Characterization and corrosion behaviour of CoNi alloys obtained by mechanical alloying

CoNi alloys including Co30Ni70, Co50Ni50 and Co70Ni30 were prepared via mechanical alloying using Co and Ni powders. The crystallinity and short-range order were studied using X-ray diffraction and X-ray absorption spectroscopy. The results show that the milling process increases the number of vacancies, especially around the Co atoms, while the milling time decreases the crystalline size and enhances the crystallinity. X-ray photoelectron spectroscopy was used to characterise the chemical composition of the samples surface. The magnetic properties were analysed using zero-field cooling, field cooling and a magnetic hysteresis loops. The magnetic saturation moment is approximately 1.05 μB/atom; this value decreases with the mechanical alloying time, and it is proportional to the cobalt concentration. The polarization and impedance curves in different media (NaCl, H2SO4 and NaOH) showed similar corrosion resistance values. The corrosion resistance increased in the order NaCl, H2SO4 and NaOH. A good passivation layer was formed in NaOH due to the cobalt and nickel oxides on the particle surfaces.