Insights into the role of W/B alloying on high-temperature oxidation behavior of Ti42Al5Mn alloy

Abstract

In this study, the oxidation behavior of Ti42Al5Mn, Ti42Al5Mn0.5 W, Ti42Al5Mn0.5W0.1B, and Ti42Al5Mn0.8 W was investigated at 800 °C. Due to the inability to form a dense protective Al2O3 layer, Ti42Al5Mn suffered severe spallation during oxidation at 800 °C and the mass gain was significant. The intermediate layer between the scale and the substrate was first composed of Laves/Z phase but changed to α2/Z phase with prolonged oxidation. The intermediate layer with high Ti/Al ratio favors the formation of a thick Al2O3 + TiO2 mixed layer in the oxide scale which is prone to initiate cracks and cause the spalling of oxides. The doping of W in TiO2 effectively inhibited its generation and promoted the formation of a dense Al2O3 layer, resulting in a significant improvement in the oxidation resistance of the alloy. Compared to Ti42Al5Mn alloy, Ti42Al5Mn0.8 W showed no spallation after 300 h cyclic oxidation and the kinetic curve changed from liner law to parabolic law. The intermediate layer of Ti42Al5Mn0.8 W alloy was composed of a single Laves phase and remained unchanged even after 1000 h oxidation at 800 ℃, offering a favorable basis for the generation of a stable protective oxide layer in the alloy. The addition of 0.1 at.% B to Ti42Al5Mn0.5 W alloy refined its microstructure and further improved its spallation resistance to a level close to that of Ti42Al5Mn0.8 W alloy.