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A blade made out of tungsten alloy that’s also electrically heated to 3000C. The shape and sharpness is similar to a katana.

The user carries a battery pack that provides enough energy for the sword to last about 3 hours.

The dimensions of the blade is 75cm long, 3cm wide and a thickness of 6.7mm at its thickest point.

How would it do against plate armour, chainmail and of course, bare skin?

Ps:Don’t worry about the weight there’s a guy strong enough to wield it in my universe.

I got my idea from here: https://youtu.be/_efVoeiSKP0

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    $\begingroup$ @GreenieE.-ReinstateMonica wont that weaken or softening the steel structure ? $\endgroup$
    – Li Jun
    Commented Feb 15, 2020 at 7:00
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    $\begingroup$ @GreenieE.-ReinstateMonica the blade’ll melt though. $\endgroup$
    – In the name of the story
    Commented Feb 15, 2020 at 7:38
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    $\begingroup$ Have you considered using your superpowered battery pack in combination with a metal cutting laser? $\endgroup$
    – Scott Whitlock
    Commented Feb 15, 2020 at 13:43
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    $\begingroup$ @Scott Whitlock What’s the range of the laser? $\endgroup$
    – In the name of the story
    Commented Feb 15, 2020 at 14:34
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    $\begingroup$ @Inthenameofthestory I love all of this a lot but (a) tungsten is not relevant, honest. it would be "hyper ceramics" or some other mystery material (b) I think the fascinating science Q that some smart person on here could answer is what would be the temperature involved $\endgroup$
    – Fattie
    Commented Feb 16, 2020 at 17:07

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It would damage itself more than the opponent.
As other answers mentioned, Tungsten would be much too brittle to use, and shatter at the first strike(s). If this can be overcome by changing the metal composition, you would run into different problems like heat dissapation making the handle too hot to hold.

Even if a structurally sound and handleable sword could be made with a portable battery, it wouldn't be very effective against plate armour.

Plate armour is already rivaling swords on structural integrety, rendering swords almost useless if not used as a stabbing implement. If the swords structural integrety was lowered even further by heating it up, it would have much higher chances of breaking, especially when used for stabbing.

Apart from that, a single strike from a heated sword to a plate of steel would probably not transfer enough heat quickly enough to have much effect in the first place. The time of contact is not long enough for the heat transfer, and the heat might be damaging, but would quickly be dissapated by the surrounding armour.

To add to this, it would be completely impossible to keep any kind of edge on the sword. It is already hard to not destroy the edge of a sword by hitting anything hard, especially so when the sword is weakened by heat. A single strike would roll and chip the edge blunter than a rock.

As for attacks against chain mail, this would be a bit more effective, but would still be quite damaging to the sword, and the heat would still not have much added value.

Against bare skin, a sword is a sword. It will cut. But of course hitting any kind of bone would again be damaging to the sword. The heat would actually work against you when attacking an unarmoured opponent, because it would cauturise the wound instantly, minimising blood loss. The worst problem with superficial wounds would be the n-th degree burn, while painful and damaging, this has a much larger window of being treatable than gushing blood loss.

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    $\begingroup$ I agree, a heated sword in general is pointless unless it's lightsaber-hot. Swords and katanas in particular are designed for slashing at enemies and inflicting blood loss. $\endgroup$
    – Dragongeek
    Commented Feb 15, 2020 at 19:51
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    $\begingroup$ I suggest looking into the "forged in fire" series available on YouTube. It is a smiting competition, and the weapons tests at the end will show you exactly how fragile even well made swords can be. $\endgroup$
    – Plutian
    Commented Feb 16, 2020 at 8:49
  • $\begingroup$ Indeed, over plate armour, I believe the most effective attack is actually brute strength to deliver a heavy, blunt blow, which will ideally break through the armour, or else dent it considerably. Even if neither of those take place, the force of the blow will still be felt by the person inside, even though spread over a larger area by the armour. Chain mail is a sort of "flexible plate armour", and a heavy blow would be very effective there. $\endgroup$
    – Ralph Bolton
    Commented Feb 17, 2020 at 9:35
  • $\begingroup$ @Dragongeek even “lightsaber-hot” will only help when you have the plot on your side… $\endgroup$
    – Holger
    Commented Feb 17, 2020 at 9:39
  • $\begingroup$ @RalphBolton Typically under the armour there would be a heavy quilted coat that would insulate against a lot of heat. with a lot of luck you could have it catch fire dense linnen under armour doesn't sound easily flammable. $\endgroup$
    – Borgh
    Commented Feb 17, 2020 at 10:36
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Yes, you have an effective weapon here. Just throw away the useless sword and find a way to get the battery pack to release all its energy at once instead of over three hours. It contains a lot of energy, and will make an excellent explosive device.

