Alloy Phase Diagram Database™


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minute (angular)
second (angular)
degree (angular)
degree Celsius
degree Fahrenheit
allotropic transformation
Change in phase with a change in temperature at the same composition.
(1) A near synonym for polymorphism. Allotropy is generally restricted to describing polymorphic behavior in elements, terminal phases, and alloys whose behavior closely parallels that of the predominant chemical element. (2) The existence of a substance, especially a chemical element, in two or more physical states (for example, crystals).
(1) A substance having metallic properties and being composed of two or more chemical elements of which at least one is a metal. (2) To make or melt an alloy.
alloy powder, alloyed powder
A metal powder consisting of at least two chemical elements that are partially or completely alloyed with each other.
alloy steel
Steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus) within the limits recognized for constructional alloy steels, added to effect changes in mechanical or physical properties.
alloy system
A complete series of compositions produced by mixing in all proportions any group of two or more chemical elements, at least one of which is a metal.
alloying element
A chemical element added to and remaining in a metal that changes structure and properties.
alpha brass
A solid-solution phase of one or more alloying elements in copper having the same crystal lattice as copper.
alpha ferrite
See ferrite
alpha iron
The body-centered cubic form of pure iron, stable below 910 °C.
Not having a crystal structure; noncrystalline.
amorphous solid
A rigid material whose structure lacks crystalline periodicity; that is, the pattern of its constituent atoms or molecules does not repeat periodically in three dimensions.
Ångstrom (unit)
A unit of linear measure equal to 10-10 m, or 0.1 nm (nanometer), sometimes used to express small distances such as interatomic distances and some wavelengths.
The characteristic of exhibiting different values of a property in different directions with respect to a fixed reference system in the material.
APDIC diagram
A diagram reviewed under the auspices of the Alloy Phase Diagram International Commission
apparent density
(1) The weight per unit volume of a powder, in contrast to the weight per unit volume of the individual particles. (2) The weight per unit volume of a porous solid, where the unit volume is determined from external dimensions of the mass. Apparent density is always less than the true density of the material itself.
atomic percent
atomic number (Z)
The number of protons in an atomic nucleus, which determines the individuality of the atom as a chemical element.
atomic percent
The number of atoms of a chemical element in a total of 100 representative atoms of a substance.
boiling point
body-centered cubic
body-centered tetragonal
binary alloy
An alloy containing only two chemical elements.
binary system
The complete series of compositions produced by mixing a pair of chemical elements in all proportions.
bivariant equilibrium
If both the pressure and temperature in a unary system are freely and arbitrarily selected, the situation corresponds to having two degrees of freedom, and the phase rule says that only one phase can exit in stable equilibrium (p = 1 - 2 + 2). This situation is called bivariant equilibrium.
body-centered cubic
A common metallic crystal structure consisting of a cubic unit cell with atoms located at all eight corners and a single atom at the cube center.
body-centered tetragonal
A body-centered cubic crystal structure that has been tetragonally distorted by the presence of extra atoms of carbon.
Boltzmann constant
A thermal energy constant having the value of 1.38 x 10-23 J/K ( 8.62 x 10-5 eV/K).
An isothermal reversible reaction in which a solid is converted into a second solid and a liquid. With L denoting a liquid phase, and S1 and S2 denoting solid phases, S1 ↔ S2 + L. Also known as metatectic.
cell parameters
Unit cell edge lengths (a, b, c) in nanometers and interaxial angles (α, β, γ) in degrees
A hard (800 HV), brittle compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements. The highest cementite contents are observed in white cast irons, which are used in applications where high wear resistance is required.
close-packed hexagonal
A crystal structure found for some metals. The cph unit cell is of hexagonal geometry and is generated by the stacking of close-packed planes of atoms.
cubic centimeters
concentration range
Range of composition presented in the diagram in atomic percent. Diagrams may be presented in full (0-100 at.%) composition or partial composition.
congruent melting
An isothermal or isobaric melting in which both the solid and liquid phases have the same composition throughout the transformation.
congruent transformation
An isothermal or isobaric phase change in metals in which both of the phases concerned have the same composition throughout the process.
conjugate phase
In microstructural analysis, those states of matter of unique composition that coexist at equilibrium at a single point in temperature and pressure. For example, the two coexisting phases of a two-phase equilibrium.
