Cool, but I wonder about stiffness. When I was an aero engineer, we tended to use aluminum because most of our designs were limited by stiffness, not strength. Since aluminum is lighter than either steel or titanium, you can take advantage of geometry (which greatly impacts stiffness) without sacrificing weight. Strength was only rarely the bottleneck. Interestingly, the stiffness to weight ratio of aluminum, steel and titanium are all approximately equal.
We did occasionally use titanium, but usually some sort of steel was a better choice when strength was the issue. It's just the way it works out. It's also worth noting that for the work I did, cost was never an issue (NASA) - material costs were basically insignificant. We could use whatever we wanted.
The problem with aluminium is its resilience, not its strength. You are right that overall structural performance is governed more by geometry than by material strength (resisting moment is m^4 (area times quadratic distance of center of mass), although there are gotchas like lateral torsional buckling, which require bracing) the main problem with aluminium is that cyclical tensile loading leads to material fatigue with a effective material strength of 0%, while other metals can be counted on for at least 50% strength.
I'm not sure if you are familiar with it, but I believe that was the core problem with the aluminum-hulled Type 21 frigates of the Royal Navy. The cyclic stress imparted on the hull by wave action resulted in severe hull cracking and a relatively expensive refit to brace the hull. It also contributed to one of the frigates being sunk in the Falklands.
That's a really good point. Interestingly, the Nature Letter (paywall) [0] doesn't seem to mention the aerospace industry at all. It's more targeted toward structural and automotive applications. I'm not sure where The Economist picked up the aerospace narrative.
From the conclusions of the Nature letter: "These findings provide a new alloy-design route to lightweight steels, demonstrating that the combination of specific strength and ductility accessible to steels is greater than previously thought, and increasing the density-compensated tensile damage tolerance of structural metal for terrestrial applications."
Yeah, I don't know much about the auto industry. The basics of stiffness driven designs, though, I suspect would be the same. As would the desire for lower weight. The obvious difference being that when we made a single satellite, material costs were negligible. When you make millions of cars, they're not. That said, there are probably quite a few steel parts in a car that are not stiffness driven, so that could be a big deal if this material works out.
As I understand it, at the macro level auto design is mostly stiffness-driven. But since they use stampings everywhere, strength matters since stronger materials can be made thinner without buckling (hence your roughly tubular section is stiffer for the same weight).
Just as an aside, when I was working at a bike shop, we had a guy come in and was looking for a road bike. After some small talk, he told me he owned a cryogenics lab and said they could freeze anything, including bike parts. Doing so, made them permanently in the range of 20-30% stiffer than the original material. Most guys at the shop thought about frames, cranksets, drivetrains, forks etc. Places on the bike which experience high levels of torsional flex and stress.
I'm wondering how many engineers ever thought about using cryogenics to enhance the stiffness properties of metals to achieve higher levels of performance.
The cost to do it was around $1,500 if I remember correctly. A pretty small fee to get what I'd consider a big gain in performance.
I'm not aware of any cryo process that increases stiffness. Usually, it's more of a machinabily/stability thing they're after. But I've seen many miraculous claims in what I'd call "hobby industries" for cryo treatment. There are guys who freeze gun barrels, for example - with wild benefits that never seem to really bear fruit. I'd be highly skeptical of such claims.
I'm just wondering, how well is the influence of frame stiffness on racing performance studied and understood?
I have no personal experience in this matter, but recently I was reading some random stuff on the 'net and I found these guys swearing by flexible steel tubing:
I don't have much experience with cryo treating, but heat treating to gain strength is quite commonly done, especially for metals that are too hard to work in their strongest state, or for metals that lose their heat treat when welded.
You have way more insight than I do. What you describe reminds me of a complicated webbing of aluminum to hold everything in place. If I understand you correctly having access to a titanium equivalent could do two things. One, you could reduce part count, replace an array of aluminum supports with one titanium part. If the strength and weight are about the same, the simpler design seems better to me. Two, you could free up some space for other stuff. I'm thinking fuel tanks in wings, but i'm not even at the level of armchair aerospace engineer. There are probably many cases where aluminum is lighter but bulkier. Opening up a channel to simplify wiring, or hydraulics could be helpful.
