00:09okay so last time we already uh
00:12discussed about the uh the shear force
00:15okay uh the critical reserved shear
00:18now is the stress required for sleep to
00:24uh we can realize that the number of
00:32the sleeping process of the madams
00:38therefore the higher
00:40number of sleep systems
00:43uh give the more sleep plan and
00:46directions that's mean
00:50that the high ductility right
00:54related with the high ductility
01:00we can look at the different crystal
01:03with different sleep system for example
01:15for hcp structure which is the uh
01:20uh the fuel slip system
01:22only three slip system
01:24therefore it's our ductility
01:28okay and so the uh fcc structure
01:34okay as uh they have the high ductility
01:38and for bcc structure
01:42uh they can have up to 48 sleep systems
01:46okay it's very cocktail okay it's very
01:52crow sleep occurs when a dislocation
01:54moving along the subsistence
01:57starts moving in a different sleep
01:59system when it encounters an obstacle
02:04that's a barrier okay as i mentioned
02:07before uh when this sleeping process
02:10okay the dislocation moves right the
02:15and when the dislocation
02:17encounter a barrier they cannot keep
02:20moving they cannot keep moving you stop
02:23and it will know i will move in a
02:26different sleep system
02:28it kind of uh change its uh orientation
02:33for sleeping okay for sleeping
02:37okay so let's look at the closed system
02:42of sleep plan and sleep direction
02:46and the sleep plan is the highest
03:05and the sleep directions
03:09are with the highest linear density
03:18direction right direction
03:21okay therefore uh for uh uh fcc
03:28whose close pack plan is one one one
03:36okay and it's closed pack direction or
03:39the sleep direction is
03:46one zero family on your family okay
03:50if we can look at the top view of the
03:54this is the one one plan and here's the
04:05therefore the bcc's crystal has 48
04:08have up to 48 sleep systems
04:15therefore they have the good strength
04:17and the moderate uh ductility for fcc
04:19crystal has 12 sleep systems
04:22okay with low b of the age ratio
04:25you have the moderate trends and good
04:27activity and for the hcp structure it
04:29has only three sleep system
04:32therefore the most of the hcp structure
04:37brittle at room temperature okay at room
04:42okay so how to define the uh we already
04:46defined a sleep plan
04:48this direction and what is b over a
04:53we already we mentioned here the b over
05:04what what's the definition of the b over
05:10as be over a ratio decreases the shear
05:13stress required to cause sleep decrease
05:18that means we just need the lower shear
05:20stress to mic sleep occur
05:32plan it's the sleep plan right
05:34this is a sleep plan
05:43okay we can say the b
05:44is the uh the uh is called the uh
05:48interplanetary distance between
05:50the uh close pack plan
05:53okay because back plan and a
05:56is the lattice parameter
05:59so as the ratio of b over a decreases
06:02the the stress required to cause
06:13and this is a compare this figure shows
06:16the the compare between sleep process
06:20in the twin as i already
06:22mentioned previously
06:28occurs along a sleep plan right a sleep
06:36when the train occur along the training
06:39plan tuning plan is like a mirror
06:42right it's like a mirror as the shear
06:46on the crystal structure
06:49in the in the uh the crystal structure
06:55the twinning plant it's the uh
07:01okay so it's it's original structure
07:06when when the shear stress applied on it
07:10training plan the tuning plan and the
07:12crystal structure has a marrow alone
07:18okay it's a longer tuning plan
07:26so you can imagine that uh why we we saw
07:30the uh the lower b over a ratio right
07:33here that's mean the interplan distance
07:36because the lattice parameter is a
07:38constant right and the interplanetary
07:42or we say the d spacing
07:44of the close pack plan
07:49doesn't mean the shear stress required
07:54to to to make the sleep process
08:05if a is a constant if i is a constant
08:12aside the uh the short distance between
08:15the the interplanetary distance
08:19can reduce the shear stress
08:28so you can think of this way as this b
08:35decreases that's mean
08:45uh we can say we have high stiffness we
08:46have a high stiffness
08:50the atoms right we have the high
08:52stiffness do have you uh you still
08:55remember we we have uh have this plot
09:00right this point is r naught
09:04right and this is the repulsion
09:21all right therefore if the
09:22interplanetary distance has shorter
09:27i can reach the equilibrium
09:30uh distance between two atoms or or
09:34particles that's mean the uh high
09:38the high stiffness the slope the slope
09:49figure the slope of the f over
09:55okay therefore the high stiffness
10:00assuming they are not easy to break
10:02right the atom is not easy to break
10:06okay therefore the bounding force
10:08between this this this direction this
10:15okay than this therefore
10:19when we apply a shear
10:24bonds are not easy to be broken
10:27okay therefore this direction is
10:30stronger than this this this direction
10:35okay so that's that's the reason why the
10:38crystal plan or the crystal structure
10:41will slide along this
10:46okay it's not this direction is not easy
10:48to be broken and this direction is easy
10:52okay it's easy to sleep
10:59so this figure shows the uh the slip
11:01season with different structure metal
11:04structure okay as i already mentioned
11:06for example like the fcc structure we
11:08have the the highest
11:10uh the the close pack plan
11:13right and we have the close pack
11:14direction right here
11:18okay so you can try to plot
11:21uh this uh slip system
11:24with different crystal structure
11:27okay i just give you an example for
11:32whose sleep plan is one family and its
11:35sleep directions are 110.
