Thermal oxidation behaviour of bulk titanium with nanocrystalline surface layer

The oxidation behaviour of a novel Ti with a nanocrystalline (NC) surface layer, made by surface mechanical attrition treatment (SMAT Ti), has been investigated in air at 500∼700 °C. SMAT Ti can react with oxygen and form oxide particles even at 500 °C, while that of coarse-grained Ti (CG Ti) is about 600 °C. Ti shows a different colour at each temperature, which is attributed to the light interference phenomena. The SMAT Ti shows a thicker, denser oxide layer as compared with that of CG Ti. It originates from the numerous grain boundaries and dislocations on the SMAT Ti surface.