Fracture and corrosion behaviors of Ni-Ti superelastic alloy under sustained tensile loading in neutral fluoride solution containing hydrogen peroxide

The fracture and corrosion behaviors of Ni-Ti superelastic alloy have been investigated by carrying out sustained tensile-loading tests in neutral 2% NaF aqueous solutions containing various H ₂O ₂ concentrations. The times to fracture in solutions with 0.001 M, 0.01 M and 1 M H ₂O ₂ are shorter than that in a solution without H ₂O ₂. In the solution with 0.1 M H ₂O ₂, however, the time to fracture becomes long and the fractographic features are markedly changed. On the basis of the polarization behavior, corrosion is enhanced with increasing H ₂O ₂ concentration. Under an applied stress above the critical stress for the stress-induced martensite transformation, the fluctuations of corrosion potential and corrosion current density become larger than those without the applied stress. The present results suggest that the fracture and corrosion behaviors of the alloy in neutral fluoride solutions are sensitively affected by the H ₂O ₂ concentration, but the relationship between fracture and corrosion does not always straightforwardly correspond to the H ₂O ₂ concentration.