Materials

Front 1

point defects

Back 1

vacancy

extra atom(impurity)

Front 2

grain boundary

Back 2

planar defect

Front 3

edge dislocation

Back 3

line defect-edge of extra half plane

burgers vector is perpundicular to shear vector

Front 4

dislocations in shearing

Back 4

permanent deformation

shear strength=shear stress required to move a dislocation

consecutive breakage of atomic bonds

Front 5

point defects types

Back 5

* frenkel defect: displacement of an atom from its lattice position to an interstitial site,cation ( vacancy-intestital pairs)

*schottky defect: the charged is netural by removing atoms (vacancy pairs)

Front 6

frank partial dislocation

Back 6

Front 7

Hume-Rothery rules

Back 7

• size factor: the atoms must be of similar size, with no more than 15% difference in atomic radius,
• crystal structure: the materials must have the same crystal structure
• valence: the atoms must have the same valence;
• electronegativity: the atoms must have approximately the same electronegativity.

Front 8

radiation damage

Back 8

makes it more brittle

Displaced Electrons (ionization)
• Displaced Atoms by Elastic Collision
• Fission and Thermal Spikes

Front 9

Peierls Nabarro stress

Back 9

force needed to move a dislocation within a plane of atoms in the unit cell. The magnitude varies periodically as the dislocation moves within the plane. Peierls stress depends on the size and width of a dislocation and the distance between planes.

stress lowest along close packed planes(a largest)

and close packed directions (b smallest)

Front 10

Peierls Nabarro stress conn

Back 10

material crystal width stress temp-dep

metal FCC wide very small negligible

metal BCC narrow moderate strong

ceramic ionic narrow large strong

ceramic covalent very n very large strong

Front 11

total,partial and extended dislocations

Back 11

total into partials

creates extended dislocations

creates stacking fault bounded by shockley partial dislocations

burgers vector and fault in the same plane

picture

Front 12

Frank-Reed source

Back 12

formation of dislocation loop by the frank-read mechanism

Front 13

screw dislocations

Back 13

burgers vector is parallel to shear

Front 14

dislocation loop

Back 14

Front 15

dislocation interaction

Back 15

Two dislocations of the same sign on
the same plane will repel one another
•two dislocations of opposite sign on the
same slip plane will attract one another
• dislocations of the same sign moving on
different slip planes may be attracted to
one another, and possibly form
dislocation arrays

Front 16

stacking faults fcc

Back 16

intrinsic

shockley partial dislocations

vacancy condensation(frank partial dislocations) don't move

extrinsic or double

precipitation

shockley partials on two slip planes

Front 17

Frank’s rule

Back 17

b3^2<b2^2+b1^2 has to be true for reaction to occur

Front 18

lomer lock fcc

Back 18

Front 19

jogs and kinks

Back 19

Kink – in the same slip plane
- do not inhibit the movement of
the dislocation
- may assist its motion, as atoms
or vacancies diffusing to them
may enable the dislocation to
move at stresses below the
critical resolved shear stress
Jog – in the different slip
plane

Front 20

jogs and kinks

Back 20

jogs: up-differance then screw

kink: foward-differance than screw

Front 21

Cross slip of Screw Dislocations

Back 21

Front 22

Dislocation-Dislocation Interactions

Back 22

same slip plane

* pileup

*annihilation

intersecting planes

* repulsion

*attraction

*jogs

junctions and locks

Front 23

tilt boundaries

twist boundaries

Back 23

Front 24

Coincidence Boundaries

Back 24

incoherent like ordinary grain boundary. Majority of atoms do not correspond to lattice points of
other crystal

Front 25

Coherent Twin Boundaries

Back 25

• Energy of a Twin boundary is generally about 0.1 ygb

Front 26

Grain Size vs. Volume Fraction of Intercrystal Regions

Back 26

Front 27

twinning

Back 27

only mechanism for heterogenous plastic flow

Front 28

twinning conn

Back 28

Bursting of twins during
straining may lead to sudden
drop in stress in the stress vs
strain curve.

