It's quite well known for being difficult to machine generally.

Titanium is very hard to work with; for instance the carbide coatings on many drill-bits can cause it to degrade over time. Tooling for production of the blackbirds was a challenge in and of itself, as little was known about working with titanium at the time.

The more you cut titanium the harder it gets. It can eat even carbide drill / mill tools. Welding it is a nightmare.

Very much unworkable. I got a chunk of titanium tubing at some point of my more metal oriented years and tried to do something useful with it, it ate up my tools pretty quickly. Typical standing time for a regular HSS bit was < 1 hole. Carbide did a bit better, but still that too went much faster than usual.