00:10okay so let's look like the uh
00:14the imperfection or defect in
00:17the atomic and ionic arrangement
00:20so in this chapter we are going to learn
00:23the different types of defects
00:25such as a point defect in the crystal
00:28like a vacancy or substitutional or into
00:32tissue atoms okay i'll explain this
00:37and also we're going to discuss about
00:42like the dislocation
00:45okay and the dislocations can be
00:49classified into two types of
00:51dislocations one is the h dislocation
00:56a dislocation and yeah there is is the
01:11okay it's called the sleep system
01:14and the sleep system
01:20the sleep plan and sleep direction
01:26we're gonna explain what the uh area
01:30defect is which is the uh uh gram gram
01:34boundary and the grain size
01:38okay so basically we have uh
01:41uh three types of the imperfections or
01:44three types of uh defect first is point
01:46defect okay point defect
01:55like they are like the vacancy atoms and
02:00atoms and the substitution atoms
02:06defect is called the line defect
02:10which is the uh dislocations
02:12okay and this location basically have
02:24makes the dislocation okay
02:27we're going to discuss this later
02:31and the third types of the imperfection
02:39like uh a grand boundaries or and
02:52okay so let's look at the point defect
02:55which are localized disrupted
03:06the point defects are localized
03:11otherwise perfect atom or ionic
03:13arrangement in your crystal structure
03:16that means as we answer those point
03:20defect it could be the vacancy or
03:23substitutional atoms or tissue atoms
03:28the effect of those interruptions from
03:33overfed over the surrounding region
03:36that's mean when you insert
03:43you insert point defect
03:47surround that point defect
03:55okay and this distortion or disruptions
04:01materials properties
04:05okay often these defects are caused
04:08by the introduction of
04:20insert those uh point defect atoms
04:24during the process during process
04:30we have the manufacturing process
04:34and we can just insert those uh point
04:37defect just like for example like metal
04:39alloy like the steel
04:45the in the point defect
04:48atom of steel is carbon atoms right
04:52carbon atoms also for the
04:54semiconductor we can dope
04:59uh point defect we can do like like for
05:05phosphor or sulfur or germania into the
05:09silicon silicon wafer
05:14that can just modify its property elect
05:20okay you can modify the electrical
05:24okay so let's look at this picture
05:28what i already described before is the
05:30point defect different types of point
05:33defect first is the vacancy
05:36is the vacancy that's mean the lattice
05:40or the original atom leave
05:52the position here is empty
05:57okay and also we can
06:00look at uh the second type of defects
06:02called the the second type of point
06:04defect is called inter tissue defect
06:11the different types of atoms
06:16into its interstitial site
06:24radius i mean the size of this
06:28could be larger or smaller than the
06:32lattice okay it could be larger or
06:37a lot of uh those uh inter tissue sites
06:49already discussed about this uh
06:50substitution atoms right that's mean
06:56atom or the original atom
07:01a specific substitutional impurity atom
07:11okay so let's look at the effects
07:14from those point in fact so the first uh
07:18figure shows the vacancy right we have a
07:22okay the lattice atoms
07:25uh move to somewhere okay and the
07:28vacancy remains and those remained
07:33because the uh disrupted
07:38okay so when these that can deform and
07:41the low co lattice will be distorted
07:49total okay or disrupted
07:55okay and if we put the uh
07:58interest tissue atom into the
08:00interstitial site like here
08:08larger or smaller okay this into tissue
08:11atom could be larger or smaller than
08:14that of those interstitial sites
08:16okay no matter what no matter what no
08:18matter is larger or smaller
08:25for its surroundings i mean it's the
08:28surrounding lattice will be disrupted
08:31okay it will be disrupted
08:33okay this the same effects of those
08:36substitutional atoms like heat this and
08:46lattice surroundings will be disrupted
08:56and the surrounding will be distorted
08:58lattice around this will be distorted or
09:02okay and for the figure e
09:04as the uh shows it's called the french
09:07defect that's mean the lattice atom
09:12the interstitial site
09:14originally it's here right and it moved
09:18move to here or here
09:22okay so it's called the vanco defect
09:26and the figure f represents this called
09:32always happened in ionic materials or
09:39okay so for the ionic materials
09:53therefore the vacancy could
09:59for remaining or for uh remain
10:03uh its neutrality its nutrition charge
10:06infinity okay the cat ions
10:18okay so let's look at the point defect
10:22it's like the point effect
10:24as i already described that uh vacancy
10:27is when an atom or ion
10:30is missing from its or
10:34from its normal site in crystal
10:40okay and the vacancy concentration in
