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Mechanical properties of steel 12: dislocations and other defects

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the slip planes but they're basically intersecting every time 1 1 1 direction to look down the differences if I were to look down
this axis yes I would I would basically see 6 the
6 1 1 over claims that this would be 1 1 1 direction and these would be free 1 1 play this and in between these 1 0 planes but also 1 1 2 planes that serve principal at this location that's oriented along this axis and can just moved into any but 1 of these flexible many options to buy and it doesn't very easily because it's not that his dislocations of the social so that's and that's part of the slides here and it's a
very slow today must be Friday afternoon systems personal the "quotation mark that's disappointed what I
was telling you this is crossly and dislocations "quotation mark locations in city all 4 tires easily to address the concern of century In the case of SEC it can equally be easy but the material has to have a high-sticking fold energy not to be devoted to its location should be dissociated and interviews with members of what was a high stacking fault eligible Lewis of about 100 million chose square meters now that up to now we've we've we've discussed and dislocations that dissociate dislocations that exert a forces on each other and what happens if I if dislocation crash into each other on the run run into each other and so what happens out what it in specific cases we get junk To dislocations will for a 3rd dislocation and that whether or not this happens depends on the the B Square criteria cut took 1 of the and the the injunctions that it is the and then when I I went to the dislocations we act together usually it's only a piece of their their whole length that we act together there's that word in meat and as I say former 3rd dislocation and it may be that this 3rd dislocation of does not move as recently as the 2 other segments for reasons of may be related to the structure or for intrinsic reasons because France's tuber perspective of the dislocation is multiplied is this is this and make it the glide dislocations OK and so that means that junctions will act as main points more or less strong opening and that and it's a very important aspect of strain hardening that's what happens when locations meet each other so to 1 of the I'm a dislocation junction but is there or the product of dislocation reaction to the report restrain ending as it stepped up and I and some of these dislocation jobs can be Cecile in the this dislocation people they dig you will save a dislocation is glitz filed that music and movie or its Cecile if it says houses like it's dislocation that just doesn't look like it's very strongly yes and his how much truth stress you apply it just cannot move but and so by end because these junctions can be Cecile it will take a lot of force 2 get the rest of the dislocations to move when they will act also as barriers to other dislocation so that all increases the flow stressed strain hardening in other words to want 1 of these common junction in bcc irony is the 8 upon too 1 0 0 0 dislocation junction and its former simply by having to co-plaintiff screw dislocations react in the reaction in here all illustrated in a moment so a upon to and 1 1 bar 1 plus the upon too 1 bar 1 1 if you some these 2 factors you did should get so the upon too 2 0 0 4 8 1 0 gives this is of a different burden because he's very different Burgers vector than this 1 right so 1st of all question is do you correct the thousands of these reactions if you want right of whether noted not they will happen you check this by be doing to be square criteria because rejected the square so the square of the 1st of dislocation BPS 2nd this focus was saying some that then you find 1 . 5 times a square and that's obviously larger than worth took so yes the reaction is energetically favorable so it will it will happen and about and when it does happen in practice and so if you're having a ready of screw dislocations flipped from as critics of the cities of dislocations lines yes on 8 4 1 1 plane here once 1 of these screw sets of dislocations has critics Oakridge has this Burgers vector upon 2 1 1 minus 1 and the other set is the upon 2 1 bar 1 1 and where they meet yes they conform 8 1 it is a wonderful this location and and you see this is actually happens in practice by it is location scooters locations in our BCC Ireland actually steal them and in certain areas these dislocations will form this kind of honeycomb pattern the nest of where these these little segments here are of the state 1 for tensions because so and you can hear this this works again you can you can use this term very as simply let's see right I'm going to put this like this now and the reason why I just want you to look if you look this way this at the start a cathedral each it's square right it because it does look hexagonal life and that's because we're looking down the wonderful old direction OK so went with dislike this appear in and so if that the incidents of this kind the direction disguises x-direction was wider as of this plane here is 1 1 1 older people can and that is I told you that all these ventures here are Barbara respect for this flight of it so would would we basically have here so let's I have to make a drawing to the mutual interest to interview and so on so say we have a screw dislocations like this right more than that have a burger vector asbestos and you have put screw dislocations like this which have a Burgers factor like this so now I'm
