[HN Gopher] Some alloys don't change size when heated - recent w...
___________________________________________________________________
Some alloys don't change size when heated - recent work on why
Author : _Microft
Score : 86 points
Date : 2023-07-27 18:18 UTC (4 hours ago)
(HTM) web link (www.caltech.edu)
(TXT) w3m dump (www.caltech.edu)
| iancmceachern wrote:
| You can do this with composites too. You can even create
| materials with slightly negative CTEs
| metal_am wrote:
| The article somewhat downplays the historical understanding of
| this. (It's understandable! This is a dense topic!) The impact of
| spin states has been known for a looong time. My first
| introduction to the topic was Zener's 1955 paper The Impact of
| Magnetism on Metallurgy.
| lr4444lr wrote:
| Cool. What would applications be here? Could we for example make
| basic alloys of vehicles, railroad tracks, and refrigeration
| systems more resilient when they undergo temperature variations,
| and therefore last longer?
| buryat wrote:
| who needs to read the article?
|
| > That anomalous behavior makes these alloys useful in
| applications where extreme precision is required, such as in
| the manufacture of parts for clocks, telescopes, and other fine
| instruments.
| bediger4000 wrote:
| Traditionally, holding optics or some other delicate sensors
| that we want to stay aligned, or at least point in the same
| direction consistently.
| ScoobleDoodle wrote:
| Blackbird SR-72? SR-71 leaks before take off in anticipation of
| the thermal expansion plugging everything up.
|
| https://nodum.org/was-sr-71-blackbird-leaking-fuel/
| brilee wrote:
| The heat generated by drag at such high speeds means that
| titanium was, at the time, the only suitable material due to
| is high melting temperature.
| barelyauser wrote:
| Not high melting point but its ability to remain strong at
| high temperature.
| hinkley wrote:
| An annealed aircraft is not a particularly safe aircraft,
| yes.
| nuancebydefault wrote:
| From the understanding of the mechanisms that cause this
| invariance, many other applications could be derived, that even
| don't need the invariance property. For example materials of
| which cooling systems (e.g. Peltier-like) can be made. Also
| their measurement methods seem pretty advanced and could be
| used within other research like in the area of nano technology.
| mitthrowaway2 wrote:
| Yes, the main value would probably be in better understanding
| the temperature / pressure / volume / magnetism relationship
| within invar-like materials. Perhaps the result will be new
| piezomagnetic applications, or magnetocooling applications,
| and so on.
| sadhorse wrote:
| Only precision applications can afford the high cost of
| specialized materials. All the things you mentioned are
| unrelated, as they are cost driven and steel will always win.
| metal_am wrote:
| Forms and tooling for composites are a big one in the aerospace
| world. Keeps dimensional stability better through autoclave
| cycles.
| hinkley wrote:
| I was going to say something similar but then I started
| having doubts.
|
| For precision instruments you probably want devices that have
| exactly the same modulus of expansion as what you are
| cutting. So that 0.15m is always 0.15m no matter the
| temperature of the factory.
|
| For molds you would want the outer mold to shrink slower than
| the molded material, but would you perhaps not want an inner
| mold to shrink faster? So that the material pulls away from
| both as it cures/cools (I'm asking, I don't know)?
| burnished wrote:
| No need - you ever cross a bridge and note a mesh of metal
| teeth? Thats for thermal expansion. Its already designed around
| and isnt generally noticeable - for steel it is 0.0000065 /
| degF [0].
|
| [0] https://www.metalsales.us.com/thermal-expansion
| loeg wrote:
| Would be nice to not have the holes though.
| burnished wrote:
| Why is that? I've already put all my knowledge on the topic
| on display so I can't tell if this is a joke about
| aesthetics or if there is actually something neat having to
| do with the gaps
| hinkley wrote:
| I know from tales of professional cycling that those
| metal bridges are vastly disproportionately responsible
| for broken bones.
|
| They're also squirrely when wet, and if you've ever
| ridden across one on a bike or a motorcycle, they are
| fucking terrifying because you can see the river below
| you, and the railings for some reason tend to be very
| low.
|
| And while I understand that many bridges don't really
| prevent runoff into the water flowing beneath them, metal
| mesh bridges really can't.
| maxbond wrote:
| I'm not sure you're talking about the same thing though,
| I think they meant these thermal expansion joints, not
| necessarily a bridge made from metal mesh:
|
| https://i.pinimg.com/originals/4d/82/91/4d8291e022bd14c87
| 985...