10:45follows and it's called arrhenius type
10:48behavior or the arena's equation
10:58so it is an experimental function that
11:08okay so let's define this equation
11:12this is the number of point defect in
11:17vacancy right the number of vacancies
11:20and this is the number of potential
11:23vacant sites or we can say it's just the
11:26lattice point okay that is atom
11:29okay and it's an exponential function
11:31it's an exponential function
11:44okay and t is temperature in kelvin r is
11:48a constant it's a boltzmann constant
11:53so what is activation energy
12:00what is activation energy
12:02uh give us an example
12:04for any chemical reactions for any
12:11we need the catalyst
12:13we need callus to facilitate its
12:19okay so for example we have the
12:21reactants and we have the product
12:26if this reaction this uh
12:30reactions without any catalyst
12:33we need higher energy
12:36we need a higher energy
12:38to make the chemical reaction occur
12:45enzyme is the catalyst
12:47we need it maybe we need a higher
12:52to trigger this chemical reaction
12:56if we adding some catalyst add in some
13:04enzyme and this activation energy
13:10could be reduced originally we need a
13:14to trigger this chemical reaction
13:17and when we adding some
13:19uh callous or enzyme this activation
13:26maybe we don't need so
13:30okay we need some like maybe like room
13:34maybe 100 celsius just like that okay
13:41okay so let's look at the equation the
13:47so uh this is the number of defect
13:49number of the vacancy and this n means
13:52the number of the potential defect set
13:55or we can say it just uh each lattice
13:57side is h that decide is
14:00a potential backhand side vacancy side
14:07activation energy k in kelvin
14:12sorry p in kelvin and k is the postman
14:16it's a postman constant
14:24is the right front experiment therefore
14:26we can get qv we can get the activation
14:29energy from an experiment therefore we
14:35so how to measure it
14:39we can use the method is called the
14:41differential thermal expansion method
14:44basically you have to measure the uh
14:50in the space man and the lattice
14:57of course we have those uh machine
14:59that we can major this uh the thermal
15:02expansion coefficient
15:04therefore like this we can measure the
15:06uh the coefficient of uh
15:09thumb expansion and the temperature k
15:15and we can get the uh concentration of
15:22okay is the uh dimension no change in
15:26this material sample and this
15:28uh lattice parameter change
15:31okay and this is a concentration of
15:34interstitial site or inter tissue
15:36concentration okay it can be calculated
15:39and it can be estimated
15:44therefore we can measure the
15:48uh defect concentration or the vacancy
15:53with respect to the temperature in
15:57figure out oh it's an exponential
15:59function it's exponential dependence
16:03okay it's an exponential dependence
16:06and then we can transfer we can replot
16:10this exponential function
16:12into a linear function into a linear
16:15function how we just take the the nature
16:19and the inverse of temperature
16:23and we can replace this exponential
16:30okay a linear function
16:33and then the slope of this linear
16:40it's a function of activation energy
16:43so this term is the slope of this linear
16:49okay this is the slope
16:52of this linear function
16:55okay and k is constant right k is
16:57constant therefore we can figure out
16:59what's this uh activation energy is
17:10okay so let's look at some point defect
17:19defect is formed when an extra atom is
17:24inserted into the crystal structure at
17:27normally unoccupied position
17:31although smaller than atoms and into
17:34tissue atoms introduce
17:46vicinity this means the surrounding
17:48surrounding and those localized stress
17:56often strengthens strengthens
18:02okay as i already mentioned those point
18:06distorted or disrupted the lattice
18:10vicinity and this distortion will cause
18:15or the localized stress this pre-stress
18:18will strengthen the materials property
18:25okay so the substitution of the effect
18:30uh one lattice atoms or ions is replaced
18:34by different atoms or ions
18:38okay and the substitutional atoms
18:41uh if they have different sizes then the
18:46disturbing their surroundings
18:49okay disturbing because of different
18:54then different size than the regular
18:58therefore the lattice
19:00will be this disturbance will be
19:02disturbing okay and the substitution
19:06uh over increase the strength of the
19:10as i already explained
19:16the point defect has the significant
19:22on strengthening the materials
19:25especially for metal materials metallic
19:30okay due to the lattice distortion
19:32okay due to lattice distortion
19:39okay in other point defect like uh
19:41institution c is created when the atom
19:44identical to lattice atoms
19:47uh occupied the uh the
19:53so what i mentioned in previously like
19:59the this is the interstitial c that's
20:03uh the lattice atom the original atom
20:06is inserted into the interstitial site
