TEM observation of oxide scale formed on a Ti-Al-Zr alloy oxidized at 360 deg C in alkaline steam

摘要

Ti-Al-Zr alloy has been oxidized at 360 deg C in alkaline steam at a pressure of 10.3 +- 0.7 MPa. Cross-sectional transmission electron microscopy (TEM) observations indicated that the oxide scale of Ti-Al-Zr alloy was composed of outer and inner subscales, in which the outer layer consists of anatase-TiO_2 and the inner layer a mixture of TiO and Ti_2O. The thickness of the Ti_2O, TiO and anatase-TiO_2 were approximately 50, 100 and 400 nm, respectively. These results were confirmed by X-ray energy dispersive spectrometry (EDS) measurements. The enhanced corrosion of titanium alloys in LiOH solution is attributed to a high hexagonal Ti_2O to tetragonal TiO_2 phase transformation rate induced by the substitution of Li~+ for Ti~(4+) in the oxide layer.