2003 Volume 44 Issue 7 Pages 1405-1411
The Ti–18Nb–4Sn alloy has been confirmed to possess much higher corrosion resistance compared to the NiTi alloy throughout immersion time up to 604.8 ks in a 0.05 mass% HCl at 310 K open to air. The Ti–18Nb–4Sn alloy shows higher open circuit potential, compared to titanium metal and NiTi alloy. The higher open circuit potential results in an increase in the thickness of the passive film formed on the alloy. The passive film on the Ti–18Nb–4Sn alloy is rich in niobium as well as tin due to preferential dissolution of titanium. The degree of enrichment of niobium and tin in the film increases with an increase in immersion time. On the other hand, the passive film on the NiTi alloy consists exclusively of titanium. The angle-resolved XPS analysis reveals that the outer part of the passive film on the Ti–18Nb–4Sn alloy is rich in niobium and deficient in titanium. Furthermore, the passive film on the Ti–18Nb–4Sn alloy is composed of a double oxyhydroxide containing titanium, niobium and tin cations. It can, therefore, be said that the formation of the thick and homogeneous double oxyhydroxide film whose outer part is rich in niobium seems responsible for the excellent corrosion resistance of the Ti–18Nb–4Sn alloy.