Prof. Rajesh is actually an exception among the "teachers" here. All the professors here are great engineers/scientists, but VERY FEW are great teachers.
Then why bcc are brittle and the fcc are highly ductile in nature even though bcc has more slip systems(48) than the fcc(12) slip systems? Can you explain this question in terms of CRSS? sir
BCC have fewer atoms pert unit cell and their APF is low compared to FCC . Due to this , BCC don't have well defined slip systems (not having a truly closed packed plane) .This makes BCC more brittle
Sir I have a doubt that as we know in plastic deformation no internal crystal structure changes only unit cells slip over one another then isit possible every time that they are slipped only one direction if not then automatically crystal structure break because repeatation of unit cell will not be happened regularly?? Then what is happening there really??
{110} is the closest possible plane in BCC, and it does have two close-packed directions in it (the two body diagonals of the type lying in it). Thus it is a good candidate for slip plane. However, in reality in BCC crystals the slip planes are not always {110} but the slip direction is almost always type. Thus a BCC crystal is found to slip on several planes containing the directions .
Sir for hcp you gave 0001 as plane and 11-20 as direction. But if we take only the hexagonal P lattice then plane will be 001 but what will be the direction. Is it necessary to give slip plane and direction in the way you wrote or can it be given by considering hexagonal P lattice
@@rajeshprasad101 but can't we give slip plane and slip direction for hcp with 3 index. Because for four index we are required to consider more than one unit cell
By x-ray diffraction one knows the crystal structure. And by deformation experiments on single crystals one establishes the type of slip plane. Then one simply determines how many such planes are consistent with the crystal structure.
12 slip systems of type {110} are most favourable slip systems, i.e., they have lowest critical resolved shear stress (CRSS). However, in some bcc metals, like alpha-Fe, {112} and {123} slip systems have only slightly higher CRSS, and so are also counted as favourable slip system,. As there are 12 slip systems of type {112} and 24 of type {123} this brings the total number to be 48.
The spacing between planes is inversely proportional to the atomic density within the plane. Thus close-packed planes are farthest apart. This weakens the bonding between the planes and so makes it easier for slip to happen. Slip happens by movement of dislocations. The dislocations create slip in the direction of their Burgers vector. Burgers vectors happen to be shortest lattice translations. Thus it is most likely to find shortest lattice translation and hence the Burgers vector in the close packed directions.
@@introductiontomaterialsscience sir you write burger vector are smallest lattice translation.. Is it related to elastic energy store which increase with increase in burger vector and crystal try to minimize its energy. So burger vector is smallest lattice translation. I don't understand about why slip planes are closely packed planes. Can you have any video lecture on it??
@@introductiontomaterialsscience Sir, can you please tell why spacing between planes is inversely proportional to the atomic density within the plane ? i.e. why closes packed planes are most widely spaced planes ? Also, I am getting confused with contradiction that interplanar spacing in case of (111) plane for FCC is lesser than that of (110) & (100) planes but despite of that why (111) is regarded as the most widely spaced plane ?
@@viralgadhiya6550 Bro, it depends on planar density (no. of atoms per unit area). Just calculate this for respective slip plane, you will get to know. This is the answer for your last part question on why slip planes are closely packed planes.
@@introductiontomaterialsscience Sir , this question was asked from me in an interview for phd. The exact question was : " Do you know about trophographically close packed planes in superalloys ? " Thats y, i asked you about the same . . .
@@rajeshprasad101 I think the question was (or should have been) "topologically closed packed phases" (TCP phases such as Laves, sigma, etc.). The question was not relevant to the topic of this video!
Excellent lectures...that's why its called an IIT ...Thank you very much sir😊😊😊
Prof. Rajesh is actually an exception among the "teachers" here. All the professors here are great engineers/scientists, but VERY FEW are great teachers.
@@SoumilSahu True indeed, Mr. Sahu :p
It's difficult to find good teachers in iit/ nit . Sir you are one of them 🙏
how to find that {111} have four plain and have 6 direction
Thank you from Turkey 🇹🇷🇹🇷
Tell your Erdogan to not intervene in other countries matter.
@@motiontv3621😂😂
Sir , in ccp why can't we take {110} as a slip planes...even these planes can be seen as a closely packed planes.
Sir I found in some textbook that BCC has 48 slip systems, is that true?
Those slip system are not active slip system.
Please see reply to Abhishek Kumar.
Thank you for the lecture sir, you are helping so many students!
Is it possible for slipping and twinning to occur in the same grain?
It is possible.
i think sir, you are the best teacher of metallurgy.kaas app hamare college me hote
In HCP, sometimes prismatic plane (10-10) and pyramidal plane (10-11) also act as slip planes
You are right. The basal plane is the most important slip plane but not the only one.