20:13and a french defect is a pair of vacancy
20:22okay when the lattice atom
20:25jump to an interstitial site
20:27okay so we have the lattice atom here
20:30and you jump to here we might jump
20:32through here you might jump to here
20:35okay we'll jump to those interstitial
20:39it's called the franco defect franco
20:44okay and the shacky defect is unique to
20:47ionic materials or ionic bonding
20:50to preserve electrical neutrality in
20:57for example for this material we have
21:03however for this whole materials
21:07it's still neutral it is still neutral
21:14okay it must be neutral
21:18so for example for these ionic materials
21:22if we want to dope or we want to add in
21:28some charge positive charge cat ion two
21:42the new trilogy must be
21:46therefore when we adding uh the extra
21:49two positive charge ion here
21:54doesn't mean what does mean the two
22:03okay to maintain each neutrality
22:07so add in two plus cat ion and remove
22:12so what's the consequences what's the
22:17one vacuum site remained right
22:25okay and this material is still
22:28neutral it's still neutral you still
22:36okay so next i'm gonna
22:39talk about the line defect dislocations
22:44okay these locations are like
22:46imperfection or line defect
22:48okay in the perfect crystal in an
22:51otherwise perfect crystal they are
22:54present in all materials including
22:56ceramics and polymers and they're
22:57especially useful to explain in
22:59deformation and strengthening in
23:02and basically there are three types of
23:04dislocations i already mentioned before
23:07it's a screw h and mix
23:16metal rod and we apply a tensile stress
23:26if we keep keep applying a load a tensor
23:37okay inside this this metal rod
23:43inside this metal rod
23:46the face or the the crystal
23:50we'll sleep as i mentioned
23:54you will sleep along the plan this plan
24:11tensile force on a metal rod
24:13and inside these materials
24:16the shear force will make the crystal
24:36following its sleep direction and follow
24:40a close-packed direction
24:42okay to produce the permanent
24:44deformation or the plastic deformation
24:51so let's look at the
24:53line defect this location
24:59so the light defects a one-dimensional
25:01defect around which atoms are misaligned
25:06so i already mentioned there are two
25:09okay let's focus on the first two types
25:12okay first is uh the
25:18okay for a dislocation extra half plan
25:21of atoms is insert in a crystal
25:25and the b vector perpendicular to the
25:28dislocation line the b is the burgers
25:34okay b is the burgers vector burgers
25:36factor i'll explain this later okay
25:40and the second type of dislocation is
25:42the screw dislocation
25:44okay and spiral planar ramp
25:48resulting from the shear deformation
25:52okay the screw dislocations are due to
25:54the atomic plants forming a spiral rep
26:01is parallel to the dislocation line
26:05okay it's parallel to
26:07the dislocation line
26:11okay let's look at what is the age and
26:14what is the screw dislocations
26:22the upper figure shows the age
26:25this location and the bottom one shows
26:33and as i already mentioned we are for
26:36the 80s location and extra plan
26:39extra plan of atoms form
26:43okay when we apply a shear force
26:50force there's one extra plant form
26:55and this atom moves from this point this
26:58original point to here
27:04is called the burgers vector
27:08okay it's called the burgers vector
27:14that's the reason why we we say we
27:16mentioned that the burgers vector is
27:20perpendicular to the dislocation line
27:24okay this is the burgers vector
27:26it's a dislocation line so
27:31perpendicular where crystal materials is
27:35when the shear force applied to the
27:43okay for the age dislocations
27:45that the burgers vector is perpendicular
27:48to this location line
27:54for the screw dislocation so the screw
27:58you can see it's this location is right
28:05sure i will explain what shear force is
28:10and this lattice atom move
28:15when the shear force applies from here
28:20okay and this direction is called the
28:24okay it's called the burke's vector
28:26and for the scrooge location the burgers
28:28vector is parallel to
28:35or we can say the burst vector is
28:38perpendicular to the direction of this
28:45and no matter its age or screw
28:48dislocation the result the final result
28:52the final results are identical as being
29:04okay and this plan is the uh
29:09and this plan is the
29:28okay so let's look at the uh screw this
29:31location we just called one atom seek
29:35and we apply the shear shear force
29:40okay we'll apply a shear force
29:45will move from the original sides to
29:56so this is the burgers vector
29:59right this purpose factor and the locus
30:04screw dislocation for example uh
30:14it's a spiral planar ramp
30:18okay it's a spy it's a spiral wow
30:26planner ramp like this
30:30okay can you imagine that it's a spiral
30:36that's the reason why we call it screw
30:40okay screw this location
30:45and the same thing for the uh age
