Tham khảo tài liệu 'materials science and engineering handbook part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Rhenium and Its Alloys Rhenium is a strong ductile refractory metal with an hep crystal structure. It has a very high density g cm3 or lb and melting point 3180 C or 5755 F . It has good mechanical stability at elevated temperatures offering good resistance to thermal shock and wear and higher creep resistance and strength than the other refractory elements. The annealed condition showing a room-temperature tensile strength of 1170 MPa 170 ksi still has a tensile strength of about 48 MPa 7 ksi at a temperature as high as 2710 C 4910 F . Rhenium is used for electrical contacts thermocouples fdaments for electrical devices including large-diameter lamp filaments. Because it is in short supply it is costly and used mostly as an alloying addition to the other refractory alloys. Rhenium is primarily made using P M techniques with some also made by arc melting in an inert atmosphere. It has high cold ductility but because of its very high work-hardening rate it requires the use of light deformation passes with frequent intermediate anneals either stress relieving or recrystallizing at 1225 to 1625 C 2237 to 2960 F in vacuum or dry H2 or H2-N2 mixtures. Hot deformation must be carried out in vacuum or hydrogen to prevent hot cracking caused by formation of the low-melting-point oxide that penetrates grain boundaries during hot working in air. This is one case where the metal has a higher temperature stability than its oxide the metal catastrophically oxidizes in air at moderately elevated temperatures forming Re2O7 which melts at 297 C 567 F and boils at 363 C 685 F billowing off as a white cloud. Thus the metal must be protected from oxidation during processing or while in service. A coating of iridium has been used. Because rhenium does not form a carbide it is resistant to carbonaceous environments and is suitable for use in contact with graphite. The high work-hardening rate of rhenium at room temperature translates into rapid increases in strength .
