The Influence of Pre-oxidation in a Silica-powder Pack on the Cyclic Oxidation Behavior of High Nb-TiAl Alloys

摘要

The lightweight TiAl alloys exhibit a large number of outstanding properties at high temperature. However, the actual service of TiAl alloy has been hindered by their poor oxidation resistance above 700°C. Nb addition is benefit to the oxidation resistance of TiAl, while pre-oxidation under low oxygen pressure at high temperature is an effective measure for improving the oxidation resistance of TiAl alloys. Considering the differences of oxidation behavior between high Nb-TiAl and TiAl alloys, the influence of pre-oxidation on the cyclic oxidation behaviors of high Nb-TiAl alloys was investigated in air at 900°C. The pre-oxidation was performed by heating the specimens,buried in silica powder and encapsulated in a silica tube under a vacuum of 1.3×10-3 Pa,at 9001050°C for 16 hours. The scales formed by preoxidation were very adherent and protective. After cyclic oxidation for 200 cycles (200 hours), the mass gain of pre-oxidized alloy was about 10%-40% of that of untreated alloy. The least mass gain had been got at the 1050°C. This excellent oxidation resistance is attributed to the formation of dense Al2O3-rich layer and the extremely dense rutile layer.