Effects of CsCl content on microstructure and mechanical properties of electrodeposited rhenium coatings in NaCl-KCl-CsCl molten salts

Abstract

Refractory rhenium (Re) has a wide application prospect in the field of aerospace. Electrodeposition technology in molten salts could be used to prepare high-quality Re coatings with thicknesses from several microns up to several millimeters efficiently. For understanding the influences of molten salt composition on the microstructure and properties of the electrodeposited Re coatings, the effects of CsCl content on the microstructure and mechanical properties of the electrodeposited Re coatings in NaCl-KCl-CsCl molten salts were studied in this paper. The results showed that the nodulation tendency on the Re coating surface is weakened with increasing CsCl content, resulting in an improved coating apparent quality. The tensile strength of the electrodeposited Re decreased slightly with increasing CsCl, with a minimum value of 748 MPa. The fracture elongations of the as-electrodeposited Re coatings were less than 5%, and increased slightly with increasing CsCl content. The grain growth of the Re coatings, prepared in the melts with a relatively higher CsCl content, becomes insignificant after high-temperature annealing, indicating that the microstructure stability of the Re coating at high temperatures is improved with increasing CsCl content. After annealing at 1000–1600 °C in hydrogen atmosphere, the elongations of the Re coatings steadily increased to 15–20%. Based on the coating quality and mechanical properties, the optimal CsCl content in the molten salts was 40–60 wt%. The electroformed Re in these melts, followed by an annealing at 1400–1600 °C in hydrogen, has a tensile strength over 700 MPa and an elongation of ~20%.