Effect of electrolysis parameters and electrolyte anionic composition on roughness of hafnium coatings

The process of electrodeposition of hafnium coatings on 1 mm thickness niobium substrate from solution NaCl-KCl-K2HfF6 without additions or with NaF additions is investigated. Morphology of hafnium coatings was studied using scanning electron microscopy. It was ascertained that the dependendce of coating roughness (root-mean-square deviation of profile) on cathodic current density at the temperatures of 973, 1023, 1073 K have the maxima at current density 0.02 A/cm2 in the melt NaCl-KCl-K2HfF6. The conclusion is made that micropassivation of crystal faces affects significantly the process of electrocrystallization in the given melt. It is shown that introduction of NaF into the melt results in depassivation of crystal faces, i.e. in coating roughening