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    $\begingroup$ Or maybe you can arrange to electrocute someone with that battery pack. $\endgroup$
    – Joshua
    Commented Feb 17, 2020 at 4:06
  • $\begingroup$ Do power a railgun, perhaps? $\endgroup$
    – Holger
    Commented Feb 17, 2020 at 9:37
  • $\begingroup$ I think you can simply re-invent the Taser. Touch the armor with the blade, and allow the battery to discharge into the blade. Blade of Doom: kills on touch. $\endgroup$
    – Enric Naval
    Commented Feb 17, 2020 at 12:29
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    $\begingroup$ Indeed, if you can engineer and charge the battery, you can probably engineer all sorts of exotic looking effects and weaponry. If you can keep a tungsten stick at 3000C, why not keep a big bowl of lead solder at just 200C and fling that about at your enemies? You could probably engineer a Van-de-Graaf device to shoot lightening at your (metal clad) enemies. A whole load of lightening buzzing and cracking on the back of a cart being pushed towards a medieval soldier would probably be enough to make them turn and run - no swords required. $\endgroup$
    – Ralph Bolton
    Commented Feb 17, 2020 at 12:45
  • $\begingroup$ @EnricNaval Wear a long, metal coat between the battery pack that touches the ground - then just prod your enemy with a pole that carries the positive voltage. $\endgroup$
    – towe
    Commented Feb 17, 2020 at 15:25
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Tungsten is very brittle. So brittle that it shatters when hit.

Your warrior will be helpless on the battlefield after the first blow.

Summary: it will work very poorly.

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    $\begingroup$ @Ryan_L Because it’s very dense. It doesn’t matter if the core of an armour-piercing shell is brittle, because if it fractures the pieces will still keep going in the same direction. $\endgroup$
    – Mike Scott
    Commented Feb 15, 2020 at 7:00
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    $\begingroup$ Even if it were structurally sound, the sword would not transfer enough heat to make a difference in a fight. The only real effect it would have is lightly cauturizing wounds which would be counter productive. $\endgroup$
    – Dragongeek
    Commented Feb 15, 2020 at 19:53
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    $\begingroup$ @RyanL With reference to the answer, how often does an armour-piercing shell need to try for a second blow? $\endgroup$
    – Graham
    Commented Feb 15, 2020 at 22:07
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    $\begingroup$ -1 from me. This is too simplistic. a) – is tungsten still as brittle at 3000°C as it is at room temperature? I don't know, but I doubt it b) this sword has a very strong effect that's quite independent of its mechanical characteristics. It would probably not need to deal out blows like you would with a normal sword. $\endgroup$
    – leftaroundabout
    Commented Feb 16, 2020 at 15:16
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    $\begingroup$ This answer is incorrect. Tungsten has a ductile-to-brittle transition temperature of around 400 C. See hal.archives-ouvertes.fr/jpa-00253413/document. So at 3000 C, it will certainly not undergo brittle failure (i.e., shattering) $\endgroup$
    – Aliden
    Commented Feb 16, 2020 at 21:37
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3000C is very, very hot. Steel forges and glassblowers operate around 1000C. They wear protective gear just to stand near the stuff.

I know volcanologists have issues with their gear spontaneously catching fire due to the heat off of lava flows (again, roughly 1000C). Granted, the flows are a lot bigger than this sword. Still, I think contactless ignition would be a recurring threat.