(1) One of the ingredients that make up a chemical system. (2) A phase or a combination of phases that occurs in a characteristic configuration in an alloy microstructure.
constitution diagram
See phase diagram
heat capacity
close-packed hexagonal
critical point
(1) The temperature or pressure at which a change in crystal structure, phase, or physical properties occurs. Also termed transformation temperature. (2) In an equilibrium diagram, that combination of composition, temperature, and pressure at which the phases of an inhomogeneous system are in equilibrium.
critical temperature
That temperature above which the vapor phase cannot be condensed to liquid by an increase in pressure. Synonymous with critical point if pressure is constant.
(1) A solid composed of atoms, ions, or molecules arranged in a pattern that is repetitive in three dimensions. (2) That form, or particle, or piece of a substance in which its atoms are distributed in one specific orderly geometrical array, called a "lattice," essentially throughout. Crystals exhibit characteristic optical and other properties and growth or cleavage surfaces, in characteristic directions.
crystal system
One of seven groups into which all crystals may be divided; triclinic, monoclinic, orthorhombic, hexagonal, rhombohedral, tetragonal, and cubic.
cubic plane
A plane perpendicular to any one of the three crystallographic axes of the cubic (isometric) system; the Miller indices are {100}.
Curie temperature
The temperature marking the transition between ferromagnetism and paramagnetism, or between the ferroelectric phase and the paraelectric phase. Also known as Curie point. See also ferromagnetism and paramagnetism.
density ratio
The ratio of the determined density of a powder compact to the absolute density of atoms of the same composition, usually expressed as a percentage. Also referred to as percent theoretical density.
density, absolute
The mass per unit volume of a solid material, expressed in g/cm3, kg/m3, lb/ft3, or Mg/m3.
density, Mg/m3
Density (mass per unit volume) of the phase in megagrams per cubic meter
(1) Spreading of a constituent in a gas, liquid, or solid, tending to make the composition of all parts uniform. (2) The spontaneous movement of atoms or molecules to new sites within a material.
electromotive force
(1) The force that determines the flow of electricity; a difference of electric potential. (2) Electrical potential; voltage.
element phase
Phase of the pure chemical elements in this system.
electromotive force
emission spectroscopy
The branch of spectroscopy treating the theory, interpretation, and application of spectra originating in the emission of electromagnetic radiation by atoms, ions, radicals, and molecules.
The relation of crystal forms of the same substance in which one form is stable above a certain temperature and the other form is stable below that temperature. For example, ferrite and austenite are enantiotropic in ferrous alloys.
Thermal energy changes under constant pressure (again neglecting any field effects) are most conveniently expressed in terms of the enthalpy, H, of a system. Enthalpy, also called heat content, is defined by: H =U + pV Enthalpy, like internal energy, is a function of the state of the system, as is the product pV.
Thermodynamic function defined so that when a small quantity of heat dQ is received by a system at temperature T, the entropy, S, is increased by dQ/T, provided that no irreversible change takes place in the system. Nil at absolute zero. Associated with degree of disorder.
The dynamic condition of physical, chemical, mechanical, or atomic balance that appears to be a condition of rest rather than one of change. There are three types of equilibria: stable, metastable, and unstable. Stable equilibrium exists when the object is in its lowest energy condition; metastable equilibrium exists when additional energy must be introduced before the object can reach true stability; unstable equilibrium exists when no additional energy is needed before reaching metastability or stability. Although true stable equilibrium conditions seldom exist, the study of equilibrium system is extremely valuable, because it constitutes a limiting condition from which actual conditions can be estimated.
equilibrium diagram
A graph of the temperature, pressure, and composition limits of phase fields in an alloy system as they exist under conditions of thermodynamical equilibrium. In metal systems, pressure is usually considered constant. Compare with phase diagram.
