My story involves sword of very high quality; they use lasers to cut, but have a metal reinforcement. The monsters the characters encounter and fight have lava as their 'life liquid'. If someone were to cut such a monster, the lava would seep out. This leads me to wonder: is there a metal with a high enough melting point to be resistant to lava?
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7$\begingroup$ Fox, you need to let us know how long the metal will be exposed to or submerged in the lava and you need to let us know what temperature your lava will get to $\endgroup$– JamesCommented Sep 29, 2016 at 14:03
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11$\begingroup$ Indeed, even a little research would have improved the question, and the answers are readily available in Wikipedia. $\endgroup$– John DallmanCommented Sep 29, 2016 at 14:28
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6$\begingroup$ A reminder to commenters that we are generally supposed to accept the premise of the question and answer the question that was asked. $\endgroup$– JamesCommented Sep 29, 2016 at 18:19
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6$\begingroup$ You say "they use lasers to cut." Does this mean high tech, such as lasers, are used to craft the swords? Or does it mean that the "sword" is a metal core that projects some sort of laser blade? $\endgroup$– EthanCommented Sep 29, 2016 at 19:21
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5$\begingroup$ @James The question isn't well-formed. Resistance to attack by high temperature molten rock has little to do with melting point. Melting point just puts a hard limit on feasibility. Most metals with sufficient melting points are going to heat up beyond their ideal operating temperatures, retain that heat, and begin oxidizing rapidly in atmosphere. They will also lose a lot of their strength and durability. Some alloys might literally fall apart. I would count "resistant" to mean "maintain expected functionality and durability," in which case the answer is basically no, except... $\endgroup$– do-the-thing-pleaseCommented Sep 29, 2016 at 22:15
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12 Answers
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Upon a very quick check it looks like titanium has a melting point of around 1600ºC and magma has an average temperature of around 700ºC to 1300ºC. Given that you could pretty quickly assume that as long as your characters aren't just running every enemy creature straight through and leaving their weapons inside their adversaries for long periods the swords would hold their tensile strength pretty well.
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15$\begingroup$ And if that isn't good enough, tungsten melts at 3422ºC, which should stand up to any lava. $\endgroup$ Commented Sep 29, 2016 at 14:26
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13$\begingroup$ Tungsten is very brittle though, not great sword material. en.wikipedia.org/wiki/Tungsten $\endgroup$ Commented Sep 29, 2016 at 16:16
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52$\begingroup$ You do have to worry about tempering effects. Heat which may not melt the sword can still permanently alter its properties. $\endgroup$– JeutnargCommented Sep 29, 2016 at 17:29
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7$\begingroup$ The equilibrium homologous temperature of 1300 C lava relative to titanium is about 0.84, at which point titanium would almost certainly have lost enough of its strength to become more like modeling clay than metal. Tungsten would be closer to 0.42, and would lose less strength, though it has even greater affinity for oxygen than titanium and would probably corrode more rapidly. $\endgroup$ Commented Sep 29, 2016 at 22:10
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21$\begingroup$ Forget pure tungsten or titanium. Try a carbide (tungsten, titanium, boron etc.), cobalt infused tungsten carbide powder is what they make rock drills and high performance jackhammer tips out of... it also retains most of it's room temp strength even when red hot. Or Nickel Aluminide which actually gets stronger as it heats up (until ~800'C then it gets softer again) $\endgroup$– SamwiseCommented Sep 29, 2016 at 23:39
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OK, I think melting point is the wrong thing to think about here. The first thing is specific heat capacity, which tells us how much heat energy is needed to raise the temperature of 1kg of a substance by 1 Kelvin.
So, a metal with high specific heat capacity can absorb more energy without ill effects. Here's a table to peruse.
Of course, this does have to be balanced against the other physical properties of the sword - to quote Donal Noye of the Night's Watch: "Robert was the true steel. Stannis is pure iron, black and hard and strong, yes, but brittle, the way iron gets. He'll break before he bends. And Renly, that one, he's copper, bright and shiny, pretty to look at but not worth all that much at the end of the day". So that will also have an influence on the metal you choose.
Secondly, we have to think about the construction of the sword. Many traditional designs balance just forward of the crossguard, which means a large proportion of their mass is in the hilt end. This can be used as a heat sink for the blade portion, allowing a quantity of energy to be absorbed with less effect to the whole.
