预氧化对Co-Al-W基高温合金高温氧化和热腐蚀行为的影响

In 2006, stable γ' phase was found in Co-Al-W alloy, which provides a new way for developing Co-based superalloys. In order to meet the requirements for applications, the Co-Al-W-based superalloys need to have good oxidation and corrosion resistance. But the oxidation and corrosion resistance of the Co-Al-W-based superalloys is relatively low. In this work, pre-oxidation treatments were used to improve the oxidation and corrosion resistance. Three types of pre-oxidation treatments were carried out at 900℃ (in air), 950℃ (in air) and 1000℃ (in 1%O₂+99%Ar), which were marked as 900-PreO, 950-PreO and 1000-LPreO, respectively. High temperature oxidation tests of both the pre-oxidation treated and untreated superalloys were carried out at 1000℃. And hot corrosion behaviors were also investigated at both 800 and 850℃. XRD, SEM and EDS were used to examine the characteristics of the oxidation and corrosion behaviors. The results show that the pre-oxide layers of the superalloys after different pre-oxidation treatments are compact. During oxidation at 1000℃, the Cr₂O₃ scale in 900-PreO treated superalloy is oxidized to form volatile products, and the diffusion resistance of both oxygen and the metal elements through the oxide layer is poor. In 1000-LPreO treated superalloy, serious spallation of the oxides occurs and leads to poor oxidation resistance. In 950-PreO treated superalloy, since the continuous CoCr₂O₄ and Al₂O₃ scales help to reduce the diffusion of oxygen and the metal elements, the mass gain of 950-PreO treated superalloy is consequently decreased. During the hot corrosion process, the preoxide layer of 950-PreO treated superalloy can hinder the diffusion of corrosive medium. Therefore, the corrosion resistance can be significantly improved by 950-PreO treatment, and the mass gain is decreased by over 80%.