(1) An isothermal reversible reaction in which a liquid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. With L denoting a liquid phase, and S1 and S2 denoting solid phases, L ↔ S1 + S2. (2) An alloy having the composition indicated by the eutectic point on a phase diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectic reaction often in the form of regular arrays of lamellas or rods.
eutectic melting
Melting of localized microscopic areas whose composition corresponds to that of the eutectic in the system.
eutectic point
The composition of a liquid phase in univariant equilibrium with two or more solid phases; the lowest melting alloy of a composition series.
(1) An isothermal reversible reaction in which a solid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. With S1, S2, and S3 denoting solid phases, S3 ↔ S1 + S2. (2) An alloy having the composition indicated by the eutectoid point on a phase diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectoid reaction.
eutectoid point
The composition of a solid phase that undergoes univariant transformation into two or more other solid phases upon cooling.
face-centered cubic
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.
face-centered tetragonal
A face-centered crystal structure that results from stretching a cubic lattice along one of its lattice vectors so that the cube becomes a right parallelepiped.
face-centered cubic
face-centered tetragonal
(1) A solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated (for instance, as chromium ferrite), the solute is generally assumed to be carbon. On some equilibrium diagrams, there are two ferrite regions separated by an austenite area. The lower area is α-ferrite; the upper, δ-ferrite. If there is no designation, α-ferrite is assumed. (2) An essentially carbon-free solid solution in which α-iron is the solvent and which is characterized by a body-centered cubic crystal structure. Fully ferritic steels are only obtained when the carbon content is quite low. The most obvious microstructural features in such metals are the ferrite grain boundaries.
A property exhibited by certain metals, alloys, and compounds of the transition (iron group), rare-earth, and actinide elements in which, below a certain temperature termed the Curie temperature, the atomic magnetic moments tend to line up in a common direction. Ferromagnetism is characterized by the strong attraction of one magnetized body for another. See also Curie temperature. Compare with paramagnetism.
Standardized formula for the specific compound (phase).
Gibbs energy
gram atom
Gibbs energy
The maximum useful work obtainable from a chemical system without net change in temperature or pressure.
heat capacity
Amount of heat dQ that has to be added to a system to increase its temperature by a small amount dT. For solids, the heat capacity determined at constant pressure, Cp, is virtually identical to the heat capacity determined at constant volume, CV, at low temperature. Also called specific heat in the literature.
high temperature
hypereutectic alloy
In an alloy system exhibiting a eutectic, any alloy whose composition has an excess of alloying element compared with the eutectic composition and whose equilibrium microstructure contains some eutectic structure.
hypereutectoid alloy
In an alloy system exhibiting a eutectoid, any alloy whose composition has an excess of alloying element compared with the eutectoid composition, and whose equilibrium microstructure contains some eutectoid structure.
hypoeutectic alloy
In an alloy system exhibiting a eutectic, any alloy whose composition has an excess of base metal compared with the eutectic composition and whose equilibrium microstructure contains some eutectic structure.
hypoeutectoid alloy
In an alloy system exhibiting a eutectoid, any alloy whose composition has an excess of base metal compared with the eutectoid composition and whose equilibrium microstructure contains some eutectoid structure.
intermediate phase
In an alloy or a chemical system, a distinguishable homogeneous phase whose composition range does not extend to any of the pure components of the system.
intermetallic compound
An intermediate phase in an alloy system, having a narrow range of homogeneity and relatively simple stoichiometric proportions; the nature of the atomic binding can be of various types, ranging from metallic to ionic.
intermetallic phase
A compounds, or intermediate solid solution, containing two or more metals, which usually has a composition, characteristic properties, and crystal structure different from those of the pure components of the system.
interstitial solid solution
A type of solid solution that sometimes forms in alloy systems having two elements of widely different atomic sizes. Elements of small atomic size, such as carbon, hydrogen, and nitrogen, often dissolve in solid metals to form this solid solution. The space lattice is similar to that of the pure metal, and the atoms of carbon, hydrogen, and nitrogen occupy the spaces or interstices between the metal atoms. See also substitutional solid solution.
invariant equilibrium
A stable state among the phases of a system in which none of the external variables, such as pressure, temperature or concentration, may be varied without causing a decrease in the number of phases present.
invariant point
A point on a binary phase diagram at which three phases are in equilibrium.
