Lecture 10 : Basics of Materials Science-XIII - Part 1

[Music] students welcome to lecture number 10 so I hope you are able to understand the basics of Material Science we are way behind discussing the AIML first we need to build out the foundation then we can discuss about a IML how to utilize that that's the major important aspect rather for you so hence first have some patience and try to understand these basic aspects So today we're going to discuss electrical properties but before that let us take a stock of the things which you have done in the last lecture so again and again I'm telling you this aspects we need to know very nicely our very importantly rather the correlation between structure and properties and that correlation is only possible when you know how to connect processing with the structure because processing is something which helps us to make components using different materials and once you make it we make certain kind of a structure or rather micro structure and that in turn determines the properties so we discussed about mechanical properties in the last two three lectures now we'll discuss about the functional properties like electrical magnetic Electronics properties so electrical properties are very important because many of the materials are used in the world basically based on their good electrical properties most important example is copper oxygen free copper which is used as electrical cable worldwide why copper is used what the advantage of copper all these things must be known right because when we used copper started using copper rather as an electrical cable we never done any machine learning calculations to understand why copper or rather nobody has actually did a design the copper came into picture B because it is easily available Earth abundant cheaper than many metals like gold and silver and it has a reasonably good electrical conductivity and another important aspect of copper is it can be made into different shapes because copper as you know is an as FCC crystal structure so therefore it has many sleep systems it can be easily deformed in different kinds of shaps wi rods whatever you want so these all together give copper the advantage and that's why you cannot have a cble in the world made up of other than anything else other than copper we cannot even think about it whether you will have Gaffin and Earth ST which has come into picture recently but you can't even dream of using replacing copper by graphine as electrical conductor so let's talk about a little bit about that as you have understood that components are subjected to the service conditions so therefore selections of material will depend on the properties which will allow you to match its properties with the service conditions as well as the manufacturing process you adopt to make them because if you cannot make them with any manufacturing process then it's not of use you will you will you know I'll talk about it maybe not be today next lecture you know there are a lot of superconductors they are fancy materials they can actually reduce the electrical losses transmission losses extensively but they're expensive and most important thing is it is not easy to make them in shape we want so therefore manufacturing ability of any material is of Paramount importance if you cannot manufacture it can be used well we talked about mechanical properties especially we talked about tensile properties because material can undergo lot of different kinds of stress or loading like tensile loading compressive loading Shia loading we talked about it a lot but finally I discuss only ttile testing because that is the predominant testing method used in the world for ductile materials for br materials we use compress testing compress testing is you know exactly done in the same setup as as a tensile testing machine but loading directions are different so material which are likely to bitt or likely to show bitt less must be tested using compression setup tensile testing is no good for them tens testing is useful for material which shows which show dity this is a snapshot of the tensil St C you can see here nicely the elastic plus plastic portion and the different stages of denell testing for a sample then we talked about it effect of strain rate how strain rate can affect materials or strength of material stand is defined as a Epsilon doal D Epsilon by DT and that is a constitutive relationship which is given by Sigma T = to C Epsilon do to^ M and sigma T is the tensile true stess C is a constant and Epsilon dot is standed m is what stain rate sensitivity you have to understand one thing this is a constitution relationship like this one Sigma T is equal to K Epsilon dot these two are fundamental equations they are widely used in modeling processes modeling different materials so please keep in mind and I talked I showed you some values of m m is normally very low most less than 0.1 but there are cases where a can be go as high as 05 to point8 like in case of tianium 6 selenium 4um allies but normally it doesn't go very high but there are few cases where it can go even much High it can go close to one that's what super plastic deformation can happen the material can be deform extensively almost like a 800 to 1,000 percentage increase of its original length possible without any failure that's why the super plastic Behavior comes in picture metallic Alloys and some Ceramics also show super plastic behavior and we understand super plastic behavior is different from normal tensile Behavior but you should know this there are set of materials which show super plastic Behavior then I talked about a little bit about fatigue fatigue is uh more in know real life situations there are vibrations in automobiles aircraft compressor pumps even swaying of bees buildings all lead to fatig ftig is a word which is widely used by human sometime I get tired I said I'm fed so fting means you have undergone cyclic loading cyclic stress and strain basically stress in human life stress is very common and if this stress is positive and negative then you started feeling fatig so fetic is exactly same materials are subject to cyclic loading strile or compressive or even both this what we discussed here you have in the first case a you can see the loading is changing from tension to compression and there is a sinal nature of variation of the load in the second CL it is only tension but the nature of loading is science fle in reality the stress of stress or VAR on the stress as function of Cycles maybe a much complex that's what is shown in she you can see it in C and this is what is experienced by an aircraft Wing when subjected to periodic unpredictable oflo due to wind gust and this is very very common by the way so therefore the modeling fatig is not an easy task you have to understand I not talked about it different models of fa ftig because