3D Printing Doubles the Strength of Stainless Steel (sciencemag.org)

sciencehabit writes: Researchers have come up with a way to 3D print tough and flexible stainless steel, an advance that could lead to faster and cheaper ways to make everything from rocket engines to parts for nuclear reactors and oil rigs. The team designed a computer-controlled process to not only create dense stainless steel layers, but to more tightly control the structure of their material from the nanoscale to micron scale. That allows the printer to build in tiny cell wall-like structures on each scale that prevent fractures and other common problems. Tests showed that under certain conditions the final 3D printed stainless steels were up to three times stronger than steels made by conventional techniques and yet still ductile.
The work was done using a commercially-available 3D printer, according to Science magazine. "That makes it likely that other groups will be able to quickly follow their lead to make a wide array of high-strength stainless steel parts for everything from fuel tanks in airplanes to pressure tubes in nuclear power plants."

Comments

Metal and Plastic

[irrational_design]

So we can now 3D print metal and plastic. I think I remember reading about the 3D printing of organic material (or maybe that was just conceptual - e.g., printing someone a new liver). What materials can we not 3D print, yet?

Re:Metal and Plastic

[FatdogHaiku]

Here you go:
https://en.wikipedia.org/wiki/3D_bioprinting

Re: Metal and Plastic

[JaredOfEuropa]

Useful stuff is already being printed. Parts that are lighter and stronger than the ones they are replacing, and are more expensive or pretty much impossible to make by traditional methods (casting, machining). Obviously not very interesting for mass produced consumer goods (yet), but this is already being used in (petro)chemical process technology and military applications, and the aircraft industry is taking note as well. There are plenty of experiments in aircraft, at this time mostly with non structural parts where weight can be saved. The other day I saw some nice (and thoroughly weird looking) suspension arms for a low production volume sports car, printed in titanium.

Re: Metal and Plastic

[oic0]

Patents killed is mostly. It cost to much to do anything with the stuff because the patent holders were harsh. Isnt that great? if you think of something first, you can hold the whole human race back if you're a jerk.

Re: Metal and Plastic

[Anonymous Coward]

Even at a thousand times the cost of other methods, that would still be quite useful. Multiple projects I've worked on had a component that was struggling with multiple constraints, and spending a lot of money to make that part work saves money for the whole project. For example, we had a project where one part could be made using tradional methods, but would be larger due to give access to machine some required features and to have enough room to assemble with fasteners or welding. Making that part bigger meant other parts got larger, limiting what shops could make it, making transportation more difficult, etc, and would have ballooned the cost of the whole machine from $10M to $50M. Spending $500k to have the critical part 3d printed instead of $10k to be traditionally machined (not counting extra engineering required to make sure assembly worked) was a hell of a lot cheaper since the part was smaller. Even if we had to pay x1000 times as much, $10M for the part, it would have been cheaper than the extra $40M needed to make the rest of the machine accommodate a larger, more traditional part.

Re: Metal and Plastic

[DontBeAMoran]

That very similar to what happened to me. I needed eight plastic end caps for square metal tubes. I could've gone online to order injection-molded ones at $2 a pop, pay $20 for shipping and wait almost a week to receive them or just 3D-print them myself at $2.50 a pop and have them the day I needed them. Bonus points: I could have them in any colour I wanted as long as I had filament in that colour!

...but I didn't have the colour I wanted on hand, so I went online and paid $40 for a spool of filament, paid $20 for shipping, waited a week to receive it and then spent the day printing them.

The morale of the story is, if you have a 3D printer, make sure you have your favorite colours of filament in stock. Not everything has to be black or white.

Re: Metal and Plastic

[MightyYar]

you can hold the whole human race back

Yeah, but not for long. And you set off a furious race to find workarounds, which itself often advances the state of the art.