Another name for a vertical section.
isothermal section
A two-dimensional horizontal slice of a ternary phase diagram at a specified temperature.
Having uniform properties in all directions. The measured properties of an isotropic material are independent of the axis of testing.
The condition of having the same values of properties in all directions.
Boltzmann constant
lattice constants
See lattice parameter.
lattice parameter
The length of any side of a unit cell of a given crystal structure. The term is also used for the fractional coordinates x, y, and z of lattice points when these are variable.
(1) The lowest temperature at which a metal or an alloy is completely liquid.(2) In a phase diagram, the locus of points representing the temperatures at which the various compositions in the system begin to freeze on cooling or finish melting on heating. See also solidus.
liquidus projection
A ternary diagram that depicts the liquidus surface as projected onto a plane.
low temperature
melting point
mechanical property
A property of a material that reveals its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit. Compare with physical property.
melting point
The temperature at which a pure metal, compound, or eutectic changes from solid to liquid; the temperature at which the liquid and the solid are at equilibrium.
melting range
The range of temperatures over which an alloy other than a compound or eutectic changes from solid to liquid; the range of temperatures from solidus to liquidus at any given composition on a phase diagram.
metallic glass
A noncrystalline metal or alloy, commonly produced by drastic supercooling of a molten alloy, by molecular deposition, which involves growth from the vapor phase (e.g., thermal evaporation and sputtering) or from a liquid phase (e.g., electroless deposition and electrodeposition), or by external action techniques (e.g., ion implantation and ion beam mixing).
(1) Of a material not truly stable with respect to some transition, conversion, or reaction but stabilized kinetically either by rapid cooling or by some molecular characteristics as, for example, by the extremely high viscosity of polymers. (2) Possessing a state of pseudoequilibrium that has a free energy higher than that of the true equilibrium state.
metastable phase
Under some conditions, metastable crystal structures can form instead of stable structure. Rapid freezing is a common method of producing metastable structures, but some (such as Fe3C, or cementite) are produced at moderately slow cooling rates. With extremely rapid freezing, even thermodynamically unstable structures (such as amorphous metal glasses) can be produced.
An isothermal reversible reaction in which a solid is converted into a second solid and a liquid. With L denoting a liquid phase, and S1 and S2 denoting solid phases, S1 ↔ S2 + L. Also known as catectic.
miscibility gap
A region of multiphase equilibrium. It is commonly applied to the specific case in which an otherwise continuous series of liquid or solid solutions is interrupted over a limited temperature range by a two-phase field terminating at a critical point.
modulus of elasticity (E)
(1) The measure of rigidity or stiffness of a material; the ratio of stress, below the proportional limit, to the corresponding strain. If a tensile stress of 13.8 MPa (2.0 ksi) results in an elongation of 1.0%, the modulus of elasticity is 13.8 MPa (2.0 ksi) divided by 0.01, or 1380 MPa (200 ksi). (2) In terms of the stress-strain curve, the modulus of elasticity is the slope of the stress-strain curve in the range of linear proportionality of stress to strain. Also known as Young's modulus. For materials that do not conform to Hooke's law throughout the elastic range, the slope of either the tangent to the stress-strain curve at the origin or at low stress, the secant drawn from the origin to any specified point on the stress-strain curve, or the chord connecting any two specific points on the stress-strain curve is usually taken to be the modulus of elasticity. In these cases, the modulus is referred to as the tangent modulus, secant modulus, or chord modulus, respectively.
An isothermal reversible reaction in a binary system, in which a liquid on cooling decomposes into a second liquid of a different composition and a solid. It differs from a eutectic in that only one of the two products of the reaction is below its freezing range. With L denoting a liquid phase and S denoting solid phases, L1 ↔ S + L2.
