Materials Science Glossary - C
calcination. A high-temperature reaction whereby one solid material dissociates to form a gas and another solid. It is one step in the production of cement.
Calphad: Calculation of phase diagrams. Computer coupling of phase diagrams and thermochemistry.
Phase diagrams are a very powerful tool for predicting the state of a system under different conditions. The Calphad approach is based on the fact that a phase diagram is a manifestation of the equilibrium thermodynamic properties of the system. It is thus possible to calculate a phase diagram by modeling the thermodynamic properties of all the phases in a system. By combining the models for several low-order systems it is possible to construct multi-component databases, which can be used to predict the state of multi-component alloys. Obvious applications include the direct calculation of phase diagrams, phase equilibria and thermodynamic properties such as Gibbs energies, chemical potentials, activities, enthalpies and heat capacities using software such as →Thermo-Calc. The Calphad method also forms the basis for simulation of phase transformations using →phase-field or diffusion simulation methods and for process simulation. This makes it one of the key tools for ICME (Integrated Computational Materials Engineering).
capacitance (C). The charge-storing ability of a capacitor, defined as the magnitude of charge stored on either plate divided by the applied voltage.
Capillary length. The length defined by the balance of capillary and hydrostatic pressures.
carbon–carbon composite. A composite composed of continuous fibers of carbon that are embedded in a carbon matrix.The matrix was originally a polymer resin that was subsequently pyrolyzed to form carbon.
Carbonitriding (Nicarbing). A process in which a ferrous alloy is case hardened by first being heated in a gaseous atmosphere of such composition that the alloy absorbs carbon and nitrogen simultaneously, and then being cooled at a rate that will produce desired properties.
carburizing. The process by which the surface carbon concentration of a ferrous alloy is increased by diffusion from the surrounding environment. Typically in such a process a carbon gradient inward from the surface is formed by diffusion, enabling the surface layer to be hardened by either quenching directly from the carbonizing temperature or by cooling to room temperature, then re-austenitizing and quenching. The introduction of carbon into the surface layer is usually applied to steels having a low carbon content (case hardening steel). It may be effected by heating in a solid, liquid or gaseous carbon-containing medium, which at high temperatures provides a supply of carbon for absorption by the material being carburized. By controlling the temperature and time of treatment, the concentration of carbon in the surface of the steel and the depth of
penetration may be varied over wide limits. In the original process of box- or pack-carburizing, the steel is heated to the necessary temperature in a solid carburizing compound, usually a mixture of hardwood charcoal and an oxide or carbonate of the alkalies or alkaline earths. Gas carburizing is finding increasing use because it gives better control over the carbon content of the case.
case hardening. Hardening of the outer surface (or “case”) of a steel component by a carburizing or nitriding process; used to improve wear and fatigue resistance.
cast iron. A ferrous alloy with a carbon content greater than the maximum solubility in austenite at the eutectic temperature. Most commercial cast irons contain between 1.8 and 4.5 wt% C. This means that carbon is present in excess of the amount which can be retained in solid solution in austenite at the eutectic temperature. In addition to carbon, there are also present, varying amounts of silicon (1-3 wt%), manganese, sulphur and phosphorus. These irons can normally be divided into the following types: Grey cast iron, in which all or part of the carbon content is in the form of graphite distributed through the metal as flakes which are responsible for the inherently poor shock-resistance and relatively low mechanical properties of the material; White cast iron, in which practically the whole of the carbon is retained in chemical combination with the iron as carbide of iron, Fe C. This compound has a silver-white colour and the fractures of the cast iron are white. White iron is very
hard and brittle and practically unmachinable, and is used chiefly as an intermediate product in the production of malleable iron castings or a thin hard layer on the surface of a softer iron casting; Malleable cast iron is cast white and then annealed at about 850o C. to remove carbon (White-heart process) or to convert the cementite to rosettes of graphite (Black-heart Process). It is distinguished from grey and white cast iron by exhibiting some elongation and reduction of area in a tensile test; Spheroidal Graphite cast iron, in which, as the name implies, the graphite is in spheroidal form instead of flakes, as found in grey cast iron. The production of this iron involves the addition of an appropriate amount of either magnesium or cerium to the molten iron shortly before casting. The mechanical strength is doubled and such castings show measurable
ductility and greatly increased shock resistance. Alloy Cast Iron contains a specially added element or elements in amounts sufficient to produce a measurable modification of the physical properties.
