Mechanical properties of steel 17: solid solution strengthening

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Mechanical properties of steel 17: solid solution strengthening
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The 17th in a series of lectures given by Professor Bruno de Cooman of the Graduate Institute of Ferrous Technology, POSTECH, South Korea. Continues with the story of solid solution strengthening of iron an steel.
Keywords The Graduate Institute of Ferrous Technology (GIFT)
Steel Cartridge (firearms) Ship class Air compressor Screw Slip (ceramics) Forging Gas turbine Remotely operated underwater vehicle Stock (firearms)
Steel Air compressor Clothing sizes Überschallstaustrahltriebwerk Ammunition Sizing Matrix (printing) Avro Canada CF-105 Arrow Thrust reversal Screw Spare part Forging Kümpeln Kümpeln Bookbinding
Allradantrieb Hot working Barrel Cluster munition Roots-type supercharger Gentleman Spare part International Space Station Model building Van Ship breaking Tin can European Train Control System Steel Bending (metalworking) Monorail Clothing sizes Brush Roots-type supercharger Turning Angle of attack Sizing Gentleman Cartridge (firearms) Photographic processing Plane (tool) Remotely operated underwater vehicle Book design Workshop Model building Kümpeln Friction
Widerstandsschweißen Typesetting Hot working Tin can Suitcase Wood drying Roots-type supercharger Ship class Alcohol proof Commodore MAX Machine Forging Ship of the line Engine Firearm Material International Space Station Typesetting Truck Steel Outsourcing Cartridge (firearms) Matrix (printing) Moving walkway Scooter (motorcycle) Single-cylinder engine Model building
Typesetting Ford Focus Hot working Mechanic Bomb Key (engineering) Ford Transit Linen Sizing Continuous track Wolframdraht Spare part Plane (tool) Single-cylinder engine Ship of the line Firearm Material International Space Station
Tin can Steel Reamer Pit prop Gemstone Railroad car Engine-generator Überschallstaustrahltriebwerk Mechanical watch Gentleman Remotely operated underwater vehicle Firearm Material Gun
Steel Pit prop Mechanical watch Mechanic Firearm
so we were wrong the discussing solid solutions hardening and we would have been considering a theory where where we look at the edge dislocations and an atom at certain distance from that edge dislocations and that atom has the purely delectation all of the effect on the latter's means it's it's either compressed by the surrounding letters or its under tension isotropic please under tension and so we went through the Syrian and and we calculated what would happen for instance for of atoms like manganese ore or silicon and variety and so I told you that the way you you were calculated the the interaction forests is but 1st of determining due to the interaction energy and then up there is a function of position and and doing a derivative of tests the interactions so that you would 1 you're able to and from the derivative then determine what is the maximum interaction force because the fact that a dislocation has an aura .period defect substitution Aladdin has honored the stock it will of course depend on the relative position so but and there so this is what is this energy but comes out to be of course its function of X and Y In the In this the the position of the US atom and then you make the derivative of this interaction energies interaction energy looks like those in this case it's an attractive interactions between the the atom and the L a dislocation food for the particular position we've chosen and and what would I plot here is that the forests on the on the on the solid concern and this would force on dislocations is to reverse course like this it used to balance the budget so at a news see this as the the force the position curve and then and and this allows us to determine what would be the maximum forces In this case it symmetrical so it's it's this value here if I had put them in this particular case about it not shown but the we have an interest in the area and an attractive interactions with the potential well women potential well here against them because of the relative position of wine the why position of the the item if if I had put it on the other side of the slip playing the interaction be repulsive yes because as you know in an atom if it has a if it's misspending and it's larger than an iron actor yes it will be under compression and it will be preferred who prefer to be in the Lotus disliked play so whether or not it's attractive or repulsive depends on the on the position of the atom with respect to the discipline Texas and and and we could on the rise the deceased maximum value here and we found 1 . 6 cent at Miami 11 where already introduced kind of forces yesterday and I also told you that and then you could do with this theoretical way already could just use 8 a simplification of the theory was where you if you if you were if you know the Delta value you just use G B squared times Delta divided by class and then and just to show you that that it's it's very close to what what you get with the the more correct equation you find the same value directions but still In this particular case we have assumed that we have this edge dislocation and be when atoms which gives you an isotropic lattice still attention or lettuce contraction and the very often in introductory material science courses it is said that there they will because Of these Charest field around and edged at rather screw dislocations there will not be interaction between that kind of actor which has a purely tational field and its crew dislocation and our hand-waving argument would be well there is no debilitation or compression around an edge as screw dislocations and done so that's not true right the interaction of solutes with substitution will and interstitial atoms is about to sign the strength of the interaction that's not the case for for far-right definitely not the case screw dislocation and Greece interact strongly with solutes both as a strong with solid 1st of all Weld 1
