There is a scale called vickers. What precisely it measures though I
am not sure. If you have a 1998/99 Hoover and Strong catalog on page
10 it lists the vickers scale numbers for many metals and alloys
(though not titanium) in its soft tempered state. There it also
states that “vickers scale is used to test the tempers of precious
metals. We have provided these numbers for you to compare against
metals that you may be familiar with. Our sheet and wire tempers
will run 50 - 100 points higher than soft temper matierials”.
For example it gives a vickers soft temper number of pure platinum at
52V and pure gold at 30 V. The 18 K gold alloys range from 265V for
nickel white gold to 104V for yellow. Platinum alloys range from
117V for 90% pt/ir to 130V for plat/s+.
Platinum is, in your words, “tougher (resistant to breaking) than
gold” in that platinum alloys are of a higher karat (90 %) than
commercially used gold alloys (41.6 to 75%). Pure platinum vs pure
gold is a tough one. They are both very resistant to breaking as
they do not age or work harden. As far as scratching goes, again it
depends on what alloy you are talking about. Pure metals are equally
awful in the scratch test catagory. I would suggest talking to a
metalurgist. Call the people at Hoover and talk to thier
metalurgist, I can’t remember his name but he recently won an award
for a paper he wrote on metals. He would be a wealth of knowledge.