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Arthur T Knackerbracket has found the following story:
For millennia, metallurgists have been meticulously tweaking the ingredients of steel to enhance its properties. As a result, several variants of steel exist today; but one type, called martensitic steel, stands out from its steel cousins as stronger and more cost-effective to produce. Hence, martensitic steels naturally lend themselves to applications in the aerospace, automotive and defense industries, among others, where high-strength, lightweight parts need to be manufactured without boosting the cost.
However, for these and other applications, the metals have to be built into complex structures with minimal loss of strength and durability. Researchers from Texas A&M University, in collaboration with scientists in the Air Force Research Laboratory, have now developed guidelines that allow 3D printing of martensitic steels into very sturdy, defect-free objects of nearly any shape.
"Strong and tough steels have tremendous applications but the strongest ones are usually expensive -- the one exception being martensitic steels that are relatively inexpensive, costing less than a dollar per pound," said Dr. Ibrahim Karaman, Chevron Professor I and head of the Department of Materials Science and Engineering. "We have developed a framework so that 3D printing of these hard steels is possible into any desired geometry and the final object will be virtually defect-free."
Although the procedure developed was initially for martensitic steels, researchers from the Texas A&M said they have made their guidelines general enough so that the same 3D printing pipeline can be used to build intricate objects from other metals and alloys as well.
The findings of the study were reported in the December issue of the journal Acta Materialia.
[...] "Although we started with a focus on 3D printing of martensitic steels, we have since created a more universal printing pipeline," said Karaman. "Also, our guidelines simplify the art of 3D printing metals so that the final product is without porosities, which is an important development for all type of metal additive manufacturing industries that make parts as simple as screws to more complex ones like landing gears, gearboxes or turbines."
Journal Reference:
Raiyan Seede, David Shoukr, Bing Zhang, Austin Whitt, Sean Gibbons, Philip Flater, Alaa Elwany, Raymundo Arroyave, Ibrahim Karaman. An ultra-high strength martensitic steel fabricated using selective laser melting additive manufacturing: Densification, microstructure, and mechanical properties. Acta Materialia, 2020; 186: 199 DOI: 10.1016/j.actamat.2019.12.037
(Score: 2, Interesting) by Anonymous Coward on Monday April 20 2020, @05:46PM (7 children)
A few minutes of refreshing the metallurgy courses I took, a coon's age ago.
As I thought, martensite is formed by very rapid cooling, it doesn't appear in the normal steel phase diagram like this detailed version, because the diagram lacks the dynamics of freezing directly from a liquid and "non-crystalline" state,
https://www.tf.uni-kiel.de/matwis/amat/iss/kap_6/illustr/s6_1_2.html [uni-kiel.de]
Some of the basics are covered here, https://en.wikipedia.org/wiki/Martensite [wikipedia.org]
A lot of development has gone into steel alloys that can give good properties *without* this very rapid cooling, because it's basically impossible to rapidly cool the internals of a thick part. Steel just doesn't conduct heat fast enough. Quenching in super cold (ie, liquid nitrogen) is sometimes claimed to help, but I believe the gains are not large(?)
If the 3-D printer delivers small drops of liquid metal to build up the part, it should be easy to get martensite, since contact cooling with previously solidified metal is very rapid. And the quench rate should be roughly the same all the way through the part.
Years ago I remember reading about some experiments in rapid cooling--a thin jet of liquid steel was aimed at a cold, rotating, steel drum. When it came in contact the cooling rate was extremely fast, much faster than can be achieved with liquid (water or oil) quenching.
The thing that always amazes me is that 3-D printing can produce dense parts, it just seems that adding up droplets would result in voids. Anyone understand this part of the process?
(Score: 3, Redundant) by aristarchus on Monday April 20 2020, @07:39PM (1 child)
It is called "printing", and that suggests and additive process, squirting out molten steel like plastic, but I have not heard of this being achieved. What are the nozzles made of? Voids are the least of your problems, the entire product may be more ceramic than metal. Most metal 3D "printing" is actually sintering, using lasers to melt a layer from metal "dust" or particles. Not sure how that could produce martensite.
Seems like all you have to do these days is say "3D printing", and the need for details, plausibility, or a national lock-down just goes away, magically.
(Score: -1, Offtopic) by Anonymous Coward on Monday April 20 2020, @09:18PM
https://en.wikipedia.org/wiki/Laser_printing [wikipedia.org]
(Score: 4, Informative) by Kitsune008 on Tuesday April 21 2020, @03:08PM (4 children)
In this case, the metal is deposited in thin layers as a powder, then fused with a laser. Normally you would still get some voids, but what they are doing is experimenting with different laser settings, then plugging the results into a predictive modelling program that will give them the best range of laser settings to use. They claim that with just a few tests, their modelling program can accurately predict the correct settings for any metal/alloy to reduce/eliminate voids or porosity.
I hope this answers your question. :-)
(Score: 2) by Osamabobama on Tuesday April 21 2020, @08:08PM
This sounds like Design of Experiments [asq.org] methodology. There's probably a complex model behind it and software to automate the thinking that make it seem more novel.
Appended to the end of comments you post. Max: 120 chars.
(Score: 2) by aristarchus on Tuesday April 21 2020, @09:36PM (2 children)
Porosity question, but not the martensite question, which seemed the point of the Fine Article?
(Score: 2) by Kitsune008 on Wednesday April 22 2020, @01:43AM (1 child)
I think you missed the point of TFS, much less TFA.
From the summary:
They specifically developed this technique with martensite steels, for martensite steels.
With this technique, they claim it not only works for martensite steel, but all metals/alloys.
(Score: 2) by aristarchus on Wednesday April 22 2020, @02:15AM
But martensite steel is not an alloy, it is a crystalline structure of carbon steels, one destroyed by melting heat, or even fusing heat, and only produced by rapid cooling, as mentioned by a previous poster. Do not make me have to go read the original article! Please!