两种新型低铼单晶高温合金的高温氧化行为

High-Temperature Oxidation Behavior of two Novel Low-Re Single Crystal Superalloys

摘要:

为满足先进燃气轮机叶片的需求，开发低成本、高性能镍基单晶高温合金已成为一种趋势。本工作对比研究了两种新型低Re单晶高温合金A1、A2与商用DD5合金在1100℃循环氧化100 h的氧化行为。采用静态增重法评价了合金的氧化性，利用XRD、SEM及EDS系统分析了合金的氧化动力学、氧化产物演变及氧化层结构。结果表明：A1合金表面形成了约7 μm厚的连续致密Al2O3层，氧化增重最低（平均氧化速率K''=0.0081 g/(m2·h)），氧化皮剥落量最小（G''=0.28 g/m2），抗氧化性能最优。A2合金因Cr含量不足（6.5%），NiO和尖晶石优先形成并主导氧化路径，形成疏松混合氧化层，内层形成不连续的Al2O3，氧化皮严重剥落（G''=15 g/m2），抗氧化性能最差。DD5合金虽Cr含量（7%）较高，但因没有Hf等元素协同调控，高Re含量（3%）的DD5内层未形成连续Al2O3，并出现内氮化，抗氧化性能介于两者之间。合金元素对不同合金氧化过程的协同作用，使得三种合金具有不同的氧化机制。

Abstract:

Developing low-cost, high-performance nickel-based single crystal superalloys has become an inevitable trend to fulfill the performance requirements of advanced gas turbine blades. In this study, the cyclic oxidation behavior of two novel low-Re single crystal superalloys, A1 and A2, was systematically compared with that of the commercial DD5 alloy at 1100?°C for 100?h. The oxidation resistance of the target alloys was assessed via the static weight gain method. The oxidation kinetics, evolution of oxidation products, and oxide scale structure were comprehensively analyzed using XRD, SEM, and EDS. The results show that a continuous and dense Al?O? layer with a thickness of approximately 7?μm is formed on the surface of A1 alloy. This alloy exhibits the lowest mass gain (average oxidation rate K''= 0.0081?g/(m2·h)) and the minimal oxide scale spallation (G''= 0.28?g/m2), indicative of its superior oxidation resistance among the three alloys. For the A2 alloy, due to its insufficient Cr content (6.5%), NiO and spinel preferentially form and dominate the oxidation path. This leads to the formation of a loose multilayer mixed oxide scale with a discontinuous inner Al?O? layer, accompanied by severe scale spallation (G''= 15?g/m2), resulting in the poorest oxidation resistance. Although the DD5 alloy has a relatively higher Cr content (7%), the absence of synergistic regulating elements such as Hf, coupled with its high Re content (3%), gives rise to the lack of a continuous inner Al?O? layer and the occurrence of internal nitridation. Accordingly, its oxidation resistance is inferior to that of A1 but superior to that of A2. The synergistic effects of alloying elements during the oxidation processes induce distinct differences in the oxidation mechanisms of the three tested alloys.