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2$\begingroup$ Specific heat capacity is a good start -- but there are also issues with steels that occur way before melting point (i.e. loss of temper and strength due to allotrope-like behavior). There are alloying tricks (cobalt, for instance) that can be used to add high-temperature strength to steel, but would the society in question know about that? $\endgroup$ Commented Sep 29, 2016 at 21:24
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$\begingroup$ True, but it does also raise the question of how long the lava would remain in contact with the blade. $\endgroup$– user27924Commented Sep 30, 2016 at 21:36
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There's a better alloy.
The exotic alloy, which is a combination of the rare metal hafnium, carbon and nitrogen, would only begin to melt into a liquid at temperatures of more than 4,126°C (7,460°F) - two thirds the temperature of the surface of the sun.
I think that would be strong enough to suit most purposes.
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8$\begingroup$ Melting isn't the primary concern though; Metal will alter its properties enough to basically destroy swords well before their melting points. $\endgroup$– CubicCommented Sep 29, 2016 at 17:45
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My perfect fantasy blade is made of -- real substance, not a joke -- transparent aluminum. Aluminium Oxynitride: Melting point of about 4000 deg F. Light weight, slightly flexible, and at 1" thick it is capable of parrying a 50 caliber bullet fired point blank.
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17$\begingroup$ It's also handy for turning a cargo bay into a whale tank. $\endgroup$ Commented Sep 29, 2016 at 21:20
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3$\begingroup$ Steel has 25 times better fracture toughness. Chip this, and it shatters on your next blow... $\endgroup$– YakkCommented Sep 30, 2016 at 3:39
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3$\begingroup$ I always thought that "transparent aluminum" was supposed to be corundum (aluminum oxide,) one of the strongest materials known. It's got a hardness of 9 on the Mohs scale (diamond is 10) and is significantly tougher (more impact resistant). Corundum has been known since ancient times, primarily in two forms that make it colored and less clear due to impurities: the red form is commonly known as "ruby," and the blue variety, "sapphire." $\endgroup$ Commented Sep 30, 2016 at 18:53
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$\begingroup$ This stuff rings like metal when you hit it. Corundum doesn't do that, so i don't think of it as a metal when handling it. But it's all marketing. :-) $\endgroup$– SRMCommented Sep 30, 2016 at 21:50
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If you're looking for heat resistance, the first thing that comes to mind is a refractory material. Unfortunately, these are usually ceramics and somewhat brittle - but that's where composite materials come in!
You could have a ceramic sword with steel reinforcement inside - think of reinforced concrete. Or, a steel core with ceramic coating/insulation.
You're cutting through monsters, which implies fairly brief contact with the high-temperature lava. You're not submerging this sword in a lava pit. The ceramic outer layer should sufficiently protect the metal inside from the higher temperatures. It helps that ceramics have a significantly lower thermal conductivity than most metals, so it won't even absorb as much heat from its surroundings.
This also adds a cooldown element, if you want.
You're still going to want to avoid large shocks that might crack the ceramic. But you have a laser cutting edge anyway, and lava has a rather high viscosity - so it's unlikely to flow into small cracks.
This is also kind of a solved problem. Where else do we encounter high temperatures in the order of 1300ºC? Jet engines!
The top gas temperature in a modern jet turbine is more like 1500°C, and the turbine blades tolerate temperatures of around 1200°C.
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$\begingroup$ However, turbine blades don't handle mechanical stress well, you can't even kill geese without them breaking. $\endgroup$ Commented Sep 30, 2016 at 15:16
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1$\begingroup$ @Guntram Considering the speeds they would have been moving at (both plane airspeed and rotational speed of the turbine), that's probably a whole lot more stress than a hand-wielded sword could ever cause. The turbine already has to withstand a fair bit of stress in normal operation (think combustion, pressure). Also, the sword in question doesn't cut by mechanical action anyway. $\endgroup$– BobCommented Sep 30, 2016 at 16:45
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$\begingroup$ yeah, 10-20 tonnes of force is not uncommon on the blades right behind the combustor $\endgroup$– SamwiseCommented Oct 3, 2016 at 17:18
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Why to use bulk materials only?
You can use conventional material for the body, cover it with thermall barrier coating and protect it with hard coating.
So when you start with titanium blade, cober it with 200 um TBC and then cover it with 200 um alpha-alumina you will get weapon that sustain 2000 °C for reasonable time. The blade will be also very hard through wide range of temperatures. One can prepare coatings with hardness ranging from ~5 to ~15 GPa (HV 5000 ~ HV 15 000). Nanohardness in martensite vary from 0.2-1 GPa (HV 200 ~ HV 1000).
