§1. Course handouts and orientation [00:03]
There are two more sets of handouts up here, anybody want one? If you didn't get one, just drop by my secretary's office, she's got more. It's just so many that I could fit on that cart without rearranging it. Those things on the first page actually have some of the evaluations from the early years of the course. Some students say you can get as much or as little as you want out of this class — it depends on how much time you want to put into it.
In there in the one that says one, there's a chapter 16, which is something I wrote about twenty years ago for a book that the mechanical engineering department was going to publish, which I don't think they ever got around to publishing. It was supposed to be on manufacturing. I just took all my lecture notes on the welding and joining stuff and condensed everything down to about thirty pages. So if you want to learn everything about the twenty-five lectures, you can just read those thirty pages. At the back of chapter 16 are ten problems which would be the problem set for your assignment. MIT requires me to grade an assignment in order to give a grade, so that's why you have an assignment in this course. If I didn't have to give you an assignment I wouldn't, okay. Some of these references are getting kind of long in the tooth, but they're still general things, and for whatever it's worth, you can decide to read them or not. Some people try to read them all, which I wouldn't do.
There's a copy of my World Trade Center paper. We'll probably talk about that at some point. For a long time, that was the most referenced article on the World Trade Center collapse. I was number one on Google, I think I'm number two now. All the conspiracy theorists hate me because I explained it. In fact the BBC is doing a documentary, and next Thursday — not this Thursday but next Thursday — I'll be down in the Washington area and they want me to meet with them, because they're doing a documentary on the World Trade Center. By the way, it was the airplanes. It wasn't a government conspiracy. I'll tell you some of my favorite stories on those things later. It's amazing what people can believe.
My favorite evaluation of all time is the student who said he just wanted to know what I taught at lunchtime because I got breakfast. He just wanted to know what other course he could take at lunchtime to get a free lunch.
§2. MP35N: properties, cold work, and section-size limits [03:35]
A number of things to clean up from last time. I finally found the properties of MP35N. Here are the typical room-temperature tensile properties of MP35N as a function of the amount of cold work. The yield strength in a completely annealed condition is only 60 ksi. That's nothing to write home about. Low-strength steel is 36 ksi; it's not hard to get 100 ksi steel; 60 ksi is sort of in between. But it can go up to 235 ksi with 65% cold work. And if you do an aging treatment, you can get it up to 290 or 300 ksi tensile strength. This is better than most aircraft landing gears, which are kind of the epitome of high-strength steel. Ten percent elongation and 48% reduction in area — that's pretty incredible, to get that much stretch out of something that strong.
The problem is you can't make it in really big sections, because it has to be cold-worked. And what are you going to cold-work it with once it starts getting up to these strengths? All the other tools are just going to break.
Student: What do you mean by cold work?
Cold work is deforming and shaping the material at room temperature. However, room temperature is a relative thing. For tungsten, room temperature is 2,000 degrees. It's the temperature at which the material does not self-anneal. At higher temperatures — if you're interested in materials science — the dislocations will annihilate themselves. But with cold work you're at a low enough temperature that if you deform the metal you form these tangles of dislocations and they stay there and they actually make it stronger. If you're not a materials scientist you don't even know what a dislocation in a crystal is. Basically, cold work is working at a temperature such that the material doesn't self-anneal, doesn't recrystallize. It maintains the deformed microstructure on the atomic scale.
All materials will cold-work. The cold-working temperature for lead is below room temperature. The cold-working temperature for steel is actually around 400 or 500 degrees Fahrenheit. Anything below that, it doesn't stress-relieve itself. For tungsten it's even higher. For MP35N it's probably in the 300 or 400 degree Fahrenheit range. It doesn't soften while you're working it; it just gets harder and harder. If you look at the stress-strain curve — stress and strain, you come up to yield strength and it just keeps going and going — anything above the yield strength, if it maintains its strength, you've worked it to that strength level. But if you heat it up it'll come back down. If you anneal it, it'll come back down and it would yield again at a lower stress.
In a blacksmith forge, when the steel gets red hot, that stuff is plastic and you can form it. You can put it back in the furnace, heat it up again, and it will soften and you can re-hammer it. I wrote my junior humanities assignment on the history of the hardening of steel. The ability to form a material in a soft condition and then strengthen it or harden it is a very important property. How do you make clay pots? You take nice soft clay, you can form it any way you want, then you put it in a furnace, heat it up, and it becomes hard, and it becomes a piece of dinnerware or bakeware. If you just had clay, it wouldn't be very useful — soft clay to bake bread in, if it just fell apart.
By heat treatment, steel can go from these types of strengths to these types of strength, but not with these types of ductilities, not with this ability to stretch and absorb energy. Ordinarily, as you go higher and higher up on that curve, your ability to absorb energy gets less. For those of you in the Navy who go underwater, it's very important to have something that has not only strength but the ability to absorb energy, because if someone starts exploding things next to you, you want something that doesn't shatter. Glass makes great research submarines or deep divables, but it doesn't make a very good thing to take undex — underwater explosion. If you could make an MP35N submarine — first of all, if you could afford something 200 times the cost of steel, and if you could get it in thick enough sections — it would be corrosion-resistant, and it would take explosions with fantastic properties.
The problem is you can't make it in plate form. You can't make it in a diameter much above 2 inches, because you've got to mechanically form it, and there are no tools in the world that wouldn't break in trying to break a great big cast piece down to a smaller piece. You can get it in wire form or sheet form. Wire form is great because you can pull it through carbide or even diamond dies — there are materials hard enough. But you can't pull great big plates of this material through some die. You don't have the diamonds and you don't have the force to pull it. So that kind of takes care of that.
§3. Velcro and the case for fastening [10:31]
There's one type of fastener that's used very commonly that was a bit of serendipity, and it's called Velcro. Anybody know how Velcro was discovered? Here's the cockle-bur. This guy was walking through the Alps and he came back and noticed he had all these cockle-burs on his pants, and he thought, I wonder why they stick to my pants like that. So he put them under a microscope and noticed that the end of each of the cockle-burs has a little hook on it. And he realized that his wool pants also had all these little loops. He said that might be interesting as a type of adhesive. So he took plastics, made a bunch of loops and a bunch of little hooks, and that was the invention of Velcro — actually a sort of interesting fastener.
I've given you in the handout some references. This is the best book on bolting that I know of: John Bickford. He's retired now, but he's an MIT mechanical engineer. This is the third edition. If you're interested in bolting of bridges and buildings, this book by John Fisher — John's still alive, he's probably well into his 80s now — he was a civil engineer at Lehigh University and he basically looked at bolts for bridges and buildings, and how to put big arrays of bolts on things.
If you start thinking about fastening, what are the advantages of fastening over other joining technologies?
Student: Quicker than welding.
