Lecture 05 : Basics of Materials Science - IV

[Music] welcome back students so this is the second part of the lecture five what I discussed was put together in this slide which is the last slide in the previous part of the lecture and you know nature and properties of material depends on chemistry adment of the atoms the materials the defect structures so we have seen that in it is the particular atom type that is a composition the arrangements inside the material or the space whether it's a one dimension two dimensional or three dimensional space that large extent determines the properties of material hence big step or important stem in understanding properties of material is to understand this internal structure that's what we have seen and we are taking a step to understand that now we'll talk about a little bit about bonding of the atoms their arrangements and Etc before we talk about engineering materials so structures has two types obviously internal structures one is the atomic structure and the crystal structure which you have discussed then you also have a micro structures which consis of phases and defects and their distributions more about this will disc discuss lat lectures or later chapter that's what I've written and important aspect for you to understand that it is this micro structure which can be telled by mechanical or by processing actually so a typical component or any kind of device you can think of could be hybrid with many materials and may have different kinds of micr structures so when you put them together we should know how to put them together right then only we can get best performance possible this is something which is not easy to understand at the beginning but as we go alone you'll see that any typical component has many many comp parts and that's why I call them as a hybrid consisting of many things and their connections are very important whether you talk about a mobile phone or a laptop or a computer many components they put together to give you the best performance so you also need to know how they are connected well in this slide I put together everything all the details what you have learned this is very important slides so you see we start with the atom or specific type of atoms or whatever it consisting of any material atoms arranged to give you a crystal crystals will arrange to give a structure right that's what we know and this crystals will also be depending on atoms bonding between the atom that's what is your electromagnetic or what is called the atomic bonding structures and all these things together these things together when they come in a macro level or sorry micro level it form a micro structures micro will consis of phases and defects and the distribution forget about isual part now this is not need not to be discussed at the beginning now defects can be vacancies we talked about it dislocations twins gun boundaries voids cracks many things right that's what it is and this is this is what you were talking about different kinds of defect like these are the twins grains boundaries you can see twin boundaries and this is a two-phase structure you have a boundaries between the two phases one is your actually there are more than that more than two phases actually looks like the three pH structure one is green then you have a red they have a black so you can have multiple Pages present in the material and all these things together forms a component and component is produced by these processing routes casting forming welding powder mety Machining or even thin flame routs many roots so you can clearly see if you want to understand these components we need to understand we need to start from atoms and slowly build this connections and once we know each connections then only we can predict the material properties that's what it is so I request you to go through all these things little more detailed manner don't only think that simply by listening this lectures or slides you'll understand very everything please read some study material books which are already given to you at the beginning or any standard St books will give you a lot of insight what is happening in the material so uh that's what we call is a material science I hope I have given you and as you have seen or probably you have heard there are many properties which are micr structure sensitive and they actually are controlled by the mic exerise control so let's talk about little bit about things which you talk about this the how the atoms are bonded together here we know that bonding is a very commonly taught even in first year of physics or any engineering courses it is taught so we have two types of bonds strong interactions weak interactions right strong interaction leads to ionic bonds in which two different ions form like a sodium chloride structure you have a sodium ion form by removing one electron that's what is called na+ and then chlorine ion chlorine atom will receive that electron from a chlorine ion by the way they can actually complete the octat right very simple and then they can come together because they are all different charges they can come very easily together attract each other and form a bond that's called ionic bond this is a very strong bond actually because bond is formed by two different ions you can also have calent bonds like in case of silicon or in case of carbon you know Carbon has four electrons the outer cells so we can actually have sharing of electrons between the atoms and form a covalent type of bonds and these bonds actually are very important in the sense that they are going to give you strength like diamond diamond has a strong calent bonds and this calent bonds gives Diamond one of the hardest material in the world and third type of bond is called a metallic bond in case of ionic bond there is electron transfer right from sodium to chlorine in of coent bond there's no electron transfer there sharing of electron happen between the two atoms or two pieces basically in metallic bonds none of this happens in metallic bonds every atom donate outside electrons and this electrons then can hover around to the whole material they're free to move that's why they are called electron cloud and this electron cloud move inside the material depending on the charge availability depending on the potential applied so therefore metallic bond basically nothing but this positive ions as you've seen in the crystal structure these are positive Pines and then you have what you have this metallic electron cloud moving inside the material so this electron cloud is not confined to any atom they are free to move anywhere that's why is called a metallic bonding so bond is weak compared to calent and ionic bonds but since electron cloud is present they can go anywhere and they can actually take the charge from one place to other place to apply potential that gives you electrical conductivity thermal conductivity many other important material properties then you can also have what is know as a weak interactions weak interaction means the strength of this interactions are very weak one is very important one is called hydrogen bonds you know between two water molecules you can have hydrogen bonds possible you probably have read about it okay okay hydogen man is a very weak bond which can be broken very easily you can also have V all bonds if you have pces or molecules which have some charge differences then it can also lead to a bond formation these are called Vall forces and this bonds can be easily broken by breaking these bonds you can actually form different kinds of material in today's world 2D materials are basically formed by breaking these kind of weak bonds like graphine is Bally a single sheet of carbon form from Gra F by breaking the bonds between the two layers that's what happens so this electron interactions which leading to formation of different kinds of bonds in the materials has a profound influence on the properties especially physical mechanical and electronic