[petertodd]

A lot heavier actually.

In an application like a stepladder, you have to work with certain minimum dimensions for the stepladder to be practical (eg rungs and sides have to fit in the hands nicely). You also have to have certain minimum thicknesses on the parts to have sufficient resistance to local deformation (eg dropping a hammer on the rungs). That forces the parts to be significantly larger and stronger than they otherwise would be. Which makes very lightweight metals like magnesium and aluminum the better choice, as you can make thick parts at the required dimensions at very little weight.

Climbing gear is a great example of this. Even though there's a segment of that market for which money is no object, the only use for titanium in climbing gear is certain specialized applications where corrosion resistance is important. Eg fixed gear mounted on sea-side cliffs. Because climbing gear has to have certain minimum dimensions to avoid damaging ropes, the very low density of aluminum wins over titanium's higher density/higher strength.

If you made a carabiner out of titanium it'd be stronger than necessary, and a lot heavier.

[TylerE]

This is also why aircraft use aluminum, despite the major downsides (finite fatigue life, mainly). There’s just no way steel would work (far too heavy). Titanium is awesome but a royal pain to work with. Carbon fiber is starting to come in but it has issues to - although they’ll be overcome with time.

[dredmorbius]

The Soviet Mikoyan-Gurevich MiG-25 was manufactured principally from stainless steel.

The result was a stunningly fast fighter aircraft, capable of Mach 3.2, though in practice engine overheating restricted operation maximum to Mach 2.83 (3,000 km/h), and even that for only 5 minutes at a time as the airframe and fuel would overheat. The MiG-25's mass necessitated huge wings (and overall dimensions), and limited maneuverability. Steel however provided better thermal-tolerance capabilities than aluminium, and lower cost and easier fabrication than titanium.

First flight 1964, introduced to active service in 1970.

That said, the aircraft is notable as an exception to your generally-applicable rule.

<https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25>

I suspect carbon fibre would also have thermal limitations for high-speed aircraft.

[sufficer]

This aircraft also sparked development of the F15 which was superior to anything soviet for 10+ years

[vGPU]

Sure but the f15 didn’t start production until almost a decade later.

[j_apes]

Steel structure won't be necessarily heavier cause density and strength are almost thrice as much as aluminium ? I think the issue with steel is that it for the required strength, the structure would be too thin that it would buckle under compression much sooner.

[scheme271]

Titanium also doesn't have the resistance to abrasion that other metals have. There's stories of titanium bike frames being ruined because the rear tire was mounted incorrectly and ended up rubbing on the frame during a ride.

[londons_explore]

If you can 3D print titanium, then you can make a honeycomb structure overcoming this problem.

[bch]

What is the response to stress by this build method? Will it fail gracefully over a lifetime of stresses? Any single big stress-event?

In terms of (rigid, diamond-frame) bicycles, this is why I’m still firmly in the steel camp. No aluminium, no carbon; just steel. It really does have an excellent combination of nice ride quality, low weight, high strength, good failure mode (I’ve broken a few frames, and they tend to just bend/sag, vs the rapid unscheduled disassembling of carbon/Al).

[londons_explore]

I can't comment on the plasticity of titanium.

But complex microstructures can be designed to have non-sudden failures. Eg. you could ensure that a visible crack appears at 0.75x the ultimate strength, yet doesn't fail till 1.0x the strength.

You can also design structures so that a 'crack' is either 1mm wide or not there at all (ie. no hairline cracks).

such features of microstructures are not free though - you will lose strength/weight to get them.

[lmm]

> In terms of (rigid, diamond-frame) bicycles, this is why I’m still firmly in the steel camp. No aluminium, no carbon; just steel. It really does have an excellent combination of nice ride quality, low weight, high strength, good failure mode (I’ve broken a few frames, and they tend to just bend/sag, vs the rapid unscheduled disassembling of carbon/Al).

Bicycles don't have the minimum size problem GGP is talking about. Titanium is pretty much the perfect frame material (if you can afford it) - all the nice things you list (a bit stiffer than steel, but ride quality is still decent), but substantially lighter.

[jdietrich]

>Bicycles don't have the minimum size problem GGP is talking about.

They do, in a slightly different way. Bicycle frames are (broadly) stiffness-critical structures. Wider-diameter tubes have a higher specific stiffness because of the increased moment of inertia - that's why we use structures like tubes and I-beams instead of solid bars. Steel frames have skinny tubes, because they're limited by the minimum wall thickness of the tubing; increase the diameter too much and you have a tube that is very vulnerable to dents and very prone to buckling. Steel racing frames of the 1970s are remarkably flimsy, because framebuilders were pushing wall thickness to the absolute limit.

Aluminium bicycle frames are only lighter because the lower density allows you to retain an acceptable wall thickness on larger-diameter tubes. An aluminium frame with the same tube diameters as a steel frame would be considerably heavier than the steel frame, because an aluminium frame needs to be overbuilt to compensate for the lack of a defined fatigue limit.

All common steel alloys have essentially the same stiffness (~207GPa), but higher-strength steels allow us to use wider-diameter tubes with thinner wall sections; incidentally, this is why it's quite pointless to use an expensive tubeset in a lugged frame. CFRP obviously has immense specific stiffness, but it also allows frame designers to really optimise the geometry and use the material more efficiently.

Titanium is a really nice frame material, but it does have some significant issues in practical use. Titanium is very prone to embrittlement if there is any amount of contamination in the weld. Most framebuilders aren't capable of maintaining the level of cleanliness and the comprehensive gas purging required to produce really good welds in titanium, so it's very common to see titanium frames eventually crack around the welds.

To my mind the perfect material for a non-sporting frame was the superb Reynolds 953 maraging steel, but unfortunately it is no longer available. Reynolds 931 and KVA MS2 are still very good materials, particularly when fillet brazed rather than welded. CFRP obviously wins out in terms of pure performance, but I'm not sure that I'd ever trust an old and battle-scarred carbon frame on a hard descent.

[bch]

> Bicycles don't have the minimum size problem GGP is talking about

Good point.

> Titanium is pretty much the perfect frame material[…]

Anecdotally - I understand it’s tougher to work with at about every single step. I’ve seen too many cracked Ti bikes/parts to sign up, I think. I understand the lust though.

[PakG1]

Coincidentally, you can. https://www.sciencedirect.com/science/article/abs/pii/S00260...

[tako]

NI think AI assisted development needs comments to make better informed decisions about the code Needed to accomplish the task.

[BobaFloutist]

Can you 3D print metals yet? That sounds quite difficult.

[mhb]

Prototyping - Metal 3D Printing - Dan Gelbart

https://youtu.be/nyYcomX7Lus?si=E-B5VkFeX9W0Twc4

[smazga]

Sort of! https://thevirtualfoundry.com

Not directly extruding it, but the end result is metal.