WEBVTT 00:00:00.030 --> 00:00:02.400 The following content is provided under a Creative 00:00:02.400 --> 00:00:03.830 Commons license. 00:00:03.830 --> 00:00:06.860 Your support will MIT OpenCourseWare continue to 00:00:06.860 --> 00:00:10.510 offer high-quality educational resources for free. 00:00:10.510 --> 00:00:13.390 To make a donation or view additional materials from 00:00:13.390 --> 00:00:17.490 hundreds of MIT courses, visit MIT OpenCourseWare at 00:00:17.490 --> 00:00:18.740 ocw.mit.edu. 00:00:20.856 --> 00:00:23.410 PROFESSOR: Today, big announcement. 00:00:23.410 --> 00:00:24.650 Wednesday, no lecture. 00:00:24.650 --> 00:00:28.880 Instead, Celebration Part 2. 00:00:28.880 --> 00:00:30.370 And I'm going to say a few words about it. 00:00:30.370 --> 00:00:31.840 There is the room assignments. 00:00:31.840 --> 00:00:33.310 I think they're the same as last time. 00:00:35.920 --> 00:00:39.800 If you miss the exam because of illness, there will be a 00:00:39.800 --> 00:00:42.090 make-up test on November 4th during class. 00:00:42.090 --> 00:00:44.060 There's no weekly quiz tomorrow. 00:00:44.060 --> 00:00:47.820 I'll be available for office hours 4:00 to 5:30 this 00:00:47.820 --> 00:00:51.350 afternoon over here at 8-205. 00:00:51.350 --> 00:00:52.490 So a couple of things. 00:00:52.490 --> 00:00:55.820 I'm going to say few words about the 00:00:55.820 --> 00:00:58.100 quiz, the test, rather. 00:00:58.100 --> 00:00:59.560 The celebration. 00:00:59.560 --> 00:01:03.820 So the coverage is going to go starting from the time of the 00:01:03.820 --> 00:01:08.170 last celebration up through now, but I think in view of 00:01:08.170 --> 00:01:11.720 the fact that we started defects on Friday, and my 00:01:11.720 --> 00:01:14.730 thanks go to Professor Demkowicz, who jumped in the 00:01:14.730 --> 00:01:18.320 breach and lectured in my place so that I could get 00:01:18.320 --> 00:01:21.180 drawn into some of the activities associated with the 00:01:21.180 --> 00:01:23.740 visit of the President. 00:01:23.740 --> 00:01:29.420 You will not have had the time to go through your recitation 00:01:29.420 --> 00:01:31.150 cycle on this new material. 00:01:31.150 --> 00:01:33.482 So I'm not going to put anything on defects on the 00:01:33.482 --> 00:01:34.300 exam, all right? 00:01:34.300 --> 00:01:39.000 So we'll go up through the end of the unit on x-rays right up 00:01:39.000 --> 00:01:41.470 through Bragg's Law, indexing crystals. 00:01:41.470 --> 00:01:43.930 So that starting Friday, defects. 00:01:43.930 --> 00:01:46.550 I'm not going to teach you Friday, teach you Monday, 00:01:46.550 --> 00:01:48.140 examine you Wednesday and Tuesday. 00:01:48.140 --> 00:01:50.670 Tomorrow I expect you're going to have all sorts of 00:01:50.670 --> 00:01:53.830 review-oriented activities in your recitation. 00:01:53.830 --> 00:01:57.700 So I don't want you torn between trying to master a lot 00:01:57.700 --> 00:01:59.660 of this new material, which is quite different from what you 00:01:59.660 --> 00:02:03.230 had in high school, and at the same time trying to have a 00:02:03.230 --> 00:02:06.940 catch up on capturing all that material since the second 00:02:06.940 --> 00:02:09.180 test. 00:02:09.180 --> 00:02:12.470 So that having been said, I'm going to remind you. 00:02:12.470 --> 00:02:14.460 I'm going to basically say the same thing I said before the 00:02:14.460 --> 00:02:19.380 first celebration, but we need to be reminded. 00:02:19.380 --> 00:02:21.310 So what's the purpose of the test? 00:02:21.310 --> 00:02:25.040 The purpose of the test is to give you a status report and 00:02:25.040 --> 00:02:26.280 send you a message. 00:02:26.280 --> 00:02:28.930 And there's really only two answers here that we're 00:02:28.930 --> 00:02:29.540 looking for. 00:02:29.540 --> 00:02:31.290 You're either going to get a smiley face or you're going to 00:02:31.290 --> 00:02:32.170 get a frowny face. 00:02:32.170 --> 00:02:34.090 That's all it's about. 00:02:34.090 --> 00:02:38.710 I don't care whether it's a 78 or a 75, but 00:02:38.710 --> 00:02:40.130 hard 50 is a pass. 00:02:40.130 --> 00:02:43.530 And if you're not mastering the material, I intend to tell 00:02:43.530 --> 00:02:46.810 you so and then invite you in so that we can figure out how 00:02:46.810 --> 00:02:48.900 to get you through. 00:02:48.900 --> 00:02:51.500 Because everybody in this room has the intellectual apparatus 00:02:51.500 --> 00:02:52.730 to pass this class. 00:02:52.730 --> 00:02:56.120 Some of you just are not managing your time well and 00:02:56.120 --> 00:02:57.890 you need to be told that. 00:02:57.890 --> 00:02:59.320 So we will tell you that. 00:02:59.320 --> 00:03:00.900 With one of these. 00:03:00.900 --> 00:03:02.640 That's going to be the message. 00:03:02.640 --> 00:03:05.220 Go to the right room. 00:03:05.220 --> 00:03:08.340 Bring five things with you: Periodic Table, table of 00:03:08.340 --> 00:03:13.600 constants, your age sheet, calculator, and a pen, 00:03:13.600 --> 00:03:15.190 something to write with. 00:03:15.190 --> 00:03:16.930 You'll write on the question paper. 00:03:16.930 --> 00:03:19.000 No wireless devices. 00:03:19.000 --> 00:03:19.790 Shut them off. 00:03:19.790 --> 00:03:20.630 Don't even bring them. 00:03:20.630 --> 00:03:22.710 What do you need your cell phone for? 00:03:22.710 --> 00:03:24.756 Don't need it during a test. 00:03:24.756 --> 00:03:31.190 We're going to start at 11:05 promptly and stop at 11:55. 00:03:31.190 --> 00:03:32.650 What's the strategy? 00:03:32.650 --> 00:03:35.190 Read the entire paper. 00:03:35.190 --> 00:03:36.580 Try every question. 00:03:36.580 --> 00:03:37.660 You know this. 00:03:37.660 --> 00:03:40.100 You get part marks if you write something. 00:03:40.100 --> 00:03:41.280 If you don't write anything for the 00:03:41.280 --> 00:03:42.910 question, you get a zero. 00:03:42.910 --> 00:03:44.990 So try every question. 00:03:44.990 --> 00:03:46.420 And start with the easy one. 00:03:46.420 --> 00:03:48.520 The easy one for you may not be the easy one for your 00:03:48.520 --> 00:03:50.690 neighbor, but how do you know what the easy one is? 00:03:50.690 --> 00:03:53.790 I just put them down as they came out of my mind. 00:03:53.790 --> 00:03:56.790 I didn't put them down in ascending order of difficulty, 00:03:56.790 --> 00:03:59.570 chronological order, topical order. 00:03:59.570 --> 00:04:00.580 They're just-- 00:04:00.580 --> 00:04:01.830 they're there. 00:04:04.520 --> 00:04:11.155 Leave tracks, tell us how you got to the answer, Work 00:04:11.155 --> 00:04:12.250 parametrically. 00:04:12.250 --> 00:04:14.500 Don't start plugging in numbers on the first line, 00:04:14.500 --> 00:04:16.170 because if you make a computational error on the 00:04:16.170 --> 00:04:19.540 first line and drag it through the entire derivation, you'll 00:04:19.540 --> 00:04:20.505 make a mess of things. 00:04:20.505 --> 00:04:24.880 You'll have wavelengths, size of distance here to Chicago, 00:04:24.880 --> 00:04:26.900 light moving at ten times its normal speed 00:04:26.900 --> 00:04:27.760 and stuff like that. 00:04:27.760 --> 00:04:29.510 It's no good. 00:04:29.510 --> 00:04:31.610 Focus on the question. 00:04:31.610 --> 00:04:34.570 Don't just say, oh, it's something to do with x-rays, 00:04:34.570 --> 00:04:37.110 just give me some stuff that you memorized about x-rays, 00:04:37.110 --> 00:04:39.720 some stuff you wrote down in your age sheet about x-rays. 00:04:39.720 --> 00:04:41.420 If it's not about the question that we asked, 00:04:41.420 --> 00:04:42.120 I'll give you a zero. 00:04:42.120 --> 00:04:43.660 I don't care how much you write. 00:04:43.660 --> 00:04:46.490 Write on the topic. 00:04:46.490 --> 00:04:47.890 And refer to electronic structure. 00:04:47.890 --> 00:04:50.960 When you don't know what to say, start talking to me about 00:04:50.960 --> 00:04:53.170 electronic structure. 00:04:53.170 --> 00:04:54.820 That's the theme of chemistry. 00:04:54.820 --> 00:04:58.660 electronic structure dictates behavior. 00:04:58.660 --> 00:05:00.510 So talk to me about electronic structure. 00:05:00.510 --> 00:05:01.760 Do your own work. 00:05:04.720 --> 00:05:08.040 And lastly, it says something here, oh, good luck. 00:05:08.040 --> 00:05:08.650 That's what it says. 00:05:08.650 --> 00:05:10.240 Good luck. 00:05:10.240 --> 00:05:12.380 So last day, Professor Demkowicz 00:05:12.380 --> 00:05:14.220 got to the line defects. 00:05:14.220 --> 00:05:17.680 He was talking to us about line defects and how they have 00:05:17.680 --> 00:05:21.220 an impact on behavior. 00:05:21.220 --> 00:05:25.780 So I wanted to pick up the treatment there. 00:05:25.780 --> 00:05:28.690 So what's the whole issue behind line defects? 