An alloy of iron and aluminium is as good as titanium, at a tenth of the cost
economist.com
economist.com
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.
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.)
I'm glad to have 6061 on my bike instead.
Thanks!
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.
How are you defining strength? Tensile 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.
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.
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 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:
https://janheine.wordpress.com/2011/10/03/science-and-bicycl...
https://janheine.wordpress.com/2014/11/23/what-is-planing/
I don't know what to think about this.
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."
[0]: http://www.nature.com/nature/journal/v518/n7537/full/nature1...
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.
"There is, of course, many a slip ’twixt laboratory bench and production line"
http://www.nature.com/nature/journal/v518/n7537/full/nature1...
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.
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?
(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.)
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.
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.
http://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25
"The MiG-25 was constructed from 80% nickel steel alloy, 11% aluminium, and 9% titanium."
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.
" 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.
always been useless for
applications such as aircraft.
For its time the MiG-25 will undoubtedly turn out to be a much finer engineering achievement than today's F-35.
[1] https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25#Operat...
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.
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.
Prices: http://www.metalprices.com/metal/steel/steelbenchmarker-cold... http://www.metalprices.com/metal/aluminum/aluminum-6061-extr... http://www.metalprices.com/metal/titanium/titanium-ingot-6al...
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.
They're symbols. They bring people together around a common talking point, to recognise and remember who we are and what we can do together.
If it really needs a purpose the Very Tall Tower could be an awesome base-jumping venue.
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?
>> 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?
«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)
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."
I guess Rearden was based on real life Andrew Carnegie who helped ignite the use of steel for construction (http://en.wikipedia.org/wiki/Andrew_Carnegie).
I assume Ayn Rand based all her characters on former industry giants (railroads, steel, oil).
>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?
I would have thought every alloy combination would have been tried by now, but I guess there's still new things to be learned.
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).
Is that literally how you feel?
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.
After all, the fast majority of applications are satisfied just fine by cast iron, brass or pewter. At the time at least.
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.