I don’t know the physics behind any of this, but you’re right about lead softening metal. As for cobalt increasing the strength, I’ve fought with M2 steel castings that hadn’t been heat treated, that were basically indestructible. In fact, I’ve got a small hunk in my tool box that after a lot of grinding, I’ve managed to shape into a wedge to use for getting stuff out of nooks and crannies. Heat treating this would no doubt change it’s characteristics in some way, but I can tell you that it can take more sheer abuse than any other steel I’ve ever seen, without deformation, chipping, or anything else. If I could afford it, I’d buy nothing but M2 cutting tools, since the stuff is so tough.
I hope you don’t work for Pratt & Whitney, 'cause you won’t be for much longer.
Why? Didn’t it work out in practice?
No I don’t work for P@W having been retired since 2981.
Preview? I don’t need no stinking preview. That’s P&W and 1981. Other than that, the post was just fine.
I know very little about metallurgy or solid state physics, but I remember an illustration I saw somewhere: It showed that having a homogenous mixture of a single element tends to allow the layers of atoms (all the same, thus the same size) to slide fairly easily against one another, which leads to poor shear strength and easy bending. Adding in some other element, such as carbon or cobalt, breaks up that even stacking of atoms, and making the resulting alloy less easily bent.
Did that make any sense?
throw in my tuppence.
The reason most rigid materials are brittle is that they have no resistance to crack propagation. Cracks will destroy almost anything, so tough materials such as bones, wood etc have to have way of stopping cracks growing. This is usually due to composite structure, where a crack gets stopped at a boundary. This is why most glasses are brittle - they have no boundaries in them and so nothing to prevent the crack growing.
Metals are able to stop cracks by a number of mechanisms including microflow and composite or microcrystalline structures