of the things we all assume in in our theories assist by such repeat the of iron and is not isotropic so that definitely is an important correction the risk is that you a small village Haitian associated with screw dislocations and in Austin at in Austinite of course but we have a relatively low stacking fault energy so the even the screw dislocation will be dissociated Inc 2 partials and he's always have an edge component that so I deserve some general arguments that you that you can be righted theoretically also OK right so let's now we turn our attention to the I'm the another aspect of the interaction between the 2 of them the solitude and dislocation and we can think of the solutes as regions small spheres where modulus is different as much of this is different so you have different elastic properties and so on so if you should consider a volume be due but that the volume of the size of burgers factor is to 3 directions with which certain shear modulus it's around solid after so if I put in a piece of screw dislocations in that region but you know I can calculate the energy because I know what the energies of dislocation and we saw these formulas in the past so this would a would apply this formal at times by you here and this would give me vests found were kept I and so I can compare this to be energy From that the dislocation has and the normal actors and so I get but difference in energy and energy change which can be an increase in energy a decrease in energy depending on the relative differences so so I did it change in In energy of 2 dislocation which which is simply this equation here and delta G where input altitude altitude being the difference between modulus of the solutes around solitude and indeed in the lattice right so named the derived is for screw dislocation of 4 edge dislocation and so on if this delta G here is negative I get a locally reduced energy but the dislocation and basically the but the dislocation is bound to be a solutes because of this reason reason that this is lower energy piece yet so a soft after for instance are like a vacancy or soft patina will will therefore have an attractive interaction with the with the dislocation and it's the reverse if we have a very rigid at over a hard act to us but the interaction will be mostly repulsive so a way to an To get an idea of the change in that the anatomy has on Monday this week and we can determine the parameter epsilon gene which which gives quantitative measure for the change of the relative change of the modulus which concentration so we basically do is you make different alloys has with increasing amount of the solitude and you measure the elastic properties you measure the shear modulus OK so but this is what you get basically but if if I have to you mentioned have this location here and have some solutes happened there yes and if this solid album has a lower the modulus then the Gladys then I will have more attractive interaction and if it has if it's a harder there will be a repulsive interaction has going and so on using the these but 2 parameters we can basically as long as we have Epsilon and Delta we can basically you have an ideal determine how much the the strength of the the interaction will be the retaining forced maximum return force on the items will be so let's go this so what the way you you can't have to think about the the atoms is not really like atoms you like little regions of and the dislocation will have an impact on this afternoon it will begin change influence that the it's it's it's volume for instance the edge dislocations in the and compression particle the solid will be compressed or it will be expanded this end and so the size will be changed by the hydrostatic part of the stresses and the shape will be changed by the sheer part of the distress that so but then so this is an
example for instance for of carry calculations you can make for chromium and for phosphorus for manganese and silicon where we know the Epsilon and d I Delta should be this should be dealt with the developments books consists of small that metal and and you can see you know what kind of interaction is more dominant 4 and and and you can determine also how large is the the interaction on the basis of this steps along and and Delta values before and so on To see here for chromium you see I have I would do it looks like compulsive interactions and I have the so the size misfits positive the modulus miss this positive right so far it's a repulsive interaction between dislocation and the at the end of the stew besides misfit is is dominant and if we look at different elements of what we find is that most of the time the size misfit this appears to be most important if you if you use this approach accepted for phosphorus we have apparently very strongly consider a high values here a very strong modulus Miss apparently but it's so so far and we have said so but if we know we can calculate interaction energy we can also calculated that the force that 1 single item will have on the piece of dislocation units up but that doesn't mean that's not enough for us to calculate it to radically the 1 then due to the solid solution strengthened as another element that we need a new remember the as the basic formula of theory is that the critical shear stress 2 of them to get to the dislocation to pass an obstacle is not only dependent on the maximum force in which we just looked at but