# Suitable alloys of platinum or gold for weaponry

In the magic system I'm developing, denser metals (like platinum or gold) can store up energy in order to fuel spells at the user's need. A weapon made of said metals would be very useful, since the wielder would be able to store vast amounts of power into it (and even place enchantments into the blade), and it would also be incredibly expensive and rare (which those metals already are).

However, those metals are also unsuitable for use as weaponry, which leads to the question: are there any alloys of them which would be suitable for, say, making swords and axes? Alloys aren't as efficient as the pure material for storage, but would still be a lot more efficient than something made of steel, or even lead.

• What have you searched on your own? – L.Dutch Jul 12 '20 at 17:34
• AFAIK, platinum-iridium alloy is the only alloy of platinum made in bulk (where "bulk" is to be understood as suitable for a precious metal) specifically for its hardness. It has a hardness midway between mild steel and hardened steel; that is, much better than ancient Roman swords of soft iron, a little worse than medieval Damascus steel swords. (And let's hope that the magic system allows for modern-ish metallurgy; platinum cannot be processed with medieval technology, having a very high melting point.) – AlexP Jul 12 '20 at 17:53
• @Tantalus'touch. Higher densities would be better for energy storage, but would make the weapons too heavy to wield properly. A balance between density, hardness and durability would be best, as the weapon would need to keep an edge, be able to take a few hits, and still be useful as a "magic battery". I can't reasonably want something as good as steel, and I don't want to handwave it – Nightingale Jul 12 '20 at 17:58
• Why make a gold sword? I could beat a man with a gold sword with a normal sword and a gold bar in my pocket. I have a stronger, sharper sword and a larger, purer mass of gold. Mixing the two just creates a weaker version of both. – Thorne Jul 13 '20 at 6:51
• A side note: In your world you could also make fake gold swords or whatever you like by coating a sword with TiN. Its shingy golden color matches that of actual gold very closely. Nowadays we use physical or chemical vapor deposition techniques to deposit TiN, I guess you would have to search for a suitable method if you are interested. I can image the look on the adventurers face when the gold sword from the dragon's stache is really just a replica. – And Jul 13 '20 at 10:33

What you want is β-Ti3Au which technically is an intermetallic of gold and titanium. Apparently Tony Stark was right about a titanium gold alloy being a good choice for his suits.

https://phys.org/news/2016-07-lab-titanium-gold-alloy-harder-steels.html

The density is similar to titanium. Harder than steel, half the specific gravity.

A sword forged from this stuff would certainly be magical. Lighter, stronger, harder, sharper, corrosion resistant and extremely difficult to forge. It's difficult to form the alloy in the first place, and then you get the α-phase (same hardness as straight titanium). The harder β-phase forms only at extremely high temperatures.

Oh and it's a red-gold colour. You can give it various conflicting backstories of being forged with the blood of dragons and suchlike.

I was thinking about how mediaeval smiths might produce such a thing and you're going to love the answer: in the side of a volcano. And he'll still need coal dust and a fan. How exactly the smith is supposed to survive in such an environment is your problem. I expect that such weapons will have been made by your gods, giving a whole new meaning to "limited edition".

A regular forge won't be hot enough. It will return the material to the α-phase, which is not a horrible material for a sword but won't hold an edge the way the β-phase will. Any reforging of the Sword that was Broken would be an epic quest in itself; you would need to enlist the aid of your world's equivalent to Hephaestus/Vulcan.

Note that being very hard and keeping a superb edge is not the same as unbreakable. With stupid handling such a sword would be easier to break than iron because where iron will bend, this will snap.

It would be within the strength of a big fighter to apply enough torsion to snap it. But this only improves the item from a game perspective because players take care about how they use it, or face the ire of other players for destroying a unique item that's nearly impossible to reforge.

These physical qualities also affect the type of sword. To mitigate the risk of shattering, the blade needs significant depth in the cutting plane — like a scimitar. Long and thin is just begging for failure (but you might start out this way and have Vulcan fix the design flaw if they've been good little players).

Interesting comments. I don't think having half the density of steel represents a problem. Have you ever lifted a real sword? They're heavy! A lighter sword is a speed and stamina advantage.

The tensile strength of mild steel is about 400MPa with a Young's Modulus of 210GPa. By contrast most titanium alloys have a tensile strength from 1000 to 1390MPa and a Young's Modulus of 103GPa .

Straight titanium is similar in hardness to 304 stainless steel, and although I could not find a hardness value for beta βTi3Au it is widely described as "four times harder than titanium" hence my razor blade comments.

Bronze swords were thicker to offset the lower material strength. With half the density you can double the thickness and come out the same weight. While aluminium bronzes can have up to 780MPa tensile strength, the alloys available to the Greeks were about 230MPa.

• This is just plain awesome! It would make an amazing magical weapon! – Vaccano Jul 13 '20 at 16:39
• The best part is it's not made up. – Peter Wone Jul 13 '20 at 23:11
• While I'm not sure it answers the question, I do have to say it's too good not to bring up! – DWKraus Jul 14 '20 at 1:19
• Not only this fits all the criteria, but the material also looks awesome. Found my magic sword – Nightingale Jul 14 '20 at 1:57
• Any sufficiently advanced technology is indistinguishable from magic - Arthur C Clarke – Peter Wone Jul 14 '20 at 3:16

Crushing weapons:

I was going to go with the inlay answer, but as another alternative, why aren't your magical weapons metal staves, rods, and Maces? Here, other than a strong handle, the weight of the weapon is what makes it effective. I don't know what properties your magic imbues, so I can't speak for what magical properties the weapon would have. Mass in a crushing weapon is valuable to cripple and maim armored OR unarmored opponents; By the time knights started wearing plate armor, sharp swords were undesirable and good only for fighting lesser opponents.

