Refractory Alloys: Vanadium, niobium, molybdenum, tungsten

Refractory metals as a class of materials are understood to share the common properties of very high melting temperature and mechanical properties and wear resistance. A narrowly defined class of refractory metals would include metals with melting points >2000°C: niobium, chromium, molybdenum, tantalum, tungsten, and rhenium [1], while a wider class would also include those with melting points above 1850°C: vanadium, hafnium, titanium, zirconium, ruthenium, osmium, rhodium, and iridium. The current practical application of refractory metals is relatively widespread (though arguably for specialty application) with examples being casting molds, wire filaments, reactant vessels for corrosive materials, hard tooling, and a myriad of applications where high density is desired. Because refractory metals are a class of materials possessing extraordinary high-temperature properties, they are perennial contenders for high-temperature nuclear applications. However, their use to date has been limited, due in part to the difficulty in fabricating high-performance refractory parts and their environmental degradation including irradiation effects. The following sections will discuss the current processing routes being taken to produce nuclear-grade refractory alloys, a general discussion of their properties, and the effects of irradiation on the materials.