A reaction in a system containing two solid solution phases, S1' and S1'' in which S1' decomposes into S1'' and a new phase S2:
S1' ↔ S1'' + S2
The ability of a solid to exist in two or more forms (crystal structures), but in which one form is the stable modification at all temperatures and pressures. Ferrite and martensite are a monotropic pair below the temperature at which austenite begins to form, for example, in steels. Alternate spelling is monotrophism.
The characteristic shape, form, or surface texture or contours of the crystals, grains, or particles of (or in) a material, generally on a microscopic scale.
nature of investigation
The method of the investigation used to gather data for the diagram, such as "experimental" or "calculated."
A property exhibited by substances that, when placed in a magnetic field, are magnetized parallel to the field to an extent proportional to the field (except at very low temperatures or in extremely large magnetic fields). Compare with ferromagnetism.
Pearson symbol
Three-part symbol used to classify crystal structures.
An isothermal reversible reaction in which, upon cooling, a solid and a liquid phase transform into a solid phase having a different composition. With L denoting a liquid phase, and S1 and S2 denoting solid phases, L + S1 ↔ S2.
An isothermal reversible reaction in which two solids transform into a solid phase having a different composition. With S1, S2, and S3 denoting solid phases, S1 + S2 ↔ S3.
A physically homogeneous and distinct portion of a material system.
phase change
The transition from one physical state to another, such as gas to liquid, liquid to solid, gas to solid, or vice versa.
phase diagram
A graphical representation of the temperature and composition limits of phase fields in an alloy or ceramic system as they actually exist under the specific conditions of heating or cooling. A phase diagram may be an equilibrium diagram, an approximation to an equilibrium diagram, or a representation of metastable conditions or phases. Synonymous with constitution diagram. Compare with equilibrium diagram.
phase rule
The maximum number of phases (P) that may coexist at equilibrium is two, plus the number of components (C) in the mixture, minus the number of degrees of freedom (F): P + FC + 2.
physical property
A property of a material that is relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of thermal expansion, magnetic permeability, and lattice parameter. Does not include chemical reactivity. Compare with mechanical property.
Poisson's ratio (v)
The absolute value of the ratio of transverse (lateral) strain to the corresponding axial strain resulting from uniformly distributed axial stress below the proportional limit of the material.
Pertaining to a solid comprised of many crystals or crystallites, intimately bonded together. May be homogeneous (one substance) or heterogeneous (two or more crystal types or compositions).
A general term for the ability of a solid to exist in more than one form. In metals, alloys, and similar substances, this usually means the ability to exist in two or more crystal structures, or in an amorphous state and at least one crystal structure. See also allotropy, enantiotropy, and monotropism.
parts per billion
parts per million
In metals, the separation of a new phase from solid or liquid solution, usually with changing conditions of temperature, pressure, or both.
Representative substance (element or phase) with the same crystal structure as this phase.
pseudobinary system
(1) A three-component or ternary alloy system in which an intermediate phase acts as a component. (2) A vertical section through a ternary diagram.
quasi-binary system
In a ternary or higher-order system, a linear composition series between two substances each of which exhibits congruent melting, wherein all equilibria, at all temperatures or pressures, involve only phases having compositions occurring in the linear series, so that the series may be represented as a binary on a phase diagram.
rare earth
Expression that indicates a change of phase.
reaction type
The general category of reaction that occurs.
room temperature
second (time)
sublimation point
selected-area electron diffraction
solid solution
A single, solid, homogeneous crystalline phase containing two or more chemical species.
(1) The highest temperature at which a metal or alloy is completely solid. (2) In a phase diagram, the locus of points representing the temperatures at which various compositions stop freezing upon cooling or begin to melt upon heating. See also liquidus.
The component of either a liquid or solid solution that is present to a lesser or minor extent; the component that is dissolved in the solvent.