00:05:28.690 --> 00:05:33.790 Well, what line defects do is they explain this anomalous 00:05:33.790 --> 00:05:37.496 behavior where the measured value of yield strength-- 00:05:42.630 --> 00:05:45.900 so I'm going to write sigma y; sigma is 00:05:45.900 --> 00:05:49.350 the symbol for strength. 00:05:49.350 --> 00:05:58.060 the yield strength as measured is on the order of only about 00:05:58.060 --> 00:06:01.120 1/10 of the theoretical value. 00:06:01.120 --> 00:06:05.010 It's only about 1/10 of the theoretical value for the 00:06:05.010 --> 00:06:06.280 yield strength. 00:06:06.280 --> 00:06:07.200 You might, say, wait a minute. 00:06:07.200 --> 00:06:09.020 How do you get that theoretical value? 00:06:09.020 --> 00:06:10.860 You can calculate this. 00:06:10.860 --> 00:06:12.100 Not too badly. 00:06:12.100 --> 00:06:16.090 If I take a look at a system of atoms, and this could be a 00:06:16.090 --> 00:06:19.130 metallic crystal, you could argue that there are metallic 00:06:19.130 --> 00:06:22.360 bonds between all of these atoms. And if what I wanted to 00:06:22.360 --> 00:06:25.270 do to shear something-- 00:06:25.270 --> 00:06:27.610 so this is the yield strength for shear-- 00:06:27.610 --> 00:06:31.620 if I wanted to shear the top plane of atoms versus the 00:06:31.620 --> 00:06:34.190 bottom plane of atoms, can you see that to a first 00:06:34.190 --> 00:06:37.170 approximation, the energy required would be the energy 00:06:37.170 --> 00:06:38.780 to break each one of these bonds? 00:06:38.780 --> 00:06:41.930 Because I have to break the bond to release the plane and 00:06:41.930 --> 00:06:43.180 then move it. 00:06:43.180 --> 00:06:45.340 So if you make an estimation on the 00:06:45.340 --> 00:06:46.590 basis of bond strength-- 00:06:49.690 --> 00:06:56.990 so you take individual bond strength times bond density or 00:06:56.990 --> 00:06:58.730 bond concentration. 00:06:58.730 --> 00:07:00.620 When I say density, I don't necessarily mean 00:07:00.620 --> 00:07:01.760 mass per unit volume. 00:07:01.760 --> 00:07:03.910 I could mean bonds per unit area. 00:07:03.910 --> 00:07:05.550 You saw your homework questions. 00:07:05.550 --> 00:07:08.410 How many atoms per unit length? 00:07:08.410 --> 00:07:10.210 And we said what's the linear density? 00:07:10.210 --> 00:07:11.530 And some people were saying, but density is 00:07:11.530 --> 00:07:12.460 mass per unit volume. 00:07:12.460 --> 00:07:15.370 No, I'm counting atoms per unit length. 00:07:15.370 --> 00:07:17.940 Open your mind, OK? 00:07:17.940 --> 00:07:20.060 So bond strength, what's bond density? 00:07:20.060 --> 00:07:22.460 That's atoms per unit area. 00:07:22.460 --> 00:07:25.380 So we can calculate this and we're way off. 00:07:25.380 --> 00:07:28.090 We're way off by about a factor of 10. 00:07:28.090 --> 00:07:30.820 So it was the dislocation that allowed us to 00:07:30.820 --> 00:07:32.650 explain why this happens. 00:07:32.650 --> 00:07:37.870 And it was the work of two scientists, one by the name of 00:07:37.870 --> 00:07:44.490 Orowan in Hungary and Taylor in the UK. 00:07:44.490 --> 00:07:49.290 Orowan, after World War II, went to the UK and then 00:07:49.290 --> 00:07:50.755 ultimately came to MIT. 00:07:50.755 --> 00:07:54.550 And he spent most of this later part of his career here 00:07:54.550 --> 00:07:56.350 in the Mechanical Engineering Department, 00:07:56.350 --> 00:07:58.300 from which he retired. 00:07:58.300 --> 00:08:00.880 And actually, he's too modest to say it, but Professor 00:08:00.880 --> 00:08:06.000 Demkowicz, his PhD was for Professor Argon, and Professor 00:08:06.000 --> 00:08:08.630 Argon was one of Orowan's students. 00:08:08.630 --> 00:08:10.760 So this is direct lineage. 00:08:10.760 --> 00:08:15.180 This is all very clear, so he was the appropriate person to 00:08:15.180 --> 00:08:16.770 introduce dislocations. 00:08:16.770 --> 00:08:18.210 So what did Orowan do? 00:08:18.210 --> 00:08:21.840 Orowan came up with this idea of an interruption. 00:08:21.840 --> 00:08:22.790 And how did he get it? 00:08:22.790 --> 00:08:26.770 It shows how to look around and, in 00:08:26.770 --> 00:08:30.270 the world, see analogies. 00:08:30.270 --> 00:08:32.830 Now, we didn't have the powerful electron microscopes 00:08:32.830 --> 00:08:33.760 then that we have today. 00:08:33.760 --> 00:08:36.900 This was in the 1930s, so people didn't even agree on an 00:08:36.900 --> 00:08:38.980 atomic view of things. 00:08:38.980 --> 00:08:42.610 So people were thinking, thinking, thinking. 00:08:42.610 --> 00:08:43.900 So this is the dislocation. 00:08:43.900 --> 00:08:44.540 You can see. 00:08:44.540 --> 00:08:46.930 Here, we have three rows of atoms, now there's two rows of 00:08:46.930 --> 00:08:49.510 atoms. The middle row stops there. 00:08:49.510 --> 00:08:51.750 And I'll show you what the consequence of that is in 00:08:51.750 --> 00:08:56.040 terms of being able to shear the crystal of lower values of 00:08:56.040 --> 00:08:57.720 applied stress. 00:08:57.720 --> 00:08:59.390 So that's the dislocation. 00:08:59.390 --> 00:09:00.260 You can see here. 00:09:00.260 --> 00:09:03.820 If you break this bond and then propagate that through, 00:09:03.820 --> 00:09:05.180 you don't have to shear them all. 00:09:05.180 --> 00:09:08.590 You break them one at a time. 00:09:08.590 --> 00:09:12.500 So Orowan came home one day in Budapest, and the cleaning 00:09:12.500 --> 00:09:17.760 woman was moving the runner on a hallway, the story goes, and 00:09:17.760 --> 00:09:20.120 she was about to move the runner. 00:09:20.120 --> 00:09:22.700 And Orowan came up the stairs and offered to help her, and 00:09:22.700 --> 00:09:25.440 she told him, get out of the way. 00:09:25.440 --> 00:09:26.320 Academic. 00:09:26.320 --> 00:09:30.140 And what she did, instead of pulling the rug, she did what 00:09:30.140 --> 00:09:31.820 we see in the cartoon here. 00:09:31.820 --> 00:09:34.810 She put a little kink in the rug, snapped her foot and 00:09:34.810 --> 00:09:38.400 propagated the kink and moved the rug a half a foot down the 00:09:38.400 --> 00:09:40.710 hallway with minimal energy. 00:09:40.710 --> 00:09:43.720 Instead of having to pull the rug with it's coefficient of 00:09:43.720 --> 00:09:47.150 fraction over three, four meters, all she had to do was 00:09:47.150 --> 00:09:48.970 come up with enough energy to make the kink and 00:09:48.970 --> 00:09:50.010 then stamp the foot. 00:09:50.010 --> 00:09:52.120 This person's really doing it the hard way. 00:09:52.120 --> 00:09:52.750 I don't know. 00:09:52.750 --> 00:09:54.070 This guy must have taken classes in 00:09:54.070 --> 00:09:55.030 chemistry or something. 00:09:55.030 --> 00:09:57.290 But see, all you've got to do-- 00:09:57.290 --> 00:09:59.310 once you get that kind you just push 00:09:59.310 --> 00:10:01.600 and it'll go by itself. 00:10:01.600 --> 00:10:05.660 So Orowan said could this be a metaphor for what's going on 00:10:05.660 --> 00:10:07.350 at the atomic level? 00:10:07.350 --> 00:10:09.070 And that's where it came up with this idea of the 00:10:09.070 --> 00:10:10.320 dislocation. 00:10:12.080 --> 00:10:13.860 So there we have it. 00:10:17.370 --> 00:10:19.990 So where do we find the dislocations? 00:10:19.990 --> 00:10:21.070 Where do we find them? 00:10:21.070 --> 00:10:21.790 So what is it? 00:10:21.790 --> 00:10:22.810 The dislocation-- 00:10:22.810 --> 00:10:24.980 I keep talking about it, what is it? 00:10:24.980 --> 00:10:29.920 The dislocation, this is, if you like, it's a line defect. 00:10:29.920 --> 00:10:44.050 It's a line defect formed by misregistry of atoms. And with 00:10:44.050 --> 00:10:51.005 the misregistry, that leads to a reduction in bond density. 00:11:01.950 --> 00:11:05.800 And that broken bond is like the hole, if you like, in the 00:11:05.800 --> 00:11:07.610 valence band. 00:11:07.610 --> 00:11:09.385 It can propagate very easily. 00:11:12.380 --> 00:11:14.840 We're going to learn a little bit later in the lecture where 00:11:14.840 --> 00:11:18.650 we find dislocations and how they contribute. 00:11:18.650 --> 00:11:22.700 But I want you to hold that in near-term memory. 00:11:22.700 --> 00:11:23.070 OK. 00:11:23.070 --> 00:11:24.950 So we're going down the list of the 00:11:24.950 --> 00:11:28.630 different types of defects. 00:11:28.630 --> 00:11:31.950 Oh here, I found this off a coffee table book that's 00:11:31.950 --> 00:11:33.640 indicating-- 00:11:33.640 --> 00:11:34.865 I think this is a crummy analogy. 00:11:34.865 --> 00:11:37.320 It shows this caterpillar moving by. 00:11:37.320 --> 00:11:40.200 Instead of moving all of its legs, it causes this thing-- 00:11:40.200 --> 00:11:42.980 I think this is a bad analogy. 00:11:42.980 --> 00:11:43.790 Just look down here. 00:11:43.790 --> 00:11:45.370 You see, you breaking this. 00:11:45.370 --> 00:11:48.440 And once you break this, you just keep moving it along. 