If you chose more complex material for the surface finish, you can top the hardness up to 30 GPa (HV 30 000)...
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Flowing lava typically burns around 1200 (red) to 1600 (orange) degrees Fahrenheit. Using this page at Engineering Toolbox.com to view the various melting points of metals and alloys, you can see that there are a lot of various options.
Some of these options include:
- Aluminum Bronze
- Iron
- Red Brass
- Silicon
- Rhenium
- Nickel
- Gold
- Copper
- Cobalt
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1$\begingroup$ Lava can be quite a bit hotter than that, Wikipedia cites ~1300 - ~2200 degrees Fahrenheit. Also, good luck with a golden sword even at room temperature. $\endgroup$ Commented Sep 30, 2016 at 15:12
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$\begingroup$ @Guntram Blohm. Yes it can. But I went with the average temperature of lava that you can tell by color livescience.com/32643-how-hot-is-lava.html. Gold is just one of the options I threw out there for the temperature it will melt at. There are many metals that he could use in his story per the link I provided in the answer $\endgroup$– IT_UserCommented Sep 30, 2016 at 15:25
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Does it have to be metal? Carbon fiber has a very high melting point. Bonus point, it would be light and a high quality carbon fiber blade could keep its shape for a long time.
answered Sep 29, 2016 at 18:24
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5$\begingroup$ Carbon fiber has a high melting point, but it will burn at high temperatures (~400 C). The report helpfully points out that carbon fiber is better than aluminum because it holds its shape while burning, while aluminum will melt...but its still on fire. $\endgroup$ Commented Sep 29, 2016 at 18:52
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13$\begingroup$ @kingledion Ah, the legendary Flaming Sword $\endgroup$– MichaelCommented Sep 29, 2016 at 19:11
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$\begingroup$ @cem-kalyoncu None of those things (aside from "being light") are true about any kind of CFRP, the high-temperature properties of which depend almost entirely on the properties of their epoxy. While their high strength (but low toughness) and high stiffness (and hence a tendency to shatter) makes carbon fibre reinforced plastics ideal for racecar chassis, those properties are the opposite of what you want in a blade. There's a reason you don't see anyone making CFRP kitchen knives. $\endgroup$– RiotCommented Sep 29, 2016 at 19:11
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$\begingroup$ I never tried cf for cutting but it sure is tough. sharp edges are quite... well... sharp. And burning sword, hell yea $\endgroup$ Commented Sep 29, 2016 at 19:19
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Why not create a sword with internal channels that circulate a COOLING FLUID? Could be like the executioner sword from Gene Wolfe's "New Sun" that has a slug of mercury that can flow to the tip. But in this case it is liquid nitrogen or something, the sword hilt reservoir is filled right before battle.
The sword also doesn't have to be homogenous, it could be more like a Koa sword (Polynesian weapon with a wood "blade" embedded with shark tooth cutting edges). The "blade" is material with low heat conductivity and high strength and only the edges are high temp edged metal. This way as the metal edges lose temper and dull, they can easily be replaced after the battle but the weapon as a whole retains integrity and doesn't heat up because it has low conductivity. For bashing apart lava monsters this should suffice. Enough cutting ability to pierce the skin, then enough heat resistance to widen the opening and puncture any (?) internal organs.
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$\begingroup$ Water as a cooling fluid will vastly outperform liquid nitrogen here. $\endgroup$ Commented Oct 1, 2016 at 13:12
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Most metals we'd consider making a sword of can take a splash of lava. We're not talking about immersing the blade in a lava flow, here.
After any fight, swords require maintenance. Your friendly armorer will retemper the blade as necessary.
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A sword made of tungsten has the highest melting point in pure form, but if you wanted to coat it with the alloy tantalum hafnium carbide, you will have the perfect weapon to carry if you visit Lava Tree State Monument in Hawaii.
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Take a look at the metal cups that are used to scoop up lava for analysis. Guessing they may just be stainless steel or wrought or cast nickel.
You could also actively cool by making passages and injecting compressed air.
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$\begingroup$ Actually, the usual procedure for sampling lava is to use a geologist's hammer (steel) to pull a sample out of a flow and drop it in a water-filled bucket. Melting point doesn't really matter there, since the hammer isn't in contact with the lava for very long. See youtube.com/watch?v=rxJeY4C6SL4 $\endgroup$– MarkCommented Oct 2, 2016 at 0:47