going back here this factor here In this vector here let's make the sum of these 2 factors to the sum of these 2 vectors this this is the same 1 here right so this pleasant this as he is but that's not the right time and not the right is not the right reaction it's 1 of the that involved cities but anyway it's very good that it happened so if I that's the incorrect assaults of this Burgers vector of these guys are like this that and the Burgers vector of this these guys it is in this direction than I have this Burgers vectors and disappearance of the sum of these 2 sisters 1 here right and think it's a it's been it's parallel to this this is the direction we want to do and that and incident and this isn't a new 1 of 2 0 0 0 1 type of proposed that you had seen it originally I'm no it wasn't intended at this point in his erection when I tried to react and if I get this factor so that that wouldn't happen because to be square would not be a small but it's a possibility as I said you know you can do any type of reactions you want so I took scissors will only happen you know for these 2 specific factors and they have to be in the school orientation so it is yes but that's that's basically what I want to do that's 1 type of the junction and which is common in the BCC L In FCC it's a lot more difficult to make a quick drawing for 4 reasons related to the fact that are dislocation of dissociate so I've tried to do this here for what is known as a lower Cottrell junction amusingly short Elsie junction now and would basically with which you basically looking at Is there the reaction of the problem in the street this with my name take this is basically like this so you've got this gliders White playing Issac the glide plane as this 1 here discipline here and on my text from the true that he drawn in news Mike attributed to have another 2 1 1 1 place and that's that's this guy here this week consider intersect here and they have so he added they have a common life right so what we would we basically describing is I have a dislocation here knows this means that interacts as with any at this location on the on this plane here 10 it in the way that is shown here and in the way it's in the drawing the intersect here there's this dislocation meets this but scientists in this particular case what happens of course is so this is the stacking fault and this is the 2nd Court of Justice location this this location here will 1 day intersect this is week meets disco and in certain cases not nor the many possibilities against but in certain cases this location will be 4 here at this intersection which has data the bird expected is Delta also the delta of and that is a the delta of Delta alpha is so you can see this this a Burgos factor is this is dislocation which does not belong to With which does not lie Excuse me in the ABC plane and it doesn't lie all the at the scene the plane either so when you have a dislocation with the Burgos factor yes that's not part of the glide plane than the dislocation cannot move right because of it it the this OK system has to move inside it's like playing Soderberg a spectrum must be parallel at least parallel to the blight like this but when the diverse circus perpendicular to the glide plane or at an uncle and it is stuck right because it's become go-anywhere it's not it's not on its glide flight there and you have very Cecile junction now I need to check something here because if they don't write to that so if you have your notes that somebody Prentice print this thing from the class if you didn't you should check this reaction here because it means it should be dealt a B plus the Delta right now it's it's the something else I don't know why but and that's what we call on Alomar Cottrell lock and what is interesting at this lower Cottrell lock is that this is that this is this entire pieces called the lower court ruling is that it consists of 3 pure edge dislocations that means the burger Specter is perpendicular to the line direction can very strong junction and yes all of the
dislocations can interact they do so in bcc iron gamma irony in a different way at In BCC we get these 8 1 0 0 Burgers vector in the SEC all Semitic skills would get lower cultural In this city there are also interesting things that and an FCC so if that happened and that's that the dessert things called charts so they usually we think of dislocations that is being in the glide play but they can parts of it can move to a different Golightly and we've already seen that that can have France's when you get crossing when you get across so if we go back here if I have the dislocation here years this which which crossed slips To displaying here now I create and the dislocation to screw dislocation then goes on to go back to a parallel plain like this because it's on this the plane across slips on this 1 and then across its back on the parallel plain since then these pieces of dislocations here these pieces we called jocks yes this is a burger Specter being this is the line direction your original line directions this is of course the line dislocation line on this what is important is that if you look at these jobs the dislocation whatever it does it always keeps its burgers factor because it's always the same here it's a screw dislocations here it's critics of it but at the job it's an edge dislocation Brian it's an education yes and DEC and and jobs and as agreed so these are very tiny sect and ended the day