The trouble is that it's not a lot of space, and it's not as simple as stiffness/weight of the material. Think about something simple like a structural tube. The diameter of the tube has significantly more impact on it's stiffness than it's material. So if you use a 30% lighter, but strong enough material, you can add 30% to the cross sectional area of the tube- which means you can make it a bit bigger in diameter, which will have potentially huge impacts on overall structural stiffness. Note that adding 30% more material will add at least 30% more strength to the part (huge oversimplification here, but just for arguments sake, we'll use that simple tensile case).
Titanium was useful when we needed very high strength on a very large part - a good example is the trunnions that attach payloads to the space shuttle cargo bay. These are large metal bars a little over 3 inches in diameter and maybe a couple feet in length. Aluminum is not strong enough. Steel would be punishingly heavy. (do the math - these things are beasts). So titanium can be a good fit for stuff like that.
But most steel parts were small - things like bolts, rod ends an the like. They tend to be specialized with very specific detailed requirements for things like fatigue, frictional characteristics, and that sort of thing. Because they are small, the weight just isn't that big an issue. Bigger stuff was almost always aluminum, which is actually a lot stronger than most folks realize. At least, the good stuff is.
Titanium also has some other odd properties that make it troublesome in space. I wasn't a materials guy, but they were always bitching about "hydrogen embrittlement" and the fact that large titanium parts do not burn up on re-entry like aluminum does, which presents a debris hazard to people on the ground. (I don't know how big a problem that really is, but people didn't want to be dumping space junk on top of people's heads. Honestly, I just took this on faith - people were concerned about it, but it always struck me as odd.)
By 'aluminum' do you mean 'duralumin' or just aluminum? My uncle had a few tiles of duralumin in garage, and I remember it was definitely a lot harder than plain aluminum.
Almost everything we used was plain old 6061 aluminum - the "standard" alloy everyone uses for everything. If a little more strength was needed, 7075 would usually do the trick.
Funny that I've started to think of Apple's easily CNC'd aluminium as the standard instead of 6061. That Apple stuff is about as strong as wax, not even as tough as others' plastic shells. Sure looks good on my iPhone and MacBook, though.
Amazing and useful write-up to a non-engineer audience such as myself. This is very relevant to my participation in the Local Motors LITECAR challenge (goal: reduce curb weight significantly with developing tech for 10 year outlood) sponsored by ARPA-E. If you have any references for "materials" type people with composite experience, I'd love to have a technical partner with whom to expand on my entry and share the prize money. I can be reached through the contest site or rockstarguitaristforhire at the service of mail by the big G. My apology if this strays too much, I just really enjoyed this response and felt excited about pushing boundaries.
It's been years since I worked in the industry so I don't know anyone, but I did spend a couple years designing composite structures and testing the materials. The basics of composites are learned in undergrad mechanical engineering, and you can generally apply them in real life. It's not that complicated. Where composites get tricky is in the details - de-lamination, manufacturing nits, that sort of thing. I would look at engineering schools - someone in a masters program with an interest in composites would get you quite a bit of useful knowledge. Structural composites get tricky, though. Things that are easy with metal (for example, bolting parts together) get hard with composites, and you really have to think hard or you give up all the benefits of composites when you have to engineer around their limitations.
Oh, i think i get it. The materials are different, but not different enough for a whole different design - you can't generally simplify out parts. Some strut being 1cm across vs 1.2 cm across doesn't buy you much.
To better understand the comment above you need to understand stiffness. When you take a wire of steel, which is very strong, you'll find you can actually bend it very easily. If this kind of stress is what the material will face, you could replace the wire by a thin tube which will be much more rigid -- you probably don't want your structure bending and deforming. In this case, where stiffness is more important, it's more important that the material is light so you can make it larger yet proportionally stiffer per unit weight by using an adequate structure -- e.g. a tube or large diameter (this is because the bending stiffness increases more-than-linearly with diameter).
Now suppose instead you were trying to traction the wire (pull it). There's no structural change that will make it stiffer -- in this case all you may want is that it is very strong -- in which case you simply go for the best strength/weight or just pure strength.
If you went for a compression stress however you'd probably want that same bending stiffness (by making a hollow tube) because rarely the force is perfectly axial.
Just the opposite. 1.2cm vs 1cm might be a world of difference. And if weight is a concern, you might be stuck with a 1cm tube, which might be less stiff than the 1.2 cm tube even if it's made out of a stiffer material.
The idea is that design is material dependent. You can't assume you can just swap out parts for lighter/stronger/stiffer parts and still have everything work.
'As good as' is a silly phrase to use in metallurgy. Are we talking machinability, castability, tensile strength or hardness. Not to mention less obvious issues like food safety or resistance to corrosion?
