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58 Cards in this Set
- Front
- Back
Metals
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-arranged in very orderly manner
-relatively dense -stiff, strong, ductile, resistant to fracture -good conductors of heat, electricity |
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Ceramics
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-compounds between metallic and nonmetallic elements
-most frequently oxides, nitrides, and carbides -relatively stiff and strong -extremely brittle, highly susceptible to failure -insulative to heat and electricity |
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Polymers
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-low densities
-not stiff and strong -extremely ductile and pliable -tendency to soften/decompose at modest temps |
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Composites
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-composed of two or more individual materials
-naturally occurring also: wood, bone - |
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Bohr Atomic Model
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-electrons assumed to revolve around atomic nucleus in discrete orbitals
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Quantum-Mechanical Principle
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-energies of electrons are quantized (only allowed to have specific values of energy)
-electrons have energy levels or states |
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Electropositive Elements
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-elements capable of giving up their few valence electrons to become positive ions
-farther left and to the bottom of periodic table |
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Electronegative Elements
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-elements on right-hand side of table
-readily accept electrons to form negatively-charged ions |
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Ionic Bonding
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-always found in elements composed of both metallic and non-metallic elements
-metallic elements give up electrons to nonmetallic atoms -all elements become ions -coulombic bonding force -non-directional -high bonding energy -materials w/ this bond tend to be hard, brittle, electrically, and thermally insulative |
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Nondirectional Bond
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-magnitude of the bond is equal in all directions
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Covalent Bonding
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-sharing of electrons between adjacent atoms
-directional |
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Directional Bond
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-bond only exists between specific atoms and only in the direction between one atom and another that participates in electron sharing
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Metallic Bonding
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-nondirectional
-free electrons: explains conductivity of metals |
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Crystalline Material
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-atoms are situated in repeating or periodic array over large atomic distances
-"long range order" |
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Crystal Structure
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-the manner in which atoms, ions, or molecules are spatially arranged
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Unit Cell
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-small repeat entities
-basic structural unit or building block of a crystal structure -defines crystal structure |
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Face-Centered Cubic Crystal Structure
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-atoms located at each of the corners and the centers of the cube faces
-total of four atoms in each cell -coordination number = 12 -APF = .74 |
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Body-Centered Cubic Crystal Structure
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-atoms located at all 8 corners and a single atom at the cube center
-total of 2 atoms in each cell -coordination number = 8 -APF = .68 |
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Hexagonal Close-Packed Crystal Structure
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-coordination number = 12
-APF = .74 |
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Atomic Packing Factor
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-(volume of atoms in unit cell)/(total unit cell volume)
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Single Crystal
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-when the periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen w/out interruption
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Grains
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-small crystals
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Anisotropy
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-when the properties (ie, conductivity) depends on the orientation of the crystal and the direction
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Isotropic
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-measured properties are independent of the direction of the measurement
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Vacancy
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-point defect
-a normally occupied lattice site where the atom is missing -number increases w/ temperature |
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Self-Interstitial
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-an atom from the crystal is crowded into a small void space that under ordinary circumstances is not occupied
-introduces relatively large distortions in metals so is not highly probably in metals |
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Alloys
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-metals in which impurity atoms have been added intentionally to impart specific characteristics to the material
-impurities count as point defects |
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Substitutional Solid Solutions
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-solute or impurity atoms replace the host atoms
-likely if atomic size is comparable -if crystal structure is the same -if electronegativity is similar -if valences are similar |
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Interstitial Solid Solution
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-impurity atoms fill the voids among the host atoms
-unlikely if high packing factor -atomic diameter needs to be substantially smaller than that of the host atoms |
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Edge Dislocation
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-an extra portion of a plane of atoms, or half-plane, the edge of which terminates w/in the crystal
-linear defect, centers on the line that is defined along the end of the extra half-plane of atoms |
