Effects of Al, Cr, and Ti on the Oxidation Behaviors of Multi-component γ/γʹ CoNi-Based Superalloys

Abstract

The effects of Al, Cr, and Ti on the oxidation behaviors of multi-component γ/γʹ CoNi-based superalloys, Co–30Ni–(6–8)Al–3W–1Ta–(3–6)Ti–(12–14)Cr, were investigated at 800, 900, and 1000 °C for 100 h. The results show that Al has a superior effect for improving the oxidation resistance of the alloys in comparison with Cr, particularly at 900 and 1000 °C, while Ti was detrimental to the oxidation performance of the alloys. Oxidation resistance of alloys containing 6 at.% Al were primarily provided by Cr2O3 layer, which was not sufficiently protective at 900 and 1000 °C. Continuous Al2O3 layers could form in alloys containing 8 at.% Al at 800 and 1000 °C, but failed at 900 °C. Higher content of Cr can assist the formation of continuous Al2O3 layer. For the target service temperature of 800 °C or below, alloys with lower Al and higher Ti content may be suitable since higher solvus temperature and volume fraction of the γʹ phase could be achieved with sufficient oxidation resistance provided by dense Cr2O3 layer. While for a higher target service temperature above 900 °C, higher content of Al (≥8 at.%) is required to form continuous Al2O3 layer. The current study is helpful to understand the oxidation behavior of multi-component CoNi-based superalloys and provide guidance for alloy composition design and optimization.