1- The Structure Of Metals

Front 1

atomic structure

Back 1

arrangement of atoms

Front 2

properties

Back 2

atomic structure, composition of the metal, impurities and vacancies in the atomic structure, grain size, grain boundaries, ...

Front 3

ion

Back 3

an atom with too many or too few electrons

Front 4

anion

Back 4

negatively charged atom (results from too many electrons)

Front 5

cation

Back 5

positively charged atom (results from too few electrons)

Front 6

molecule

Back 6

multiple atoms combined through transferred or shared electrons

Front 7

bonds

Back 7

-attractive forces that hold molecules together
-types: strong, van der Waals

Front 8

primary or strong bonds

Back 8

ionic bonds, covalent bonds, metallic bonds

Front 9

ionic bonds

Back 9

-strong bond
-electrons from an outer orbit are transferred
-ex: Na+ and Cl- = table salt

Front 10

covalent bonds

Back 10

-strong bond
-electrons in outer orbits are shared by atoms to form molecules
-ex: H2O

Front 11

metallic bonds

Back 11

-bonds formed by metals and alloys because they have few electrons in outer orbits
-electrons are shared by all atoms in contact ("electron cloud")
-results in high thermal and electrical conductivity

Front 12

van der Waals forces

Back 12

-weak bonds
-attraction of opposite charges
-ex: big O, little H2, dipole

Front 13

Why are protons relevant to metals?

Back 13

determine whether an atom with be metallic, nonmetallic, or semi-metallic

Front 14

crystals

Back 14

orderly configurations of atoms

Front 15

crystal structure

Back 15

the atomic arrangement of atoms

Front 16

unit cell

Back 16

-the smallest group of atoms showing the characteristic lattice structure of a particular metal
-building block of a crystal

Front 17

basic atomic arrangements

Back 17

bcc (body-centered cubic)
fcc (face-centered cubic)
hcp (hexagonal close-packed)

Front 18

hard-ball model

Back 18

can be likened to tennis balls arranged in various configurations in a box

Front 19

bcc

Back 19

-body-centered cubic
-1 tennis ball in center
-8 eighth balls

Front 20

properties

Back 20

-atomic structure
-composition of metal
-vacancies
-impurities
-grain size
-grain boundaries

Front 21

strong bonds

Back 21

-ionic
-covalent
-metallic

Front 22

ionic bond

Back 22

-strong bond between 2 ions
-electrons from outer orbit are transferred
-ex: Na+ and Cl-

Front 23

covalent bond

Back 23

-strong bond
-electrons are shared to from molecules
-low electrical conductivity, high hardness (diamond)

Front 24

metallic bond

Back 24

-strong bond
-electrons are shared between all atoms in contact ("electron cloud")
-high termal and electrical conductivity

Front 25

van der Waals forces

Back 25

-weak attractions between molecules
-results from attraction of opposite charges without electron charges
-ex: h2o, dipole

Front 26

crystals

Back 26

various configurations of atoms

Front 27

crystal structure

Back 27

the atomic arrangement of atoms

Front 28

unit cell

Back 28

-the smallest group of atoms showing the characteristic lattice structure of a particular metal
-building blocks of crystals

Front 29

bcc

Back 29

-body-centered cubic
-1 centers
-(1/8)8 corners

Front 30

fcc

Back 30

-face-centered cubic
-4 halfs
-(1/8)8 corners

Front 31

hcp

Back 31

-hexagonal close-packed

Front 32

basal planes

Back 32

top and bottom planes in hcp

Front 33

alloying

Back 33

modifying crystals by adding atoms of some other metal(s)

Front 34

why do metals form different crystal structures?

Back 34

to minimize energy required to fill space

Front 35

allotropism

Back 35

the appearance of more than one type of crystal structure

Front 36

polymorphism

Back 36

the appearance of more than one type of crystal structure

Front 37

elastic deformation

Back 37

-first stage when a single crystal is subjected to an external force
-it returns to it's original shape when the force is removed

Front 38

plastic deformation

Back 38

-takes place for sufficient force on a crystal structure
-it does not return to it's original shape when the force is removed

Front 39

slip plane

Back 39

-mechanism of plastic deformation
-slipping of one plane of atoms over an adjacent plane under shear stress
-ex: like sliding playing cards against eachother (slip plane is the playing card)

Front 40

shear stress

Back 40

the ratio of applied shearing force to the cross-sectional area being sheared (like playing cards sliding against each other)

Front 41

critical shear stress

Back 41

the amount of shear stress required to cause permanent deformation

Front 42

maximum atomic density

Back 42

slip takes place in closely packed planes and closely pack directions (b/a, a= spacing of atomic planes, b=inversely porportional to the atomic density in the atomic plane)

Front 43

anisotropy

Back 43

a single crystal exhibits different properties when tested in different directions
-ex: plywood is stronger in planar direction than in thickness direction

Front 44

twinning

Back 44

-a portion of the crystal forms a mirror image of itself across the plane of twinning
-usually occurs in hcp metals

Front 45

mechinisms of plastic deformation

Back 45

-the slipping of one plane of atoms over an adjacent plane
-twinning

Front 46

slip system

Back 46

-combination of a slip plane and its direction of slip
-metals with 5 or more slip systems are considered ductile

Front 47

how many possible slip systems are there in a bcc crystal?

