Corrosion behavior of magnetron sputtered α-Ta coatings on smooth and rough steel substrates

α-Ta coatings on smooth and rough steel substrates (AISI 4340) were studied in an effort to assess the resulting porosity and corrosion behavior. While the long-range crystallographic orientation of the coatings was found to be affected by the surface roughness, the short-range structure was invariant. Peak broadening in X-ray diffraction patterns attributed to microstrain and particle size was observed for coatings on both types of substrates as compared to Ta powder. Although the roughness was two orders of magnitude greater for the coatings deposited on the rough substrates than the smooth ones, the porosity was not significantly different. Furthermore, electrochemical impedance behavior over long exposure times of coatings deposited on smooth and rough steel substrates was similar to that of Ta foil. These results demonstrate that substrate roughness appears to have little to no effect on the coating quality with respect to corrosion performance for 50 μm coatings.