First-principles investigation on the adsorption and dissociation of O2 and H2O molecules on the Ni-rich TiNi alloy surface

The excellent corrosion resistance of Ti-Ni binary alloy highly depends on the thin passive films spontaneously formed on the surface. For the Ni-rich 60NiTi, the TiNi3 phase would coexist with the B2 TiNi matrix phase after the final heat treatment, affecting the formation of passive films. In this study, the adsorption and dissociation of O-2 molecule on the TiNi (1 1 0) and TiNi3 (1 1 0) surface are investigated by the DFT method to have an insight into the distinction of oxidation behavior between TiNi and TiNi3 phase. Subsequently, the interaction of H2O molecule with the most stable O-2 adsorption configuration is further studied in order to clarify the atomistic evolution process when the oxidized surface is exposed to the wet air and erosion solution. The calculated results implied that the O-2-TiNi/H2O system exhibits the physisorption nature of the H2O molecule. However, the H2O molecule, when interacted with the O-2-TiNi3 configuration, can be dissociated into OH group and H atom. These then were captured to create the Ti-O, Ni-O and H-O bond. This study may provide the useful details involved in the formation of oxide/alloy interface on the Ni-rich TiNi alloy as well as the interaction of oxide/alloy with the water solution.