I wonder... (metallurgical thoughts)

"BaconSandwich is tasty." (baconsandwich) 03/10/2015 at 14:36 • Filed to: None

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I can't quite remember where I saw it (either here on Oppo or over on Ars Technica), but someone was showing how turbine blades are being made from a single crystal of metal. When casting, the metal first goes through a sort of pig-tail shaped tube into the main casting chamber. When things start to cool, it eventually forms a large, single crystal for the bulk of the turbine blade.

Now I'm wondering - are automotive manufacturers already using processes like this to form connecting rods, pistons, etc.? Would there be any advantage to doing so over other processes, like forging?

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$kaycog > BaconSandwich is tasty. 03/10/2015 at 14:45

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This? http://oppositelock.jalopnik.com/power-this-is-…

spanfucker retire bitch > BaconSandwich is tasty. 03/10/2015 at 14:47

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Inconel I believe is one of those "super alloys" and Porsche used it for the 918's exhaust system.

Mr. Ontop, No Strokes, No Smokes...Goes Fast. > BaconSandwich is tasty. 03/10/2015 at 14:47

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Damnit. I knew the exact right person to ask about this, my uncle. he was in the steel industry pretty much his entire life. He would have known....and then I remember that he just died two months ago.....He didn't like me very much, but there was a certain amount of respect I had for him. He knew his stuff.. doz unexpected feelz.

BaconSandwich is tasty. > $kaycog 03/10/2015 at 14:50

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That's the one!

BaconSandwich is tasty. > Mr. Ontop, No Strokes, No Smokes...Goes Fast. 03/10/2015 at 14:51

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Hmm, sad. :(

TJDMAX > BaconSandwich is tasty. 03/10/2015 at 14:53

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Working for an automotive engine design company i can shed some insight on why i think the automotive industry doesn't use this form of manufacturing. One reason is cost. Not that i think the manufacturing process is more expensive than standard casting (although it probably is) but it sounds like it takes longer to cast each part and you have to be very careful in how you cast each part which slows production and increases cost.

Another reason is that engines in vehicles don't run for as long as those in airplanes. Nor do they have to follow as strict durability and maintenance requirements. Plane engines are working constantly for 15 hours straight sometimes. Car engines hardly run that long uninterrupted and even if they did there is a range of loads on a car engine. Between accelerating and stopping and cruising and idling all those conditions can make it so that the engine isn't constantly under high loads. Also, If a fan blade on a 787 goes out at 600+mph and 35,000ft it could be tremendously catastrophic. If your engine block gets a crack on the highway you likely won't die. The engine would just make a whole lot of noises and you would be able to get to the side of the road safely.

But probably the biggest reason is that in an engine you want a blend of material because different elements will provide different benefits to an engine. A cast iron block will have elements in there that increase the strength but others that provide lower friction, or are harder to prevent erosion of the bores etc.

So while i don't have an exact reason why the automotive industry doesn't use this technology i have some safe assumptions...

Hope this helps.

BaconSandwich is tasty. > TJDMAX 03/10/2015 at 15:01

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Very interesting! I greatly appreciate your answer. I imagine the F1 teams are already likely all over this sort of thing.

MrDakka > BaconSandwich is tasty. 03/10/2015 at 15:08

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Yes and no.

Mechanically speaking, it would be great. You can get much closer tolerances, the engine could hotter and at higher pressures, but it would stupidly expensive and take forever to make compared to normal engines; not to mention all the retraining and tooling needed to replace the conventional methods.

The whole point of single crystal parts is to eliminate grain boundaries. Doing so gets rid of the defects that arise from having grain boundaries in the first place. For gas turbine blades, this is significant because of the low thermal creep property that is inherent in single crystals. In addition if you make it right, you can get increased yield strengths.

Personally I think that bulk nanophase materials would make a bigger impact in the automotive industry than single crystal parts at a much lower cost.

Tapas > spanfucker retire bitch 03/10/2015 at 15:09

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Not really.

Short answer to this (and OP's question) is that these are cost prohibitive.

Inconel is expensive as hell and its more difficult to shape, machine and weld. Its a Nickel based alloy.

To give you an idea, Steel is around $590 per tonne. Nickel is a little more than $14000 per tonne - per the London Metal Exchange. So this, plus the more expensive cost to process the Inconel.

