Wire drawing thesis project on superconducting wire production

Tom's house tutor's doctoral thesis on severely deformed niobium as a superconductor; the wavy-slip picture in Backofen.

John Wulff had worked on niobium-titanium. Niobium-titanium had a critical temperature of about 9 Kelvin, so you were only about double that. A typical field might be six Tesla. That's okay but it's not great. Then a guy named Mark Benz, who had done his doctoral thesis here in steelmaking, went to work for General Electric Research, and they came up with niobium-3-tin. This is about what I was going to lecture on today. In niobium-3-tin, they found that if they put one percent zirconium in there, they could internally oxidize it and form zirconium oxide precipitates on a nanometer scale. I can use that term today; we didn't call them nanometer back then. They had to be like 100 nanometers apart — 20 or 30 nanometer precipitates — because that's what gave you a good critical field. If you had really pure stuff, you wouldn't get decent properties. In Backofen, the wavy slip of the niobium that had been drawn 88% — Backofen got that picture from one of John Wulff's students back in the 60s, because they were working on severely deformed niobium. My house tutor did his doctoral thesis on severely deformed niobium as a superconductor. There's a picture in here, and I showed you the wavy slip when we talked about asymmetric deformation.

Tom's undergraduate thesis: $1,000 worth of diamond dies bought in 5% increments, which Tom now identifies as the wrong approach — should have used 30–50% draws to avoid high-delta operations and centerline cracking.

I used to think, when I was a bachelor's student here doing wire drawing for my thesis to make superconducting wires, that I would do better with small reductions. I had a great big set of wire dies — you could buy diamond dies for 20 bucks apiece back then. I had a government research contract, so I went out and bought $1,000 worth of dies in 5% increments. That was the wrong way to go. You should be doing 30 or 40 or 50% draws, not 5 or 10% draws, because with 5 or 10% draws you get lousy deltas. High-delta operations let you crack the center, and you also get very inhomogeneous deformation. This is the highest delta operation among these four.