Quicker than welding, and it doesn't require all the procedure qualification that you have to do for welding. With welding you actually have to work out a procedure that works. It's not too hard to figure out the procedure for putting a bolt in a hole and turning the nut. You've got to put the right torque on, but that's about it. Much easier for repair and maintenance. It can be disassembled. How do you disassemble a weld? You've got to cut it out, grind it out — it's a pain in the neck. Bolting is great for low-volume manufacturing. If you only have to make one of a kind, or a hundred of a kind. But somewhere between ten of a kind and a thousand of a kind, it becomes cheaper to braze or solder or weld. You can amortize the cost of developing the procedure over a lot of parts, whereas if you're only putting one together, bolting is a lot easier to design.
But what are the disadvantages? Ease of assembly, low volume, and field assembly are on the plus side. The disadvantages: higher cost in high volume. It's very difficult to automate. Start thinking about the manual dexterity it takes to put a bolt in a hole and then turn a nut, and not turn it too hard or too soft. If you start thinking of how a robot could do that, a robot has to have a range of mechanical force sensitivity that is sort of natural to us but not natural to a robot. Also to be able to put it in a hole, or to recognize that a hole is not perfectly circular. These are things that we can recognize.
NIST did a study a number of years ago and found that the average IQ of a robot is 10. That's because robots can't reason, they can't adapt. Same thing with computers — they don't really have the ability to reason and adapt. I used to give talks at General Motors. They were trying to replace all their workforce with robots, which said something about what management thought about the quality of the workforce. They were trying to upgrade with robots. So they figured that most of their laborers had an IQ of less than 10. I used to point out — they didn't like it — maybe it was the management that had an IQ less than 10.
It's less than full joint strength. We used to rivet bridges together, but the amount of extra material you had to use when you overlap those things was horrendous. The first big all-welded project was the Big Inch pipeline in the 1930s. It was the 30-inch pipeline from Louisiana to New Jersey. The reason they welded it, even though welding had not been used for really critical applications, was because if you had riveted something like that, there would have been a substantial increase in the amount of material, and can you imagine all those bolted flanges and joints, and all the leaks they would have had? If something's going to fail, it fails at the joint.
We talked about needing the right clamp-up — it can't be too much or too little. Fatigue: you put a hole in something, you just increase the stress concentration by a factor of three, so you're going to have fatigue problems. And it's also only really good in either shear or tension. It's not particularly great in compression — it's just holding things in place at that point. It's not very good in multiaxial loading. If you've got some combined loading of shear and tension, it's not easy to design, because a bolt has a strong direction just like the trunk of a tree has a strong direction and a weak direction. Bolts have the same type of problem. So there's a host of good points and bad points. The bad points tend to outweigh the good points in most cases.
§4. Bolt preload, reuse, and high-strength applications [17:41]
The whole bolting process is actually best analyzed as clamp-up and springs — relative stiffnesses between the bolt and the plate. Another problem with bolts: I talked about the plus-or-minus 30% variation in torque. What I didn't tell you is that when you reuse bolts, the torque to acquire the preload goes down and down as the bolt works its way in and smooths out all the rough spots and the friction coefficient drops. It takes less torque to get the same clamp-up. So if you reuse bolts, who knows where you are on this curve? It's a factor of two, it's more than 30% — it's 50%.
The other problem with reusing bolts: bolts are often loaded to about 75% of their yield strength. Bickford's book talks about that. If you do that and then put some service loads or excursions on top of that 75%, you'll often start to yield the threads. It might be micro-yielding, but now things don't fit up quite as well. So typically you never reuse high-strength bolts. They're one-time-article use. Who was talking about Morgrip bolts and propellers? One of you had an experience — you probably didn't reuse the Morgrips, did you? Threw them away after one use.
Student: Right, they had brand new ones when they replaced the blades.
And that's because even though you're measuring stretch, they've stretched, the thread fit is not what it used to be because you had micro-yielding.
Student: What about bolt tightness checks? They do that every four or five years on ships.
They didn't completely remove the bolt; they just go in and retorque. That's not the same as actually removing the bolt.
Student: Right.
And it's not just propellers — it's aircraft, it's bridges and buildings when you're using high-strength bolts. The rule, and for automobiles, racing cars: high-strength bolts are one-time use. Most people don't know that, but I've been to a number of aviation accidents where people reused the bolts. They don't have the same fatigue strength because they don't have the same clamp-up. So the long-term properties are not the same when you reuse high-strength bolts. Not everybody understands that.
Student: Is the spring force [...]
Where I showed you clamp-up: you torque it to let's say 75% of yield. Because it's competing springs, think of the two plates you're bolting together as having a certain springiness, a spring constant. Think of the bolt as having a spring constant — one's in tension, one's in compression — but they're not the same spring constant K. Different values of K. If you want to analyze how the bolted joint behaves, you analyze it as coupled springs in parallel. A 10% variation in stress on the bolt could be a 50% variation on the plate, or vice versa, depending on the variations in the spring constant. You have to worry about both displacement and force in parallel springs. Force is minus kx for a spring. Or energy is one-half kx squared. The bolt has a value of K, the plate has a value of K, those two values are different, and now you have two springs acting in parallel. You've got to work out the math for these coupled equations for energy and force, and a small variation in one can be a big variation in the other.
Student: What's the difference with studs?
First of all, a stud is not typically loaded to 75%. It's loaded to 25% or something. When I'm talking high-strength bolts, I'm talking about bolts that are going to be loaded to like 75% of yield, in critical, high-strength applications. Low-strength applications like studs, it's usually just for placing things on. On a submarine you've got a million studs just hanging stuff off the side — just hangers.
Student: And we can't talk about what we're hanging.
Right. Okay, that gives you a little bit on bolting, and there are some references in the notes if you ever need to go back to things. I use Bickford's book about once a month.
§5. Structural materials, cost per pound, and the X-33 [23:13]
Now, when you go to the lectures that are going to be on video — and I think you ought to start with the material selection lectures, there are twelve to fifteen of those — it'll mesh in a little bit better. But I talk about the variations in the cost of a material. This course is really supposed to be about how to manufacture structural materials. Structural materials differ from other materials. The Japanese call them structural and functional materials. Functional materials we use because of some property other than mechanical. Structural materials — you're talking about structure, you're talking about mechanical properties. We have MP35N, the wonderful metal of all, the greatest metal of all.
Structural materials, by their very nature, are used in very large volumes. You can't build a nano-bridge — it doesn't go all the way across the river. The stiffness of anything is going to be proportional to its cross-sectional area and its modulus. And we only have so much to play with in the world, because Young's modulus is determined by the strength of the chemical bond. Steel and cobalt alloys and nickel alloys are all around 30 million, but the best you can get is molybdenum and tungsten and carbon at around 60 million. So you can only get a factor of two in stiffness above steel. Aluminum is 10 million, three times less than steel, which creates some problems when you're trying to design.
One of the problems with the Visby — do you know what the Visby is? It's the Swedish all-aluminum or composite corvette. The Visby has problems with hogging. Basically, a ship in heavy seas becomes a beam between the waves. Composites and aluminum just don't have the stiffness to make big long bridges between two waves. In heavy seas they tend to break in two. Not good.