|
| I know that picture is a mesh, I thought it had the best
| detail, but they're on paved bridges too:
|
| https://siamagazin.com/wp-
| content/uploads/2018/03/23h32h-min...
| hinkley wrote:
| I think they meant the former, because otherwise having
| expansion joints that don't expand doesn't really
| accomplish anything. The concrete still expands, hence
| the need for the joints.
| maxbond wrote:
| My reading is that they were saying this expansionless
| material isn't likely to be useful for bridges, because
| thermal expansion is well managed by these traditional
| techniques.
|
| I agree though that both the thermal coefficient of the
| teeth probably don't impact their performance (the
| expansion in the teeth relative to the width of the gap
| is negligible, so we can probably pretend we're using
| expansionless teeth already), and I've never had an
| accident on one of these bridges, but I'm sure you're
| right and that the mesh concentrates the force on your
| bones like a golf club.
| pfdietz wrote:
| And because this material is 35% nickel. Nickel costs
| $21/kg.
| Cthulhu_ wrote:
| Well, they knew the effect existed, so applications are already
| in use; this just explains the how, which I'm sure makes the
| effect more predictable - and allows for researchers to find
| more alloys with this effect in a focused manner, instead of
| via trial and error.
|
| As for applications, it probably won't be garden variety
| appliances, thermal expansion isn't much of an issue there and
| designs for all of the things you mentioned have been tweaked a
| hundred years ago to deal with thermal expansion (although
| railroad tracks are still an issue sometimes). And of course
| there's other parameters, like wear resistance; nickel is a
| pretty soft metal I believe.
|
| But, things like precision industry or space will find a use
| for this. Sattelites have to deal with hundreds of degrees of
| temperature variation.
| UniverseHacker wrote:
| I disagree, even modern cars have a lot of unsolved problems
| with thermal expansion and cracking causing failures of
| cylinder heads, gaskets, exhaust manifolds, turbochargers,
| etc.
|
| It may be solved in principle, but certainly not in practice.
| barelyauser wrote:
| There are problems that are game stoppers and there are
| problems that are unavoidable. Cars work. Yes, if you drive
| 1 million miles you will have cracks in the engine due to
| thermal expansion, but who cares? Make a new engine and get
| over it.
|
| Now consider a space elevator. Material problems are a game
| stopper.
| MichaelZuo wrote:
| These problems are already solved for very high end
| aftermarket exhaust systems, which use Inconel.
| dublinben wrote:
| "Modern" cars run on electricity and don't have any of
| those parts or their corresponding problems.
| barelyauser wrote:
| Your "modern" cars have cooling loops for their battery,
| therefore cyclic thermal fatigue.
| zdragnar wrote:
| Plus the bearings, heat from (regenerative) braking, and
| I'm sure a few other parts.
| scythe wrote:
| I haven't looked it up, but I'm sure the magnitude of
| thermal cycling in a battery is way less than in a
| combustion engine.
| burnished wrote:
| I think the important bit is that this isnt 'a lot' of
| systems, it is comparatively few.
| exmadscientist wrote:
| Invar is actually a _very bad_ material for most uses,
| because having zero CTE usually won 't match the _rest_ of
| your system 's _nonzero_ CTE. So things will fail pretty
| quickly.
|
| Matching CTE is a big deal in careful engineering. "Alloy 42"
| is a great example of that in action: it's an invar-like
| alloy with its CTE matched to silicon, so chip lead frames
| expand with silicon dies as they heat up during operation.
| Not that many things use lead frames anymore....
| Kirby64 wrote:
| What do you mean? MOST ICs use lead frames still. Although
| there is a large push in consumer electronics to use flip
| chip or CSP devices, I would suggest that most devices are
| still using lead frames. Any plastic packaged device is
| lead frame based.
| exmadscientist wrote:
| Sorry, you're right, I was thinking of the newer stuff
| (flip-chip, wafer-scale, nearly-bare-die, etc). It's also
| interesting just how few leadframes are magnetic these
| days, even for something ancient like a SOIC-8. I don't
| know what they use; I guess it's not very important if
| there isn't much power dissipation.
| mechhacker wrote:
| I didn't even know that they didn't have a good explanation
| related to magnets, as invar for example has a curie point,
| above which it loses it's neutral thermal expansion
| properties.
|
| I've seen it used for low temp things or tooling but for that
| reason it can't be used for anything really high temperature.
