Most of the semi-litrate teachers of our education system, who don't even know how to teach should follow this extraordinary professor.The man is really extraordinary.A genuine accademichian.
His class is easy to understand than any other. Easy for beginners to learn . Our professors are teaching as like we know everything but you sir amazing i love your way of teaching
Great videos! One quick question, and i think this might be the key to understand these diagrams: At the eutectic point, when going from liquid to solid, there is 18 wt% alpha and 97 wt% beta, but shouldnt they add up to 100 wt%? I would appriciate an answer that makes me understand this diagram better! Keep creating good videos so the world can become smarter! Thanks :)
Actually Alpha is a solid solution of Sn in Pb containing 18% Sn. Thus it contains 82% Pb. This of course adds up to 100%. Similarly Beta is a solid solution of Pb in Sn. It contains 3 % Pb in 97% Sn. Again it adds upto 100. If you calculate % of alpha and beta in the eutectic mixture, they will be different values and again will add up to 100. Thus, by applying lever rule just below the eutectic horizontal for an alloy of eutectic composition (62 wt% Sn), there is (97-62)*100/(97-18)=44.3% alpha in the eutectic mixture. In this alpha there is 18% Sn and 82%Pb. Amount of beta in the eutectic mixture is 100-44.3
When the whole alloy is homogeneous in terms of composition, why do the α and β phases evolve alternatively resulting in tubular structures rather than spheroidal structures throughout?
It depends on the interplay of thermodynamics and kinetics. Thermodynamics dictate which phase or phase mixture is stable at a given tempearture and composition. Above the eutectic tempearture liquid phase of homogeneous composition is the stable phase. But below this tempearture the liquid phase becomes unstable with respect to a mixture of to solid phases. This mixture is called the eutectic mixture. But how the two solid phases will nucleate and grow from the liquid phase depends on the kinetics. This in the end decides whether the structure will be globular, rod like or lamellar.
Sir if we draw a cooling curve of a composition passes through @+L region a curved downward slope appears. What the curved slope represents in the cooling curve?
This is a deep question. The answer lies in the thermodynamics of the alloy. The phase or phase-mixture present at any given composition or temperature is the one that minimises the Gibbs free energy of the alloy. Thus the entire phase diagram is actually graphical representation of this thermodynamic condition. I have not been able to answer your question. i have just given a suggestion.
You have asked a very difficult question. I do not have an answer now, but I will certainly like to look it up. All the phase diagram and the eutectic reaction is telling us that two phases will form from the liquid on cooling. But the phase diagram cannot indicate that they will be lamellar. It is an experimental fact that they are lamellar in the case of Pb-Sn. But other kinds of eutectics are also known: rod eutectic (one phase is rods and the other a continuous matrix) or Chinese script eutectic (two phases very intimately mixed). One thing is clear that it is a question of kinetics rather than thermodynamics. I say this because in the lamellar eutectic there is a very high level of alpha/beta interfacial energy. Thermodynamically the system should try to decrease the energy and so the two phases should separate out with a single alpha/beta boundary. The fact they form so many interfaces must be facilitating the kinetics of the transformation. But, of course, I have not answered your question :-(
Alpha and beta have different crystal structures and different compositions. Alpha: CCP and Pb rich. Beta: BCT with two atoms per lattice point (motif) and Sn rich.
Dear sir, I have small confusion about the eutectic microstructure which I have not been able to clear for a long time. My question is: "Won't there be any grain and grain boundaries in this kind of microstructure? And also, what is the interface or boundary between the alpha and beta phase is called in this context?"
A grain boundary separates two regions which have the same crystal structure and composition but different orientation. Since the alpha and beta phases of a eutectic microstructure have different crystal structures and/or compositions they are not grain boundaries. They are called phase boundaries. Sometimes they are also called interphase boundaries. To the best of my knowledge, alpha and beta phases are single crystals, so they do not have any grain boundary.
Thank you so much for your response sir ! So the alpha and beta phase are the single crystals but arranged in a lamellar fashion, am I correct? And also, each of these phase will have different orientations?
So it means, grain boundary is in a single phase (Alpha Or Beta) only and a boundary to separate different orientation of a single phase (alpha Or Beta). And on the other hand phase boundary present in more than 1 phase as the name is suggesting and separates 2 phases (Alpha and Beta). Sir, Am I right?
Most of the semi-litrate teachers of our education system, who don't even know how to teach should follow this extraordinary professor.The man is really extraordinary.A genuine accademichian.
His class is easy to understand than any other.
Easy for beginners to learn .
Our professors are teaching as like we know everything but you sir amazing i love your way of teaching
sir, I just wanna say you're awesome
Great job sir. Very good material science content in youtube. Also Thanks for replying to all comments , sir.
You are legendary sir !! Better understood
Thankyou so much sir for your efforrts. you're too good 🌺 nd tomorrow i'll attempt my quiz easily 🙆
Great videos!
One quick question, and i think this might be the key to understand these diagrams:
At the eutectic point, when going from liquid to solid, there is 18 wt% alpha and 97 wt% beta, but shouldnt they add up to 100 wt%?
I would appriciate an answer that makes me understand this diagram better!
Keep creating good videos so the world can become smarter!