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    $\begingroup$ Yep. The radiated power grows with the fourth power of the temperature: Twice as hot, 16 times the power output! Going from 1000°C to 3000°C you go from 1273K to 3273K, which is a factor of 2.57, which translates to a power output factor of 44x. $\endgroup$
    – cmaster - reinstate monica
    Commented Feb 15, 2020 at 8:32
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    $\begingroup$ To add to this, I would imagine the blade would be impossible to hold. You can't have a blade of 3000°, and have no heat dissapate into the tang keeping it cool enough to handle. Touching the sword would burn your hands instantly regardless of any protective equipment. $\endgroup$
    – Plutian
    Commented Feb 15, 2020 at 9:44
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    $\begingroup$ @user72381 don't forget the guy in the video is only playing with his sword for short moments. $\endgroup$
    – The Square-Cube Law
    Commented Feb 15, 2020 at 12:12
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    $\begingroup$ This is the correct answer. That sword, if you can hold it at all, would probably prevent anybody from getting in melee range alive in the first place. $\endgroup$
    – leftaroundabout
    Commented Feb 16, 2020 at 15:18
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    $\begingroup$ @SRM “medieval era knights” with EM countermeasures? Rather unlikely… $\endgroup$
    – Holger
    Commented Feb 17, 2020 at 14:34
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Your blade is about 150 cm^3 of tungsten, roughly 3 kg. That's a lot of mass to heat up and maintain at 3000 K. The surface area of your sword is about 550 cm^2. More surface area will radiate away the energy faster requiring a large battery and also melting the user.

All that heat will be right near your face and hands making it possibly impossible to hold without bulky thermal protection. Even if you were, the chaos of combat might result in your arm being jostled and that 3000 C blade brushing against YOU.

And, as others have noted, it won't even work against armor.

Swords were not terribly effective on the battlefield. They required being in close combat which makes it more likely you'll get injured. They require lots of room to swing, which means your allies have to stay well away from you leaving you fighting isolated. Movies which depict battles as a mixed brawl of individual sword battles are fantasy. Victorious ancient and medieval armies fought in tight formations. An isolated warrior is a dead warrior.

Swords are the service pistol of melee combat. They were a backup weapon you use when you lose your main weapon. Or used for duels.

If the sword wasn't your main weapon, what was? The polearm. And the ultimate expression of the polearm was the pike.

What you want is a heated pike. And you want a lot of them. And you probably want to scale it back to 1000 C.

Only heat the tip. It's much less mass to heat up and much smaller surface area to radiate that heat away meaning a smaller battery and potentially more pikemen. Add a bit of very high temperature insulation between the hot tip and the pole. The pole itself could be wood, good insulation, or perhaps aluminum. To protect the wiring from the battery to the tip, run it inside protected channel in the pole, or perhaps make the pole hollow. Having the heated tip at the end of a long pole keeps it well away from the user avoiding baking the user or their buddies next to them on the line.

Expecting to repeatedly bash anything at 3000 C against other things and expect to have anything but a lump of hot slag left over is ambitious. Scale it back to a mere 1000 C. Use a superalloy designed to hold together at that temperature. They will also be stronger, lighter, and sharper than tungsten. At the end of a pole you'll appreciate the reduced weight.

Thrusting with a sharp, light 1000 C alloy tipped pike is more likely to penetrate armor than slashing with a heavy, dull tungsten sword. Even if it doesn't penetrate it still scare the hell out of the enemy line.

Ancient and medieval warfare was a lot less stabbing and a lot more pushing, "the awful push of pike", with the goal of disrupting the enemy's formation. Even if you don't penetrate their armor, the enemy isn't going to want to confront a wall of lava-hot pikes. They will probably attempt to back away disrupting their formation and giving you victory.

enter image description here

Like this, but also on fire.

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    $\begingroup$ until the handle of your pike bursts into flames, the blade too, because metallic titanium burns in air at 600 degree , all for no benefit. $\endgroup$
    – John
    Commented Feb 16, 2020 at 5:58
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    $\begingroup$ "And the ultimate expression of the polearm was the pike." Halberdiers would probably disagree. $\endgroup$
    – nick012000
    Commented Feb 16, 2020 at 6:51
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    $\begingroup$ @nick012000 Pikemen and halberdiers did disagree. Extensively. Violently. $\endgroup$
    – Schwern
    Commented Feb 16, 2020 at 6:54
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    $\begingroup$ If the alloy does not burn at those tempratures there is not enough titanium in it to call it titanium, also again it offers no benefit. $\endgroup$
    – John
    Commented Feb 16, 2020 at 13:45
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    $\begingroup$ @nick012000 well......... pike formation that consist of pike,halberd, zweihander and gun later become only pike and gun for a reason. $\endgroup$
    – Li Jun
    Commented Feb 17, 2020 at 5:07
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As a very gross oversimplification, a knight in full armor was battered down, not cut down. That's why many knights carried a mace instead of a sword. Sure, a war hammer was used to penetrate the armor, but that was no sword, either.

Heating the sword means that a little heat is transferred on a blow, but as a gut feeling that won't be the main damaging mechanism to the armor or to the person under that armor. The contact just isn't long enough.

