一种含铼单晶高温合金的恒温氧化行为

Isothermal Oxidation Behavior of Single-Crystal Ni-Base Superalloy Containing Rhenium in Air

采用X射线衍射(XRD),扫描电镜(SEM)及能谱(EDAX)等手段,研究了含铼单晶高温合金DD32的高温氧化行为。结果表明,氧化初期增重迅速,由NiO的形成和生长控制,符合抛物线规律;随着氧化时间的延长,氧化增重变得十分缓慢,由α-Al2O3的形成和生长控制。在900,1000℃时的氧化膜由3层组成,最外层为(Ni,Co)O层,中间层由复杂化合物以及尖晶石化合物等组成,内层为靠近基体合金的连续的Al2O3层。氧化过程中,分布在中间层的富Re和W相起到"扩散障"的作用,降低基体合金中Al向外的扩散速率,在内层形成均匀连续的Al2O3氧化膜层,进而抑制氧化膜生长,导致氧化速率降低。

The high temperature oxidation behavior of the single-crystal Ni-base superalloy DD32 containing rhenium was investigated at 900 ℃ and 1000 ℃ in air by using SEM, XRD, and SEM/EDAX. It is found that there are two oxidation stages in the oxidation kinetics curves at 900 ℃ and 1000 ℃. In the initial stage, the mass gain rapidly increases and basically obeys a parabola law due to the formation and growth of NiO. In the second oxidation stage, it obeys the asymptotic level linear law with the oxidation time increasing to a critical time when the mass gain goes to be slow, and the Kp value corresponds to the formation and growth of Al2O3. There are three layers for the oxidation film at 900 ℃ and 1000 ℃： an outer layer of columnar （Ni,Co）O, an intermediate layer mainly composed of complex oxides and a small amount of spinels, and a continuous inner layer of α-Al2O3. The phase rich in Re and W precipitates may play a role of ＂diffusion barrier＂, which is distributed in the intermediate layer during oxidation, effectively decreases the diffusion rate of Al element in the substrate outward. As a result, a continuous oxide layer of Al2O3 is formed in the inner layer to restrain the growth of oxide film and decrease the oxidation rate.