There are very many alloys of both aluminium and steel all of which have there uses. To say this one is as good as titanium means very little.
The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys
So presumably it is stronger and somewhat more workable than titanium.
Then there's yield strength, ultimate strength, magnetic properties, heat/cold compatibility, toughness, ductility, density, weldability, modulus of elasticity and aesthetics.
From TFA: "Dr Kim has produced a material which has the strength and the lightness of titanium alloys but will, when produced at scale, cost a tenth as much."
Now that nature lets you read articles for free you can actually go and read the original paper.
In the paper the authors had to heat treat the steel at 900 °C for 15 mins to generate the microstructure that gave the properties they wanted.
So, what does welding do to the microstructure? Does this material need to be heat treated again at 900 °C after welding? Does the the hard-but-brittle B2 intermetallic reform in the HAZ?
That's a really interesting question, and I'm not sure what the answer should be. According to the authors, the B2 intermetallic forms in small particles during recrystallization at 900 C because of the influence of the nickel, so you might expect a similar high rate of particle nucleation in the wake of the melt pool, resulting in small, dispersed particles. Then again, you might get coarse intermetallic phases instead, resulting in a brittle weld.
In either case, the advantage of the B2 particles is that they allow a high degree of strengthening during work hardening, which would be done before welding. Any subsequent heat treatment would tend to undo that work hardening.
Interesting question, although I'm not sure it applies much in the real world. Aren't the welds themselves typically the weakest link in a build? Seems like the engineering tricks used to keep welds under stress from ripping apart would also benefit the affected metal in the HAZ.
Yep! Generally if your weld breaks before the material in the HAZ it is considered a bad weld and certified welders working under structural standards are generally required to produce welds that are stronger than this.
(Not actually a certified welder right now, but I have a brief familiarity with the D1 structural standards as getting a cert is something I've looked into.)
>By manipulating the structure of steel on a nanometre scale, Dr Kim has produced a material which has the strength and the lightness of titanium alloys but will, when produced at scale, cost a tenth as much.
i wonder what if the same to be applied to titanium.
>Steel is useful because it is strong and cheap. But it is also heavy. It has, therefore, always been useless for applications such as aircraft.
The Sierras also had titanium pressure hulls. Both classes suffered from major maintenance issues, though, because the titanium was prone to cracking from the severe pressure changes during dives. The Soviets switched back to steel for the Akula class.
The grains they are talking about are forming out of the iron and aluminum in the alloy. So the same type of thing (a lighter alloy with a crystal structure that leads to good properties) might apply to titanium, but the ingredients wouldn't necessarily be the same.
The graphite pencil might be a finer engineering achievement than today's F-35, in that you can take one out of the package without it setting itself on fire, and you don't have to wait 4 years before actually writing anything with it.
The MiG-25 was one fast mother, despite having to change those huge engines often... It did achieve a world record in altitude. Read more about the design and construction here:
> "It turned out that the weight of the aircraft necessitated large wings."
As opposed to other combat aircrafts featuring large wings for high-altitude performance and maneuverability.
Before we diss steel as viable aircraft material, note that weight was increased both by heavy engines† and presumeably heavy avionics, as those were based on vacuum tubes.
Including a 600kW (!) radar, if we are to quote Wikipedia everywhere.
† the engines alone, at 4900kg a pair are 25% of MiG's dry weight, add some overhead for support structures necessited by their sheer power. For contrast, F/A-18's engines are 20% of dry weight.
of course. At those speeds you don't have much choice of materials - basically either steel or titanium - and that choice results in the huge difference in weight and thus in range. Compare MiG-25 with Blackbird:
" On the SR-71, titanium was used for 85% of the structure, with much of the rest polymer composite materials."
But you just can't build your interceptor/fighter force out of titanium - it is extremely cost prohibitive. The point here is that steel is pretty legitimate aircraft material in specific part of the performance/cost envelope.
So the steel companies are finally getting scared enough to innovate. There are people trying to dramatically reduce the cost of titanium, Ford is dumping steel for aluminum, composites are even replacing aluminum in aircraft. Steel is starting to look like a relic of the 1700's rather than the great material it has been for so long.
When I worked in EVs, one of the old timers (a guy almost 80 years old) told me the best steel for the motors should have some Boron in it. Some particular alloy that would have lower core loss at higher frequencies. But none of the big steel companies were interested in making it for us. They just wanted to make what they make.
