Ni-Fe-Mn-(nano)Al2O3 Coating with Modulated Composition and Grain Size

Composition modulated nanocomposite of Ni-Fe-Mn-Al2O3 coatings were fabricated on mild steel using single bath technique through alternative variation of duty cycle at constant frequency (VD) and repeated alteration of frequency at constant duty cycle (VF). The number of layers was 32 and thickness of each layer was 2.5 mu m. The results of microstructure examination by SEM and EDS for VD coatings exhibited that Fe/Al2O3-rich layers adjacent to Mn rich ones were deposited in a frequent manner. In the case of VF coatings, alternative variation of frequency did not affect the chemical composition of matrix and only changed the content of embedded nanoparticles. The microhardness of Ni-Fe-Mn-Al2O3 multilayers compared to monolithic and multilayer Ni-Fe-Al2O3 of the same thickness was significantly increased because of Mn incorporation into the matrix. The corrosion resistance was found to be better for VD coating in comparison to the VF ones.