of the time constent because of the you know discussion to be limited to certain aspects but one can go to that book by George Eder I shown you in the last class and understand how this is important ftic is normally characterized by as CS Trace versus number of Cycles CS we can determine the fetic limit for Paras metal very easily for non press metal it is not so easy just like ill stress in case of tensile testing for non- press and feros the last I talk about right CP is time dependent high temperature deformation well it can be room temperature also some metals like lead tin they show cre Beav room temperature because their meling temperature very low let's talk about shoulder allies which is used in the electronic devices like in case of phones mobile phones cameras or in case of computers or laptops or tabs we use that they are the circuits are joined by shoulders and we use a lead shoulder still today and therefore they can undergo scrip at room temperature if we don't cool them they may break even at low stress that's what happens many of the Cs back down because of mechanical stress it has fallen down if your phone might have fallen down on the floor and then starts not working because some solar joints might have broken so therefore creep can happen at room temperature also but we are talking about creep in jet engines that happens at high temperature it's basically happens due to high temperature deformation time depend deformations that's why it happens and we use super Alloys for these kind of engines and supera is a complex chemistry you know you can see from here also it contains almost like a 10 to 12 elements and creep is what steny St if it's less than ill St also if it's subjected to a specimen Li temperature it will elongate continuously until it raptures it's a long-term phenomenon important in design of steam or gas T engines of an aircraft so you understand that and cryp crab is like this stain versus temperature at certain constant load and this shows the three stages of creep primary secondary and tertiary what is important for is the secondary CP that's why the CP R which is nothing but deep Sal by DT is almost constant and that's something which is we like to operate in that resign very clearly so if you want to have a low at high temperature you need to have a single crystals because is something which is governed by G boundary sliding so better to have some kind of a single Crystal without many G boundaries then it is possible to have reduce the CP and then I little bit discuss about stress and for the for the living cells but again this work was done by subba sures and J B long back 20 three but is very important that we can understand that finally we talk about physical property like density Ming temperature Pacific and other things then I told you that this s something we'll discuss later let's talk about a little bit more on these aspects before we go into electrical properties as you know if I plot let's say if I have a liquid ice water right let's say if I have water now water may not be let's take a metallic liquid let's a pure copper melted down and then you cooling it down if I plot relative volume volume per unit weight as you cool down this will vary like this first it will drop and then there's a slope change why this slope change because if you cool rapidly to bypass formation of crystals or grains then you will be able to freeze like a glassa structures there'll be small change in relative volume but suppose if you allow the liquid to solidify by formation of crystals and this will lead to formation of spe to generation of future heat of fusion then this volume will drastically drop to a lower value well let's understandable let's say density density is nothing but mass per volume right density is nothing but mass per volume so crystals has higher density compared to Glass because crystals are more packed structures we have discussed about it glasses are random so there are more open structures so therefore density of glass is lower than the density of crystals so mass is same so that mean volume should change right and for the crystals volume is smaller that's why they have a high density for amoral structure volume is higher there's more speed space that's why it is that so now question is if I freeze a liquid to Glass volume relative volume will not change much it will change a little bit because there will be reement of atoms or relaxation of atoms once is become solid so liquid to solid to P it freees a glass is demarcated by change of viscosity nothing else there are minute change of structures at the atomic scale there may be some small changes but overall atoms will remain random or semi- random structures so that's what happened that's why TG is known as a glass tensent temperature there a temperature below which a liquid is frozen into glass without formation of any crystals so now Glass is very important material right I talked about metallic glass these are the taken from or National Lab in us this scientists have discovered a new B metallic glass steel B for steel that is non magnetic room temperature and significantly harder than in the conventional steel this is available in this article you can see here this is what is mentioned you can go through this golf flops are made using ball metalic class I talked about it right for the gulf bats you need High resilience resilience means what Sigma y² by 2 e Sigma resilience is what resilience is something known as Sigma y sare by 2 e so resilience is Sigma y² by 2 e for the glass both Sigma is Sigma Y is very high and E also is very high very strip so if you have stess and curve like this very strip very high even if it breaks little bit doesn't matter so you have a very high a under the curve that's what is called Regence R so glasses have that that's why they are used as a golf club they have a little bit of dity also compared to the window glasses that's another reason they are used you know silicate glass as you know they have a based on the silica structure or basically this is structure of quad quad is what S2 and silica is basically you know it's like a tal structure you have a atom the center which is called silicon atom and four coin you remember the tetradon right tetradon is like this just now I shown you this is a tetradon and u this tetradon is basically has a four corners and there's a central atom okay these are the four coordinates and inside in the center Center of of the tetradon you have a silicon atoms that's what can be marked like this okay this is silicon atom this is oxygen atom this network actually forms all across the material and this is a threedimensional network that is the structure of the Silicon glasses and that's why silicon glasses actually for this crystaline ones this is a this network is very order for non-crystalline or glass is this is random that's a difference