also 1 over Al yes but the reciprocal of the spacing between the the solutes and that as a lexical this quite a a challenge to determine but because of the well 1st of all we would need to know what distributions of our atoms necessarily I end up and and and and the for instance in this simple case here I could have dislocations moved this way and and I can determine what Alice very simple from geometry here L would be 1 golfer and square where n is the plane a density of my items here that would be simple but even then stated dislocation moves this way knows or at a slightly different angle the the distance Is would be different if so obviously determining L this is not a simple or a simple task and obviously is that this is got some statistics it into it and so on and that's what you know along with a big part of the of solid solution strengthening theories are about is trying to determine what is the average spacing between obstacles in a in a particular solid solution that Alamo Kent and so on and a different models of obviously not of people say different things so 1 of 2 the models that which of Fleischer Fidel mobile and assumes risible that you have it the interaction which the localized yes and then it also assumes that when the dislocations moved through the lattice yes you have a special steady-state situation I mean that means that when a dislocation is released by an obstacle yes it goes into a situation where that looks that's very similar to the situation it used to be here so if it's released from 1 obstacle it gets out bye 1 obstacle so this is shown here with the means to do it in simple terms like this is this location and have a shear stress working on it at 1 time it gets released by this obstacle yes the next step is it's called by 1 obstacle again and we get a steady situation I I should be shown here as it is written here on the side of the mean distance is assumed is computed by summing up during the we have a steady-state situation every time a dislocation breaks away by a solid from solutes it's captured by another yes and this allows us 2 they say that the when the dislocation sweeps when it does this step when it to the surface it's sweeps yes this 1 solitude in that service yes and that all said stated that surfaces of El effective square yes you can calculate this but assuming some geometry and I in the ways we can get the but from the surface that you calculate you can and square root of that surface for each actor so that gives you a planar density also solutes and in so you can get L determined all that away the but when you do this yes you find I'm not going to go through the theory here because most of it just man you find that the the strengthening effect proportional to the square root of the atomic the concentration of the sort but then the other theories out there you he said and at the other extreme yes the dislocation does not interact locally with the solutes they entrapment more diffuse the shape of the dislocation is due to the internal stresses or field around the solid so we have solutes the former random array Of .period White defective really attractive or repulsive now and then you get some kind of but no two-dimensional the patter of attraction and repulsion and dislocation kind of finds its way In addition to it into an equilibrium position such bend into curved shape by these elect it so there is no shop place where you can see where there is a localized interaction between location and appointees so this is a prescient continuous contact with this interaction field known as it is is different modules I and be a different model strengthening solid solutions strengthening that comes out of this theory has a different dependency all these solutes concentration 2 thirds rather than 1 that but this series it is also available for where you pursue the clustering of the atoms rather than them being disbursed this and that what do we have to say about these theories from Kent but let me just you can't In this particular model which is Multan a barrel Busch
Series which is heavy on the statistics yes the the formula the equation for the maximum interaction energy is also different and the reason why this is this has to do With the fact that we don't have a localized interaction with the diffuse interaction having said this the f max still depends on this Gration shown here are still depends on the modulus yes and on the but the fact of the solid on the modulus and the effect of the solitude of the uh a lattice parameter so once we know this has again the many parameters in this theory gives us but we can calculate this we know these parameters the solid solution strengthening on the basis of the series points this case this particular look in the barrel of the Bush so we can calculate a solid solutions strengthening From a soluble by multiplying the share the fact you have on the increase in the share stressed to move the dislocations in the presence of solutes times and the Taylor factor and the factors b Verve strategy shear modulus W. This is the and because the interaction is diffuse W tells me how far the the influence Of the solutes reaches its a few times a Burgers factor but this is a numerical parameters and and then you see here the modulus change and the delta of the but the fact of the solutes on the lattice brush and then you have the numerical parameter here Alpha which which is available from the air and sea are concentration to that too the having said that it's just that there are theories where the interactions that are derived from a localized interact strongly of the very localized entrenched to very diffuse interaction solid solution strengthening remains 1 of the things that is difficult to tackle