In a phase or equilibrium diagram, the locus of points representing the temperature at which solid phases with various compositions coexist with other solid phases, that is, the limits of solid solubility.
space group
Space group notation is a symbolic description of the space lattice and symmetry of the crystal. It consists of the symbol for the space lattice followed by letters and numbers that designate the symmetry of the crystal. Overbars are presented in line before the related character.
space lattice
A regular, periodic array of points (lattice points) in space that represents the locations of atoms of the same kind in a perfect crystal. The concept may be extended, where appropriate, to crystalline compounds and other substances, in which case the lattice points often represent locations of groups of atoms of identical composition, arrangement, and orientation.
sublimation point
The temperature at which, when the pressure is below the triple point, a solid when heated changes directly to a gas, i.e., the value of the solid-gas phase boundary at a given pressure.
substitutional element
An alloying element with an atomic size and other features similar to the solvent that can replace or substitute for the solvent atoms in the lattice and form a significant region of solid solution in the phase diagram.
substitutional solid solution
A solid solution in which the solvent and solute atoms are located randomly at the atom sites in the crystal structure of the solution. See also interstitial solid solution.
An isothermal reversible reaction in which a liquid solution is transformed into a liquid of a different composition and a solid. With L denoting a liquid phase, and S denoting a solid phase, L1 + L2 ↔ S.
triple point
Curie temperature
transmission electron microscopy
terminal phase
A solid solution having a restricted range of compositions, one end of the range being a pure component of an alloy system.
terminal solid solution
In a multicomponent system, any solid phase of limited composition range that includes the composition of one of the components of the system. See also solid solution.
ternary alloy
An alloy that contains three chemical elements.
ternary system
The complete series of compositions produced by mixing three chemical elements in all proportions.
Theorem of Le Châtelier
The theorem of Henri Le Châtelier, which is based on thermodynamic principles, states that if a system in equilibrium is subjected to a constraint by which the equilibrium is altered, a reaction occurs that opposes the constraint, i.e., a reaction that partially nullifies the alteration.
Néel temperature
transformation temperature
The temperature at which a change in phase occurs. This term is sometimes used to denote the limiting temperature of a transformation range.
transition lattice
An unstable crystallographic configuration that forms as an intermediate step in a solid-state reaction such as precipitation from solid solution or eutectoid decomposition.
transition phase
A nonequilibrium state that appears in a chemical system in the course of transformation between two equilibrium states.
transition point
At a stated pressure, the temperature (or at a stated temperature, the pressure) at which two solid phases exist in equilibrium--that is, an allotropic transformation temperature (or pressure).
transition temperature
(1) An arbitrarily defined temperature that lies within the temperature range in which metal fracture characteristics (as usually determined by tests of notched specimens) change rapidly, such as the ductile-to-brittle transition temperature (DBTT). The DBTT can be assessed in several ways, the most common being the temperature for 50% ductile and 50% brittle fracture (50% fracture appearance transition temperature, or FATT), or the lowest temperature at which the fracture is 100% ductile (100% fibrous criterion). (2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature.
triple point
(1) A point on a phase diagram where three phases of a substance coexist in equilibrium. (2) The intersection of the boundaries of three adjoining grains, as observed in a metallographic section.
cell parameter
A parallelepiped element of crystal structure, containing a certain number of atoms, the repetition of which through space will build up the complete crystal.
univariant equilibrium
A stable state among several phases equal to one more than the number of components, that is, have one degree of freedom.
vertical section
A two-dimensional vertical slice of a ternary phase diagram often taken through one corner (one component) and a congruently melting binary compound that appears on the opposite face.
volume, nm3
Volume of the unit cell in cubic nanometers
weight percent
X-ray diffraction (XRD)
An analytical technique in which measurements are made of the angles at which x-rays are preferentially scattered from a sample (as well as of the intensities scattered at various angles) in order to deduce information on the crystalline nature of the sample--its crystal structure, orientations, and so on.
X-ray diffraction
Young's modulus
A term used synonymously with modulus of elasticity. The ratio of tensile or compressive stresses to the resulting strain. See also modulus of elasticity.

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ASM Alloy Phase Diagrams Center, P. Villars, editor-in-chief; H. Okamoto and K. Cenzual, section editors;, ASM International, Materials Park, OH, USA, 2006-2016