11:42okay so let's look at the surface defect
11:48which includes the boundary the grain
11:50boundary and the plant
11:53therefore the surface defects are
11:54boundaries or plants
12:03two regions which might have
12:05stem crystal structure for different
12:10and the materials in uh internal surface
12:13represents the surface where the crystal
12:16rapidly ends and the surface atoms have
12:21and the surface might rot in and very
12:24that's mean the boundary the grand
12:28the grain boundaries are very
12:32okay are very active
12:35okay so let's look at the sun
12:37let's show you a figure first okay for
12:41uh we have the uh for example this is
12:43the scn uh scanning electron microscope
12:48with uh different gram
12:50uh grain size and green boundary
12:52for example this is the grand size
12:56this is the grand size is the gram this
13:14inferences on the materials the mat over
13:17the metals urine stress
13:24the effect of the grain size
13:27is highly emphasis on the
13:31of the metal or steel
13:35okay so you can imagine that
13:44if you have a painting you have a
13:46colored pen we have a die down
13:52the uniformity of this painting
13:59right if the grain size is not
14:02it's not identical mostly identical
14:07okay so let me ask you guys the
14:10this is the grand boundary
14:12okay this is a grand boundary and we
14:15have a different orientation for for
14:16example this surface
14:19maybe is one one one
14:32uh if we have a higher density of uh
14:34grand boundary for example we have this
14:36is a grain boundary it's a grand
14:38boundary grand boundary okay such like
14:43so the higher density or the higher
14:46number of gram boundary
14:48gives the higher strength
14:50gives the higher mechanical strength or
14:58higher number of grain boundary gives
15:01the higher mechanical strength
15:14so the answer is right here
15:19will increase the material strength
15:21by reducing grand size
15:25increase the grand boundary we can
15:28we can increase the material strength by
15:30reducing grain size or increased screen
15:37this is the reason why the dislocations
15:39can only travel short distance so
16:08this is our grand boundary right uh sure
16:11this is our grand boundary right when
16:15when when the stress applied to these
16:17materials the dislocation occurs right
16:20for example whether this location here
16:23age dislocation we have the edge
16:27uh we have age dislocation okay so when
16:30the dislocation keep moving keep moving
16:34when it encounters grand boundary
16:36will be stopped so the grain boundaries
16:40can be regarded as a barrier or the
16:44dislocation movement
16:47okay so for example when this this
16:49dislocation move move move oh he
16:55and this grand boundary move oh there's
16:58no barrier okay therefore they can keep
17:02okay okay in other words if we have a
17:08of if we increase the number of grain
17:11boundaries for example if we have our
17:12grand boundary grand boundary grand
17:16grand boundary such like this
17:21okay so what's why the higher density of
17:26has the effect um enhance its uh
17:30mechanical property or strength why
17:40because that this load the distance of
17:43movement is short right so if we have
17:46the higher number or a higher number of
17:49grain boundary what's going to happen
17:51for example this dislocation when he
17:56it will be stopped right when he moved
17:58in this direction oop stop it
18:01it encounter a barrier right and when
18:04this dislocation keep moving keep moving
18:07he encounter a barrier it stops moving
18:11the same the dislocation moving oh he
18:17it stops to moving all right stop the
18:20therefore the uh therefore that's why we
18:23sign we can increase the material
18:28increasing the ground boundaries
18:30this way the dislocations can only
18:32travel a short distance
18:35okay can travel a short distance
18:41okay so let's look at the equation
18:44called the the whole path equation which
18:47is relates to the grain size to urine
18:50stress okay i will mention i will
18:54uh the ear stresses okay so when we have
18:59uh uh a metal rod and we apply a tensile
19:04especially for the uh for the metal
19:08and we got a strength and the stress
19:11so we have this stress and strength
19:18okay and we will get a stress called the
19:21ear stress the uni stress
19:24means when we apply our stress
19:30below the unit stress
19:32that's mean the elastic deformation
19:36occurs okay when we apply a stress
19:42which is higher than the uh the unit
