Author Topic: What Are the Strongest Alloys?  (Read 30420 times)

Offline sanman

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What Are the Strongest Alloys?
« on: 02/05/2015 03:44 am »
What are the strongest alloys for building spacecraft? While we all know that carbon composites are generally lighter, they can't be used everywhere, and their strength is of course directional.

I remember reading in the past about how alloys from Titanium, Beryllium and Chromium were the best for aerospace, and how the Orion capsule is using even lighter aluminum-lithium alloys.

Here's a report about the development of a new alloy which is supposedly as light as aluminum and at least as strong than titanium:

http://www.spacedaily.com/reports/New_high_entropy_alloy_light_as_aluminum_as_strong_as_titanium_999.html

Quote
Researchers from North Carolina State University and Qatar University have developed a new "high-entropy" metal alloy that has a higher strength-to-weight ratio than any other existing metal material.
...
"The density is comparable to aluminum, but it is stronger than titanium alloys," says Dr. Carl Koch, Kobe Steel Distinguished Professor of Materials Science and Engineering at NC State and senior author of a paper on the work.

"It has a combination of high strength and low density that is, as far as we can tell, unmatched by any other metallic material. The strength-to-weight ratio is comparable to some ceramics, but we think it's tougher - less brittle - than ceramics."

Here's also an interesting article from The Economist talking about a new iron-aluminum-nickel alloy that is claimed to have comparable strength to titanium, but at a tenth the cost:

http://www.economist.com/news/science-and-technology/21642107-alloy-iron-and-aluminium-good-titanium-tenth

How much scope is there for further improvements in alloy properties, and what are the best candidates?

Offline Hanelyp

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Re: What Are the Strongest Alloys?
« Reply #1 on: 02/05/2015 04:17 am »
Strongest for what kind of loads?  At what temperature?  What other operating conditions?  Some alloys that deliver superior performance at modest temperature lose most of their strength before they get very warm.  Extremely hard high tensile materials can be brittle.  Carbon fiber is very strong, and retains strength at high temperatures, but burns if you get it hot in an oxygen atmosphere.

Offline CyclerPilot

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Re: What Are the Strongest Alloys?
« Reply #2 on: 02/05/2015 05:00 am »
Hanelyp has it right.  There are other factors to consider.  The primary property is strength to weight, but other properties can make our break its utility for a given application.
 
Aluminum lithium alloys work well because they combine good strength to weight, good toughness, and are relatively easy to process (weldable, machinable, etc.)

Titanium based alloys all suffer from being difficult/expensive to process.  They absorb oxygen at elevated temps, and become brittle.

The two you linked both seem to be sacrificing ductility for tensile strength, but there probably is some net benefit.  If they have a fatigue limit, they could have one advantage over aluminum alloys.

The cool thing about metallurgy is that an addition of just a few percent or a different heat treat can greatly change the properties of an alloy and fix a shortcoming.  When there is a large financial incentive, more materials research is done, and they hone in on some ideal alloys (see nickel superalloys as an example).

Offline john smith 19

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Re: What Are the Strongest Alloys?
« Reply #3 on: 02/05/2015 06:06 am »
Here's a report about the development of a new alloy which is supposedly as light as aluminum and at least as strong than titanium:

http://www.spacedaily.com/reports/New_high_entropy_alloy_light_as_aluminum_as_strong_as_titanium_999.html

Here's also an interesting article from The Economist talking about a new iron-aluminum-nickel alloy that is claimed to have comparable strength to titanium, but at a tenth the cost:

http://www.economist.com/news/science-and-technology/21642107-alloy-iron-and-aluminium-good-titanium-tenth

How much scope is there for further improvements in alloy properties, and what are the best candidates?
Actually between these 2 I'd say quite a lot. The second is more interesting than the first since it's the sort of notion any metallurgist could have had in say the last century (large scale Aluminum alloy use got going with airships) but it looks like this guy has made it work, and that  I suspect needed a lot of modelling and diagnostic tools that didn't exist for most of that time.

