Black titanium is one of the most important (and rare) resources in FO76. It is used to craft and repair power armor. In addition to stocking up on this resource, you should also pick up the perk card that reduces the cost of crafting and repairing PA. There are other valuable resources used while doing this so it really pays off to have this perk fully upgraded.
To get black titanium, you can either kill enemies (Mole Miners) that sometimes drop gear which yields it upon scrapping, or set up an extractor via your camp at a resource node. Preferably close to a workshop that also has it available for farming.
You can then go to Blackwater Mine and keep killing mobs that respawn every 20 minutes or so while playing the game as usually. Or you can just relog and keep farming them that way.
You will lose the workshop in that case.