Thanks :)
Actually Alpha is a solid solution of Sn in Pb containing 18% Sn. Thus it contains 82% Pb. This of course adds up to 100%. Similarly Beta is a solid solution of Pb in Sn. It contains 3 % Pb in 97% Sn. Again it adds upto 100. If you calculate % of alpha and beta in the eutectic mixture, they will be different values and again will add up to 100. Thus, by applying lever rule just below the eutectic horizontal for an alloy of eutectic composition (62 wt% Sn), there is (97-62)*100/(97-18)=44.3% alpha in the eutectic mixture. In this alpha there is 18% Sn and 82%Pb. Amount of beta in the eutectic mixture is 100-44.3
18 percent tin and 97 percent tin. Thats what these numbers mean. Alfa and beta have relative proportions of 55 percent and 45 percent.
hmm
When the whole alloy is homogeneous in terms of composition, why do the α and β phases evolve alternatively resulting in tubular structures rather than spheroidal structures throughout?
It depends on the interplay of thermodynamics and kinetics. Thermodynamics dictate which phase or phase mixture is stable at a given tempearture and composition. Above the eutectic tempearture liquid phase of homogeneous composition is the stable phase. But below this tempearture the liquid phase becomes unstable with respect to a mixture of to solid phases. This mixture is called the eutectic mixture. But how the two solid phases will nucleate and grow from the liquid phase depends on the kinetics. This in the end decides whether the structure will be globular, rod like or lamellar.
Nice explanation sir ji 🙏
Sir if we draw a cooling curve of a composition passes through @+L region a curved downward slope appears. What the curved slope represents in the cooling curve?
When the system cools through alpha+L region the time-temperature shows a change of slope.
Many thanks from Egypt
Running this video on 1.75x works pretty well. I hope yt provides 2.5x as well :( Thanks for the explaination tho
Same feeling.
Question : why the solid to liquid transition temperature range is varying with respect to composition , sir?
This is a deep question. The answer lies in the thermodynamics of the alloy. The phase or phase-mixture present at any given composition or temperature is the one that minimises the Gibbs free energy of the alloy. Thus the entire phase diagram is actually graphical representation of this thermodynamic condition. I have not been able to answer your question. i have just given a suggestion.
Sir,why do we get alpha and beta microstructure in a lamellar type only?
You have asked a very difficult question. I do not have an answer now, but I will certainly like to look it up.
All the phase diagram and the eutectic reaction is telling us that two phases will form from the liquid on cooling. But the phase diagram cannot indicate that they will be lamellar. It is an experimental fact that they are lamellar in the case of Pb-Sn. But other kinds of eutectics are also known: rod eutectic (one phase is rods and the other a continuous matrix) or Chinese script eutectic (two phases very intimately mixed).
One thing is clear that it is a question of kinetics rather than thermodynamics. I say this because in the lamellar eutectic there is a very high level of alpha/beta interfacial energy. Thermodynamically the system should try to decrease the energy and so the two phases should separate out with a single alpha/beta boundary. The fact they form so many interfaces must be facilitating the kinetics of the transformation.
But, of course, I have not answered your question :-(
@@introductiontomaterialsscience Thank you for the reply sir
What is the microstructure difference between alpha and beta??
Alpha and beta have different crystal structures and different compositions. Alpha: CCP and Pb rich. Beta: BCT with two atoms per lattice point (motif) and Sn rich.
Thanks Sir ❤✌
👍👍👍👍👍👍👍👍
Sir, why does Eutectic point exist in the first place? What makes the temperature for melting the lowest at this composition?
This is a difficult question. I do not have an answer :-(
@@rajeshprasadlectures Thank you for the reply, Sir. Your lectures are excellent.
Sir , May you tell us which book is beneficial to study the material science deeply ?
Callister is good if you belong to mechanical engineering
What is meaning of beta sir ?
Dear sir,
I have small confusion about the eutectic microstructure which I have not been able to clear for a long time.
My question is:
"Won't there be any grain and grain boundaries in this kind of microstructure? And also, what is the interface or boundary between the alpha and beta phase is called in this context?"
A grain boundary separates two regions which have the same crystal structure and composition but different orientation. Since the alpha and beta phases of a eutectic microstructure have different crystal structures and/or compositions they are not grain boundaries. They are called phase boundaries. Sometimes they are also called interphase boundaries.
To the best of my knowledge, alpha and beta phases are single crystals, so they do not have any grain boundary.
Thank you so much for your response sir ! So the alpha and beta phase are the single crystals but arranged in a lamellar fashion, am I correct? And also, each of these phase will have different orientations?
@@Bablu194 That is right.
So it means, grain boundary is in a single phase (Alpha Or Beta) only and a boundary to separate different orientation of a single phase (alpha Or Beta).
And on the other hand phase boundary present in more than 1 phase as the name is suggesting and separates 2 phases (Alpha and Beta). Sir, Am I right?
Can one apply Lever rule in (@+B) region.
Yes, Lever rule can only be applied in the two-phase region.
Introduction to Materials Science and Engineering
Thank you Sir for your precious reply.
sir, is Eutectic reaction reversible or not
It is reversible.
Invariant Reaction
4:03 why sum of alpha and beta is not 100
Did u get the answer for it , even I have this doubt...