Yeah, I remember the whole vibranium/adamantium thing –they were supposed to be incompatable as alloys, but some bonding “x-factor” got into the mix of one particular batch before casting, making it unique…or so I remember (did they retcon it?)

I think the angle they took in the movie was the way to go: just make it vibranium, & make the stuff so rare that there’s only enough for one shield. Why would you need to add indestructibility to a metal that absorbs the energy of everything thrown at it, anyway?