Yes, Nickel is only a majority percentage of Inconel so this doesnt give you the exact price. And, a much smaller percentage of Nickel is also used in steel. But it gives you a rough idea.

Tapas > BaconSandwich is tasty. 03/10/2015 at 15:12

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Possible, but it would make cars way too expensive to make.

The auto manufacturers would have to invest heavily in new equipment or find another vendor that will make their investment and scale up production to churn out the hundreds of cars made everyday, with a reasonable cost.

Just look into the difference in cost of a turbine blade and a car panel. The blade would be more expensive by a factor of about 20.

Besides cost, the single crystal wouldn't be able to withstand torsional or flexing forces very well. Single crystals take forces in only a few specific directions very well ( which depending on a bunch of other things)

They work well as turbine blades because the direction of force is in one direction...

BaconSandwich is tasty. > MrDakka 03/10/2015 at 15:12

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Bulk nanophase materials?

MrDakka > spanfucker retire bitch 03/10/2015 at 15:12

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But is it a single crystal part? Inconel is just a family of superalloys, it can be polycrystalline or monocrystalline

BaconSandwich is tasty. > Tapas 03/10/2015 at 15:13

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Perhaps this becomes an opportunity for the after-market club. Want stronger connecting rods, etc.? Yes, you can get them, but you'll pay for them.

BaconSandwich is tasty. > BaconSandwich is tasty. 03/10/2015 at 15:14

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Doing some reading - http://en.wikipedia.org/wiki/Nanophase… . Not a whole lot on Wikipedia on them.

garagemonkee > BaconSandwich is tasty. 03/10/2015 at 15:17

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another thing to think about, at least in mass production, is how many use "cracked" connecting rods. The rod is cast/forged in a single piece, then cracked at the end to make the split so that you can install it over the crankshaft. Instead of all the machining time required. A single crystal would probably make this impossible, at least from a mass-production standpoint.

TJDMAX > BaconSandwich is tasty. 03/10/2015 at 15:18

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Yes and no. Remember that casting in general is best when you're making many many copies of the same part. I would guess that F1 teams are constantly changing components designs to be lighter / stronger / more efficient etc. So while i don't work for a F1 team i can almost guarantee that the big ones aren't using cast pieces because it costs so much to make a mold for a component and then have to make a new mold every time the component changes slightly.

Some manufacturing styles i think you would be impressed by are sintered metal or powdered metal processes.

MrDakka > BaconSandwich is tasty. 03/10/2015 at 15:18

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Basically large USABLE chunks of nanomaterials instead of laboratory sample sizes

Just google nanocrystalline/phase metal/ceramic for more info.

https://nanosteelco.com/

http://www.modumetal.com/

GTI Sprinks > TJDMAX 03/10/2015 at 15:19

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Best reply. Bravo.

Technology like this is always trickle down. Starts with high-tech mil applications then trickles down to commercial airliners. Once it becomes more readily available it might trickle down to high performance niche automotive. Once it makes it there it may make it down to consumer level automotive.

Tapas > BaconSandwich is tasty. 03/10/2015 at 15:25

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Thats possible, just incredibly expensive to engineer.

BaconSandwich is tasty. > MrDakka 03/10/2015 at 15:25

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Interesting. Hadn't heard of it until today.

TJDMAX > GTI Sprinks 03/10/2015 at 15:26

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Definitely true. But even if it somehow becomes cheaper (somethings are just complicated to do and thus will always be expensive to manufacture) there are still benefits in the automotive world of having blended materials, and at the same time there just isn't a performance demand for that high of precision or strength. But we shall see....At least for now most manufacturing techniques are pretty much the same as 30+ years ago. Forging, casting, machining etc. Sure the technology has gotten better so production has increased and quality too, but the processes haven't changed.

spanfucker retire bitch > MrDakka 03/10/2015 at 16:22

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Don't know, go to Wiki.

Kailand09 > TJDMAX 03/10/2015 at 18:24

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Don't forget about the additive manufacturing methods with 3D sand printing for endless cast possibilities nowadays.

Though you are spot on, I doubt they really do much cast.