There's a whole range of the cost of these things, and the value of a pound saved in something like a ship or a railroad car is about 20 cents over the life of the vehicle. This is in one of the handouts for today. This is an article I wrote when I was on a committee. It was a little bit of a problem being on this committee because everybody was interested in nanotechnology and all this other stuff, and we were all supposed to be writing part of this report. I decided I couldn't write any of this report because I didn't believe in what they were talking about. So I wrote a chapter, which they made an appendix. It's a summary of Tom Eagar's feelings, and another person's, about the high-level strategic view of structural materials.
There is a plot in here which I stole from Jack Westbrook, an MIT grad. He did this in something like the 1960s for General Electric when he worked there. This is pounds per year versus dollars per pound for structural materials. There is a correlation: the less something costs, the more you'll use it. But the interesting thing is that the slope here is greater than the iso-market size. So if you can reduce the cost by a factor of two, in the long run you'll increase the consumption by a factor of four and double your market. That's the long-term view.
The material we use in the greatest volume is crushed rock. It has a very low value. These are old numbers, so rather than a tenth of a cent a pound, maybe crushed rock is two cents a pound now. Whatever it is, it's still pretty cheap. The problem with something like that is you can't afford to transport it very far. Who's going to be shipping tons of crushed rock from China to the United States? It doesn't make any sense. Cement is the largest volume of manufactured material in the world — two billion tons a year. We can ship cement around the world if you're going to use slave labor and cheap energy to produce it. But in general, cement plants dot the country because you can't ship it by truck or rail more than about 500 to 1,000 miles.
My father worked for a cement company, and one of the big innovations for one of the cement companies he worked with: they had one big plant in Vinea, New York, and they had supply depots all up and down the Atlantic coast and they barged it to each one. So the reason I lived in Virginia Beach was that my father worked in Chesapeake, Virginia, where they had a supply depot. Cement was made in New York, barged to Chesapeake, Virginia, and then trucked for a couple hundred miles all through North Carolina and Virginia. They had another depot in Baltimore or Philadelphia. So transportation costs are very important when you get to materials down here.
Up here there's a structural material called diamond. It's not used in very large volumes. I actually have some diamond here. [Tom produces a sample of brazed diamond.] This is a little diamond made by Kinik, and it's brazed diamonds. [Tom shows a pad conditioner.] Kinik makes what's called a pad conditioner. This is sort of a functional material — diamond's a structural material — but it's fairly pricey. It can't be made in large size. They make it in 1- or 2-millimeter-thick sheets, very expensive as a semiconductor substrate because it has the best thermal properties in the world. It can conduct heat away from a semiconductor better than anything else. For a diamond pad conditioner or a diamond sharpener, it is being used as a structural material. It can abrade other materials better than anything else.
The pad conditioner: someone described the buildup of a semiconductor. You lay down some copper on the surface, or aluminum, then you put something else on top, and after a while the thing looks like the Rocky Mountains on a microscopic scale. Every now and then you have to planarize the surface, and you come along with a chemical and mechanical abrasive to flatten off the semiconductor before you continue to put more layers on. Modern semiconductors take 200 to 400 processing steps. Lay something down, take something off, oxidize something, put something else down, in all these different patterns. [Tom locates a semiconductor chip and passes it around.] This is a 15-year-old Intel chip, a Pentium 5 chip, but you can see the semiconductors on there. As they get smaller and smaller, they have to come along and abrade the surface, and the pad conditioner is basically a diamond that gets all the gunk off the polishing pad. When you're dealing with microns and submicron polishing, you have to have a perfectly planar surface. So you have to dress your polishing wheel, and the diamond pad conditioner is the thing that dresses it.
The highest-value structural materials are worth about $20,000 a pound. They go into — does anyone know what they go into?
Student: Spacecraft.
Spacecraft. The value of a pound saved on the space shuttle is $20,000 a pound, because that's what it costs to get a pound in orbit. So now they say, oh, we're going to colonize the moon. Yeah — at $20,000 a pound, how much do you weigh? How much will it cost to get you to the moon, along with all the food and water you're going to need? The International Space Station — those people are costing us $20,000 a pound. And look at what we've benefited from it. Look at the cost-benefit ratio.
Student: We got Tang.
Yeah, well, not from the International Space Station.
Student: Pictures?
Most expensive pictures. GPS actually has paid for itself in lots of other commercial ways. $20,000 — going to the moon and stuff is probably higher than that, but that's an order-of-magnitude number.
The original goal of the space shuttle was to get the cost — from back in the 1970s it was $10,000 a pound, I added a little for inflation. The space shuttle was supposed to get it down to $1,000 a pound, but that was if we had one to twenty shuttle flights per year. I don't think we got anywhere close to that. So the actual cost of the space shuttle may have been slightly more than single rocket shots. They didn't know that when they started. Let's not get into the space shuttle right now — it's depressing for me as a taxpayer.
[Tom hands a piece of HY-80 around.] This is a piece of HY-80, made by our friends down there in Groton. You'll feel the weight and density. As-fabricated, that's probably two or three bucks a pound for the cost of what you're going to float or sink, as the case may be. [Tom hands a piece of X-33 composite around.] That is a piece of the X-33 space plane that cost $12,000 a pound for that composite. So you've got $2 a pound and you've got $12,000 a pound. But it's light, isn't it? It's not as strong and it's more brittle. It wouldn't do well in an explosion. But you can get things into space and still have some payload left over. You can afford it at $12,000 a pound. You could make an Indianapolis racer out of that material, but you can't afford to make a Ford Taurus out of it and sell it to anybody.
So you now know something about the cost of materials, which can vary widely over about five orders of magnitude.
§6. The X-33 space plane and rapid prototyping [37:15]
Student: What is that from?
That's a honeycomb. That's the story of the X-33 space plane. After the first Gulf War — I like questions, it causes me to digress — after the first Gulf War, the Defense Department really felt a great need for what they called rapid prototyping. We were developing things like 3D printing. They found in the war that the war didn't last five or six years. They actually found they needed things and they needed to be able to develop them within two weeks or a month, rather than three or four years. So they decided to do the X-33. NASA let a contract for $1.3 billion, and if I remember correctly it was supposed to be 33 months from let of contract to first flight.
They spent the first part of their Gantt chart trying to make 3D carbon composites. [Tom shows a carbon composite tube.] This is a piece of carbon composite that was made for chemical reasons. As a tube, it was going to be a filter, because carbon has fantastic corrosion resistance in all kinds of acids and other chemicals. If you wanted to retrieve your spent catalyst in a chemical plant — which might be made out of rhodium or platinum or iridium — you could have filtered it through that carbon composite.