| Terr_ wrote:
| > That anomalous behavior makes these alloys useful in
| applications where extreme precision is required, such as in
| the manufacture of parts for clocks, telescopes, and other fine
| instruments.
| JKCalhoun wrote:
| Tangent: reminded me for some reason of the lengths (ha ha)
| clock makers went to to account for the expansion and
| contractions of the clock pendulum. To keep consistent time the
| length of the pendulum too needed to remain constant. Enter the
| brilliant John Harrison:
|
| https://en.wikipedia.org/wiki/Gridiron_pendulum
| golem14 wrote:
| https://en.wikipedia.org/wiki/Invar gives a few hints.
| bluGill wrote:
| Probably not. You typically cannot change one variable in
| isolation with an alloy, so while you can gain in one area
| other things change as well. Strength - both compression and
| tension, hardness, resistance to bending, springiness, melting
| temperature, are just a few of the properties (note that the
| properties have engineering names and common names - I mixed
| with no concern so there is duplication)
| w10-1 wrote:
| A summary to motivate reading the paper:
|
| Invar, a nickle-iron alloy, was commercially highly relevant for
| accuracy of mechanical watch balance springs in the 19th century.
| Investigations of that presumably lead to the 1920 Nobel in
| physics.
|
| The article claims to produce the first equation to model this
| effect accurately, together with an experimental technique to
| validate the main components. This would support in-silico
| material exploration, esp. predictions for high temperatures that
| induce expansion.
|
| But because this demonstrates phase shifts in how electrons
| interact, the significance could be broader that just the use of
| constant-size invar (iron/nickel alloy).
|
| Paper excerpts:
|
| ----
|
| Here we use a thermodynamic Maxwell relation to explicitly
| separate the contributions to thermal expansion from phonons and
| spins. [...] These two contributions were measured by nuclear
| resonant X-ray scattering on Invar under pressure. We find that a
| competition with phonons is necessary to complete the explanation
| of the near-zero thermal expansion of Invar.
|
| An advantage to [our] equation is that the two main components of
| thermal expansion--phonon and magnetic--can be experimentally
| obtained by nuclear resonant X-ray scattering
|
| Excellent agreement between experiment and theory is found. There
| is a remarkable spin-lattice coupling, and a precise cancellation
| of the phonon and spin contributions that causes the anomalously
| low thermal expansion in Invar near ambient conditions of T and
| P. Furthermore, the transition to a more typical thermal
| expansion at higher pressures is shown to arise from the magnetic
| transition to the paramagnetic state that quenches the negative
| contribution from the spin system. Finally, the electronic
| contribution is found to have only a small effect on thermal
| expansion.
| MichaelZuo wrote:
| It's a very interesting effect, magnetism 'perfectly cancelling'
| out thermal expansion.
|
| Are there any other cases where magnetism is responsible for
| something this subtle?
| mturmon wrote:
| How about the Zeeman effect, in which strong magnetic fields in
| locations where light is emitted, will cause the spectral lines
| associated with emitting material to split?
|
| The strength of the magnetic field is encoded in how broadly
| the line is split, allowing us to make spatially-resolved maps
| of the magnetic field of the Sun ("magnetograms").
|
| Like getting the chemical composition of the emitting surface
| of the Sun, it's the kind of thing you'd think sounds
| impossible until some clever physicist figures out how to
| exploit it.
|
| See the little animation at the top of the page:
| https://en.wikipedia.org/wiki/Zeeman_effect
| RugnirViking wrote:
| I dont remember what its called but I always liked the magnetic
| braking thing where if you drop a ferrous cylinder through a
| copper tube it falls slowly with constant speed, because the
| magnetism induces current which induces a braking force
| cromwellian wrote:
| Hot take: If the Earth's core is Iron-Nickel, is it an Invar, and
| therefore, there's an effect too reduce earthquakes from
| expansion from heat movement being lower, or is the pressure
| alone enough to counteract that?
| 0xfae wrote:
| The core of the earth changes temperature very slowly. So any
| effect is probably pretty minimal.
|
| I would guess that comparatively huge thermal characteristics
| from the churning and moving of the crust and mantle due to
| plate tectonics probably overshadows this.
| pfdietz wrote:
| The core of the Earth is also far beyond the
| temperature/pressure at which this invar effect occurs.
___________________________________________________________________
(page generated 2023-07-27 23:00 UTC)