Improvement in Oxidation Resistance of the Ti-31∼39 mass%Al Alloys by Heat Treatment under a Low Partial Pressure Oxygen Atmosphere

Abstract

The heat treatment under a low partial pressure oxygen atmosphere has previously been developed to get an excellent oxidation resistance of intermetallic compound TiAl in the cyclic oxidation test at 900°C. In this study, oxidation behaviors of Ti-31∼39 mass% Al alloys and Ti-36 mass% Al alloys with different oxygen contents up to 0.38 mass% were investigated in cyclic oxidation tests at 900 and 950°C from a viewpoint of the effect of the heat treatment stated above. The mass gain due to cyclic oxidation test of the specimens without the heat treatment decreased with increasing the aluminum content of the alloy, while it was independent of the oxygen content at 900 and 950°C. The specimens with higher oxygen contents than 0.12 mass%, however, were found to form oxide TiO2 even at such a low temperature as 700°C. The effect of the heat treatment was reduced at 950°C tests. The higher the aluminum content of the alloy, the longer the duration in which the excellent oxidation resistance was maintained in the cyclic test. The heat treatment at 1000°C improved the oxidation resistance of the alloys containing oxygen up to 0.12 mass%, and was not effective for higher oxygen alloys. The optimum condition of the heat treatment under a low partial pressure oxygen atmosphere was concluded to be a vicinity of a temperature of 975°C and an air pressure of 1.3×10−3 Pa for 16 h.