Met-232 Exam 2

Front 1

diffusion

Back 1

material transport by atomic motion

Front 2

interdiffusion

Back 2

changes in concentration that occur over time
macroscopic perspective
net drift or transport of atoms from high to low concentration regions

Front 3

impurity diffusion

Back 3

in interdiffusion, the impurity atoms substitute for host atoms

Front 4

interstitial diffusion

Back 4

atoms that migrate from an interstitial position to a neighboring one that is empty.

Front 5

diffusion flux

Back 5

(J), defined as the mass/#atoms(M) diffusing through and perpendicular to a unit cross-sectional area of solid per unit of time.
J = M / At

Front 6

steady-state diffusion

Back 6

diffusion of atoms of a gas through a plate of metal for which the concentrations or pressures of the diffusing species on both surfaces of the plate are held constant

Front 7

concentration profile

Back 7

curve of concentration (C) plotted versus position/distance (x)

Front 8

concentration gradient

Back 8

the slope at a particular point on the concentration profile curve

Front 9

diffusion coefficient

Back 9

constant of proportionality, expressed in square meters per second

Front 10

Fick's first law

Back 10

J = -D ( dC / dx )

Front 11

driving force

Back 11

what compels a reaction to occur

Front 12

Fick's second law

Back 12

sigC/sigt = D ( sig^2 C / sig x^2 )

Front 13

carburizing

Back 13

increasing the surface concentration of carbon to harden the surface of a steel above that of its interior

Front 14

activation energy

Back 14

Qd
the energy required to produce the diffusive motion of one mole of atoms

Front 15

engineering stress

Back 15

sigma = F / Ao
F = instantaneous load
Ao = original cross-sectional area before load is applied

Front 16

engineering strain

Back 16

E = (lt - lo) / lo or delta(l) / lo
lo is the original length before load is applied
lt is the instantaneous length

Front 17

modulus of elasticity

Back 17

sigma = E * e
sigma being engineering stress
e being engineering strain
table 6.1 has E for some metals

Front 18

elastic deformation

Back 18

deformation in which stress and strain are proportional

Front 19

anelasticity

Back 19

time dependent elastic behavior

Front 20

Poisson's ratio

Back 20

v
ratio of lateral and axial strains, or
v = -Ex/Ez = -Ey/Ez

Front 21

plastic deformation

Back 21

when a material is deformed beyond the point where stress is no longer proportional to strain
permanent, nonrecoverable deformation occurs

Front 22

yielding

Back 22

the stress level at which plastic deformation occurs

Front 23

proportional limit

Back 23

initial departure form linearity of the stress-strain curve

Front 24

yield strength

Back 24

stress-strain curve as it bends over in the plastic region

Front 25

tensile strength

Back 25

stress at the maximum on the engineering stress-strain curve

Front 26

ductility

Back 26

measure of the degree of plastic deformation that has been sustained at fracture

Front 27

toughness

Back 27

property that is indicative of a materials resistance to fracture when a crack is present
or
ability of a material to absorb energy and plastically deform before fracturing

Front 28

true stress

Back 28

load (F) divided by the instantaneous cross-sectional area (At) over which deformation is occuring
sigmaT = F / At

Front 29

true strain

Back 29

ET = ln( lt / lo)

Front 30

hardness

Back 30

measure of a material's resistance to localized plastic deformation (ie. small dent or a scratch)
indicator of strength
used extensively for quality control
testing is essentially non-destructive

Front 31

5 Common hardness tests

Back 31

brinell
vickers
knoop
rockwell
scleroscope
mohs

Front 32

scleroscope hardness test

Back 32

field test - drop ball, measure rebound, correlate to hardness

Front 33

mohs hardness test

Back 33

for minerals - the scratch test

Front 34

slip

Back 34

plastic deformation produced by dislocation motion

Front 35

slip plane

Back 35

the crystallographic plane along which the dislocation line traverses

Front 36

dislocation density

Back 36

number of dislocations, expressed as total dislocation length per unit volume

Front 37

lattice strain

Back 37

compressive, tensile, and shear strains within a lattice

Front 38

slip system

Back 38

combination of the slip plane and slip direction.
depends on the crystal structure of the metal

Front 39

solid-solution strengthening

Back 39

strengthen and harden metals by alloying with impurity atoms that go into either substitutional or interstitial solid solution

Front 40

strain hardening

Back 40

where a ductile metal becomes harder and stronger as it is plastically deformed
sometimes called work hardening

Front 41

cold working

Back 41

strain hardening, called cold working because deformation takes place at temperatures that are relatively cold compared to the melting point of the metal

Front 42

critical resolved shear stress

Back 42

Stress operating on a slip system due to an applied tensile stress
Slip begins within the single crystal where the shear stress on the slip plane in the slip direction reaches a critical level

Front 43

recovery

Back 43

thermal energy allows dislocations to re-arrange into low energy configurations
no new grains produce
internal stresses are relieved

Front 44

recrystallization

Back 44

nucleation and growth of "strain free" grains
hardness/strength decreases, ductility increases

Front 45

grain growth

Back 45

recrystallized grains grow to a terminal size

Front 46

2 types of fractures and their speeds

Back 46

ductile: slow crack propagation
brittle: rapid crack propagation

Front 47

ductile fracture progression

Back 47

1.neck forms and microvoids are created within metal
2.micro voids coalesce into a large crack
3.crack propagates to edge and cone fracture results

Front 48

brittle fracture progression

Back 48

1.crack propagates very rapidly, giving a relatively smooth surface

Front 49

chevron

Back 49

V shape where brittle fracture initiated

Front 50

crack propagation types (2)

Back 50

intergranular - crack follows grain boundaries
transgranular - crack cuts across grain

Front 51

fracture toughness

Back 51

measure of a materials resistance to brittle fracture when a crack is present

Front 52

plane strain

Back 52

when specimen thickness is much greater than the crack dimensions

Front 53

fatigue

Back 53

form of failure that occurs in structures subjected to dynamic and fluctuating stresses (ie. bridges, aircraft, machine components)

Front 54

fatigue strength

Back 54

stress level at which failure will occur for some specified number of cycles

Front 55

fatigue life

Back 55

number of cycles to cause failure at a specified stress level

Front 56

case hardening

Back 56

technique which both surface hardness and fatigue life are enhanced for steel alloys, by carburizing or nitriding process

Front 57

thermal fatigue

Back 57

fatigue at elevated temperatures caused by fluctuating thermal stresses

Front 58

corrosion fatigue

Back 58

fatigue caused by simultaneous action of cyclic stress and chemical attack

Front 59

creep

Back 59

time-dependent and permanent deformation of materials when subjected to a constant load or stress