For the X-33 space plane, they were going to make it out of woven 3D — it was going to be a ring-stiffened cylinder. You guys in the Navy underwater Navy know what a ring-stiffened cylinder is. Then they priced it out and found it was going to blow the budget by a factor of four or five, so they decided they couldn't do it. They were left with about one month to go to finish the design. They had spent about six months designing this thing they couldn't afford. No one bothered to check the price early on. So they had to slap something together in one month. They could buy that honeycomb — Nextel, a very similar polymer to Nomex or Kevlar. And they could buy carbon fiber tape in a polymer resin, and they could make these. They spent about $30 million of the $50 million on all the fixtures, and then they wound up all these things.
They made this thing about the size of a two-story house. It only weighed 2,000 pounds, even though it had Inconel inserts for the fasteners and support struts. They took it down to Huntsville and filled it up with liquid hydrogen. That's the only place you can get 5,000 gallons of liquid hydrogen. Not everybody has that. Tends to be explosive. They made two of these, had just finished doing it, it was successful, and they were giving each other high-fives, when on the video camera they saw all the frost pop off and it turned out they had sprung a leak. No one had checked the permeability of the carbon composite for liquid or gaseous hydrogen.
Actually, someone at Michoud, NASA's research labs down in Louisiana, had given them some numbers. This gets into the politics. They had given the contract to the Lockheed Martin Skunk Works in Palmdale, California, where they built the F-117 fighter — the stealth fighter — in secret. That tank was built in the same hangar, the top-secret hangar where they built the F-117. It was the production facility for F-117 fighters. NASA, to do this rapid prototyping, knew that regular old defense contractors could never do something quickly or within budget, so they gave this $1.3 billion contract to the Skunk Works, and the Skunk Works spent the first four or five months of their six-month budget designing something that was unaffordable. So they slapped together this other design in one month, built it, had a few problems in the fabrication, and then tested it and had a big problem. Eventually NASA cancelled the whole project.
That was supposed to be the replacement for the space shuttle. If you want a liquid hydrogen tank twice the size of this room — actually bigger, about the size of a small two-story house — they've got one in Palmdale you can have, cheap. I've seen it sitting right there. No one knows what to do with it. Only cost them $50 million apiece for the two of them. 2,000 pounds divided into $50 million, you can figure the price.
Student: That's the empty weight?
That's the empty weight.
Student: [question]
One of the ways to be able to make single-stage-to-orbit spacecraft — that was what the space shuttle was supposed to be in the original 1970s design and concept. It was supposed to be single-stage-to-orbit, and they found they couldn't do it. They had to have these big external tanks and solid rockets, which were expendable. Sort of reusable but not really. They decided that X-33 was supposed to be single-stage-to-orbit. You could take it up, bring it back, refuel it, take off like an airplane, and you don't have to throw away external tanks. If you could have done that, you might have gotten the price down from $20,000 to $1,000 or $2,000, and it would have been a game-changer for putting things in space.
They're still trying to figure out how to do that. To do it, you have to have multifunction materials. The tanks were supposed to be the structural part. They not only had to hold liquid hydrogen, they also had to provide the mechanical properties for the whole structure. It's amazing what these little groups in the Pentagon can come up with for ideas, when you have no constraints — you're not constrained by any science or physics. You just say, oh, wouldn't it be great if Buck Rogers could communicate by mental telepathy. So they'll spend a hundred million on studying mental telepathy and that way we'll really improve our C4I, C3I, C5I — boy, those C's proliferate.
Student: C5ISR?
They've got whole teams thinking of these acronyms.
§7. Engineering disciplines and the history of MIT departments [45:46]
Let's talk a little bit about the difference between structural materials and functional materials. Materials processing is energy interacting with matter. You can't change the shape or the composition of something without doing something to it. And that means you have to input energy. There are a number of different types of energy. There's thermal energy, and Wolfgang Pauli gave an interesting definition of thermal energy: heat is a disordered form of energy. Heat is atoms vibrating in all kinds of random directions. Work is basically the atoms working, pushing all in some uniform manner. Some people talk about work as the atoms in a military formation, all going in the same direction, whereas heat is a political formation, everybody going in their own direction.
Later on in the notes, when you get to non-destructive testing, I use the same definition. It's energy interacting with matter. You can't measure something unless you probe it with some form of energy. If you want to get to basic physics, that's the uncertainty principle. There's a certain minimum amount of energy you have to put into something.
There are lots of different types of energy. Thermal — we do heat treatments. Mechanical — we do mechanical forming. Electrical, chemical, and nuclear. The reason I blocked these off like this is that these four happen to be four of the eight departments in the School of Engineering at MIT. The other four — actually five now — are civil engineering, materials engineering, bioengineering, Aero and Astro, and the engineering systems division.
Does anybody know why it's called civil engineering? Engineering was invented in the 1700s at École Polytechnique in France, and the word engineer comes from the French ingénieur, which means maker of war machines. What was the first engineering school in the United States, in 1797 if I've got the date right, over here on the Hudson River? I was going to ask the Army guy. 1802 actually — I think it was when Congress passed the law. They may have opened their doors in 1802, but 1797 may have been when Congress commissioned. And until 1844 or 1845, the commandant of West Point had to come from the Corps of Engineers. It was their engineering school.
In 1823, the second engineering school in the United States was founded in Troy, New York. Anybody know what's in Troy, New York? RPI, Rensselaer Polytechnic. Anybody here can spell Rensselaer?
Student: R-E-N-S-S-E-L-A-E-R?
R-E-N-S-S-E-L-A-E-R. Not everybody can spell it. Not even some of the people who go there. In 1823 Rensselaer opened its doors. What was happening in New York state in 1823 that they needed engineers? The Erie Canal. They needed people to design bridges — not military breastworks, but canals. So they formed an engineering school. But to distinguish it from West Point, which was military engineering, they called their one course of study civil engineering, to distinguish it from military engineering. That's how we got the name civil engineering.
Arguably, MIT was the third engineering school in the country. Now University of Michigan claims that in the 1840s they had an engineering school, but I don't know — the students must have all been bears. I don't know that there were that many farmers or lumberjacks in Michigan studying engineering. But MIT was the first school that broke engineering down into multiple disciplines. What is Course 1 at MIT? Civil engineering, because that had already existed at RPI. What is Course 2? Mechanical. What's Course 3 in 1865? Mining. Metallurgy did not enter the title until 1888, and materials did not enter the title until 1974. Four was architecture. Five was chemistry. Six — I have no idea what it was, but whatever it was, it died, and it became electrical engineering in the 1890s.
Why did we have electrical engineering in the 1890s? What two competitors were fighting for the electrical industry in the 1880s? Westinghouse and Edison. And someone said GE. Who was the founder of General Electric? There were two founders. One was Thomas Edison. The other was Elihu Thompson, who spent one year as president of MIT. Thomas Edison had 400 patents, more than anybody else in the country at the time. Elihu Thompson had 380, number two. Elihu Thompson was a professor of electrical engineering at MIT, and the two of them formed General Electric, right up here on the Lynn River. It's called the Lynn River Works for General Electric, the original plant.