00:11:48.440 --> 00:11:51.030 Propagate the single broken bond instead of breaking them 00:11:51.030 --> 00:11:54.200 all at once. 00:11:54.200 --> 00:11:58.100 I don't think the caterpillar moves that way, anyway. 00:11:58.100 --> 00:12:00.950 It's cute, but it's wrong. 00:12:00.950 --> 00:12:03.030 This is a dislocation. 00:12:03.030 --> 00:12:04.490 I don't think it has anything to do with mechanical 00:12:04.490 --> 00:12:07.100 behavior, but it's a misregistry. 00:12:07.100 --> 00:12:07.890 So you can-- 00:12:07.890 --> 00:12:11.060 these guys, they write the books and they come up with 00:12:11.060 --> 00:12:12.590 this stuff and you study it, and you're 00:12:12.590 --> 00:12:13.520 going, I don't get it. 00:12:13.520 --> 00:12:13.980 You know what? 00:12:13.980 --> 00:12:14.820 You shouldn't get it. 00:12:14.820 --> 00:12:15.770 Because this is crummy. 00:12:15.770 --> 00:12:17.020 It doesn't make any sense. 00:12:20.440 --> 00:12:23.690 How does that impact the yield stress of the corn? 00:12:26.330 --> 00:12:27.980 Someday you could write a book. 00:12:27.980 --> 00:12:29.560 Better one than this. 00:12:29.560 --> 00:12:30.580 All right, so now we're going to go to 00:12:30.580 --> 00:12:31.830 two-dimensional defects. 00:12:31.830 --> 00:12:34.170 Let's go to two-dimensional defects. 00:12:34.170 --> 00:12:38.680 So two-dimensional defects, there's a couple types. 00:12:38.680 --> 00:12:40.960 The dislocation is one dimensional. 00:12:40.960 --> 00:12:42.210 Two-dimensional defects. 00:12:45.220 --> 00:12:46.030 There's two types. 00:12:46.030 --> 00:12:48.250 One is the free surface. 00:12:48.250 --> 00:12:50.470 We're going to call the free surface a defect, and I'll 00:12:50.470 --> 00:12:51.970 explain why in a second. 00:12:51.970 --> 00:12:54.630 And then internal surfaces. 00:12:54.630 --> 00:12:55.670 Internal-- 00:12:55.670 --> 00:12:58.250 I'm going to use surface in quotation marks-- they're 00:12:58.250 --> 00:12:59.500 interfaces. 00:12:59.500 --> 00:13:02.740 And there's different types of them, OK? 00:13:02.740 --> 00:13:05.710 An interface. 00:13:05.710 --> 00:13:07.630 There's an interface inside the thing. 00:13:07.630 --> 00:13:09.400 So what's the physics here? 00:13:09.400 --> 00:13:11.660 Surfaces are high-energy regions. 00:13:11.660 --> 00:13:12.410 Why? 00:13:12.410 --> 00:13:16.020 Because when you're inside the crystal, you have the 00:13:16.020 --> 00:13:18.250 prescribed number of nearest neighbors. 00:13:18.250 --> 00:13:19.950 Let's say you're in an FCC crystal. 00:13:19.950 --> 00:13:21.350 You're an aluminum atom. 00:13:21.350 --> 00:13:23.560 So you're an aluminum atom and you've got 12 nearest 00:13:23.560 --> 00:13:26.180 neighbors because you're FCC, except if 00:13:26.180 --> 00:13:27.410 you're at the free surface. 00:13:27.410 --> 00:13:29.810 If you're an aluminum atom at the free surface you don't 00:13:29.810 --> 00:13:30.920 have 12 nearest neighbors. 00:13:30.920 --> 00:13:33.770 Because if I look down I've got aluminum atoms all over. 00:13:33.770 --> 00:13:36.130 If I look up, I've got nothing. 00:13:36.130 --> 00:13:38.740 So axiomatically, I've got a different number of bonds. 00:13:38.740 --> 00:13:39.775 Why do we form bonds? 00:13:39.775 --> 00:13:42.240 We form bonds in order to lower the 00:13:42.240 --> 00:13:43.480 energy of the system. 00:13:43.480 --> 00:13:46.850 But axiomatically, the ones at the top can't form the same 00:13:46.850 --> 00:13:48.530 number of bonds, so they are not in the 00:13:48.530 --> 00:13:50.820 same low energy state. 00:13:50.820 --> 00:13:55.520 So once you get the connection between lower number of bonds, 00:13:55.520 --> 00:13:59.590 higher energy state, then any place, free surface, internal 00:13:59.590 --> 00:14:04.010 surface, is going to be relatively high energy. 00:14:04.010 --> 00:14:15.570 Relatively higher energy than atoms in the matrix. 00:14:15.570 --> 00:14:16.080 Matrix. 00:14:16.080 --> 00:14:17.060 What do I mean by matrix? 00:14:17.060 --> 00:14:19.900 In the middle of a crystal. 00:14:19.900 --> 00:14:21.820 In the matrix, OK? 00:14:21.820 --> 00:14:27.200 So that means that it's not quite as tightly bound, so the 00:14:27.200 --> 00:14:31.550 consequence of this is if they're high-energy regions, 00:14:31.550 --> 00:14:34.410 so high-energy implies higher reactivity. 00:14:37.870 --> 00:14:40.950 And that can be good or it can be bad. 00:14:40.950 --> 00:14:46.870 It can be good if you're trying to design a catalyst. 00:14:46.870 --> 00:14:49.590 And it can be bad in the case of corrosion. 00:14:49.590 --> 00:14:51.170 Where do you think corrosion occurs? 00:14:51.170 --> 00:14:52.620 Not deep inside the crystal. 00:14:52.620 --> 00:14:56.340 It occurs at the surface along the grain boundary. 00:14:56.340 --> 00:14:59.160 So here's a cartoon that shows different 00:14:59.160 --> 00:15:01.070 regions within the crystal. 00:15:01.070 --> 00:15:03.550 And Professor Demkowicz showed you on Friday-- 00:15:03.550 --> 00:15:07.060 and I'll cut to the thing in a second, the Atomix. 00:15:07.060 --> 00:15:10.520 but here we see atoms. So this is a simple cubic, this is 00:15:10.520 --> 00:15:11.970 simple cubic, this is simple cubic. 00:15:11.970 --> 00:15:15.050 But when they meet they don't line up. 00:15:15.050 --> 00:15:17.700 They don't line up because this formed from 00:15:17.700 --> 00:15:19.340 solidification from the melt. 00:15:19.340 --> 00:15:21.300 So there might have been a seed here 00:15:21.300 --> 00:15:22.170 and it grows outward. 00:15:22.170 --> 00:15:23.480 A seed here and it grows outward. 00:15:23.480 --> 00:15:24.680 A seed here and it grows outward. 00:15:24.680 --> 00:15:27.290 And when they grow outward they impinge, but they're not 00:15:27.290 --> 00:15:29.300 all growing with the same orientation. 00:15:29.300 --> 00:15:31.350 You already know what the planes are. 00:15:31.350 --> 00:15:32.990 And they could even be the same plane, but they're 00:15:32.990 --> 00:15:35.810 starting from a different point. 00:15:35.810 --> 00:15:38.240 So there's this misregistry here. 00:15:38.240 --> 00:15:40.490 But it's not a misregistry like the dislocation. 00:15:40.490 --> 00:15:42.460 It's a two dimensional misregistry. 00:15:42.460 --> 00:15:44.810 Actually, let's cut to the document camera. 00:15:44.810 --> 00:15:46.060 Dave, could we do that please? 00:15:48.500 --> 00:15:50.020 OK, so here's Atomix. 00:15:50.020 --> 00:15:55.820 This was, as explained, an object of art made by Francois 00:15:55.820 --> 00:15:59.330 Dallegret in Quebec in the '60s. 00:15:59.330 --> 00:16:00.270 So it's kinetic. 00:16:00.270 --> 00:16:03.390 It's supposed to be after the artist, see? 00:16:03.390 --> 00:16:04.040 You know, you, too. 00:16:04.040 --> 00:16:05.940 You pick it up on a coffee table, you put it down, now 00:16:05.940 --> 00:16:09.930 you have become the artist. You become the artist. 00:16:09.930 --> 00:16:11.330 Postmodernism. 00:16:11.330 --> 00:16:12.890 After the death of the artist. See? 00:16:12.890 --> 00:16:13.950 I'm an artist. Look. 00:16:13.950 --> 00:16:17.720 I'm an artist. One of my best works. 00:16:17.720 --> 00:16:21.130 So a couple of my professors at the University of Toronto 00:16:21.130 --> 00:16:23.680 were at a cocktail party one night and they saw this thing 00:16:23.680 --> 00:16:24.490 on a table. 00:16:24.490 --> 00:16:26.380 Must've been a wild party because they kept looking at 00:16:26.380 --> 00:16:27.110 this thing. 00:16:27.110 --> 00:16:29.740 Finally decided to write a paper about it. 00:16:29.740 --> 00:16:33.230 And as Professor Demkowicz said, I bet Francois Dallegret 00:16:33.230 --> 00:16:36.340 sold more of these to professors of material science 00:16:36.340 --> 00:16:38.640 than he sold to art collectors. 00:16:38.640 --> 00:16:41.460 So it's 200 ball bearings strategically placed between 00:16:41.460 --> 00:16:43.110 two plates of plexiglass. 00:16:43.110 --> 00:16:45.940 And as he pointed out on Friday, you can't get 00:16:45.940 --> 00:16:49.210 everything to go away in terms of dislocations, but now you 00:16:49.210 --> 00:16:51.200 can see misregistry-- 00:16:51.200 --> 00:16:53.640 pardon me, vacancies here. 00:16:53.640 --> 00:16:55.480 Here's a stacking fault and so on. 00:16:55.480 --> 00:16:57.210 And now here you see grain boundaries. 00:16:57.210 --> 00:16:58.280 There's the free surface. 00:16:58.280 --> 00:16:59.630 Here's the vapor phase. 00:16:59.630 --> 00:17:00.100 Everything. 00:17:00.100 --> 00:17:00.980 We're having a lot of fun, here. 00:17:00.980 --> 00:17:03.020 So we can look at it again. 00:17:03.020 --> 00:17:03.690 We can change. 00:17:03.690 --> 00:17:04.670 We'll try to anneal it. 00:17:04.670 --> 00:17:06.100 So how do we anneal it? 00:17:06.100 --> 00:17:07.880 You put it in an oven and you eat it. 00:17:07.880 --> 00:17:11.370 This is the mechanical equivalent of annealing. 