GTI Sprinks > TJDMAX 03/11/2015 at 08:25

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100% agree. It's all materials optimization, and single crystal metal parts are not going to be perfect in every situation. One of the most memorable stories the head of my materials science department in college ever told was talking about how his saab turbo compressor wheel blew and how it was this fragile piece of ceramic and why we can't just build them out of just any material. Right tool for the right job, and right material for the right tool.

You can tell a Finn but you can't tell him much > BaconSandwich is tasty. 03/11/2015 at 15:10

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I see $kay posted the link below, but I had something on single crystal turbine blades a while back. For things like connecting rods it wouldn't make sense. The reason that single crystal materials are used in turbines is because of the operating conditions. The turbine blades operate at very high steady state stresses and temperatures very near their melting points. This increases the risk of creep failure to the point that a single crystal blade is required to survive in the operating conditions. Creep occurs in a material when it is subject to a steady load over time. Instead of quickly stretching and failing it will stretch over time in the direction of the load. Creep becomes worse as a material operates closer to its melting point. In the case of gas turbines some turbines have turbine entry temperatures that are actually higher than the melting point of the turbine blades.

Figure 8 demonstrates a couple of the technological advances that Rolls-Royce has employed in its successful turbine blade design and material definition, thereby allowing it to employ a TET above the melting point of the alloy (TET > 1500 C, alloy melting point about 1350 C). The key advances have been the manufacture of single-crystal blades, with internal cooling channels, and, latterly, thermal barrier coatings. Cooler air (air at 700 C) is bled off from the compressor and passed through the turbine blades. Small laser-drilled holes in the surface of the blade allow the cooler air to flow over the working surfaces, protecting them from the hot gas stream. In a later development ceramic materials have been deposited onto the blade surfaces, further protecting them from the aggressive environment and allowing yet higher TETs to be achieved. Source with Figure 8 on page 510 .

A connecting rod isn't subjected to anywhere near the stresses of a turbine blade and the temperatures are an order of magnitude lower. Connecting rods are subjected to fatigue loading where the rod oscillates between tension and compression loading as the piston reciprocates. Since there is no steady state load there isn't loading that would generate creep failure. To avoid fatigue failure you want to keep the stress in the part below the endurance limit of the material. Since single crystal materials can have a lower yield strength they will have a lower endurance limit. Making a conrod out of a single crystal would give you a more expensive part that performs worse in the loading conditions it is subjected to.

If you look at the chart which is either below or next to this or wherever Kinja decides to put it, the blue curve is the S-N curve for steel. It graphs the number of cycles that a steel part can withstand subject to a given stress before it fails. Generally speaking steel parts are designed so that the stress is below the flat part of the line as this gives them a theoretically infinite life.

Even for the case of something like an exhaust valve it wouldn't make sense to go to a single crystal. Like the conrod, an exhaust valve is subject to fatigue loading, not creep loading like a turbine blade sees.

One interesting trick that manufacturers have used to keep exhaust valves cool is sodium filled valves. The stems are hollow and then partially filled with sodium metal under a vacuum. The sodium at the low pressures in the tube is a liquid at room temperature and a gas at engine temperature. As the valve goes back and forth the sodium bounces from one end to the other. At the combustion chamber end the sodium turns from a liquid to a gas which takes a lot of heat out of the valve. At the other end it turns from a gas back into a liquid which transfers the heat from the combustion chamber to the oil and/or coolant in the heads. The valve stem acts as a heat pipe to transfer heat from the hot combustion chamber to the coolant systems.

BaconSandwich is tasty. > You can tell a Finn but you can't tell him much 03/11/2015 at 15:36

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Wow. That's one heck of an awesome answer! I had always thought that sodium valves were some sort of metal treatment, not actually vacuum sealed with liquid/gas sodium in them. Very interesting!

Axel-Ripper > You can tell a Finn but you can't tell him much 03/11/2015 at 15:42

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Also not to mention that sometimes you'd rather have connecting rods that aren't 100% rigid. Top fuel dragsters for example run billet aluminum connecting rods. If they run hardened steel rods the vibrations transferred through them will destroy the crankshaft.

You can tell a Finn but you can't tell him much > Axel-Ripper 03/11/2015 at 16:06

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Top Fuel is a whole different problem/question/animal. Just to be clear, even steel or titanium conrods deform under load, just not as much as aluminum. I also feel the need to mention that connecting rods are heat treated, not hardened.