so you can either form silica which which forms you know different kind of Crystal structures autonomic ronal and glass is like a random arment of that silicon tetr well there are different kinds of glasses the one which is show this one you see this is called Bristol glaze which is used for the cups and then you have S lime glass which is what is used in the Windows window panes and they are actually contents of sodium sodium o oxide na2o Co S2 this is sodium gas and this is both silicate gas which used in the labs of experiments pipets Baker many things and you have also vitri silica so V silica is 100% silica that also can be glass but that is very very rarely used normally use a Bor silicate glass window glass we can also use fiber glass which are nothing but e glass there you have five inside so this you see the chemistry is very important remember we talked about glass at the beginning first lecture to impress you upon why machine learning is important look at the you know chemical component of glass it can be many si2 b23 l23 n2o co MGO k2o zno PBO many other things depending on the type of glass to given our perspectives we know tough and glasses many of these you know glasses on the car windows are toughen glasses they have little bit of k2o this K potassium ion which is bigger than sodium ions replace some the sodium ions and creates a surface compressive stress and that protects makes it tough so that it doesn't break please go back to discussion the toughness how the toughness is Define so tough glasses are very important even if you give a punch to the glass it will not break so that's about the glasses and our things let's talk about a little bit of electrical properties remember Glass is very important component that's what I thought I should spend some time well Electric properties means what you have to differentiate between conductors semiconductors insulators and if I take a single structure high tension cable this is high tension cable structure I can see all of them the this cable is Conductor it's conduct liity this is an insulator which is making this cable separated from from this structure structur structure from this you know this steel structure so that even if high voltage is to this cble this will not make this steel structure conduct City that's why this is this is basically ceramic this a peline ceramic usually used for this you must have seen this kind of things when you go on the roadside when you see this high tension cbles this a very widely observed so you see in the same structure you have insulator conductor both patients semiconductors we'll talk about a little later this s where sem are very widely used okay this is can taken from this we it silo.com and they are actually producing this kind of chips silicon chips and as you can see structure is so complex so you have silic semiconductor this kind of different kind of structures are built up I don't know to discuss about lot of these things you can see different kinds of things that you silica poly silicon okay teen tungen T aluminium even say you know aluminium copper silicon nitrate all are used this is what is you know say silicon is a semiconductor so it's all about electrons in solids and their ability to move around within the solid that's what it is in case of mechanical beh it's all about defects Point defects line defects or Surface defs here it is all about electrons so do we have electrons free floating around us do you think in air what do you think obviously not electrons are not freely forming in air if it was that then air could have been conducting electricity like anything it was have been very difficult to live in this world because you have electrical wires around it they could have simply make the air charged and that could affect our human life unfortunately hair is not conductor to electricity but that's probably one Fortune for us so electrical conduction is given by what Ohms law and it is classical ohms law it's taught in school physics now B is equal to I into r v is the voltage drop and that is nothing but J by C J is the current density and C is the Kum that's equal to current which is in amps nothing but K per second and R is a resistance R is basically a constant and this is called ohms the resistance is called home this is called This is called a Oh's law that was discovered by oh and you know then we can always convert the resistance into material property that's called resistivity so resistance is not material properties resistance can depends on many things like it depends on area depends on the length of the wire so if I talk about resistivity it can be like this row is equal to R into a by L so r a is the area and L is the current path flow path that the length of the quare we always talk about it and this row is independent of anything it's basically material property and we can use this to differentiate between conductor semiconductor and insulator so we can always Define conductivity conductivity is nothing but 1 by row so either you discuss this electrical conduction in terms of row or in terms of Sigma which is remember this Sigma is different this Sigma is not same as the stress this is the electrical conductivity well to give perspectives let's talk about values of in a conductivity for Metals metals are highly conductive toity so they have a high value of conductivity you need ohm M universe so you can see copper 6.0 multip by 10 7 massive electrical conductivity compared to silver copper silver is hardly one 6.8 nothing much right so why you use silver copper is cheaper widely available and it has almost close to same iron house has quite a bit less electrical conductivity so that's why iron is not used Steels are not used as as a cable steel could have been used though it was much cheaper but copper is used because copper has much higher conductivity if you consider semiconductors silicon I told you right germanium also semiconductor because they comes in the same column of period table silicon has a conductivity of 4us 4 you can see almost 11 or of magnitude less gerum has better but 2 zero Calum aside which is a Compound Semiconductor it has much slower 10us 6 M so that's what it is these are all taken from cis's book selected values are taken from book of kalister and R Swit if you can refer that what about Ceramics well just now we talked about s lime glass Ceramics has a conductivity of 10us 10 10- 11 concretes 10 - 9 aluminum oxide 10-3 what about polymers polyer which is we are using as a material for our shs 10 minus 14 polyethylene which is used as a power pack or pouch in everyday life 10- 15 - 70 they're all insulators they don't contract electricity so you know now the values you know that how to differentiate them well let us stop here the part one of the lecture and we'll talk more about this in the next part thank you [Music] [Music] [Music]