Similarly, heavy axes relied on small cutting blades and a lot of force and leverage. Plate everything but add mass with gold (not sure why lead isn't on top, as it's cheap, but hey, your rules).

If these weapons are merely batteries for magical storage, A simple Gold rod (perhaps with a steel shaft in the middle) would be an almost hallmark weapon of wizards. Just flashing a golden mace would say "Don't mess with me, I'm a wizard." On the other hand, stealing a wizard's rod would leave him vulnerable. I'd suggest a sort of breastplate with gold strapped directly to the wizard's body.

• Now I'm feeling like a real dingus for not thinking of maces and staves sooner. +1 – Nightingale Jul 12 '20 at 19:40
• Lead is less than 60% the density of Gold, so you for the same weight you can have a smaller weapon, and a higher density (which may mean more magic stored). Lead is better than Silver though - both denser and cheaper. – Chronocidal Jul 13 '20 at 10:24
• "...golden breastplate" -3 defensive roll for lightning attacks :) – Peter Wone Jul 14 '20 at 4:16
• @ Renan I considered that, which was why I suggested a steel core. My specific thought was actually a flanged mace with a big mass of gold at the center for most of the mass. Honestly, I suspect if you're a wizard, you're mostly using this as a magic sink, and an old-fashioned weapon works best for actual fighting. But in a battle, it's the weapon you have, not the weapon you want. – DWKraus Jul 14 '20 at 21:41
• @Renan more likely to make a hollow core to fill with gold. it will hold the shape of a staff, it will just weigh several hundred pounds, the wizard would be ripped. . – John Jul 16 '20 at 19:41

# Use Gold Inlays instead of Alloys

Unless there's a strict requirement for the entire blade to be made of gold/platinum, don't use alloys. There will be plenty of compromises in quality, hardness, cost and utility that you may not want to make.

## Cost

Getting a high quality and hard alloy from gold or platinum maybe possible but expensive. A claymore (2.5kg) made of pure gold (to establish an upper bound) would be USD\$144K. Compare that a ton of steel is USD\$980.

## Workmanship

It's easy to find a blacksmith to work iron. It's easy to find a jeweler to work gold and platinum. It's very rare to find someon who can do both. Unless there's a very long history of this kind of workmanship, the number of practitioners in magical sword making is going to be very small.

## Material Compromises

Gold is very soft with a hardness of 2.5. Platinum is 3.5. Iron is 4.0 (source) Any alloy of gold or platinum is going to have to fight that lack of hardness. The metallurgy could get quite complicated to get satisfactory alloys.

## Recommendations

Do a gold or platinum inlay instead of alloy. This allows your blacksmiths to forge a good sword and your jewelers to do beautiful work. The complexities of metallurgy to go away too.

• I like that idea very much, but the fact that a gold weapon is enormously expensive and hard to make is actually interesting to me, as I was envisioning those weapons as a super rare, "found one on a dragon's hoard" kind of thing. – Nightingale Jul 12 '20 at 18:59
• Just a note, the hardness of elemental iron is fairly low, but the actual iron used to make swords contains many different compounds, especially martensite, which is a product of heat treatment, that are quite a bit harder, increasing the difference between gold/platinum and "iron" swords. – Joel Keene Jul 13 '20 at 1:57

Don't make an alloy

Use the gold in other ways. Use gold for the pommel to counterbalance the blade. Use gold inlay on the blade. Put some gold in the grip.

This way you don't weaken the steel of the blade and don't ruin the purity of the gold battery.

• "Pommel" was literally the first thing that came to mind. Hardness doesn't matter there, and weight is even advantageous. – DevSolar Jul 15 '20 at 11:08
• gold inlay was actually \, well not common, but common for nobility. – John Jul 16 '20 at 19:28

Magic power steering

People love gold swords. Sometimes they have them in weddings even. But in real life gold is heavy and soft so it would not make a very functional tool. Even those wedding swords are not solid because they would be so heavy they would pull the groom's pants down.

I am reminded of the stealth aircraft which require a "fly-by-wire" interface because they are inherently unstable and unaerodynamic. Without the tech they cannot fly. So too your gold sword. As made it is pretty much unusable except for pulling down grooms' pants. But lay on that magic and it becomes light and sharp and also whatever else you want - maybe it can be thrown accurately and return to your hand, or sing songs around the campfire.

People who are digging magic swords might not need to see accurate metallurgy. Make your sword solid gold and maximally awesome. If the magic has the potential of wearing off, make your your grooms have maximally awesome undershorts.

Metals having density around 20:

Gold (density 19.3) is soft and not really good material for weaponry. But it can make a good decoration.

Light platinides Rutenium, Rhodium, Paladium and especially heavy platinides (Osmium, Iridium, Platinum) are extremely hard. Osmium is densest - something like 22.5

Tungsten - density 19.3 (like gold), but a lot harder. Crazy metallurgy, hardest to melt (not that others are a lot easier...)

Uranium - density 19.1 . It contains a lot of magic by itself.

In our everyday world, 90% Platinum + 10% Iridium alloy is used for creating measurement standards exactly because it is hard. I am almost sure that it is harder than steel.

Any item made from these metals is surprisingly heavy. For comparison - iron is 7.6, lead is 11.2, copper is 8.9.

Why can't a gold or platinum weapon be magically hardened? Not only would the cost of making such a weapon be great, but you could have varying levels of hardness based on how complex the magic is. This would introduce varying levels of cost and could also introduce the need to "refuel" the weapon, which would prevent infinite weapons and create true loss. True loss is what keeps an economy going!