properties so it is important to understand these aspects very well so I'll provide you some different types of bonds like calent Bond materials has a high melting temperature hardness is obviously high that deely poor because hardness is high right like diamond diamond is a very hard material but it's very brittle if you throw it off it will break like a pieces elal conductivity is very low examples are dond camic silicon germanium they all actually are having calent time Bonds in fact many carbonis materials has calent tyes of bonds ionic bonds have very high melting temperature many of the ionic bond compounds are M temperature quite high they also very hard and ble sodium chloride is you know it's basically common salt it's basically very hard but it is also ble it has no free electron available so that's why there's no electrical conductivity zinc sulfide cium chloride also examples of that metallic bonds metalic temperature can vary depending on the kind of atom present because electrons are basically in a c of pool dity is quite High because they can atoms can easily move from one place to Other Place bonds are not so strong they have hard elal conductive because of the large amount of electrons present free to move inside the material examples of iron copper silver then you can have Vandal bonds Vandal materials have very low melting temperature same thing to for the hyen bonds also and they are Bally soft materials very soft they have no hardness because their bond sign is very low for the both the Pall and hydrogen bonds electrical conductivity is exactly low same as like a calent bonded materials pandal bonds present in all our rare the neon argon Krypton all the gases which are present on the extreme right of the periodic table right and hydrogen bond is present from Ice between the two water molecules so you probably have understood by now the nature of bonding and the atomic structure they play The crucial low and determination of these properties properties I'm showing in front of you in this list and both these natural bonding and atomic structures are results of part results of electronic interactions so we we start from electrons electron interly to bond formation between the atoms then atoms lead arrang in a different way lead to crystals Crystal different way leads to micro structures and that's how the whole structures can be built up so I'll talk about this aspect later later uh Material Science relies on four important pillars one is called electromagnetic structures which you have seen and then you have Crystal structures or physical structures other than that you also have to understand thermodynamics how these structures are stabilized what are the energetics of the structures and similarly you have to understand how fast these structures can be transformed from the one to other that's why determine the kinetics so these four pillars actually are very basic things of Material Science once you know this four pillar very well you can actually design and develop new materials easily so I'll not talk about much of this but I'll move forward and give you some perspectives of uh this aspects so we have talked about all kinds of structures right so let me give you some glimpses of engineering materials which can be used as for you like a standard to design a new materials so as you have to talked about it about materials you have Metals Ceramics and polymers but since Metals actually are large in numbers in a periodic table we can combine them one group and all else everything else like Ceramics composite polymers can be non-metals that's what I see and then metals can be subgrouped into two parts because of the wide use of feros we also divide non feros ferah means iron based basically Steels cast IR actually ferah that's why you call as one group and they are the largest T material use in the world so this is how actually one can look at the whole material world if you are preference to Metals then you have feros and non ferus preference to non-metals you have composite Ceramics Plastics or polymers actually well for the FAS the important aspect is steel actually and you know we'll talk about a little bit on this aspect steel is actually nothing but iron I already talked about a little bit of carbon carbon can be very small very from 02 to point about 1 percentage 2% is Extreme we can talk about 2% but we never have a steel with 2% we% of carbon normally varies from 02 to about 1% and Steels can be classified into two parts one is called plain carbon steel alloy steel plain carbon steel means it's iron little bit of carbon and some very small impu like phosphorus sulfur manganese alloy steel means we add other elements inally like let's say stainless steel it's alloy steel we have lot of chromium and nickel present in the stainless steel tool steel it has chromium mly many things present interally added that's the difference between plain carbon steel and allo steel plain carbon steel will not have this element present or interestingly added allo steel will have that added so you know I don't want to give you this perspectives in a detail manner just to show you the Steels actually are based on this phase diagram which is called iron carbon or iron carbide phase diagram and this is the basis for our steel and the castan as you can clearly see that this is Pon and this is somewhere going to f3c which is nothing but six contain about 6.67 we% of carbon F3 compound actually and I told you iron has a three crystal structure BCC at room temperature FCC in the intermate temperature and BCC at high temperature that's called Alpha Gamma and Delta Alpha is BC structure room temperature gamma is FC structure at high temperature or intermediate temperature rather and Delta is basically a BC structure again at high temperature and if you add carbon everything gets changed that's why this diagram is talking about it and the gamma iron which is nothing but a iron in carbon in a solute solution way is basically present in the oxit OR gamma iron and maximum of carbon can be there in about 2.08% that's why theoretically speaking we Define Steels contain 02 to. 28% of carbon but practically speaking most of the steel contain less than about 1% carbon majority of Steel content carbon concent 2 to.5 per that is called mild stees so therefore practically definition is carbon concentration is about 0 to 1% cast on the other hand contain large amount of carbon it can contain about 3.5 to about 4.5 or even 4.8% of carbon this domain actually you can clearly see that's what the castar and domains are that's why the reason I wanted to see show you this diagram this is the steel this is the castan and this is the basis for all the Steels in the literature so let's stop there you know we'll talk about different aspects of these phases in the next lecture you can have compounds like f3c you can also have gamma solute Solutions you should know what is what and how they are actually depends on a little bit of understanding of the subject is also required to know how the steel structures develop how the cast structure develop and how they determine the material properties so with this let us stop and I will you know discuss more about this in the next lecture and uh please uh most important uh you know thing for you to know is that you know I cannot teach everything in detail manner because our basic Focus will be on how to use Ai and ml artificial intelligence and machine learning to designer materials so that's why I can spend little time to give you some idea of material science engineering but if you want to know more about it details about it please read standard State books textbooks or you can even go through some other nptl lectures which are available on steals or physical matology of materials that can provide you much better perspectives but nonetheless whatever I'm giving you that is enough for you to have very basic understanding of the subject okay thank you [Music] [Music] [Music]