If the alloy can be welded like Steel, rather than Aluminum, with closer to Aluminum's density this could be a real winner, as well as opening up the field for other 2 main element alloys
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Offline Prober

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Re: What Are the Strongest Alloys?
« Reply #4 on: 02/05/2015 03:51 pm »
Hanelyp has it right.  There are other factors to consider.  The primary property is strength to weight, but other properties can make our break its utility for a given application.
 
Aluminum lithium alloys work well because they combine good strength to weight, good toughness, and are relatively easy to process (weldable, machinable, etc.)

Titanium based alloys all suffer from being difficult/expensive to process.  They absorb oxygen at elevated temps, and become brittle.

The two you linked both seem to be sacrificing ductility for tensile strength, but there probably is some net benefit.  If they have a fatigue limit, they could have one advantage over aluminum alloys.

The cool thing about metallurgy is that an addition of just a few percent or a different heat treat can greatly change the properties of an alloy and fix a shortcoming.  When there is a large financial incentive, more materials research is done, and they hone in on some ideal alloys (see nickel superalloys as an example).

see things are much different in Additive manufacturing as we control each and every layer for all parameters.  This applies to metals, plastics or composites, It's still a very much new science but loaded with a great deal of excitement. 
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Offline Fsci123

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Re: What Are the Strongest Alloys?
« Reply #5 on: 02/07/2015 04:03 pm »
Why aren't carbon composites suitable on spacecraft? It would seem that in a microgravity environment with little external acceleration(like on a space station module) they would be perfect for the job.

Offline Robotbeat

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Re: What Are the Strongest Alloys?
« Reply #6 on: 02/07/2015 04:19 pm »
They DO use carbon composites on spacecraft. It's just that aluminum is a lot easier to machine and overall is simpler to design and use.

BTW, an important property that aerospace designers optimize for is elastic modulus, i.e. stiffness. It is, however, inversely proportional to resilience (given the same strength) from a mathematical point of view. In other words, stiffer structures are more brittle. Personally, I think stiffness is over-rated (toughness is likewise under-rated), at least in aerospace, since it leads to operational and fabrication complexities. But of course, this strongly depends on your application.
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Offline cambrianera

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Re: What Are the Strongest Alloys?
« Reply #7 on: 02/07/2015 04:44 pm »
BTW, an important property that aerospace designers optimize for is elastic modulus, i.e. stiffness. It is, however, inversely proportional to resilience (given the same strength) from a mathematical point of view. In other words, stiffer structures are more brittle. Personally, I think stiffness is over-rated (toughness is likewise under-rated), at least in aerospace, since it leads to operational and fabrication complexities. But of course, this strongly depends on your application.
No, stiffness and resilience are only loosely related.
Stiffness is the reaction of material to external forces, resilience is the capacity of material to absorb and dissipate great amount of energy before breaking
The complementary (inverse) of stiffness is flexibility
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Offline Robotbeat

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Re: What Are the Strongest Alloys?
« Reply #8 on: 02/07/2015 05:40 pm »
BTW, an important property that aerospace designers optimize for is elastic modulus, i.e. stiffness. It is, however, inversely proportional to resilience (given the same strength) from a mathematical point of view. In other words, stiffer structures are more brittle. Personally, I think stiffness is over-rated (toughness is likewise under-rated), at least in aerospace, since it leads to operational and fabrication complexities. But of course, this strongly depends on your application.
No, stiffness and resilience are only loosely related.
Stiffness is the reaction of material to external forces, resilience is the capacity of material to absorb and dissipate great amount of energy before breaking
The complementary (inverse) of stiffness is flexibility
Oh, I'm quite right, I assure you! Check it for yourself. (It's kind of interesting, actually, though really pretty simple.)

You are right that resilience is the capacity of a material to absorb and dissipate energy before breaking (or actually, in the case of resilience, it's /yielding/, but for toughness it's breaking). But this is, mathematically, inversely proportional to stiffness for the same strength. See here:
http://en.wikipedia.org/wiki/Resilience

U is resilience, E is Young's modulus. (Sigma is stress, and Sigmay is the stress at yield, i.e. the yield strength.) Very clearly, they are inversely proportional.

The reason for this is simple. Stiffness is the slope of the stress vs strain curve (especially in the elastic region). Resilience is the area under the stress vs strain curve in the elastic region, and yield strength is the limit of elastic strain.

