4. Highly refractory metals and alloys

These are metallic materials whose high melting point (MP) enables them to be used at high temperatures. These include molybdenum (Mo), tungsten (W) and tantalum (Ta).

In addition to chromium (Cr) and cobalt (Co), these metals also include "exotic" metals in American terminology, such as titanium (Ti), zirconium (Zr) and hafnium (Hf), niobium (Nb), vanadium (V) and tantalum (Ta). The first three belong to column IV B and the last three to column V B of the periodic table of elements, which explains their respective structural analogies (table 6 ).