Lecture 06 : Basics of Materials Science - V (Part 01)

[Music] students welcome to the lecture number six and this is the course on a IML in materials engineering hope you are enjoying the lectures and in this portion of the lectures I've been discussing about the basics of Material Science so let's continue on that because these aspects you must have clear idea in your mind if you want to design materials using machine learning or deep learning approaches so first obviously we are going to do some recap as usual and I've been telling this again and again to you that basics of material science engineering is basically the connection between processing structure and properties almost all materials are processed to give different kinds of components right so hence you want to make something out of a material you need to use some processing route and depending on the type of routes you're going to use the material structure will change and that's why you can create different kinds of structures and which in turn will have a direct correlation with the property so that's why it is important to understand these certain aspect so that you can actually design materials with Target properties and hence use structure as a playing Ground to achieve those properties so with this let's begin and you know structure means different kind of structures this I've been telling you again and again please keep in mind that's why you have been telling first one is OB atomic structure because every material in this world is made of basically or basic unit called atom and when atoms actually assemble it can form Crystal or amoral structures we have not discussed it amoral structure so far we'll do it later so we have discussed about crystalline materials so once you know at a group of atoms come together and they arrange in a definite way or regular fashion it form a crystal and when the crystals actually arrange in the three dimensional space they can form micro structure and properties means we're talking about mechanical physical magnetic Electronics electrical all these kinds of properties you are important for you to understand rather fully understand this correlation between structure with the properties and as far crystal structure is concerned most of the metals actually crystallizes in three different structures first one is a body Center Cube that is called BCC structure and it is a very simple unit cell I can draw it here and show you that okay so this is the unit cell you can draw your cell that's why I'm drawing and in this unit cell Each corner will be occupied by one atom along with that you'll have a atom in the center now Center atom can be different type or same type if it's different type then it's a order BC structure forget about that simply consider the central atomies all same type then is basically called a simple or PCC structure okay so that's what it is because this atom is at the center of the unit cell that's why it is called a body Center cubic structure very important materials like ion mum Tung and chromium these are widely used they crystallizes the crystallize in the structure and that's why is important in fact there are other materials also have shown this kind of crystal structure many Ceramics also well second important structure which we discussed which is prevalently present in material system is f Center cubic structure so therefore let's say I draw the unit cell so you should follow me because this is something you should know very well how to draw it otherwise if you want to teach like me you may not be able to do it yourself this is a cubic cell so now place the atoms so you have atoms Each corner of the UN cell right you can see that and you also atom in the F centers so there are six pH centers that's why there are six atom in the face centers and there are eight Corners that's why the face Center cubic itself and you know in this case effective number of atom is four why it is four because each cor atom is giving 1/8 because each unit cell can be shared with eight other unit cells which you can do yourself very easily that's so 1 by 8 into 8 is 1 and each phase is shared with another un cell that's why each face set atom gives half so 6 into half is three so 1 + 3 is 6 for body C the Cub un cell the effect atom is two you have eight atoms in the coordinates that gives One Atom 1 by 8 into 8 basically 1 by 8 into 8 plus the central atom is inside the unit cell so it belongs to the unit cell that's why it is one that's gives you two so I can write down 1 by 8 here into 8 + half into 6 that gives you 4 so this is the effective number of atoms in the FCC that's why you see FCC is more dense back structure the the B CER cubic structure has about 68% space is filled and fenter cubic has about 74% space is filled so Body Center cubic structure is more open than the F Center cubic structure P center CU structure is called a close pack structure because atoms are basically touching each other in this kind of structure Body Center cubic structure is not a close pack structure so many important metal like copper which is used in IC applications silver gold nickel lead aluminium actually form penter cubic structure if you know Ceramics like carides many of the carides actually form fenter cubic structures Tangen caride is one such naum carbide many carbides actually form P cubic structure and the last important structure is hexagonal close pack structure and this structure is also widely seen in material system system okay both in metals and Ceramics so let me draw an hexagonal cuic unit cell so first I draw an hexagon and I draw a little bit perspective way so that you can see the whole unit cell very nicely this is an hexagon then I take this things up connect it I also take this up connect it then I also take this up connect it okay then this one connect it okay okay this is hexagon is now you can see here hexagon has a each pH of the hexagon has a center Center is occupied by one atom corers of hexagon is occupied by each cor Ed by one atom so and in addition to there are three atom inside okay so actually speaking if I draw this one let's do that yeah I can take out this in cell which you can clearly see I'm marking it with with this red color thing I'll draw it here also I draw it here for your purpose so that you can understand this is a rhombohedron okay not a cube rron basically rbus in three dimensional so Each corner of the Rus one atom and you know here at the center you have