30:48location with a half plan
30:59okay and we apply a shear force
31:07okay and this half plan half half plane
31:12okay we are move depending on the
31:15the shear force you apply okay
31:27so we just look at the line defect screw
31:30the age location right for eight ages
31:34location we have extra plant of atoms
31:38and for the a screw dislocation of the
31:47it's a spiral wrap okay it's a spiral
31:54okay and this case is only for pure
31:58force pure shear stress
32:01okay and mostly uh the materials
32:05uh will be under gold uh mix makes a
32:14for example we have a metal rod and this
32:20a torsion we might apply a bending we
32:29okay so therefore the dislocation inside
32:38age this location or school dislocation
32:41it must be a mixed dislocation
32:44coexistence okay coexisting
32:51the age dislocation it's location
32:57okay it's for the ages location
33:02therefore as what i mentioned
33:07for a materials for sample for what like
33:15when we apply a tensile we apply a
33:18torsion we apply a bending
33:20stress on this sample this look this
33:23location must be mixed
33:26okay therefore we have the uh
33:29we have the h dislocation here and we
33:34screw dislocation here
33:39right it must be mixed
33:51okay it's a 3d image of the uh
33:56basically justification
34:01as i mentioned previously
34:05right i mentioned the stress it's a
34:07shear stress and no more stress
34:10okay so what is normal and what is the
34:17for normal stress for normal stress
34:21is that a force applied to
34:26apply perpendicular to the area of
34:28interest and for shear force
34:31act parallel to the area of interest
34:35okay one is perpendicular and for the
34:38shear it is the uh parallel to the area
34:42okay and when a plan when the plan when
34:47both dislocation line
34:50and the burgers vector
34:52is known as the sleep plan
34:57like this i show you this picture
35:08okay for a plan contain a dislocation
35:12this is a dislocation line and this is
35:18the dislocation line and the burgers
35:20vector is the sleep plan therefore the
35:24where is the sleep plan here right
35:33right here is the sleep it's a this plan
35:36it's the plan i draw it
35:49is the sleep plan or the close pack plan
35:58that's the what the it's mentioned here
36:02when the plan that contains both this
36:04location line and burgers pattern
36:07is known as the sleep plan
36:10and if a significantly large force is
36:14uh power parallel to
36:17that is the slip direction and this
36:20locations can move in your crystal via a
36:24sleep process okay therefore we have to
36:27figure out what's this
36:29the force the shear force right the
36:31force applied to power uh the the force
36:34is applied parallel to right
36:36so that's the shear force how large is
36:39of this shear force to trigger
36:42the dislocation occur
36:50so there's the scientists uh it's called
36:55it defines a stress it defines a stress
36:59to make the dislocation
37:02and this uh sleep process to occur
37:07okay so as what i mentioned that the uh
37:11a combination of a sleep plan and the
37:16forms a sleep system
37:24and what's this in a barrel stress
37:33a dislocation between equilibrium
37:39it's a uh ps the variable stress
37:43okay so exponential function
37:47case exponential function function also
37:49it is derived from experiment
37:52it's the right front experiment
37:55okay here c and the k
38:01different materials so it's materials
38:06it's material dependent
38:11what the interspacing
38:13the the interplant this uh spacing is
38:16the d spacing we already mentioned in
38:18the previous chapter that xrd
38:21x-ray diffraction can figure out what
38:24the d spacing is between two adjacent
38:28okay and b is the burgers vector
38:31magnitude of the burgers factor
38:38okay so we can measure the d spacing
38:41and we do the experiment and we figure
38:43out the c and the k the constant
38:48with respect to different types of
38:51or different types of atoms
38:58so we can observe those dislocations
39:02under uh scanning electron microscope
39:07those dislocation can be clearly
39:11under the microscope
39:12okay under microscope
39:23determine most likely active sleep
39:26systems are the slip direction should
39:30or a small repeat distance
39:39should have the high density or small
39:42repetition what's that mean that's mean
39:57right close back direction
39:59you have the higher higher density right
40:06should have the higher planetary density
40:21combination of these two
40:23is called the sleep system
40:27it's called a sleep system
40:30okay and dislocation
40:32do not easily move in material with
40:39in other words we can say that these
40:41locations do not easily
40:47a strong a strong bonding
40:50in the primary bonding
40:55not just covalent ionic
40:57steel like materials with ionic bonding
40:59are also resistant to sleep
41:03okay because it's strong bonding with
41:05two atoms or two ions
41:13move them apart it's not easy
41:18okay so as i already mentioned what is
41:24a different crystal structure