Front 29

twinning hcp

Back 29

In HCP metals, slip is restricted
to basal plane
– Twinning contributes to plastic
deformation
– Twinning also reorients crystals to
favor further basal slip on

In HCP metals,

Front 30

twinning hcp conn

Back 30

Twinning results in a compression
or elongation along the c-axis, depending on the ratio c/a. For c/a >√3
(the case of Zn and Cd), twinning occurs on (10¯1 ¯2) [10¯1¯1] when the
metal is compressed along the c-axis. When c/a >√3 , the twinning
shear is zero. For c/a <√3 (the case of Mg and Be), twinning occurs
under tension along the c-axis.

Front 31

Stress Required for Twinning and Slip

Back 31

Front 32

Stress Required for Twinning and Slip conn

Back 32

•Slip and twinning can be regarded as competing deformation mechanisms
•Increase in strain rate or temperature tend to favor twinning over slip
•Twinning is not a thermally activated process – low dependence on temperature
•Slip mechanism (dislocation motion) has strong dependence on temperatures

Front 33

slip vs twinning

Back 33

As the stacking-fault energy of an alloy is
decreased, it’s tendency to deform by twinning
increases
•Twinning generates internal barriers for slip and
breaks down materials microstructure into
progressively smaller domains - results in increased
work-hardening

Front 34

frank vs shockley dislocations

Back 34

frank: A partial dislocation whose Burger's vector is not parallel to the fault plane, so that it can only diffuse and not glide, in contrast to a Schockley partial dislocation.

schockley: same plane can move or glide

Front 35

grain size strengthening

Back 35

is a method of strengthening materials by changing their average grain size. It is based on the observation that grain boundaries impede dislocation movement and that the number of dislocations within a grain have an effect on how easily dislocations can traverse grain boundaries and travel from grain to grain. So, by changing grain size one can influence dislocation movement and yield strength.

Front 36

hall-petch plot

Back 36

more info

Front 37

cottrell theory-frank-read source

Back 37

• Frank–Read source operating in center of grain
1 and producing two pileups at grain boundaries
• The Frank–Read source in grain 2 is activated
by stress concentration.

Front 38

cottrell theory-frank-read source

Back 38

• Recognized that the it is impossible for dislocations to “burst” through
grain boundaries.
• Assumed that the stress concentration due to dislocation pileup in one
grain can activate dislocation source in adjacent grain

Front 39

li's theory

Back 39

• Grain boundary is the source of dislocations
• Yield stress is the stress required to move dislocation
through the “forest” of dislocation pileups
– Flow stress is related to the dislocation density

Front 40

meyers-ashworth theory

Back 40

Front 41

meyers-ashworth theory

Back 41

Deformation stages in a polycrystal

*Start of deformation

*localized plastic flow in the grain-boundary regions (micoryielding)

*A work-hardened grain-boundary
layer that effectively reinforces the
microstructure.

Front 42

work is proptional

Back 42

work is proptional to bergues vector squared

Front 43

metal working methods

Back 43

rolling:metal is squeezed between two rollers

forging: die is compressed to the forms

wire drawing: wire is pulled

extrusion: object is pushed through a die

stamping: design is compressed on the lower side which has the design

Front 44

work hardening graph

Back 44

Front 45

Critical Resolved Shear Stress

Back 45

τCRSS - the minimum resolved shear stress
required to begin plastic deformation or slip
• Depends on Temperature, strain rate, and material
• The system on which slip occurs has the largest Schmid factor

max when both angles are 45 degrees

Front 46

Slip Plane and Slip Direction-Schmid Law

Back 46

If the loading direction is [123] for an FCC crystal, then the Schmid factor
of various slip systems can be calculated by obtaining
• angles of [If the loading direction is [123] for an FCC crystal, then the Schmid factor
of various slip systems can be calculated by obtaining (Brute Force)
• angles of [123] with <111> (perpendicular to the slip planes) - theta
• angles of [123] with <110> (slip direction) - 

123] with <111> (perpendicular to the slip planes) - alpha

oppisite for BCC
• angles of [123] with <110> (slip direction) - 

Front 47

Ledge Formation in Grain Boundary

Back 47

Grain-boundary dislocations can group together and form grain boundary ledges
or
Under applied tension, lattice dislocations can move from a grain through the GB to
the adjoining grain and causes a heterogeneous shear of the GB, forming a ledge

Front 48

Engineering Stress-Strain

Back 48

Deformation at low to moderate temperatures work hardens metals

At high temperatures – dislocations generated by deformation are annealed out