Electrical engineering didn't come around until the 1880s. Chemical engineering — where was that discovered? In the 1890s, there were guys named Arthur D. Little and William Walker. Walker Memorial used to be the cafeteria. Anybody ever heard of Arthur D. Little? He was the first management consultant. So we gave the world management consultancy. With the good comes the bad.
What was the first school to have nuclear engineering, in 1962? MIT, very good. The first school to have an Aeronautics department was MIT, about 1918. Bioengineering, we were very late getting into. The engineering systems division, we certainly weren't the first.
I'll tell you the secret about ESD. The original name for that, which only survived one draft of the report, was the Division of Engineering Management. I know this quite well because I wrote the report. I also had a guy named Todd Magnanti from the Management School on the committee, and I knew he would kill it because the Sloan School owns the M-word at MIT. The engineering school is not allowed to use it. But if you went back to before 1950, there was a Department of Engineering Management within the School of Engineering. And this guy Alfred Sloan — who was Alfred Sloan?
Student: [Sloans?]
Yeah, but before that he basically put together General Motors. He took Chevy and Buick and Pontiac and Cadillac and grouped them together, and he showed how to manage a big automobile company. He was an MIT grad. Around 1950 he gave a very large sum of money to MIT to teach management. We had a Department of Engineering Management at the time, and they took that department and built a school. What happens when you change the title of something — you build walls between the institutions. Big organizations, when they don't want people to talk to each other, give one of them a bigger title than someone else, and they won't talk.
Management was removed from engineering education in 1950 at MIT. If you read this report that formed ESD in 1996, it has a disclaimer at the bottom of the first page — I know, because I wrote it — and it says there's nothing new in this report that hasn't been reported in at least half a dozen studies in the last twenty years. What is different is that if we don't do something about bringing management back into education, we're going to lose our leadership in engineering education. That's what the engineering systems division is supposed to be about.
Doug Lemmberg was on the committee with me, and he saw this whole structure as a way to create a division of bioengineering, which was easier to form than the engineering systems division. He formed the division of bioengineering, which after about seven or eight years became the department of bioengineering. People don't realize that this was actually my vision — that by creating these perpendicular structures of departments and divisions, you would be able to kill departments and create new departments, which otherwise in the organizational structure of MIT and most other organizations you can't do. Once you form something new you'll never get rid of it. Talk to the French — the French can't kill anything. Well, they can kill lots of people, but they can't kill anything that should be killed organizationally.
§8. Structural vs. functional materials and the ceramics critique [57:50]
There are lots of different types of properties on materials, which we'll talk about after we take a 10-minute break. For 21st-century defense needs, you're going to have to read that eventually when you go through the material selection lectures. Another paper I'll hand out now is the future of metals.
The history of this paper is that around 1990, I was sick of listening to people talk about fine ceramics and how they were going to make ceramic engines. I worked for the Office of Naval Research in Tokyo, Japan in the mid-80s, and they would have a ceramics conference at Shinjuku station and two million Japanese would come to this display of fine ceramics. Only like four square blocks of people.
Student: They huddle.
The Japanese just thought ceramics were wonderful. You can get ceramic scissors and knives. I have ceramic knives at home and they work really well — they chip easily, but stay sharp if they don't chip. They're a little pricey, but they work well. The problem with a ceramic engine is when it breaks, it really breaks. It doesn't just wear out, it shatters. So I used to go to some of these conferences, and with my personality, I'd just get up and tell people. The thing I used to say is that the only structural materials that have been made out of ceramics are Portland cement and toilet bowls. High-volume structural ceramics: Portland cement and toilet bowls. And I'd throw in the kitchen sink, but you have to line it with cast iron to give it fracture resistance. If you dropped a pot in a toilet bowl, you'd crack it. I said this at conferences full of ceramists, and they didn't take it well, for some reason. I never could figure these things out — that was part of my problem.
So I wrote this article, published in the Welding Journal because there was a society that would listen to me. I stole a plot from somebody, I can't remember who, which is the volume of metals and which ones are used in what quantities in the world. Out of 100 pounds of metal produced in the world, 95 pounds are steel. 2% is aluminum, 1.2% is copper. You've got a little zinc, titanium, magnesium, tin — titanium together with the others is only a tenth of a percent. So if you see that I spend a lot of time talking about steel, hopefully you'll come to understand there's a reason for that.
People use materials for a host of reasons. Structural materials, we're interested in mechanical properties. One of the problems: most people try to measure mechanical properties in terms of the force of fracture, but in fact you also have to worry about the energy of fracture. Force of fracture: how many pounds to break a bar in two. Energy of fracture: what happens when you hit it with a hammer and impact it. The US Navy was kind of the scientific leader after World War II, because of the Liberty ships and figuring out why those Liberty ships broke into two. A lot of our use of the science of fracture mechanics and the understanding of the energy requirements for mechanical design came out of work at the Naval Research Laboratory.
Most things you read about in the Wall Street Journal or Scientific American have nothing to do with structural materials. They have to do with fancy chemical, magnetic, electrical, optical, thermal, other types of properties. You can start combining them too. What's a piezoelectric crystal? Voltage. You apply a force and you get electricity out, or you apply electricity and you get a force out. That's sonar — piezoelectric crystals.
Superconductivity: zero resistance, only occurs at low temperatures. There are people who have been working for 20 years on a more efficient refrigerator that uses magnetothermal effects — magnetic fields to generate cold. A refrigerator is just a heat engine, so hot and cold using magnetism.
Thermoelectric: anybody know what thermoelectric materials are used for? I happen to have one here. [Tom produces a thermoelectric module.] This is bismuth telluride, little rectangles in here, with aluminum plasma-sprayed between, and polymer insulators. This will put out 5 volts of electricity if you put a temperature differential of like 20 degrees centigrade across it. The bismuth telluride or lead telluride is a semiconductor material from group 2-6. In a temperature gradient it will give you 5 volts of energy. They use this on pipelines in the middle of nowhere, where you have no electricity, to power the sensors that tell you if you've got flow in your pipeline or the temperature of what's going through. It's very reliable as long as you have a source of heat.
What's the source of heat? The pipeline's a gas pipeline. All you have to do is have a very fine platinum catalyst on one side that will oxidize some of the gas. We call this a Coleman lantern — you ever seen a Coleman gas lantern? It has a little mantle, a silk bag.
Student: They don't make them anymore.
I probably have some in my garage somewhere because I have some of those old Coleman lanterns. Silk is interesting because it's got a lot of silica in it. When you heat this thing up you form a little quartz bag, and it's platinized — it's got a little bit of platinum on it. Makes a platinum catalyst. Platinum catalysts are very good for oxidizing hydrocarbons. That's why we use them in catalytic converters.