cathode. The electrode in an electrochemical reaction, electrochemical cell or in any related galvanic couple at which the reduction reaction occurs; thus the cathode is the electrode that receives electrons from an external circuit and transfers those to the material that is being reduced.
cathodic protection. A means of corrosion prevention whereby electrons are supplied to the structure to be protected from an external source such as another more reactive metal or a dc power supply.
cation. A positively charged metallic ion.
cement. A substance (often a ceramic) that by chemical reaction binds particulate aggregates into a cohesive structure. With hydraulic cements the chemical reaction is one of hydration, involving water.
cementite. Iron carbide (Fe3C).
ceramic. A compound of metallic and nonmetallic elements, for which the interatomic bonding is predominantly ionic.
ceramic-matrix composite (CMC).
A composite for which both matrix and dispersed phases are ceramic materials. The dispersed phase is normally added to improve fracture toughness.
cermet. A composite material consisting of a combination of ceramic and metallic materials. The most common cermets are the cemented carbides, composed of an extremely hard ceramic (e.g.,WC,TiC), bonded together by a ductile metal such as cobalt or nickel.
chain-folded model. For crystalline polymers, a model that describes the structure of platelet crystallites. Molecular alignment is accomplished by chain folding that occurs at the crystallite faces.
Charpy test or Charpy notch test. One of two types of tests (see also Izod test) that can be used to measure the toughness, more precisely, it refers to the impact energy or notch toughness of a standard notched specimen. An impact blow is imparted to the specimen by means of a weighted pendulum.
cis. For polymers, a prefix denoting a type of molecular structure. For some unsaturated carbon chain atoms within a repeat unit, a side atom or group may be situated on one side of the double bond or directly opposite at a 180° rotation position. In a cis structure, two such side groups within the same repeat unit reside on the same side (e.g., cis-isoprene).
coarse pearlite. Pearlite for which the alternating ferrite and cementite layers are relatively thick. This is achieved by very large preceding austentite grains and/ or long holding times in the upper pearlite regime e.g. during the patenting treatment.
coercivity (or coercive field, Hc). The externally applied magnetic field that is required to reduce to zero the magnetic flux density of a magnetized ferromagnetic or ferrimagnetic material.
cold working. The irreversible plastic deformation of a metal, alloy or compound at a temperature below which it recrystallizes or undergoes substantial thermally activated processes such as diffusion or grain growth. This temperature can be quite different for different materials.
colorant. An additive that imparts a specific color to a polymer.
complete wetting. A zero contact or dihedral angle of a phase at an interface
complexions. Equilibrium 2D state at an interface, characterized by an interfacial excess of chemical components and/or structural order parameters, at prescribed chemical potentials
compacted graphite iron. A cast iron that is alloyed with silicon and a small amount of magnesium, cerium, or other additives, in which the graphite exists as wormlike-shaped particles.
component. A chemical constituent (element or compound) of an alloy that may be used to specify its composition. Moste metallic alloys are multi-component materials, i.e. they consist of many elements.
composition (Ci). The relative content of a particular element or constituent (i) within an alloy, usually expressed in weight percent or atom percent.
concentration gradient (dC/dx). The spatial slope of the concentration profile at a specific position.
concentration polarization. The condition wherein the rate of an electrochemical reaction is limited by the rate of diffusion in the solution.
concentration profile. The curve that results when the concentration of a chemical species is plotted versus position in a material.
concrete. A composite material consisting of aggregate particles bound together in a solid body by a cement.
condensation (or step reaction) polymerization. The formation of polymer macromolecules by an intermolecular reaction, usually with the production of a by-product of low molecular weight, such as water.
conduction band. For electrical insulators and semiconductors, the lowest-lying electron energy band that is empty of electrons at 0 K. Conduction electrons are those that have been excited to states within this band.
conductivity, electrical . The proportionality constant between current density and applied electric field; also, a measure of the ease with which a material is capable of conducting an electric current.
congruent transformation. A transformation of one phase to another of the same composition.
continuous cooling transformation (CCT) diagram. A plot of temperature versus the logarithm of time for a steel alloy of definite composition. It is used to indicate when transformations occur as the initially austenitized material is continuously cooled at a specified rate; in addition, the final microstructure and mechanical characteristics may be predicted.