19:44stress we will apply stress higher than
19:45unit stress for example here
19:49that's mean the plastic plastic
19:54okay that's mean when we release the
19:56force or when we release the stress
20:00the dimension change will not return to
20:04its original dimension
20:09okay therefore this equation
20:12is coming from experiment
20:16okay that's mean okay we
20:18uh we fabricate alloy or metal
20:22and we measure its grain size
20:25by microscope we i just observe
20:30via microscope and we do the tensile
20:32test cancer test we can have this stress
20:38find out we figure out the yearly stress
20:41from this stress and strength curve
20:43corresponding to the grain size
20:47okay and we work on the numerous
20:51we will get this linear equation this uh
20:55whole patch equation right here
20:58okay therefore it's from experiment
21:01okay and the d here is the uh average
21:03diameter of the grain we can major from
21:07and the sigma y is the year stress
21:10you can measure it from the tensor test
21:13and the sigma naught and the kite
21:17are constants for different materials
21:20okay from different materials
21:22for engineer we like
21:25to put all those unknowns into
21:30therefore from this experiment
21:33we figure out this equation this linear
21:35equation and we can plot this in linear
21:38right therefore we can find the relation
21:41between your stress and the grain size
21:47right we can find the ear stress
21:50corresponding to the different grain
21:53okay therefore we can test the different
21:57process or different
22:00metals or different alloys
22:08and there's the other way of specifying
22:10the grain size is the stm the stm the
22:15when we observe it under the uh
22:21times of the optical microscope
22:26so the end defined as the
22:33two of the power n minus one
22:37which represent the number of grams per
22:45okay that's mean for example we have the
22:52under optical microscope we have the one
22:59one inch square the area and we observe
23:05a per unit area okay per unit area
23:10okay and we figure out the number of n
23:15and we plot this n into here
23:18and we can get this capital n okay the
23:25is the uh the standard of stm
23:29to define the grand size
23:32to define the uh yeah the number of
23:34grain size the higher end means the
23:37higher number of grams per
23:40per unit area that's the inch square
23:45okay and the small angle grand boundary
23:47is an array of of this location that
23:49produces more misorientation between
23:59uh let's show you a 3d picture like this
24:03so when we observe the grain size from a
24:07no matter the optical or the t and
24:13this grand size is a 3d structure right
24:18this grain science has adapts into the
24:22the depth therefore we can plot this uh
24:24edge grain size in 3d right like this
24:29right and there's a small this is the uh
24:36and this is the the other gram
24:40and this is the grand boundary
24:44this is the grand boundary it's a
24:46okay and this small angle grand boundary
24:49is right here this is a small angle
24:54okay and the gram my twisted
24:57this gram my twist it
25:02okay therefore this region is the grand
25:07okay it's the grand boundary
25:09it is from the three three dimensional
25:13perspective to look at the grain
25:17different from the tem is the
25:21uh electron microscope
25:24we can look at the small angle grand
25:26boundary right here right this is a
25:29small angle right here
25:33orientation right here and the other
25:42it's called a surface defect
25:45and uh as i mentioned
25:47uh previously the train boundary
25:54which there is a mirror image
25:59of the crystal structure liver will
26:04a stress on the metal
26:08crystal deformation might be sleep
26:14okay or training for example we have the
26:17uh crystal structure like this and we
26:21when we apply a shear stress on it so
26:24the atoms move right atoms move
26:30if we can observe a twin plane a twin
26:36like a mirror right like a mirror what's
26:39the characteristic of of the mirror
26:43the image is symmetric right it's a
26:48if this atomic structure deform
26:52if there's a mirror plan
26:57deformation or this process as the 20
27:01okay it's training okay so we can we can
27:03look at the the structure is it's mirror
27:09right it's a symmetric
27:14this is the mirror this is the mirror
27:17and it's just a metric
27:24okay so we can look at the different
27:30or the twinning the sleeping process or
27:35okay it's the process of training this
