熔模铸造Co22合金的高温氧化性及氧化层生长

Oxidation Behavior and Growth Mechanism of Oxide Layer on a Co22 Co-base Cast Superalloy at High Temperatures

研究了熔模铸造钴基高温合金22Co-21Ni-29Cr-2.2Nb-Fe在1 050、1 150和1 250℃下的恒温氧化行为,并采用X射线衍射仪、扫描电镜及能谱仪分析了合金氧化层形貌及成分。结果表明,Co22合金在1 050～1 250℃下的氧化增重遵守二次抛物线规律,且随着温度的升高而增大;合金在氧化后形成了连续的氧化层,其中内层为Cr2O3氧化膜,外层由（Fe,Ni,Co,Cr）3O4尖晶石和少量的CrNbO4构成。合金氧化层的生长可分为3个阶段,第1阶段氧化层为Cr2O3氧化膜,第2阶段氧化层由内Cr2O3层与离散分布在外表面的Fe,Ni,Co和Nb的氧化物组成,且在氧化层的外表面出现了沿基体晶界分布的岛状氧化物区,第3阶段形成了外（Fe、Ni、Co、Cr）3O4尖晶石-内Cr2O3的双层氧化层结构并伴有少量的CrNbO4离散分布于外表面。

The oxidation behavior of a novel 22Co-29Cr-21Ni-2.2Nb-Fe Co-base superalloy with about22% Co（Co22for short）was analyzed at 1 050 ℃,1 150 ℃ and 1 250 ℃,and the oxidation products were observed by scanning electronic microscopy and X-ray diffraction,EDS.The thermogravimetric results reveal that oxidation kinetics of the alloy obeys parabolic law,and the oxidation rates are increased with the temperature increase.The oxidized layers formed on all specimens consist of Cr2O3,（Fe,Ni,Co,Cr）3O4spinels and CrNbO4 in internal layer and continuous Cr2O3 layer formed exactly on top of substrate as the inner layer.The mechanism of oxide layers formation is suggested to be divided into three-stage：firstly,Cr2O3 is formed as a continuous and protective layer,then Fe,Co,Ni,Nb ions diffuse to scale-gas interface to form nodules,finally,the nodules grow bigger and（Fe,Ni,Co,Cr）3O4-Cr2O3 double layer is formed.