The effect of Ni and Si additions on the oxidation behaviour of Co-17Re-18Cr alloys

•Increasing Ni additions improve the oxidation behaviour of Co-17Re-18Cr alloys due to enhanced Cr activity.•Higher Ni contents accelerate the formation of the σ phase at elevated temperatures deteriorating the oxidation behaviour.•A Si addition of 2 at.% shows a positive effect on the oxidation behaviour of the Co-17Re-18Cr-15Ni alloy at 900 °C–1100 °C.•Si improves the oxidation resistance by enhancing the Cr activity but also influences the alloy microstructure.