There are exceptions... my hometown has a historically protected bridge. The reason it is historically protected is that it is a unique draw bridge design and I don't think there are any other surviving examples. The reason there are no other surviving examples is it is needlessly complex and thus prone to breakdown and relatively expensive to maintain. The reason it is needlessly complex is it had to work around a draw-bridge (Strauss and Scherzer bascule) patent and so used a Rall bascule design. This design was abandoned after the patent ran out. Because it sucked. Pretty soon the bridge will be 90 years old, and they are stuck with 90 years of extra maintenance and downtime because of the patent situation in 1930.

Re: Metal and Plastic

[MightyYar]

We regularly use printed "lost wax" plugs for making investment castings, and we've done so for about 20 years. Removing the casting step would be fantastic.

Re: Metal and Plastic

[slew]

The reason it is needlessly complex is it had to work around a draw-bridge (Strauss and Scherzer bascule) patent and so used a Rall bascule design. This design was abandoned after the patent ran out. Because it sucked. Pretty soon the bridge will be 90 years old, and they are stuck with 90 years of extra maintenance and downtime because of the patent situation in 1930.

Another way to look at this is that the people that decided to work around instead of license the patent didn't take into consideration the future value of the 90 years of extra maintenance and down time when they made their decision to not license the patent? Maybe it was pennywise-poundfoolish?

Of course for some people, their politics simply doesn't accept the idea that a patent is something that encourages the sharing of innovations. That's kind of like buying a knockoff widget and complaining that it isn't as reliable as the name-brand version and blaming your choice in product on the patent system...

Re: Metal and Plastic

[Solandri]

Even at a thousand times the cost of other methods, that would still be quite useful.

While there are a myriad of factors which go into selecting the proper material for a design, the general criteria that steel is best at is strength per unit cost. If you can pay more, more exotic materials like titanium, tungsten, chromium, or amorphous ("glass") metals are stronger per unit volume than steel. If you need lighter weight, aluminum and magnesium tend to have more strength per unit mass. If you need temperature resistance, niobium, molybdenum tend to be better. etc.

That said, a 2-3x strength increase is just huge, and could upset some of the generalities I listed above. It's been a decade since I delved into materials science, but a 2-3x stronger steel could displace both glass metals for strength per volume, and aluminum for strength per weight.

The latter would have serious implications for the aerospace industry. The big drawback of aluminum (other than relatively low melting point, which isn't an issue in subsonic flight) is that it has a fatigue limit. With a steel structure, you can design it so that repeatedly flexing it no longer causes it to weaken. Aluminum has no such point - flexing it will always cause it to weaken (which is why it was stupid to make Curiosity's wheels out of aluminum). Fatigue failure of aluminum has been the cause of numerous airliner accidents, from the original de Havilland Comet, to Aloha 243, to JAL 123 (greatest loss of life from a single aircraft accident). It's why pressurized airframes are retired and destroyed after about 75,000-100,000 flights. If 3D printed steel has a higher strength per weight than aluminum, it would revolutionize aircraft design.

Re: Metal and Plastic

[careysub]

Aluminum has no such point - flexing it will always cause it to weaken (which is why it was stupid to make Curiosity's wheels out of aluminum).

Reading the article and consulting NASA information about the Curiosity mission does not support the assertion that the wheel design was in any way "stupid".

According to the article you link to the (many) components of Curiosity were not tested to destruction but were tested a maximum of three times the expected mission life without failing. Curiosity was never intended to last "forever" but to last for its two year mission life which involved an 8 km trip to Aeolis Mons, its mission target. With a three-fold mission life testing program this suggests that the rover could be expected to last up to 6 years and travel 24 km before failures would likely end the mission, but anything over the original mission specification is gravy. Curiosity has now traveled 17.5 km.

Again, according to the article, what they have observed is cracks in two treads in one wheel. Test data indicates that when there are three cracked treads the wheel is at 60% of its service life. Currently there are only two, so it is at less than 60% of its service life. But let us suppose that it is at 60%, then it should be good for 29.2 km, i.e. for another 12 km, which is over three times the planned mission. But since it is only two treads, it should be more than that. What's more this is only in one wheel so far, and Curiosity can travel on five good wheels, so the service life limitation from wheel wear is likely to be quite substantially more than another 12 km. By then lots of other components will have exceeded their 3-fold mission life testing and be candidates for failure.