41:29is the closed pack right closed pack
41:40right so for example the fcc structure
41:43what's the close-packed plan of fcc
41:49what's the cross back plan of fcc let's
41:52for example we have a
42:08it's one one one right is this plan
42:11this is a one one one plan
42:16right so this plan is one one one
42:19so it's it is it's close back plan
42:22therefore it is its sleep plan so when
42:26we apply a force where we apply a
42:28tensile force on the fcc metals
42:36occurs along the one one one surface
42:43okay and the direction
42:45the slip direction is what
42:57here here therefore what's the the sleep
43:00direction of fcc structure is
43:18therefore what i say the sleep plan
43:21represents close pack plan
43:24in a crystal structure and the slip
43:26direction represents the close-packed
43:28direction in a crystal structure
43:35okay so the significance of the
43:38dislocations as in the in the previous
43:40already mentioned when we apply a force
43:47when this force reached a certain
43:50value a specific strength
43:55trigger the sleep process
44:00that's mean this material start
44:09okay therefore plastic deformation is in
44:18in other words elastic elastic
44:37so what's the deformations of elastic
44:40and the plastic deformation
44:45yeah reversible and in reversible so we
44:48apply a tensile force on the metal rods
44:52the force is released
44:54as removed the force is removed
44:58the dimension will return to its
45:03and it is called the elastic deformation
45:13cannot return to its original dimension
45:17that's mean the permanent the permanent
45:20deformation occurs right
45:22so we can say it is the plastic
45:27okay and applying stress causes
45:30movement and the uh cumulative sleep of
45:34new mirrors dislocations causes plastic
45:39it's a relation between this the um
45:45of numerous dislocation
45:49causes the plastic formation
45:54okay i remember already
45:58so you can try an experiment you can use
46:01the uh the paperclip
46:05just uh make a stretch to stretch it to
46:07make a straight and just keep bending it
46:10just keep bending this paperclip
46:13what's going to happen
46:14you increase the dislocation
46:17inside this paperclip
46:19so you will feel well this paperclip
46:22uh become harder and harder
46:24right become harder and harder
46:29it's going to be broken
46:31right it's going to be broken
46:37okay so let's look at the other
46:43to define the dislocation
46:45previously already mentioned the stress
46:47is called an embarrassed
46:52right to define okay so what's the uh uh
46:57what's the uh the shear force to trigger
47:03the other law is called the scheme slot
47:09okay so what is scheme is law
47:14schemes law gives the re re
47:17resolve shear stress
47:19in the slip direction
47:24is the uh result of shear stress
47:27as already mentioned what is shear
47:32the shear force divided by area
47:36right what is normal stress
47:38is the tensile stress tensile force
47:44the cross-section area
47:49okay so this stress this resolve shear
47:52stress is different from
47:54uh the the barrel stress because the
47:57scheme is law is derived from
48:04the materials prop up crystal materials
48:09so let's look at this
48:12let's look at this when we have a metal
48:14rod and we apply a force right just
48:18you can use any tensile stress machine
48:23okay and the normal stress equals to
48:28area and this area is the cross section
48:35and this plan this plan is the
48:38sleep plan or we can say it's the close
48:49direction as we assume it
48:52and the angle between the normal force
48:55that we apply and the sleep
48:58direction is called lambda here
49:02okay and the normal to the sleep plan
49:11okay the normal to the same plan
49:14and the angle between the normal to
49:17sleep plan and the normal force
49:27therefore we can figure out the shear
49:33right shear force from this triangle
49:39from this triangle goes lambda
49:44right so we can find the shear
49:53and also we can find the uh
49:55the area of sleep plan here
50:07okay from this triangle therefore the
50:10the area of sleep plan equals to the a
50:12naught divided by cosine phi
50:22therefore we can figure out what the the
50:24shear stress is the shear stress is
50:28what the shear force
50:38substitute this to here
50:48and then we can figure out this called
50:51resolve shear stress we can figure out
51:01do you know what sign
51:07and the critical resolve shear stress is
51:09the stress required for sleep occur
51:13it's the same concept
51:15as that we mentioned before the virus
51:18stress the viral stress
51:21therefore when the the the shear stress
51:23equals to the critical resolution stress
51:29okay the sleep occurs okay with the
51:32shear stress equals to the critical
51:42okay so i'm gonna uh stop the course
51:45here and i will continue next week for
51:50the crystal structure the sleep system
51:52okay i'll explain more about uh the
51:56inferences of the sleep system
52:00and what's the effect of this sleep
52:02system correlated to the mechanical