down there not more than a few 2 lattice planes Hi these jobs so you can't really see them out in the unity of which you can see the direct consequences of their presents do for instance you get these things and this is obviously something happens to this dislocation which makes it go here and then go back and so forth what what is it is just a point where the dislocation is stuck yes and it continues to move any trails behind it To dislocations itself going 2 wars stepping .period away from it so and we call this a dipole dipole so died polls when using dipole in you Mike rastructure and you'd be quite a few here and the 1 here you hear us you know that here there is a jog on the dislocation small bits edge dislocations Of that keeps it that means the dislocation another area effect of the presence of jobs are these little loops you see here this is structure and "quotation mark salutes all lots of little This is a very nice 1 here you can see I think and we call this the day has a name :colon Debary Debary so how do we form but these jocks well you can foreign jobs as a result of cross yet and we've already seen yes or you can form jobs as a result of dislocations intersection this 2 possible let's 1st have a look at the crossing so safe In a dislocation forums this what this would this thing here is this this this and this and this slip plane of my dislocations is not on the air this is not the job jockeys just kinks when the dislocation of they're very careful here I don't don't get you wordsmith mix-ups of this said this is a glide plane now you dislocation you screw dislocations here and when it moves it will move like this vital get larger for instance site but if you if you look very careful and you really high magnification if you could do this nite which you would find out is that the dislocations actually jump a little bit pieces of them jump from what we call from 1 part Valley to the other and these little pieces of dislocation that you form and musical cakes can they have nothing to do with that but without them being not related to the the chalks here
right which which connecting pieces of the dislocation from 1 glide plane to the other glide by and the chances are that have very low mobility and act as a pinpoint the edge jocks but so we rights switch it which you get this you can form a came on the glide plane with if it's a screw dislocations there's nothing that prevents from forming a kink on another slip rights of France's here this is a screw dislocation you have these 3 or 6 1 1 0 0 planes yes and this is disappear forms on this glide plane and it forms a kink on this glide by now the still kinks moved towards each other and they form a job so this is the job dispatch job here which considers location so it wouldn't describe this occasion tries to continue moving it drags this dislocation behind that slow mobility dislocation and you get to the formation of this dipole these 2 parallel dislocation another possibility is that dislocations cutting each other OK so here I have a screw dislocation this guy here and here I have a screw dislocation on and other playing on another 1 1 0 0 tie place but with let's assume this screws where it does not move it does not and this screw dislocations moves from right to left look at what what does it mean this bird respected it basically means that the crystals this shift but yes when you pass that you when you pass the people at the glide plane of the dislocation you shift the McChrystal gets shifted so when this dislocation cuts through this guy here it gets shift it shifted upward by this amount and so it's the same dislocation but it's I have edge job in and again so this is low mobility it acts as a painting .period my screw dislocations can continue to move to the to the left and it trails these 2 pieces of this location behind now it's better the dipole the screw dislocations areas a squeeze location but the dipole yes you can see has and edge h components has so it means that you can think of it as an extra half plane inserted in the structure it will come back to that in a moment of 1st I want to say for and how that how do we form these this so-called Debary these little dislocation loops in the forint steals of foreign the BCC Ira well this happens when you form multipole jocks and say for instance it is I have the a screw dislocation that moves to the I to the last year and then this part of the dislocation goes through a number of jobs and ends up on this glides plane yes nothing prevents the other screw dislocations segment to go through also successive jock formations and so they can mete out back they can meet again at a higher level and that they leave behind basically a dislocation yes let me explained this With the simple situation I have this so say I have this location the forms 80 just a single 1 them but this this piece here it is on a on the high here at the higher level right on the higher level so so so this dislocation the solicitors can move on and it drags this this thing behind it yes when this moves on can also drag this but I can do this this location here can also form on itself the job yes and also create jobs and rejoined this piece yes and so as a consequence they will leave behind but a dipole alone indictable and if I go back to some of the microprocessor you conceded that Kurds apparently rather frequently
what you can see here some of these staples like this type you deserve this seems like it's all by itself right so it can get pinched off if you use the contrail of the dipole Poland and the patented dipole can get pinched off can these these notes here are basically the
