Metal Alloys of the Future?

hey folks today we're going to take this glass slide which has been coated with a special arrangement of metals and stick it under the spicy flashlight to make some high entropy alloy nanoparticles high entropy alloys are this really exciting new field in metallurgy and material science which really has started to take off in just the last 20 years or so most metals that you interact with on a daily basis are some kind of alloy it's multiple metals mixed together the vast majority of alloys are a binary or trinary system with other various trace elements mixed in if we look at pure aluminum for example we can see that it naturally forms what's called a face centered cubic structure so if we visualize a cube and put an atom of aluminum at all the corners as well as on all the faces that's a face centered cubic and that's what aluminum like 100 pure aluminum will do by itself when we start alloying in additional elements those elements will replace one of the positions on the cube so maybe we'll replace this corner with a silicon and replace that face with a magnesium and this will form a 6061 style aluminum alloy this is known as substitutional alloying where you're substituting in individual atoms at kind of select places around the crystal 6061 has 95 to 96 aluminum so the bulk of it is just aluminum and it has about one percent each of magnesium and silicon plus a bunch of trace elements if you start to add too much of an alloying element you start to get what's known as intermetallic regions and this is where the individual elements start to group up into dense regions of just say aluminum and magnesium and then you get these boundaries between the aluminum and magnesium that start to form their own intermetallic it has material properties that might not be desirable so for this reason alloys tend to be predominantly one element with just a little bit added in and we can graph this in like a triangle-shaped phase diagram if we put one element at each corner aluminum magnesium silicon you can see that we tend to stay in the corners it's mostly aluminum with a little bit of silicon and a little bit of magnesium the region inside of this phase diagram chart is kind of like the here be dragons on an old map lots of things can happen there it's difficult to model and predict and we generally just avoid it and that brings us to high entropy alloys instead of having one major constituent we instead have five or more elements that are all in equal atomic proportions on the surface this seems kind of ridiculous based on everything i just described but instead researchers found that for certain elements this random mixture just forms a cubic structure as if it was a single element so instead of getting an alloy with a bunch of intermetallics or even separating into distinct phases you get just a unified alloy and what makes these new alloys so fascinating is that each position on the crystal structure has a unique local environment so typically an alloy will have you know 95 percent one element and then small substitutions so you have two different local scenarios an atom either sees all of its surrounding neighbors being the same as it or it has one substituted element of something else but in these high entropy situations every single location in the crystal structure across the whole alloy is probably unique because it has a different element on each corner surrounding it and this can lead to some really interesting material properties they found that some of these alloys are super hard and also tough meaning that you can bend it a fair amount before it breaks this is a really strange property which is kind of hard to wrap your head around because we typically associate hardness with brittle materials think of like glass it's very hard but if you flex it too much it just shatters into a bunch of pieces whereas something like a piece of aluminum is not terribly hard you can dent it pretty easily but it will bend a long way before it breaks so having both a hard and ductile or malleable material is really counter-intuitive and it's due to these individual atoms mixing in such a way that you get these strange properties and the more research has gone into this we found more and more interesting things some of these high entropy alloys appear to be superconductors some are paramagnetic or super paramagnetic there's a lot of interesting work at the nanoparticle region for things like catalysts if you'd like to learn more about the real hardcore details about how these high entropy alloys work i'll link a bunch of really good lectures down in the video description so that brings us back to my shop and attempting to make some high entropy alloys myself there are lots of different ways you can make them typically you start with a bunch of the alloying elements mix it all up and put it in something like a vacuum arc furnace or bark plasma sintering something like that which mashes all the elements together in a big ball of like heat and energy another common method is to take all the elements and put them in a high energy ball mill and just like mash them into each other repeatedly eventually the individual grains will kind of just plastically smush into each other and you'll start to form these alloys kind of as a cold process yet another method starts with precursor metals that are like chlorides of the metal and you can hit it with a laser and it decomposes into nanoparticles of the high entropy alloy so i saw a paper on that and it got me thinking if you could maybe do a variation of that effect where you sputter coat thin films of different metals onto a glass slide so that you have alternating layers of aluminum nickel zirconium iron you know etc etc and then hit it with a laser to ablate it into a solution similar to the nanoparticle video that i did previously and so if you're lucky when some of those particles kind of coalesce and solidify after being ablated you'll form high entropy alloy combinations so i coated onto this glass slide 100 nanometers each of aluminum nickel copper zirconium and iron for the first batch and then another batch i added tungsten and chromium onto the top we put it under the fiber laser add a little bit of deionized water underneath the slide to catch all the particles coming off and then we just hit it with the laser at different settings to see what happens it quickly became obvious that this procedure was ripping off large chunks of the thin film so rather than ablating all of it into like a molten material it was ablating a hole but also peeling off just large pieces of film you could see it floating around in the solution and this is because the base layer doesn't have great adhesion to the glass and once you stack up that many layers of metal there's a lot of internal stresses and so it wants to peel off anyway so i also tried the reverse where the liquid is on top of the glass slide and we're shooting through the liquid and it's kind of ablating upwards hopefully to reduce some of that peeling effect so i should probably note that we are right on the edge of my metallurgy knowledge so if i'm saying anything grossly incorrect or you just have extra details to share please feel free to leave a comment down below and i'll compile it all into an addendum and pin it at the top of the video okay cool let's start to dig into some of the data unfortunately for both you and me there is way too much data to go through in this video there are literally thousands of