Structure and Polarization Properties of Zn–Nb Films Formed on Steel Sheet by Sputtering

Zn–Nb films were formed on a steel sheet by helicon plasma sputtering in an argon gas atmosphere at 1.0 Pa, at RF power of 50 W and DC power of 50 mA. The structure and polarization properties of these films were studied using EPMA, X-ray diffraction and polarization curve measurements. Zn plate-like crystals in Zn–Nb films decreased with increasing Nb content, resulting in a smooth surface over the entire film at Nb content of 30 mass% and above. The preferred orientation plane of Zn plate-like crystals was (0002) at 0 mass% Nb, while the orientation indices of (1011) and (1010)Zn increased with rising Nb content. At 30–60 mass% Nb, the X-ray diffraction spectra showed a halo pattern characteristic of an amorphous structure. The corrosion current of Zn–Nb films, which was determined by polarization curves in 3% NaCl solution, decreased with increasing Nb content to reach a minimum value at 30–60 mass% Nb, corresponding to an amorphous structure.