Caltech rapid solidification metallic ribbon research

Pol Duwez's 1960s discovery: pouring iron-boron brazing-alloy melts onto a spinning copper wheel produces paper-thin ribbons at million-degree-per-second solidification rates, yielding amorphous metals with 500 ksi strength and stainless-grade corrosion resistance without chromium. DoD/NSF spent hundreds of millions in the 1970s–80s on this research line. Used as the prototype "great properties, can't make it bulk" cautionary case.

So it turns out, in the 1960s, the guy at Caltech took some iron-boron alloys — that are actually basically just brazing alloys — which melt at a fairly low temperature, sort of like cast iron. He took a spinning copper wheel going at thousands of surface feet per minute, and they would pour the molten metal on it as a liquid spray, and it would come spinning off as a thin sheet. You could roll off sheets two to six, twelve inches wide, about as thick as a piece of paper — rapidly solidified metal, and you lose all crystalline structure. You have no dendrites. Ordinarily these things would be full of dendrites, but it's so thin it cools so quickly. They called it rapid solidification. In the best cases they got solidification rates of a million degrees per second. So this thing's solidifying so fast that you end up getting a very homogeneous structure. It's not all that different than the Hazelett process except you don't even need a top band, because it's just a thin layer, and it's solidifying so fast that this thing only has to be about two inches long.

1960s Caltech work spreading nickel-boron liquid on a 60-mph-surface-speed water-cooled spinning copper drum, achieving ~10⁶ °C/s cooling and producing paper-thin amorphous foils. Triggered the 1970s rapid-solidification powder/foil research wave.

Various people will seize on certain improvements. As far as making glassy metals, we'll talk about this a little bit later, I guess next Monday. One way to make glassy metals is rapid solidification. Back in the 1960s, Professor Paul Duwez at Caltech found that if he spread liquid metals — in this case nickel and boron — on a fast-spinning water-cooled copper disc, he could spin off foils. The drum might be spinning at 60 miles per hour surface speed. He could spin off little thin foils, not much thicker than a piece of paper, that cooled at a million degrees per second. If you do that, you can keep the metal from crystallizing. It would end up with a glassy structure.