00:17:11.370 --> 00:17:13.930 I'm tapping it, for those of you in the back. 00:17:13.930 --> 00:17:18.180 Now, I'm going to put it down and you see I have a much more 00:17:18.180 --> 00:17:20.070 refined structure. 00:17:20.070 --> 00:17:22.210 So now you can see a large section 00:17:22.210 --> 00:17:24.070 here of a single crystal. 00:17:24.070 --> 00:17:26.010 Each one of these is called a grain. 00:17:26.010 --> 00:17:28.200 A grain is a zone that is a single 00:17:28.200 --> 00:17:30.200 crystal with some defects. 00:17:30.200 --> 00:17:31.510 You can see the vacancies. 00:17:31.510 --> 00:17:33.390 And then look at the grain boundary here. 00:17:33.390 --> 00:17:36.370 See this is a nice crystal, this is a nice crystal. 00:17:36.370 --> 00:17:39.160 So one grain, two grains, and there's the grain boundary 00:17:39.160 --> 00:17:41.340 where these don't line up with those. 00:17:41.340 --> 00:17:44.510 Because they started from a different angle so they can't 00:17:44.510 --> 00:17:46.290 impinge and blend. 00:17:46.290 --> 00:17:48.460 There's grain boundaries here, here, here, and there's 00:17:48.460 --> 00:17:49.670 beautiful stuff. 00:17:49.670 --> 00:17:51.700 You can see dislocations. 00:17:51.700 --> 00:17:52.150 Everything. 00:17:52.150 --> 00:17:55.230 And I know he showed you at the end the Bragg bubble wrap. 00:17:55.230 --> 00:17:55.660 And you could see-- 00:17:55.660 --> 00:17:56.770 [SOUND EFFECT] 00:17:56.770 --> 00:17:58.200 PROFESSOR: --dislocations zipping. 00:17:58.200 --> 00:18:00.720 When people were trying to compress the bubble wrap, the 00:18:00.720 --> 00:18:03.830 way the bubble wrap was compressing the bubbles didn't 00:18:03.830 --> 00:18:05.490 all get flat. 00:18:05.490 --> 00:18:09.790 The bubbled glided over one another, and the dislocations 00:18:09.790 --> 00:18:12.840 relieved the stress. 00:18:12.840 --> 00:18:14.090 See what I'm telling you here? 00:18:14.090 --> 00:18:16.390 What I'm telling you here is something that you don't get 00:18:16.390 --> 00:18:18.380 in a Gen Chem class anywhere else. 00:18:18.380 --> 00:18:21.440 If I told you about the chemical origins of 00:18:21.440 --> 00:18:23.920 reactivity, you'd go, yeah, that's chemistry. 00:18:23.920 --> 00:18:25.470 But what are we talking about here? 00:18:25.470 --> 00:18:27.430 We're talking about the chemical origins 00:18:27.430 --> 00:18:29.450 of mechanical behavior. 00:18:29.450 --> 00:18:31.900 Now that's different. 00:18:31.900 --> 00:18:33.610 The chemical origins of mechanical 00:18:33.610 --> 00:18:36.420 behavior: only in 3.091. 00:18:36.420 --> 00:18:37.320 And why shouldn't we? 00:18:37.320 --> 00:18:40.300 Because at the end, everything is chemistry. 00:18:40.300 --> 00:18:41.700 Everything is chemistry. 00:18:41.700 --> 00:18:45.540 The rest is stamp collecting. 00:18:45.540 --> 00:18:47.710 So the grain-- 00:18:47.710 --> 00:18:49.060 make sure we know where the grain is. 00:18:49.060 --> 00:18:53.130 The grain is like, I want to call single crystal. 00:18:53.130 --> 00:18:55.820 The grain is like a single crystal. 00:18:55.820 --> 00:18:59.310 And the grains are separated by grain boundaries. 00:18:59.310 --> 00:19:03.350 So by managing grain boundaries, control of grain 00:19:03.350 --> 00:19:09.040 boundaries, or if you like, management a grain boundaries, 00:19:09.040 --> 00:19:14.620 this has an impact on mechanical properties. 00:19:14.620 --> 00:19:17.810 This is called grain boundary engineering. 00:19:17.810 --> 00:19:21.130 How we control mechanical properties. 00:19:21.130 --> 00:19:23.890 Grain boundary engineering. 00:19:23.890 --> 00:19:28.065 So for example, if we want high strength-- 00:19:33.770 --> 00:19:37.800 and I just told you that the dislocations will allow the 00:19:37.800 --> 00:19:38.880 atoms to glide. 00:19:38.880 --> 00:19:41.760 Can you see that if the dislocation is present in this 00:19:41.760 --> 00:19:45.320 large grain on the bottom here and the dislocation, just as 00:19:45.320 --> 00:19:48.470 in the bubble wrap movie, is zipping across, what happens 00:19:48.470 --> 00:19:50.730 when it gets to the grain boundary? 00:19:50.730 --> 00:19:53.010 The misregistry of atoms stops that 00:19:53.010 --> 00:19:55.730 dislocation dead in its tracks. 00:19:55.730 --> 00:19:58.720 So if I want high strength, do I want a large number of grain 00:19:58.720 --> 00:20:00.180 boundaries per unit area? 00:20:00.180 --> 00:20:03.380 Or a small number of grain boundaries per unit area if my 00:20:03.380 --> 00:20:06.440 goal is to stop the dislocations? 00:20:06.440 --> 00:20:08.200 I want a high number. 00:20:08.200 --> 00:20:12.530 High strength means fine grain structure. 00:20:12.530 --> 00:20:16.110 Fine grained means small grain size. 00:20:16.110 --> 00:20:17.360 Fine grain structure. 00:20:19.840 --> 00:20:21.460 You can think of it as like a river. 00:20:21.460 --> 00:20:23.220 You know, you're running, running, running-- all of a 00:20:23.220 --> 00:20:28.010 sudden, you stop because you've got to ford the river. 00:20:28.010 --> 00:20:30.200 On the other hand, if you want high ductility-- 00:20:33.030 --> 00:20:34.370 why would you want ductility? 00:20:34.370 --> 00:20:37.410 For example, you want to make a beverage container. 00:20:37.410 --> 00:20:39.350 How do you make a beverage container? 00:20:39.350 --> 00:20:40.500 Not by casting. 00:20:40.500 --> 00:20:44.910 You take a sheet of aluminum and you punch it and you cause 00:20:44.910 --> 00:20:46.190 it to deep draw. 00:20:46.190 --> 00:20:48.610 That's atoms sliding over atoms. 00:20:48.610 --> 00:20:51.400 So do I want to facilitate that process or do I want to 00:20:51.400 --> 00:20:52.630 impede the process? 00:20:52.630 --> 00:20:55.210 Well, to facilitate the process, I want to make it as 00:20:55.210 --> 00:20:57.730 easy as possible for those atoms to 00:20:57.730 --> 00:20:59.320 glide over one another. 00:20:59.320 --> 00:21:01.820 So high ductility means coarse grain structure. 00:21:07.330 --> 00:21:12.970 Coarse grain means large, if you 00:21:12.970 --> 00:21:14.920 like, large grain diameter. 00:21:14.920 --> 00:21:21.330 Fine grain structure means small diameter. 00:21:21.330 --> 00:21:23.510 So there we go. 00:21:23.510 --> 00:21:24.190 That's the beginning. 00:21:24.190 --> 00:21:26.960 And there's a lot more to it, but I just wanted you to see 00:21:26.960 --> 00:21:27.730 that there is something. 00:21:27.730 --> 00:21:30.430 And David, may we cut back to the slides, please? 00:21:34.150 --> 00:21:35.660 OK, I think the next one shows. 00:21:35.660 --> 00:21:38.480 All right, so this is a-- 00:21:38.480 --> 00:21:39.500 oh, we don't want to hear that. 00:21:39.500 --> 00:21:41.630 Whoops! 00:21:41.630 --> 00:21:43.050 Well, I've got music embedded in this one. 00:21:43.050 --> 00:21:44.450 This is Philip Glass. 00:21:44.450 --> 00:21:45.170 [MUSIC PLAYING] 00:21:45.170 --> 00:21:47.430 PROFESSOR: Because we're going to talk about glasses later. 00:21:47.430 --> 00:21:48.660 Koyaanisqatsi. 00:21:48.660 --> 00:21:49.480 It's beautiful. 00:21:49.480 --> 00:21:50.540 Can you feel the bass? 00:21:50.540 --> 00:21:52.020 There's the subwoofer right here. 00:21:52.020 --> 00:21:53.652 You stand right here. 00:21:53.652 --> 00:21:56.780 It's like a message. 00:21:56.780 --> 00:21:58.290 Low frequency, of course. 00:21:58.290 --> 00:21:59.260 All right, so here's this. 00:21:59.260 --> 00:22:01.430 But this is a piece of copper. 00:22:01.430 --> 00:22:05.090 Now, this was the advent of modern materials 00:22:05.090 --> 00:22:08.810 characterization when Sorby, in the late 1800s, figured out 00:22:08.810 --> 00:22:12.750 that if you polish the piece of metal supersmooth-- 00:22:12.750 --> 00:22:14.500 that's good, huh? 00:22:14.500 --> 00:22:16.330 Maybe we better turn the volume down. 00:22:16.330 --> 00:22:17.230 I can't compete with these. 00:22:17.230 --> 00:22:18.340 There's more of them than me. 00:22:18.340 --> 00:22:19.900 I can't compete. 00:22:19.900 --> 00:22:22.090 That's called the mute button. 00:22:22.090 --> 00:22:22.550 [MUSIC ENDS] 00:22:22.550 --> 00:22:23.570 PROFESSOR: So what did he do? 00:22:23.570 --> 00:22:28.160 He polished the copper and then he etched it. 00:22:28.160 --> 00:22:30.910 And what happens with an acid etch? 00:22:30.910 --> 00:22:33.540 It will etch at different rates because the different 00:22:33.540 --> 00:22:35.830 grains have different atom densities. 00:22:35.830 --> 00:22:39.460 You see, if I take a piece of metal and I polish it super, 00:22:39.460 --> 00:22:42.470 super bright and I shine a light on it and look at it in 00:22:42.470 --> 00:22:43.980 a microscope, what am I going to see? 00:22:43.980 --> 00:22:45.900 I'm going to see my eyeball, right? 