Effect of Ni on the corrosion resistance and passivation characteristics of Ni-Mn-Ga-Gd shape memory alloys in sodium chloride solutions

This paper investigates the effect of different Ni contents on the corrosion and passivation behavior of Ni 54+ x Mn 25 Ga 20.9- x Gd 0.1 ( x = 0, 1, 2, 3, 4) shape memory alloy in a 3.5 wt% NaCl solution. Using scanning electron microscope, electrochemical workstation, and X-ray photoelectron spectroscopy. The results indicate that the corrosion resistance of single-phase alloys initially increases and then decreases as the Ni content ranges from x = 0 to 3, with the best corrosion resistance observed at x = 2. The passive film of the alloy mainly consists of NiO, Ni(OH) 2 , and Ga 2 O 3 . Both NiO and Ga 2 O 3 positively affect the corrosion resistance of the passive film. In the range of 54 to 57 at% Ni content, the alloy remains a single-phase alloy. The elements Ni and Ga work together in the passivation film and at a Ni content of 56 at% to reach equilibrium, which provides the best corrosion resistance for single phase alloys . When the Ni content reaches 58 at%, the second phase appears in the form of a nickel-rich phase. Typically, intergranular corrosion preferentially corrodes the second phase, but in this study, the second phase is a nickel-rich phase with some corrosion resistance, which improves the overall corrosion resistance of the alloy.