Corrosion Behavior of Amorphous-Nanocrystalline Ni50Ti50 Shape Memory Alloy

Abstract

In the present study, the corrosion behaviors of amorphous-nanocrystalline Ni50Ti50 shape memory alloy with different crystallite sizes were investigated. The Ni50Ti50 homogenized specimens were hot rolled and annealed at 950°C. Thereafter, the nanocrystalline Ni50Ti50 specimens with different crystalline sizes in the range of 40-350 nm were prepared by cold rolling and annealing at temperature range of 400 to 900°C. The corrosion resistance of Ni50Ti50 specimen with coarse grain size has significantly increased after cold rolling as a result of the formation of amorphous-nanocrystalline structure. The amorphous and nanocrystalline (with the crystallite size of about 40 nm) Ni50Ti50 samples exhibited the best corrosion resistance in the 5% HCl electrolyte with the corrosion potential and corrosion current density of about –197 mV and 2.34×10-6 A/cm2, respectively. This effect can be attributed to the higher density of crystalline defects in amorphous and nanocrystalline structures to quickly form protective films on the surface