Improvement in high temperature oxidation resistance of TiAl-Mn intermetallic compound by preoxidation in CO-CO{sub}2 gas mixture

摘要

The oxidation behaviour of (Ti-44.9Al)-1.6Mn (at.-%) preoxidised at high temperatures in a CO-CO{sub}2 gas mixture with a very low equilibrium partial pressure of oxygen was investigated by a cyclic oxidation test at 1000℃ in static air. TheTiAl-Mn specimens were preoxidised in the temperature range 900-1000℃ for various times (10-50 h) in CO-CO{sub}2 gas mixtures with various ratios of partial pressure P{sub}(CO{sub}2)/P{sub}(CO) and were subsequently examined by X-ray diffractometry,scanning electron microscopy, and energy dispersive X-ray spectroscopy. In the cyclic oxidation test, the TiAl-Mn preoxidised at 975℃ for 20 h in CO-CO{sub}2 with a P{sub}(CO{sub}2)/P{sub}(CO) of 3:7 showed excellent oxidation resistance up to 600 h.This is attributed to the formation of a continuous fiat Al{sub}2O{sub}3 rich layer beneath the outer mixed oxide layer generated during the CO-CO{sub}2 preoxidation. Furthermore, the parabolic rate constant for the early stages of cyclic oxidation wasdetermined to be 1.7l×10{sup}-11 kg{sup}2 m{sup}-4 s{sup}-1 for the above specimen.