theoretically yes and there are more than 1 theory and there are more than 1 theory there's more than 1 Martin borrow Teri respect the series won't go into this but at the end of the day would you find our theories which said the strengthening is proportional to the concentration atomic concentration of the solid to one-half other theories to two-thirds of the theories proportional succeed the concentration that's the 1 I remembered sweet you lost empirically but there are theories that they give a proportionality would the C the 4th third-seeded 5 even in and of course you will say on of walls are simple we can check this series bye just checking this out you know just measuring Webster was this the strengthening caused by solely as a function of the concentration of trouble areas it's a very simple idea but it doesn't work in practice because we and the amount of alloy but we can do is always very small yes for instance if you say for instance silica afford to name a few small example as yet selected you cannot add to Silicon indefinitely very quickly you run into a problem that you will have ordered structure and ordered structure which has properties with a very different from the start the simple random solid solution that's and that's not that difficulty has blessed the experimental difficulties of related to getting very pure binary alloys and has meant that To this day you know there are many cases situation where we don't know what the theory is better than the other but anyway of In the all just give you my case theory that I prefer to use is allowed Bush during which so it's diffuse interaction and prejudices and it is the situation for France's nitrogen in also thick steel so the theory that you use as a increase of me the strength Due to solid solution hardening by nitrogen but the numerator constant which is all the time numerical promise like the modulus etc at times the square root of the concentration of legend hides the this parameter that contains the effect on the modulus an effect on the lattice parameter of the song jokes what you have to do to tune approaches experimental you have to look at you will have his own in the lattice parameter change with the nitrogen ,comma how does the modulus change with the nitrogen content that so you see here I do have a value for Delta but the modulus changes very small yes so but you can put it equal to 0 and that's why I am in the equation on the underwriters Delta to distant and in and here we have the measurements the increase of the yield strength as a function of this parameter and where we have determined K to be 1 . 7 times G square root of after due to serves as and you find what you should find this will alive straight talk from that kind of thing it tells us but something about the way nitrogen the strengthens all Semitic steals it's on I have a random the the nitrogen randomly position and that it has mainly in effect by delectation of the the LAT is and other and the dislocations and it's a diffuse interaction that is the conclusion another example here the recently .period is the same
approach because this discusses the substitution of Parliament aluminum in Austin at the gallery strengthening again numerical parameter modulus in this case square root of the concentration atomic of the aluminum times this past and which to the two-thirds which contains the parameters giving me the modulus change and the lattice parameter change which is shown here in this case so again lattice parameter expands as I put in my alumina the shear modulus in this case decreases as I add aluminum cans and again I can plot the increase of the strength as a function of the square root of the atomic Moeller dense concentrations of aluminum times the S 0 parameter to the there's at the straight line that I and II may obtain a straight line for the parameter of being about 4 . 4 7 4 against tells me that I'm looking at it dislocations or influenced by an internal stress field around the the dislocations and could not with the interstitials it's a bit different was that different because as I said that their Gladys the formation around interstitial Maine variety is as strong tribunal distortion and in Austinite I can do I can also have a the 2 tribal distortions in the interstitial is associated with a substitution or after and in both of these cases yes In both these cases these the calculation of the interaction energy and the calculation of the force that the this location has what that the point defect the interstitial carbon or nitrogen have on the dislocation becomes very complex because in this case I need to take into account crystallography and the Orient the relative orientation of the the tribunal defect which respected the dislocation the previous that when we did the calculation of the interaction which is an edge dislocation and it didn't really matter we didn't really have to take into account persuasively too much because the atom is just resistance in all of this the spherical region that would expand the isotropic or be contracted as drop of this case doesn't work that way so for instance you you have to have a screw dislocations were and this is school dislocation with the important parameters stress parameters that we have to consider then you have to look at you are lattice distortion era your carbon atom yes and if your scooters location member in Alto Parana dislocation on 1 1 1 direction and so on Europe you need to calculate what will be the interaction energy between your the carbon atom distorted Lacoste lattice distortion here for all the possible positions this so you basically look at your unit-cell you put in your carbon atoms and then you let your unit-cell rotating around this do the axis of his