Microstructure and mechanical properties of rhenium prepared by electroforming in NaCl-KCl-CsCl-K2ReCl6 molten salts

Rhenium plates of ~ 250 μm thick were prepared by electroforming in NaCl-KCl-CsCl-K2ReCl6 molten salts. The as-deposited rhenium has a near-columnar, fiber-like grain structure and a laminar and twin substructure. The tensile strength and fracture elongation of as-deposited rhenium tested at room temperature were 1040 ± 40 MPa and 8 ± 1.2%, respectively. After annealing at 1000 °C to 1600 °C for 1 h, the grain configuration changed as follows: near-columnar and fiber-like structure → fine equiaxed grain structure → coarse equiaxed grain structure → coarse equiaxed grain mixed with large columnar grain structure. A better combination of strength (744 MPa) and plasticity (18.8%) was obtained by annealing at 1400 °C for 1 h. The grain configuration and substructure, residual stress and oxygen content affect rhenium's mechanical properties with the oxygen content appearing to play a dominant role.