So even if it's not as great as it sounds, I'm glad somebody is doing something with steel.
As a materials engineer who works for a steel company (although my background is in blast furnaces and iron ore smelting - not micro alloying) maybe I can shed some light.
It largely comes down to enconomies of scale you can certainly make specialised grades of steel but often times it is not profitable to do so. Steelmaking is like most manufacturing process, cost decreases with scale. Usually the specialised grades simply aren't in high enough demand to recoup the costs involved in producing them.
For some grades the techniques to produce them are suitably differnt from standard grades that lines needs to be diverted and retooled to handle them, which impacts on yield and causes losses due to downtime etc. Not to mention many of the specialised alloying elements like Niobium etc. are also stupidly expensive. Buying these in small quanities is probably not ideal and I'd imagine its probably risky to buy in bulk because orders may not be filled quickly and business doesn't tend to like having capital tied up in raw material stockpiles.
Competition is also very fierce, for a while there has been an excess of steel capacity largely driven by rapid expansion of China's steelmaking capacity. So there is a lot of pressure on keeping operating costs per tonne low all of this kind of leads companies towards where the biggest returns are, which is producing the high volume steels at lowest cost. Thus most of research effort gets directed here as well. Thats not to say R&D isn't happening into specialised grades, its just not where the big payoffs are currently.
The yield strength of that new material is from about 1 GPa to 1.4 GPa, vs. 830 MPa for Ti6Al4V (Steel and Aluminium vary, depending on the alloy).
It has a density of 6.82 g/cm3, vs 4.43 for the titanium alloy, 7.85 for ordinary steel or 2.70 for 6061 Aluminium.
Apparently Ti6Al4V costs around $20/kg, so the new alloy would cost around $2/kg, vs. around $2.70/kg for 6061 Aluminium or $0.85/kg for cold-rolled steel.
As for the modulus of elasticity, it isn't mentioned in the article. The usual figure for steel is 210 GPa. The titanium alloy is around 114 GPa, and 6061 Aluminium is 69 GPa.
The low density is fairly big new. Compared to mild steel, you can have a 15% larger volume for the same weight, so you might be ahead on stiffness even if the MoE is smaller.
It will be good if this is real. Nature articles about nanotechnology which claim "huge breakthrough to be commercialized real soon now" are all too frequent. Then we never hear about the technology again.
For aerospace, the big advantage of titanium is a high melting point. This material won't have that, which is probably why the authors talk about automotive applications. For automotive applications, a question is whether these new properties will survive ordinary manufacturing processes. Casting, probably not, but maybe the process can be applied to castings later as a heat-treating step. What about rolling and stamping?
In the original article they say they cold-roll, recrystallize, then strain harden. So definitely no casting, because the recrystallization is where the magic happens. Rolling and casting should be fine though. They say that the alloy is mostly compatible with current steel processing infrastructure, so it looks promising.
With aircraft the basic issue is strength to weight, not just weight. If the material is stronger you can use less of it. The trend today is to make aircraft out of really strong fibres embedded in plastic.
Since the original paper is behind a paywall (at least for me), can anyone explain the specifics of what the researchers did to produce this new alloy?
>> Dr Kim and his colleagues have, however, found that a fifth ingredient, nickel, overcomes this problem.
I'd imagine that it didn't take a world-class team of scientists to have come up with the idea of alloying using nickel. There is no way materials scientists and metallurgists hadn't tried this by now, so what did they do differently?
Materials Science PhD student here, I'll do my best.
The morphology of the brittle B2-FeAl intermetallic compound is the key. In the conventional lightweight steel alloys, the B2 intermetallics make the alloy brittle (so they don't work harden very well), so in the past researchers optimized their alloys to avoid forming these intermetallics [0]. The nickel promotes the nucleation of the intermetallic particles during heat treatment [1], so that you get a more-or-less uniform distribution of many nanocrystalline B2 particles, instead of a smaller number of larger or more clustered B2 domains. The small B2 particles contribute to strain hardening by pinning dislocation motion, without reducing the ductility of the alloy.
From the Nature letter:
[0]: "One of the general concepts employed until now in the alloy design of Fe-Al-Mn-C-based, high-aluminium, low-density steel has been the suppression of ‘brittle’ intermetallic compound formation by stabilizing the ‘ductile’ austenite matrix."