[Tom shows a stainless steel catalytic converter.] This is not your typical ceramic catalytic converter. I could have brought a ceramic one, but they're heavier. This one's made out of a very fancy stainless steel and they would platinize the exhaust. It's very lightweight. They wanted to design that because most of your emissions problems are when you first start up the vehicle. The catalyst isn't working when it's cold. When you start up the vehicle, all your emissions go right out the back until you heat up the catalyst and it starts working. If you've got a big thermal mass, it takes longer to heat up, and so it might be two or three minutes where you're spewing out all kinds of pollutants. You'll pass the test at the shop if you've run your car for 10 or 15 minutes, but if you went in fresh and tried to pass the test, your catalytic converter isn't working — you'll flunk the state inspection.
Student: My car will actually fail after a few minutes.
What kind of car do you have?
Student: An old BMW. Catalytic converter is very far back.
It cools quickly. This one would cool quickly but it would also heat quickly because it has much less thermal mass. You have to use a fancy stainless steel to make it, and it's platinized. You're looking at chemical properties — the platinum. You're looking at thermal properties — the small mass so it can heat up quickly.
There are all kinds of different properties. The thermoelectric thing — they use them anywhere they need very reliable electricity for sensors, where you can't hook into the power grid easily. There are lots of defense applications for that. These get the high press because there's big value added in many cases, very small amounts of materials but lots of value added. Do you want to make a dollar off a million tons of material — a dollar per pound off a million tons of material — or do you want to make a penny or even a dollar off a million ounces of material? It's a big difference in what goes into the bank.
§9. The dollars-per-mole argument and Soviet titanium [68:23]
The big volume industries — this is part of the future-of-metals paper — are the structural materials industries. There are two billion tons of cement, one billion tons per year of steel. The steel industry is five to ten times the semiconductor industry. You wouldn't get that impression by reading The Economist or the Wall Street Journal. That's why I wrote the article. Most people didn't believe it except people in the steel industry — they thought it was wonderful. In fact, we know more about steel than we do about silicon, because it's just a bigger industry.
The Army did a big study about fifteen years ago, when everybody was talking about titanium and aluminum armor and ceramic armor. The Army did a study of what material they would be purchasing the most of over the next 25 years. After spending a couple million dollars doing the study, they came to the conclusion they would buy more steel than any other material. I would have taken that contract for a couple million dollars — would have taken about ten minutes to write the paper.
Let's take steel and compare it on a dollars-per-mole basis to silicon. If steel sells for $1,000 a ton — these are rough numbers — that's a dollar a kilo. There's 7.9 grams per cubic centimeter, that's the density. There's 56 grams per mole. All this tells you that the value of a mole of steel is a nickel per mole of atoms.
Silicon, on the other hand: if I'm talking about something that's 1 square centimeter, like that little Intel Pentium 5 chip I sent around, about a square centimeter, let's say it's 10 microns thick. It might be 100 microns thick, but who cares. You could lay down a vapor, a thin film, only 10 microns, that would have all the functions you need. That means it's about 1/1000th of a cubic centimeter, which is about 10 to the minus 4 moles. That thing is going to be worth at least 10 bucks, if not 100 bucks. So you end up with something like $100,000 per mole for silicon as a semiconductor.
Now you can see why people in Wall Street or The Economist are so enamored with functional materials. You don't use very much of it, but it's got a high value. I took it down to a value per mole. All you really need to know is these bottom-line numbers. Maybe they're off by a factor of ten, but who cares. We're talking about approximately a millionfold difference between how society values a structural material compared to one of our more glamorous functional materials. Not all functional materials are as valuable per pound as silicon, but silicon is a reasonable benchmark. That's why there's all this glam-tech.
A friend of mine — he wasn't always a friend of mine. When I first started as an assistant professor at MIT and he saw my name tag at a conference and saw MIT, he decided to battle me for the next five or ten years. We'd go to Navy titanium conferences. This guy was Mr. Titanium in the country. His name is Jim Williams, and when I started as an assistant professor here, he was starting as a professor at Carnegie Mellon University. We were both competing for Navy money in titanium. This was just before what the Soviets call their titanium submarine — the Alpha sub. I remember I was coming back from Europe and reading the International Herald Tribune when I read about the Alpha sub in 1980.
This was a real wakeup call for the US Navy, that the Soviets had built the titanium sub before we had. Of course they later found out in the next few years that it was noisy as could be. Even though it could go faster under the water than our destroyers could go on top of the water, and it could dive deeper than the collapse depth of our depth charges, you didn't have any problem tracking it because it was very noisy. And within three to four years you didn't have any problem tracking it because it didn't go out of the harbor — it had so many cracks you couldn't dive it. Part of that was the politics. In the Soviet Union, the Naval Research Laboratory had identified some fracture problems with titanium that they hadn't solved. I remember going to some of these conferences and people said, how did the Soviets solve this problem? In a few years we learned they hadn't solved the problem — they just built the ship. So the Alpha subs didn't have a very long lifetime.
§10. Why vapor deposition cannot make structural materials [74:55]
So there's this huge difference in value. I did this little calculation of processing rate. When they said, Tom, you've got to teach something broader than just welding, you've got to tell people about vapor deposition and casting, I started to think about vapor deposition this spring. I decided I'd do a calculation, because I couldn't think of any structural material that's made by vapor deposition. I can think of coatings that are put on structural materials. Vapor deposition is extremely important for functional materials — that's how we make silicon semiconductors. We chemically vapor-deposit or physically vapor-deposit layers, and then we planarize the surface.
Many of the faculty in this department who are into functional materials would want someone to teach vapor deposition. But I'm supposed to be the structural guy. I used to do vapor deposition when I did my thesis and worked in superconductivity, but I haven't done any for thirty years. I did learn enough about vapor deposition that I decided I could prove why we don't use it to make structural materials. And it's not that complex.
The first thing you need to know is the Langmuir. There's this guy Irving Langmuir who worked at General Electric Research Labs about a hundred years ago. He was a pretty good scientist — won the Nobel Prize for his study of surfaces. He was interested in surfaces for lots of reasons. He was interested in tungsten light bulbs and how the tungsten vaporized from the surface, because that's how the old tungsten light bulbs burned out. You basically had tungsten vaporizing away from the hot filament, and the filament finally fractured in two — a vaporization, degradation, erosion by vaporization. Langmuir did a lot of fundamental scientific studies on vaporization. We now have a scientific term called the Langmuir, and it works out to about 10 to the minus 8 atmosphere-seconds.
When you get to the joining portion of the course, weeks from now, you'll hear about the Langmuir when we talk about surface contamination and how you have to get rid of it before you bond something. The Langmuir tells you, from the kinetic theory of gases — we know these little atoms are bouncing around in this room — if we want to know how long it takes to form one monolayer of atoms on the surface of this table, assuming every one that hits sticks, it's 10 to the minus 8 atmosphere-seconds. Because this room is at one atmosphere. If I were at 10 to the minus 8 atmospheres I'd have a very difficult time breathing, but it would take 1 second to form a monolayer of gas. If I were in deep space at 10 to the minus 14 atmospheres, it would take 10 to the 6 seconds to form a monolayer. That's what we mean by atmosphere-seconds — just how fast the atoms are bouncing around at approximately room temperature. There might be a factor of three in here, but when you're talking about 8 orders of magnitude, who cares. There's also a sticking coefficient that's not 100%.