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Dislocation Line
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-line running along the extra half-plane of atoms in an edge dislocations
-atoms above are squeezed together, below are pulled apart |
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Screw Dislocation
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-dislocation occurs in twisting fashion
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Interdiffusion/Impurity Diffusion
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-process by which atoms of one metal diffuse into another
-can be observed by changes in composition and/or characteristics (ie, with an alloy) |
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Self-Diffusion
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-occurs in pure metals
-all atoms exchanging positions are of the same type -can't be observed by changes in composition and/or characteristics |
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Vacancy Diffusion
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-the interchange of an atom from a normal lattice position to an adjacent empty lattice site
-necessitates the presence of vacancies |
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Interstitial Diffusion
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-involves atoms that migrate from an interstitial position to a neighboring empty one
-typical w/ smaller atoms (ie, hydrogen, oxygen, etc) -typically more rapid b/c atoms are smaller and therefore more mobile, also b/c probability of movement is more likely than for vacancies |
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Diffusion Flux
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-the rate of mass transfer
-J |
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Fick's First Law
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J = -D (dC/dx)
-direction of diffusion is down the concentration gradient (from high to low concentration) -true for steady-state diffusion |
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Elastic Deformation
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-deformation in which strain and stress are proportional
-nonpermanent--when load is removed, specimen returns to original shape |
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Plastic Deformation
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-permanent, nonrecoverable deformation
-corresponds to the breaking of bonds and then re-forming of new bonds -accomplished through slip (movement of dislocations) |
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Yield Strength
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-stress value where plastic deformation begins to occur
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Tensile Strength
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-maximum stress on the engineering stress-strain curve
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Ductility
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-measure of the degree of plastic deformation that has been sustained at fracture
-percent elongation -indicates the degree to which a structure will deform plastically b/f fracture |
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Resilience
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-capacity of a material to absorb energy when it is deformed elastically and then, upon unloading, to have this energy recovered
-area under the elastic portion of the curve |
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Toughness
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-ability of a material to absorb energy and plastically deform before fracturing
-total area under the curve |
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Hardness
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-measure of a material's resistance to localized plastic deformation (indent or scratch)
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Slip
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-the process by which plastic deformation is produced by dislocation motion
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Slip System
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-the combination of the preferred plane and preferred direction along which dislocation motion occurs
-plane will have the most dense atomic packing -several may exist for a particular structure -more = more ductile material |
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Strengthening Techniques
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-rely on the principle that restricting or hindering dislocation motion renders a material harder and stronger
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Strengthening by Grain Size Reduction
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-smaller grain size = less movement of dislocations
-much harder for dislocations to travel across grain boundaries |
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Solid-Solution Strengthening
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-strengthening and hardening metals by alloying them with impurity atoms
-increases tensile and yield strengths b/c alloys typically less soft than pure metals -works by imposing lattice strains on surrounding host atoms, and prevents dislocations from moving |
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Strain Hardening/Cold Working
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-process by which ductile metal becomes harder and stronger as it is plastically deformed
-defined as percent change in area -will lose ductility, but will strengthen and harden |
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Recrystallization
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-formation of a new set of strain-free and equiaxed grains
-restores mechanical properties that were changed during cold-working --> becomes more ductile, less strong |
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Ductile Fracture
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-substantial plastic deformation w/ high energy absorption b/f failure
-process proceeds slowly as crack grows -necking b/f failure; cup-and-cone fracture |
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Brittle Fracture
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-little or no plastic deformation b/f failure
-cracks spread extremely rapidly -no necking; crack is perpendicular to direction of applied stress |
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Transgranular
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-fracture crack that goes through grain boundaries
-typical w/ brittle fractures |
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Intergranular
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-fracture crack that goes along grain boundaries
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Fatigue
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-form of failure that occurs in structures subjected to dynamic and fluctuating stresses
-failure can occur at a lower stress level than tensile or yield stress -usually brittle-like, even in ductile metals |