Cohesive Zone Model. The damage D in cohesive model is described as proportional of the effective to the maximum separation by complete material failure. Description of cleavage failure by means of a Cohesive Zone Model. The dissipated energy of the cohesive elements serves as a failure criterion.
coordination number. The number of atomic or ionic nearest neighbors.
copolymer. A polymer that consists of two or more dissimilar repeat units in combination along its molecular chains.
corrosion. Deteriorative loss of a metal as a result of dissolution environmental
corrosion fatigue. A type of failure that results from the simultaneous action of a cyclic stress and chemical attack.
corrosion penetration rate (CPR). Thickness loss of material per unit of time as a result of corrosion; usually expressed in terms of mils per year or millimeters per year.
coulombic force. A force between charged particles such as ions; the force is attractive when the particles are of opposite charge.
covalent bond. A primary interatomic bond that is formed by the sharing of electrons between neighboring atoms.
creep. The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures. In many metallic alloys it is assisted by diffusion and dislocation climb in addition to the other, regularly occurring deformation processes. Reducing climb processes is essential in the design of turbine alloys or any other high temperature alloys.
crevice corrosion. A form of corrosion that occurs within narrow crevices and under deposits of dirt or corrosion products (i.e., in regions of localized depletion of oxygen
in the solution).
critical point wetting. A term introduced by J. Cahn to describe a transition from partial wetting to complete wetting as a bulk critical point is approached. For example, when two liquids coexist within a miscibility gap with an external third phase like a gas or a solid wall, and are heated towards the critical point, both
the difference between their interfacial energies with the third phase, as well as the energy of the liquid–liquid interface separating them, vanish. Since the difference between the interfacial energies of the two liquids with the third phase vanishes faster than the liquid–liquid interfacial energy, complete wetting of one of the two liquid in contact with the third phase on the other liquid arises before the bulk critical point is reached
critical resolved shear stress ( crss). The shear stress, resolved within a slip plane and direction, that is required to initiate slip.
crosslinked polymer. A polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds.
crystalline. The state of a solid material characterized by a periodic and repeating three-dimensional array of atoms, ions, or molecules.
crystallinity. For polymers, the state wherein a periodic and repeating atomic arrangement is achieved by molecular chain alignment.
crystallite. A region within a crystalline polymer in which all the molecular chains are ordered and aligned.
crystallization (glass-ceramics). The process in which a glass (noncrystalline or vitreous solid) transforms to a crystalline solid.
CP-FEM: Crystal Plasticity – Finite Element Method. Finite Element Method restricting the mechanical degrees of freedom to the crystallographic slip and twin systems of the crystal. The Finite Element Method (FEM) can be viewed as a quasi-standard for simulating micromechanical deformation processes. In the standard form the materials are modelled as continuum that can be elastically and/or plastically deformed. It is, however, known since the 1930s that crystals deform plastically by the motion of dislocations along specific shear direction and planes. This dislocation motion creates a shear of the crystal lattice on distinct planes in distinct directions. In terms of a continuum method like the FEM this means that the plastic part of the deformation has to be built from these elementary shears. The resulting method has been called Crystal Plasticity-Finite Element Method or CP-FEM in short. The first simulations using this approach have been performed by Peirce et al. in 1982. Since then the CP-FEM has matured into an extremely versatile tool for describing the mechanical response of crystalline materials on all length scales from single crystals to engineering parts. While it originally accounted for dislocation slip as only deformation mechanism by now there exist extensions of CP-FEM that also account for other deformation mechanisms such as the →TWIP and the →TRIP effect.
CP-Steel: Complex Phase-Steel. CP-Steels are characterized by a mixed microstructure, mainly consisting of bainitic components. Due to their fine microstructure they show very high strengths with a good cold formability and have good hole expansion values and good bending properties.
crystal structure. For crystalline materials, the manner in which atoms or ions are arrayed in space. It is defined in terms of the unit cell geometry and the atom positions
within the unit cell.
crystal system. A scheme by which crystal structures are classified according to unit cell geometry.This geometry is specified in terms of the relationships between edge lengths
and interaxial angles. There are seven different crystal systems.
Curie temperature (Tc). The temperature above which a ferromagnetic or ferrimagnetic material becomes paramagnetic.