00:22:45.900 --> 00:22:46.910 I'll blind myself. 00:22:46.910 --> 00:22:48.930 So the key was to etch. 00:22:48.930 --> 00:22:50.330 And then when you etch, you differentiate 00:22:50.330 --> 00:22:52.120 the different grains. 00:22:52.120 --> 00:22:53.970 So that's what you're looking at-- the grain boundaries. 00:22:53.970 --> 00:22:56.740 And this is now the same thing, only under a field ion 00:22:56.740 --> 00:22:57.280 microscope. 00:22:57.280 --> 00:22:59.130 This is a bicrystal of tungsten. 00:22:59.130 --> 00:23:01.290 It's hard to see, but this is all one. 00:23:01.290 --> 00:23:03.150 This looks like a lolly pattern, doesn't it? 00:23:03.150 --> 00:23:04.620 You can see the symmetry here. 00:23:04.620 --> 00:23:05.750 I don't know if you can see right here. 00:23:05.750 --> 00:23:08.690 There's a line, sort of v-shaped here. 00:23:08.690 --> 00:23:09.990 And that's the second crystal. 00:23:09.990 --> 00:23:12.940 So there's one crystal here, a second crystal here. 00:23:12.940 --> 00:23:15.115 So this two-dimensional defect is now characterized. 00:23:18.600 --> 00:23:20.550 And we'll get to that later. 00:23:20.550 --> 00:23:20.820 OK. 00:23:20.820 --> 00:23:23.760 So now we want to do three-dimensional defects. 00:23:23.760 --> 00:23:25.420 What are the three-dimensional defects? 00:23:25.420 --> 00:23:31.140 Three-dimensional defects are important. 00:23:31.140 --> 00:23:37.190 And they have beneficial and they have harmful 00:23:37.190 --> 00:23:38.580 consequences. 00:23:38.580 --> 00:23:40.760 Three-dimensional defects. 00:23:40.760 --> 00:23:44.430 The dominant mechanism here is coalescence. 00:23:44.430 --> 00:23:48.580 So three-dimensional defects formed by coalescence. 00:23:51.800 --> 00:23:53.340 And you can coalesce two things. 00:23:53.340 --> 00:23:59.982 You can coalesce voids, or you can coalesce-- 00:23:59.982 --> 00:24:04.240 actually, you can coalesce void, and you can coalesce-- 00:24:04.240 --> 00:24:06.520 I'm going to use Democritus talk here. 00:24:06.520 --> 00:24:09.815 You can coalesce void, or you can coalesce being. 00:24:12.870 --> 00:24:13.930 What do I mean by that? 00:24:13.930 --> 00:24:18.560 Well, void, this could be a vacancy cluster. 00:24:18.560 --> 00:24:22.550 So if you have a large number of vacancies coalescing, 00:24:22.550 --> 00:24:25.200 you'll actually end up with a hole, a blow 00:24:25.200 --> 00:24:26.520 hole inside the material. 00:24:26.520 --> 00:24:28.580 And as you can imagine, that has the 00:24:28.580 --> 00:24:30.960 mechanical strength of nothing. 00:24:30.960 --> 00:24:33.310 That's bad. 00:24:33.310 --> 00:24:34.560 And being? 00:24:36.760 --> 00:24:38.457 This could be impurity clusters. 00:24:41.800 --> 00:24:44.070 And there's two types of impurities, as we've learned. 00:24:44.070 --> 00:24:46.880 There are good impurities, such as dopants, and there are 00:24:46.880 --> 00:24:52.220 bad impurities such as contaminants. 00:24:52.220 --> 00:24:54.330 And what can they do to the mechanical 00:24:54.330 --> 00:24:57.550 properties if they are bad? 00:24:57.550 --> 00:25:00.620 So what I like to say is impurity clusters-- 00:25:00.620 --> 00:25:03.410 so we've got, for example, there are good 00:25:03.410 --> 00:25:05.580 ones that are managed. 00:25:05.580 --> 00:25:09.260 The ones that are managed can be used to our advantage. 00:25:09.260 --> 00:25:11.430 So I'm going to say the managed ones get a smiley 00:25:11.430 --> 00:25:14.770 face, and the ones that are uncontrolled-- 00:25:14.770 --> 00:25:16.440 I'll give you a vivid example of that at 00:25:16.440 --> 00:25:17.680 the end of the lecture. 00:25:17.680 --> 00:25:21.700 Uncontrolled, they get a frowny face, and they can lead 00:25:21.700 --> 00:25:26.020 to major disasters. 00:25:26.020 --> 00:25:30.930 So for example, you're really talking about clusters that 00:25:30.930 --> 00:25:32.980 exsolve as a separate phase. 00:25:32.980 --> 00:25:36.110 So these things exist as a separate phase. 00:25:44.170 --> 00:25:46.160 So they're no longer dissolved. 00:25:46.160 --> 00:25:52.000 And these precipitates, some of these impurity clusters, if 00:25:52.000 --> 00:25:54.050 they're managed, we can call them precipitates. 00:25:58.880 --> 00:26:01.350 i'll give you an example of precipitates. 00:26:01.350 --> 00:26:04.860 Some of you might be going home at some point in the not 00:26:04.860 --> 00:26:07.230 too distant future, maybe for Thanksgiving. 00:26:07.230 --> 00:26:10.740 And if you're flying on an airplane, the airplane is made 00:26:10.740 --> 00:26:12.240 of an aluminum alloy. 00:26:12.240 --> 00:26:13.550 Aluminum copper. 00:26:13.550 --> 00:26:17.560 And one of the precipitates that you can form is various 00:26:17.560 --> 00:26:21.290 copper-aluminum compounds. 00:26:21.290 --> 00:26:27.240 And these form precipitates that the volume of 00:26:27.240 --> 00:26:33.680 copper-aluminum 2 is greater than the volume of the 00:26:33.680 --> 00:26:35.450 constituents. 00:26:35.450 --> 00:26:38.700 So if you take a copper atom and two aluminum atoms in the 00:26:38.700 --> 00:26:41.940 lattice and they react to form copper-aluminum 2, there's a 00:26:41.940 --> 00:26:43.120 volume increase. 00:26:43.120 --> 00:26:47.120 And so that works to give you constituents. 00:26:47.120 --> 00:26:47.720 Isn't that great? 00:26:47.720 --> 00:26:50.560 I left you in suspense there as to rest of the word. 00:26:50.560 --> 00:26:51.480 So what happens? 00:26:51.480 --> 00:26:54.460 This works a little bit the way carbon does in iron, where 00:26:54.460 --> 00:26:57.530 carbon atom is bigger than the interstitial void space in 00:26:57.530 --> 00:27:02.570 iron, and that force fit leads to a strengthening. 00:27:02.570 --> 00:27:05.000 This leads to a strengthening, oK? 00:27:05.000 --> 00:27:06.250 So that's good. 00:27:08.520 --> 00:27:11.400 So this is called precipitation hardening. 00:27:11.400 --> 00:27:13.790 I'm just going write precipitation pptn, 00:27:13.790 --> 00:27:16.300 precipitation hardening. 00:27:16.300 --> 00:27:20.060 Very important in metallurgy. 00:27:20.060 --> 00:27:26.140 Whereas carbon in iron is called solution hardening. 00:27:26.140 --> 00:27:28.680 Because it doesn't exist as a separate phase. 00:27:28.680 --> 00:27:32.310 The carbon atom is sitting on an interstitial site so it's a 00:27:32.310 --> 00:27:34.760 force fit, but it's still within the lattice, whereas 00:27:34.760 --> 00:27:38.880 the copper-aluminum actually exists as a precipitate 00:27:38.880 --> 00:27:41.390 outside the lattice. 00:27:41.390 --> 00:27:43.940 So there we go. 00:27:43.940 --> 00:27:46.027 In order to give you a little bit more, I said we're going 00:27:46.027 --> 00:27:49.380 to talk about the chemical origins 00:27:49.380 --> 00:27:50.860 of mechanical behavior. 00:27:50.860 --> 00:27:55.350 And I want to show you how this all leads to 00:27:55.350 --> 00:27:57.990 strengthening, strengthening in terms of the yield. 00:27:57.990 --> 00:28:00.080 So let's talk about deformation and the 00:28:00.080 --> 00:28:02.260 relationship to chemistry. 00:28:02.260 --> 00:28:03.510 There's two types of deformation. 00:28:06.840 --> 00:28:10.900 And this really accounts for the importance of metals in 00:28:10.900 --> 00:28:12.640 the history of man. 00:28:12.640 --> 00:28:14.150 Why? 00:28:14.150 --> 00:28:16.660 Because they have this unique property. 00:28:16.660 --> 00:28:18.930 Until the modern era, when we discovered plastics. 00:28:18.930 --> 00:28:23.060 But until modern era, metals are deformable. 00:28:23.060 --> 00:28:26.700 They can deform without breaking. 00:28:26.700 --> 00:28:30.740 That's what made them so desirable as materials of 00:28:30.740 --> 00:28:32.240 construction. 00:28:32.240 --> 00:28:34.820 So I'm going to talk about deformation, 00:28:34.820 --> 00:28:35.750 how we deform them. 00:28:35.750 --> 00:28:39.950 So really, metallurgy consists of-- 00:28:39.950 --> 00:28:44.230 really, there's two major divisions of metallurgy. 00:28:44.230 --> 00:28:48.380 The first part is chemical, chemical metallurgy, and 00:28:48.380 --> 00:28:52.630 that's called dirt to metal. 00:28:52.630 --> 00:28:53.520 That's the conversion. 00:28:53.520 --> 00:28:55.670 This is the intensive chemistry. 00:28:55.670 --> 00:28:59.140 And then the second part is called physical metallurgy, 00:28:59.140 --> 00:29:01.130 which is what I'm going to talk about next. 00:29:01.130 --> 00:29:02.950 Physical, which is change of shape. 00:29:07.590 --> 00:29:09.690 That relies on the ductility. 00:29:09.690 --> 00:29:10.520 So deformation. 00:29:10.520 --> 00:29:12.290 There's two types of deformation. 00:29:12.290 --> 00:29:14.760 The first one is called elastic deformation. 00:29:17.720 --> 00:29:18.970 And it is reversible. 