To relate this to energy absorption, consider that energy is force times distance. Another way of defining elastic modulus (i.e. stiffness or Young's Modulus) is how much strain it takes to reach yield strength (the limit of the linear region). If it takes more strain, then the material has less stiffness. Strain is proportional to the distance that the material is deforming, thus to find the energy absorbed (per unit volume), you're just finding the area of that triangle, i.e. the maximum strain (before yield) times the yield strength (i.e. maximum stress before yield). So, you get the equation above.

tl;dr: Yield strength is height of the triangle (whose area is defined as resilience), elastic modulus is the slope. If the height of the triangle is the same, then a greater slope will mean a smaller area triangle.
« Last Edit: 02/07/2015 05:53 pm by Robotbeat »
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Offline Robotbeat

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Re: What Are the Strongest Alloys?
« Reply #9 on: 02/07/2015 05:46 pm »
Note that I'm almost always careful to research stuff before I post a claim (and I word it very carefully) because on the Internet I KNOW someone will try to correct me if they think I'm wrong. :)
« Last Edit: 02/07/2015 05:48 pm by Robotbeat »
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Offline cambrianera

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Re: What Are the Strongest Alloys?
« Reply #10 on: 02/07/2015 06:08 pm »
Unfortunately you are still wrong.
The formula you show is valid only for the linear part of the stress-strain curve; from the Wikipedia article:
The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without creating a permanent distortion. It can be calculated by integrating the stress-strain curve from zero to the elastic limit.
Integrating the linear part you get that formula.
But true resilient material can be recognized by the elastoplastic stress-strain curve (slope then a constant stress deformation) and here the formula has no validity.
I stress, stiffness and resilience are only loosely related.
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Offline cambrianera

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Re: What Are the Strongest Alloys?
« Reply #11 on: 02/07/2015 06:46 pm »
Food for thought: which material is stiffer, and which is more resilient?
Black curve or red curve?
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Offline Robotbeat

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Re: What Are the Strongest Alloys?
« Reply #12 on: 02/07/2015 07:02 pm »
Trick question. The red curve isn't linear, you just added it. :) It doesn't obey Hooke's Law, so we can't talk about resilience in the textbook sense. But if we were to force the conversation, you'd have to use a much lower yield strength for the red curve since it loses linearity much sooner than the black curve.

Also, the area shaded under the curve in your picture is toughness, not resilience.

A nice "ah, you're right! I was mistaken. That is kind of interesting." would've sufficed. :)

How are you even arguing about this, by the way? It's literally basic textbook material science stuff.
« Last Edit: 02/07/2015 07:03 pm by Robotbeat »
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Offline Lee Jay

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Re: What Are the Strongest Alloys?
« Reply #13 on: 02/07/2015 07:04 pm »
You two are talking past each other.  Resilience is about the linear portion of the stress-strain curve (resistance to yielding or plastic deformation, if you will).  After that, you're talking about ductility, malleability, and more generally plasticity.  Toughness is more of a resistance to crack growth once a crack has already formed.  All of these are relevant to different situations.

Offline Robotbeat

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Re: What Are the Strongest Alloys?
« Reply #14 on: 02/07/2015 07:11 pm »
Unfortunately you are still wrong.
The formula you show is valid only for the linear part of the stress-strain curve; from the Wikipedia article:
The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without creating a permanent distortion. It can be calculated by integrating the stress-strain curve from zero to the elastic limit.
Integrating the linear part you get that formula.
But true resilient material can be recognized by the elastoplastic stress-strain curve (slope then a constant stress deformation) and here the formula has no validity.
Nope! That's toughness, not resilience. Either use the industry standard, textbook definitions or don't go correcting people who do. By standard definitions, I'm clearly right and you're clearly wrong (in your contradiction). No shame in that, by the way.


