What performance limits restrict large-scale popularization of these four metals?

Tantalum and niobium are scarce rare mineral resources, leading to extremely high raw material prices compared with nickel and ordinary steel. Zirconium needs strict inert atmosphere protection during all high-temperature processing, increasing manufacturing complexity and energy costs. Pure nickel has weak resistance to fluoride and concentrated reducing acid media, so it cannot replace tantalum and niobium in severe acid working conditions. All four metals cannot withstand strong alkaline molten salts at ultra-high temperatures, limiting their use in high-temperature alkali metallurgy reaction equipment.