relatively similar processes to create right Of course you can imagine that if if you have made a very large gains there is little chance that this this location will by chance by a nose statistical Cheswold will rejoin the other 1 because we would have to make very specific King's so what happens to any of them the edge jog it is now depends very much on the height of this these job 1 of the things it's interesting is that if you look at the the dipole that is behind this trailing behind these screw dislocations with job if you look down the this is the dipole here this stifle can have an interstitial nature it can look as if you consists of 2 edge dislocations oriented like this To the edge dislocations oriented like this this means that the structure is as if you had made there is an extra half plane of atoms inside the dipole this structure means that there is a missing role of atoms inside valuable so it may sound strange but dislocations create point defects this way it did like you they make vacancies they make interstitials yes it doesn't happen when the job is very large and mysteries talk about supra jobs and cheaper jobs dangers activists as spending pinning points and that this will be the a screw dislocations that our hanging on our part of it associated with it rather than behave as if In on the job wasn't there and they have this spending and actually allowed by you looping around this pending .period Of these scooters Liberace can actually act as sources of dislocation and dislocations of the world will talk about this in a moment the
reps let's say something about this interesting aspect of this locations when you take a piece of I'll fire you and the strain and you measure the density no you find that the more you strain the lauded density it's not a big effect but it's there so yeah this is the decrease in density as to the more you strain to material that the hired a decrease in it is the density that's measurable effect and the reduction in density is due to 1st of all to effect is personal that lot this bill lactation that usually surrounds the dislocation core bank the vacancies at the forum by the motion of Cecile jobs to do the jobs that I just drew you tend to be vacancy producing John so let's read what's on the slide here with the plastic deformation issue a significant increase In point defects in particular vacancies and because the the concentration of vacancies much-larger would then the thermodynamic lead stable concentration we talk about excess vacancies Texas so yes and no you can also form vacancies and self interstitials but that hats at higher temperatures when the dislocations edge dislocations moved out of their plight like that that happens with edged is focus it's a it's a temperature effect news relating this but if you have at this location here well this is the extra blamed this dislocation it doesn't have to to stick to its quietly yes it can it can move to a higher glide without the processes of a jock formations that I just described that happens at high temperatures and high temperatures dislocations can climb out also there glide planes by absorbing or emitting point defects as tool for instance if this extra have blamed absorbent emits less say safety and interstitial atom it so it will move up 1 lattice yesterday and it will have created an interstitial that said that kind of emotional dislocation motion and which is not to glide and we call non conservative motion of right up we we know from measurements that too bad we produce about 10 times more vacancies as a result of defamation then interstitials and the values can really reaches high sentiments for and that this is it's really high valuations close to melting temperature concentration of vacancy and so and as a result you get the uh they an increase in volume per for the same number of of at times it's selects let's have look at whether we can calculate what this increase in decrease in density rather well and so will just simply calculate the effect of data what is the lactation associated with dislocations these lattice debilitation areas In a uh a around the core of an edge dislocations corresponds to LAT displaying that's threaded by the dislocation through to an addition of 2 vacancies this as we know the local density the little concentrations of vacancies around the has when you add it is equivalent in the lattice expansion as which is equivalent to adding 2 vacancies so that's on what it so we'll ask me what I do know that's right what Furcal their measurements and then there is a technique called the Positron Annihilation Spectroscopy which allows you to study .period defects in metals and from these studies we can we can learn a lot about you know how many defects we create in in Endesa in materials like steel or irony is and and and find out the status of so now let's see what we do here but what we can use this you would happens in India Ireland which we take a cue of very large cube of ,comma Byron 1 meter Cuban sized lattice parameters .period 36 and we have this locations the densities of Road D In each dislocation creates a lot as delectation of equal to 2 atoms the volumes per playing that its threats so you know you can calculate the number of Byron patterns In a cubic meter is simply dies With this formula here it's a lot of atoms then you can calculate number of vacancies and basically you just to count the number of 1 1 0 0 planes has been in beta here you count the