Mse 170 Exam 1

Front 1

Metals

Back 1

-arranged in very orderly manner
-relatively dense
-stiff, strong, ductile, resistant to fracture
-good conductors of heat, electricity

Front 2

Ceramics

Back 2

-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

Front 3

Polymers

Back 3

-low densities
-not stiff and strong
-extremely ductile and pliable
-tendency to soften/decompose at modest temps

Front 4

Composites

Back 4

-composed of two or more individual materials
-naturally occurring also: wood, bone
-

Front 5

Bohr Atomic Model

Back 5

-electrons assumed to revolve around atomic nucleus in discrete orbitals

Front 6

Quantum-Mechanical Principle

Back 6

-energies of electrons are quantized (only allowed to have specific values of energy)
-electrons have energy levels or states

Front 7

Electropositive Elements

Back 7

-elements capable of giving up their few valence electrons to become positive ions
-farther left and to the bottom of periodic table

Front 8

Electronegative Elements

Back 8

-elements on right-hand side of table
-readily accept electrons to form negatively-charged ions

Front 9

Ionic Bonding

Back 9

-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

Front 10

Nondirectional Bond

Back 10

-magnitude of the bond is equal in all directions

Front 11

Covalent Bonding

Back 11

-sharing of electrons between adjacent atoms
-directional

Front 12

Directional Bond

Back 12

-bond only exists between specific atoms and only in the direction between one atom and another that participates in electron sharing

Front 13

Metallic Bonding

Back 13

-nondirectional
-free electrons: explains conductivity of metals

Front 14

Crystalline Material

Back 14

-atoms are situated in repeating or periodic array over large atomic distances
-"long range order"

Front 15

Crystal Structure

Back 15

-the manner in which atoms, ions, or molecules are spatially arranged

Front 16

Unit Cell

Back 16

-small repeat entities
-basic structural unit or building block of a crystal structure
-defines crystal structure

Front 17

Face-Centered Cubic Crystal Structure

Back 17

-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

Front 18

Body-Centered Cubic Crystal Structure

Back 18

-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

Front 19

Hexagonal Close-Packed Crystal Structure

Back 19

-coordination number = 12
-APF = .74

Front 20

Atomic Packing Factor

Back 20

-(volume of atoms in unit cell)/(total unit cell volume)

Front 21

Single Crystal

Back 21

-when the periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen w/out interruption

Front 22

Grains

Back 22

-small crystals

Front 23

Anisotropy

Back 23

-when the properties (ie, conductivity) depends on the orientation of the crystal and the direction

Front 24

Isotropic

Back 24

-measured properties are independent of the direction of the measurement

Front 25

Vacancy

Back 25

-point defect
-a normally occupied lattice site where the atom is missing
-number increases w/ temperature

Front 26

Self-Interstitial

Back 26

-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

Front 27

Alloys

Back 27

-metals in which impurity atoms have been added intentionally to impart specific characteristics to the material
-impurities count as point defects

Front 28

Substitutional Solid Solutions

Back 28

-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

Front 29

Interstitial Solid Solution

Back 29

-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

Front 30

Edge Dislocation

Back 30

-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

Front 31

Dislocation Line

Back 31

-line running along the extra half-plane of atoms in an edge dislocations
-atoms above are squeezed together, below are pulled apart

Front 32

Screw Dislocation

Back 32

-dislocation occurs in twisting fashion

Front 33

Interdiffusion/Impurity Diffusion

Back 33

-process by which atoms of one metal diffuse into another
-can be observed by changes in composition and/or characteristics (ie, with an alloy)

Front 34

Self-Diffusion

Back 34

-occurs in pure metals
-all atoms exchanging positions are of the same type
-can't be observed by changes in composition and/or characteristics

Front 35

Vacancy Diffusion

Back 35

-the interchange of an atom from a normal lattice position to an adjacent empty lattice site
-necessitates the presence of vacancies

Front 36

Interstitial Diffusion

Back 36

-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

Front 37

Diffusion Flux

Back 37

-the rate of mass transfer
-J

Front 38

Fick's First Law

Back 38

J = -D (dC/dx)

-direction of diffusion is down the concentration gradient (from high to low concentration)
-true for steady-state diffusion

Front 39

Elastic Deformation

Back 39

-deformation in which strain and stress are proportional
-nonpermanent--when load is removed, specimen returns to original shape

Front 40

Plastic Deformation

Back 40

-permanent, nonrecoverable deformation
-corresponds to the breaking of bonds and then re-forming of new bonds
-accomplished through slip (movement of dislocations)

Front 41

Yield Strength

Back 41

-stress value where plastic deformation begins to occur

Front 42

Tensile Strength

Back 42

-maximum stress on the engineering stress-strain curve

Front 43

Ductility

Back 43

-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

Front 44

Resilience

Back 44

-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

Front 45

Toughness

Back 45

-ability of a material to absorb energy and plastically deform before fracturing
-total area under the curve

Front 46

Hardness

Back 46

-measure of a material's resistance to localized plastic deformation (indent or scratch)

Front 47

Slip

Back 47

-the process by which plastic deformation is produced by dislocation motion

Front 48

Slip System

Back 48

-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

Front 49

Strengthening Techniques

Back 49

-rely on the principle that restricting or hindering dislocation motion renders a material harder and stronger

Front 50

Strengthening by Grain Size Reduction

Back 50

-smaller grain size = less movement of dislocations
-much harder for dislocations to travel across grain boundaries

Front 51

Solid-Solution Strengthening

Back 51

-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

Front 52

Strain Hardening/Cold Working

Back 52

-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

Front 53

Recrystallization

Back 53

-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

Front 54

Ductile Fracture

Back 54

-substantial plastic deformation w/ high energy absorption b/f failure
-process proceeds slowly as crack grows
-necking b/f failure; cup-and-cone fracture

Front 55

Brittle Fracture

Back 55

-little or no plastic deformation b/f failure
-cracks spread extremely rapidly
-no necking; crack is perpendicular to direction of applied stress

Front 56

Transgranular

Back 56

-fracture crack that goes through grain boundaries
-typical w/ brittle fractures

Front 57

Intergranular

Back 57

-fracture crack that goes along grain boundaries

Front 58

Fatigue

Back 58

-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