school dislocation OK so it involves limit of matrix calculation I will just where you and the people who were interested I will put it in the course material on Tony class but I'm not going to discuss it just for you know if you're interested you can go through with it this this involves no matrix calculations so put their money into the economy class you can have a look at it and and and that the source of an idea of how these things are being done right and it turns out that you know if you good from this analysis that the maximum interaction energy is 1 the the India carbon atoms has this position with respect to the screw dislocations and this but the opposition is the position where the fight is equal to 0 1 of the things again that actually happened at GFT His death a lot of people will say there no carbon atoms this will not interact with screw dislocations in Alpha units and that's on the basis of you have a screw dislocation and you have a point defect which has purely tational field yes there will be no interaction if if you assume that it's it's isotropic the situation but aides screw dislocations on edge this or whatever the Soviet have always has a very strong interaction with the tribunal the defects a very strong interaction and so if we calculates the we go to the calculations which were filled with some of the plants as I said you have the interaction energy as a function of the position of the atom and and then if you do too derivative of this you can you can get the interaction of force that's a function of position such in and open them and don't forget this can happen in bcc any necessary but in the case of SEC it's important it's you always need 2 atoms in Europe In your defect you always need carbon atom plus a substitution to created tribunal distortion now this is there was a way way we discussing this anyway I told you that already many times that the solubility of carbon in Alpha iron was here at room temperature and so it doesn't really matter that it has a very strong effect on a very strong lattice
distorting effect but because no Al-Faran firing you can't this all that anyway and if you try to do it instead of having a lot of carbon in solution you get copyrights yes senator however In this important in many engineering steels we we have Martin side we we use Martin site and so we have in that case we can basically forced the carbon to be in solution we we make a supersaturated solution of carbon emissions Sara that's when we do get a very strong To tribunal lattice distortion and we also get a very pronounced strengthening Due to the carbon in solution this is a plot here's an idea it also it illustrates 2 things the 1st of all that as you increase the carbon content the strength will increase and the list despite the strength increase is very very large defect is a very large and the other thing that's interesting it also illustrates the fact that I it's actually difficult to decide even on the basis of good data what there's the precise interaction between the dislocation in the carbon because you can see here for the good equations which will allow you to predict reliably predict the strength of Martin side if you know how much carbon is in solid solution and you see I have 2 to equation where the strength is proportional to the carbon concentration 1 equation words proportional to the square root of the carbon and 1 equation was proportionate to the carbon to the one-third right and if you plot them on top of each other while the you know it's like here for the linear and for the square root dependents you can't see a big difference right and that's that's no 1 1 of the difficulty they we have with solid solution strengthening its the data on using the data to to fit the model is that the office of the lottery not satisfied 1 of the important things also that this time plot illustrates and I want to underline this this is a very often you will hear people sigh In relation to steals that Martin side is very hard and brittle that Martin site is now is not hard and it's the carbon in Super saturation that makes sense Britain and how hard it is no carbon in Super saturation Martin site is pretty soft so you always have to make the distinction between Martin side which is a Microsoft truck truck resulting from a Martin said transformation which can happen With or without carbon yes but if it happens in the presence of carbon and you get carbon supersaturated then you get a more brittle material that's very hard yes you can make there are steals will will get talk about those later wrong where you're the carbon content just to you very very low 100 ppm and this is a problem Mora aging steel has and a very soft you while you make the aging still very soft you can buy cold worked on can work all work Martin side during easily against and you make them strong by precipitating making precipitates precipitation hardening the the Michael strapped for cash you know ,comma In solution no a few more points here 1 of strengthening before we close this chapter so smoke or drink basically as I already told you is when temperature the situation room temperature Beijing a situation where carbon that is in the vicinity of dislocations hand at basically hopped into 1 of these energetically favorable positions and and pain as at work the dislocations this way so it's instantaneous process it's stress induced because the stress of the the distance surrounding the dislocation allowance facilitates the champion of the carbon you don't need much carbon insult solution very low levels ppm levels of carbon free carbon will already calls this effect and in remembrance of the fact that you see at low amounts of defamation so when the dislocation and seasonal and