If I had one atmosphere of cobalt vapor in a container — so the same density as the air here, that's a lot of cobalt vapor — does anyone have any idea how much energy it would take to create a mole of cobalt vapor?
Student: A lot.
A lot, yes, very good answer. There's something called Richard's rule. Before I get to Richard's rule, let me give you where we go.
We go from basic thermodynamics. We know that a crystal is a regular arrangement of atoms, and a liquid is an arrangement that's not quite as regular. To go from the crystalline form to the liquid or glassy form, I have to break about 10% of the bonds. Here I have bonds in every direction — this is a two-dimensional crystal but it's really three dimensions. To go from solid to liquid, I have 10% fewer bonds, because it's more open. Most things expand as a liquid because the bonds are breaking, you have more void space in between. To go to a gas or vapor, you have to break all the bonds. This is approximately correct, because there's about 8 to 10 atomic distances between atoms at room temperature in the vapor.
What's the easy way to calculate that? If I had a pound of water and converted it to steam at room temperature, what would the volume increase be? You could go through the ideal gas law. Water is 1 gram per cubic centimeter. This would be a great problem set for an undergraduate, converting units and doing PV equals RT. I'm not going to do that to you. But does anybody have an idea what the approximate volume change is? Or the volume change of methane when it goes from liquid natural gas to gaseous methane at room temperature? We're bringing in ships of LNG into Boston Harbor — these ships are 120,000 tons.
Student: 10 to the 3.
Very good. It's actually around 600 or 800 for methane, but for water it's about 800. I like a thousand, because I can take the cube root of a thousand more easily than I can the cube root of 800 — though the cube root of 800 is about 9, the cube root of 600 is about 8. Whether it's 600, 800, or a thousand, that means the distance between atoms at room temperature in the vapor phase is about 8 to 10 times what it is in the solid or liquid, because they're in contact in the liquid and solid. A thousandfold increase in volume when you vaporize at room temperature — we're not talking high temperatures — you take the cube root of that, you know why I'm taking the cube root, right?
We know from thermodynamics that's true, because there's something called Richard's rule from metallurgical thermodynamics. Richard's rule says the heat of melting divided by the temperature of melting, for going from solid to liquid, is 8 to 16 joules per degree. If you plot the heat of fusion versus the melting temperature for lots of elements, they're on this slope of about 8.4 joules per degree. That's Richard's rule. You have to break 10% of your bonds to go from solid to liquid.
Then there's Trouton's rule, which is 10 times that — it's 88 joules. Heat of evaporation versus temperature, slope of 88 — or here it seems a little steeper, maybe 160. You've got to break ten times as many bonds, because if you're talking about an FCC crystal, face-centered cubic, how many nearest neighbors does it have? Twelve. To break all the bonds, I've got to break 12. If it's a liquid, maybe I have to break 1.2 bonds. So the heat of fusion is 1/10th the heat of vaporization. It takes a lot of energy to vaporize something.
Let's say I wanted to make a cobalt structural material. Cobalt is very expensive. I might need it for an aerospace thing, so at $20,000 a pound I can afford to make a spacecraft structural material by vapor deposition. How long would it take, at one atmosphere, to lay down a monolayer? 10 to the minus 8 seconds. In 1 second I'd lay down 10 to the 8 monolayers. That's about this thick in 1 second. On the handout, the rest of this, I calculate molar volume for lots of different metals. You find that in general, just the atomic weight and the density — or you can look at the radius — the size of atoms doesn't vary a whole lot, it's one or two angstroms radius.
The molar volume is about 10 cubic centimeters per mole. Maybe 20, maybe 7, or 4 and a half. Aluminum is exactly 10. But about 10 cubic centimeters per mole. That means 1 cubic centimeter is a tenth of a mole, is 10 to the 22 atoms. The cube root of that is about 2 times 10 to the 7. That means I can lay down a centimeter of material in about 1 second, if I have 100% sticking coefficient and the Langmuir. If I had one atmosphere of cobalt vapor, I could build it up a centimeter a second. That sounds pretty good.
Except one of the problems with vapor deposition is it tends to lay down everywhere. It's indiscriminate. Vaporization is caused by heat, and as Pauli said, heat is a disordered form of energy. Not only does it lay down where I want it to, it lays down all over the rest of my chamber. In no time my chamber fills itself with a solid mass of cobalt. Vapor deposition processes tend to work at pressures of 10 to the minus 6 atmospheres or something. The actual production rate by vapor deposition, on the back side here, is a few microns to hundreds of microns per hour. It rarely goes above a millimeter per hour.
It's going to take 10 times the energy to vaporize the material. If it's a structural material I've got to use it in very large volumes. I have a tremendous amount of energy to form the vapor, and then I'm going to grow it at most a millimeter an hour, maybe a tenth of a millimeter an hour, and I'm going to have to go in and clean 90% of my stuff off the rest of the chamber, because only about 10% gets onto the surface I really want. Does this sound practical for forming large-volume structural materials? If I want to lay down 100 angstroms on a piece of silicon, the economics work out fine for something with $100,000 per mole value. But for something with a 10-cents-per-mole value, it's a lot harder to justify vapor deposition.
§11. Bulk metallic glasses and why we cast from the liquid [89:55]
Student: What's the advantage of vapor deposition if you were to [...]
Since no one's really done it, it's not clear what the advantage would be. One advantage is you probably could make glassy materials that potentially could be very pure, if you spend even more on purifying. If you make glassy materials, we know that some glassy materials — and I was looking for my metglass material, I must have thrown it out or loaned it to somebody on the no-return plan — you can make sheets of glassy material that will be stronger than MP35N. It'll only be about 10 microns thick, but if you could vapor-deposit that and make bulk materials, it could be stronger and more corrosion-resistant. Better than MP35N.
Student: So are there people out there trying to make it better, like if you were to lower the pressure a lot and slow the process down and control it better?
Various people will seize on certain improvements. As far as making glassy metals, we'll talk about this a little bit later, I guess next Monday. One way to make glassy metals is rapid solidification. Back in the 1960s, Professor Paul Duwez at Caltech found that if he spread liquid metals — in this case nickel and boron — on a fast-spinning water-cooled copper disc, he could spin off foils. The drum might be spinning at 60 miles per hour surface speed. He could spin off little thin foils, not much thicker than a piece of paper, that cooled at a million degrees per second. If you do that, you can keep the metal from crystallizing. It would end up with a glassy structure.
