The surface oxide layer of a titanium alloy treated by mechanochemical polishing (MCP) was characterized using a scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), X-ray photoelectoron spectoroscopy (XPS), auger electoron spectoroscopy (AES) and secondary ion mass spectrometry (SIMS). The results showed that surface oxide layer was amorphous titanium oxide and had about 5 nm thickness. At the interface between surface oxide layer and

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... ate, there was a region of high hydrogen concentration. In the same region, the Ti F chemical component was found. It seems that this interface layer acts as a barrier for the bulk hydrogen diŠusion, and gives low hydrogen concentration at the surface layer resulting in the low outgassing property in the titanium materials.