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Materials Final Exam
| Term | Definition |
|---|---|
| Activation energy | The energy required to cause a particular reaction to occur. |
| Age hardening | three step heat treatment used primarily for nonferrous alloys and stainless steels where the material is heated to a single phase region, quenched to form a supersaturated solid solution and then alloyed to age either naturally at room temperature or art |
| Allotropy | The characteristic of a material being able to exist in more than one crystal structure. |
| Amorphous material | Materials that have no long-range order (only short range order). |
| Anisotropic | Having different properties in different directions |
| Artificial aging | Aging at temperatures greater than room temperature but lower than the solvus temperature. |
| Austenite | Name for FCC iron |
| Austenitizing | Forming a homogeneous material comprised of all austenite by heating a ferrous alloy above its upper critical temperature to within the austenite phase region of the phase diagram for sufficient time; generally the first step for heat treatments of ferro |
| Bainite | Two-phase microconstituent containing ferrite and cementite |
| Binding energy | The energy required to separate two atoms an infinite distance apart. |
| Bravais lattice | The fourteen possible lattices that can be created using lattice points, examples of some Bravais lattices include, HCP, BCC and FCC |
| Burgers vector | The direction and distance a dislocation moves in each step |
| Cast iron | Ferrous alloys containing sufficient carbon so that the eutectic reaction occurs during solidification |
| Cementite | Hard, brittle intermetallic compound (Fe3C) |
| Close-packed directions | Directions in a crystal along which atoms are in contact |
| Coefficient of thermal expansion | The amount by which a material changes its dimensions when the temperature changes. |
| Coherent precipitate | A crystalline precipitate that forms from solid solution with an orientation that maintains continuity between the crystal lattice of the precipitate and the lattice of the matrix, usually accompanied by some strain in both lattices. |
| Cold working | Deformation of a material below its recrystallization temperature |
| Coordination number | The number of nearest neighbors to an atom in its atomic arrangement |
| Covalent bond | A very strong type of primary bond formed between two atoms when the atoms share their valence electrons |
| Creep | Time dependant permanent deformation at high temperatures occurring at constant load or constant stress |
| Critical radius | The minimum size that must be formed by atoms clustering together in a liquid before a solid particle is stable and can grow; less than the critical radius, the particle is an embryo, greater than the critical radius the particle is a nucleus |
| Cross slip | The change in the slip system of a dislocation |
| Cross-linking | The process where polymer chains become attached together creating a polymer that is much stronger with lower ductility. |
| Crystal structure | The arrangement of atoms in a material into a repeatable lattice |
| Degree of polymerization | The number of monomers in a polymer; the length of a molecular chain |
| Dendrite | The tree like structure of a solid that grows when an undercooled liquid nucleates |
| Directions of form | Crystallographic directions that have the same characteristics, although their sense is different; generic directions |
| Dislocation | A line imperfection in the lattice of a crystalline material |
| Dispersion strengthening | Increasing the strength of a material by mixing more than one phase. |
| Ductility | The ability of a material to be permanently deformed without breaking |
| Edge dislocation | A dislocation introduced to the lattice by adding an extra half plane of atoms, the burgers vector for an edge dislocation is perpendicular to the dislocation line |
| Elastic deformation | Deformation that is recovered when the load is removed. |
| Elastomers | Polymers possessing exceptional elastic deformation due to the fact that they molecular chains that comprise these materials are highly coiled. |
| Embryo | A tiny particle of solid that forms from the liquid as the atoms cluster together, but is not stable enough to grow (smaller than the critical radius). |
| Endurance limit | The stress below which a material will not fail in a fatigue test regardless of the number of cycles applied |
| Engineering strain | The amount that a material deforms per unit length when pulled or pushed (l / l0). |
| Engineering stress | The applied load divided by the original cross-sectional area. |
| Eutectic | Three phase reaction where a liquid phase changes to two solid phases upon cooling. |
| Eutectoid | Three phase reaction where a solid phase transforms into two solid phases upon cooling |
| Ferrite | A solid solution of one or more elements in BCC iron , the BCC phase on the iron-carbide phase diagram |
| Frank- Read Source | The microstructural mechanism responsible for dislocation multiplication during strain hardening; a pinned dislocation under applied stress produces additional dislocations |
| Glass ceramics | Ceramics shapes formed in the glassy state and allowed to partially crystallize during heat treatment, an example of a glass ceramic is corning ware |
| Grain boundary diffusion | Diffusion of atoms along a grain boundary |
| Grain | A portion of solid material within which the lattice is identical and is oriented in only one direction |
| Growth | The physical processes by which a new phase increases in size |
| Guinier Preston (GP) zones | Tiny clusters of atoms that form early on in the age-hardening process |
| Hardenability | A measure of the depth to which a specific ferrous alloy may be hardened by the formation of martensite upon quenching from a temperature above the upper critical temperature, the Jominy Bar test is used to provide a measure of hardenability |
