Materials Science Glossary - F

face-centered cubic (FCC). A crystal structure found in some of the common elemental metals. Within the cubic unit cell, atoms are located at all corner and face-centered positions.

fatigue. Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses.

fatigue life (Nf). The total number of stress cycles that will cause a fatigue failure at some specified stress amplitude.

fatigue limit. For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail.

fatigue strength. The maximum stress level that a material can sustain, without failing, for some specified number of cycles.

Fermi energy (Ef). For a metal, the energy corresponding to the highest filled electron state at 0 K. Can be also considered as the chemical potential of the electrons.

ferrimagnetism. Permanent and large magnetizations found in some ceramic materials. It results from antiparallel

spin coupling and incomplete magnetic moment cancellation.

ferrite (ceramic). Ceramic oxide materials composed of both divalent and trivalent cations (e.g., Fe2_ and Fe3_), some of which are ferrimagnetic.

ferrite (iron). Body-centered cubic iron; also iron and steel alloys that have the BCC crystal structure.

ferroelectric. A dielectric material that may exhibit polarization in the absence of an electric field.

ferromagnetism. Permanent and large magnetizations found in some metals (e.g., Fe, Ni, Co, Gd, Dy) that result from the spontaneous parallel alignment of neighboring magnetic moments.

ferrous alloy. A metal alloy for which iron is the prime constituent.

fiber. Any polymer, metal, or ceramic that has been drawn into a long and thin filament.

fiber-reinforced composite. A composite in which the dispersed phase is in the form of a fiber (i.e., a filament that has a large length-to diameter ratio).

fiber reinforcement. Strengthening or reinforcement of a relatively weak material by embedding a strong fiber phase within the weak matrix material 

Fick’s first law. The diffusion flux is proportional to the concentration gradient. This relationship is employed for steady-state diffusion situations.

Fick’s second law. The time rate of change of concentration is proportional to the second derivative of concentration. This relationship is employed in non steady-state diffusion situations.

filler. An inert foreign substance added to a polymer to improve or modify its properties.

fine pearlite. Pearlite in which the alternating ferrite and cementite layers are relatively thin.

firing. A high-temperature heat treatment that increases the density and strength of a ceramic piece.

flame retardant. A polymer additive that increases flammability resistance.

flexural strength ( fs). Stress at fracture from a bend (or flexure) test.

fluorescence. Luminescence that occurs for times much less than a second after an electron excitation event.

foam. A polymer that has been made porous (or spongelike) by the incorporation of gas bubbles.

forging. Mechanical forming of a metal by heating and hammering. More specific, forging is manufacturing process where metal is pressed, pounded or squeezed under great pressure into high strength parts known as forgings. The process is normally (but not always) performed hot (i.e. at high homologous temperatures) by preheating the metal to a desired temperature before it is worked. It is important to note that the forging process is entirely different from the casting (or foundry) process, as metal used to make forged parts is never melted and poured (as in the casting process). The forging process can assist to create parts that are stronger than those manufactured by any other metalworking process. This is why forgings are almost always used where reliability and human safety are critical such as in the manufacturing of many aerospace parts. Hence, we rarely see such forgings, as they are normally component parts contained inside assembled items such airplanes, automobiles, tractors, ships, oil drilling equipment, engines, missiles and all kinds of capital equipment - to name a few. Important types of forging processes include Impression Die Forging; Open Die Forging; and Rolled Ring Forging.

forward bias. The conducting bias for a p–n junction rectifier such that electron flow is to the n side of the junction.

fracture mechanics. A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture.

fracture toughness (Kc). The measure of a material’s resistance to fracture when a pre-crack or some porosity or similar type of initial small scale damage is present. Fracture toughness generally depends on temperature, environmental conditions such as the presence of corrosive attack, loading rate, the composition of the material and its microstructure, together with geometric effects associated with the actual design of the part that is being probed together with the specifics of the loading type. Fracture toughness is a critical input parameter for fracture-mechanics based fitness-for-service assessments, an indication of the amount of stress required to propagate a preexisting flaw. It is a very important material property since the occurrence of flaws is not completely avoidable in the processing, fabrication, or service of a material/component.

Flaws may appear as cracks, voids, metallurgical inclusions, weld defects, design discontinuities, or some combination thereof.  Since one typically has to assume that now material is entirely devoid of any initial pre-damage, it is common practice to assume that a flaw of some chosen size will be present in some number of components and use the linear elastic fracture mechanics (LEFM) approach to design critical components. This approach uses the flaw size and features, component geometry, loading conditions and the material property called fracture toughness to evaluate the ability of a component containing a flaw to resist fracture. A parameter called the stress-intensity factor (K) is used to determine the fracture toughness of most materials. A Roman numeral subscript indicates the mode of fracture and the three basic types of modes of fracture. Mode I fracture is the condition in which the crack plane is normal to the direction of largest tensile loading. This is the most commonly encountered type of fracture mode. The stress intensity factor is a function of loading, crack size, and structural geometry.

free electron. An electron that has been excited into an energy state above the Fermi energy (or into the conduction band for semiconductors and insulators) and may participate in the electrical conduction process.

free energy. A thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system. At equilibrium, the free energy is at a minimum.

Frenkel defect. In an ionic solid, a cation–vacancy and cation–interstitial pair.

full annealing. For ferrous alloys, austenitizing, followed by cooling slowly to room temperature.

functionality. The number of covalent bonds that a monomer can form when reacting with other monomers.