两种铸造镍基合金的高温氧化行为

利用热重分析法、XRD和SEM (EDS)对比研究了700℃超超临界发电机组用K317和K325铸造合金在900和1000℃大气环境下氧化行为。结果表明,K317的氧化性能要优于K325。在900℃氧化时,2种合金的氧化增重遵循抛物线规律,而在1000℃氧化时,氧化增重均分段遵循抛物线规律。K317的氧化膜分3层,外层是NiO、TiO_2和NiCr_2O_4,中间层是致密的Cr_2O_3,内层是内氧化产物Al_2O_3。而K325的氧化膜分2层,外层是NiO, NiCr_2O_4和Nb_2O_5,内层是致密的Cr_2O_3和嵌入的Nb_2O_5颗粒,没有内氧化现象发生。在1000℃氧化时,K325中的Mo严重被氧化形成挥发性MoO_3;同时氧化膜发生了局部剥落现象,氧化膜的附着性相对较差。

High Temperature Oxidation Behaviors of Two Cast Ni-based Superalloys

High temperature oxidation behaviors of cast K317 and K325 alloy at 900°C and 1000°C in air environment are contrastively investigated by TGA, XRD and SEM (EDS). The results show that K317 alloy has a superior oxidation resistance compared with K325 alloy. The kinetic curves of two alloys oxidized at 900°C for 100 h obey the parabolic rate law while those at 1000°C obey sectionally the parabolic rate law. The oxide structure of K317, from the top surface down to the base material, consists of NiO-TiO₂-NiCr₂O₄ composite oxide, Cr₂O₃ oxide dense band and Al₂O₃ internal oxide. In comparison, internal oxidation is not observed in K325 alloy whose oxide layer is composed by two oxide layers: NiO-NiCr₂O₄-Nb₂O₅ composite oxide and Cr₂O₃ oxide layer. Serious MoO₃ volatilization and oxide spallation take place in K325 alloy after the oxidation at 1000°C for 100h. In addition, the adhesion property of K325 alloy is worse than that of K317 alloy due to the occurrence of the micro-voids on the oxide layer/substrate interface.