Tantalum capacitors are only "trivial to substitute" in some applications; as someone who works in electronic hardware, I can assure you that it is often impossible to use any other part, and achieve the same performance.

Sorry, you're right - tant caps are irreplacable in some applications. I overcorrected on madaxe_again's assertation that tantalum used universally in electronics, when really the number of places that it's used, and couldn't be replaced if supply was cut off, isn't huge. That number certainly isn't zero though.

TIG welding (Tungsten, Inert Gas) is pretty common. To substitute it, you would have to find another metal with a similar high melting point.