00:29:21.570 --> 00:29:24.055 So it is strain only under stress. 00:29:30.600 --> 00:29:34.820 Or if you like, displacement only under applied force. 00:29:34.820 --> 00:29:37.690 So this is Hooke's Law. 00:29:37.690 --> 00:29:38.940 Hooke's Law applies. 00:29:42.390 --> 00:29:44.520 So let's take a look. 00:29:44.520 --> 00:29:49.190 I'm going to draw a little curve here. 00:29:49.190 --> 00:29:50.460 You've seen this before. 00:29:50.460 --> 00:29:54.120 I'm going to draw one of these energy curves. 00:29:54.120 --> 00:30:01.230 So this is interatomic separation, which we might use 00:30:01.230 --> 00:30:03.050 the lower case r. 00:30:03.050 --> 00:30:06.210 And this is the potential energy that's stored between 00:30:06.210 --> 00:30:08.620 two atoms. Remember, when they're far apart, they want 00:30:08.620 --> 00:30:09.040 to attract. 00:30:09.040 --> 00:30:11.420 When they get too close together, their electronic 00:30:11.420 --> 00:30:12.250 shells repel. 00:30:12.250 --> 00:30:14.010 So we've got-- 00:30:14.010 --> 00:30:15.260 time for colored chalk-- 00:30:20.620 --> 00:30:22.790 we have the attractive component, 00:30:22.790 --> 00:30:26.350 which looks like this. 00:30:26.350 --> 00:30:28.770 And then we have the repulsive component, which looks 00:30:28.770 --> 00:30:31.090 something like this. 00:30:31.090 --> 00:30:33.090 And then we put the two of them together, and I think we 00:30:33.090 --> 00:30:37.060 did this for ions, but there's an analogous one for other 00:30:37.060 --> 00:30:40.340 materials, and so you add the two of these, and you 00:30:40.340 --> 00:30:44.550 eventually end up like this, where this is r naught. 00:30:44.550 --> 00:30:46.356 r naught, the optimum separation. 00:30:49.250 --> 00:30:52.310 Here's attraction, this is repulsion, 00:30:52.310 --> 00:30:53.500 et cetera, et cetera. 00:30:53.500 --> 00:30:56.230 So this is e minimum. 00:30:56.230 --> 00:30:57.450 We've seen all of that before. 00:30:57.450 --> 00:31:00.590 Now what's this have to do with mechanical behavior? 00:31:00.590 --> 00:31:03.660 Well, I'll take it just a little bit farther. 00:31:03.660 --> 00:31:05.110 And so I'm going to take the derivative of that 00:31:05.110 --> 00:31:06.700 and look at the force. 00:31:06.700 --> 00:31:08.510 All right, so now I'm going to take the first 00:31:08.510 --> 00:31:09.640 derivative of that. 00:31:09.640 --> 00:31:18.470 So this is going to be force, which is equal to de dr. Force 00:31:18.470 --> 00:31:21.150 is the derivative of energy. 00:31:21.150 --> 00:31:22.540 And what do I find? 00:31:22.540 --> 00:31:23.570 Well, look. 00:31:23.570 --> 00:31:27.270 If I take this derivative, below r equals r naught. 00:31:27.270 --> 00:31:28.490 I've got a negative slope. 00:31:28.490 --> 00:31:30.250 Above r equals r naught-- 00:31:30.250 --> 00:31:31.270 I have a positive slope. 00:31:31.270 --> 00:31:34.290 And at r equals r naught, zero slope. 00:31:34.290 --> 00:31:35.930 So I'm want to put that down here. 00:31:35.930 --> 00:31:41.780 So it's zero right at r equals r naught, and above r equals r 00:31:41.780 --> 00:31:43.470 naught it's positive, and below r equals 00:31:43.470 --> 00:31:47.110 r naught it's negative. 00:31:47.110 --> 00:31:50.410 Not to scale. 00:31:50.410 --> 00:31:52.510 But one thing is certain. 00:31:52.510 --> 00:31:55.330 It is positive above r equals r naught, negative below r 00:31:55.330 --> 00:31:58.010 equals r naught, and to a first approximation, I can 00:31:58.010 --> 00:32:07.270 linearize about r equals r naught, Or Emin. 00:32:07.270 --> 00:32:09.410 So what's the real shape of this thing? 00:32:09.410 --> 00:32:11.770 You could use a Taylor series if you want. 00:32:11.770 --> 00:32:13.820 And just take the first-- what's the first term of a 00:32:13.820 --> 00:32:14.410 Taylor series? 00:32:14.410 --> 00:32:14.960 Constant. 00:32:14.960 --> 00:32:16.360 Second term, linear. 00:32:16.360 --> 00:32:18.780 Third term is squared, da, da, da, da. 00:32:18.780 --> 00:32:22.270 So neglect higher order terms. You get a straight line. 00:32:22.270 --> 00:32:23.960 And what does this mean? 00:32:23.960 --> 00:32:29.020 It means that if I try to disturb the atoms from one 00:32:29.020 --> 00:32:33.120 another and move them away from their rest position, 00:32:33.120 --> 00:32:36.260 there's a force that pulls them back, and the force is 00:32:36.260 --> 00:32:38.300 proportional to the displacement. 00:32:38.300 --> 00:32:42.990 If I move the atoms farther apart by a distance r1, I get 00:32:42.990 --> 00:32:44.010 a certain force. 00:32:44.010 --> 00:32:45.800 If I move them apart by r2-- 00:32:45.800 --> 00:32:47.010 2 times r1-- 00:32:47.010 --> 00:32:50.060 I get twice the force. 00:32:50.060 --> 00:32:50.960 It's linear. 00:32:50.960 --> 00:32:53.200 Now let's go over here. 00:32:53.200 --> 00:32:56.020 Now let's draw another analogy. 00:32:56.020 --> 00:33:01.880 So here I've got something that's pegged. 00:33:01.880 --> 00:33:05.500 And now I'm going to put a spring onto this secure wall. 00:33:05.500 --> 00:33:09.620 So here's my spring, and I'm going to hang 00:33:09.620 --> 00:33:12.050 a mass on the spring. 00:33:12.050 --> 00:33:13.550 Now I'm going to bring this into Hooke's Law. 00:33:13.550 --> 00:33:15.140 I'm going to show you that what you know to be Hooke's 00:33:15.140 --> 00:33:17.780 Law is a direct consequence of this. 00:33:17.780 --> 00:33:19.750 The atomic origin. 00:33:19.750 --> 00:33:20.970 So what's the force on this? 00:33:20.970 --> 00:33:23.620 There's a force on this, and that's equal to product of the 00:33:23.620 --> 00:33:26.580 mass times the gravitational constant. 00:33:26.580 --> 00:33:28.590 And if there were no mass, this spring would be 00:33:28.590 --> 00:33:30.820 compressed and it might be sitting here. 00:33:30.820 --> 00:33:32.710 I will call this x naught. 00:33:32.710 --> 00:33:35.660 And now that I put the spring here I'll 00:33:35.660 --> 00:33:37.835 measures, say, this point. 00:33:37.835 --> 00:33:41.250 And this point here is now at some value x. 00:33:41.250 --> 00:33:44.610 So this is the displacement, isn't it? 00:33:44.610 --> 00:33:46.140 This is the delta x. 00:33:46.140 --> 00:33:52.310 So Hooke's Law is simply f equals k delta x, isn't it? 00:33:52.310 --> 00:33:55.505 If I double the delta x, requires double the force. 00:33:55.505 --> 00:33:58.370 Well, that's this. 00:33:58.370 --> 00:34:00.310 This analogy goes right down. 00:34:00.310 --> 00:34:03.910 And if I remove the mass it springs back, which is what I 00:34:03.910 --> 00:34:05.620 meant when I said it's reversible. 00:34:05.620 --> 00:34:07.170 This is not permanent. 00:34:07.170 --> 00:34:08.990 No stress, no strain. 00:34:08.990 --> 00:34:10.330 Strain is the deformation. 00:34:10.330 --> 00:34:12.494 No deformation, no force. 00:34:12.494 --> 00:34:16.130 If I put a force, non-zero force, non-zero deformation. 00:34:16.130 --> 00:34:17.900 By the way, Hooke-- 00:34:17.900 --> 00:34:20.400 little bit of culture-- 00:34:20.400 --> 00:34:26.940 Hooke announced Hooke's Law in 1676. 00:34:26.940 --> 00:34:28.789 Here's how Hooke's Law was first published. 00:34:37.000 --> 00:34:41.020 It's an anagram and it's in Latin. 00:34:41.020 --> 00:34:45.000 And it was in a book entitled A Decimate of the Centesms of 00:34:45.000 --> 00:34:50.070 the Inventions I Intend to Reveal, which is English for, 00:34:50.070 --> 00:34:53.090 This is a Tenth of the Hundreds of the Inventions I 00:34:53.090 --> 00:34:53.650 Intend to Reveal. 00:34:53.650 --> 00:34:57.150 He did not suffer from an overabundance of modesty. 00:34:57.150 --> 00:35:01.240 Actually, Hooke and Newton sparred. 00:35:01.240 --> 00:35:02.780 They hated each other's guts. 00:35:02.780 --> 00:35:05.260 They fought bitterly. 00:35:05.260 --> 00:35:06.260 Two giant egos. 00:35:06.260 --> 00:35:07.540 Anyway, so here's the thing. 00:35:07.540 --> 00:35:15.380 So in 1679 he published a book called De Restitutiva. 00:35:15.380 --> 00:35:17.430 On The Spring. 00:35:17.430 --> 00:35:18.580 Very presumptuous. 00:35:18.580 --> 00:35:20.020 On The Spring. 00:35:20.020 --> 00:35:27.970 And here it is in its unraveled, ut tensio, sic vis. 00:35:27.970 --> 00:35:31.820 As the extension, so the force. 00:35:31.820 --> 00:35:32.670 Nice, huh? 00:35:32.670 --> 00:35:34.120 This is u. 00:35:34.120 --> 00:35:36.450 That's why the u, but it's really v. 00:35:36.450 --> 00:35:38.470 Vis. 00:35:38.470 --> 00:35:40.240 We get the English word vim from this. 00:35:40.240 --> 00:35:43.550 This is the accusative form of vis. 00:35:43.550 --> 00:35:46.910 The Romans didn't care between the u and v. 00:35:46.910 --> 00:35:51.090 In fact, if you go on the steps of 77 and you come up, 00:35:51.090 --> 00:35:55.330 it says Massachusetts Institute of Technology, you 00:35:55.330 --> 00:35:56.160 ever notice this? 00:35:56.160 --> 00:35:57.360 Yeah. 00:35:57.360 --> 00:35:58.710 I always thought that that's because the 00:35:58.710 --> 00:35:59.800 Romans, they couldn't-- 00:35:59.800 --> 00:36:00.110 no. 00:36:00.110 --> 00:36:02.560 And I thought, well, maybe it's because it's hard to make 00:36:02.560 --> 00:36:05.170 a u, but then it says Institute of-- 00:36:05.170 --> 00:36:07.020 I figure if you can make one of these, you should be able 00:36:07.020 --> 00:36:07.780 to make one of these. 