I'm not a materials guy personally so won't be the best person to explain the exact science behind them, but they're definitely a really impressive bit of engineering. I had a quick browse of this article and it seems to give a pretty good rundown of their history and why their properties are so useful for jet engines https://www.americanscientist.org/article/each-blade-a-singl...

Wow... Mindblowing stuff. Long but woth reading.

They are grown as single metal crystals in order to avoid the weaknesses of joints. They are very strong!

Well, clearly you're not a pilot. :P

https://www.theengineer.co.uk/rolls-royce-single-crystal-tur...