[1]: "To expand the stability domain of B2 above the recrystallization temperature (normally, 800–900 °C) of deformed austenite, the alloying recipe of an austenitic low-density steel was modified by adding 5 weight per cent nickel (Ni), which is one of the most effective elements for forming B2 with aluminium."
Since this is mostly undecipherable for me, I'll just quote:
«A common method of uniformly distributing fine particles in a matrix is to make the best use of highly potent nucleation sites for inducing the precipitation of the particles. In this study, potential nucleation sites for B2 during annealing of wrought sheet steel include (1) grain boundaries or edges of recrystallized austenite crystals and (2) deformation shear bands, which are common in hot- or cold-worked low-density steel. To expand the stability domain of B2 above the recrystallization temperature (normally, 800–900 °C) of deformed austenite, the alloying recipe of an austenitic low-density steel was modified by adding 5 weight per cent nickel (Ni), which is one of the most effective elements for forming B2 with aluminium. The addition of Ni to low-density steel may appear to conflict with the collective wisdom of ferrous alloy design; Ni has been regarded merely as a well-known austenite stabilizer like Mn and C; and Ni has been little noticed in low-density steel design, mainly because it is not a critical determinant of the density in ferrous alloys.» (citations omitted)
Don't know why you are being downvoted, these guys are notable for being perceived as not giving fig for what other people thought, and being successful doing it.
>An alloy of iron, aluminium and carbon (steel’s other essential ingredient) is too brittle to be useful. Adding manganese helps a bit, but not enough for aluminium-steel to be used in vehicles.
>Dr Kim and his colleagues have, however, found that a fifth ingredient, nickel, overcomes this problem.
As far as I know turbine blades are typically made of iron-nickel alloys. What is the new part of this discovery?
Which is all great but as far as I'm aware one of the major reasons for titanium's use was its high melting point. Nothing is said of how this compares here.
This, if it works, is worth quite literally millions as times as much as another "social network" or stupid app, but I'll wager the team aren't "acqui-hired" for $19Bn.
I'm interested in where you came up with the "literal" worth comparison.
Perhaps what you meant to say is that, "I personally feel that this new steel alloy is worth more than whatsapp, and, I would be personally prepared to pay at a valuation of 1 million times greater than the whatsappp valuation. So, going back in time, if I had a choice of owning 10% of whatsapp for a $10,000 investment (valuing whatsapp at $100K), or 0.00001% of the company producing this alloy (valuing it at $100B, or 1 million times as much as whatsapp, I would take the 0.00001% for my $10,000 instead of the 10% share of whatsapp for $10,000).
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Why? Are there really that many use cases for titanium? I used to make nuclear submarines, I have actually designed a bunch of things that use super alloys that cost 10x what titanium costs. But even then, the fast majority of things I designed used "regular" steel or aluminum. There just aren't that many applications where you need something like that.
You need the combination of caring a lot about weight, strength, and size. That's not that common. The only time you need a better material is when all three of those things are inflexible. Otherwise I can make a bigger part, or switch to steel, or switch to aluminum.
Aluminium was a useless novelty because we were unable to manufacture lots of it back then. Something to do with electrolysis requiring lots of electricity, I believe, and there weren't a huge number of electric powerplants operating in 1880.
The Hall-Heroult process did not exist, regardless of powerplants. Aluminum was more expensive than gold because it could only be produced by non-electric vacuum smelting. (While there was not a "huge number" of generators there was enough electric infrastructure in 1880 to support electric cars.) If the HH process existed a decade earlier it would have been used a decade earlier.
Krschultz was being small minded by saying that titanium is expensive, exotic and not useful compared to the cheap metals we have. While forgetting that we didn't always have those metals cheaply.
I was going for sarcasm, but oh well. And you could argue that the HH process would have been invented earlier if electrical powerplants has been invented earlier; the simultaneity of these two historical events is remarkable: the world's first public powerplant opened just 4 years before the discovery of the HH process.
I do not think you can make the comparison. The article is about a science paper, and you are talking about the company Whatsapp. Facebook had already explained why they bought it at this cost. The kind of Titanium here (Ti6Alv4V) does not seem to be that good, so "it seems" we should not be too optimistic here (but I'm just a developer, correct me if I'm wrong).
We did occasionally use titanium, but usually some sort of steel was a better choice when strength was the issue. It's just the way it works out. It's also worth noting that for the work I did, cost was never an issue (NASA) - material costs were basically insignificant. We could use whatever we wanted.