00:36:07.780 --> 00:36:11.280 So if you can tell me why they do it that way, I might be 00:36:11.280 --> 00:36:13.530 able to find another Periodic Table beach towel. 00:36:13.530 --> 00:36:15.420 So that's another thing. 00:36:17.970 --> 00:36:18.270 All right. 00:36:18.270 --> 00:36:22.100 So that's the elastic deformation. 00:36:22.100 --> 00:36:24.770 And now we want to look at the other type of deformation, and 00:36:24.770 --> 00:36:26.373 that's called plastic deformation. 00:36:29.070 --> 00:36:30.320 And that's permanent. 00:36:35.200 --> 00:36:36.735 It's a permanent shape change. 00:36:39.240 --> 00:36:41.420 So let's get that up here. 00:36:41.420 --> 00:36:44.970 Permanent shape change. 00:36:44.970 --> 00:36:46.560 And this requires ductility. 00:36:46.560 --> 00:36:48.050 Because otherwise you'll have fracture. 00:36:48.050 --> 00:36:50.790 If you take something that has no ductility and you apply a 00:36:50.790 --> 00:36:53.640 super critical force, you just crack everything. 00:36:53.640 --> 00:36:56.670 So ductility allows for the atoms to 00:36:56.670 --> 00:36:59.670 glide over one another. 00:36:59.670 --> 00:37:00.920 So what is the mechanism? 00:37:05.620 --> 00:37:09.435 The mechanism for plastic deformation? 00:37:17.920 --> 00:37:20.700 Plastic deformation in crystals, we're talking about 00:37:20.700 --> 00:37:23.080 here, not liquids. 00:37:23.080 --> 00:37:25.280 It's called slip. 00:37:25.280 --> 00:37:27.230 Atom's slip over one another. 00:37:27.230 --> 00:37:30.780 So time for one more cartoon. 00:37:30.780 --> 00:37:33.270 So I'm going to say, well, what happens if I 00:37:33.270 --> 00:37:36.770 start again with this? 00:37:36.770 --> 00:37:40.170 I'm going to put a thin wire, a thin wire of metal. 00:37:40.170 --> 00:37:43.020 Make it an FCC metal, let's say it's copper, and I'm going 00:37:43.020 --> 00:37:44.730 to put a mass here-- 00:37:44.730 --> 00:37:46.180 a honking big mass-- 00:37:46.180 --> 00:37:49.250 it's going to give me a force, and the force is great enough 00:37:49.250 --> 00:37:52.820 that it is actually going to cause the wire to elongate. 00:37:52.820 --> 00:37:54.970 That is permanent shape change. 00:37:54.970 --> 00:37:56.430 So what's going on? 00:37:56.430 --> 00:37:58.790 Well, let's take this and blow it up. 00:37:58.790 --> 00:38:03.190 When we blow it up, we have what's on the screen. 00:38:03.190 --> 00:38:07.260 We have grains of different size. 00:38:07.260 --> 00:38:09.100 And I'm just going to show atomic planes. 00:38:09.100 --> 00:38:10.470 And that's why we have grains, right? 00:38:10.470 --> 00:38:13.510 Because the atomic planes don't line up. 00:38:13.510 --> 00:38:15.430 There's a misregistry along here. 00:38:20.160 --> 00:38:22.720 So now I want to go down to the atomic level. 00:38:22.720 --> 00:38:25.590 So now I'm going to take this and blow it up. 00:38:25.590 --> 00:38:26.970 And what do I see here? 00:38:26.970 --> 00:38:30.010 I see atoms like so. 00:38:30.010 --> 00:38:31.920 I'm going to use that hard-sphere, 00:38:31.920 --> 00:38:34.630 close-packed model. 00:38:34.630 --> 00:38:36.030 So here's the force. 00:38:36.030 --> 00:38:37.970 The force is vertical, agreed? 00:38:37.970 --> 00:38:39.960 We've got the mass and it's pulling straight down 00:38:39.960 --> 00:38:41.110 according to gravity. 00:38:41.110 --> 00:38:43.330 So what's going on at the atomic dimension? 00:38:43.330 --> 00:38:47.210 Because ultimately, this is what we're working with. 00:38:47.210 --> 00:38:48.830 So what happens? 00:38:48.830 --> 00:38:51.370 One possibility, and don't laugh-- this was actually 00:38:51.370 --> 00:38:52.180 suggested-- 00:38:52.180 --> 00:38:56.100 when you cause extension in this manner, you actually take 00:38:56.100 --> 00:38:58.600 some of these and you can turn them into 00:38:58.600 --> 00:39:02.070 elongated atoms. No, no. 00:39:02.070 --> 00:39:03.710 That's no good. 00:39:03.710 --> 00:39:06.610 What in fact happens is slip. 00:39:06.610 --> 00:39:12.820 So the force-- in fact, let me be more specific-- 00:39:18.720 --> 00:39:25.850 the applied force is resolved at atomic level. 00:39:30.080 --> 00:39:34.380 So what happens is that the atoms slip over one another 00:39:34.380 --> 00:39:38.770 because they can slip along the planes that have the least 00:39:38.770 --> 00:39:40.400 bonding between them, right? 00:39:40.400 --> 00:39:42.820 The chain is as strong as its weakest link. 00:39:42.820 --> 00:39:47.130 So what will happen here is that in order to affect the 00:39:47.130 --> 00:39:52.380 elongation, these will move relative to one another along 00:39:52.380 --> 00:39:54.030 this slip plane. 00:39:54.030 --> 00:39:58.655 This is resolved at the atomic level along slip planes. 00:40:01.610 --> 00:40:04.140 I'll write that larger for the people way, 00:40:04.140 --> 00:40:05.510 way up in the back. 00:40:05.510 --> 00:40:06.760 I haven't forgotten about you. 00:40:13.870 --> 00:40:15.190 And what's the slip plane? 00:40:15.190 --> 00:40:17.620 How do I determine which is the slip plane? 00:40:17.620 --> 00:40:20.080 The slip plane it's going to be the plane that's strongest 00:40:20.080 --> 00:40:22.680 because it retains its integrity. 00:40:22.680 --> 00:40:25.180 So which plane will be the strongest? 00:40:25.180 --> 00:40:26.780 The one with the most bonds. 00:40:26.780 --> 00:40:28.730 And which plane has the most bonds? 00:40:28.730 --> 00:40:32.430 The plane with the highest number of atoms per unit area. 00:40:32.430 --> 00:40:34.480 And that's why we study this stuff. 00:40:34.480 --> 00:40:37.280 Because now we know, in an FCC crystal, 00:40:37.280 --> 00:40:41.720 which plane will slide. 00:40:41.720 --> 00:40:46.570 So in FCC, the high-intensity plane is 1 1 1. 00:40:46.570 --> 00:40:49.980 So the 1 1 1 planes do the sliding one over another. 00:40:49.980 --> 00:40:53.420 And they'll zigzag the way you saw in the bubble wrap movie. 00:40:53.420 --> 00:40:59.890 They'll zigzag down, across, across, across, But from a 00:40:59.890 --> 00:41:02.560 distance, it appears as the thing is elongating. 00:41:02.560 --> 00:41:06.590 But at the atomic level, it's zigzagging along the 00:41:06.590 --> 00:41:07.440 close-packed planes. 00:41:07.440 --> 00:41:09.240 Now I'm in a close-packed plane. 00:41:09.240 --> 00:41:11.930 By the way, if I have the highest density in the plane 00:41:11.930 --> 00:41:16.470 of the floor, can you understand that orthogonal to 00:41:16.470 --> 00:41:19.132 the plane on the floor, I must have the weakest density? 00:41:19.132 --> 00:41:20.880 All right, now I'm in the plane. 00:41:20.880 --> 00:41:22.150 Which direction in the plane? 00:41:22.150 --> 00:41:23.820 Any direction? 00:41:23.820 --> 00:41:26.330 I'm going to push, I'm going to push some pasta. 00:41:26.330 --> 00:41:29.990 I'm going to push uncooked pasta or cooked pasta? 00:41:29.990 --> 00:41:31.740 Do you want to push on a rope? 00:41:31.740 --> 00:41:34.150 Do you want to push on a broom handle? 00:41:34.150 --> 00:41:35.320 The stiff. 00:41:35.320 --> 00:41:38.460 So how do I determine, within the plane, which direction is 00:41:38.460 --> 00:41:41.230 the stiffest direction? 00:41:41.230 --> 00:41:44.430 The one with the most atoms, which is the close-packed 00:41:44.430 --> 00:41:45.900 direction when I'm in the plane. 00:41:45.900 --> 00:41:48.670 So if I'm in the 1 1 1 plane, which direction? 00:41:48.670 --> 00:41:50.250 The 0 1 1 direction. 00:41:50.250 --> 00:41:54.480 So this is direct line of sight from the original 00:41:54.480 --> 00:41:55.790 crystallography. 00:41:55.790 --> 00:41:59.390 So that's how we get the slip. 00:41:59.390 --> 00:42:03.640 And in BCC the highest density plane is 0 1 1 and so on. 00:42:03.640 --> 00:42:07.830 And the close-packed plane simply means 1 1 1, because 00:42:07.830 --> 00:42:11.140 FCC is the closest-packed structure, so that's a 00:42:11.140 --> 00:42:12.010 close-packed plane. 00:42:12.010 --> 00:42:14.910 Otherwise, they're planes of highest density. 00:42:14.910 --> 00:42:15.860 It's a trivial-- 00:42:15.860 --> 00:42:17.930 forget the last column-- it's pedantry. 00:42:17.930 --> 00:42:18.940 Forget it. 00:42:18.940 --> 00:42:21.050 I'm sorry I have it up there. 00:42:21.050 --> 00:42:23.370 So this is the slip system. 