one atom so therefore how many effective number atoms hexagon Crystal has let us do it from the hexagon six will be 1 by 6 into 6 and that means 6 + 6 is 12 so 12 1X 6 by 12 and then there are two atoms on the face Center so 1X 2 by two because this is shared and there are three atom inside so 2 + 1 + 3 6 right and here you see there are only two atoms because inside one atom and there are coordinates as eight coordinates as one by8 so you can consider each of these any of these as a unit cell doesn't matter that's how it test understood hexagonal clack structure is close packed again it has uh 24% space occupied by the crystals only remaining space about 36% space is vacant just like a standard cubic structure and many of the important Metals magnesium titanium zinc as well as many of the Ceramics will crystallize in this like aluminium oxide okay is one of the important Ceramics which forms hexagonal Crystal structures many Ceramics are there I can't remember all of them now but they form this Crystal stru these three actually are very important they are very important crystal structure in materials they are widely seen in material system they are widely seen in the matrial structure so therefore please remember these aspects very well now from the crystal how do you start from the micro structure very easy you can actually put crystals large numbers and from grains right I already talked about it and then between two grains you will have boundaries where the atoms are not arranged properly HP that's why they called G boundaries so by this way you can form the whole micr structure so now you can see that there are two aspects here in a normal material in the micro structures one is the green where elment of atoms are regular other one is the boundary that's why the bound atoms are hly aligned or placed so therefore G boundaries are having lot of free space present where atoms can migrate a lot of things can happen okay and this is an important area of subject and G boundaries can also be different types which we are not going to discuss but there are different types they can also play role in determining the mechanical physical properties this is a picture of the optical microgap of pure iron you can see here this I've been showing you for last three lectures so after that we talked about something about imperf this is very important actually that's why I'm talking to you again and again because no crystal is perfect including silicon single crystals which use for your devices like mobile phones or laptops or any electronic devices by the way washing machines they have chips and each chips has silicon single crystals so they are also not perfect there are defects inside it in perfe Rise form because of inability of Sol solidifying material to continue replicating the units properly or it can be also introduced in purposely like allowing can lead to or deformation can lead to the three types of defects we talked about it Point defects line defects and plan defects Point defects is nothing but a vacany so in a metallic structure vacancies have no charge so it can be simply Bing of one atom form his location like here you can clearly see this one atom here is missing so this atom here is missing right so this is what is called vency but for Ceramics is a charg compounds or charge material so therefore you cannot have one atom missing this will lead to imbalance of charges that's why either you have both the atoms missing that's called ionic pair vency or you can have interstitial possible then there's no loss of any charge or otherwise you can have Frankle defects like atom is displaced from his original position to some intertial position okay this is very unable situation you can see here atom cannot remain but nonetheless it happens so you can create all kinds of defects then you have a line defect which is nothing but a connected group of Point effects that from a line L structure and we talked about two dislocation age and screw this age dislocation is nothing but extra row atom extra row of atom you can see here this is the extra row of atom here this one which is missing at the bottom below this and this is your sleep plane correct that's why this is the symbol it is used and screw dis location is basically it's just like a spiral with a lat structure wrapped around the imperfection line it's just like a screw if you take a screw and put inside a wood so that's what it will look like it's a screw moving inside a crystal so if you look at from this side it looks like a screw so you can also have planner defects the defects which are extend in plane like boundaries like twinning is one such gun b is another one twinning is basically large scale deformation it is such way that one part of the crystal is a mirror image of the other part of the crystal that's why a twin is called you can see there a twin plane here this part of the crystal is Mir image of this part of the crystal same thing here twin plane can be extended area also this part of the crystal is M of the other part of the crystal on the this right side so in the micro structure it will look like a this kind of objects you can see that it's an extra row atom that means if I draw a green it will look like this that's why is a tnis so this is something which you are understanding slowly that atoms the chemistry of our pieces of the atoms they are the most important unit of the materials and it's not only that it is the way they arrange in a crystal that actually is from the internal structure of material so internal structure we mean arrangement of the atoms basically and this can dictate micro structure subst structures or even many other things which we are not talking about it in addition to that you have electronic structure electrons actually bonds with different atoms and that's also dictates material properties yesterday in the last lecture I talked about it so let's talk about little bit more on this so this is something I showed you that atoms are the basic unit they form Crystal Crystal form micro structures or structures okay here and then it forms a component so this is macro scale and this is microscale so there's a connection between these two and this connection is basically trying to understand micr structure will con phases and the defects and defects can be frequency dislocation twins G boundaries voids cracks everything and this can be controlled by this processes the casting metal forming powder metal welding or Machining