The structural, magnetic, and tribological properties of nanocrystalline Fe-Ni permalloy and Fe-Ni-TiO2 composite coatings produced by pulse electro co-deposition

Highlights: • The structure, magnetic and tribological properties of coatings was investigated. • Mixture morphologies of small needles and fine cauliflower were observed. • The coatings showed two phase solid solutions at high current densities. • M_s and H_c values of the coatings changed by chemical composition and grain size. • The both adhesive and abrasive mechanisms were observed in Fe-Ni-TiO₂ coatings. In this study, nanocrystalline Fe-Ni permalloy and Fe-Ni-TiO₂ composite coatings were prepared by pulse electrodeposition technique and the effect of current density at five levels was investigated. Morphology of the surface, chemical composition, microstructure, magnetic behavior, hardness and wear properties of the coatings were studied by means of SEM, EDS, XRD, VSM, Vickers microhardness tester and the wear testing instrument of pin-on-disk type. The results showed the mixture morphologies of small needles and fine cauliflower for the coatings prepared at low current densities. Ni content increased in expense of Fe content due to anomalous deposition at higher current densities and the amount of TiO₂ nanoparticles in the coatings were also increased. X-ray diffraction patterns showed BCC structure as the dominant phase. However, by increasing the current density, two phase structures of BCC and FCC were detected. It was observed that the current density has a positive effect on grain refinement of Fe-Ni and Fe-Ni-TiO₂ coatings. The results of VSM measurements demonstrated that the saturation magnetization (M_s) decreased and coercivity (H_c) increased by increasing the current density due to a reduction of Fe content and grain size. The highest saturation magnetization and lowest coercivity were obtained at 10 mA/cm² for all coatings. Saturation magnetization values for the Fe-Ni-TiO₂ coatings were lower than those of the Fe-Ni coatings. Moreover, the wear resistance and hardness of the coatings can be largely improved by reducing the grain size and Fe content in Fe-Ni matrix. Also, the friction coefficient and the wear rate values of Fe-Ni-TiO₂ coatings were lower than those of Fe-Ni coatings due to the grain refinement and dispersion strengthening mechanisms. The adhesive type mechanism and the wear debris were observed on the worn surface of Fe-Ni coatings. While by increasing the TiO₂ nanoparticles, the abrasive grooves and wear debris on the worn surface were reduced and the worn surfaces of coatings showed both adhesive and abrasive wear mechanisms.