number of the length of dislocation that you have so that gives you a and you multiplied by 2 of them gives you the amount of vacancies that you've created so you have basically this number of at times this number of vacancies and then you can be calculated the density with and without the these vacancies and calculated decrease in density and and when you get this number this number multiplied with dislocation density which have you worked you'll find values that are of no comparable to what is measured here at the end of you can also use this this method and some people have used it To measure dislocation density the use of density measurements are small but the measurable you just need a good a density but but to conventional density measurements as and power you might rate as a function of strange you as soon as said here that killed around 2 atoms at 2 vacancies added poor threaded plane I am done then you'll get a dislocation density pretty unusual way to determine dislocation density but it works out these the represents just but we had a new probably wonder Well you know all of the Jamaican error but you make an error because they're they're like someone dynamically stable vacancies you right but at room temperature their number is very very much smaller than the 2 vacancies you've created of soaring the volume change you if you have generated by deformation so now we know we come to the aspect of degeneration of dislocations now and then the the generation of dislocation is usually with which we young we say is that the focus of our generated by Frank Reed sources and Frank Rich sources you can it that would make you have them in the SEC or BCC metals and alloys here will will facility traded with the for the C C R and this process is called double-crossed yes that's double-crossed slips which is something I just explain to you guessed is 1 of the mechanisms by which we can make Frank Reed in In BCC up in BC metals actually BC metals and alloys with so how does it work don't and right so the so the top picture is this again something that we I had to do with illustrated here so what what we have is let's this so we will go back here to so here I have a screw loose again in a 1 0 claim that this this is so I wanted to imagine that there are 1 1 0 0 planes parallel rights justice is the not the only 1 1 0 planes many of them apparently so and in here however this location has made AT jog yes and and it's decided to glide on this 1 disk like himself so so here I had my burgers served like here at my Burgers factor here His here and in here also have prospective symbol respect and these are the the jocks right until that and have told you that the jobs are not the kind of Cecile advantages stalled moved because at this location to do this work is moving on this plane there this little piece of dislocation it has the Burgos factor in and is a line that's not on a glide is modified the lighting the situation so it's basically stuck there the so this dislocation here can expand Will it if when I increase the faucet will expand and become very very large like this distance what is happening here under the effect of the externally applied stress will have share stresses on the glider planes and dislocation well become half cervical cancer and and then I should have brought this with me because you can actually illustrate this very nicely he said at the the once your Europe the radius of this dislocation segment is half the distance between these 2 each job stress needed to increase the diameter because of this the Of this at this location decreases right it actually decreases areas I don't know if you've ever tried to squeeze a balloon between 2 poles yes you at the beginning it's difficult but once you have reached the balloon has reached a certain size on the on the other side of the polls it pops it flops throw all bytes sec review never ever done besides me was going to illustrate this so this is this instability pork know that instability .period this is precisely this year the move will spontaneously expand after you've reached this critical value of the radius prior to the Rangers being half the distance between the 2 stupidity to dilute expands continues to expand and curls back like this way and what happens there this here 1st let's do this as an exercise the Marburger Spector was this this was the president to bringing points and now designed to pending points out the this location has now expanded To this shape so what so Burgos factor is the same everywhere right this this and this this divergence factor of these 2 pieces so now let's say we we have chosen this as our work line direction so far and that means that have followed the lines on this side this is the line direction on this side the line direction this and this directions :colon and so so let's look on on this side I have lined direction is in this direction Bloomberg respective points to the right here and so on this so if I look in this direction down the slip playing this here has the it's an edge dislocations the extra have claimed the low the glass this 1 here now I know so my the blind direction the various factors so we extra have played is on top comes from the top so like best what do we remember To dislocations edge dislocations on the same glide plane on the same glide by on the single-aisle planes suit day on a different signs against their will attract each other they will attract each other this is Europe you remember just arrived at this time and this 1 here this is actually the 1 this condition