In short the wheels seem more than adequately spec'd and tested for the mission. It is unlikely that they will end up the cause of mission end, which in any case will be well more than three times the original planned mission. Putting 100 km wheels on Curiosity (for example) would simply have driven up cost, reduced the weight budget for some other items, all without meaningfully extending the mission potential life.

Re:Will this stainless steel rust?

[pubwvj]

There are many different grades of stainless steel that trade off cost and specific abilities. Some stainless steels have strong resistance to corrosion (rust) but that can cost more and trade off other things like workability, strength, ability to hold an edge on a knife, etc.

One big issue is if you have the stainless steel item against another metal in a rust inducing situation the other metal, such as plain iron, may rust faster and leave a stain on the stainless steel. For this reason I space my stainless steel items apart or stack in the right order to not cause rusting.

what "steel yourself" really means

[epine]

Just last night I read an entire chapter of Rust: The Longest War (2016) devoted to Harry Brearley, one among many to discover stainless steel, but the first who completely refused to shut up about it.

It was obvious to many involved that stainless steel cutlery (and certain engine parts) was the way of the future, but it took decades for most innovations in steel to find widespread commercial adoption, because every new steel at first mainly served to ruin available tooling.

I'm sure there was a slow back and forth between improved tooling, and adjusting the stainless steel to best get along with the improved tooling, but it was always slow work, and usually outside of the five-year investment cycle that made your boss loud and proud of your accomplishments.

That's why it finally took a nutter to not shut up.

Jonathan Waldman has done quite a bit of research and his writing style has an engaging tone, but there's also some kind of weird semantic deficit in his narrative structure that's difficult to diagnose in a single pass.

Be prepared for loosely grouped splotches of colour. This book has high geek appeal, but will irritate actual historians and engineers.

Re:What do you mean "strength"?

[ShanghaiBill]

I’m obviously no expert, but even I know you can't just say "strength".

Also, "under certain conditions"... Could you get any more weasely?

The weasel words came from the journalist, who felt a need to dumb things down for a general audience.

The actual paper is much more specific and unambiguous.

Under certain conditions.

[fahrbot-bot]

Tests showed that under certain conditions the final 3D printed stainless steels were up to three times stronger than steels made by conventional techniques and yet still ductile.

And under *other* conditions? TFA doesn't say.

Re:Under certain conditions.

[Anonymous Coward]

Reading the TFA, the authors compare the 3-D printed material with a cast and a wrought version.

Evidently the printed material is about 3 times (Yield Strength: 590 MPa / 86 ksi vs 160 MPa / 23 ksi) stronger than the reference casting.
But steel castings are KNOWN to be porous, full of inclusions and very low strength. They are, however, cheap.

It is an improvement on the wrought (YTS 590MPa vs 365 MPa & UTS 700 MPa vs 555 MPa & similar elongation)

High strength it is not. The aerospace industry will start to get interested when the Ultimate Strength approaches existing stainless materials (160 ksi / 1.1 GPa).

There is no mention of fatigue properties in the conclusions.

Is the process robust? Can it be replicated often with little change in the properties?

This is another step in the right direction and will open a number of useful applications.

Why one material?

[John.Banister]

If they have micron scale control, why continuously print from one material? Couldn't they make a structural center alloy that makes a gradual change (in a subsurface adjustment zone) into a protective surface alloy? In the center, they could even print micro-scale collection of overlapping unyielding hard plates for ultra impact resistance joined by a perfectly formulated softer steel for macro-scale malleability.

Often, stiffness is more important.

[rsmith]

When designing machinery or constructions, deflection under load is often the limiting factor. In those cases the stiffness of the construction is much more important than the strength of the material.

Now the stiffness of a construction is determined by both the shape and the material stiffness or Young's Modulus.

But AFAICT, little if any progress has been made in improving the Young's Modulus of alloys.

Additionally, often the ultimate strength of metals isn't really important in a design. In general designers want to make sure that the stresses in the material don't exceed the proportionality limit.