okay so I'll not talk much of these aspects we'll directly go to the engineering materials which started in the last lecture engineering materials are can be two types metal and nonmetals non-metal means polymer Ceramics Composites and metals means FAS and non feras because feras is the largest quantity we use in the world we produce about 1 1,800 million tons of Steels per year in the world so that's why is the largest T of material use after Concrete in this world and that's why they group together in feros and everything else is non ferus so feros metal means Steels Steels are nothing but iron and carbon alloy with a little bit of carbon about 02 to about 2% carbon and they can be plain carbon steel All Steel plain carbon Steels will have no allo elements added they are basically like having carbon concentration varying from2 to 1 weight per and some other things like impurities like phosphorus sulfur or maganese can be present where the alloy Steels have many alloy elements like chromium nickel tungsten Molly they added interally to create Alloys so this phase diagram I don't want to discuss much but let me only tell you that this is the basis for the steel and Caston so steel composition is varying from about 0 to about 1 percentage cast perc 3.5 to about 4.5 percentage this is what it is carbon concentration so this part of the phase diagram is important part Ste so here you can see this is FCC oite phase and then you have parite this is called BCC phage this is Alpha iron and then you have centi which is nothing but a carbide I already discussed about it that if you add carbon to iron it is going to form carbides so this is this mixture of iron and carbide which actually gives you the best properties of the steel and steel is a material which can be modeled actually very interestingly it has a lot of data to do a machine learning Bas or deep daring Bas model so in a micro structure there will be two types of things possible one is a solute Solutions other one is a compound so let's talk about a little bit of solute Solutions because solute Solutions are more widely seen like here in case of iron carbon this IDE which FCC solute solution of iron with carbon so carbon is small quantity but iron is the largest species large species means majority species and carbon is added in a minor quantity that's why this is a Sol solution of carbon in Iron similarly Alpha also is a solute solution but it has very less amount of carbon about 02 we% of carbon that's what but centi is not a solute solution but it's a compound okay so in a phase diagram or phase mixture you can either have a solute solution or have a compound and compounds can be fixed toet or can be variable stomry possible so but here f3c is a strict stomry it has has a fixed composition of carbon about 6.6 78% carbon and so IFC if you look at it has carbon about 6.67 weight percentage and iron is remaining that's about 93 uh you know 33 weight per. so total will go up to 100% that's what is the content of carbon but it has a fixed isometry that is you cannot change carbon concentration much in the i3c or cementite so that is what we are discussing a little bit more in detail manner so that understand so what are solute solutions they are less like a liquid solution if I take sugar and put in water and St it sugar will dissolve in water and that's nothing but a liquid solution of sugar in water you can add even salt also that will also dissolve in water right or let's talk about even glucose in water you add glucose into water it will form a liquid solution whether same thing can be done in solids or not that's the question actually asking yes it is true same thing can be done in solid also if I add nickel into copper it forms solid solution difference between solid and liquid is what only in state liquid means it's liquid state solid means in solid state so here we are showing a phas diagram of copper and nickel this side is copper and this side is nickel so this is copper side this is nickel side you can see this is 100% this is 100% copper pure nickel and pure copper and in between you have a lens sep region is what is called Liquid Plus solid region below which you have a Sol solution called Alpha and since nickel and copper are both from FCC right Nel copper you have seen both of them form FCC crystal structure they have a similar like latice parameters and they both are metals same almost similar row of periodic tables no not same row Peri same column but they are similar properties actually so they mix together nicely and form solid solution that's something which is unique for the NC and copper and this is what it is shown so in all concentration of nickel and copper you can form solute Solutions so we'll show you in detail manner solute Solutions can be two types one is where you add substitute in solute solution that means you are adding an atom which is replacing the other atom like if I take a nickel and replace nickel atoms by copper then it form a Subs solute solution you can see here copper and zinc also form a Subs Sol solu right hand side you can see here these are zinc atoms the these gray atoms and the other atoms actually copper so you can have mixture of two atoms possible on the other hand you can also have interstial solute solution what are these this actually iron atom let's say and these are carbon atoms if atoms are the solute solution atom is small solute atom is small okay by the way here the majority atom is called solvent and the minority atom is called solute very clearly right solvent atoms actually large number solute atoms are small number that's why they solvent atoms called majority and solute atoms are called minority so here you can see both of them have same size almost similar size right copper and zinc has almost similar size copper and nickel has almost similar size but iron and carbon has different size car is carbon is very very small compared to Iron so it cannot replace carbon iron atom it can only goes into the voids or the intertial positions of the iron latice so iron is a FCC or BCC ltis it can go there that's what it is so you can see in the three dimensional picture also the black atoms are carbon atoms so we'll talk about much how this voids already have talked about some of the voids and other things tal voids in Diamond cubic structure we'll talk more about it how it this atoms can go inside the voids and form a solute solution in the next part of the lecture thank you [Music] [Music] [Music]