Effect of Ti and Ta content on oxidation resistance of Co-Ni-based superalloys

Co-Ni-based superalloys possess the capability to function at elevated temperatures and exhibit superior hot corrosion and thermal fatigue resistance. Therefore, they are expected to serve as crucial high-temperature structural materials for aero-engine and gas turbine hot-end components. In our previous work, we elucidated the influence of Ti and Ta on the high-temperature mechanical properties of the alloys. However, the intricate interplay among the elements also significantly affects the oxidation resistance of the alloys. In this paper, Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5-x)Ta alloys (x = 1, 2, 3, 4) with varying Ti and Ta contents were designed and synthesized, and their oxidation resistance was studied from 800°C to 1000°C. After oxidation at three test conditions, 800°C for 200 h, 900°C for 200 h and 1000°C for 50 h, the main structure of the oxide layer of the alloy is spinel, Cr₂O₃ and Al₂O₃ in order from outside to inside. The oxides formed by Ta, W, and Mo are produced below the Cr₂O₃ layer. The findings reveal that the interaction of Ti and Ta elements imparts the highest oxidation resistance to the 3Ti2Ta alloy. Conversely, an excessive amount of Ti or Ta has an adverse effect on the oxidation resistance of the alloy. This study firstly reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloy with a high Al content and explains the formation mechanism of holes in the oxide layer. These results provide a basis for understanding the effect of the interaction of alloying elements on the oxidation resistance of the alloy.