Influence of small amounts of Si and Cr on the high temperature oxidation behavior of novel cobalt base superalloys

Abstract

The effect of small amounts of Si and Cr on the high temperature oxidation of alloys based on Co-9Al-9W was investigated at 900 °C. The results show that the effect of Si additions on oxidation resistance was more pronounced than for Cr additions. An addition of 4 at.% Cr was insufficient to produce a protective layer, while 2 at.% Si led to the formation of a dense, continuous Al2O3 scale. The thermodynamics and kinetics for Al2O3 layer formation were analyzed by combining CALPHAD and Wagnerʼs theory.