枝晶生长方向对单晶高温合金DD10氧化行为的影响

The Influence of Dendrite Growth Direction on the Oxidation Behavior of Single-Crystal Superalloy DD10

为了探究镍基单晶高温合金在垂直和平行于一次枝晶生长方向的表面氧化膜的演化过程,采用连续质量增加法研究了1050℃下镍基单晶高温合金DD10的氧化行为,使用扫描电镜(SEM)及能谱仪(EDS)、X射线衍射仪(XRD)、电子探针(EPMA)对合金垂直和平行于一次枝晶生长方向的表面及氧化膜形貌、元素分布等进行了分析。结果表明:枝晶生长方向对DD10合金的氧化动力学规律和氧化膜结构没有影响,合金垂直面和平行面氧化动力学都呈现分阶段现象,第1阶段遵循立方增重规律,第2阶段为渐进水平线规律。氧化膜结构分为3层,外表层由柱状Ni_(x)(Co)_(1-x)O构成,中间层由复杂尖晶石组成,内层由连续Al_(2)O_(3)构成。但枝晶生长方向对合金的氧化增重速率有着显著影响,合金垂直面的氧化速率常数为k_(1)=5.96×10^(-3)mg^(2)/(cm^(4)·s),平行面的氧化速率常数为k_(2)=6.24×10^(-3)mg^(2)/(cm^(4)·s),合金平行面氧化膜初期生长速率大于垂直面。这主要是由于平行于枝晶的生长方向具有更多的γ-γ’相界面,为氧化物的形核提供了大量的非均匀形核位置和更多的短路扩散路径,导致了平行生长方向在第1阶段展现出更高的氧化速率。随着氧化时间的延长,不同枝晶方向内层均形成了连续致密的Al2O3,有效阻碍了金属阳离子的外扩散,氧化速率差异减小。

For investigating the evolution process of surface oxide film on nickel based single crystal superalloys perpendicular and parallel to the direction of primary dendrite growth,the oxidation behavior of nickel based single crystal superalloys DD10 at 1050℃was studied by the method of continuous weight increase.The surface and oxide film morphology,element distribution,etc.of the alloy perpendicular and parallel to the primary dendrite growth direction were analyzed by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffraction(XRD)and electron probe microanalysis(EPMA).Results showed that the growth direction of dendrites had no effect on the oxidation kinetics and oxide film structure of DD10 alloy.The oxidation kinetics of the alloy in both vertical and parallel planes exhibited a staged phenomenon:The first stage followed the cubic weight gain law,while the second stage followed the asymptotic horizontal line law.Furthermore,the oxide film structure was divided into three layers,with the outer layer composed of columnar Ni_(x)(Co)_(1-x)O,the middle layer composed of complex spinel,and the inner layer composed of continuous Al_(2)O_(3).However,the growth direction of dendrite had a significant effect on the rate of oxidation weight gain of the alloy.The oxidation rate constant of the vertical plane of the alloy was k_(1)=5.96×10^(-3)mg^(2)/(cm^(4)·s),and the oxidation rate constant of the parallel plane was k_(2)=6.24×10^(-3)mg^(2)/(cm^(4)·s).Meanwhile,the initial growth rate of the oxide film on the parallel surface of the alloy was greater than that on the vertical surface,which mainly resulted from that the presence of moreγ-γ'phase interfaces parallel to the growth direction of the dendrites could provide a large number of non-uniform nucleation sites and more short-circuit diffusion paths for the nucleation of oxides,and thereby cause higher oxidation rates in the first stage for parallel growth directions.With the increase of oxidation time,the inner layers of different dendritic directions all formed a continuous dense Al_(2)O_(3),which effectively hindered the outward diffusion of metal cations,and reduced the difference in oxidation rates.