so get formation of Gloucester's by diffusion by short-range diffusion so this is not just a 2nd remark this isn't this is nothing to do with Cottrell atmosphere formation right travel atmosphere formation is a long-term process units that requires at temperatures in excess of 100 degrees so there is no longer range diffuse and it only requires 1 diffusional so I'm so basically over the I I told you so if you take a material carbon steel and you performance is no upper yield point here is to stop the defamation you repeated after a few seconds as defined suddenly there's a deal .period and I'm so you can look at the kind that takes over this of processed so here you have a change in the the amount this Delta this increase in the yield strength there and you can see from the the makes change in slope of this increase determined the kind that takes of this this listen quartering process that takes about 10 seconds here to have a very pronounced effect the pronounced yield and then you can relate this with all of the disconnect went the diffusion time kinetics the time it takes for instance in this case it's for nitrogen to do with single diffusional hot and you can compared the kinetics but with the time it takes for To achieve the maximum Snook aging
has and and you get the same kind so that basically it's important to smoke or drink is just 1 single chairman of the uh back to general carbon atoms in the vicinity of the dislocation can you count on this type of ordering yes 2 hours to really strengthen steals for it it is not really if you are if if you look at the amount of nitrogen In decision that the increase in the yield strength you get from that effect is about 10 major task so it's not really much not really much at all so it can be beneficial in some time but it's not you know it's not never going to give you a major the increase in instructor we look at later on in the course will we will we will look at the effect of what happens when you hate to material up a little bit and you and you get a long-range diffusion where you have lots of carbon atoms moving towards dislocation you get what's called you probably familiar with the work could travel atmosphere is yes then you can achieve 30 to 50 might make a Pascal increase instructor that's more appreciable but to Snook ordering itself is only about 10 make pass focus and finally I I want to mention 1 thing since and which is very important and that's it we've been talking up to now about solid solutions strength yes however yes solid solutions strength this is very often associated also with solid solution softened so let me put it this way when when we look at pure iron as a function of temperature yes you know that we have strength contributions to the strength which are 80 thermal not the function of the the temperature flat this a strength here and 18 a temperature dependent part yes as part of the a thermal the contributions we have for instance the lattice track and and and the other part is while the other parts like grain boundaries as good and if we look at sea after securing there is a contribution due to solid solution strength from and so but when I add 8 more solutes like silica as the basically means that and the every time I add more selected by increased the solid solution strengthening them but what happens is not theirs the solid solution strengthening effect does not hold at lower temperatures at lower temperatures we get a softened this shown here for this is that the the fact there is a schematic which shows what the solid solutions offering so the black line gives me the the thermal the this part of the the strength of our fire yes the Red Line shows me what happens when that had been alloy and element so indeed flat part I get an increase solid solution heartening indeed temperature dependent part I get decreases so I could soften for instance cited it you can do look at the experimental data has shown here so what is this is a little bit too complex diagrams graphs here Mitchell if you give me some 20 20 years it will be clear with me so I'm here I only on the Y axis equity atomic bomb ratio means that the ratio the difference between the the size of the solitude with respect to the size of Byron enacted divided by the size of the Irish actor so irony well I realize what I write is no what we want so the system is in the ratio of the atom divided but the ratio of the size of the atom divided by the size of the Army surprise them and 4 other allying elements such as manganese can be slightly lower or Lallemand suggests tungsten I know you will be entitled New Item higher incidences these items will have a large positive Delta value has and these items will have but a negative Delta felt according to this view and of course we know that the strengthening is a function of the atomic mister so if I look at the the increase of the Vickers hardness With the concentration I find not surprisingly that the larger the misspent is the higher the increase in Stratford whether it's smaller at slightly smaller at or slightly larger at him but if I do the same test yes at lower temperatures a matter the liquid nitrogen temperature I don't find this I find that the alloy the allies results In this softening I get negative values for the this is a negative more negative values to outlying softens the material so here you have some data for instance for manganese OK so let me use of tens perhaps you so this year