Back 47

48

Front 48

how many possible slip systems are there in a fcc crystal?

Back 48

12

Front 49

how many possible slip systems are there in a hcp crystal?

Back 49

3

Front 50

point defects

Back 50

-vacancy (missing atom)
-interstitial atom (extra atom)
-impurity (foreign atom that has replaced the atom of the pure metal)

Front 51

linear defects (one dimensional)

Back 51

-dislocations

Front 52

planar defects (two dimensional)

Back 52

-grain boundaries
-phase boundaries

Front 53

volume imperfections (bulk)

Back 53

-voids
-inclusions (nonmetallic elements such as oxide)
-phases
-cracks

Front 54

what are the categories of defects and imperfections?

Back 54

1. point defects
2. linear defects (1D)
3. planar defects (2D)
4. volume imperfections (bulk)

Front 55

structure sensitive properties

Back 55

-mechanical and electrical properties of metals that are adversely affected by defects
-yield stress, fracture strength, electrical conductivity

Front 56

structure insensitive properties

Back 56

-physical and chemical properties of metals that are not sensitive to defects
-melting point, specific hear, coefficient of thermal expansion, and elastic constants (modulus of elasticity and modulus of rigidity)

Front 57

what are dislocations?

Back 57

defects in the orderly arrangement of a metal's atomic structure

Front 58

what are the types of dislocations?

Back 58

-edge (earthworm, carpet analogy)
-screw (atomic planes form a spiral ramp)

Front 59

work hardening (strain hardening)

Back 59

increase in the overall strength and hardness of a metal due to the increased shear stress req'd to overcome entanglements and impediments

Front 60

grain

Back 60

when molten metal begins to solidify, crystals begin to from independently of each other at various locations, those crystals grow into a "crystalline structure" known as a grain

Front 61

nucleation

Back 61

the initial stage of crystal formation

Front 62

grain boundaries

Back 62

-surfaces that separate individual grains
-influence strength, ductility, and strain hardening

Front 63

isotropic

Back 63

properties do not vary with direction of testing

Front 64

orange peel

Back 64

-rough surface appearance on sheet metal, caused by large grains, when stretched or subjected to bulk deformation such as compression in forging

Front 65

creep

Back 65

elongation under stress over time, usually at elevated temperatures

Front 66

grain-boundary embrittlement

Back 66

-when exposed to low-melting-point metals, a normally ductile and strong metal can crack when subjected to very low external stresses
-ex: aluminum wetted with mercury-zinc...

Front 67

hot shortness

Back 67

-crumbling along the grain boundaries caused by plastic deformation at elevated temperatures
-leaded brass, antimony in copper
-work at low temp to avoid

Front 68

temper embrittlement

Back 68

-in alloy steels, caused by segregation of impurities to the grain boundaries

Front 69

equiaxed grains

Back 69

grains having equal dimensions in all directions

Front 70

cold working

Back 70

process involving plastic deformation at room temperature

Front 71

what properties does anisotropy influence?

Back 71

mechanical and physical

Front 72

what are the 2 types of anisotropy?

Back 72

-preferred orientation
-mechanical fibering

Front 73

crystallographic anisotropy

Back 73

-preferred orientation
-under tension, slip planes and slip bands tend to align themselves in the direction of the tensile force
-under compression, "..." of the compressive force

Front 74

recovery

Back 74

-stresses in the highly deformed regions of the metal piece are relieved
-occurs below the recrystallization temperature

Front 75

polygonization

Back 75

process where subgrain boundaries begin to form

Front 76

recrystallization

Back 76

process in which new equiaxed and strain-free grains are formed, replacing older grains

Front 77

recrystallizaton temperature

Back 77

temp at which complete recrystallizaton occurs within 1 hour
-decreases density, lowers strength, raises ductility

Front 78

stored energy

Back 78

amt of energy stored in dislocations

Front 79

diffusion

Back 79

movement and exchange of atoms across grain boundaries

Front 80

what are the effects of recrystallization on temperature by cold working?

Back 80

a. for const deformation by cold working, time decreases with temp
b. the more prior cold work, the lower the temp req'd for recrystallization
c. the higher the deformation, the smaller the grain size
d. some anisotropy persists after recrystallization, to restore isotropy, temp higher than that req'd for recrystallization necessary

Front 81

what 3 event take place during grain growth?

Back 81

recovery, recrystallization, grain growth

Front 82

grain growth

Back 82

-phenomenon where if temp is raised further, grains can exceed original grain size
-adversely affects mechanical properties

Front 83

warm working

Back 83

plastic deformation carried out at intermediate temperatures

Front 84

homologous temperature (formula)

Back 84

T/Tm
T= working temp
Tm= melting point of the metal