Then why bcc are brittle and the fcc are highly ductile in nature even though bcc has more slip systems(48) than the fcc(12) slip systems?
Can you explain this question in terms of CRSS? sir
BCC have fewer atoms pert unit cell and their APF is low compared to FCC . Due to this , BCC don't have well defined slip systems (not having a truly closed packed plane) .This makes BCC more brittle
Sir I have a doubt that as we know in plastic deformation no internal crystal structure changes only unit cells slip over one another then isit possible every time that they are slipped only one direction if not then automatically crystal structure break because repeatation of unit cell will not be happened regularly??
Then what is happening there really??
Not able to understand your question. Could you try to express it differently?
Sir pls suggest book or notes for this slip
Sir, there is no closed packed plane for BCC crystal structure then why are we considering {110} plane as a closed packed plane?
{110} is the closest possible plane in BCC, and it does have two close-packed directions in it (the two body diagonals of the type lying in it). Thus it is a good candidate for slip plane. However, in reality in BCC crystals the slip planes are not always {110} but the slip direction is almost always type. Thus a BCC crystal is found to slip on several planes containing the directions .
Sir for hcp you gave 0001 as plane and 11-20 as direction. But if we take only the hexagonal P lattice then plane will be 001 but what will be the direction. Is it necessary to give slip plane and direction in the way you wrote or can it be given by considering hexagonal P lattice
The issue here is not primitive vs. nonprimitive but three-index vs. four index.
@@rajeshprasad101 but can't we give slip plane and slip direction for hcp with 3 index. Because for four index we are required to consider more than one unit cell
tq sir and education centr of iit delhi
I have a question sir… Is it possible to have slip without dislocation?
Well, theoretically it is possible, but will require very high stress. So practically, is always with help of dislocations.
Thank you sir.
Sir how are slip systems counted , is it by microscope .
By x-ray diffraction one knows the crystal structure. And by deformation experiments on single crystals one establishes the type of slip plane. Then one simply determines how many such planes are consistent with the crystal structure.
In book, I have read that in bcc there are 48 slip system
Can you please explain why so?
12 slip systems of type {110} are most favourable slip systems, i.e., they have lowest critical resolved shear stress (CRSS). However, in some bcc metals, like alpha-Fe, {112} and {123} slip systems have only slightly higher CRSS, and so are also counted as favourable slip system,. As there are 12 slip systems of type {112} and 24 of type {123} this brings the total number to be 48.
Can slip occur on a polycrystalline material or is it limited to only single crystal?
Yes. But the analysis becomes more difficult due to the presence of grain boundaries.
Introduction to Materials Science and Engineering thanks alot. Your lectures are very informative and helpful.
why slip occur in closely packed plane and in closely packed direction??
The spacing between planes is inversely proportional to the atomic density within the plane. Thus close-packed planes are farthest apart. This weakens the bonding between the planes and so makes it easier for slip to happen.
Slip happens by movement of dislocations. The dislocations create slip in the direction of their Burgers vector. Burgers vectors happen to be shortest lattice translations. Thus it is most likely to find shortest lattice translation and hence the Burgers vector in the close packed directions.
@@introductiontomaterialsscience sir you write burger vector are smallest lattice translation.. Is it related to elastic energy store which increase with increase in burger vector and crystal try to minimize its energy. So burger vector is smallest lattice translation.
I don't understand about why slip planes are closely packed planes. Can you have any video lecture on it??
@@introductiontomaterialsscience Sir, can you please tell why spacing between planes is inversely proportional to the atomic density within the plane ? i.e. why closes packed planes are most widely spaced planes ? Also, I am getting confused with contradiction that interplanar spacing in case of (111) plane for FCC is lesser than that of (110) & (100) planes but despite of that why (111) is regarded as the most widely spaced plane ?
@@viralgadhiya6550 Bro, it depends on planar density (no. of atoms per unit area). Just calculate this for respective slip plane, you will get to know. This is the answer for your last part question on why slip planes are closely packed planes.
Excellent
BUT BCC structure have 48 plane systems ????
Please see reply to Abhishek Kumar.
Sir, can you please tell that what are topographically closed packed planes ??
??
@@introductiontomaterialsscience
Sir , this question was asked from me in an interview for phd. The exact question was : " Do you know about trophographically close packed planes in superalloys ? "
Thats y, i asked you about the same . . .
@@ayay9835 I really have no clue.
@@rajeshprasad101 Thankyou for your time sir.
@@rajeshprasad101 I think the question was (or should have been) "topologically closed packed phases" (TCP phases such as Laves, sigma, etc.). The question was not relevant to the topic of this video!