ELI5 Titanium - why is it the metal most used in surgeries?

Why did the CIA secretly buy Soviet metal to build the very plane designed to spy on them? How does a metal named after Greek Titans manage to fuse physically with living human bone? If titanium is the ninth-most abundant element on Earth, why is it still so expensive to produce? And how did common chlorinated tap water nearly destroy the manufacturing of the world’s fastest titanium jet?

... we explain like I'm five

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