Quote
I stress, stiffness and resilience are only loosely related.
Except they aren't "loosely related." Elastic modulus (i.e. stiffness) and resilience are inversely proportional, as any material science textbook would show you. There's no "loosely" in there, it flows directly from the definitions. Good pun, by the way! :))
« Last Edit: 02/07/2015 07:15 pm by Robotbeat »
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Offline cambrianera

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Re: What Are the Strongest Alloys?
« Reply #15 on: 02/07/2015 08:01 pm »
Unfortunately you are still wrong.
The formula you show is valid only for the linear part of the stress-strain curve; from the Wikipedia article:
The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without creating a permanent distortion. It can be calculated by integrating the stress-strain curve from zero to the elastic limit.
Integrating the linear part you get that formula.
But true resilient material can be recognized by the elastoplastic stress-strain curve (slope then a constant stress deformation) and here the formula has no validity.
Nope! That's toughness, not resilience. Either use the industry standard, textbook definitions or don't go correcting people who do. By standard definitions, I'm clearly right and you're clearly wrong (in your contradiction). No shame in that, by the way.


Quote
I stress, stiffness and resilience are only loosely related.
Except they aren't "loosely related." Elastic modulus (i.e. stiffness) and resilience are inversely proportional, as any material science textbook would show you. There's no "loosely" in there, it flows directly from the definitions. Good pun, by the way! :))

Ok, you are right on that, I stumbled badly upon a nice "false friend", no way to turn  it otherwise.
Nevertheless, you mix the terms wildly in your original post:
BTW, an important property that aerospace designers optimize for is elastic modulus, i.e. stiffness. It is, however, inversely proportional to resilience (given the same strength) from a mathematical point of view. In other words, stiffer structures are more brittle. Personally, I think stiffness is over-rated (toughness is likewise under-rated), at least in aerospace, since it leads to operational and fabrication complexities. But of course, this strongly depends on your application.
(bold mine)
And in this case, stiffness and brittleness/toughness are loosely related.
Oh to be young again. . .

Offline Robotbeat

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Re: What Are the Strongest Alloys?
« Reply #16 on: 02/07/2015 08:21 pm »
I still stand behind that statement, too. It's not "wrong," in the strict sense and some of it is subjective (ie my opinion about what is under- or over-rated). Toughness /is/ important and tends to be inversely proportional to stiffness, although not in the strict way that resilience is (although of course toughness includes resilience).

Anyway, strength is itself quite important to toughness and resilience. But it is also correlated with elastic modulus (though of course not in the strict sense).
« Last Edit: 02/07/2015 08:22 pm by Robotbeat »
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Offline sanman

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Re: What Are the Strongest Alloys?
« Reply #17 on: 02/19/2015 12:19 pm »
A company called Modumetal has come out with a new nano-laminated metal process which apparently increases strength tenfold and can also be used to increase corrosion resistance:

http://www.technologyreview.com/news/534796/nano-manufacturing-makes-steel-10-times-stronger/

Hmm, I wonder if this process is compatible with 3D printing?

Maybe the increased corrosion resistance could be useful for an RD-180 style of closed-cycle engine.

Offline john smith 19

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Re: What Are the Strongest Alloys?
« Reply #18 on: 02/19/2015 01:57 pm »
A company called Modumetal has come out with a new nano-laminated metal process which apparently increases strength tenfold and can also be used to increase corrosion resistance:

http://www.technologyreview.com/news/534796/nano-manufacturing-makes-steel-10-times-stronger/

Hmm, I wonder if this process is compatible with 3D printing?

Maybe the increased corrosion resistance could be useful for an RD-180 style of closed-cycle engine.
Not really. It's an electroforming method to mfg large ingots by varying the voltage in the bath. IIRC that varies what element plates out, giving something akin to a Samurai sword (layers of high carbon steel folded over with layers of low carbon steel) to give a very strong, but quite expensive article.

As with all such developments you have zero pedigree in terms of down stream processes you can use or life expectancy estimates. It should be very good, but until they make stuff out of it and put them in oil fields (there partner is an oil company) who knows?
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Offline sanman

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Re: What Are the Strongest Alloys?
« Reply #19 on: 02/19/2015 02:18 pm »
I thought electroforming is already the method of choice for fabricating regenerative cooling channels.

The reason why I mentioned 3D printing, is because this technique of varying the voltage as you go could then be used to manipulate the material properties on the small scale, across the printing process.

There has already been research into electroforming as a 3d printing technique, using lasers to thermally catalyze where the deposition occurs.

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