| Hardness Test | A quick, easy and cheap test that measures the resistance of a material to penetration by a sharp object. Some examples include the Brinell and Rockwell tests |
| Heterogeneous nucleation | Formation of a critically sized solid from the liquid on an impurity surface or the surface of the mold wall |
| Homogeneous nucleation | Formation of a critically sized solid from the spontaneous cluster of atoms due to severe undercooling |
| Hot working | Deformation of a material above the recrystallization temperature |
| Hume-Rothery Rules | Necessary but not sufficient conditions that an alloy system must meet in order to display unlimited solubility; includes same crystal structure, similar atomic size, same valence, similar electronegativity |
| Hypereutectic alloy | For an alloy system displaying a eutectic, an alloy for which the concentration of the solute is greater than the eutectic composition. |
| Hypoeutectic alloy | For an alloy system displaying a eutectic, an alloy for which the concentration of the solute is less than the eutectic composition |
| Impact energy | A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to a very rapid (impact) loading. Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the d |
| Intermetallic compound | A compound of two or more metals that has unique composition and structure, most intermetallics are hard and brittle |
| Interstitial defect | A point defect produced when an atom is placed into the lattice at a site that is normally not a lattice point |
| Interstitial diffusion | Diffusion of different atoms from one interstitial position to another |
| Interstitial site | A location between the normal atom or ions in a crystal into which another atom can be placed |
| Ionic bond | The bond formed between two different atoms when one atom donates its valence electrons to the second atom and the two ions are held together by Columbic (strong electrostatic attraction). |
| Isomorphous phase diagram | A phase diagram that displays unlimited solid solubility (single solid phase). |
| Isotropy | Having the same properties in all directions |
| Lattice parameters | The lengths of the sides of the unit cell and the angles between those sides |
| Lattice | A collection of points that divide space into smaller equally sized segments; the regular geometrical arrangements of points in crystal space |
| Lever law | A technique used to determine the amount of each phase in a two-phase system |
| Liquidus | The temperature on the phase diagram at which the first solid begins to form. |
| Local solidification time | The time required for a particular location in a casting to solidify once nucleation has begun |
| Martensite | A metastable phase formed in steel by diffusionaless athermal transformation, this phase is very strong, but very brittle. |
| Mechanical properties | Properties of a material that describe a material’s response to an applied force |
| Metallic bond | Type of primary atomic bond where positively charged atom cores are held together by the mutually electrostatic attraction to the negatively charged electron cloud or sea of electrons |
| Miscibility gap | A region where two liquid phases do not mix or are not soluble in one another |
| Modulus of elasticity | Young’s modulus:, slope of the stress strain curve in the linear or elastic region. |
| Monotectic | Three phase reaction where a liquid phase changes to a liquid phase and a solid phase. |
| Natural aging | Spontaneous aging of a supersaturated solid solution at room temperature. |
| Nonferrous alloys | An alloy based on a metal other than iron |
| Nonstoichiometric intermetallic compound | An intermetallic compound that can exist over a range of compositions. |
| Normalizing | A simple heat treatment obtained by austenitizing and air-cooling to produce a pearlite microstructure in steels |
| Nucleation | The initial stages in a phase transformation. It is evidenced by the formation of small, stable particles (nuclei) of the new phase which are capable of growing. |
| Nucleus | A tiny stable particle of solid that forms from the liquid as atoms cluster together, the radius of the nucleus is greater than some critical radius |
| Offset yield strength | A yield strength obtained graphically that describes the stress that gives no more than a specified amount of plastic deformation |
| Packing factor | The fraction of space occupied by the atoms |
| Pearlite | A two-phase lamellar microconstituent in steel made up of ferrite and cementite; this microstructure is relatively soft and ductile, formed from slow, near equilibrium cooling rates |
| Percent elongation | The total percent increase in length of a specimen during a tensile test (change in length /original length). |
| Peritectic | A three-phase reaction where a solid phase and liquid phase transform to a single solid phase upon cooling |
| Peritectoid | A three-phase reaction where two solid phases transform to a single solid phase upon cooling |
| Pearlite | A garden additive used to help impart thermal resistance in homemade bricks. |
| Phase | A material having the same composition, structure and properties under equilibrium conditions |
| Physical properties | Describe a materials response to an applied field |
| Planar growth | The growth of a smooth solid-liquid interface where no undercooling is present. |
| Planes of form | Crystallographic planes that have the same characteristic although their orientation is different, denoted by { }, generic planes |
| Plastic deformation | Permanent deformation in a material. For metals plastic deformation occurs by the movement of dislocations through the material. |
| Point defects | Zero dimensional imperfections that are located at a single point, examples include vacancies, substitutional, interstitials |
| Polygonized substructure | A subgrain structure produced during the recovery (early) stages of annealing where the dislocations do not decrease in number, but they rearrange themselves into this polygonized substructure |