but here we have a candidate we have situation when where worldwide is 0 0 why 0 so I think this was fixed over 1 year so an Expo over wide it is infinite so it's basically an attractive interaction and of course when they attract each other yes I the stew Will I just annihilate them they will recreate them and when they do this to you dislocation and up it basically this off it is also very interesting but beckoned disappear suddenly but and this is what happens to the stupid edge parts will this disappear may leave behind a dislocation loop yes and by the leave behind this segment here has which is actually nothing else and the or regional segment and the process can repeat itself now that it tended to repeat itself for ever it's a good question well let's see this is just in preparation for something in the future but if you have a dislocation and then this thing creates another dislocations and another dislocation if I look on this side this was the that's the look on this side here I have an edge dislocations and so on yes so and this was mine the factory along the dislocation life so all the dislocations here look like best yes so they all repel each other so if we a reach for instance the grain boundary here Nancy these dislocations will will stop moving yes and they will repelled each other making it harder and harder for us and because of his back stressed making it harder and harder for us to make new dislocations and that basically stops the production of the of New dislocation this is a very important mechanism In in iron and steel for Riddick steel pieces the irony related to the internal generation of dislocations in I think this the thing all right so what is it what is this this distress relations while Missouri you we have seen this before I half what does it take where the shear stresses it takes to get a certain radius right we know this formula which we've used it to calculate France's which was distressed in this fatigue sample used is it yet a picture so we use the same formula which relates the shear stress on the dislocation and the glide plane on the dislocation and the radius and say I don't know if we have a 82 Apasco shares sure modulus and but the structure of . 2 for 8 which would be about the story for the situation for Gulf Arab this form basic tells us about 10 dividers by data Pascal so that means that Our due shear stress required to activate the Frank Reed soars but whale decrease with increasing the increasing the length here on the wandered far apart it's easier to do generate dislocation and when it's very very even when the point of very close so it's diagram here is I have to that you have an increase With the decrease in parts of this is 1 it's because this is linear would 1 over so when they when Europe edge jobs are very close to each other it's harder to initiate to get Frank Reed sources to to to activate Frank Rich sources then went there far apart it's kind of interesting right is an interesting because if you make your In grain size for its very very small really small like you know if you wanted to 450 nanometers what happens then obviously these 2 .period yes you have to be within the crystal right so it basically also means that when you make very small crystals it becomes very hard 2 generate this location right and if you could generate terms these whatever painting .period would be so close to each other as it didn't really need a huge forces to get them make dislocations there is 1 of the reasons that among many y now no structured materials their plasticity cannot depend only on dislocations because you know you there is a fundamental problem about even making them case the other thing is of course because the grain sizes so small very quickly even if you manage to make I even if you manage to make activate Frank resources they quickly run into but barriers fundamental barriers grain boundaries to their glass and again you cannot generate many dislocation has many dislocated so it hasn't been as impact on your classes so this is it I mean this is a real simple formula but it's very has to keep the key and so on there a key meaning and admits it's and it's also actually quite useful because of that it do this the kind of results you get from my numbers you get from a very realistic right so let's close this that year by I'm talking about the safe few things about both defects in in the inquiry the KLA of vacancies and interstitials but before I I do this idea I think too will take a break and for until 20 pass 5 and will finish will we started in about less than 10 minutes to get a chance to bring something
Gebr. Frank KG
Satz <Drucktechnik>
Ford Focus
Flügel <Technik>
ISS <Raumfahrt>
Buick Century
Elektrolokomotive Baureihe 80
Band <Textilien>


Formale Metadaten

Titel Mechanical properties of steel 12: dislocations and other defects
Serientitel Mechanical properties of steel
Teil 12
Anzahl der Teile 24
Autor Cooman, Bruno C. de
Lizenz CC-Namensnennung 3.0 Unported:
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DOI 10.5446/18317
Herausgeber University of Cambridge
Erscheinungsjahr 2013
Sprache Englisch

Inhaltliche Metadaten

Fachgebiet Technik
Abstract The 12th in a series of lectures given by Professor Bruno de Cooman of the Graduate Institute of Ferrous Technology, POSTECH, South Korea. Continues the discussion of dislocations and other defects in steels, including for example, jogs and vacancies.
Schlagwörter The Graduate Institute of Ferrous Technology (GIFT)

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