression for a thermally activated process, such as diffusion.

Maxwell-Boltzmann distribution

a description of the relative distribution of molecular energies in a gas.

thermal activation

an atomic-scale process in which an energy barrier is overcome by thermal energy.

rate-limiting step

slowest step of a process that involves several sequential steps.

thermal vibration

direct result from point defects of atoms in the crystal structure.

as temperatures increase, the vibration _______.

increases

diffusion

the movement of molecules from an area of higher concentration to an area of lower concentration.

vacancy migitation

movement of vacancies in the course of atomic diffusion without significant crystal-structure distortion.

Random-walk

the atomic migration in which the direction of each step is random.

Fick’s First Law

the diffusive flux to the concentration under the assumption of steady state.

D

diffusion coefficient (diffusivity)

Jx

flux

Fick’s Second Law

predicts how diffusion causes the concentration to change with respect to time.

Gaussian error function (erf)

a mathematical function based on the integration of the “bell” shaped curve.

Steady-state

diffusion that doesn’t change with time.

Case Hardening

the surface that is hardened by the diffusion of atoms.

solid solution

the atomic-scale intermixing of more than one atomic species in the solid state.

solute

the species dissolving in a solvent to form a solution.

solvent

the species into which a solute is dissolved in order to form a solution.

substitutional solid

an atomic-scale combination of more than one kind of atom, with a solute atom substituting for a solvent atom at an atomic lattice site.

hume-rothery

the four criteria for complete miscibility in metallic solid solutions.

disordered solutioon

a solid solution in which the solute atoms are arranged in an irregular fashion.

ordered solution

a solid solution in which the solute atoms are arranged in a regular pattern.

nonstoichiometric solution

an scale combination of more than one kind of atom

interstitial solid

compound in a chemical compound in which variations in ionic charge lead to variations in the ratio of chemical elements

point defects

imperfections associated with the crystalline point lattice

vacnacy

unoccupied atom site

interstitial atom

an atom occupying an interstitial site not normally occupied in the perfect crystal structure.

schottky defect

pair of oppositely chraged ion vacancies.

frankel defect

a vacancy-interstitalcy combination

linear defects

one dimensional and associated with mechanical deformation.

dislocations

linear defects in a crystalline solid.

burgers vector

the displacement vector necessary to close a stepwise loop around the defect.

edge dislocation

linear defect which runs along the edge

screw dislocation

linear defect that is parallel to the dislocation line.

interfacial

two dimensional disorder in a crystalline structure.

twin boundary

separates two crystalline regions that are structurally mirror images of each other.

Hurth-Pound model

an atomistic model of the ledge-like strucutre

grai boudnary

the region between two adjacent single crystals or grains.

tilt boundary

the grain boundary associated with the tilting of a common crystallographic direction in two adjacent grains.

grain-size number

the average grain size in a microstrucutre and defined by N=2^G-1.

amorphous solids

noncrystalline and lack long-range crystalline structure.

zachaiasen model

random network theory of glass structure

bernal model

atomic structure of an amorphous metal as a connected set of polyhedral.

dc/dx

concentration gradient