discourages the 0 per cent manganese right when I had manganese and I'm looking at room temperature route around 300 Calvin I saying I and manganese it gets stronger more manganese against even stronger and that a lot of manganese it's very strong but you see here at these 2 levels here 1 about 2 per cent as I go to lower temperatures the strength has decreased same here with Nicole this is our original data for all of our sins as increased Nicole at room temperature I get hardening but the little room temperature I get softening the something is happening here that but we don't really like and which which we need to explain it all because how can it be that you haven't actor and in at 1 temperature it does 1 thing and the other temperatures the other thing so there's something wrong with the theory right no there's nothing wrong with that theory the reason why we see the softening in Alpha this is related to the structure of the cost structure of the screw dislocations you remember that the reason why we have a very strong increase In indeed the thermal part of the it's the strength of our is related to the fact that the cost structure of the dislocation is spread out over different planes yes and that is what happening 1 would what's happening when you put in solutes the solutes well haven't effect on this grand Of the at the core of the dislocations screw dislocations and well what is kind at the conclusion when it becomes it basically means that it reduces the spread the court Of the I screw dislocations so in fact it's not really a bad thing that is very good thing because this is a very high increase in the 4th dress yes but for is actually the problem because it makes it very difficult for this August the move ii 2 the 4 yes the formation in of of very difficult as I reduce the temperature by allying it I'd make it easier again this and that's where these allowing element in this alloy softening it becomes important as a matter of fact then 1 of the ways in which people design the steals where it's very critical 2 make sure that the the so-called ductile too brittle transition temperature is very low this is a adding a nickel and nickel we get this is enough of this softening effect at low temperatures that that the ducked out brittle temperature it decreased so what happens How can we explain but without going into too much series L what is happening here how can we have at low temperature in easier the glide knows that high temperature and more difficult to light up the obstacles .period effects were politicians here have you remember that at lower temperatures so in this region here where we have is strong pronounced the thermal component to the flu stressed we have the double king the king pair the mechanism of screw dislocation motion yes and there too important energies here because as I said 1st of all you need to know create the kinks In the double came quickly Asian energy and then you need to have the Kinks moved along these there potential sale laterally 2 Have the dislocations with distribution moved so what dough went to these solutes do well they facilitate the formation of double kings bye reducing the double kink nuclear nation energies it's about . 6 so you add solitude that decreases so it's easier to make and the reason why is it easier was simply because the but the spread of the HIV court Of the screw dislocation is reduced debt as president would do and then on the other hand they he increased the kink migration energy so the energy that's required for the Kings to move laterally yes so and it in and that's that's the reason why at low temperature you get a pronounced softening because the booking energy goes down and at higher temperature you get remember at higher temperature dislocations Will across many apparel spelling the piles of hills has so and then if they encounter they the nickel atoms of manganese out of these will work as obstacles yes that is the key to the solid solution Suffolk and again I want to stress the fact that this is
not necessarily it was
adapting so I have 1 2
more minutes and I just want to
introduce what will be
talking about on Monday
so that last lectures we've been we've been talking about How dislocations the motion is influenced by the solutes as they move in and in the Indigo lightly and then we saw the 2 important parameters there that this the strength of the interaction between the point defect the solutes and dislocation and the ending the distance the average distance between the the assault and although I said you know you have theories and you could calculate that there's I'm in general the results that you get from doing that it desire when it comes to calculate solid solution on not much better than if you had used an empirical approach yes so unless you're doing really advanced research in solid solution hardening you know you're welcome to use the empirical approach you will get a pretty good data are although they you know you may not have a strong theoretical basis for your results alternatively of course if you doing a PhD on solid solution strengthening it's better to have to have a look at the feelings that so we have dislocations as as we strain materials we use generate dislocations and by Frank resources and is dislocations will run into each other that will give you hardening from a point of view of strengthening yes it's not a really interesting way to strengthen the material because if you do that uh you know increasing the dislocation density and using that as a way to strengthen the tip of course use plasticity so it's not that we don't use that you know if if a car maker once a high strength material Posco doesn't deform the material and then deliver it right that's and so that's not a strengthening however we look into it because it will allow us To calculate stress-strain curves yes and you will see that in the coming elections how we can do this and so it's kind of useful after all OK so we'll talk about this summer


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