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A question that arose from here.
Say we have a planet with a different percentage of various elements than Earth, but steam train technology, and we were striving for train track longevity. Is there any metal/ceramic/alloy/layering system that could provide a similar experience as standard steel, but last for longer?
I know, it surprised me too. Its the most wear resistant metal alloy known.
To quote
tires made from it would only lose a single layer of atoms after a mile of constant skidding
It responds to heating differently than most alloys hardening it on the nanoscale because the grain structure does not change under heat or stress once set. This material vastly outperforms any other known metal alloy for wear resistance. It turns out hardness is not the best predictor of wear resistance but how materials react to friction heating. Matching sapphire and diamond for non-metals without their extreme brittleness. As a side benefit it is also extremally resistant to corrosion.
It will need to be wider and more solidly built than current rails due to lower overall strength but you might need that anyway. It also have very very low friction which is bad for train tracks, train tracks need decent friction for the wheels to grip the rails. So if you use it you need to increase grip possibly by changing the contact shape or some other method that might make a good follow up question.
Another option is to make the rails of something else and coat it with this alloy.
As a side benefit it is an very good electric conductor so you could have electrically powered rails.
A great idea from a commenter below, cog assisted railways did exist, Called rack railway they had a cog toothed track along side the normal rail anywhere the train had to climb, places were friction might not be enough to grip the rails. a toothed cog on the axle would pull the train along no matter the grade.
https://onlinelibrary.wiley.com/doi/full/10.1002/adma.201802026
https://www.materialstoday.com/metals-alloys/news/new-platinumgold-alloy-most-wearresistant/
So, we can look at the real world to see what goes into a tracks longevity. As expected, there is no easy answer.
According to this your standard gravel bed might last 15 years, despite the tracks in theory being in for up to 100 years. If you use concrete and steel elements the entire thing might last 30.
Of course, "last" is somewhat of a relative term. These figures, probably, assume for instance someone is there to remove plants.
This will not last 30 years.
And this is not really an issue you can just engineer away. Even if you elevate the entire track on a concrete wall, like this;
Dirt, Water and Seeds will get up there and will start to deteriorate the track. That being said, elevating the entire track will improve its longevity because it just takes longer for dirt and stuff to accumulate.
Note, that i have not even touched on using other metals. Because the actual physical rail isnt what is going to break first. Its the sleepers, ballasts and other parts which will fail first and make the entire track unusable. You can live with the rail warping a bit. You positively cannot live with the sleepers being eaten up by worms.
So, Imo, the main thing you would want to do is elevate the track a couple of meters perhaps with a base shape that prevents anything from growing up easily. You then want to make sure the top of your elevation structure is build so rain does not accumulate and can flush out dirt. Since you are already using approximately all the concrete in the world the sleepers are obviously out of it as well. And then make the rails stainless so they dont rust away.
Provided there is no earthquake or major change in the local geography that wall with a track on it should be usable for quiet a long time.
But, to be fair, you would have to replace the trains, too.
If money is no impediment, an artificially built, fast-running water channel can be used to transport massive amounts of load with minimum to no downtime. You just place stuff on a special cargo boat on the fast-track river, and someone down the line will pull it off from it by means of diverging the flow temporarily to an unloading area.
Your cargo wouldn't need an engine to carry them, as the power would be provided by the water.
With the proper engineering, this system also doubles as an irrigation system for the huge swat of land it can cross, enabling once unproductive land to be used for crops and animals.
By clever diverting some of this waterflow, you could use waterwheels to provide power to small devices or maintenance stations, or for ligthning up the Great Waterway.
While this system wouldn't be faster than a single train on a railroad, using water enables you to move far larger loads, way more often. Your "cargo bandwitdh" ends up being higher, even if an individual piece of cargo takes longer to send.
Aluminum bronze. Basically nearly corrosion proof mild steel. Can't be hardened but it is a bearing surface so just use more of it to support the load if cost is no object. I've heard it is difficult to machine but I've found it among the easiest materials to machine. But the kind I've experienced does not contain nickel. I think the nickel containing kinds are a bit stronger and more corrosion resistant, though.
Hopefully it's a case where the material is cheap EVERYWHERE, rather than "expensive but cost is no object" in the railway project. Otherwise the rails will get stolen in the blink of an eye. Such a world would see a very great many consumer items that use stainless steel, and industrial applications that commonly use mild steels replaced with aluminum bronze. Basically the Bronze Age taken farther into the future since copper stays cheap and abundant and there was not nearly as much motivation to force iron to work.
If money is no object / the distribution of elements is different (making it more common, perhaps?) tungsten could do the trick. It only begins to oxidize at extreme heats, and is already used in the real world as an improvement over steel in applications such as drill bits / cutting tools - it's more brittle than steel though, which is why it's usually layered over steel to support it.
It's not a different track material, but in David Brin's "The Practice Effect" they use a frictionless lubricant which increases the efficiency of rail travel and reduces the wear on the tracks to basically zero, which would improve the lifespan of your tracks. If memory serves the tracks there were a slightly guttered design, otherwise the lubricant would flow off the tracks and onto the ground.
You can look up toughest known material, which is a CrCoNi alloy. About 5 times tougher tan steel. However it was so far only created in the lab under special conditions, it's not clear whether it's possible to make rails out of it.