All through the 1970s, when I started as an assistant professor, you wanted to get money in rapidly solidified powders or rapidly solidified metallurgy. There were hundreds of millions of dollars, if not billions, because this was going to be the new way — not from the vapor phase but from the liquid phase. All you had to do was figure out how to consolidate those foils or powders into a solid material. How do we do that? We heat things up. You heat them up and all of a sudden the atoms rearrange into a crystalline form. So Bill Johnson, one of Duwez's students who's now a professor at Caltech, played around and made what they call bulk metallic glasses. He can cast things 2 or 3 mm thick and they'll still have the glassy structure of a metal. It has fantastic corrosion resistance, fantastic strength. You can't make anything an inch thick, but you can make it several millimeters thick. You could do a lot of structural things with 500 ksi strength and corrosion resistance.
It can never get above about 300 or 400 degrees, or it will revert to lousy properties. You can use it in the same temperature range as plastics. The only commercial product they ever came up with in the last 15 or 20 years was golf clubs. You can sell anything to a golfer. Any new material you want, golfers will buy it. Sports equipment is one of the leaders for new materials, because if you have no athletic skill you can purchase it with a fancy material — that's the hope. The only problem is people have learned you get about 100 shots from the golf club and then it starts to crack. So a few other problems with it. Picking out a new material, designing a new material to have all the properties — fracture resistance, corrosion resistance, strength, ductility — it's not the easiest thing in the world. If it were easy we'd all be doing it.
The US government spends billions of dollars on these things. After rapidly solidified metals, it became fine ceramics — they were going to make ceramic engines. After that, high-temperature superconductors. After that, nanotechnology. Nanotechnology has survived for twelve, fifteen years now. You can do the same analysis I just did for nanotech. If you're really talking nanotech, the particles are only 10 to 100 times greater than the atoms in size, and if you cube that, that's a thousand to a million times more atoms per particle. Nonetheless, if you compare this to liquid-phase processing — basically melting a liquid — which by the way takes how much energy compared to forming a vapor per mole? One-tenth. So it's fairly energy-efficient to melt a material rather than vaporize it.
And you can pour it into a mold — you flow it. Viscosity is the parameter of choice. Your liquid-phase processing is somewhere between 100,000 and 100 million times more efficient than vapor-phase processing. Because structural materials are used in very large volumes, as compared to often small volumes for functional materials, the reason we start with a liquid and cast virtually every structural material — every structural material starts out as a casting. That's not always true of some ceramics, but most of them, all the metals, start out as a liquid. They don't go through the vapor phase route, partly because of the energy cost, partly because of the processing rate, partly because of all the cleanup, because vapor processing is sort of indiscriminate — it coats everything.
Student: What if you were to make something like [...] that would be able to make MP35.
Actually MP35N's not that hard to machine. They do titanium-nitride coat drill bits. You can buy them at Home Depot and they cost pennies more than a regular steel drill bit. It's a steel drill bit but the surface has been coated, and that's a structural coating by vapor deposition — but it's not the overall drill bit. If you made a titanium-nitride drill bit, the first time you drilled, you'd shatter it. As a thin film, it has very good wear resistance, which is what you're using it for.
Student: Technically there would be structural applications for very small amounts.
Oh yeah, absolutely. We do vapor-deposit things on structural materials — there's no question about it. Titanium nitride on drill bits. Corrosion-resistant coatings. We do lots of vapor deposition, and someday I'll add it to this course — maybe not this year, maybe next year — about why we do it. But we're not doing it for the underlying thing that's going to support the load. We're doing it for wear resistance or corrosion resistance or some other function.
Student: Surgical tweezers?
Surgical tweezers — if we're talking nano-tweezers, yes, you could do it by vapor deposition, you may need to. But if you're talking about the old kind of blood-and-guts tweezers, that you're going to pull a splinter out of somebody or a kidney stone, you're still going to make that by liquid-phase processing.
Student: You keep saying one of the problems is cleanup. In deposition, it seems like a natural thing to mold — almost like a pipe. Why can't vapor deposition [...] you deform it and move it to an interior, like a reverse mold?
The Army's been trying to do that for gun barrels for years. They've been trying to put vapor-deposited structural coatings on the inside of gun barrels, because they have propellants that will wipe out the gun barrel after one shot. Very good propellants, but they're not good on gun barrels. It's good if you're making gun barrels and selling them, but it's not good if you're the Army buying them. It sort of limits the functional geometry of the parts you want to make. We like to make things in all kinds of shapes.
So yes, you can think of things — like the Army and gun barrels, where you're trying to lay something down on the inside. The Army's developed all kinds of techniques over the last 100 years. Right now the big thing is chromium — they just electroplate chromium on the inside. They've tried all kinds of vapor deposition. They know there are better materials than chromium, but there's nothing as cheap.
If we're talking aerospace, if I thought really hard, I might think of a vapor-deposited structural aerospace material. You guys are going to go out in the real world, and in a few years you'll see something and say, ah, Professor Eagar was wrong, I found a vapor-deposited structural material. If you come back and tell me I was an idiot, I'm going to say, what was the price, what was the function? I'm going to hold my ground and say you're not going to make bridges out of it, you're not going to make Ford Tauruses out of it. You might make Indianapolis racers, you might make spacecraft.
I can think of cases where they made 2 mm thick diamond films, not just for the thermal properties but for some structural properties. They make diamond windows in certain infrared devices, and it has to have structural properties — also optical properties, to transmit the infrared. But they're not real big. They might be one or two inches in diameter. You're not going to build a ship out of it. You're not going to build a car out of it. You could, but there are only a couple of people in the world who could afford to buy the product.
We're talking about imparting geometry and function at a reasonable cost. Structural materials: imparting geometry, mechanical properties, probably large volumes, at a reasonable cost. If you put all three of those together, I could find an example where you want to take any one or maybe two, but when you put all three together, you really are restricted. And cost is the killer.
The Navy wanted to build an all-composite submarine after the Alpha sub. Many people in the Navy went up to the Hill and told Congress, we'll build a titanium submarine. Congress said, no, we're not going to be second. They took away from Captain Fireball the $100 million design budget for the Seawolf in the mid-80s. Congress zeroed it and gave the money to DARPA to design something beyond titanium. A bunch of admirals went up to the Hill, and Congress gave back Captain Fireball his $100 million for design. They also kept the $100 million for DARPA. I went to the workshop with a bunch of other people in Reston, Virginia. It was a three-day workshop. In some of the other videos you'll hear the stories of that. But the composites guys came in, and they must have been some of the people in the defense department thinking about what you can do when you're not limited by science or physics or chemistry — when you can just conceive of the inconceivable.
It's like the National Aerospace Plane — what a waste of money. These are the people who gave us things like Star Wars. Not that some things didn't come out of those, but not the product they were selling.
So there's processing rate, and we will get to other things. Casting is the next thing. I didn't get to it today, but we will get to it. It'll be on Monday. And tomorrow you're going to be here at 6:30 or 7:30 and you can watch the movies.