And here we are back in the Kemper Hall Laboratories here at UC Davis. And today, we're gonna talk about making things fast and slow. [MUSIC] So let's begin talking about making things fast and slow by making something slow. Think metal casting, a case in which us engineers were making things or manufacturing practical materials. And so in this simple experiment that we do here in the teaching laboratories at UC Davis we create a map of the 10 bismuth system and we'll show an example of that in a moment. The experiment is a simple one. We take a test tube with a small amount of alloy of tin and bismuth in some particular ratio. And an alloy is no more than two metallic elements together in a single material. We put that test tube into this low temperature furnace, and allow it to melt. And then take that melted alloy and place it into this insulated beaker. And then take this all to a work station, where we can monitor the temperature as it slowly cools. And then we'll see the results of that in the phase diagram map that we'll create at the board. So here we've plotted the results of the Tin-Bi experiment in which we've summarize the results of monitoring the cooling of these individual alloys of tin and bismuth. And we've created a map, a map just like a map of the State of California. But instead of it showing the various counties, it's showing various faze regions that are produced. So it's a tremendous amount of information here about a wide range of alloy compositions in one graphical image. Overall, we have the temperature as the vertical scale and so you see how High we had to heat the material, each alloy in order to get up into this region, this part of the map which corresponds to the liquid phase. So from this area called the liquidus line and above, we have the liquid phase. That region is for any composition, temperature combination, indicates that the material is in a completely liquid state. The alloy is in completely liquid state. Each of these data points that we've summarize here from our experiments, represents a change in the cooling grade for those individual alloys as they were cooling in those test tubes and being monitored at the work stations. The laws of thermodynamics indicate that as a liquid begins to crystallize and form a solid that there will be a change in the cooling rate. And that break in the cooling curve, that temperature versus time plot that's being made at the work stations, give us these various data points. So for example, at 40 for the test tube that had a 40% bismuth, 60% tin alloy then we begin to see crystallization around that temperature somewhere between 150 and 200 degrees centigrade. And then upon further cooling we saw another break in the cooling curve around this temperature of between 100 and 150 degrees centigrade. So what was happening is that we have moved from the single phase liquid part of the map into in this case, in this temperature range, in a region defined by this boundary roughly triangular shaped region that is liquid plus a solid phase that we'll call beta. Beta representing this region over here in the phase diagram. This part of the map which is a single phase solid solution region. So again, we're seeing that as we cool down to about this temperature oh, roughly 180 degrees centigrade, we saw the change of slope representing the beginning of the beta phase precipitation. And then cooling on down to this temperature of about 130 degrees. Then the whole system crystallized and we go into this region, this part of the map which is alpha plus beta with the alpha phase being this very small part of the map over here. So again, we've now labelled all parts of the map just as if we were to go and label all the counties in the state of California on the California map. We've now indicated all the regions of this map that would represent the various phases. And because I chose this experimental area, let me finish that off accurately by saying this is liquid plus alpha. So again, single phase liquid, single phase solid, so-called beta which is a tin rich with a small amount of bismuth. Over here, single phase solid solution. Bismuth with a small amount of tin in it. And in these various two phase regions up above, this horizontal temperature range, we find that this part of the map, this region is liquid plus beta, liquid and beta being the adjacent basis. And then this region being liquid plus alpha, those being the neighbors of that region. The important point to make is this sharp solidification temperature all the way across is referred to as the eutectic temperature. Now eutectic is a word as in the Greek language it simply means easily melted. And it’s called that because this particular point in the liquid phase region, where the system is entirely liquid, represents a particular alloy composition just above 60 weight percent bismuth in which the material is 100% liquid down to that very low, roughly 130 degree centigrade temperature. And so this is indicating the lowest melting point of any composition in this entire range. And that then is a most if you will, easily melted alloy composition in the entire range. And so again, this is given the Greek term eutectic composition and eutectic temperature. So again, that's the eutectic point right there. So then again, one image summarizes the nature of this alloy system in a very powerful and straight forward way. So, this summarizes what happens in terms of the overall process of metal casting for any range of possible metal alloy systems. We're gonna now move over to another part of the laboratory and look at a very famous phase diagram, in fact the most important phase diagram in the materials engineering world. And that is one that involves not only a eutectic reaction, but also a eutectoid reaction and that simply means eutectic like reaction in which we have an entirely solid phase transformation taking place. A very important in the steel industry and we're gonna look at a particular phase diagram that describes that in which we have a solid phase so-called gamma phase austenite solid solution. Transforming to a ferrite nearly pure iron with a small amount of carbon in it plus a ceramic like composition, an iron carbide. Fe3C, a system also called cementite. So we look at the phase diagram that involves this system, and it really summarizes a tremendous amount of important information about a very important engineering system. So let's look at that now. So as I said, this diagram over my shoulder is the most important single phase diagram in the field of material science because it really summarizes in one graphical image, really the whole story of iron and steel making. So central to everything that we think of in terms of traditional engineering. So we see on the left side of the diagram, the story of steel making up to 2% Carbon additions. We have a very eutectoid or eutectic like reaction in which ostenoid is transforming at the eutectoid temperature to ferrite and cementite. On the right side of the diagram, we have the story of making cast iron and the iron industry. And in that case we have a eutectic reaction very much like what we saw in the tin business experiment. So again, one graphical image is summarizing so much as of what happens in this very important iron and steel industry. And again, we're using a simple map of temperature versus composition in this iron carbon system to tell that story.