27:36so for the sleep we have a city plan
27:39right here right here the close pack
27:42for the training we have the training
27:48okay it's a mirror okay
27:53okay so the same example when we have
28:00okay have a structure like this and
28:03apply and apply the uh the stress on it
28:07so after deformation after the atomic
28:13for example the atom from here to move
28:16to here the atom from here to move to
28:19the atom from here to move to here
28:26atoms move like this
28:31if we can find a twin plant under a
28:36that means we find a plant
28:38and the uh the atomic arrangement
28:42their atomic arrangements are symmetric
28:45along that plane so we can find the the
28:47symmetric atomic structure this
28:55and we can say okay it's a twin it's a
28:57training process okay it's a training
28:59process but not a sleep process okay but
29:06so we can observe some uh i just show
29:19okay so it's created from the
29:22fib focus item being okay you just uh
29:31and we can observe the structure is the
29:34this is the mirror right
29:37it's a mirror plant that's a twin plant
29:39and we have a symmetric
29:42structure we have a symmetric structure
29:50okay along this mirror plane
29:53okay therefore can say oh this structure
30:02okay it's a trim plane okay so if you
30:04guys want to realize more about 5b you
30:06can discuss this later or you can
30:08leave a message for me i just wanna this
30:11this figure just wanna shows you uh okay
30:14we can observe that clearly
30:19structures are symmetric along that twin
30:32of defects okay so as we already
30:35mentioned previously that the defects
30:37play an important role in controlling
30:39the mechanical property of materials
30:42okay usually matters by interfering with
30:45sleep and strengthening the metal
30:49okay when the defect you can think of
30:50what kind of defect you want to you want
30:52to apply to this material to stress its
30:56normal soiling and the defect already
31:01uh what the point defect the line defect
31:04and the surface defect
31:07and all those uh the the the the
31:11the function of those defect is to
31:14strength the materials property or the
31:19okay so we can it can think of okay so
31:23what kind of defect we should apply to
31:28point defect or dislocation
31:31or the grand boundary
31:33okay so if if you're an engineer a
31:37you have to think of
31:40what type what types of defects
31:43can enhance the highest
31:45mechanical strength with the lowest cost
31:48with the lowest cost
31:53has the last effect on
31:55ceramics well because the ceramics has
31:59the higher harness the nut of metals
32:02okay when the defect form in ceramics
32:10let's meet higher porosity
32:16calculate it or when we paralysis the
32:21there's some poor pores inside the
32:27the the the property the characteristic
32:29of islamics is brittle right it's it's
32:31brittle if if there there are some pores
32:40fragile right more fragile
32:44and the strength hardening is
32:50increase the dislocation density
32:54when this location density increased
32:59doesn't mean what that means
33:05other dislocations to move because this
33:08location will be stopped by
33:13okay the same the same concept of the
33:16the grand boundary which is the barrier
33:20this location moving right
33:23the same concept as strength hardening
33:30okay so the effect of the strength
33:36mechanical property can be
33:38returned or released by heat treatment
33:42or we can call it annealing okay we can
33:48when the materials become harder
33:52shrek hardening and we put this material
33:55into oven or furnace
33:57to anneal it to heat treat it at a
34:00certain temperature for a long time for
34:03certain time for a certain time and its
34:13okay we are recrystallized
34:19solid solution strengthening takes place
34:21when the atom called ions as a gas
34:24materials are incorporated into a
34:29i would discuss this uh in uh next few
34:44as the inter tissue or substitutional
34:51two strengths to kind of point the
34:53effect it's kind of a point defect to
35:01and the first translated grain size i
35:05right um the grain size strengthening
35:07occurs by increasing the number of
35:09grains or reducing the grain size
35:12or we can uh increase the grain boundary
35:16that can be regarded as the uh the
35:18barrier or obstacles of dislocation
35:28i will start we'll end up here
35:31and next chapter we're gonna discuss
35:33about the uh the diffusion the atoms or
35:38inside the materials