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  • $\begingroup$ or pierce the armor gap, at least sword can be use to pierce or bashing, usually by half swording, or bashing using murder stroke, but the real weapon to kill knight is dagger anyway if you dont want to take prisoner since is easier to pierce the gap in the eye. i wonder will it increase overheating though, thats one of problem with full plate armor. $\endgroup$
    – Li Jun
    Commented Feb 15, 2020 at 7:55
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Never mind its brittleness at 3000C or otherwise ...

unless your sword fights are in a perfect vacuum or a halon or noble gas atmosphere, it'll burn with the oxygen in air long before it reaches 3000K.

Anywhere tungsten is heated it is kept enveloped in inert gas - either as a lightbulb filament, in the glass envelope - or as a TIG welding rod where T refers to Tungsten, and IG refers to a plume of inert gas (often argon) around the weld.

You are now holding a hilt...

A couple of references... confirming the glass envelope is to keep oxygen away from the filament and combusting tungsten wire as part of another experiment. I still can't view even the abstract of that Springer article. However its MSDS (pdf) lists it as a flammable hazard in the powder form, but heating it to white heat doesn't seem like a good idea.

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  • $\begingroup$ @Aliden Having difficulty finding something non-paywalled, other than rather chatty threads on welding fora... and link.springer.com/article/10.1007%2FBF00743115 --- can't even see teh abstract! $\endgroup$
    – user_1818839
    Commented Feb 16, 2020 at 21:51
  • $\begingroup$ best to far... home.howstuffworks.com/light-bulb2.htm $\endgroup$
    – user_1818839
    Commented Feb 16, 2020 at 21:56
  • $\begingroup$ What about this? link.springer.com/article/10.1007/BF00743115 It looks like there might be sufficient information on the first page $\endgroup$
    – Aliden
    Commented Feb 16, 2020 at 21:58
  • $\begingroup$ @Aliden after reading that article, I'm convinced that even without actual combustion the oxidation will be extremely problematic. Oxides of tungsten actually melt at a much lower temperature than tungsten itself, so any oxide coating that forms will slough off. Effectively the blade would oxidize continually. Swinging it around would spray molten WO everywhere, not desirable. $\endgroup$
    – barbecue
    Commented Feb 17, 2020 at 19:52
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The heat adds absolutely no advantage against an armored opponent. To do damage, you'd have to hold the heated sword against the foe long enough for significant heat transfer to take place. But the foe is encased in steel, which is a good conductor & radiator of heat, so it disperses over the piece of armor that you're hitting, with some of it radiating away. Meanwhile the foe is most likely wearing a nice insulated gambeson https://en.wikipedia.org/wiki/Gambeson or other padding under the armor, so it will take a while for the heat to penetrate deep enough to affect him.

Bottom line: while you'll frantically trying to hold your glowing hot sword against the foe's armor (while trying to avoid your own sword :-)), he twists around, inserts his dagger in one of your armor's joints, and kills you.

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Considering tungsten's melting point is 3,422 °C, your champion would be swinging something akin to a very hot wet noodle, so not very effective. Realize a blade in medieval times had semi-sharp edges, not to specifically cut through things, but to rather concentrate the force of the inertial energy being brought to bear by it. Even though tungsten is quite a bit heavier in weight per cubic amount than steel, if the weapon is a hot noodle, it would just deform as it hit something rather than cutting through it. Your champion would be much better off just swinging a cold blade made of tungsten than they would be by swinging the hot noodle. More than likely they'd do more damage to themselves than they would their opponent.

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    $\begingroup$ This answer assumes exactly the opposite of the “tungsten is too brittle” ones. I'm pretty sure tungsten at 3000°C is not “wet noodle” soft, nor as brittle as at room temperature, but I don't know. If you do know, add a reference to the answer. Else this answer is just speculation. $\endgroup$
    – leftaroundabout
    Commented Feb 16, 2020 at 15:13
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    $\begingroup$ ...and, if it were wet-noodle-soft, then this would actually probably make it more effective, not less. Soft means more contact surface means quicker heat transfer. $\endgroup$
    – leftaroundabout
    Commented Feb 16, 2020 at 15:20
  • $\begingroup$ You'll have contact surface once until it deforms out of shape. Then, as it deforms around the object, it'll get stuck. 3000 °C is ~300 °C above what would be considered forging temperature. Forging temperature is where it would make the metal easier to move and shape. Anything above that only makes it easier to move and softer still. This makes it an infeasible prospect. I didn't even go into the amount of energy it would take to heat and hold the blade to the temps you are describing. In a normal forge you cannot even get it to this temperature. You'd need an arc furnace for it to happen $\endgroup$
    – Pᴀᴜʟsᴛᴇʀ2
    Commented Feb 16, 2020 at 16:27
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TL; DR - Hot sword is better for roasting its wielder than chopping up their enemies

