If diamond is the strongest natural substance, how can it be improved and/or made into an alloy?

I know it sounds crazy, but I've bin pondering the idea for a while now for an upcoming fictional novel i want to write; but i also want to be as accurate as i can. From what i understand, diamond is the strongest natural substance on top of durable. And can withstand grate deals of punishment by both time and Earths constant anticlimactic changes, but it isn't invincible. So what i want to know is how can its longevity and strength can be improved when it is also already part of the best our earth has to offer? And how may i write about it in a form that resembles metal or an alloy, that seems believable? I look forward to your answers!