White gold class ring hardening consultation

Early-1980s consulting case. Gold company wanted harder white gold to resist wear on class rings. Tom prescribed 0.2% nickel addition with solutionize-quench-age treatment, leveraging Ni₃Al-style precipitation in the existing 10% Ni white gold base. Result: 450 Vickers hardness.

It turns out nickel and aluminum form a Ni₃Al that melts at 2,000 degrees centigrade. Nickel melts at like 1650 centigrade — higher than steel, but not much higher. The Ni₃Al melts at 2,000 centigrade. Same thing with Ni₃Ti. Nickel and titanium love each other, nickel and aluminum love each other, and they form this ordered intermetallic. I was once asked, when I consulted for a gold company down there back in the early '80s — they said, well, can you develop a harder white gold? People were choosing white gold for their class rings, and they wanted a hard white gold that wouldn't wear out. I looked — it turns out white gold is just gold-copper-silver with some nickel in it, maybe 10% nickel. I was teaching thermo at the time, so I took my phase diagram books home and looked. I said: add two-tenths of a percent nickel to your white gold, heat it up to this temperature to solutionize it, quench it, and then heat it up to an intermediate temperature, and see if you can get precipitation hardening. Precipitation hardening: 450 Vickers.