Because it can be fabricated. Molybdenum machines, forms and welds with reasonable effort where pure tungsten is brittle and largely restricted to ground or sintered shapes, and it is around half the density. For hot zone structure, boats, supports and shielding, those practical advantages outweigh tungsten's higher melting point.

A titanium-zirconium-molybdenum alloy with a much higher recrystallisation temperature, better high-temperature strength and better creep resistance than pure molybdenum. It is specified where a part must carry load while hot, or where pure molybdenum would grain-coarsen and embrittle over repeated thermal cycles.

Its ductile-to-brittle transition temperature sits near room temperature and rises once the metal has recrystallised from prolonged high-temperature exposure. A component that was reasonably tough when installed can therefore be brittle when the furnace is opened, and cracking during removal or handling is common. Handle used hot-zone parts with care.

No. Above roughly 600 degrees Celsius it oxidises rapidly and molybdenum trioxide volatilises away rather than forming a protective layer, so the part is steadily consumed. Service requires vacuum, hydrogen or inert atmosphere, or a protective coating for limited excursions.

Better than tungsten and worse than steel. Sharp carbide tooling, light positive cuts and rigid workholding are needed, and it tends to chip at exit edges because of its limited room-temperature ductility. Warming the workpiece slightly improves behaviour on more demanding operations, and grinding is used for finishing.

Its low thermal expansion is close to that of silicon and some ceramics, so a molybdenum mounting plate or heat spreader does not stress the components it carries as temperature cycles, while its good thermal conductivity carries heat away. Sputtering targets and thin-film electrodes are further applications.

Rod, bar, sheet, plate, foil and wire in pure molybdenum, with TZM available in the more common sections. Sheet is widely used for hot zone shielding. Availability is narrower than for ordinary metals and lead times can be long on larger sections, so early confirmation is sensible on a project.