00:42:23.370 --> 00:42:30.270 So the slip system is the combination of 00:42:30.270 --> 00:42:32.700 close-packed plane-- 00:42:32.700 --> 00:42:38.370 or closest-packed plane-- close-packed plane and the 00:42:38.370 --> 00:42:41.160 close-packed direction. 00:42:41.160 --> 00:42:43.020 They all have close-packed directions because we've got 00:42:43.020 --> 00:42:44.250 atoms touching. 00:42:44.250 --> 00:42:49.570 Close-packed direction. 00:42:49.570 --> 00:42:52.060 That's how it deforms. And then if I get a dislocation in 00:42:52.060 --> 00:42:53.435 a close-packed plane, voom! 00:42:53.435 --> 00:42:55.180 Away they go. 00:42:55.180 --> 00:42:57.330 1/10 of the applied sheer stress theoretical. 00:43:02.440 --> 00:43:07.770 So if you want to get it down to a simple phrase, you can 00:43:07.770 --> 00:43:11.560 say, what causes slip? 00:43:11.560 --> 00:43:15.680 Atoms slip, dislocations glide. 00:43:20.340 --> 00:43:22.480 But please don't think for one minute-- listen to me 00:43:22.480 --> 00:43:24.410 carefully-- a lot of students come away from this and they 00:43:24.410 --> 00:43:28.770 say, oh, I know why we have deformation. 00:43:28.770 --> 00:43:30.220 Because of dislocations. 00:43:30.220 --> 00:43:32.680 No, no, no, no. 00:43:32.680 --> 00:43:34.600 Atoms will slip no matter what. 00:43:34.600 --> 00:43:37.280 It's just that you're going to pay a lot more to cause the 00:43:37.280 --> 00:43:38.450 deformation. 00:43:38.450 --> 00:43:46.760 The dislocations allow you to have slip at lower cost. 00:43:46.760 --> 00:43:48.190 Yeah, this is good. 00:43:48.190 --> 00:43:53.260 And I think we're probably at the point where I can show you 00:43:53.260 --> 00:43:56.620 the enormous consequences of a three-dimensional defect. 00:43:56.620 --> 00:43:58.880 Why did the Titanic sink? 00:43:58.880 --> 00:44:02.030 It's a story of three-dimensional defects and 00:44:02.030 --> 00:44:03.550 human greed. 00:44:03.550 --> 00:44:06.710 So this Tim Fecke at the National Institutes of 00:44:06.710 --> 00:44:10.900 Standards and Technology with an optical microscope and a 00:44:10.900 --> 00:44:12.430 rivet from the Titanic. 00:44:12.430 --> 00:44:14.710 And what I'm going to show you in the rivet is a 00:44:14.710 --> 00:44:18.520 three-dimensional defect that took the boat down. 00:44:18.520 --> 00:44:22.620 So this is the microstructure and what they're doing is 00:44:22.620 --> 00:44:25.950 they're showing you a blow up of this section of the rivet. 00:44:25.950 --> 00:44:28.450 Now, the rivet is made of steel. 00:44:28.450 --> 00:44:31.130 Before I can explain to you what's going on there, I have 00:44:31.130 --> 00:44:31.510 to show you-- 00:44:31.510 --> 00:44:31.845 [MUSIC STARTS] 00:44:31.845 --> 00:44:32.900 PROFESSOR: Oh, shut up. 00:44:32.900 --> 00:44:34.300 [MUSIC ENDS] 00:44:34.300 --> 00:44:35.950 PROFESSOR: All right, so this is how they made steel. 00:44:35.950 --> 00:44:39.470 Imagine this area the front of 10-250 as an open-hearth 00:44:39.470 --> 00:44:43.120 furnace, and I'm up to about my knees in liquid iron. 00:44:43.120 --> 00:44:45.880 And on top of the liquid iron is a slag made of silica, 00:44:45.880 --> 00:44:47.590 calcia, and alumina. 00:44:47.590 --> 00:44:50.380 It's the stuff when it solidifies it makes something 00:44:50.380 --> 00:44:52.940 not too different from window glass. 00:44:52.940 --> 00:44:55.800 But we use it for refining to get some of the impurities out 00:44:55.800 --> 00:44:56.200 of the metal. 00:44:56.200 --> 00:44:59.180 And those impurities go up into the slag phase. 00:44:59.180 --> 00:45:01.665 And to keep this thing it about 1,300 degrees 00:45:01.665 --> 00:45:03.380 Centigrade, you've got burners. 00:45:03.380 --> 00:45:03.970 Two. 00:45:03.970 --> 00:45:05.413 One at each end like dragons-- 00:45:05.413 --> 00:45:06.400 [SOUND EFFECT] 00:45:06.400 --> 00:45:10.320 PROFESSOR: --blowing flame into here for about 12 hours. 00:45:10.320 --> 00:45:11.510 12 hours. 00:45:11.510 --> 00:45:13.480 And that's what it took to make a heat of 00:45:13.480 --> 00:45:16.060 steel back in 1910. 00:45:16.060 --> 00:45:18.690 This was made in Ireland, which was, at that time, part 00:45:18.690 --> 00:45:21.460 of the United Kingdom. 00:45:21.460 --> 00:45:25.690 So on that day that they made the heat of steel that 00:45:25.690 --> 00:45:28.550 ultimately was shaped into rivets, evidently somebody 00:45:28.550 --> 00:45:32.320 became greedy, and instead of waiting long enough for the 00:45:32.320 --> 00:45:37.120 slag to phase separate and form a film on the surface of 00:45:37.120 --> 00:45:41.220 the metals, much like oil and water don't mix, but you can 00:45:41.220 --> 00:45:44.880 shake them up in your salad dressing application tool 00:45:44.880 --> 00:45:47.010 device and then pour it on quickly. 00:45:47.010 --> 00:45:50.120 But if you let it sit they phase separate. 00:45:50.120 --> 00:45:52.340 Well, somebody didn't allow this to phase separate. 00:45:52.340 --> 00:45:54.350 They were told, pour the heat anyways. 00:45:54.350 --> 00:45:58.680 So now you have globs of what is the precursor to silicate 00:45:58.680 --> 00:46:00.620 glass in the metal. 00:46:00.620 --> 00:46:03.870 And now we take the metal and we cut it into little billets 00:46:03.870 --> 00:46:06.750 and the billets are extruded to form rivets. 00:46:06.750 --> 00:46:08.850 And then the rivets look like this, where 00:46:08.850 --> 00:46:10.460 you have glass stringers. 00:46:10.460 --> 00:46:13.570 Three-dimensional defects, impurity clusters, 00:46:13.570 --> 00:46:14.730 uncontrolled. 00:46:14.730 --> 00:46:16.960 What are the mechanical properties of steel? 00:46:16.960 --> 00:46:17.930 Strong. 00:46:17.930 --> 00:46:18.770 Ductile. 00:46:18.770 --> 00:46:19.220 Tough. 00:46:19.220 --> 00:46:20.560 What does toughness mean? 00:46:20.560 --> 00:46:22.360 Impactability. 00:46:22.360 --> 00:46:24.510 When you say someone is tough, it means they know how to take 00:46:24.510 --> 00:46:29.110 a hit, whereas hardness means it takes enormous strength to 00:46:29.110 --> 00:46:30.440 cause deformation. 00:46:30.440 --> 00:46:31.850 They're very different. 00:46:31.850 --> 00:46:32.380 You know? 00:46:32.380 --> 00:46:34.010 You say someone is tough, you mean one thing. 00:46:34.010 --> 00:46:35.780 You say they're strong, it's different. 00:46:35.780 --> 00:46:37.920 You can be strong and yet not tough. 00:46:37.920 --> 00:46:41.180 You can be strong and brittle, so you can't take a hit. 00:46:41.180 --> 00:46:42.670 I know a lot of people like that. 00:46:42.670 --> 00:46:43.840 That can't take a hit. 00:46:43.840 --> 00:46:46.100 Anyway, so enough about the people. 00:46:46.100 --> 00:46:48.050 So here are the stringers. 00:46:48.050 --> 00:46:49.020 So what happened? 00:46:49.020 --> 00:46:50.150 What do you think the mechanical 00:46:50.150 --> 00:46:51.260 strength of this is? 00:46:51.260 --> 00:46:54.190 If you have an impact like so, instead of having the 00:46:54.190 --> 00:46:57.300 toughness to absorb the impact, these things broke. 00:46:57.300 --> 00:47:00.450 This is like perforations on a sheet of postage stamps. 00:47:00.450 --> 00:47:03.890 And so these rivets were on the hull. 00:47:03.890 --> 00:47:06.090 And when the ship hit the iceberg, what should have 00:47:06.090 --> 00:47:09.400 happened is there should have an a small hole, the water 00:47:09.400 --> 00:47:13.760 would've taken, who knows, a day or two to fill up, and 00:47:13.760 --> 00:47:15.740 there was plenty of time to get rescue vessels. 00:47:15.740 --> 00:47:18.940 Instead, these rivets were brittle, thanks to this. 00:47:18.940 --> 00:47:20.600 And so they just unzipped. 00:47:20.600 --> 00:47:21.930 Just pop, pop, pop, pop, pop, pop, pop. 00:47:21.930 --> 00:47:24.970 Opened up a giant hole and then took on the water. 00:47:24.970 --> 00:47:27.040 Now, did nobody check? 00:47:29.570 --> 00:47:32.310 Along the way, no inspection of the steel? 00:47:32.310 --> 00:47:33.680 Nobody looked? 00:47:33.680 --> 00:47:36.130 The guys that we're doing the riveting, they must have known 00:47:36.130 --> 00:47:38.310 the rivets were acting strange. 00:47:38.310 --> 00:47:41.490 They must have broken a lot of them just putting them in. 00:47:41.490 --> 00:47:42.770 But hey, it's not my job. 00:47:42.770 --> 00:47:43.480 Not my job. 00:47:43.480 --> 00:47:44.170 Not my job. 00:47:44.170 --> 00:47:48.370 No testing anywhere along the way. 00:47:48.370 --> 00:47:50.840 What's shocking is not human greed. 00:47:50.840 --> 00:47:52.110 That's as old as humanity. 00:47:52.110 --> 00:47:54.860 What's shocking is there was no checks. 00:47:54.860 --> 00:47:59.020 So we have a different way to make vessels like this today. 00:47:59.020 --> 00:48:01.400 But that's the story, right there.