Rhenium is a refractory metal, but unlike other refractory metals (W, Mo, Nb, and Ta), it does not form a carbide and the crystal structure is not body-centered cubic. Rhenium has a hexagonal closed-packed crystal structure with c/a ratio of 1.615. It has a melting point of 3180 °C (second highest only to tungsten) and the third highest density of all metals at 21.04 g/cm~3. Rhenium is extremely stiff with an elastic modulus of 420 GPa (more than twice that of steel) [1]. Rhenium is immune to thermal shock and has no ductile brittle transition temperature. This material is extremely difficult to process due to a work-hardening coefficient greater than 0.5 (higher than copper) [2] and rhenium oxidizes (sublimates) in air at around 400°C [3]. Because of the high melting temperature and oxidation issues, rhenium is manufactured via powder metallurgy for large scale production; however, extremely high temperature are required for sintering and hot isostatic pressing to consolidate to sufficient density for subsequent deformation processing.
展开▼