| Polymorphism | Allotropy or being able to exist in more than one crystal structure. |
| Pouring temperature | The temperature of a metal when it is poured into a mold |
| Precipitate | A solid phase that forms during age hardening from the original matrix when the solubility limit is exceeded |
| Recovery | A stage in the annealing process where the material is subjected to a low temperature heat treatment (below Trc) causing the dislocations to rearrange themselves into a polygonized substructure, this stage of annealing eliminates residual stresses, restor |
| Recrystallization | A stage in the annealing process where the material is subjected to a medium temperature heat treatment (above Trc) where the dislocations are removed from the material and new grains nucleate and grow; eliminates all of the effects of strain hardening ex |
| Repeat distance | The distance from one lattice point to an adjacent lattice point along a specific direction |
| Screw dislocation | A dislocation produced by skewing the crystal one atomic plane, Burgers vector is parallel to the dislocation line |
| Secondary bond | Relatively weak bonds, such as Van der Waals and hydrogen bonds, that typically join molecules to one another. |
| Self-diffusion | The random movement of atoms within a pure metal |
| Slip | The movement of dislocations in a metal which leads to permanent deformation |
| Solid solution | A homogeneous crystalline phase that contains two or more chemical species. Both substitutional and interstitial solid solutions are possible |
| Solidus | The temperature on a phase diagram below which all the liquid has completely solidified |
| Solution treatment | The first step in age hardening where the material is heated above its solvus temperature to form a single phase solid solution by dissolving precipitate particles |
| Solvus | A solubility line on a phase diagram that separates a single solid phase region from a multiple phase region, indicates the solubility limit in a material |
| Stainless steel | A group of ferrous alloys that contain at least 12% Cr. |
| Stoichiometric intermetallic | An intermetallic compound that exists at a single composition, seen on the phase diagram as a vertical line. |
| Strain hardening | A method of strengthening a metal by increasing the number of dislocations by plastically deforming the metal |
| Substitutional defect | A point defect in a crystalline material produced when an atom is removed from a regular lattice position and replaced with another type of atom. |
| Superheat | The pouring temperature minus the equilibrium freezing temperature. |
| Supersaturated solid solution | A solution formed as part of the precipitation hardening sequence when the material is cooled rapidly from a single phase region to a two phase region; the rapid cooling prevents diffusion from occurring so that the second phase cannot nucleate and grow, |
| Surface defects | Two dimensional imperfections in a crystalline material such as grain boundaries, stacking faults, twin boundaries, the material surface and small angle grain boundaries. |
| Surface diffusion | The fastest type of diffusion where atoms diffuse along material surfaces |
| Temper designation | A shorthand notation used to describe the processing of an alloy. |
| Tempering | Process where a hardened steel or cast iron is reheated to some temperature below the eutectoid temperature for the purpose of decreasing the hardness and increasing toughness by restoring some of the ductility, In steels tempering is generally done by he |
| Thermal arrest | A plateau of cooling curve during solidification caused by the latent heat of fusion that is emitted during solidification which effectively heats the cooling liquid |
| Thermoplastic | A type of polymer that can be heated and reformed multiple times, generally has good ductility but lower strength then a thermoset |
| Thermoset | A polymer with a three-dimensional network structure that cannot be heated and reformed, generally more brittle, but stronger than a thermoplastic |
| Tie line | A horizontal line drawn in a two-phase region of a phase diagram that helps to determine the composition of each phase |
| Total solidification time | The time required for a casting to solidify after the casting has been poured into the mold |
| Toughness | A qualitative measure of the impact resistance of a material, a function of the strength and ductility of a material, can be determined from the area under the true stress-true strain curve |
| Transition temperature | The temperature below which a material behaves in a brittle manner in an impact test |
| Undercooling | The temperature to which a liquid metal must be cooled below the equilibrium freezing temperature before nucleation occurs. |
| Unit cell | A subdivision of the lattice that still retains the overall characteristics of the entire lattice; the basic building block of a crystalline material |
| Vacancy diffusion | A mechanism of diffusion where a diffusing atom leaves a regular lattice position to fill a vacancy site |
| Vacancy | A point defect where an atom is missing from a regular lattice site |
| Valence | The number of electrons in an atom that take place in bonding or chemical reactions |
| Van der Waals bond | A type of secondary bond caused by a weak electrostatic attraction between polar molecules. |
| Viscoelasticity | The deformation of a polymer by viscous flow of the chains or segments of the chain where the stress is applied |
| Volume diffusion | The slowest type of diffusion where the diffusing species moves through the interior or volume of the grains where the atoms are most efficiently packed. |
| Wrought alloys | Alloys that are shaped by a deformation process |
| Yield strength | The stress level in a material where permanent deformation begins to occur, on a stress-strain curve the yield strength separates the elastic from the plastic region of the curve |
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