Looking at this from a heat transfer perspective, this sword has some problems that are going to make it unusable. dspeyer's answer notes the danger of spontaneous ignition of clothing. I'm going to address what happens to the wielder in the case where nothing spontaneously ignites. For the sake of simplicity, I'm going to treat the sword as a cylinder with a diameter of 3 cm and a height of 75 cm being held 60 cm in front of a plane 50 cm wide.

Mockup of person holding sword

Assuming the sword acts as a blackbody, it will transfer heat via thermal radiation to something at body temperature at a rate of: $$\dot{Q}' = \pi d \sigma\left(T_{sword}^4 - T_{body}^4\right)$$ which gives a heat transfer rate of 613 kW/m. With a 75 cm long sword, we're looking at a heat output of 460 kW. This heat will be released in all directions, so looking at the fraction of a circle surrounding the sword the "body" blocks, it will only receive 1/8 of that power, or 57.8 kW.

Let's put that number in perspective. If I take 100 kg of water (which is a not-too-terrible model of your swordsman) and start putting heat into it at 57.8 kW, I can take it from body temperature (37 C) to the temperature at which death will almost certainly occur (44 C) in under a minute.

In other words, it doesn't matter how effective a weapon the sword is. It will kill its wielder before it can ever be used.

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  • $\begingroup$ So you're basically holding 460 one-kilowatt electric radiators at arm's length...sir knight wielding it is going to need some pretty good insulation/cooling. I reckon he would blister and drop it rather than dying though :) $\endgroup$
    – David Hambling
    Commented Feb 17, 2020 at 19:42
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Also, doing some math on that battery...

The sword is about 1000x the volume of a light bulb filament. Assuming the energy cost is linear in volume (because I don't want to do really difficult math), this means we need 100kw. For 3 hours, 300kwh.

Our best LiON batteries get a bit under 300wh/kg, so this will weigh a metric ton.

It would require only 30kg of gasoline, but a highly efficient fuel cell (an internal combustion engine isn't nearly efficient enough). Also, the gasoline may ignite from being near the sword.

Or you could do it with 200 milligrams of reactor-grade uranium, which means you can afford to compensate for an inefficient engine by increasing the fuel 10-fold.

Or 12 micrograms of antimatter, which might be easier to build a backpack-sized reactor for. Also much easier to blow up the entire battlefield. On purpose or by accident.

As for 300kwh released at once as an explosion, that's 1000 hand grenades, but roughly a third the power of the smallest bombs the US air force typically drops.

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    $\begingroup$ Energy dissipation only scales with the surface area, not the volume. Consequently, your numbers are way off. $\endgroup$
    – cmaster - reinstate monica
    Commented Feb 15, 2020 at 8:34
  • $\begingroup$ Yes, but actually I daresay even the surface area will be more than 1000× of a light bulb filament. $\endgroup$
    – leftaroundabout
    Commented Feb 16, 2020 at 15:24
  • $\begingroup$ "Our best LiON batteries get a bit under 300wh/kg, so this will weigh a metric ton." The Hacksmith built one of these with a battery pack you can wear on your back; also the one they built only needed 20kW. $\endgroup$
    – nick012000
    Commented Feb 17, 2020 at 5:54
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Tungsten is a useless material for this application, as it's very brittle. Its more useful cousin is tungsten carbide, which is a lot tougher, but it's still very brittle compared to most steels. Most steels and titanium alloys get soft when heated, so if you want a heated weapon, your options are either tungsten carbide, or a super-alloy.

Inconel springs to mind, or Hastelloy. Both are trademarked though, so a "nickle super-alloy" is your best bet. There are some of the best alloys under high temperature conditions, as the get tougher with increasing temperature. However, 3000 C is definitely out of range for most materials. 1000 C is already extremely hot.

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If you could make a glowing sword people would either revere you as some kind of saint or fear you as some kind of witch and have you put to death so actually your glowing sword, back pack and whatnot would actually be the least of your worries, I'd be more inclined to use the sword to make toast...that's a win for everyone.

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