Effect of Reaction Temperature on the Molten Salt Electrodeposition of Silicide Coating on Molybdenum Substrate and its Oxidation Behavior

Abstract

Silicide coatings were successfully prepared on Mo substrates using NaCl-KCl-NaF molten salt as the reaction medium and K2SiF6 as the silicon source. The electrochemical reduction mechanism of Si(IV) was studied by cyclic voltammetry and chronoamperometry technology. The effect of reaction temperature on the phase composition, microstructure, and growth kinetics of the electrodeposited coatings were investigated in detail. The long-term oxidation behaviors of Mo and MoSi2-coated Mo samples at 873 K were also compared. The results revealed that the electrodeposition of silicide coatings was closely related to the reaction temperature. Dense and coherent single-layer MoSi2 coatings could be obtained at 1023 and 1073 K, while double-layer coatings with inner MoSi2 layer and outer Si layer could be obtained at 1123 K. Under the same electrodeposition time, the overall thickness of the silicide coatings increased with the reaction temperature. Moreover, long-term oxidation tests at 873 K proved that MoSi2 coatings could effectively prevent the Mo substrate from pest oxidation. The mass gain of the MoSi2-coated Mo sample was only 0.46 wt.% after 500 h of oxidation, which could be attributed to the formation of the continuous SiO2 protective layer.