particles in these samples that i collected and it's only a fraction of the sample total so i'm going to give you kind of a quick overview of the highlights the different features that i saw while looking through all this and show you kind of some of the failure cases what they look like and hopefully some of the successful cases so the most prevalent feature by far are these large fragments of the thin film that just flaked off kind of end mass the layers that i sputtered are a hundred nanometers thick and so these flakes are usually four to five hundred nanometers thick depending on how many of the layers actually stuck together and you can see some start to peel off in different locations if we look at large particles say 10 to 30 microns you'll often see kind of a round spherical blob that has a mix of a few elements and then a smaller hemisphere is kind of dotting the surface the hemispheres tend to be made of nickel and copper alloyed together while the main bulk of the material tends to be zirconium and aluminum and iron kind of floats in between depending on the individual particle so what's happening here is when the material is ablated and it's in its molten state there's enough material that as it hits the liquid it's not immediately quenched so there's a little bit of time that it has to cool down and that's just enough time for the different elements to segregate and separate into different phases so you tend to see the nickel and copper kind of move to the edges of the material while the aluminum and zirconium stay in the middle so this is kind of a failure case and it's not what we want this is not a high entropy alloy it's really just multiple alloys kind of glommed onto each other the smaller the size the better the outcome tends to be i assume this is because the particles just quench much much faster there's not a lot of material and so all the molten elements are frozen in place much quicker and it's more likely to get a good result as we move to smaller particle size say two to five microns we tend to get better results so you'll still see kind of split or bimodal distributions like this particle but you also start to see more even distributions of the elements of the small particles i should note that the vast majority of them are not even close to high entropy alloys most of them have two or maybe three elements they might be kind of separated into different phases or just be one homogenous mass of say copper and nickel so a lot of the particles are not at all useful and frankly there are so many particles i didn't have a chance to analyze even a significant fraction of them so it's hard to say how many of them are in this kind of useless category furthermore the smaller the particles the harder they are to analyze because there is a resolution limit to the eds detector which is generating these element spectrum so i tried to focus on particles that were greater than say 500 nanometers because below that i don't know if i really trust the resolution of this system which is unfortunate because likely the best candidates are the really small nanoparticles from 15 to 100 nanometers but we just can't look at them on my machine so here is a reasonably decent result you can see that the nickel and copper still kind of separated into their own phases but are more evenly distributed across the whole particle and this one is even better the nickel has some like hot spots that you can tell is starting to separate but there's a nice background of both nickel and copper across the whole thing the aluminum zirconium don't seem to really be separated at all and the iron is also a pretty consistent background this third particle was from the test run where i included chromium and tungsten so we can see a different mix of elements here but the nickel chromium aluminum and iron are all pretty evenly distributed with a little bit of a lump of tungsten on the top i wanted to get a good image of the individual layers stacked up on the glass slide so i embedded it in some resin and did kind of a cross-section lapping and polishing it unfortunately the pictures just didn't turn out they looked like garbage but i did manage to find a piece of the thin film that had kind of flaked off during the procedure and we can see it on edge so we can actually see the individual elements stacked up from bottom to top we can see there's copper nickel zirconium aluminum and iron the copper was the first layer put down on the glass slide and the iron was the last an interesting thing you can note is that the nickel spectrum has a faint line near the top which is where the iron is the sputter target was actually invar which is a combination of nickel and iron and so there's a little bit of nickel that leaked through on the iron layer because of that to show two pretty good examples which i am fairly confident about this first one is zirconium aluminum iron nickel copper and they all have a pretty even distribution of the elements across the whole particle the copper is pretty weak so there's not a whole lot of copper or even nickel that's incorporated into this particular particle and there's a little bit of a hot spot on the iron but it's a fairly even distribution and it was sitting directly on the silicon substrate so there's not any like extra background contributing to this particular spectrum so i feel pretty good in saying that this is probably a high entropy alloy kind of micro particle it's probably about two microns wide this last particle i think is just very visually interesting which is why i chose to show it it's kind of got a i don't know an octahedral type shape to it but we can very clearly see all the individual elements in the same octahedral pattern this came from the chromium tungsten run so we can see the addition of chromium in this particular particle but no tungsten generally speaking i found the chromium really helped homogenize the individual particles even when the particle clearly had separated a little bit the addition of the chromium really seemed to tie in the aluminum zirconium and iron a little bit better into the whole particle so i think chromium's probably important for this cast of characters tungsten was kind of a dud it didn't seem to like play nice with anybody and always kind of separated out into its own phase and that's not terribly surprising considering it's a refractory metal and the rest of these very much are not the most well studied kind of an original high entropy alloy is the cantor alloy and it's composed of iron nickel chromium cobalt and manganese these are all very similar metals that have similar electrical properties and size of the actual atoms whereas i basically just tried whatever sputter targets i had on hand so this is probably not an ideal mix of elements to make a high entropy alloy but that's one of the neat things about this field is that there's just a ton of experimentation right now because no one really knows the rules to this particular game so it's a wide open field with a lot of interesting discoveries coming down the pipeline if you'd like to see all the raw data that i collected for this project it's all up on the patreon dropbox huge thanks to all my patrons i really appreciate the support if you enjoyed today's video make sure you're subscribed so you don't miss any future topics and otherwise thanks for watching see you next time

Channel: Breaking Taps

Views: 712,271

Keywords:

Id: Vq_6mAAbfFY

Length: 15min 24sec (924 seconds)

Published: Wed Aug 24 2022