Motoi Hara, Michio Inoue and Tokiko Nakagawa
Department of Materials Science and Engineering, Faculty of Engineering and Resource Science, Akita University, Akita 010-0852
The effect of trace of NaCl vapor on oxidation of Ti-6 mass%Al-4 mass%V alloy at 923 to 1073 K was investigated by measurement of mass change of specimens, observation and analysis of scales formed on the specimens. In O2 atmospheres containing NaCl vapor, the alloy was oxidized acceleratedly. An increase in concentration of NaCl vapor increased the oxidation rate of the alloy. Such an accelerated oxidation occurred at the temperatures above 973 K. Scales formed on the alloy after the accelerated oxidation consisted of rutile-TiO2. For a scale formed in O2 with 123.0 vol ppm NaCl vapor, V2O5 was observed in the vicinity of the scale/metal interface. These scales were porous, and contained voids. On the basis of the experimental results and a thermodynamical equilibrium discussion, a mechanism that NaCl vapor induced the formation of molten V2O5 to cause accelerated oxidation of the alloy was presented.
(Received January 9, 1998)
high temperature oxidation, titanium-aluminum-vanadium alloy, sodium chloride vapor, accelerated oxidation
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